We present minor axis, offset major axis and one diagonal long slit spectra for 10 E and S0 galaxies of the Coma cluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersion profiles and the H3 and H4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the line index profiles of Mg, Fe and Hβ line indices and assess their errors. The data will be used to construct dynamical models of the galaxies and study their stellar populations

Bender, R.

Corsini, E. M

Saglia, R. P

Wegner, G.

English

Dartmouth Digital Commons (Dartmouth College)

Dartmouth CollegeDartmouth Digital CommonsOpen Dartmouth: Faculty Open Access Articles9-10-2002Spatially Resolved Spectroscopy of Coma ClusterEarly-Type Galaxies - II. The Minor Axis DatasetG. WegnerDartmouth CollegeE. M. CorsiniUniversity of PaduaR. P. SagliaUniversitäts-Sternwarte MünchenR. BenderUniversitäts-Sternwarte MünchenFollow this and additional works at: https://digitalcommons.dartmouth.edu/facoaPart of the External Galaxies Commons, and the Stars, Interstellar Medium and the GalaxyCommonsThis Article is brought to you for free and open access by Dartmouth Digital Commons. It has been accepted for inclusion in Open Dartmouth: FacultyOpen Access Articles by an authorized administrator of Dartmouth Digital Commons. For more information, please contactdartmouthdigitalcommons@groups.dartmouth.edu.Recommended CitationWegner, G.; Corsini, E. M.; Saglia, R. P.; and Bender, R., "Spatially Resolved Spectroscopy of Coma Cluster Early-Type Galaxies - II.The Minor Axis Dataset" (2002). Open Dartmouth: Faculty Open Access Articles. 537.https://digitalcommons.dartmouth.edu/facoa/537A&A 395, 753–759 (2002)DOI: 10.1051/0004-6361:20021352c© ESO 2002Astronomy&AstrophysicsSpatially resolved spectroscopy of Coma cluster early-typegalaxiesII. The minor axis dataset?G. Wegner1,??, E. M. Corsini2, R. P. Saglia3,4, R. Bender3,4, D. Merkl3,5, D. Thomas3,4, J. Thomas3, and D. Mehlert61 Department of Physics and Astronomy, 6127 Wilder Laboratory, Dartmouth College, Hanover, NH 03755-3528, USA2 Dipartimento di Astronomia, Universita` di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy3 Universita¨tssternwarte Mu¨nchen, Scheinerstraße 1, 81679 Mu¨nchen, Germany4 Max-Planck-Institut fu¨r extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany5 Max-Planck-Institut fu¨r Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany6 Landessternwarte Heidelberg, Ko¨nigstuhl, 69117 Heidelberg, GermanyReceived 8 July 2002 / Accepted 10 September 2002Abstract. We present minor axis, offset major axis and one diagonal long slit spectra for 10 E and S0 galaxies of the Comacluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersion profiles and theH3 and H4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the lineindex profiles of Mg, Fe and Hβ line indices and assess their errors. The data will be used to construct dynamical models of thegalaxies and study their stellar populations.Key words. galaxies: elliptical and lenticular, cD – galaxies: kinematics and dynamics – galaxies: stellar content –galaxies: abundances – galaxies: formation1. IntroductionThis is the second of a series of papers aimed at investigatingthe stellar populations and the dynamics of early-type galax-ies in the Coma Cluster. Spanning about 4 dex in density, theComa cluster is the ideal place to investigate these galaxy prop-erties as a function of the environmental density. In the firstpaper of the series (Mehlert et al. 2000, hereafter Paper I) wepresented the galaxy sample, its selection properties, the photo-metric observations and the long-slit major axis spectra for 35 Eand S0 galaxies of the Coma Cluster. Here we complement thespectroscopic database with minor axis, offset major axis andone diagonal long slit spectra for 10 objects of the sample. Thecombined dataset allows the construction of dynamical axisym-metric models of the objects, to study the properties of the darkmatter halos of flattened, rotating E and S0 galaxies. This studySend offprint requests to: R. P. Saglia,e-mail: saglia@usm.uni-muenchen.de? Tables 3 and 4 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/395/753?? Visiting astronomer at the MDM Observatory, Kitt Peak, Arizona,operated by a consortium of the University of Michigan, DartmouthCollege and the Ohio State University, and Columbia University.is complementary to the one presented by Gerhard et al. (2001),focusing on round, non-rotating ellipticals.The properties of the stellar populations of the central re-gions of Coma cluster galaxies have been investigated in de-tail by means of long-slit (Davies et al. 1987; Jørgensenet al. 1995; Lucey et al. 1997) and fibre-fed spectrographs(Jørgensen 1999; Mobasher