J/MNRAS/518/3999 Colours from low-z LS DR9 galaxies (Liao+, 2023)
Colour gradients of low-redshift galaxies in the DESI Legacy Imaging Survey.
Liao L.-W., Cooper A.P.
<Mon. Not. R. Astron. Soc. 518, 3999 (2023)>
=2023MNRAS.518.3999L 2023MNRAS.518.3999L (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies ; Photometry ; Spectroscopy ; Optical ; Positional data ;
Redshifts ; Effective temperatures ; Stars, masses ;
Star Forming Region
Keywords: galaxies: formation - galaxies: general - galaxies: statistics -
galaxies: structure
Abstract:
Radial colour gradients within galaxies arise from gradients of
stellar age, metallicity, and dust reddening. Large samples of colour
gradients from wide- area imaging surveys can complement smaller
integral-field spectroscopy data sets and can be used to constrain
galaxy formation models. Here, we measure colour gradients for
low-redshift galaxies (z < 0.1) using photometry from the DESI Legacy
Imaging Survey DR9. Our sample comprises ∼93000 galaxies with
spectroscopic redshifts and ∼574000 galaxies with photometric
redshifts. We focus on gradients across a radial range 0.5Reff to
Reff, which corresponds to the inner disc of typical late-type
systems at low redshift. This region has been the focus of previous
statistical studies of colour gradients and has recently been explored
by spectroscopic surveys such as MaNGA. We find that the colour
gradients of most galaxies in our sample are negative (redder towards
the centre), consistent with the literature. We investigate empirical
relationships between colour gradient, average g-r and r-z colour, Mr,
M*, and sSFR. Trends of gradient strength with Mr (M*) show an
inflection around Mr~-21(log10M*/M☉ ∼10.5). Below this mass,
colour gradients become steeper with increasing M*, whereas colour
gradients in more massive galaxies become shallower. We find that
positive gradients (bluer stars at smaller radii) are typical for
galaxies of M*∼108M☉. We compare our results to age and
metallicity gradients in two data sets derived from fits of different
stellar population libraries to MaNGA spectra, but find no clear
consensus explanation for the trends we observe. Both MaNGA data sets
seem to imply a significant contribution from dust reddening, in
particular, to explain the flatness of colour gradients along the red
sequence.
Description:
In this paper, we compute colour gradients for galaxies in the DESI
Legacy Imaging Survey (Legacy Survey, LS), which provides deep
(r=23.4) imaging over ∼14000 deg2. We construct a new homogeneous
catalogue of optical galaxy colour gradient measurements at low
redshift, over as wide a range of stellar mass and colour as possible,
in order to explore large-scale trends in these gradients with other
galaxy properties (such as averaged colour, Mr, M*, and specific
star formation rate, sSFR) and to facilitate statistical comparisons
with galaxy formation models.
Our goal was to study the distribution of galaxy colour gradients and
their correlation with other photometric observables at z < 0.1. We
measured colour gradients between Reff/2 and Reff for 93680 galaxies
with spectroscopic redshifts and 574493 galaxies with photometric
redshifts, using images and photometric catalogues from the DESI
Legacy Imaging Survey DR9. We obtained M* and SFR for our
spectroscopic redshift sample using the GSWLC-X2 catalogue. The
results are presented in szdr9.dat where z is comprised between 0.008
and 0.1, r < 17.77 mag and Reff between 3 and 6 arcsec for 93680
galaxies. The pzdr9.dat present results where z is comprised between
0.008 and 0.1, r < 19 mag and Reff between 3 and 6 arcsec for 574493
galaxies.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
szdr9.dat 429 93680 The colour gradient measurements for
spectroscopic redshifts from LS DR9
pzdr9.dat 333 574493 The colour gradient measurements for photometric
redshifts from LS DR9
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See also:
J/MNRAS/506/928 : Stellar mass-size relation for low M* galaxies
(Nedkova+, 2021)
J/MNRAS/491/3562 : CALIFA ETGs spatially resolved stellar pop. (Zibetti+, 2020)
J/MNRAS/483/1862 : Metallicity gradient across the Hubble sequence
(Zhuang+, 2019)
J/MNRAS/476/1765 : MaNGA E and S galaxies properties (Li+, 2018)
J/MNRAS/371/703 : MILES library of empirical spectra (Sanchez-Blazquez+, 2006)
J/A+A/581/A103 : CALIFA survey across the Hubble sequence (Gonzalez+, 2015)
J/A+A/313/377 : Near-IR photometry of 86 galaxies. IV. (de Jong 1996)
J/ApJ/907/85 : The SAGA Survey. II. Satellite systems around galaxies
(Mao+, 2021)
J/ApJ/883/175 : First release of the MaNGA Stellar Library (MaStar)
(Yan+, 2019)
J/ApJ/766/109 : Color/age/metallicity gradients of E galaxies (Kim+, 2013)
J/ApJ/527/573 : Line Strengths in Elliptical Galaxies (Kobayashi+, 1999)
J/AJ/154/86 : MaNGA catalog, DR15 (Wake+, 2017)
J/AJ/112/2471 : The Ursa Major cluster. I. (Tully+ 1996)
J/ApJS/126/271 : Surface photometry of nearby field galaxies (Jansen+ 2000)
II/294 : The SDSS Photometric Catalog, Release 7
(Adelman-McCarthy+, 2009)
Byte-by-byte Description of file: szdr9.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Brick Name of brick in the Legacy Survey encoding
the brick sky position (brickname)
10- 14 I5 --- ObjID Catalogue object number in the corresponding
brick of the Legacy Survey (objid)
16- 34 F19.15 deg RAdeg Right ascension (J2000) (Ra)
36- 54 F19.15 deg DEdeg Declination (J2000) (Dec)
56- 69 E14.8 deg-2 RAvar Inverse variance of RAdeg excluding
astrometric calibration errors (ra_ivar)
71- 84 E14.8 deg-2 DEvar Inverse variance of DEdeg excluding
astrometric calibration errors (dec_ivar)
86- 97 E12.6 --- zspec Spectroscopic redshift from SDSS DR16
catalogue (z)
99-110 E12.6 --- e_zspec Error of the redshift (z_err)
112-130 F19.15 --- zphot ?=-99 Photometric redshift from Zhou et al.
