RAVE data has provided new results on Galactic kinematics like the kinematical decomposition of the Galactic disk. This decomposition permits to identify the different components of the disk and to characterize them in terms of scale height and scale length. With the data provided by Gaia and in particular the RVS, we will have a completly renewed view of the Galaxy. The precision of the RVS will permit to undertake a precise analysis of the kinematics of the Galactic disks. This knowledge will provide significant clues to constrain the scenarios of the Galactic disk formation

Bienaymé, O

Binney, J

Bland-Hawthorn, J

Campbell, R

Combes, F

Freeman, KC

Gibson, B

Gilmore, G

Grebel, EK

Helmi, A

Munari, U

Navarro, JF

Parker, QA

Samadi, R

Seabroke, G

Siebert, A

Siviero, A

Steinmetz, M

Veltz, L

Watson, FG

Williams, M

Wyse, RFG

Zwitter, T

English

Veltz, L.

Bienaymé, O.

Steinmetz, M.

Zwitter, T.

Watson, F.~G.

Binney, J.

Bland-Hawthorn, J.

Campbell, R. .

Freeman, K.~C.

Gibson, B.

Gilmore, G.

Grebel, E.~K.

Helmi, A.

Munari, U.

Navarro, J.~F.

Parker, Q.~A.

Seabroke, G.

Siebert, A.

Siviero, A.

Williams, M.

Wyse, R.~F.~G.

Dissertations of the University of Groningen

   University of GroningenGalactic kinematics from RAVE to Gaia-RVS DataVeltz, L.; Bienaymé, O.; Steinmetz, M.; Zwitter, T.; Watson, F.~G.; Binney, J.; Bland-Hawthorn, J.; Campbell, R. .; Freeman, K.~C.; Gibson, B.Published in:SF2A-2008IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2008Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Veltz, L., Bienaymé, O., Steinmetz, M., Zwitter, T., Watson, F. G., Binney, J., Bland-Hawthorn, J.,Campbell, R. ., Freeman, K. C., Gibson, B., Gilmore, G., Grebel, E. K., Helmi, A., Munari, U., Navarro, J. F.,Parker, Q. A., Seabroke, G., Siebert, A., Siviero, A., ... Wyse, R. F. G. (2008). Galactic kinematics fromRAVE to Gaia-RVS Data. In SF2A-2008 (pp. 47). Société Francaise d’Astronomie et d’Astrophysique(SF2A).CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 31-10-2023SF2A 2008C. Charbonnel, F. Combes and R. Samadi (eds)GALACTIC KINEMATICS FROM RAVE TO GAIA-RVS DATAVeltz, L.1, Bienaymé, O.2, Steinmetz, M.1 , Zwitter, T.3, Watson, F. G.4, Binney, J.5,Bland-Hawthorn, J.6, Campbell, R..1 , Freeman, K. C.7, Gibson, B.8, Gilmore, G.9, Grebel, E. K.10,Helmi, A.11, Munari, U.12, Navarro, J. F.13, Parker, Q. A.14, Seabroke, G.15, Siebert, A.2 , Siviero,A.12,1 , Williams, M.1 and Wyse, R. F. G.16Abstract. RAVE data has provided new results on Galactic kinematics like the kinematical decompositionof the Galactic disk. This decomposition permits to identify the different components of the disk and tocharacterize them in terms of scale height and scale length. With the data provided by Gaia and in particularthe RVS, we will have a completly renewed view of the Galaxy. The precision of the RVS will permit toundertake a precise analysis of the kinematics of the Galactic disks. This knowledge will provide significantclues to constrain the scenarios of the Galactic disk formation.1 IntroductionThe hierarchical formation scenario is a great success in describing the formation of the large-scale structureof the universe. But, the detailed mechanisms of formation of individual galaxies are still an open question.Some answers to this question rely on the knowledge of the position, the kinematics and chemical compositionof the stars of the Milky Way. Therefore, in 2000, ESA has approved the Gaia mission that will provide the 6-D(position-velocity) information for 50 millions stars in the Galaxy. The expected launch of the Gaia satelliteis planned for 2011. As a precursor in the spectroscopic area, an international cooperation called ”RAdialVelocity Experiment” (RAVE) has started in 2003 a survey of one million stars in the southern sky hemisphere(Steinmetz 2003). There has been already two data releases. The first release contains about 25 000 radialvelocity measurements (Steinmetz et al. 2006). The second data release contains about 25 000 radial velocitymeasurements more and 20000 stars for which the stellar parameters ([M/H ], log g, Teff) have been determined(Zwitter et al. 2008). The spectroscopic acquisition techniques differ between RAVE and the Gaia RadialVelocity Spectrometer (RVS), although they have almost the same resolution and wavelength range.1 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Postdam, Germany2 Observatoire Astronomique de Strasbourg, 11 rue de l’Universit, 67000 Strasbourg, France3 University of Ljubljana, Department of Physics, Jadranska 19, 1000 Ljubljana, Slovenia4 Anglo-Australian Observatory, Coonabarabran, NSW 2357, Australia5 Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, UK6 School of Physics, University of Sydney, NSW 2006, Australia7 Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia8 Centre for Astrophysics, University of Central Lancashire, Preston, UK9 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, UK10 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrae 12-14, 69120 Heidelberg,Germany11 Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, Netherlands12 Osservatorio Astronomico di Padova - INAF, Sede di Asiago, 36012 Asiago, Italy13 Department of Physics and Astronomy, University of Victoria, P.O.Box 3055, Victoria, Canada14 Department of Physics, Macquarie University, NSW 2109, Australia15 Planetary & Space Sciences Research Institute, The Open University, Milton Keynes, UK16 Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, USAc© Société Francaise d’Astronomie et d’Astrophysique (SF2A) 200848 SF2A 2008The RAVE spectra are obtained with the multi-fiber spectrograph 6dF (Watson et al. 2000) on the UKSchmidt telescope at the Anglo-Australian Observatory. Each field is observed during five exposures of 600seconds. The RVS is an integral field instrument on board of the Gaia satellite that will not use fibers (Katzet al. 2004). The observation will be done in a time delay integration scan mode. Each spectrum will beexposed for 4 seconds.The 6dF spectrograph and RVS are medium resolution instruments with R = 7500 and 11500, respectively.The spectra have a near infrared wavelength range between [8470 - 8740] Å for Gaia-RVS and [8410 - 8795]Å for RAVE. This wavelength range and resolution have three main advantages (Munari 1999, 2003). Theypresent the lowest possible contamination by telluric absorptions that will facilitate the pre- and post- Gaiamission observations from the ground. According to the Galaxy model, the largest number of stars that will beobserved by Gaia will have an energy distribution that peaks in this wavelength range due to their spectral typeor the interstellar extinction. In this wavelength range, the presence of the CaII triplet lines for cool stars, thePaschen lines for hot stars and metallic lines will be useful to determine accurately radial velocity and chemicalabundances.2 A model of Galactic kinematicsIn order to analyze the spectroscopic data in combination with the photometric information and proper motion,we have developed a self-consistant model of the Galactic disk. The disk is describe as sum of 20 isothermalstellar components with a vertical velocity dispersion σzz ranging from 10 to 70 km.s−1. The distributionfunction of each component is built from three elementary functions describing the vertical density ρi, thekinematic distribution fi (3D-gaussians) and the luminosity function φik.We define N (z, VR, Vφ, Vz ; M) to be the density of stars in the Galactic position-velocity-absolute magnitudespace:N =∑ikρi(z)fi(VR, Vφ, Vz)φik(M), (2.1)where the index i differentiates the stellar components and the index k the absolute magnitudes used to modelthe luminosity function.We insert this model in the generalized equation of stellar statistics giving:A(m, µl, µb, Vr) =∫N(z, VR, Vφ, Vz ; M) z2 ω dz. (2.2)To determine A(m), the apparent magnitude count, together with the marginal distributions of the propermotion µl and µb and the distributions of radial velocities for any direction and apparent magnitudes.Assuming the stationarity of the density distribution, the consistency between the vertical velocity σzz,i anddensity ρi(z) distributions for each stellar component i is ensured by the following expression:ρi(z) = exp(−Φ(z)/σ2zz,i)(2.3)where Φ(z) is the vertical gravitational potential at the solar Galactic position.For the vertical gravitational potential, we use the recent determination obtained by Bienaymé et al. (2006).The vertical potential is defined at the solar position by:Φ(z) = 4πG(Σ0(√z2 + D2 − D)+ ρeff z2)with Σ0 = 48 M⊙ pc−2, D = 800 pc and ρeff = 0.07 M⊙ pc−3.The kinematical model is given by shifted 3D gaussian velocity ellipsoids. For simplicity, we assume that theσRR/σφφ ratio is the same for all the stellar components. The velocity ellipsoids are inclined along the Galacticmeridian plane. The main axis of velocity ellipsoids are set parallel to confocal hyperboloids as in Stäckelpotentials. The focus is set to zhyp=6kpc on the main axis giving them realistic orientations (see Bienaymé1999).The luminosity function of each stellar component is modeled with n different kinds of stars according totheir absolute magnitude:φi(M) =∑k=1,nφik(M) =1√2πσM∑k=1,ncik e−12(M−MkσM)2Galactic kinematics from RAVE to Gaia-RVS Data 49where cik is the density for each type of star (index k) of each stellar component (index i).3 ResultsWe have have adjusted the density of each stellar component to a sample of stars extracted from the 2MASScatalogue for the photometric data, the UCAC2 catalogue for proper motion and RAVE for the radial velocity.These stars are selected in color with J-K = [0.5-0.7]. In this color interval, we have defined 4 types of stars:Stars with a mean absolute magnitude MK = −1.61 are identified to be the red clump giants (k = 1), withMK = −0.89 and MK = −0.17 are first ascent giants stars (k = 2 − 3) and with MK = 4.15 for dwarfs (k = 4).We neglected sub-giant populations with an absolute magnitude MK between 0.2 and 2. We adopt σM = 0.25for each kind of stars on the luminosity function.Adjusting the Galactic kinematical model to star counts, proper motions and radial velocities histograms,we obtained a kinematical decomposition of the Galactic disk (Fig. 1 left). The kinematical decompositionexhibits three main structures. We propose to identify the first one with vertical velocity dispersion σW =[10-25]km s−1 with the thin disk, the second with σW = [30-45] km s−1 with the thick disk. The decompositionshows a clear separation between the thin and thick components. For the third component with σW = [60-70]km s−1, the kinematical information is missing. This component could be a ’hot’ kinematically thick disk orthe halo.From the kinematical decomposition, the scale height of the thin and thick disk could be determined indepen-dently by fitting an exponential on the density ρ(z) (Fig. 1 right). We find a scale height for stellar componentswith σW = [10-25]km s−1 (thin disk) of 225±10pc, for stellar components with σW = [30-45]km s−1 (thickdisk) of 1048±36pc and the density ratio of thick to thin disk stars to be 8.7% at z=0pc. Our values are inagreement with previous determinations like the ones of Cabrera-Lavers et al. (2005) who have obtained a scaleheight of 267±13pc and 1062±52pc for the thin and thick disks respectively.Fig. 1. Left: Kinematical decomposition of the Galactic disk. Right: The logarithm of the vertical stellar density ρ(z)towards the the North Galactic Pole (dashed line) and its thin and thick disk decomposition (respectively thin and thicklines).From our model, the solar motion relative to the LSR and the asymmetric drift were also determined. Weobtained a value of u⊙=8.5±0.3km s−1, w⊙=11.1±1.0km s−1 and a thick disk lag is Vlag = 33±2km s−1 relativeto the LSR. v⊙ was fixed to = 5.2 km s−1, otherwise we could not measure the asymmetric drift.By looking at latitude |b| > 20◦, we measure a radial scale length of 2.5±0.4 kpc for the thin disk and3.5±1.0kpc for the thick disk. There is no consensus on the values of the scale length of the values of the scalelength of the thin and thick disk, but our values are in relative agreement, for example, with Ojha (2001) whofinds 2.8±0.3kpc for the thin disk and 3.70.8−0.5 kpc for the thick disk.50 SF2A 20084 ConclusionsThe fact that the decomposition of the Galactic disk reveals the kinematical separation of the thin and thethick disk puts some constraints on the scenarios of the Galactic disk formation. The thick disk could not havebeen created by a continuous ‘heating’ mechanism like the diffusion due to molecular clouds or spiral arms.The scientific use of the RAVE data has already permitted us to obtain a lot of results on Galactic structureand kinematics: constrains on the local Galactic escape speed (Smith et al. 2007), absence of the Sgr streamnear the Sun (Seabroke et al. 2008), scale height of the thin and thick disk (Veltz et al. 2008), vertical tilt ofthe ellipsoid (Siebert et al. 2008). With the accuracy and number of stars that will be observed by Gaia, thefuture is very promising for the analysis of the structure and kinematics of the disk. All these new informationswill help to improve our understanding of the formation and evolution not only of the Milky Way but also thegalaxies in general.AcknowledgmentsFunding for RAVE has been provided by the Anglo-Australian Observatory, by the Astrophysical InstitutePotsdam, by the Australian Research Council, by the German Research Foundation, by the National Institute forAstrophysics at Padova, by The Johns Hopkins University, by the Netherlands Research School for Astronomy,by the Natural Sciences and Engineering Research Council of Canada, by the Slovenian Research Agency, bythe Swiss National Science Foundation, by the National Science Foundation of the USA, by the NetherlandsOrganisation for Scientific Research, by the Particle Physics and Astronomy Research Council of the UK, byOpticon, by Strasbourg Observatory, and by the Universities of Basel, Cambridge, and Groningen.The RAVE web site is at http://www.rave-survey.org.ReferencesBienaymé, O. 1999, A&A, 341,86Bienaymé, O., Soubiran, C., Mishenina, T. V., Kovtyukh, V. V. & Siebert, A. 2006, A&A, 446, 933Cabrera-Lavers, A., Garzn, F., & Hammersley, P. L. 2005, A&A, 433, 173Katz, D., Munari, U., Cropper, et al. 2004, MNRAS, 354, 1223Munari, U. 1999, Baltic Astronomy, 8, 73Munari, U. 2003, editor, ASPC: ”GAIA Spectroscopy: Science and Technology”, 298Ojha, D. K. 2001, MNRAS, 322, 426Seabroke, G. M., Gilmore, G., Siebert, A., et al. 2008, MNRAS, 384, 11Siebert, A., Bienaymé, O., Binney, J., et al. 2008, arXiv0809.0615Smith, M. C., Ruchti, G. R., Helmi, A., Wyse, R. F. G., & Fulbright, J. P., et al. 2007, MNRAS, 379, 755Steinmetz, M 2003, ASPC: ”Gaia Spectroscopy: Science and Technology”, 298, 381Steinmetz, M., Zwitter, T., Siebert, A., et al. 2006, AJ, 132, 1645Veltz, L., Bienaymé, O.; Freeman, K. C., et al. 2008, A&A, 480, 753Watson, F. G., Parker, Q. A., Bogatu, G., et al. 2000, Proc. SPIE, 4008, 123Zwitter, T., Siebert, A., Munari, U., et al. 2008, AJ, 136, 421

