he upcoming new perspective of the high redshift Universe in the 21 cm line
of atomic hydrogen opens possibilities to explore topics of spiral disk
evolution, hitherto reserved for the optical regime. The growth of spiral gas
disks over Cosmic time can be explored with the new generation of radio
telescopes, notably the SKA, and its precursors, as accurately as with the
Hubble Space Telescope for stellar disks. Since the atomic hydrogen gas is the
building block of these disks, it should trace their formation accurately.
Morphology of HI disks can now equally be quantified over Cosmic time. In
studies of HST deep fields, the optical or UV morphology of high-redshift
galaxy disks have been characterized using a few quantities: concentration (C),
asymmetry (A), smoothness (S), second-order-moment (M20), the GINI coefficient
(G), and Ellipticity (E). We have applied these parameters across wavelengths
and compared them to the HI morphology over the THINGS sample. NGC 3184, an
unperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as
examples for quantified morphology. We find that morphology parameters
determined in HI are as good or better a tracer of interaction compared to
those in any other wavelength, notably in Asymmetry, Gini and M20. This opens
the possibility of using them in the parameterization pipeline for SKA
precursor catalogues to select interacting or harassed galaxies from their HI
morphology. Asymmetry, Gini and M20 may be redefined for use on data-cubes
rather than HI column density image.Comment: 6 pages, 3 figures, proceeding of the conference "Panoramic Radio
  Astronomy: Wide-field 1-2 GHz research on galaxy evolution", June 02 - 05
  2009, Groningen, update after small edit

A. Bouchard

B. W. Holwerda

K. Van Der Heyden

N. Prizkal

S-l. Blyth

W. J. G. De Blok

English

arXiv

The upcoming new perspective of the high redshift Universe in the 21 cm line of atomic hydrogen opens possibilities to explore topics of spiral disk evolution, hitherto reserved for the optical regime. The growth of spiral gas disks over Cosmic time can be explored with the new generation of radio telescopes, notably the SKA, and its precursors, as accurately as with the Hubble Space Telescope for stellar disks. Since the atomic hydrogen gas is the building block of these disks, it should trace their formation accurately. Morphology of HI disks can now equally be quantified over Cosmic time. In studies of HST deep fields, the optical or UV morphology of high-redshift galaxy disks have been characterized using a few quantities: concentration (C), asymmetry (A), smoothness (S), second-order-moment (M20), the GINI coefficient (G), and Ellipticity (E). We have applied these parameters across wavelengths and compared them to the HI morphology over the THINGS sample. NGC 3184, an unperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as examples for quantified morphology. We find that morphology parameters determined in HI are as good or better a tracer of interaction compared to those in any other wavelength, notably in Asymmetry, Gini and M20. This opens the possibility of using them in the parameterization pipeline for SKA precursor catalogues to select interacting or harassed galaxies from their HI morphology. Asymme try, Gini and M20 may be redefined for use on data-cubes rather than HI column density image

Blok, W.J.G. de

Holwerda, B.W.

Bouchard, A.

Blyth, S.-L.

Heyden, K. van der

Prizkal, N.