(2021MNRAS.501.3309Z 2021MNRAS.501.3309Z) (zphotmedian)
132-150 F19.15 --- e_zphot ?=-99 The error of photometric redshift
(zphotstd)
152-167 F16.14 arcsec Reff The Reff effective radius (r_size)
169-185 F17.15 arcsec e_Reff The error of Reff (r_err)
187-193 F7.4 mag gmag The g band magnitude (mag_g)
195-206 E12.6 mag e_gmag The error of g (maggerr)
208-214 F7.4 mag rmag The r band magnitude (mag_r)
216-227 E12.6 mag e_rmag The error of r (magrerr)
229-235 F7.4 mag zmag The z band magnitude (mag_z)
237-248 E12.6 mag e_zmag The error of z (magzerr)
250-266 F17.13 mag rMag The Mr absolute magnitude (Mr)
268-285 F18.15 mag g-r The g-r colour (g_r)
287-303 F17.15 mag e_g-r The error of g-r (grerr)
305-322 F18.15 mag r-z The r-z colour (r_z)
324-340 F17.15 mag e_r-z The error of r-z (rzerr)
342-350 F9.6 mag Ng-r The g-r gradient of galaxies measured at 0.5
and 1Reff, {Nabla}g-r=100 are galaxies with no
corresponding colour gradient (cgr)
352-363 E12.6 mag e_Ng-r The error of {Nabla}g-r (cgr_err)
365-373 F9.6 mag Nr-z The r-z gradient of galaxies measured at 0.5
and 1 Reff, {Nabla}r-z=100 are galaxies with
no corresponding colour gradient (crz)
375-388 E14.8 mag e_Nr-z The error of {Nabla}r-z (crz_err)
390-396 F7.3 Msun logM* ?=-99 The log10M* from the GSWLC catalogue
(stellarmass)
398-407 F10.6 Msun e_logM* ?=-99 The error of the stellar mass
(stellarmass_err)
409-418 F10.6 Msun/yr SFR ?=-99 The log(SFRSED) from the GSWLC
catalogue (SFR)
420-429 F10.6 Msun/yr e_SFR ?=-99 The error of SFR (SFR_err)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: pzdr9.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Brick Name of brick in the Legacy Survey encoding the
brick sky position (brickname)
10- 14 I5 --- ObjID Catalogue object number in the corresponding
brick of the Legacy Survey (objid)
16- 34 F19.15 deg RAdeg Right ascension (J2000) (ra)
36- 54 F19.15 deg DEdeg Declination (J2000) (dec)
56- 67 E12.6 deg-2 RAvar Inverse variance of RAdeg excluding astrometric
calibration errors (ra_ivar)
69- 80 E12.6 deg-2 DEvar Inverse variance of DEdeg excluding astrometric
calibration errors (dec_ivar)
82- 98 F17.15 --- zphot Photometric median redshift (zphotmedian)
100-116 F17.15 --- e_zphot Error of photometric redshift (zphotstd)
118-134 F17.15 arcsec Reff The Reff effective radius (r_size)
136 I1 arcsec e_Reff The error of Reff (r_err)
138-144 F7.4 mag gmag The g band magnitude (mag_g)
146-157 E12.6 mag e_gmag The error of g (maggerr)
159-165 F7.4 mag rmag The r band magnitude (mag_r)
167-178 E12.6 mag e_rmag The error of r (magrerr)
180-186 F7.4 mag zmag The z band magnitude (mag_z)
188-199 E12.6 mag e_zmag The error of z (magzerr)
201-217 F17.13 mag rMag The Mr absolute magnitude (M_r)
219-236 F18.15 mag g-r The g-r colour (g_r)
238-254 F17.15 mag e_g-r The error of g-r (grerr)
256-273 F18.15 mag r-z The r-z colour (r_z)
275-291 F17.15 mag e_r-z The error of r-z (rzerr)
293-302 F10.6 mag Ng-r The g-r gradient of galaxies measured at 0.5
and 1Reff, {Nabla}g-r=100 are galaxies with no
corresponding colour gradient (cgr)
304-312 F9.6 mag e_Ng-r The error of {Nabla}g-r (cgr_err)
314-323 F10.6 mag Nr-z The r-z gradient of galaxies measured at 0.5
and 1 Reff, {Nabla}r-z=100 are galaxies with no
corresponding colour gradient (crz)
325-333 F9.6 mag e_Nr-z The error of {Nabla}r-z (crz_err)
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 12-Jan-2026