Galactic kinematics from RAVE to Gaia-RVS Data

Bienayme, O

Grebel, E. K

Navarro, J. F

Parker, Quentin A

Seabroke, G. M

Wyse, R. F. G

Watson, F. G

Bland-Hawthorn, Jonathan

Freeman, K. C

Macquarie University ResearchOnline

Galactic kinematics from RAVE to GAIA-RVS data

University of Groningen

   University of GroningenGalactic kinematics from RAVE to Gaia-RVS DataVeltz, L.; Bienaymé, O.; Steinmetz, M.; Zwitter, T.; Watson, F.~G.; Binney, J.; Bland-Hawthorn, J.; Campbell, R. .; Freeman, K.~C.; Gibson, B.Published in:SF2A-2008IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2008Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Veltz, L., Bienaymé, O., Steinmetz, M., Zwitter, T., Watson, F. G., Binney, J., ... Wyse, R. F. G. (2008).Galactic kinematics from RAVE to Gaia-RVS Data. In SF2A-2008 (pp. 47). Société Francaise d’Astronomieet d’Astrophysique (SF2A).CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 12-11-2019SF2A 2008C. Charbonnel, F. Combes and R. Samadi (eds)GALACTIC KINEMATICS FROM RAVE TO GAIA-RVS DATAVeltz, L.1, Bienayme´, O.2, Steinmetz, M.1 , Zwitter, T.3, Watson, F. G.4, Binney, J.5,Bland-Hawthorn, J.6, Campbell, R..1 , Freeman, K. C.7, Gibson, B.8, Gilmore, G.9, Grebel, E. K.10,Helmi, A.11, Munari, U.12, Navarro, J. F.13, Parker, Q. A.14, Seabroke, G.15, Siebert, A.2 , Siviero,A.12,1 , Williams, M.1 and Wyse, R. F. G.16Abstract. RAVE data has provided new results on Galactic kinematics like the kinematical decompositionof the Galactic disk. This decomposition permits to identify the different components of the disk and tocharacterize them in terms of scale height and scale length. With the data provided by Gaia and in particularthe RVS, we will have a completly renewed view of the Galaxy. The precision of the RVS will permit toundertake a precise analysis of the kinematics of the Galactic disks. This knowledge will provide significantclues to constrain the scenarios of the Galactic disk formation.1 IntroductionThe hierarchical formation scenario is a great success in describing the formation of the large-scale structureof the universe. But, the detailed mechanisms of formation of individual galaxies are still an open question.Some answers to this question rely on the knowledge of the position, the kinematics and chemical compositionof the stars of the Milky Way. Therefore, in 2000, ESA has approved the Gaia mission that will provide the 6-D(position-velocity) information for 50 millions stars in the Galaxy. The expected launch of the Gaia satelliteis planned for 2011. As a precursor in the spectroscopic area, an international cooperation called ”RAdialVelocity Experiment” (RAVE) has started in 2003 a survey of one million stars in the southern sky hemisphere(Steinmetz 2003). There has been already two data releases. The first release contains about 25 000 radialvelocity measurements (Steinmetz et al. 2006). The second data release contains about 25 000 radial velocitymeasurements more and 20000 stars for which the stellar parameters ([M/H ], log g, Teff) have been determined(Zwitter et al. 2008). The spectroscopic acquisition techniques differ between RAVE and the Gaia RadialVelocity Spectrometer (RVS), although they have almost the same resolution and wavelength range.1 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Postdam, Germany2 Observatoire Astronomique de Strasbourg, 11 rue de l’Universit, 67000 Strasbourg, France3 University of Ljubljana, Department of Physics, Jadranska 19, 1000 Ljubljana, Slovenia4 Anglo-Australian Observatory, Coonabarabran, NSW 2357, Australia5 Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, UK6 School of Physics, University of Sydney, NSW 2006, Australia7 Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia8 Centre for Astrophysics, University of Central Lancashire, Preston, UK9 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, UK10 Astronomisches Rechen-Institut, Zentrum fu¨r Astronomie der Universita¨t Heidelberg, Mo¨nchhofstrae 12-14, 69120 Heidelberg,Germany11 Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, Netherlands12 Osservatorio Astronomico di Padova - INAF, Sede di Asiago, 36012 Asiago, Italy13 Department of Physics and Astronomy, University of Victoria, P.O.Box 3055, Victoria, Canada14 Department of Physics, Macquarie University, NSW 2109, Australia15 Planetary & Space Sciences Research Institute, The Open University, Milton Keynes, UK16 Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, USAc© Socie´te´ Francaise d’Astronomie et d’Astrophysique (SF2A) 200848 SF2A 2008The RAVE spectra are obtained with the multi-fiber spectrograph 6dF (Watson et al. 2000) on the UKSchmidt telescope at the Anglo-Australian Observatory. Each field is observed during five exposures of 600seconds. The RVS is an integral field instrument on board of the Gaia satellite that will not use fibers (Katzet al. 2004). The observation will be done in a time delay integration scan mode. Each spectrum will beexposed for 4 seconds.The 6dF spectrograph and RVS are medium resolution instruments with R = 7500 and 11500, respectively.The spectra have a near infrared wavelength range between [8470 - 8740] A˚ for Gaia-RVS and [8410 - 8795]A˚ for RAVE. This wavelength range and resolution have three main advantages (Munari 1999, 2003). Theypresent the lowest possible contamination by telluric absorptions that will facilitate the pre- and post- Gaiamission observations from the ground. According to the Galaxy model, the largest number of stars that will beobserved by Gaia will have an energy distribution that peaks in this wavelength range due to their spectral typeor the interstellar extinction. In this wavelength range, the presence of the CaII triplet lines for cool stars, thePaschen lines for hot stars and metallic lines will be useful to determine accurately radial velocity and chemicalabundances.2 A model of Galactic kinematicsIn order to analyze the spectroscopic data in combination with the photometric information and proper motion,we have developed a self-consistant model of the Galactic disk. The disk is describe as sum of 20 isothermalstellar components with a vertical velocity dispersion σzz ranging from 10 to 70 km.s−1. The distributionfunction of each component is built from three elementary functions describing the vertical density ρi, thekinematic distribution fi (3D-gaussians) and the luminosity function φik.We define N (z, VR, Vφ, Vz ;M) to be the density of stars in the Galactic position-velocity-absolute magnitudespace:N =∑ikρi(z)fi(VR, Vφ, Vz)φik(M), (2.1)where the index i differentiates the stellar components and the index k the absolute magnitudes used to modelthe luminosity function.We insert this model in the generalized equation of stellar statistics giving:A(m,µl, µb, Vr) =∫N(z, VR, Vφ, Vz ;M) z2 ω dz. (2.2)To determine A(m), the apparent magnitude count, together with the marginal distributions of the propermotion µl and µb and the distributions of radial velocities for any direction and apparent magnitudes.Assuming the stationarity of the density distribution, the consistency between the vertical velocity σzz,i anddensity ρi(z) distributions for each stellar component i is ensured by the following expression:ρi(z) = exp(−Φ(z)/σ2zz,i) (2.3)where Φ(z) is the vertical gravitational potential at the solar Galactic position.For the vertical gravitational potential, we use the recent determination obtained by Bienayme´ et al. (2006).The vertical potential is defined at the solar position by:Φ(z) = 4piG(Σ0(√z2 +D2 −D)+ ρeff z2)with Σ0 = 48M⊙ pc−2, D = 800 pc and ρeff = 0.07M⊙ pc−3.The kinematical model is given by shifted 3D gaussian velocity ellipsoids. For simplicity, we assume that theσRR/σφφ ratio is the same for all the stellar components. The velocity ellipsoids are inclined along the Galacticmeridian plane. The main axis of velocity ellipsoids are set parallel to confocal hyperboloids as in Sta¨ckelpotentials. The focus is set to zhyp=6kpc on the main axis giving them realistic orientations (see Bienayme´1999).The luminosity function of each stellar component is modeled with n different kinds of stars according totheir absolute magnitude:φi(M) =∑k=1,nφik(M) =1√2piσM∑k=1,ncik e−12(M−MkσM)2Galactic kinematics from RAVE to Gaia-RVS Data 49where cik is the density for each type of star (index k) of each stellar component (index i).3 ResultsWe have have adjusted the density of each stellar component to a sample of stars extracted from the 2MASScatalogue for the photometric data, the UCAC2 catalogue for proper motion and RAVE for the radial velocity.These stars are selected in color with J-K = [0.5-0.7]. In this color interval, we have defined 4 types of stars:Stars with a mean absolute magnitude MK = −1.61 are identified to be the red clump giants (k = 1), withMK = −0.89 and MK = −0.17 are first ascent giants stars (k = 2− 3) and with MK = 4.15 for dwarfs (k = 4).We neglected sub-giant populations with an absolute magnitude MK between 0.2 and 2. We adopt σM = 0.25for each kind of stars on the luminosity function.Adjusting the Galactic kinematical model to star counts, proper motions and radial velocities histograms,we obtained a kinematical decomposition of the Galactic disk (Fig. 1 left). The kinematical decompositionexhibits three main structures. We propose to identify the first one with vertical velocity dispersion σW =[10-25]km s−1 with the thin disk, the second with σW = [30-45] km s−1 with the thick disk. The decompositionshows a clear separation between the thin and thick components. For the third component with σW = [60-70]km s−1, the kinematical information is missing. This component could be a ’hot’ kinematically thick disk orthe halo.From the kinematical decomposition, the scale height of the thin and thick disk could be determined indepen-dently by fitting an exponential on the density ρ(z) (Fig. 1 right). We find a scale height for stellar componentswith σW = [10-25]km s−1 (thin disk) of 225±10pc, for stellar components with σW = [30-45]km s−1 (thickdisk) of 1048±36pc and the density ratio of thick to thin disk stars to be 8.7% at z=0pc. Our values are inagreement with previous determinations like the ones of Cabrera-Lavers et al. (2005) who have obtained a scaleheight of 267±13pc and 1062±52pc for the thin and thick disks respectively.Fig. 1. Left: Kinematical decomposition of the Galactic disk. Right: The logarithm of the vertical stellar density ρ(z)towards the the North Galactic Pole (dashed line) and its thin and thick disk decomposition (respectively thin and thicklines).From our model, the solar motion relative to the LSR and the asymmetric drift were also determined. Weobtained a value of u⊙=8.5±0.3km s−1, w⊙=11.1±1.0km s−1 and a thick disk lag is Vlag = 33±2km s−1 relativeto the LSR. v⊙ was fixed to = 5.2 km s−1, otherwise we could not measure the asymmetric drift.By looking at latitude |b| > 20◦, we measure a radial scale length of 2.5±0.4 kpc for the thin disk and3.5±1.0kpc for the thick disk. There is no consensus on the values of the scale length of the values of the scalelength of the thin and thick disk, but our values are in relative agreement, for example, with Ojha (2001) whofinds 2.8±0.3kpc for the thin disk and 3.70.8−0.5 kpc for the thick disk.50 SF2A 20084 ConclusionsThe fact that the decomposition of the Galactic disk reveals the kinematical separation of the thin and thethick disk puts some constraints on the scenarios of the Galactic disk formation. The thick disk could not havebeen created by a continuous ‘heating’ mechanism like the diffusion due to molecular clouds or spiral arms.The scientific use of the RAVE data has already permitted us to obtain a lot of results on Galactic structureand kinematics: constrains on the local Galactic escape speed (Smith et al. 2007), absence of the Sgr streamnear the Sun (Seabroke et al. 2008), scale height of the thin and thick disk (Veltz et al. 2008), vertical tilt ofthe ellipsoid (Siebert et al. 2008). With the accuracy and number of stars that will be observed by Gaia, thefuture is very promising for the analysis of the structure and kinematics of the disk. All these new informationswill help to improve our understanding of the formation and evolution not only of the Milky Way but also thegalaxies in general.AcknowledgmentsFunding for RAVE has been provided by the Anglo-Australian Observatory, by the Astrophysical InstitutePotsdam, by the Australian Research Council, by the German Research Foundation, by the National Institute forAstrophysics at Padova, by The Johns Hopkins University, by the Netherlands Research School for Astronomy,by the Natural Sciences and Engineering Research Council of Canada, by the Slovenian Research Agency, bythe Swiss National Science Foundation, by the National Science Foundation of the USA, by the NetherlandsOrganisation for Scientific Research, by the Particle Physics and Astronomy Research Council of the UK, byOpticon, by Strasbourg Observatory, and by the Universities of Basel, Cambridge, and Groningen.The RAVE web site is at http://www.rave-survey.org.ReferencesBienayme´, O. 1999, A&A, 341,86Bienayme´, O., Soubiran, C., Mishenina, T. V., Kovtyukh, V. V. & Siebert, A. 2006, A&A, 446, 933Cabrera-Lavers, A., Garzn, F., & Hammersley, P. L. 2005, A&A, 433, 173Katz, D., Munari, U., Cropper, et al. 2004, MNRAS, 354, 1223Munari, U. 1999, Baltic Astronomy, 8, 73Munari, U. 2003, editor, ASPC: ”GAIA Spectroscopy: Science and Technology”, 298Ojha, D. K. 2001, MNRAS, 322, 426Seabroke, G. M., Gilmore, G., Siebert, A., et al. 2008, MNRAS, 384, 11Siebert, A., Bienayme´, O., Binney, J., et al. 2008, arXiv0809.0615Smith, M. C., Ruchti, G. R., Helmi, A., Wyse, R. F. G., & Fulbright, J. P., et al. 2007, MNRAS, 379, 755Steinmetz, M 2003, ASPC: ”Gaia Spectroscopy: Science and Technology”, 298, 381Steinmetz, M., Zwitter, T., Siebert, A., et al. 2006, AJ, 132, 1645Veltz, L., Bienayme´, O.; Freeman, K. C., et al. 2008, A&A, 480, 753Watson, F. G., Parker, Q. A., Bogatu, G., et al. 2000, Proc. SPIE, 4008, 123Zwitter, T., Siebert, A., Munari, U., et al. 2008, AJ, 136, 421