ARTS repository - University of Groningen

   University of GroningenQuantified Morphology of HI Disks in the UniverseBlok, W.J.G. de; Holwerda, B.W.; Bouchard, A.; Blyth, S.-L.; Heyden, K. van der; Prizkal, N.Published in:Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolutionIMPORTANT 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:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Blok, W. J. G. D., Holwerda, B. W., Bouchard, A., Blyth, S-L., Heyden, K. V. D., & Prizkal, N. (2009).Quantified Morphology of HI Disks in the Universe. In Panoramic Radio Astronomy: Wide-field 1-2 GHzresearch on galaxy evolution University of Groningen.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: 31-10-2023arXiv:0908.0693v2  [astro-ph.CO]  6 Aug 2009Quantified Morphology of HI Disks in the UniverseB. W. Holwerda ∗, W. J. G. de Blok, A. Bouchard, S-L. Blyth, K. van der Heyden,Department of Astronomy, University of Cape Town, Private Bag X3, 7700 Rondebosch,Republic of South AfricaE-mail: holwerda@ast.uct.ac.zaN. PrizkalSpace Telescope Science Institute, Baltimore, MD 21218, USAThe upcoming new perspective of the high redshift Universe in the 21 cm line of atomic hydrogenopens possibilities to explore topics of spiral disk evoluti n, hitherto reserved for the opticalregime. The growth of spiral gas disks over Cosmic time can beexplored with the new generationof radio telescopes, notably the SKA, and its precursors, asaccurately as with the Hubble SpaceTelescope for stellar disks. Since the atomic hydrogen gas is the building block of these disks, itshould trace their formation accurately.Morphology of HI disks can now equally be quantified over Cosmic time. In studies of HSTdeep fields, the optical or UV morphology of high-redshift galaxy disks have been characterisedusing a few quantities: concentration (C), asymmetry (A), smoothness (S), second-order-moment(M20), the GINI coefficient (G), and Ellipticity (E). We have applied these parameters acrosswavelengths and compared them to the HI morphology over the THINGS sample. NGC 3184, anunperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as examples for quantifiedmorphology.We find that morphology parameters determined in HI are as good or better a tracer of interactioncompared to those in any other wavelength, notably in Asymmetry, Gini andM20. This opens thepossibility of using them in the parameterization pipelinefor SKA precursor catalogues to selectinteracting or harassed galaxies from their HI morphology. Asymmetry, Gini andM20 may beredefined for use on data-cubes rather than HI column density image.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution - PRA2009June 02 - 05 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licen. http://pos.sissa.it/Quantified HI Disk Morphology B. W. Holwerda1. IntroductionIn the coming years, the SKA precursors, MeerKAT, ASKAP, WSRT/APERTIF and EVLAwill take 21 cm line emission data of a large number of nearby and distant galaxies. The resultingdata-cubes and zero-order maps will need automated schemesfor source detection and characteri-sation. The morphology of HI disks is greatly informed by recent interaction (Hibbard etal., 2001)and harassment by passing dark matter haloes (Kazantzidis et al., 2008). Therefore an automatedmorphology classification of HI data is desirable, to comb the future catalogues of HI surveys forinteracting or perturbed galaxies. We propose to adapt morphological parameters currently in useto characterise UV/optical data of nearby and distant galaxies for use on HI data in order identifydifferent types of galaxy disks.2. Quantified MorphologyThe morphology of spiral galaxies has been quantified in Hubble Space Telescope images ofdistant galaxies and reference nearby galaxy samples in therestframe UV and optical using twoparameter schemes or a combination thereof. After the initial work by Abraham et al. (1994, 1996),the Concentration-Asymmetry-Smoothness (CAS) space was est blished by Conselice (2003) andthe Gini and Asymmetry parameters by Lotz et al. (2004). Scarlata et al. (2007) added ellipticityfor Hubble type classification. The benefits of quantified morph logy parameters are that there isno need for an observer, they can be applied to rest-frame UV images, which trace the triggeredstar-formation in interacting galaxies and the galaxies have an intrinsically high surface brightness,aiding their detection.The parameters used are:Concentration:C = 5 log( r80r20),wherer f is the radius of the circular aperture containingf percent of the light.Asymmetry:A = (I−I180)I ,whereI is the image,I180 is the image rotated by 180◦ around the galaxy’s centerSmoothness:S= (I−IS)I ,where I is the image,IS is the image smoothed with a certain kernel. The 0.2 Petrosian radiusboxcar is in use, but we used a 6" Gaussian. This is effectively a parameterized version of unsharpmasking (Takamiya, 1999; Malin & Hadley, 1997).Gini: G = 1Īn(n−1)Σi(2i −n−1)Ii ,whereIi is the value of pixel i in an ordered list,n is the number of pixels in the galaxy image, andĪ is the mean pixel value in the image. The Gini parameter is an index of equality in economics,with G=1 is perfectly unequal (all the flux in one pixel) and G=0 is perfectly equal (all pixel valuesthe same).2Quantified HI Disk Morphology B. W. HolwerdaFigure 1: THINGS H I maps (NA) for NGC 3184 and NGC 5194. The edge of the optical or stellar disk isat 3×1021 atoms cm−2, indicated by the red contour, and the extent of the HI disk (1019 atoms cm−2, theTHINGS detection limit) is marked with the blue contour.M20: the relative contribution of the 20% brightest pixels to thesecond order moment of the light inthe image. The second order moment of pixel i is defined as:Mi = Ii [(xi −xc)2+(yi −yc)2], whereIiis the value of pixel i in the image, andxi andyi are the x and y coordinates of that pixel andxc andycare the position of the galaxy’s centre. The total second order is:Mtot = ΣIi [(xi −xc)2+(yi −yc)2],andM20 is defined as:M20 = log(Σmi MiMtot), wherem is the 20% brightest pixels.Ellipticity : E = 1−B/A where A and B are the major and minor axes of the image.We note that many of these parameters need a predefined central position of the galaxy and allneed a definition of which pixels in an image belong to the object (a segmentation map). We usethe areas on the sky defined by HI contours to determine which pixels belong to our target galaxyand the dynamical centres reported in Walter et al. (2008).3. A case of two galaxies: NGC 3184 and NGC 5194The above parameters were computed within two contours, onec rr sponding to approxi-mately the extent of the stellar disk (3×1021 atoms/cm2) and one to the extent of the HI disk thatcould be observed with THINGS (Walter et al., 2008), (Figure1). We applied these contours onimages of two galaxies, NGC 3184 and NGC 5194, spanning UV, optical, near and far-infraredfrom GALEX, SDSS and Spitzer (see also Holwerda et al., 2010a, in preparation). The resultingmorphology parameter values are plotted in Figure 2, as computed in the stellar disk (red) and overthe extent of the HI disk (blue).3Quantified HI Disk Morphology B. W. HolwerdaWe note that the area over which these parameters are computed does not matter much formany of the parameters but there is extra information at eachw velength. The exception is the Giniparameter, which increases significantly from the stellar disk to the HI disk at all wavelengths. Theparameters dependence on wavelength is more significant; Asymmetry, Smoothness and Gini arehigh in star-formation and 21 cm line emission and Concentration peaks in the optical.4. HI morphology as a interaction tracerIn Figure 2 we can also compare the isolated, unperturbed galaxy NGC 3184 to the interactingNGC 5194 (M51). In the morphological parameters we can see that Concentration increases in theoptical and near-infrared from isolated to interacting. Asymmetry decreases a little from isolatedto interaction in UV and 24µm emission (the star-formation tracers) but increases for HI 21 cmemission. Both Gini andM20 increase, notably in HI. From Figure 2 we can conclude that thereis as much signal of interaction in HI as in the star-formation tracers (24µm and UV) but any HIclassification scheme will have to be fine-tuned for this signal. Fortunately, we can use existinguniform H I surveys such WHISP (van der Hulst et al., 2001) and THINGS (Walter et al., 2008) totest these morphology parameters (see Holwerda et al., 2010b,c,d, all in preparation)5. Use in Future SurveysThe coming HI surveys with the SKA precursors will produce a great number of resolved HIdatacubes, using a data-pipeline, producing data-cubes, moment order maps and a catalogue withdynamical (W20, W50, Vsys, Vrot etc.) and flux information. Morphological parameters such as theabove, CAS, Gini andM20, of the zero-order moment map (the HI surface density map) could beadded to the catalogue, with the intention to expand the catalogue’s parameter space such that firstcuts can easily be made for isolated, harassed, and interacting galaxies.6. Applicability to data-cubesThe application of morphological parameters to HI is thusfar limited to the zero-order map,predominantly for comparison to other wavelengths but one strength of HI data is its third dimen-sion, frequency. Like the spatial dimensions of the data, this i has a finite sampling and range. Inthe discussions at the Panoramic Radio Astronomy conferenc, P. Serra mentioned the possibilityof redefining these parameters for use on data-cubes. Following his suggestion, three of the aboveparameters could, in principle, easily be redefined to 3D morph logy parameters: Asymmetry, GiniandM20. In the case of asymmetry, the datacube would be mirrored around the central position (xc,yc, fc) in space and frequency, the Gini parameter would simply have more input-pixels ranked byvalue (unfortunately most of those would be essentially noise), and the second order moment of apixel i in the datacube would be redefined as:Mi = Ii [(xi −xc)2+(yi −yc)2+( fi − fc)2] with M20 tofollow (see Holwerda et al., 2010d). These three 3D morphology parameters, probably combinedwith zero-order map morphological parameters and dynamical indicators, could span a parameterspace in which it could be possible to determine which datacube has unique HI phenomena likewarps, “beards” (anomalous velocity gas on one side of the disk) and of course interaction andharassment.4Quantified HI Disk Morphology B. W. Holwerda5101520 00.511.5-6-4-2000.20.40.60.800.20.40.60.81 -1.5-1-0.50-6-4-2000.20.40.60.815101520 00.511.5-6-4-2000.20.40.60.800.20.40.60.81 -1.5-1-0.50-6-4-2000.20.40.60.81Figure 2: The six structural parameters for the isolated NGC 3184 and interacting NGC 5194 as a functionof wavelength. The values for the optical disk (red) and those f r the HI disk (blue). The dashed lines arefor the contours with equal pixel weights (set to 1) to serve as a reference (for Gini this value is 0, prefectequality). The optical values from Conselice (2003) for NGC3184 are indicated as black dots and the valuesfor the 3.6 and 24µm. from Bendo et al. (2007) are indicated with open squares.5Quantified HI Disk Morphology B. W. HolwerdaReferencesAbraham R. G., Valdes F., Yee H. K. C., van den Bergh S., 1994, ApJ 432, 75Abraham R. G., van den Bergh S., Glazebrook K., Ellis R. S., Santiago B. X., Surma P., GriffithsR. E., 1996, ApJS, 107, 1Bendo G. J., Calzetti D., Engelbracht C. W., Kennicutt R. C.,Meyer M. J., Thornley M. D., WalterF., Dale D. A., Li A., Murphy E. J., 2007, MNRAS, 380, 1313Conselice C. J., 2003, ApJS, 147, 1Hibbard J. E., van Gorkom J. H., Rupen M. P., Schiminovich D.,2001, in Astronomical Societyof the Pacific Conference Series, Vol. 240, Gas and Galaxy Evolution, Hibbard J. E., Rupen M.,van Gorkom J. H., eds., pp. 657–+Holwerda B. W., Pirzkal N., de Blok W. J. G., Blyth S.-L., Bouchard A., van der Heyden K. J.,Elson E. C., 2010a, Quantified HI Morphology I: Multiwavelength Morphology of NGC 3184and NGC 5194,in preparation—, 2010b, Quantified HI Morphology II: Multiwavelength Morphology of the THINGS Galaxies,in preparation—, 2010c, Quantified HI Morphology III: Interaction, Dynamics and Star-Formation in theTHINGS Galaxies,in preparation—, 2010c, Quantified HI Morphology IV: WHISP maps and cubes,in preparationKazantzidis S., Bullock J. S., Zentner A. R., Kravtsov A. V.,Moustakas L. A., 2008, ApJ, 688, 254Lotz J. M., Primack J., Madau P., 2004, AJ, 128, 163Malin D., Hadley B., 1997, in Astronomical Society of the Pacific Conference Series, Vol. 116,The Nature of Elliptical Galaxies; 2nd Stromlo Symposium, Arnaboldi M., Da Costa G. S., SahaP., eds., pp. 460–+Scarlata C., Carollo C. M., Lilly S., Sargent M. T., FeldmannR., Kampczyk P., Porciani C., Koeke-moer A., Scoville N., Kneib J.-P., Leauthaud A., Massey R., Rhodes J., Tasca L., Capak P., MaierC., McCracken H. J., Mobasher B., Renzini A., Taniguchi Y., Thompson D., Sheth K., Ajiki M.,Aussel H., Murayama T., Sanders D. B., Sasaki S., Shioya Y., Takahashi M., 2007, ApJS, 172,406Takamiya M., 1999, ApJS, 122, 109van der Hulst J. M., van Albada T. S., Sancisi R., 2001, in Astronomical Society of the PacificConference Series, Vol. 240, Gas and Galaxy Evolution, Hibbard J. E., Rupen M., van GorkomJ. H., eds., pp. 451–+Walter F., Brinks E., de Blok W. J. G., Bigiel F., Kennicutt R.C., Thornley M. D., Leroy A., 2008,AJ, 136, 25636