et al. 2001; Poggianti et al.2001a, b; Komiyama et al. 2002; Carter et al. 2002). Thedata presented here and in Paper I allow the study of thestellar population gradients for a restricted number of galax-ies and the empirical verification of the aperture corrections(Jørgensen et al. 1995). Morover, possible systematic differ-ences between the disk and bulge components of S0 galaxiescan be investigated.The spectroscopic observations and data reduction are de-scribed in Sect. 2. We present the derived kinematics in Sect. 3and the line indices in Sect. 4. Conclusions are drawn in Sect. 5.2. Observations and data reduction2.1. Galaxy sampleAll the observed galaxies (Table 1) belong to sample of 35 Eand S0 galaxies of the Coma cluster studied in Paper I).Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20021352754 G. Wegner et al.: Spectroscopy of Coma early-type galaxies. II.Table 1. Log of spectroscopic observations.Object Run PA Position Offset Single Exp. Time Total Exp. Time Q[] [00] [s] [h](1) (2) (3) (4) (5) (6) (7) (8)GMP 0144 4 1 MN - 5  3600 + 1776 5.5 3GMP 0282 3 135 MN - 3  3600 3.0 2GMP 0756 3 88 kMJ 5.8 N 6  3600 6.0 33 178 MN - 3  4200 3.5 2GMP 1176 1 78 MJ - 3  1800 1.5 21 78 kMJ 2.6 N 5  3600 5.0 31 168 MN - 4  3600 4.0 1GMP 1750 1 150 MN - 3  3600 3.0 1GMP 1990 1 135 kMJ 3.5 N 6  3600 6.0 21-2 45 MN - 3  3600 3.0 2GMP 3510 2 79 MN - 2  4200 2.3 2GMP 3792 1 127 MJ - 3  1800 1.5 24 127 MJ - 3  1800 1.5 31 37 MN - 3  4200 3.5 1GMP 3818 3 127 DG - 3  1800 1.5 3GMP 5975 4 113 MN - 3  3600 3.0 3Column 1: GMP No. from Godwin, Metcalfe & Peach (1983). Column 2: observing run. Column 3: slit position angle measured North throughEast. Column 4: slit position. MJ = major axis; k MJ = parallel to major axis; MN = minor axis; DG = diagonal axis. Column 5: northwardoffset of the slit with respect to galaxy center. Column 6: number and exposure time of the single exposures. Column 7: total exposure time.Column 8: estimated quality of the resulting spectrum. 1: very good; 2: good; 3: medium (see Fig. 1).For details about their morphological classification and rele-vant photometric properties (i.e. total magnitude, effective ra-dius, mean surface brightness within effective radius, elliptic-ity at effective radius and luminosity weighted a4 parameter)the reader is referred to that paper. They were selected fromthe sample of Paper I as the objects with the most extendedand precise major axis kinematics and therefore best suited fordynamical modelling, balancing the number of E and S0 types.2.2. Long-slit spectroscopyLong-slit spectroscopic data of the sample galaxies wereobtained with the 2.4-m Hiltner telescope of the MDMObservatory at Kitt Peak, Arizona, USA, during four differ-ent runs between 1999 and 2001. Details of the instrumentalset-up of the observations carried out on 16–20 April 1999(run 1), 23–26 April 1999 (run 2), 26–30 May 2000 (run 3)and 9–12 February 2001 (run 4) are given in Table 2.Minor-axis spectra were obtained for all the sample galax-ies, while offset spectra with the slit parallel to the major axiswere obtained only for GMP 0756, GMP 1176, GMP 1990.GMP 3818 was observed along a diagonal axis. In addition,we took spectra of GMP 1176 and GMP 3792 along their ma-jor axes to perform a consistency check with measurements ofkinematics and line strength indices of Paper I. The typicalTable 2. Instrumental set-up of spectroscopic observations.Parameter Run 1-2 Run 3-4Spectrograph Modular ModularGrating 1200 gr mm−1 1200 gr mm−1CCD “Charlotte” SITe “Echelle” SITePixel number 1024  1024 2048  2048Pixel size 24  24 µm2 24  24 µm2Gain 3.2 e−ADU−1 2.7 e−ADU−1RON 5.5 e− 7.9 e−Scale 0.00606 pixel−1 0.00606 pixel−1Dispersion 1.20 Å pixel−1 1.01 Å pixel−1Slit width 2.000 1.009Wavelength range 4916–5881 Å 4585–6470 ÅInstrumental FWHM 3.20 Å 3.11 ÅInstrumental σa 79 km s−1 77 km s−1Seeing FWHM 1.009–3.000 2.000–3.000a Derived at the 5170 Å Mg triplet.integration time of the galaxy spectra was 3600 s. Total inte-gration times and slit position angle of the galaxy spectra asG. Wegner et al.: Spectroscopy of Coma early-type galaxies. II. 755well as the log of the spectroscopic observations are given inTable 1. At the beginning of each exposure the galaxy was cen-tered on the slit using the guiding camera. In each run severalspectra of giant stars with spectral type ranging from late-Gto early-K were obtained to be used as templates in measuringstellar kinematics and line strength indices. The template starswere selected from Faber et al. (1985) and Gonza´lez (1993).Additionally we observed at least one flux standard star pernight to calibrate the flux of the spectra before the line indiceswere measured. Spectra of the comparison