Proceedings - University of Groningen

   University of GroningenGalactic kinematics from RAVE to Gaia-RVS DataVeltz, L.; Bienaymé, O.; Steinmetz, M.; Zwitter, T.; Watson, F.~G.; Binney, J.; Bland-Hawthorn, J.; Campbell, R. .; Freeman, K.~C.; Gibson, B.Published in:SF2A-2008IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2008Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Veltz, L., Bienaymé, O., Steinmetz, M., Zwitter, T., Watson, F. G., Binney, J., Bland-Hawthorn, J.,Campbell, R. ., Freeman, K. C., Gibson, B., Gilmore, G., Grebel, E. K., Helmi, A., Munari, U., Navarro, J. F.,Parker, Q. A., Seabroke, G., Siebert, A., Siviero, A., ... Wyse, R. F. G. (2008). Galactic kinematics fromRAVE to Gaia-RVS Data. In SF2A-2008 (pp. 47). Société Francaise d’Astronomie et d’Astrophysique(SF2A).CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 05-06-2022SF2A 2008C. Charbonnel, F. Combes and R. Samadi (eds)GALACTIC KINEMATICS FROM RAVE TO GAIA-RVS DATAVeltz, L.1, Bienaymé, O.2, Steinmetz, M.1 , Zwitter, T.3, Watson, F. G.4, Binney, J.5,Bland-Hawthorn, J.6, Campbell, R..1 , Freeman, K. C.7, Gibson, B.8, Gilmore, G.9, Grebel, E. K.10,Helmi, A.11, Munari, U.12, Navarro, J. F.13, Parker, Q. A.14, Seabroke, G.15, Siebert, A.2 , Siviero,A.12,1 , Williams, M.1 and Wyse, R. F. G.16Abstract. RAVE data has provided new results on Galactic kinematics like the kinematical decompositionof the Galactic disk. This decomposition permits to identify the different components of the disk and tocharacterize them in terms of scale height and scale length. With the data provided by Gaia and in particularthe RVS, we will have a completly renewed view of the Galaxy. The precision of the RVS will permit toundertake a precise analysis of the kinematics of the Galactic disks. This knowledge will provide significantclues to constrain the scenarios of the Galactic disk formation.1 IntroductionThe hierarchical formation scenario is a great success in describing the formation of the large-scale structureof the universe. But, the detailed mechanisms of formation of individual galaxies are still an open question.Some answers to this question rely on the knowledge of the position, the kinematics and chemical compositionof the stars of the Milky Way. Therefore, in 2000, ESA has approved the Gaia mission that will provide the 6-D(position-velocity) information for 50 millions stars in the Galaxy. The expected launch of the Gaia satelliteis planned for 2011. As a precursor in the spectroscopic area, an international cooperation called ”RAdialVelocity Experiment” (RAVE) has started in 2003 a survey of one million stars in the southern sky hemisphere(Steinmetz 2003). There has been already two data releases. The first release contains about 25 000 radialvelocity measurements (Steinmetz et al. 2006). The second data release contains about 25 000 radial velocitymeasurements more and 20000 stars for which the stellar parameters ([M/H ], log g, Teff) have been determined(Zwitter et al. 2008). The spectroscopic acquisition techniques differ between RAVE and the Gaia RadialVelocity Spectrometer (RVS), although they have almost the same resolution and wavelength range.1 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Postdam, Germany2 Observatoire Astronomique de Strasbourg, 11 rue de l’Universit, 67000 Strasbourg, France3 University of Ljubljana, Department of Physics, Jadranska 19, 1000 Ljubljana, Slovenia4 Anglo-Australian Observatory, Coonabarabran, NSW 2357, Australia5 Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, UK6 School of Physics, University of Sydney, NSW 2006, Australia7 Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia8 Centre for Astrophysics, University of Central Lancashire, Preston, UK9 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, UK10 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrae 12-14, 69120 Heidelberg,Germany11 Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, Netherlands12 Osservatorio Astronomico di Padova - INAF, Sede di Asiago, 36012 Asiago, Italy13 Department of Physics and Astronomy, University of Victoria, P.O.Box 3055, Victoria, Canada14 Department of Physics, Macquarie University, NSW 2109, Australia15 Planetary & Space Sciences Research Institute, The Open University, Milton Keynes, UK16 Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, USAc© Société Francaise d’Astronomie et d’Astrophysique (SF2A) 200848 SF2A 2008The RAVE spectra are obtained with the multi-fiber spectrograph 6dF (Watson et al. 2000) on the UKSchmidt telescope at the Anglo-Australian Observatory. Each field is observed during five exposures of 600seconds. The RVS is an integral field instrument on board of the Gaia satellite that will not use fibers (Katzet al. 2004). The observation will be done in a time delay integration scan mode. Each spectrum will beexposed for 4 seconds.The 6dF spectrograph and RVS are medium resolution instruments with R = 7500 and 11500, respectively.The spectra have a near infrared wavelength range between [8470 - 8740] Å for Gaia-RVS and [8410 - 8795]Å for RAVE. This wavelength range and resolution have three main advantages (Munari 1999, 2003). Theypresent the lowest possible contamination by telluric absorptions that will facilitate the pre- and post- Gaiamission observations from the ground. According to the Galaxy model, the largest number of stars that will beobserved by Gaia will have an energy distribution that peaks in this wavelength range due to their spectral typeor the interstellar extinction. In this wavelength range, the presence of the CaII triplet lines for cool stars, thePaschen lines for hot stars and metallic lines will be useful to determine accurately radial velocity and chemicalabundances.2 A model of Galactic kinematicsIn order to analyze the spectroscopic data in combination with the photometric information and proper motion,we have developed a self-consistant model of the Galactic disk. The disk is describe as sum of 20 isothermalstellar components with a vertical velocity dispersion σzz ranging from 10 to 70 km.s−1. The distributionfunction of each component is built from three elementary functions describing the vertical density ρi, thekinematic distribution fi (3D-gaussians) and the luminosity function φik.We define N (z, VR, Vφ, Vz ; M) to be the density of stars in the Galactic position-velocity-absolute magnitudespace:N =∑ikρi(z)fi(VR, Vφ, Vz)φik(M), (2.1)where the index i differentiates the stellar components and the index k the absolute magnitudes used to modelthe luminosity function.We insert this model in the generalized equation of stellar statistics giving:A(m, µl, µb, Vr) =∫N(z, VR, Vφ, Vz ; M) z2 ω dz. (2.2)To determine A(m), the apparent magnitude count, together with the marginal distributions of the propermotion µl and µb and the distributions of radial velocities for any direction and apparent magnitudes.Assuming the stationarity of the density distribution, the consistency between the vertical velocity σzz,i anddensity ρi(z) distributions for each stellar component i is ensured by the following expression:ρi(z) = exp(−Φ(z)/σ2zz,i)(2.3)where Φ(z) is the vertical gravitational potential at the solar Galactic position.For the vertical gravitational potential, we use the recent determination obtained by Bienaymé et al. (2006).The vertical potential is defined at the solar position by:Φ(z) = 4πG(Σ0(√z2 + D2 − D)+ ρeff z2)with Σ0 = 48 M⊙ pc−2, D = 800 pc and ρeff = 0.07 M⊙ pc−3.The kinematical model is given by shifted 3D gaussian velocity ellipsoids. For simplicity, we assume that theσRR/σφφ ratio is the same for all the stellar components. The velocity ellipsoids are inclined along the Galacticmeridian plane. The main axis of velocity ellipsoids are set parallel to confocal hyperboloids as in Stäckelpotentials. The focus is set to zhyp=6kpc on the main axis giving them realistic orientations (see Bienaymé1999).The luminosity function of each stellar component is modeled with n different kinds of stars according totheir absolute magnitude:φi(M) =∑k=1,nφik(M) =1√2πσM∑k=1,ncik e−12(M−MkσM)2Galactic kinematics from RAVE to Gaia-RVS Data 49where cik is the density for each type of star (index k) of each stellar component (index i).3 ResultsWe have have adjusted the density of each stellar component to a sample of stars extracted from the 2MASScatalogue for the photometric data, the UCAC2 catalogue for proper motion and RAVE for the radial velocity.These stars are selected in color with J-K = [0.5-0.7]. In this color interval, we have defined 4 types of stars:Stars with a mean absolute magnitude MK = −1.61 are identified to be the red clump giants (k = 1), withMK = −0.89 and MK = −0.17 are first ascent giants stars (k = 2 − 3) and with MK = 4.15 for dwarfs (k = 4).We neglected sub-giant populations with an absolute magnitude MK between 0.2 and 2. We adopt σM = 0.25for each kind of stars on the luminosity function.Adjusting the Galactic kinematical model to star counts, proper motions and radial velocities histograms,we obtained a kinematical decomposition of the Galactic disk (Fig. 1 left). The kinematical decompositionexhibits three main structures. We propose to identify the first one with vertical velocity dispersion σW =[10-25]km s−1 with the thin disk, the second with σW = [30-45] km s−1 with the thick disk. The decompositionshows a clear separation between the thin and thick components. For the third component with σW = [60-70]km s−1, the kinematical information is missing. This component could be a ’hot’ kinematically thick disk orthe halo.From the kinematical decomposition, the scale height of the thin and thick disk could be determined indepen-dently by fitting an exponential on the density ρ(z) (Fig. 1 right). We find a scale height for stellar componentswith σW = [10-25]km s−1 (thin disk) of 225±10pc, for stellar components with σW = [30-45]km s−1 (thickdisk) of 1048±36pc and the density ratio of thick to thin disk stars to be 8.7% at z=0pc. Our values are inagreement with previous determinations like the ones of Cabrera-Lavers et al. (2005) who have obtained a scaleheight of 267±13pc and 1062±52pc for the thin and thick disks respectively.Fig. 1. Left: Kinematical decomposition of the Galactic disk. Right: The logarithm of the vertical stellar density ρ(z)towards the the North Galactic Pole (dashed line) and its thin and thick disk decomposition (respectively thin and thicklines).From our model, the solar motion relative to the LSR and the asymmetric drift were also determined. Weobtained a value of u⊙=8.5±0.3km s−1, w⊙=11.1±1.0km s−1 and a thick disk lag is Vlag = 33±2km s−1 relativeto the LSR. v⊙ was fixed to = 5.2 km s−1, otherwise we could not measure the asymmetric drift.By looking at latitude |b| > 20◦, we measure a radial scale length of 2.5±0.4 kpc for the thin disk and3.5±1.0kpc for the thick disk. There is no consensus on the values of the scale length of the values of the scalelength of the thin and thick disk, but our values are in relative agreement, for example, with Ojha (2001) whofinds 2.8±0.3kpc for the thin disk and 3.70.8−0.5 kpc for the thick disk.50 SF2A 20084 ConclusionsThe fact that the decomposition of the Galactic disk reveals the kinematical separation of the thin and thethick disk puts some constraints on the scenarios of the Galactic disk formation. The thick disk could not havebeen created by a continuous ‘heating’ mechanism like the diffusion due to molecular clouds or spiral arms.The scientific use of the RAVE data has already permitted us to obtain a lot of results on Galactic structureand kinematics: constrains on the local Galactic escape speed (Smith et al. 2007), absence of the Sgr streamnear the Sun (Seabroke et al. 2008), scale height of the thin and thick disk (Veltz et al. 2008), vertical tilt ofthe ellipsoid (Siebert et al. 2008). With the accuracy and number of stars that will be observed by Gaia, thefuture is very promising for the analysis of the structure and kinematics of the disk. All these new informationswill help to improve our understanding of the formation and evolution not only of the Milky Way but also thegalaxies in general.AcknowledgmentsFunding for RAVE has been provided by the Anglo-Australian Observatory, by the Astrophysical InstitutePotsdam, by the Australian Research Council, by the German Research Foundation, by the National Institute forAstrophysics at Padova, by The Johns Hopkins University, by the Netherlands Research School for Astronomy,by the Natural Sciences and Engineering Research Council of Canada, by the Slovenian Research Agency, bythe Swiss National Science Foundation, by the National Science Foundation of the USA, by the NetherlandsOrganisation for Scientific Research, by the Particle Physics and Astronomy Research Council of the UK, byOpticon, by Strasbourg Observatory, and by the Universities of Basel, Cambridge, and Groningen.The RAVE web site is at http://www.rave-survey.org.ReferencesBienaymé, O. 1999, A&A, 341,86Bienaymé, O., Soubiran, C., Mishenina, T. V., Kovtyukh, V. V. & Siebert, A. 2006, A&A, 446, 933Cabrera-Lavers, A., Garzn, F., & Hammersley, P. L. 2005, A&A, 433, 173Katz, D., Munari, U., Cropper, et al. 2004, MNRAS, 354, 1223Munari, U. 1999, Baltic Astronomy, 8, 73Munari, U. 2003, editor, ASPC: ”GAIA Spectroscopy: Science and Technology”, 298Ojha, D. K. 2001, MNRAS, 322, 426Seabroke, G. M., Gilmore, G., Siebert, A., et al. 2008, MNRAS, 384, 11Siebert, A., Bienaymé, O., Binney, J., et al. 2008, arXiv0809.0615Smith, M. C., Ruchti, G. R., Helmi, A., Wyse, R. F. G., & Fulbright, J. P., et al. 2007, MNRAS, 379, 755Steinmetz, M 2003, ASPC: ”Gaia Spectroscopy: Science and Technology”, 298, 381Steinmetz, M., Zwitter, T., Siebert, A., et al. 2006, AJ, 132, 1645Veltz, L., Bienaymé, O.; Freeman, K. C., et al. 2008, A&A, 480, 753Watson, F. G., Parker, Q. A., Bogatu, G., et al. 2000, Proc. SPIE, 4008, 123Zwitter, T., Siebert, A., Munari, U., et al. 2008, AJ, 136, 421

Watson, F. G.