Quantified Morphology of HI Disks in the Universe

   University of GroningenQuantified Morphology of HI Disks in the UniverseBlok, W.J.G. de; Holwerda, B.W.; Bouchard, A.; Blyth, S.-L.; Heyden, K. van der; Prizkal, N.Published in:Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolutionIMPORTANT 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:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Blok, W. J. G. D., Holwerda, B. W., Bouchard, A., Blyth, S-L., Heyden, K. V. D., & Prizkal, N. (2009).Quantified Morphology of HI Disks in the Universe. In Panoramic Radio Astronomy: Wide-field 1-2 GHzresearch on galaxy evolution University of Groningen.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: 13-02-2023arXiv:0908.0693v2  [astro-ph.CO]  6 Aug 2009Quantified Morphology of HI Disks in the UniverseB. W. Holwerda ∗, W. J. G. de Blok, A. Bouchard, S-L. Blyth, K. van der Heyden,Department of Astronomy, University of Cape Town, Private Bag X3, 7700 Rondebosch,Republic of South AfricaE-mail: holwerda@ast.uct.ac.zaN. PrizkalSpace Telescope Science Institute, Baltimore, MD 21218, USAThe upcoming new perspective of the high redshift Universe in the 21 cm line of atomic hydrogenopens possibilities to explore topics of spiral disk evoluti n, hitherto reserved for the opticalregime. The growth of spiral gas disks over Cosmic time can beexplored with the new generationof radio telescopes, notably the SKA, and its precursors, asaccurately as with the Hubble SpaceTelescope for stellar disks. Since the atomic hydrogen gas is the building block of these disks, itshould trace their formation accurately.Morphology of HI disks can now equally be quantified over Cosmic time. In studies of HSTdeep fields, the optical or UV morphology of high-redshift galaxy disks have been characterisedusing a few quantities: concentration (C), asymmetry (A), smoothness (S), second-order-moment(M20), the GINI coefficient (G), and Ellipticity (E). We have applied these parameters acrosswavelengths and compared them to the HI morphology over the THINGS sample. NGC 3184, anunperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as examples for quantifiedmorphology.We find that morphology parameters determined in HI are as good or better a tracer of interactioncompared to those in any other wavelength, notably in Asymmetry, Gini andM20. This opens thepossibility of using them in the parameterization pipelinefor SKA precursor catalogues to selectinteracting or harassed galaxies from their HI morphology. Asymmetry, Gini andM20 may beredefined for use on data-cubes rather than HI column density image.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution - PRA2009June 02 - 05 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licen. http://pos.sissa.it/Quantified HI Disk Morphology B. W. Holwerda1. IntroductionIn the coming years, the SKA precursors, MeerKAT, ASKAP, WSRT/APERTIF and EVLAwill take 21 cm line emission data of a large number of nearby and distant galaxies. The resultingdata-cubes and zero-order maps will need automated schemesfor source detection and characteri-sation. The morphology of HI disks is greatly informed by recent interaction (Hibbard etal., 2001)and harassment by passing dark matter haloes (Kazantzidis et al., 2008). Therefore an automatedmorphology classification of HI data is desirable, to comb the future catalogues of HI surveys forinteracting or perturbed galaxies. We propose to adapt morphological parameters currently in useto characterise UV/optical data of nearby and distant galaxies for use on HI data in order identifydifferent types of galaxy disks.2. Quantified MorphologyThe morphology of spiral galaxies has been quantified in Hubble Space Telescope images ofdistant galaxies and reference nearby galaxy samples in therestframe UV and optical using twoparameter schemes or a combination thereof. After the initial work by Abraham et al. (1994, 1996),the Concentration-Asymmetry-Smoothness (CAS) space was est blished by Conselice (2003) andthe Gini and Asymmetry parameters by Lotz et al. (2004). Scarlata et al. (2007) added ellipticityfor Hubble type classification. The benefits of quantified morph logy parameters are that there isno need for an observer, they can be applied to rest-frame UV images, which trace the triggeredstar-formation in interacting galaxies and the galaxies have an intrinsically high surface brightness,aiding their detection.The parameters used are:Concentration:C = 5 log( r80r20),wherer f is the radius of the circular aperture containingf percent of the light.Asymmetry:A = (I−I180)I ,whereI is the image,I180 is the image rotated by 180◦ around the galaxy’s centerSmoothness:S= (I−IS)I ,where I is the image,IS is the image smoothed with a certain kernel. The 0.2 Petrosian radiusboxcar is in use, but we used a 6" Gaussian. This is effectively a parameterized version of unsharpmasking (Takamiya, 1999; Malin & Hadley, 1997).Gini: G = 1Īn(n−1)Σi(2i −n−1)Ii ,whereIi is the value of pixel i in an ordered list,n is the number of pixels in the galaxy image, andĪ is the mean pixel value in the image. The Gini parameter is an index of equality in economics,with G=1 is perfectly unequal (all the flux in one pixel) and G=0 is perfectly equal (all pixel valuesthe same).2Quantified HI Disk Morphology B. W. HolwerdaFigure 1: THINGS H I maps (NA) for NGC 3184 and NGC 5194. The edge of the optical or stellar disk isat 3×1021 atoms cm−2, indicated by the red contour, and the extent of the HI disk (1019 atoms cm−2, theTHINGS detection limit) is marked with the blue contour.M20: the relative contribution of the 20% brightest pixels to thesecond order moment of the light inthe image. The second order moment of pixel i is defined as:Mi = Ii [(xi −xc)2+(yi −yc)2], whereIiis the value of pixel i in the image, andxi andyi are the x and y coordinates of that pixel andxc andycare the position of the galaxy’s centre. The total second order is:Mtot = ΣIi [(xi −xc)2+(yi −yc)2],andM20 is defined as:M20 = log(Σmi MiMtot), wherem is the 20% brightest pixels.Ellipticity : E = 1−B/A where A and B are the major and minor axes of the image.We note that many of these parameters need a predefined central position of the galaxy and allneed a definition of which pixels in an image belong to the object (a segmentation map). We usethe areas on the sky defined by HI contours to determine which pixels belong to our target galaxyand the dynamical centres reported in Walter et al. (2008).3. A case of two galaxies: NGC 3184 and NGC 5194The above parameters were computed within two contours, onec rr sponding to approxi-mately the extent of the stellar disk (3×1021 atoms/cm2) and one to the extent of the HI disk thatcould be observed with THINGS (Walter et al., 2008), (Figure1). We applied these contours onimages of two galaxies, NGC 3184 and NGC 5194, spanning UV, optical, near and far-infraredfrom GALEX, SDSS and Spitzer (see also Holwerda et al., 2010a, in preparation). The resultingmorphology parameter values are plotted in Figure 2, as computed in the stellar disk (red) and overthe extent of the HI disk (blue).3Quantified HI Disk Morphology B. W. HolwerdaWe note that the area over which these parameters are computed does not matter much formany of the parameters but there is extra information at eachw velength. The exception is the Giniparameter, which increases significantly from the stellar disk to the HI disk at all wavelengths. Theparameters dependence on wavelength is more significant; Asymmetry, Smoothness and Gini arehigh in star-formation and 21 cm line emission and Concentration peaks in the optical.4. HI morphology as a interaction tracerIn Figure 2 we can also compare the isolated, unperturbed galaxy NGC 3184 to the interactingNGC 5194 (M51). In the morphological parameters we can see that Concentration increases in theoptical and near-infrared from isolated to interacting. Asymmetry decreases a little from isolatedto interaction in UV and 24µm emission (the star-formation tracers) but increases for HI 21 cmemission. Both Gini andM20 increase, notably in HI. From Figure 2 we can conclude that thereis as much signal of interaction in HI as in the star-formation tracers (24µm and UV) but any HIclassification scheme will have to be fine-tuned for this signal. Fortunately, we can use existinguniform H I surveys such WHISP (van der Hulst et al., 2001) and THINGS (Walter et al., 2008) totest these morphology parameters (see Holwerda et al., 2010b,c,d, all in preparation)5. Use in Future SurveysThe coming HI surveys with the SKA precursors will produce a great number of resolved HIdatacubes, using a data-pipeline, producing data-cubes, moment order maps and a catalogue withdynamical (W20, W50, Vsys, Vrot etc.) and flux information. Morphological parameters such as theabove, CAS, Gini andM20, of the zero-order moment map (the HI surface density map) could beadded to the catalogue, with the intention to expand the catalogue’s parameter space such that firstcuts can easily be made for isolated, harassed, and interacting galaxies.6. Applicability to data-cubesThe application of morphological parameters to HI is thusfar limited to the zero-order map,predominantly for comparison to other wavelengths but one strength of HI data is its third dimen-sion, frequency. Like the spatial dimensions of the data, this i has a finite sampling and range. Inthe discussions at the Panoramic Radio Astronomy conferenc, P. Serra mentioned the possibilityof redefining these parameters for use on data-cubes. Following his suggestion, three of the aboveparameters could, in principle, easily be redefined to 3D morph logy parameters: Asymmetry, GiniandM20. In the case of asymmetry, the datacube would be mirrored around the central position (xc,yc, fc) in space and frequency, the Gini parameter would simply have more input-pixels ranked byvalue (unfortunately most of those would be essentially noise), and the second order moment of apixel i in the datacube would be redefined as:Mi = Ii [(xi −xc)2+(yi −yc)2+( fi − fc)2] with M20 tofollow (see Holwerda et al., 2010d). These three 3D morphology parameters, probably combinedwith zero-order map morphological parameters and dynamical indicators, could span a parameterspace in which it could be possible to determine which datacube has unique HI phenomena likewarps, “beards” (anomalous velocity gas on one side of the disk) and of course interaction andharassment.4Quantified HI Disk Morphology B. W. Holwerda5101520 00.511.5-6-4-2000.20.40.60.800.20.40.60.81 -1.5-1-0.50-6-4-2000.20.40.60.815101520 00.511.5-6-4-2000.20.40.60.800.20.40.60.81 -1.5-1-0.50-6-4-2000.20.40.60.81Figure 2: The six structural parameters for the isolated NGC 3184 and interacting NGC 5194 as a functionof wavelength. The values for the optical disk (red) and those f r the HI disk (blue). The dashed lines arefor the contours with equal pixel weights (set to 1) to serve as a reference (for Gini this value is 0, prefectequality). The optical values from Conselice (2003) for NGC3184 are indicated as black dots and the valuesfor the 3.6 and 24µm. from Bendo et al. (2007) are indicated with open squares.5Quantified HI Disk Morphology B. W. HolwerdaReferencesAbraham R. G., Valdes F., Yee H. K. C., van den Bergh S., 1994, ApJ 432, 75Abraham R. G., van den Bergh S., Glazebrook K., Ellis R. S., Santiago B. X., Surma P., GriffithsR. E., 1996, ApJS, 107, 1Bendo G. J., Calzetti D., Engelbracht C. W., Kennicutt R. C.,Meyer M. J., Thornley M. D., WalterF., Dale D. A., Li A., Murphy E. J., 2007, MNRAS, 380, 1313Conselice C. J., 2003, ApJS, 147, 1Hibbard J. E., van Gorkom J. H., Rupen M. P., Schiminovich D.,2001, in Astronomical Societyof the Pacific Conference Series, Vol. 240, Gas and Galaxy Evolution, Hibbard J. E., Rupen M.,van Gorkom J. H., eds., pp. 657–+Holwerda B. W., Pirzkal N., de Blok W. J. G., Blyth S.-L., Bouchard A., van der Heyden K. J.,Elson E. C., 2010a, Quantified HI Morphology I: Multiwavelength Morphology of NGC 3184and NGC 5194,in preparation—, 2010b, Quantified HI Morphology II: Multiwavelength Morphology of the THINGS Galaxies,in preparation—, 2010c, Quantified HI Morphology III: Interaction, Dynamics and Star-Formation in theTHINGS Galaxies,in preparation—, 2010c, Quantified HI Morphology IV: WHISP maps and cubes,in preparationKazantzidis S., Bullock J. S., Zentner A. R., Kravtsov A. V.,Moustakas L. A., 2008, ApJ, 688, 254Lotz J. M., Primack J., Madau P., 2004, AJ, 128, 163Malin D., Hadley B., 1997, in Astronomical Society of the Pacific Conference Series, Vol. 116,The Nature of Elliptical Galaxies; 2nd Stromlo Symposium, Arnaboldi M., Da Costa G. S., SahaP., eds., pp. 460–+Scarlata C., Carollo C. M., Lilly S., Sargent M. T., FeldmannR., Kampczyk P., Porciani C., Koeke-moer A., Scoville N., Kneib J.-P., Leauthaud A., Massey R., Rhodes J., Tasca L., Capak P., MaierC., McCracken H. J., Mobasher B., Renzini A., Taniguchi Y., Thompson D., Sheth K., Ajiki M.,Aussel H., Murayama T., Sanders D. B., Sasaki S., Shioya Y., Takahashi M., 2007, ApJS, 172,406Takamiya M., 1999, ApJS, 122, 109van der Hulst J. M., van Albada T. S., Sancisi R., 2001, in Astronomical Society of the PacificConference Series, Vol. 240, Gas and Galaxy Evolution, Hibbard J. E., Rupen M., van GorkomJ. H., eds., pp. 451–+Walter F., Brinks E., de Blok W. J. G., Bigiel F., Kennicutt R.C., Thornley M. D., Leroy A., 2008,AJ, 136, 25636