Hg-Ne-Ar-Xe arclamp were taken before and/or after object exposures to al-low an accurate wavelength calibration. The value of the seeingFWHM during the observing run as measured by fitting a two-dimensional Gaussian to the guide star is given in Table 2.2.3. Basic data reductionAll the spectra were bias subtracted, flatfield corrected, cleanedof cosmic rays, corrected for bad columns and wavelength cal-ibrated using standard MIDAS1 routines. The flatfield correc-tion was performed by means of both quartz lamp and twi-light sky spectra, which were normalized and divided intoall the spectra, to correct for pixel-to-pixel sensitivity varia-tions and large-scale illumination patterns due to slit vignetting.Cosmic rays were identified and eliminated by interpolatingover as in Bender et al. (1994, BSG94 hereafter). The resid-ual cosmic rays were eliminated by manually editing the spec-tra. The wavelength calibration was performed by means ofthe MIDAS package XLONG. Each spectrum was rebinned us-ing the wavelength solution obtained from the correspondingarc-lamp spectrum. We checked that the wavelength rebinninghad been done properly by measuring the difference betweenthe measured and predicted wavelengths (Osterbrock et al.1996) for the brightest night-sky emission lines in the observedspectral range. The resulting accuracy in the wavelength cal-ibration is 0.08 Å corresponding to 5 km s−1 at 5170 Å.The instrumental resolution was derived as the mean of theGaussian FWHMs measured for a number of unblended arc-lamp lines which were distributed over the whole spectral rangeof a wavelength-calibrated spectrum. The mean FWHM of thearc-lamp lines and the corresponding instrumental resolutionderived at 5170 Å is given in Table 2. In the galaxy and thestellar spectra the contribution of the sky was determined byinterpolating along the outermost 1000−2000 at the two edgesof the slit, where the galaxy or stellar light was negligible, andthen subtracted. A sky subtraction better than 1% was achieved.All the spectra were corrected for CCD misalignment follow-ing BSG94. The spectra obtained for the same galaxy along thesame axis were coadded using the center of the stellar contin-uum as a reference. This allowed to improve the signal-to-noiseratio (S/N) of the resulting two-dimensional spectrum. A one-dimensional spectrum was obtained for each kinematical tem-plate star as well as for each flux standard star. The spectraof the kinematical Lick-system templates were deredshifted tolaboratory wavelengths.1 MIDAS is developed and maintained by the European SouthernObservatory.Fig. 1. Examples of central spectra covering the range of qual-ity classes. Relative fluxes have false zero points for viewingconvenience.3. Stellar kinematicsWe measured the stellar kinematics from the galaxy absorp-tion features present in the wavelength range and centered onthe Mg line triplet (λλ 5164, 5173, 5184 Å) by applying theFourier Correlation Quotient method (Bender 1990) as doneby BSG94.The spectra were rebinned along the dispersion directionto a natural logarithmic scale, and along the spatial directionto obtain a nearly constant S/N  20 per resolution element.In a few spectra the S/N decreases to 10 at the outermostradii. The galaxy continuum was removed row-by-row by fit-ting a fourth to sixth order polynomial. The quality of thefinal spectrum depends on the resulting S/N. In Fig. 1 weshow examples of central spectra covering the 3 quality classeslisted in Table 1. The quality parameter is 1 for S/N  100,2 for 50  S/N < 100, 3 for 20 < S/N < 50.To measure the stellar kinematics of the sample galaxieswe adopted HR 6817 (K1III) as kinematical template for runs1, 2 and 3 and HR 3427 (K0III) for run 4 and we consideredthe wavelength range 5115–5541 Å (see Fig. 1) around theMg lines of the galaxies. We derived for each galaxy spectrumthe line-of-sight velocity distribution (LOSVD) along the slitand measured its moments, namely the radial velocity v, the ve-locity dispersionσ and the values of the coefficients H3 and H4.At each radius, they have been derived by fitting the LOSVDwith a Gaussian plus third- and fourth-order Gauss-Hermitepolynomials H3 and H4, which describe the asymmetric andsymmetric deviations of the LOSVD from a pure Gaussian pro-file (van der Marel & Franx 1993; Gerhard 1993). Errors onthe LOSVD moments were derived from photon statistics andCCD read-out noise, calibrating them by Monte Carlo simu-lations as done by BSG94. In general, errors are in the range756 G. Wegner et al.: Spectroscopy of Coma early-type galaxies. II.Fig. 2. Kinematical parameters and line indices measured along the observed axes of the sample galaxies. For each axis the curves are foldedaround