Campbell, R.

Freeman, K.

Grebel, E. K.

Navarro, J. F.

Parker, Q.

Seabroke, G. M.

Wyse, R. F. G.

Open Research Online (The Open University)

University of Groningen Research Database

  
 University of Groningen
Galactic kinematics from RAVE to Gaia-RVS Data
Veltz, L.; Bienaymé, O.; Steinmetz, M.; Zwitter, T.; Watson, F.~G.; Binney, J.; Bland-
Hawthorn, J.; Campbell, R. .; Freeman, K.~C.; Gibson, B.
Published in:
SF2A-2008
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from
it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date:
2008
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Veltz, L., Bienaymé, O., Steinmetz, M., Zwitter, T., Watson, F. G., Binney, J., ... Wyse, R. F. G. (2008).
Galactic kinematics from RAVE to Gaia-RVS Data. In SF2A-2008 (pp. 47). Société Francaise d’Astronomie
et d’Astrophysique (SF2A).
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the
author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the
number of authors shown on this cover page is limited to 10 maximum.
Download date: 21-05-2019
SF2A 2008
C. Charbonnel, F. Combes and R. Samadi (eds)
GALACTIC KINEMATICS FROM RAVE TO GAIA-RVS DATA
Veltz, L.1, Bienayme´, O.2, Steinmetz, M.1 , Zwitter, T.3, Watson, F. G.4, Binney, J.5,
Bland-Hawthorn, J.6, Campbell, R..1 , Freeman, K. C.7, Gibson, B.8, Gilmore, G.9, Grebel, E. K.10,
Helmi, A.11, Munari, U.12, Navarro, J. F.13, Parker, Q. A.14, Seabroke, G.15, Siebert, A.2 , Siviero,
A.12,1 , Williams, M.1 and Wyse, R. F. G.16
Abstract. RAVE data has provided new results on Galactic kinematics like the kinematical decomposition
of the Galactic disk. This decomposition permits to identify the different components of the disk and to
characterize them in terms of scale height and scale length. With the data provided by Gaia and in particular
the RVS, we will have a completly renewed view of the Galaxy. The precision of the RVS will permit to
undertake a precise analysis of the kinematics of the Galactic disks. This knowledge will provide significant
clues to constrain the scenarios of the Galactic disk formation.
1 Introduction
The hierarchical formation scenario is a great success in describing the formation of the large-scale structure
of the universe. But, the detailed mechanisms of formation of individual galaxies are still an open question.
Some answers to this question rely on the knowledge of the position, the kinematics and chemical composition
of the stars of the Milky Way. Therefore, in 2000, ESA has approved the Gaia mission that will provide the 6-D
(position-velocity) information for 50 millions stars in the Galaxy. The expected launch of the Gaia satellite
is planned for 2011. As a precursor in the spectroscopic area, an international cooperation called ”RAdial
Velocity Experiment” (RAVE) has started in 2003 a survey of one million stars in the southern sky hemisphere
(Steinmetz 2003). There has been already two data releases. The first release contains about 25 000 radial
velocity measurements (Steinmetz et al. 2006). The second data release contains about 25 000 radial velocity
measurements more and 20000 stars for which the stellar parameters ([M/H ], log g, Teff) have been determined
(Zwitter et al. 2008). The spectroscopic acquisition techniques differ between RAVE and the Gaia Radial
Velocity Spectrometer (RVS), although they have almost the same resolution and wavelength range.
1 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Postdam, Germany
2 Observatoire Astronomique de Strasbourg, 11 rue de l’Universit, 67000 Strasbourg, France
3 University of Ljubljana, Department of Physics, Jadranska 19, 1000 Ljubljana, Slovenia
4 Anglo-Australian Observatory, Coonabarabran, NSW 2357, Australia
5 Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, UK
6 School of Physics, University of Sydney, NSW 2006, Australia
7 Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia
8 Centre for Astrophysics, University of Central Lancashire, Preston, UK
9 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, UK
10 Astronomisches Rechen-Institut, Zentrum fu¨r Astronomie der Universita¨t Heidelberg, Mo¨nchhofstrae 12-14, 69120 Heidelberg,
Germany
11 Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, Netherlands
12 Osservatorio Astronomico di Padova - INAF, Sede di Asiago, 36012 Asiago, Italy
13 Department of Physics and Astronomy, University of Victoria, P.O.Box 3055, Victoria, Canada
14 Department of Physics, Macquarie University, NSW 2109, Australia
15 Planetary & Space Sciences Research Institute, The Open University, Milton Keynes, UK
16 Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, USA
c© Socie´te´ Francaise d’Astronomie et d’Astrophysique (SF2A) 2008
48 SF2A 2008
The RAVE spectra are obtained with the multi-fiber spectrograph 6dF (Watson et al. 2000) on the UK
Schmidt telescope at the Anglo-Australian Observatory. Each field is observed during five exposures of 600
seconds. The RVS is an integral field instrument on board of the Gaia satellite that will not use fibers (Katz
et al. 2004). The observation will be done in a time delay integration scan mode. Each spectrum will be
exposed for 4 seconds.
The 6dF spectrograph and RVS are medium resolution instruments with R = 7500 and 11500, respectively.
The spectra have a near infrared wavelength range between [8470 - 8740] A˚ for Gaia-RVS and [8410 - 8795]
A˚ for RAVE. This wavelength range and resolution have three main advantages (Munari 1999, 2003). They
present the lowest possible contamination by telluric absorptions that will facilitate the pre- and post- Gaia
mission observations from the ground. According to the Galaxy model, the largest number of stars that will be
observed by Gaia will have an energy distribution that peaks in this wavelength range due to their spectral type
or the interstellar extinction. In this wavelength range, the presence of the CaII triplet lines for cool stars, the
Paschen lines for hot stars and metallic lines will be useful to determine accurately radial velocity and chemical
abundances.
2 A model of Galactic kinematics
In order to analyze the spectroscopic data in combination with the photometric information and proper motion,
we have developed a self-consistant model of the Galactic disk. The disk is describe as sum of 20 isothermal
stellar components with a vertical velocity dispersion σzz ranging from 10 to 70 km.s
−1. The distribution
function of each component is built from three elementary functions describing the vertical density ρi, the
kinematic distribution fi (3D-gaussians) and the luminosity function φik.
We define N (z, VR, Vφ, Vz ;M) to be the density of stars in the Galactic position-velocity-absolute magnitude
space:
N =
∑
ik
ρi(z)fi(VR, Vφ, Vz)φik(M), (2.1)
where the index i differentiates the stellar components and the index k the absolute magnitudes used to model
the luminosity function.
We insert this model in the generalized equation of stellar statistics giving:
A(m,µl, µb, Vr) =
∫
N(z, VR, Vφ, Vz ;M) z
2 ω dz. (2.2)
To determine A(m), the apparent magnitude count, together with the marginal distributions of the proper
motion µl and µb and the distributions of radial velocities for any direction and apparent magnitudes.