University of Groningen Research Database

  
 University of Groningen
Quantified Morphology of HI Disks in the Universe
Blok, W.J.G. de; Holwerda, B.W.; Bouchard, A.; Blyth, S.-L.; Heyden, K. van der; Prizkal, N.
Published in:
Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution
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:
2009
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Blok, W. J. G. D., Holwerda, B. W., Bouchard, A., Blyth, S-L., Heyden, K. V. D., & Prizkal, N. (2009).
Quantified Morphology of HI Disks in the Universe. In Panoramic Radio Astronomy: Wide-field 1-2 GHz
research on galaxy evolution University of Groningen.
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: 11-02-2018
ar
X
iv
:0
90
8.
06
93
v2
  [
as
tro
-p
h.C
O]
  6
 A
ug
 20
09
Quantified Morphology of HI Disks in the Universe
B. W. Holwerda∗, W. J. G. de Blok, A. Bouchard, S-L. Blyth, K. van der Heyden,
Department of Astronomy, University of Cape Town, Private Bag X3, 7700 Rondebosch,
Republic of South Africa
E-mail: holwerda@ast.uct.ac.za
N. Prizkal
Space Telescope Science Institute, Baltimore, MD 21218, USA
The upcoming new perspective of the high redshift Universe in the 21 cm line of atomic hydrogen
opens possibilities to explore topics of spiral disk evolution, hitherto reserved for the optical
regime. The growth of spiral gas disks over Cosmic time can be explored with the new generation
of radio telescopes, notably the SKA, and its precursors, as accurately as with the Hubble Space
Telescope for stellar disks. Since the atomic hydrogen gas is the building block of these disks, it
should trace their formation accurately.
Morphology of H I disks can now equally be quantified over Cosmic time. In studies of HST
deep fields, the optical or UV morphology of high-redshift galaxy disks have been characterised
using a few quantities: concentration (C), asymmetry (A), smoothness (S), second-order-moment
(M20), the GINI coefficient (G), and Ellipticity (E). We have applied these parameters across
wavelengths and compared them to the HI morphology over the THINGS sample. NGC 3184, an
unperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as examples for quantified
morphology.
We find that morphology parameters determined in H I are as good or better a tracer of interaction
compared to those in any other wavelength, notably in Asymmetry, Gini and M20. This opens the
possibility of using them in the parameterization pipeline for SKA precursor catalogues to select
interacting or harassed galaxies from their H I morphology. Asymmetry, Gini and M20 may be
redefined for use on data-cubes rather than H I column density image.
Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution - PRA2009
June 02 - 05 2009
Groningen, the Netherlands
∗Speaker.
c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/
Quantified HI Disk Morphology B. W. Holwerda
1. Introduction
In the coming years, the SKA precursors, MeerKAT, ASKAP, WSRT/APERTIF and EVLA
will take 21 cm line emission data of a large number of nearby and distant galaxies. The resulting
data-cubes and zero-order maps will need automated schemes for source detection and characteri-
sation. The morphology of H I disks is greatly informed by recent interaction (Hibbard et al., 2001)
and harassment by passing dark matter haloes (Kazantzidis et al., 2008). Therefore an automated
morphology classification of H I data is desirable, to comb the future catalogues of H I surveys for
interacting or perturbed galaxies. We propose to adapt morphological parameters currently in use
to characterise UV/optical data of nearby and distant galaxies for use on H I data in order identify
different types of galaxy disks.
2. Quantified Morphology
The morphology of spiral galaxies has been quantified in Hubble Space Telescope images of
distant galaxies and reference nearby galaxy samples in the restframe UV and optical using two
parameter schemes or a combination thereof. After the initial work by Abraham et al. (1994, 1996),
the Concentration-Asymmetry-Smoothness (CAS) space was established by Conselice (2003) and
the Gini and Asymmetry parameters by Lotz et al. (2004). Scarlata et al. (2007) added ellipticity
for Hubble type classification. The benefits of quantified morphology parameters are that there is
no need for an observer, they can be applied to rest-frame UV images, which trace the triggered
star-formation in interacting galaxies and the galaxies have an intrinsically high surface brightness,
aiding their detection.
The parameters used are:
Concentration: C = 5 log( r80
r20
),
where r f is the radius of the circular aperture containing f percent of the light.
Asymmetry: A = (I−I180)I ,
where I is the image, I180 is the image rotated by 180◦ around the galaxy’s center
Smoothness: S = (I−IS)I ,
where I is the image, IS is the image smoothed with a certain kernel. The 0.2 Petrosian radius
boxcar is in use, but we used a 6" Gaussian. This is effectively a parameterized version of unsharp
masking (Takamiya, 1999; Malin & Hadley, 1997).
Gini: G = 1
¯In(n−1)Σi(2i−n−1)Ii,
where Ii is the value of pixel i in an ordered list, n is the number of pixels in the galaxy image, and
¯I is the mean pixel value in the image. The Gini parameter is an index of equality in economics,
with G=1 is perfectly unequal (all the flux in one pixel) and G=0 is perfectly equal (all pixel values
the same).
2
Quantified HI Disk Morphology B. W. Holwerda
Figure 1: THINGS H I maps (NA) for NGC 3184 and NGC 5194. The edge of the optical or stellar disk is
at 3× 1021 atoms cm−2, indicated by the red contour, and the extent of the H I disk (1019 atoms cm−2, the
THINGS detection limit) is marked with the blue contour.
M20: the relative contribution of the 20% brightest pixels to the second order moment of the light in
the image. The second order moment of pixel i is defined as: Mi = Ii[(xi−xc)2 +(yi−yc)2], where Ii
is the value of pixel i in the image, and xi and yi are the x and y coordinates of that pixel and xc and yc
are the position of the galaxy’s centre. The total second order is: Mtot = ΣIi[(xi− xc)2 +(yi− yc)2],
and M20 is defined as: M20 = log
(
Σmi Mi
Mtot
)
, where m is the 20% brightest pixels.
Ellipticity: E = 1−B/A where A and B are the major and minor axes of the image.
We note that many of these parameters need a predefined central position of the galaxy and all
need a definition of which pixels in an image belong to the object (a segmentation map). We use
the areas on the sky defined by H I contours to determine which pixels belong to our target galaxy
and the dynamical centres reported in Walter et al. (2008).
3. A case of two galaxies: NGC 3184 and NGC 5194
The above parameters were computed within two contours, one corresponding to approxi-
mately the extent of the stellar disk (3×1021 atoms/cm2) and one to the extent of the H I disk that
