J/ApJS/268/26 Improved GALEX photometry of z<0.3 SDSS galaxies (Osborne+, 2023)
Improved GALEX UV photometry for 700000 SDSS galaxies.
Osborne C., Salim S., Boquien M., Dickinson M., Arnouts S.
<Astrophys. J. Suppl. Ser., 268, 26 (2023)>
=2023ApJS..268...26O 2023ApJS..268...26O (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, photometry; Ultraviolet; Optical
Keywords: Galaxies; Galactic and extragalactic astronomy; Galaxy photometry
Catalogs; Sky surveys; Photometry; Broadband photometry
Ultraviolet photometry; Ultraviolet astronomy
Near-ultraviolet astronomy; Star formation
Spectral energy distribution
Abstract:
The Galaxy Evolution Explorer (GALEX) satellite performed the first
and only large-area UV survey, which in tandem with the Sloan Digital
Sky Survey (SDSS) has facilitated modeling of the spectral energy
distributions of low-redshift galaxies and the determination of
various galaxy properties, in particular the star formation rate.
However, the relatively crude angular resolution of GALEX (5") made
its images susceptible to blending of sources, resulting in
potentially biased far-UV and near-UV (NUV) pipeline photometry. To
remedy this issue and take advantage of model-fit photometry, we use
the EMphot software to obtain forced GALEX photometry for ∼700000 SDSS
galaxies at z<0.3. Positional priors of target galaxies and
potentially contaminating neighbors were taken from SDSS. New
photometry is based on the best-fitting of three model profiles:
optical-like, exponential, and flat. New photometry mitigates blending
present in the original pipeline catalogs, which affected 16% of
galaxies at a level of >0.2mag and 2% at a level of >1mag. Pipeline
NUV magnitudes are severely affected (≳1mag) when the neighbor is
brighter than the target galaxy and within 10", or when the neighbor
is fainter and within ∼3" of the target. New photometry fixes
edge-of-detector bias, which affected pipeline photometry by up to
0.1mag in NUV. We present catalogs with new photometry for GALEX
observations of different depths, corresponding to the all-sky imaging
survey (AIS), medium imaging survey, and deep imaging survey. Catalogs
feature combined magnitudes for multiple detections of the same galaxy
in a survey.
Description:
The target sample of this work is comprised of galaxies included in
the GALEX-SDSS-WISE Legacy Catalog (GSWLC; Salim+ 2016ApJS..227....2S 2016ApJS..227....2S).
GALEX imaged 77% of the entire sky and 90% of the area included in
SDSS DR10. Individual GALEX observations consist of circular "tiles"
1.2° in diameter.
The largest sky coverage (27000deg2) comes from the shallow All-sky
Imaging Survey (AIS), with typical exposure times of ∼100s. The Medium
Imaging Survey (MIS) provides medium-depth (∼1500s) images (over
5000deg2), whereas the Deep Imaging Survey (DIS) has the smallest
sky coverage (365deg2) and provides the deepest images obtained by
coadding multiple visits (∼30000s). GALEX tile images have a pixel
scale of 1.5"/pixel. In order to take advantage of all GALEX imaging
regardless of the original campaign, following Salim et al. (2016) we
define AIS (GSWLC-A) as all tiles with NUV exposure time (in seconds)
tNUV≤650, MIS (GSWLC-M) as 650<tNUV<4000, and DIS (GSWLC-D) as
tNUV≥4000.
Also available is GSWLC-X (659229 galaxies), a master catalog
containing all unique galaxies and parameters associated with the
deepest of either GSWLC-A, -M, or -D. See Section 2.1.