Assuming the stationarity of the density distribution, the consistency between the vertical velocity σzz,i and
density ρi(z) distributions for each stellar component i is ensured by the following expression:
ρi(z) = exp
(−Φ(z)/σ2zz,i) (2.3)
where Φ(z) is the vertical gravitational potential at the solar Galactic position.
For the vertical gravitational potential, we use the recent determination obtained by Bienayme´ et al. (2006).
The vertical potential is defined at the solar position by:
Φ(z) = 4piG
(
Σ0
(√
z2 +D2 −D
)
+ ρeff z
2
)
with Σ0 = 48M⊙ pc
−2, D = 800 pc and ρeff = 0.07M⊙ pc
−3.
The kinematical model is given by shifted 3D gaussian velocity ellipsoids. For simplicity, we assume that the
σRR/σφφ ratio is the same for all the stellar components. The velocity ellipsoids are inclined along the Galactic
meridian plane. The main axis of velocity ellipsoids are set parallel to confocal hyperboloids as in Sta¨ckel
potentials. The focus is set to zhyp=6kpc on the main axis giving them realistic orientations (see Bienayme´
1999).
The luminosity function of each stellar component is modeled with n different kinds of stars according to
their absolute magnitude:
φi(M) =
∑
k=1,n
φik(M) =
1√
2piσM
∑
k=1,n
cik e
−
1
2
(
M−M
k
σM
)
2
Galactic kinematics from RAVE to Gaia-RVS Data 49
where cik is the density for each type of star (index k) of each stellar component (index i).
3 Results
We have have adjusted the density of each stellar component to a sample of stars extracted from the 2MASS
catalogue for the photometric data, the UCAC2 catalogue for proper motion and RAVE for the radial velocity.
These stars are selected in color with J-K = [0.5-0.7]. In this color interval, we have defined 4 types of stars:
Stars with a mean absolute magnitude MK = −1.61 are identified to be the red clump giants (k = 1), with
MK = −0.89 and MK = −0.17 are first ascent giants stars (k = 2− 3) and with MK = 4.15 for dwarfs (k = 4).
We neglected sub-giant populations with an absolute magnitude MK between 0.2 and 2. We adopt σM = 0.25
for each kind of stars on the luminosity function.
Adjusting the Galactic kinematical model to star counts, proper motions and radial velocities histograms,
we obtained a kinematical decomposition of the Galactic disk (Fig. 1 left). The kinematical decomposition
exhibits three main structures. We propose to identify the first one with vertical velocity dispersion σW =
[10-25]km s−1 with the thin disk, the second with σW = [30-45] km s
−1 with the thick disk. The decomposition
shows a clear separation between the thin and thick components. For the third component with σW = [60-70]
km s−1, the kinematical information is missing. This component could be a ’hot’ kinematically thick disk or
the halo.
From the kinematical decomposition, the scale height of the thin and thick disk could be determined indepen-
dently by fitting an exponential on the density ρ(z) (Fig. 1 right). We find a scale height for stellar components
with σW = [10-25]km s
−1 (thin disk) of 225±10pc, for stellar components with σW = [30-45]km s−1 (thick
disk) of 1048±36pc and the density ratio of thick to thin disk stars to be 8.7% at z=0pc. Our values are in
agreement with previous determinations like the ones of Cabrera-Lavers et al. (2005) who have obtained a scale
height of 267±13pc and 1062±52pc for the thin and thick disks respectively.
Fig. 1. Left: Kinematical decomposition of the Galactic disk. Right: The logarithm of the vertical stellar density ρ(z)
towards the the North Galactic Pole (dashed line) and its thin and thick disk decomposition (respectively thin and thick
lines).
From our model, the solar motion relative to the LSR and the asymmetric drift were also determined. We
obtained a value of u⊙=8.5±0.3km s−1, w⊙=11.1±1.0km s−1 and a thick disk lag is Vlag = 33±2km s−1 relative
to the LSR. v⊙ was fixed to = 5.2 km s
−1, otherwise we could not measure the asymmetric drift.
By looking at latitude |b| > 20◦, we measure a radial scale length of 2.5±0.4 kpc for the thin disk and
3.5±1.0kpc for the thick disk. There is no consensus on the values of the scale length of the values of the scale
length of the thin and thick disk, but our values are in relative agreement, for example, with Ojha (2001) who
finds 2.8±0.3kpc for the thin disk and 3.70.8−0.5 kpc for the thick disk.
50 SF2A 2008
4 Conclusions
The fact that the decomposition of the Galactic disk reveals the kinematical separation of the thin and the
thick disk puts some constraints on the scenarios of the Galactic disk formation. The thick disk could not have
been created by a continuous ‘heating’ mechanism like the diffusion due to molecular clouds or spiral arms.
The scientific use of the RAVE data has already permitted us to obtain a lot of results on Galactic structure
and kinematics: constrains on the local Galactic escape speed (Smith et al. 2007), absence of the Sgr stream
near the Sun (Seabroke et al. 2008), scale height of the thin and thick disk (Veltz et al. 2008), vertical tilt of
the ellipsoid (Siebert et al. 2008). With the accuracy and number of stars that will be observed by Gaia, the
future is very promising for the analysis of the structure and kinematics of the disk. All these new informations
will help to improve our understanding of the formation and evolution not only of the Milky Way but also the
galaxies in general.
Acknowledgments
Funding for RAVE has been provided by the Anglo-Australian Observatory, by the Astrophysical Institute
Potsdam, by the Australian Research Council, by the German Research Foundation, by the National Institute for
Astrophysics at Padova, by The Johns Hopkins University, by the Netherlands Research School for Astronomy,
by the Natural Sciences and Engineering Research Council of Canada, by the Slovenian Research Agency, by
the Swiss National Science Foundation, by the National Science Foundation of the USA, by the Netherlands
Organisation for Scientific Research, by the Particle Physics and Astronomy Research Council of the UK, by
Opticon, by Strasbourg Observatory, and by the Universities of Basel, Cambridge, and Groningen.
The RAVE web site is at http://www.rave-survey.org.
References
Bienayme´, O. 1999, A&A, 341,86
Bienayme´, O., Soubiran, C., Mishenina, T. V., Kovtyukh, V. V. & Siebert, A. 2006, A&A, 446, 933
Cabrera-Lavers, A., Garzn, F., & Hammersley, P. L. 2005, A&A, 433, 173
Katz, D., Munari, U., Cropper, et al. 2004, MNRAS, 354, 1223
Munari, U. 1999, Baltic Astronomy, 8, 73
Munari, U. 2003, editor, ASPC: ”GAIA Spectroscopy: Science and Technology”, 298
Ojha, D. K. 2001, MNRAS, 322, 426
Seabroke, G. M., Gilmore, G., Siebert, A., et al. 2008, MNRAS, 384, 11
Siebert, A., Bienayme´, O., Binney, J., et al. 2008, arXiv0809.0615
Smith, M. C., Ruchti, G. R., Helmi, A., Wyse, R. F. G., & Fulbright, J. P., et al. 2007, MNRAS, 379, 755
Steinmetz, M 2003, ASPC: ”Gaia Spectroscopy: Science and Technology”, 298, 381
Steinmetz, M., Zwitter, T., Siebert, A., et al. 2006, AJ, 132, 1645
Veltz, L., Bienayme´, O.; Freeman, K. C., et al. 2008, A&A, 480, 753
Watson, F. G., Parker, Q. A., Bogatu, G., et al. 2000, Proc. SPIE, 4008, 123
Zwitter, T., Siebert, A., Munari, U., et al. 2008, AJ, 136, 421