could be observed with THINGS (Walter et al., 2008), (Figure 1). We applied these contours on
images of two galaxies, NGC 3184 and NGC 5194, spanning UV, optical, near and far-infrared
from GALEX, SDSS and Spitzer (see also Holwerda et al., 2010a, in preparation). The resulting
morphology parameter values are plotted in Figure 2, as computed in the stellar disk (red) and over
the extent of the H I disk (blue).
3
Quantified HI Disk Morphology B. W. Holwerda
We note that the area over which these parameters are computed does not matter much for
many of the parameters but there is extra information at each wavelength. The exception is the Gini
parameter, which increases significantly from the stellar disk to the H I disk at all wavelengths. The
parameters dependence on wavelength is more significant; Asymmetry, Smoothness and Gini are
high in star-formation and 21 cm line emission and Concentration peaks in the optical.
4. HI morphology as a interaction tracer
In Figure 2 we can also compare the isolated, unperturbed galaxy NGC 3184 to the interacting
NGC 5194 (M51). In the morphological parameters we can see that Concentration increases in the
optical and near-infrared from isolated to interacting. Asymmetry decreases a little from isolated
to interaction in UV and 24 µm emission (the star-formation tracers) but increases for H I 21 cm
emission. Both Gini and M20 increase, notably in H I. From Figure 2 we can conclude that there
is as much signal of interaction in H I as in the star-formation tracers (24 µm and UV) but any H I
classification scheme will have to be fine-tuned for this signal. Fortunately, we can use existing
uniform H I surveys such WHISP (van der Hulst et al., 2001) and THINGS (Walter et al., 2008) to
test these morphology parameters (see Holwerda et al., 2010b,c,d, all in preparation)
5. Use in Future Surveys
The coming H I surveys with the SKA precursors will produce a great number of resolved H I
datacubes, using a data-pipeline, producing data-cubes, moment order maps and a catalogue with
dynamical (W20, W50, Vsys, Vrot etc.) and flux information. Morphological parameters such as the
above, CAS, Gini and M20, of the zero-order moment map (the H I surface density map) could be
added to the catalogue, with the intention to expand the catalogue’s parameter space such that first
cuts can easily be made for isolated, harassed, and interacting galaxies.
6. Applicability to data-cubes
The application of morphological parameters to H I is thusfar limited to the zero-order map,
predominantly for comparison to other wavelengths but one strength of H I data is its third dimen-
sion, frequency. Like the spatial dimensions of the data, this it has a finite sampling and range. In
the discussions at the Panoramic Radio Astronomy conference, P. Serra mentioned the possibility
of redefining these parameters for use on data-cubes. Following his suggestion, three of the above
parameters could, in principle, easily be redefined to 3D morphology parameters: Asymmetry, Gini
and M20. In the case of asymmetry, the datacube would be mirrored around the central position (xc,
yc, fc) in space and frequency, the Gini parameter would simply have more input-pixels ranked by
value (unfortunately most of those would be essentially noise), and the second order moment of a
pixel i in the datacube would be redefined as: Mi = Ii[(xi−xc)2 +(yi−yc)2 +( fi− fc)2] with M20 to
follow (see Holwerda et al., 2010d). These three 3D morphology parameters, probably combined
with zero-order map morphological parameters and dynamical indicators, could span a parameter
space in which it could be possible to determine which datacube has unique H I phenomena like
warps, “beards” (anomalous velocity gas on one side of the disk) and of course interaction and
harassment.
4
Quantified HI Disk Morphology B. W. Holwerda
5101520 00.
51
1.
5
-
6
-
4
-
2
0
0
0.
2
0.
4
0.
6
0.
8
00.
2
0.
4
0.
6
0.
8
1 -1
.5
-
1
-
0.
5
0
-
6
-
4
-
2
0
00.
2
0.
4
0.
6
0.
8
1
5101520 00.
51
1.
5
-
6
-
4
-
2
0
0
0.
2
0.
4
0.
6
0.
8
00.
2
0.
4
0.
6
0.
8
1 -1
.5
-
1
-
0.
5
0
-
6
-
4
-
2
0
00.
2
0.
4
0.
6
0.
8
1
Figure 2: The six structural parameters for the isolated NGC 3184 and interacting NGC 5194 as a function
of wavelength. The values for the optical disk (red) and those for the H I disk (blue). The dashed lines are
for the contours with equal pixel weights (set to 1) to serve as a reference (for Gini this value is 0, prefect
equality). The optical values from Conselice (2003) for NGC 3184 are indicated as black dots and the values
for the 3.6 and 24 µm. from Bendo et al. (2007) are indicated with open squares.
5
Quantified HI Disk Morphology B. W. Holwerda
References
Abraham R. G., Valdes F., Yee H. K. C., van den Bergh S., 1994, ApJ, 432, 75
Abraham R. G., van den Bergh S., Glazebrook K., Ellis R. S., Santiago B. X., Surma P., Griffiths
R. E., 1996, ApJS, 107, 1
Bendo G. J., Calzetti D., Engelbracht C. W., Kennicutt R. C., Meyer M. J., Thornley M. D., Walter
F., Dale D. A., Li A., Murphy E. J., 2007, MNRAS, 380, 1313
Conselice C. J., 2003, ApJS, 147, 1
Hibbard J. E., van Gorkom J. H., Rupen M. P., Schiminovich D., 2001, in Astronomical Society
of the Pacific Conference Series, Vol. 240, Gas and Galaxy Evolution, Hibbard J. E., Rupen M.,
van Gorkom J. H., eds., pp. 657–+
Holwerda B. W., Pirzkal N., de Blok W. J. G., Blyth S.-L., Bouchard A., van der Heyden K. J.,
Elson E. C., 2010a, Quantified HI Morphology I: Multiwavelength Morphology of NGC 3184
and NGC 5194, in preparation
—, 2010b, Quantified HI Morphology II: Multiwavelength Morphology of the THINGS Galaxies,
in preparation
—, 2010c, Quantified HI Morphology III: Interaction, Dynamics and Star-Formation in the
THINGS Galaxies, in preparation
—, 2010c, Quantified HI Morphology IV: WHISP maps and cubes, in preparation
Kazantzidis S., Bullock J. S., Zentner A. R., Kravtsov A. V., Moustakas L. A., 2008, ApJ, 688, 254
Lotz J. M., Primack J., Madau P., 2004, AJ, 128, 163
Malin D., Hadley B., 1997, in Astronomical Society of the Pacific Conference Series, Vol. 116,
The Nature of Elliptical Galaxies; 2nd Stromlo Symposium, Arnaboldi M., Da Costa G. S., Saha
P., eds., pp. 460–+
Scarlata C., Carollo C. M., Lilly S., Sargent M. T., Feldmann R., Kampczyk P., Porciani C., Koeke-
moer A., Scoville N., Kneib J.-P., Leauthaud A., Massey R., Rhodes J., Tasca L., Capak P., Maier
C., McCracken H. J., Mobasher B., Renzini A., Taniguchi Y., Thompson D., Sheth K., Ajiki M.,
Aussel H., Murayama T., Sanders D. B., Sasaki S., Shioya Y., Takahashi M., 2007, ApJS, 172,
406
Takamiya M., 1999, ApJS, 122, 109
van der Hulst J. M., van Albada T. S., Sancisi R., 2001, in Astronomical Society of the Pacific
Conference Series, Vol. 240, Gas and Galaxy Evolution, Hibbard J. E., Rupen M., van Gorkom
J. H., eds., pp. 451–+
Walter F., Brinks E., de Blok W. J. G., Bigiel F., Kennicutt R. C., Thornley M. D., Leroy A., 2008,
AJ, 136, 2563
6