To account for potential blending of targets with neighboring objects,
we also perform photometry on optical sources that lie within 20" of a
target, have u<22, and are flagged as primary objects by SDSS; no
other cuts are applied to select the neighbors. Neighbors may consist
of other GSWLC objects, foreground stars, artifacts, or galaxies
outside the redshift and brightness cuts of GSWLC. See Section 2.2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
gswlcais.dat 232 640659 GSWLC-A or the AIS survey catalog
gswlcmis.dat 232 361328 GSWLC-M or the MIS survey catalog
gswlcdis.dat 232 48401 GSWLC-D or the DIS survey catalog
gswlcx.dat 232 659229 GSWLC-X or the deepest survey catalog
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See also:
II/335 : Revised catalog of GALEX UV sources (GUVcat_AIS GR6+7) (Bianchi+ 2017)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
J/ApJS/173/185 : GALEX UV atlas of nearby galaxies (Gil de Paz+, 2007)
J/ApJ/690/1236 : COSMOS photometric redshift catalog (Ilbert+, 2009)
J/ApJ/703/517 : The Spitzer Local Volume Legacy: IR photometry (Dale+, 2009)
J/PASP/122/1397 : Spitzer Survey of Stellar Structure in Gal. (Sheth+, 2010)
J/ApJS/196/11 : Bulge+disk decompositions of SDSS galaxies (Simard+, 2011)
J/A+A/590/A102 : VIPERS Multi-Lambda Survey (Moutard+, 2016)
J/A+A/660/A69 : S4G extension for nearby early-type galaxies (Watkins+, 2022)
http://salims.pages.iu.edu/gswlc/ : GALEX-SDSS-WISE Legacy Catalog homepage
http://salims.pages.iu.edu/galex/ : Improved GALEX UV photometry cat. homepage
Byte-by-byte Description of file: gswlc*.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- objID SDSS photometric identification number
22- 42 I21 --- GALEX ?=-99 GALEX photometric identification number
44- 53 F10.6 deg RAdeg SDSS Right Ascension (J2000)
55- 64 F10.6 deg DEdeg [-11.3/78.2] SDSS Declination (J2000)
66- 100 A35 --- Tile GALEX tile name with longest exposure time;
best tile
102- 109 F8.1 s NUVexp [38/257410]?=-99 NUV exposure time for Tile
111- 118 F8.1 s FUVexp [0/140797]?=-99 FUV exposure time for Tile
120- 122 I3 --- Best [-99/2]? Best model profile flag (1)
124- 129 F6.2 mag NUVmagEM [12.5/27.7]?=-99 EMphot NUV magnitude from
Tile
131- 136 F6.2 mag e_NUVmagEM [0.01/306]?=-99 Uncertainty in NUVmagEM
138- 143 F6.2 mag FUVmagEM [14/26.8]?=-99 EMphot FUV magnitude from Tile
145- 150 F6.2 mag e_FUVmagEM [0.01/75]?=-99 Uncertainty in FUVmagEM
152- 159 F8.1 s ComNUVexp [0/332276] Sum of NUV exposure for all
detections
161- 168 F8.1 s ComFUVexp [0/208724] Sum of FUV exposure for all
detections
170- 175 F6.2 mag NUVmagCom [12.5/27.7]?=-99 Combined EMphot NUV
magnitude
177- 182 F6.2 mag e_NUVmagCom [0/306]?=-99 Uncertainty in NUVmagCom
184- 189 F6.2 mag FUVmagCom [14/27.7]?=-99 Combined EMphot FUV magnitude
191- 196 F6.2 mag e_FUVmagCom [0.01/75]?=-99 Uncertainty in FUVmagCom
198- 199 I2 --- NUVNum [0/10] Number of NUV detections
201- 202 I2 --- FUVNum [0/10] Number of FUV detections
204- 209 F6.2 mag NUVmagPipe [14.3/27.6]?=-99 GALEX pipeline NUV magnitude
211- 216 F6.2 mag e_NUVmagPipe [0/42]?=-99 Uncertainty in NUVmagPipe
218- 223 F6.2 mag FUVmagPipe [14.2/25.7]?=-99 GALEX pipeline FUV magnitude
225- 230 F6.2 mag e_FUVmagPipe [0/71]?=-99 Uncertainty in FUVmagPipe
232 I1 --- Cont [0/1] Possible contamination of UV flux
from a neighbor >20" from the target?
(0=no contamination)
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Note (1): Best model profile flag as follows:
0 = optical-like;
1 = exponential;
2 = flat;
-99 = null.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 20-Dec-2023