   University of GroningenGalactic kinematics from RAVE to Gaia-RVS DataVeltz, L.; Bienaymé, O.; Steinmetz, M.; Zwitter, T.; Watson, F.~G.; Binney, J.; Bland-Hawthorn, J.; Campbell, R. .; Freeman, K.~C.; Gibson, B.Published in:SF2A-2008IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2008Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Veltz, L., Bienaymé, O., Steinmetz, M., Zwitter, T., Watson, F. G., Binney, J., Bland-Hawthorn, J.,Campbell, R. ., Freeman, K. C., Gibson, B., Gilmore, G., Grebel, E. K., Helmi, A., Munari, U., Navarro, J. F.,Parker, Q. A., Seabroke, G., Siebert, A., Siviero, A., ... Wyse, R. F. G. (2008). Galactic kinematics fromRAVE to Gaia-RVS Data. In SF2A-2008 (pp. 47). Société Francaise d’Astronomie et d’Astrophysique(SF2A).CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 10-09-2023SF2A 2008C. Charbonnel, F. Combes and R. Samadi (eds)GALACTIC KINEMATICS FROM RAVE TO GAIA-RVS DATAVeltz, L.1, Bienaymé, O.2, Steinmetz, M.1 , Zwitter, T.3, Watson, F. G.4, Binney, J.5,Bland-Hawthorn, J.6, Campbell, R..1 , Freeman, K. C.7, Gibson, B.8, Gilmore, G.9, Grebel, E. K.10,Helmi, A.11, Munari, U.12, Navarro, J. F.13, Parker, Q. A.14, Seabroke, G.15, Siebert, A.2 , Siviero,A.12,1 , Williams, M.1 and Wyse, R. F. G.16Abstract. RAVE data has provided new results on Galactic kinematics like the kinematical decompositionof the Galactic disk. This decomposition permits to identify the different components of the disk and tocharacterize them in terms of scale height and scale length. With the data provided by Gaia and in particularthe RVS, we will have a completly renewed view of the Galaxy. The precision of the RVS will permit toundertake a precise analysis of the kinematics of the Galactic disks. This knowledge will provide significantclues to constrain the scenarios of the Galactic disk formation.1 IntroductionThe hierarchical formation scenario is a great success in describing the formation of the large-scale structureof the universe. But, the detailed mechanisms of formation of individual galaxies are still an open question.Some answers to this question rely on the knowledge of the position, the kinematics and chemical compositionof the stars of the Milky Way. Therefore, in 2000, ESA has approved the Gaia mission that will provide the 6-D(position-velocity) information for 50 millions stars in the Galaxy. The expected launch of the Gaia satelliteis planned for 2011. As a precursor in the spectroscopic area, an international cooperation called ”RAdialVelocity Experiment” (RAVE) has started in 2003 a survey of one million stars in the southern sky hemisphere(Steinmetz 2003). There has been already two data releases. The first release contains about 25 000 radialvelocity measurements (Steinmetz et al. 2006). The second data release contains about 25 000 radial velocitymeasurements more and 20000 stars for which the stellar parameters ([M/H ], log g, Teff) have been determined(Zwitter et al. 2008). The spectroscopic acquisition techniques differ between RAVE and the Gaia RadialVelocity Spectrometer (RVS), although they have almost the same resolution and wavelength range.1 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Postdam, Germany2 Observatoire Astronomique de Strasbourg, 11 rue de l’Universit, 67000 Strasbourg, France3 University of Ljubljana, Department of Physics, Jadranska 19, 1000 Ljubljana, Slovenia4 Anglo-Australian Observatory, Coonabarabran, NSW 2357, Australia5 Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, UK6 School of Physics, University of Sydney, NSW 2006, Australia7 Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia8 Centre for Astrophysics, University of Central Lancashire, Preston, UK9 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, UK10 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrae 12-14, 69120 Heidelberg,Germany11 Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, Netherlands12 Osservatorio Astronomico di Padova - INAF, Sede di Asiago, 36012 Asiago, Italy13 Department of Physics and Astronomy, University of Victoria, P.O.Box 3055, Victoria, Canada14 Department of Physics, Macquarie University, NSW 2109, Australia15 Planetary & Space Sciences Research Institute, The Open University, Milton Keynes, UK16 Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, USAc© Société Francaise d’Astronomie et d’Astrophysique (SF2A) 200848 SF2A 2008The RAVE spectra are obtained with the multi-fiber spectrograph 6dF (Watson et al. 2000) on the UKSchmidt telescope at the Anglo-Australian Observatory. Each field is observed during five exposures of 600seconds. The RVS is an integral field instrument on board of the Gaia satellite that will not use fibers (Katzet al. 2004). The observation will be done in a time delay integration scan mode. Each spectrum will beexposed for 4 seconds.The 6dF spectrograph and RVS are medium resolution instruments with R = 7500 and 11500, respectively.The spectra have a near infrared wavelength range between [8470 - 8740] Å for Gaia-RVS and [8410 - 8795]Å for RAVE. This wavelength range and resolution have three main advantages (Munari 1999, 2003). Theypresent the lowest possible contamination by telluric absorptions that will facilitate the pre- and post- Gaiamission observations from the ground. According to the Galaxy model, the largest number of stars that will beobserved by Gaia will have an energy distribution that peaks in this wavelength range due to their spectral typeor the interstellar extinction. In this wavelength range, the presence of the CaII triplet lines for cool stars, thePaschen lines for hot stars and metallic lines will be useful to determine accurately radial velocity and chemicalabundances.2 A model of Galactic kinematicsIn order to analyze the spectroscopic data in combination with the photometric information and proper motion,we have developed a self-consistant model of the Galactic disk. The disk is describe as sum of 20 isothermalstellar components with a vertical velocity dispersion σzz ranging from 10 to 70 km.s−1. The distributionfunction of each component is built from three elementary functions describing the vertical density ρi, thekinematic distribution fi (3D-gaussians) and the luminosity function φik.We define N (z, VR, Vφ, Vz ; M) to be the density of stars in the Galactic position-velocity-absolute magnitudespace:N =∑ikρi(z)fi(VR, Vφ, Vz)φik(M), (2.1)where the index i differentiates the stellar components and the index k the absolute magnitudes used to modelthe luminosity function.We insert this model in the generalized equation of stellar statistics giving:A(m, µl, µb, Vr) =∫N(z, VR, Vφ, Vz ; M) z2 ω dz. (2.2)To determine A(m), the apparent magnitude count, together with the marginal distributions of the propermotion µl and µb and the distributions of radial velocities for any direction and apparent magnitudes.Assuming the stationarity of the density distribution, the consistency between the vertical velocity σzz,i anddensity ρi(z) distributions for each stellar component i is ensured by the following expression:ρi(z) = exp(−Φ(z)/σ2zz,i)(2.3)where Φ(z) is the vertical gravitational potential at the solar Galactic position.For the vertical gravitational potential, we use the recent determination obtained by Bienaymé et al. (2006).The vertical potential is defined at the solar position by:Φ(z) = 4πG(Σ0(√z2 + D2 − D)+ ρeff z2)with Σ0 = 48 M⊙ pc−2, D = 800 pc and ρeff = 0.07 M⊙ pc−3.The kinematical model is given by shifted 3D gaussian velocity ellipsoids. For simplicity, we assume that theσRR/σφφ ratio is the same for all the stellar components. The velocity ellipsoids are inclined along the Galacticmeridian plane. The main axis of velocity ellipsoids are set parallel to confocal hyperboloids as in Stäckelpotentials. The focus is set to zhyp=6kpc on the main axis giving them realistic orientations (see Bienaymé1999).The luminosity function of each stellar component is modeled with n different kinds of stars according totheir absolute magnitude:φi(M) =∑k=1,nφik(M) =1√2πσM∑k=1,ncik e−12(M−MkσM)2Galactic kinematics from RAVE to Gaia-RVS Data 49where cik is the density for each type of star (index k) of each stellar component (index i).3 ResultsWe have have adjusted the density of each stellar component to a sample of stars extracted from the 2MASScatalogue for the photometric data, the UCAC2 catalogue for proper motion and RAVE for the radial velocity.These stars are selected in color with J-K = [0.5-0.7]. In this color interval, we have defined 4 types of stars:Stars with a mean absolute magnitude MK = −1.61 are identified to be the red clump giants (k = 1), withMK = −0.89 and MK = −0.17 are first ascent giants stars (k = 2 − 3) and with MK = 4.15 for dwarfs (k = 4).We neglected sub-giant populations with an absolute magnitude MK between 0.2 and 2. We adopt σM = 0.25for each kind of stars on the luminosity function.Adjusting the Galactic kinematical model to star counts, proper motions and radial velocities histograms,we obtained a kinematical decomposition of the Galactic disk (Fig. 1 left). The kinematical decompositionexhibits three main structures. We propose to identify the first one with vertical velocity dispersion σW =[10-25]km s−1 with the thin disk, the second with σW = [30-45] km s−1 with the thick disk. The decompositionshows a clear separation between the thin and thick components. For the third component with σW = [60-70]km s−1, the kinematical information is missing. This component could be a ’hot’ kinematically thick disk orthe halo.From the kinematical decomposition, the scale height of the thin and thick disk could be determined indepen-dently by fitting an exponential on the density ρ(z) (Fig. 1 right). We find a scale height for stellar componentswith σW = [10-25]km s−1 (thin disk) of 225±10pc, for stellar components with σW = [30-45]km s−1 (thickdisk) of 1048±36pc and the density ratio of thick to thin disk stars to be 8.7% at z=0pc. Our values are inagreement with previous determinations like the ones of Cabrera-Lavers et al. (2005) who have obtained a scaleheight of 267±13pc and 1062±52pc for the thin and thick disks respectively.Fig. 1. Left: Kinematical decomposition of the Galactic disk. Right: The logarithm of the vertical stellar density ρ(z)towards the the North Galactic Pole (dashed line) and its thin and thick disk decomposition (respectively thin and thicklines).From our model, the solar motion relative to the LSR and the asymmetric drift were also determined. Weobtained a value of u⊙=8.5±0.3km s−1, w⊙=11.1±1.0km s−1 and a thick disk lag is Vlag = 33±2km s−1 relativeto the LSR. v⊙ was fixed to = 5.2 km s−1, otherwise we could not measure the asymmetric drift.By looking at latitude |b| > 20◦, we measure a radial scale length of 2.5±0.4 kpc for the thin disk and3.5±1.0kpc for the thick disk. There is no consensus on the values of the scale length of the values of the scalelength of the thin and thick disk, but our values are in relative agreement, for example, with Ojha (2001) whofinds 2.8±0.3kpc for the thin disk and 3.70.8−0.5 kpc for the thick disk.50 SF2A 20084 ConclusionsThe fact that the decomposition of the Galactic disk reveals the kinematical separation of the thin and thethick disk puts some constraints on the scenarios of the Galactic disk formation. The thick disk could not havebeen created by a continuous ‘heating’ mechanism like the diffusion due to molecular clouds or spiral arms.The scientific use of the RAVE data has already permitted us to obtain a lot of results on Galactic structureand kinematics: constrains on the local Galactic escape speed (Smith et al. 2007), absence of the Sgr streamnear the Sun (Seabroke et al. 2008), scale height of the thin and thick disk (Veltz et al. 2008), vertical tilt ofthe ellipsoid (Siebert et al. 2008). With the accuracy and number of stars that will be observed by Gaia, thefuture is very promising for the analysis of the structure and kinematics of the disk. All these new informationswill help to improve our understanding of the formation and evolution not only of the Milky Way but also thegalaxies in general.AcknowledgmentsFunding for RAVE has been provided by the Anglo-Australian Observatory, by the Astrophysical InstitutePotsdam, by the Australian Research Council, by the German Research Foundation, by the National Institute forAstrophysics at Padova, by The Johns Hopkins University, by the Netherlands Research School for Astronomy,by the Natural Sciences and Engineering Research Council of Canada, by the Slovenian Research Agency, bythe Swiss National Science Foundation, by the National Science Foundation of the USA, by the NetherlandsOrganisation for Scientific Research, by the Particle Physics and Astronomy Research Council of the UK, byOpticon, by Strasbourg Observatory, and by the Universities of Basel, Cambridge, and Groningen.The RAVE web site is at http://www.rave-survey.org.ReferencesBienaymé, O. 1999, A&A, 341,86Bienaymé, O., Soubiran, C., Mishenina, T. V., Kovtyukh, V. V. & Siebert, A. 2006, A&A, 446, 933Cabrera-Lavers, A., Garzn, F., & Hammersley, P. L. 2005, A&A, 433, 173Katz, D., Munari, U., Cropper, et al. 2004, MNRAS, 354, 1223Munari, U. 1999, Baltic Astronomy, 8, 73Munari, U. 2003, editor, ASPC: ”GAIA Spectroscopy: Science and Technology”, 298Ojha, D. K. 2001, MNRAS, 322, 426Seabroke, G. M., Gilmore, G., Siebert, A., et al. 2008, MNRAS, 384, 11Siebert, A., Bienaymé, O., Binney, J., et al. 2008, arXiv0809.0615Smith, M. C., Ruchti, G. R., Helmi, A., Wyse, R. F. G., & Fulbright, J. P., et al. 2007, MNRAS, 379, 755Steinmetz, M 2003, ASPC: ”Gaia Spectroscopy: Science and Technology”, 298, 381Steinmetz, M., Zwitter, T., Siebert, A., et al. 2006, AJ, 132, 1645Veltz, L., Bienaymé, O.; Freeman, K. C., et al. 2008, A&A, 480, 753Watson, F. G., Parker, Q. A., Bogatu, G., et al. 2000, Proc. SPIE, 4008, 123Zwitter, T., Siebert, A., Munari, U., et al. 2008, AJ, 136, 421