University of Groningen

   University of GroningenQuantified Morphology of HI Disks in the UniverseBlok, W.J.G. de; Holwerda, B.W.; Bouchard, A.; Blyth, S.-L.; Heyden, K. van der; Prizkal, N.Published in:Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolutionIMPORTANT 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:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Blok, W. J. G. D., Holwerda, B. W., Bouchard, A., Blyth, S-L., Heyden, K. V. D., & Prizkal, N. (2009).Quantified Morphology of HI Disks in the Universe. In Panoramic Radio Astronomy: Wide-field 1-2 GHzresearch on galaxy evolution University of Groningen.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: 12-11-2019arXiv:0908.0693v2  [astro-ph.CO]  6 Aug 2009Quantified Morphology of HI Disks in the UniverseB. W. Holwerda∗, W. J. G. de Blok, A. Bouchard, S-L. Blyth, K. van der Heyden,Department of Astronomy, University of Cape Town, Private Bag X3, 7700 Rondebosch,Republic of South AfricaE-mail: holwerda@ast.uct.ac.zaN. PrizkalSpace Telescope Science Institute, Baltimore, MD 21218, USAThe upcoming new perspective of the high redshift Universe in the 21 cm line of atomic hydrogenopens possibilities to explore topics of spiral disk evolution, hitherto reserved for the opticalregime. The growth of spiral gas disks over Cosmic time can be explored with the new generationof radio telescopes, notably the SKA, and its precursors, as accurately as with the Hubble SpaceTelescope for stellar disks. Since the atomic hydrogen gas is the building block of these disks, itshould trace their formation accurately.Morphology of H I disks can now equally be quantified over Cosmic time. In studies of HSTdeep fields, the optical or UV morphology of high-redshift galaxy disks have been characterisedusing a few quantities: concentration (C), asymmetry (A), smoothness (S), second-order-moment(M20), the GINI coefficient (G), and Ellipticity (E). We have applied these parameters acrosswavelengths and compared them to the HI morphology over the THINGS sample. NGC 3184, anunperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as examples for quantifiedmorphology.We find that morphology parameters determined in H I are as good or better a tracer of interactioncompared to those in any other wavelength, notably in Asymmetry, Gini and M20. This opens thepossibility of using them in the parameterization pipeline for SKA precursor catalogues to selectinteracting or harassed galaxies from their H I morphology. Asymmetry, Gini and M20 may beredefined for use on data-cubes rather than H I column density image.Panoramic Radio Astronomy: Wide-field 1-2 GHz research on galaxy evolution - PRA2009June 02 - 05 2009Groningen, the Netherlands∗Speaker.c© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/Quantified HI Disk Morphology B. W. Holwerda1. IntroductionIn the coming years, the SKA precursors, MeerKAT, ASKAP, WSRT/APERTIF and EVLAwill take 21 cm line emission data of a large number of nearby and distant galaxies. The resultingdata-cubes and zero-order maps will need automated schemes for source detection and characteri-sation. The morphology of H I disks is greatly informed by recent interaction (Hibbard et al., 2001)and harassment by passing dark matter haloes (Kazantzidis et al., 2008). Therefore an automatedmorphology classification of H I data is desirable, to comb the future catalogues of H I surveys forinteracting or perturbed galaxies. We propose to adapt morphological parameters currently in useto characterise UV/optical data of nearby and distant galaxies for use on H I data in order identifydifferent types of galaxy disks.2. Quantified MorphologyThe morphology of spiral galaxies has been quantified in Hubble Space Telescope images ofdistant galaxies and reference nearby galaxy samples in the restframe UV and optical using twoparameter schemes or a combination thereof. After the initial work by Abraham et al. (1994, 1996),the Concentration-Asymmetry-Smoothness (CAS) space was established by Conselice (2003) andthe Gini and Asymmetry parameters by Lotz et al. (2004). Scarlata et al. (2007) added ellipticityfor Hubble type classification. The benefits of quantified morphology parameters are that there isno need for an observer, they can be applied to rest-frame UV images, which trace the triggeredstar-formation in interacting galaxies and the galaxies have an intrinsically high surface brightness,aiding their detection.The parameters used are:Concentration: C = 5 log( r80r20),where r f is the radius of the circular aperture containing f percent of the light.Asymmetry: A = (I−I180)I ,where I is the image, I180 is the image rotated by 180◦ around the galaxy’s centerSmoothness: S = (I−IS)I ,where I is the image, IS is the image smoothed with a certain kernel. The 0.2 Petrosian radiusboxcar is in use, but we used a 6" Gaussian. This is effectively a parameterized version of unsharpmasking (Takamiya, 1999; Malin & Hadley, 1997).Gini: G = 1¯In(n−1)Σi(2i−n−1)Ii,where Ii is the value of pixel i in an ordered list, n is the number of pixels in the galaxy image, and¯I is the mean pixel value in the image. The Gini parameter is an index of equality in economics,with G=1 is perfectly unequal (all the flux in one pixel) and G=0 is perfectly equal (all pixel valuesthe same).2Quantified HI Disk Morphology B. W. HolwerdaFigure 1: THINGS H I maps (NA) for NGC 3184 and NGC 5194. The edge of the optical or stellar disk isat 3× 1021 atoms cm−2, indicated by the red contour, and the extent of the H I disk (1019 atoms cm−2, theTHINGS detection limit) is marked with the blue contour.M20: the relative contribution of the 20% brightest pixels to the second order moment of the light inthe image. The second order moment of pixel i is defined as: Mi = Ii[(xi−xc)2 +(yi−yc)2], where Iiis the value of pixel i in the image, and xi and yi are the x and y coordinates of that pixel and xc and ycare the position of the galaxy’s centre. The total second order is: Mtot = ΣIi[(xi− xc)2 +(yi− yc)2],and M20 is defined as: M20 = log(Σmi MiMtot), where m is the 20% brightest pixels.Ellipticity: E = 1−B/A where A and B are the major and minor axes of the image.We note that many of these parameters need a predefined central position of the galaxy and allneed a definition of which pixels in an image belong to the object (a segmentation map). We usethe areas on the sky defined by H I contours to determine which pixels belong to our target galaxyand the dynamical centres reported in Walter et al. (2008).3. A case of two galaxies: NGC 3184 and NGC 5194The above parameters were computed within two contours, one corresponding to approxi-mately the extent of the stellar disk (3×1021 atoms/cm2) and one to the extent of the