the nucleus and filled dots and asterisks refer to the two sides of the galaxy. The radial profiles of the line-of-sight velocity (v) afterthe subtraction of systemic velocity, velocity dispersion (σ), third (H3) and fourth (H4) order coefficient of the Gauss-Hermite decompositionof the LOSVD are shown in the left panels (from top to bottom). The radial profiles of the line indices Hβ, [MgFe], <Fe>, Mgb and Mg2 areplotted in the right panels (from top to bottom).of 3–10 km s−1 for v and σ, and of 0.01–0.04 for H3 and H4,becoming larger in the outer parts of some galaxies where for10  S/N < 20. These errors do not take into account possiblesystematic effects due to template mismatch or the presence ofdust and/or faint emission. The measured stellar kinematics arereported in Table 3 and plotted in Fig. 2.Figure 3 shows the comparison between the measurementsof v, σ, H3, and H4 along the major axis of GMP 1176and GMP 3792 obtained here and measurements obtained inPaper I. The value derived from the different datasets are inagreement within the errors. However in the case of GMP 3792the velocity dispersion measured in run 4 is systematicallylower than that measured both in Paper I and in run 1.4. Line indicesWe measured the Mg, Fe, and Hβ line strength indices follow-ing Worthey et al. (1994) from flux calibrated spectra, as donein Paper I. Spectra were rebinned in the dispersion directionas well as in the radial direction as before. We indicate theaverage Iron index with <Fe> = (Fe5270 + Fe5335)/2 (Gorgaset al. 1990) and the usual combined Magnesium-Iron indexwith [MgFe] =√Mgb < Fe > (Gonza´lez 1993). We correctedG. Wegner et al.: Spectroscopy of Coma early-type galaxies. II. 757Fig. 2. continued.all the measured indices for velocity dispersion broadening andcalibrated our measurements to the Lick systems using starsfrom Faber et al. (1985). No focus correction was applied be-cause atmospheric seeing was the dominant effect during obser-vations (see Mehlert et al. 1998 for details). Errors on indiceswere derived from photon statistics and CCD read-out noise,and calibrated by means of Monte Carlo simulations. The mea-sured values of Hβ, [MgFe], <Fe>, Mgb and Mg2 are listed inTable 4 and plotted in Fig. 2.Figure 3 shows the comparison between the measurementsof Hβ, [MgFe], <Fe>, Mgb and Mg2 along the major axis ofGMP 1176 and GMP 3792 obtained here and measurementsobtained in Paper I. The agreement within the error is excel-lent. The data we obtained in this paper are fully consistentwith those of Paper I. Indeed, Fig. 4 shows that the mean cen-tral values of σ, Hβ, [MgFe], <Fe>, Mgb and Mg2 measuredalong the minor axes of the sample galaxies within an aper-ture of 200 and those obtained along the corresponding majoraxes are in agreement within the errors, assessing that the newgalaxy dataset is on the Lick system.5. ConclusionsWe presented new radially resolved spectroscopy of 10 Eand S0 galaxies of the Coma cluster. We derived rotationcurves, velocity dispersion profiles and the H3 and H4 coeffi-cients of the Hermite decomposition of the line of sight veloc-ity distribution along the minor axis, the offset major axis andone diagonal direction. Moreover, we measured the line indexprofiles of Mg, Fe and Hβ line indices. The data complement758 G. Wegner et al.: Spectroscopy of Coma early-type galaxies. II.Fig. 2. continued.Fig. 3. Kinematical parameters (v, σ, H3, and H4) and line indices profiles (Hβ, [MgFe], <Fe>, Mgb and Mg2) along the major axis ofGMP 1176 (left panels) and GMP 3792 (right panels) measured during run 1 (open symbols) and run 4 (asterisks) compared to those obtainedby Mehlert et al. (2000, filled symbols). For each run different symbols refer to the different sides of the galaxy.G. Wegner et al.: Spectroscopy of Coma early-type galaxies. II. 759Fig. 4. Central values of σ, Hβ, [MgFe], <Fe>, Mgb and Mg2 measured along major and minor axes and averaged within an aperture of 200.the existing set along the major axis and have a precision andradial extent sufficient to construct flattened and rotating dy-namical models of the galaxies and study their radially resolvedstellar populations. Future papers of this series will addressthese issues.Acknowledgements. We acknowledge the DFG grant SFB 375.ReferencesBender, R. 1990, A&A, 229, 441Bender, R., Saglia, R. P., & Gerhard, O. 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Spatially Resolved Spectroscopy of Coma Cluster Early-Type Galaxies - II. The Minor Axis Dataset

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Spatially Resolved Spectroscopy of Coma Cluster Early-Type Galaxies - II. The Minor Axis Dataset

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