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   University of GroningenGalactic kinematics from RAVE to Gaia-RVS DataVeltz, L.; Bienaymé, O.; Steinmetz, M.; Zwitter, T.; Watson, F.~G.; Binney, J.; Bland-Hawthorn, J.; Campbell, R. .; Freeman, K.~C.; Gibson, B.Published in:SF2A-2008IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2008Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Veltz, L., Bienaymé, O., Steinmetz, M., Zwitter, T., Watson, F. G., Binney, J., Bland-Hawthorn, J.,Campbell, R. ., Freeman, K. C., Gibson, B., Gilmore, G., Grebel, E. K., Helmi, A., Munari, U., Navarro, J. F.,Parker, Q. A., Seabroke, G., Siebert, A., Siviero, A., ... Wyse, R. F. G. (2008). Galactic kinematics fromRAVE to Gaia-RVS Data. In SF2A-2008 (pp. 47). Société Francaise d’Astronomie et d’Astrophysique(SF2A).CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 05-12-2023SF2A 2008C. Charbonnel, F. Combes and R. Samadi (eds)GALACTIC KINEMATICS FROM RAVE TO GAIA-RVS DATAVeltz, L.1, Bienaymé, O.2, Steinmetz, M.1 , Zwitter, T.3, Watson, F. G.4, Binney, J.5,Bland-Hawthorn, J.6, Campbell, R..1 , Freeman, K. C.7, Gibson, B.8, Gilmore, G.9, Grebel, E. K.10,Helmi, A.11, Munari, U.12, Navarro, J. F.13, Parker, Q. A.14, Seabroke, G.15, Siebert, A.2 , Siviero,A.12,1 , Williams, M.1 and Wyse, R. F. G.16Abstract. RAVE data has provided new results on Galactic kinematics like the kinematical decompositionof the Galactic disk. This decomposition permits to identify the different components of the disk and tocharacterize them in terms of scale height and scale length. With the data provided by Gaia and in particularthe RVS, we will have a completly renewed view of the Galaxy. The precision of the RVS will permit toundertake a precise analysis of the kinematics of the Galactic disks. This knowledge will provide significantclues to constrain the scenarios of the Galactic disk formation.1 IntroductionThe hierarchical formation scenario is a great success in describing the formation of the large-scale structureof the universe. But, the detailed mechanisms of formation of individual galaxies are still an open question.Some answers to this question rely on the knowledge of the position, the kinematics and chemical compositionof the stars of the Milky Way. Therefore, in 2000, ESA has approved the Gaia mission that will provide the 6-D(position-velocity) information for 50 millions stars in the Galaxy. The expected launch of the Gaia satelliteis planned for 2011. As a precursor in the spectroscopic area, an international cooperation called ”RAdialVelocity Experiment” (RAVE) has started in 2003 a survey of one million stars in the southern sky hemisphere(Steinmetz 2003). There has been already two data releases. The first release contains about 25 000 radialvelocity measurements (Steinmetz et al. 2006). The second data release contains about 25 000 radial velocitymeasurements more and 20000 stars for which the stellar parameters ([M/H ], log g, Teff) have been determined(Zwitter et al. 2008). The spectroscopic acquisition techniques differ between RAVE and the Gaia RadialVelocity Spectrometer (RVS), although they have almost the same resolution and wavelength range.1 Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Postdam, Germany2 Observatoire Astronomique de Strasbourg, 11 rue de l’Universit, 67000 Strasbourg, France3 University of Ljubljana, Department of Physics, Jadranska 19, 1000 Ljubljana, Slovenia4 Anglo-Australian Observatory, Coonabarabran, NSW 2357, Australia5 Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford, UK6 School of Physics, University of Sydney, NSW 2006, Australia7 Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia8 Centre for Astrophysics, University of Central Lancashire, Preston, UK9 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, UK10 Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrae 12-14, 69120 Heidelberg,Germany11 Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV Groningen, Netherlands12 Osservatorio Astronomico di Padova - INAF, Sede di Asiago, 36012 Asiago, Italy13 Department of Physics and Astronomy, University of Victoria, P.O.Box 3055, Victoria, Canada14 Department of Physics, Macquarie University, NSW 2109, Australia15 Planetary & Space Sciences Research Institute, The Open University, Milton Keynes, UK16 Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, USAc© Société Francaise d’Astronomie et d’Astrophysique (SF2A) 200848 SF2A 2008The RAVE spectra are obtained with the multi-fiber spectrograph 6dF (Watson et al. 2000) on the UKSchmidt telescope at the Anglo-Australian Observatory. Each field is observed during five exposures of 600seconds. The RVS is an integral field instrument on board of the Gaia satellite that will not use fibers (Katzet al. 2004). The observation will be done in a time delay integration scan mode. Each spectrum will beexposed for 4 seconds.The 6dF spectrograph and RVS are medium resolution instruments with R = 7500 and 11500, respectively.The spectra have a near infrared wavelength range between [8470 - 8740] Å for Gaia-RVS and [8410 - 8795]Å for RAVE. This wavelength range and resolution have three main advantages (Munari 1999, 2003). Theypresent the lowest possible contamination by telluric absorptions that will facilitate the pre- and post- Gaiamission observations from the ground. According to the Galaxy model, the largest number of stars that will beobserved by Gaia will have an energy distribution that peaks in this wavelength range due to their spectral typeor the interstellar extinction. In this wavelength range, the presence of the CaII triplet lines for cool stars, thePaschen lines for hot stars and metallic lines will be useful to determine accurately radial velocity and chemicalabundances.2 A model of Galactic kinematicsIn order to analyze the spectroscopic data in combination with the photometric information and proper motion,we have developed a self-consistant model of the Galactic disk. The disk is describe as sum of 20 isothermalstellar components with a vertical velocity dispersion σzz ranging from 10 to 70 km.s−1. The distributionfunction of each component is built from three elementary functions describing the vertical density ρi, thekinematic distribution fi (3D-gaussians) and the luminosity function φik.We define N (z, VR, Vφ, Vz ; M) to be the density of stars in the Galactic position-velocity-absolute magnitudespace:N =∑ikρi(z)fi(VR, Vφ, Vz)φik(M), (2.1)where the index i differentiates the stellar components and the index k the absolute magnitudes used to modelthe luminosity function.We insert this model in the generalized equation of stellar statistics giving:A(m, µl, µb, Vr) =∫N(z, VR, Vφ, Vz ; M) z2 ω dz. (2.2)To determine A(m), the apparent magnitude count, together with the marginal distributions of the propermotion µl and µb and the distributions of radial velocities for any direction and apparent magnitudes.Assuming the stationarity of the density distribution, the consistency between the vertical velocity σzz,i anddensity ρi(z) distributions for each stellar component i is ensured by the following expression:ρi(z) = exp(−Φ(z)/σ2zz,i)(2.3)where Φ(z) is the vertical gravitational potential at the solar Galactic position.For the vertical gravitational potential, we use the recent determination obtained by Bienaymé et al. (2006).The vertical potential is defined at the solar position by:Φ(z) = 4πG(Σ0(√z2 + D2 − D)+ ρeff z2)with Σ0 = 48 M⊙ pc−2, D = 800 pc and ρeff = 0.07 M⊙ pc−3.The kinematical model is given by shifted 3D gaussian velocity ellipsoids. For simplicity, we assume that theσRR/σφφ ratio is the same for all the stellar components. The velocity ellipsoids are inclined along the Galacticmeridian plane. The main axis of velocity ellipsoids are set parallel to confocal hyperboloids as in Stäckelpotentials. The focus is set to zhyp=6kpc on the main axis giving them realistic orientations (see Bienaymé1999).The luminosity function of each stellar component is modeled with n different kinds of stars according totheir absolute magnitude:φi(M) =∑k=1,nφik(M) =1√2πσM∑k=1,ncik e−12(M−MkσM)2Galactic kinematics from RAVE to Gaia-RVS Data 49where cik is the density for each type of star (index k) of each stellar component (index i).3 ResultsWe have have adjusted the density of each stellar component to a sample of stars extracted from the 2MASScatalogue for the photometric data, the UCAC2 catalogue for proper motion and RAVE for the radial velocity.These stars are selected in color with J-K = [0.5-0.7]. In this color interval, we have defined 4 types of stars:Stars with a mean absolute magnitude MK = −1.61 are identified to be the red clump giants (k = 1), withMK = −0.89 and MK = −0.17 are first ascent giants stars (k = 2 − 3) and with MK = 4.15 for dwarfs (k = 4).We neglected sub-giant populations with an absolute magnitude MK between 0.2 and 2. We adopt σM = 0.25for each kind of stars on the luminosity function.Adjusting the Galactic kinematical model to star counts, proper motions and radial velocities histograms,we obtained a kinematical decomposition of the Galactic disk (Fig. 1 left). The kinematical decompositionexhibits three main structures. We propose to identify the first one with vertical velocity dispersion σW =[10-25]km s−1 with the thin disk, the second with σW = [30-45] km s−1 with the thick disk. The decompositionshows a clear separation between the thin and thick components. For the third component with σW = [60-70]km s−1, the kinematical information is missing. This component could be a ’hot’ kinematically thick disk orthe halo.From the kinematical decomposition, the scale height of the thin and thick disk could be determined indepen-dently by fitting an exponential on the density ρ(z) (Fig. 1 right). We find a scale height for stellar componentswith σW = [10-25]km s−1 (thin disk) of 225±10pc, for stellar components with σW = [30-45]km s−1 (thickdisk) of 1048±36pc and the density ratio of thick to thin disk stars to be 8.7% at z=0pc. Our values are inagreement with previous determinations like the ones of Cabrera-Lavers et al. (2005) who have obtained a scaleheight of 267±13pc and 1062±52pc for the thin and thick disks respectively.Fig. 1. Left: Kinematical decomposition of the Galactic disk. Right: The logarithm of the vertical stellar density ρ(z)towards the the North Galactic Pole (dashed line) and its thin and thick disk decomposition (respectively thin and thicklines).From our model, the solar motion relative to the LSR and the asymmetric drift were also determined. Weobtained a value of u⊙=8.5±0.3km s−1, w⊙=11.1±1.0km s−1 and a thick disk lag is Vlag = 33±2km s−1 relativeto the LSR. v⊙ was fixed to = 5.2 km s−1, otherwise we could not measure the asymmetric drift.By looking at latitude |b| > 20◦, we measure a radial scale length of 2.5±0.4 kpc for the thin disk and3.5±1.0kpc for the thick disk. There is no consensus on the values of the scale length of the values of the scalelength of the thin and thick disk, but our values are in relative agreement, for example, with Ojha (2001) whofinds 2.8±0.3kpc for the thin disk and 3.70.8−0.5 kpc for the thick disk.50 SF2A 20084 ConclusionsThe fact that the decomposition of the Galactic disk reveals the kinematical separation of the thin and thethick disk puts some constraints on the scenarios of the Galactic disk formation. The thick disk could not havebeen created by a continuous ‘heating’ mechanism like the diffusion due to molecular clouds or spiral arms.The scientific use of the RAVE data has already permitted us to obtain a lot of results on Galactic structureand kinematics: constrains on the local Galactic escape speed (Smith et al. 2007), absence of the Sgr streamnear the Sun (Seabroke et al. 2008), scale height of the thin and thick disk (Veltz et al. 2008), vertical tilt ofthe ellipsoid (Siebert et al. 2008). With the accuracy and number of stars that will be observed by Gaia, thefuture is very promising for the analysis of the structure and kinematics of the disk. All these new informationswill help to improve our understanding of the formation and evolution not only of the Milky Way but also thegalaxies in general.AcknowledgmentsFunding for RAVE has been provided by the Anglo-Australian Observatory, by the Astrophysical InstitutePotsdam, by the Australian Research Council, by the German Research Foundation, by the National Institute forAstrophysics at Padova, by The Johns Hopkins University, by the Netherlands Research School for Astronomy,by the Natural Sciences and Engineering Research Council of Canada, by the Slovenian Research Agency, bythe Swiss National Science Foundation, by the National Science Foundation of the USA, by the NetherlandsOrganisation for Scientific Research, by the Particle Physics and Astronomy Research Council of the UK, byOpticon, by Strasbourg Observatory, and by the Universities of Basel, Cambridge, and Groningen.The RAVE web site is at http://www.rave-survey.org.ReferencesBienaymé, O. 1999, A&A, 341,86Bienaymé, O., Soubiran, C., Mishenina, T. V., Kovtyukh, V. V. & Siebert, A. 2006, A&A, 446, 933Cabrera-Lavers, A., Garzn, F., & Hammersley, P. L. 2005, A&A, 433, 173Katz, D., Munari, U., Cropper, et al. 2004, MNRAS, 354, 1223Munari, U. 1999, Baltic Astronomy, 8, 73Munari, U. 2003, editor, ASPC: ”GAIA Spectroscopy: Science and Technology”, 298Ojha, D. K. 2001, MNRAS, 322, 426Seabroke, G. M., Gilmore, G., Siebert, A., et al. 2008, MNRAS, 384, 11Siebert, A., Bienaymé, O., Binney, J., et al. 2008, arXiv0809.0615Smith, M. C., Ruchti, G. R., Helmi, A., Wyse, R. F. G., & Fulbright, J. P., et al. 2007, MNRAS, 379, 755Steinmetz, M 2003, ASPC: ”Gaia Spectroscopy: Science and Technology”, 298, 381Steinmetz, M., Zwitter, T., Siebert, A., et al. 2006, AJ, 132, 1645Veltz, L., Bienaymé, O.; Freeman, K. C., et al. 2008, A&A, 480, 753Watson, F. G., Parker, Q. A., Bogatu, G., et al. 2000, Proc. SPIE, 4008, 123Zwitter, T., Siebert, A., Munari, U., et al. 2008, AJ, 136, 421

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Galactic kinematics from RAVE to Gaia-RVS Data

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