H I disk thatcould be observed with THINGS (Walter et al., 2008), (Figure 1). We applied these contours onimages of two galaxies, NGC 3184 and NGC 5194, spanning UV, optical, near and far-infraredfrom GALEX, SDSS and Spitzer (see also Holwerda et al., 2010a, in preparation). The resultingmorphology parameter values are plotted in Figure 2, as computed in the stellar disk (red) and overthe extent of the H I disk (blue).3Quantified HI Disk Morphology B. W. HolwerdaWe note that the area over which these parameters are computed does not matter much formany of the parameters but there is extra information at each wavelength. The exception is the Giniparameter, which increases significantly from the stellar disk to the H I disk at all wavelengths. Theparameters dependence on wavelength is more significant; Asymmetry, Smoothness and Gini arehigh in star-formation and 21 cm line emission and Concentration peaks in the optical.4. HI morphology as a interaction tracerIn Figure 2 we can also compare the isolated, unperturbed galaxy NGC 3184 to the interactingNGC 5194 (M51). In the morphological parameters we can see that Concentration increases in theoptical and near-infrared from isolated to interacting. Asymmetry decreases a little from isolatedto interaction in UV and 24 µm emission (the star-formation tracers) but increases for H I 21 cmemission. Both Gini and M20 increase, notably in H I. From Figure 2 we can conclude that thereis as much signal of interaction in H I as in the star-formation tracers (24 µm and UV) but any H Iclassification scheme will have to be fine-tuned for this signal. Fortunately, we can use existinguniform H I surveys such WHISP (van der Hulst et al., 2001) and THINGS (Walter et al., 2008) totest these morphology parameters (see Holwerda et al., 2010b,c,d, all in preparation)5. Use in Future SurveysThe coming H I surveys with the SKA precursors will produce a great number of resolved H Idatacubes, using a data-pipeline, producing data-cubes, moment order maps and a catalogue withdynamical (W20, W50, Vsys, Vrot etc.) and flux information. Morphological parameters such as theabove, CAS, Gini and M20, of the zero-order moment map (the H I surface density map) could beadded to the catalogue, with the intention to expand the catalogue’s parameter space such that firstcuts can easily be made for isolated, harassed, and interacting galaxies.6. Applicability to data-cubesThe application of morphological parameters to H I is thusfar limited to the zero-order map,predominantly for comparison to other wavelengths but one strength of H I data is its third dimen-sion, frequency. Like the spatial dimensions of the data, this it has a finite sampling and range. Inthe discussions at the Panoramic Radio Astronomy conference, P. Serra mentioned the possibilityof redefining these parameters for use on data-cubes. Following his suggestion, three of the aboveparameters could, in principle, easily be redefined to 3D morphology parameters: Asymmetry, Giniand M20. In the case of asymmetry, the datacube would be mirrored around the central position (xc,yc, fc) in space and frequency, the Gini parameter would simply have more input-pixels ranked byvalue (unfortunately most of those would be essentially noise), and the second order moment of apixel i in the datacube would be redefined as: Mi = Ii[(xi−xc)2 +(yi−yc)2 +( fi− fc)2] with M20 tofollow (see Holwerda et al., 2010d). These three 3D morphology parameters, probably combinedwith zero-order map morphological parameters and dynamical indicators, could span a parameterspace in which it could be possible to determine which datacube has unique H I phenomena likewarps, “beards” (anomalous velocity gas on one side of the disk) and of course interaction andharassment.4Quantified HI Disk Morphology B. W. Holwerda5101520 00.511.5-6-4-2000.20.40.60.800.20.40.60.81 -1.5-1-0.50-6-4-2000.20.40.60.815101520 00.511.5-6-4-2000.20.40.60.800.20.40.60.81 -1.5-1-0.50-6-4-2000.20.40.60.81Figure 2: The six structural parameters for the isolated NGC 3184 and interacting NGC 5194 as a functionof wavelength. The values for the optical disk (red) and those for the H I disk (blue). The dashed lines arefor the contours with equal pixel weights (set to 1) to serve as a reference (for Gini this value is 0, prefectequality). The optical values from Conselice (2003) for NGC 3184 are indicated as black dots and the valuesfor the 3.6 and 24 µm. from Bendo et al. (2007) are indicated with open squares.5Quantified HI Disk Morphology B. W. HolwerdaReferencesAbraham R. G., Valdes F., Yee H. K. C., van den Bergh S., 1994, ApJ, 432, 75Abraham R. G., van den Bergh S., Glazebrook K., Ellis R. S., Santiago B. X., Surma P., GriffithsR. E., 1996, ApJS, 107, 1Bendo G. J., Calzetti D., Engelbracht C. W., Kennicutt R. C., Meyer M. J., Thornley M. D., WalterF., Dale D. A., Li A., Murphy E. J., 2007, MNRAS, 380, 1313Conselice C. J., 2003, ApJS, 147, 1Hibbard J. E., van Gorkom J. H., Rupen M. P., Schiminovich D., 2001, in Astronomical Societyof the Pacific Conference Series, Vol. 240, Gas and Galaxy Evolution, Hibbard J. E., Rupen M.,van Gorkom J. H., eds., pp. 657–+Holwerda B. W., Pirzkal N., de Blok W. J. G., Blyth S.-L., Bouchard A., van der Heyden K. J.,Elson E. C., 2010a, Quantified HI Morphology I: Multiwavelength Morphology of NGC 3184and NGC 5194, in preparation—, 2010b, Quantified HI Morphology II: Multiwavelength Morphology of the THINGS Galaxies,in preparation—, 2010c, Quantified HI Morphology III: Interaction, Dynamics and Star-Formation in theTHINGS Galaxies, in preparation—, 2010c, Quantified HI Morphology IV: WHISP maps and cubes, in preparationKazantzidis S., Bullock J. S., Zentner A. R., Kravtsov A. V., Moustakas L. A., 2008, ApJ, 688, 254Lotz J. M., Primack J., Madau P., 2004, AJ, 128, 163Malin D., Hadley B., 1997, in Astronomical Society of the Pacific Conference Series, Vol. 116,The Nature of Elliptical Galaxies; 2nd Stromlo Symposium, Arnaboldi M., Da Costa G. S., SahaP., eds., pp. 460–+Scarlata C., Carollo C. M., Lilly S., Sargent M. T., Feldmann R., Kampczyk P., Porciani C., Koeke-moer A., Scoville N., Kneib J.-P., Leauthaud A., Massey R., Rhodes J., Tasca L., Capak P., MaierC., McCracken H. J., Mobasher B., Renzini A., Taniguchi Y., Thompson D., Sheth K., Ajiki M.,Aussel H., Murayama T., Sanders D. B., Sasaki S., Shioya Y., Takahashi M., 2007, ApJS, 172,406Takamiya M., 1999, ApJS, 122, 109van der Hulst J. M., van Albada T. S., Sancisi R., 2001, in Astronomical Society of the PacificConference Series, Vol. 240, Gas and Galaxy Evolution, Hibbard J. E., Rupen M., van GorkomJ. H., eds., pp. 451–+Walter F., Brinks E., de Blok W. J. G., Bigiel F., Kennicutt R. C., Thornley M. D., Leroy A., 2008,AJ, 136, 25636

NARCIS 

The upcoming new perspective of the high redshift Universe in the 21 cm line of atomic hydrogen opens possibilities to explore topics of spiral disk evolution, hitherto reserved for the optical regime. The growth of spiral gas disks over Cosmic time can be explored with the new generation of radio telescopes, notably the SKA, and its precursors, as accurately as with the Hubble Space Telescope for stellar disks. Since the atomic hydrogen gas is the building block of these disks, it should trace their formation accurately. Morphology of HI disks can now equally be quantified over Cosmic time. In studies of HST deep fields, the optical or UV morphology of high-redshift galaxy disks have been characterized using a few quantities: concentration (C), asymmetry (A), smoothness (S), second-order-moment (M20), the GINI coefficient (G), and Ellipticity (E). We have applied these parameters across wavelengths and compared them to the HI morphology over the THINGS sample. NGC 3184, an unperturbed disk, and NGC 5194, the canonical 3:1 interaction, serve as examples for quantified morphology. We find that morphology parameters determined in HI are as good or better a tracer of interaction compared to those in any other wavelength, notably in Asymmetry, Gini and M20. This opens the possibility of using them in the parameterization pipeline for SKA precursor catalogues to select interacting or harassed galaxies from their HI morphology. Asymme try, Gini and M20 may be redefined for use on data-cubes rather than HI column density image.

Heyden, K. van der,

Blyth, S.-L.,

Bouchard, A.,

Holwerda, B.W.,

Blok, W.J.G. de,

Prizkal, N.,

University of Groningen Digital Archive

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.249.7473

Quantified Morphology of HI Disks in the Universe

Abstract

Similar works

Full text

Available Versions

ARTS repository - University of Groningen

ARTS repository - University of Groningen

University of Groningen Research Database

University of Groningen

NARCIS

University of Groningen Digital Archive