Full Documentation Coming Soon! - The Siena Galaxy Atlas

Page author and contact: John Moustakas

The Siena Galaxy Atlas (SGA) is an angular diameter-limited sample of galaxies constructed as part of the DESI Legacy Imaging Surveys. It provides custom, wide-area, optical and infrared mosaics (in \(grz\) and \(W1-W4\)), azimuthally averaged surface brightness profiles, and both aperture and integrated photometry for a sample of approximately 400,000 galaxies over \(20{,}000\,\mathrm{deg}^2\).

All the code used to generate and analyze the catalog is publicly available:

The table below documents the data model of the current version of the SGA parent sample.

Name Type Units Description
SGA_ID int64   Unique identifier, corresponding to the row of the original catalog. Galaxies from HyperLeda have IDs 0-1436175; Local Group dwarfs have IDs 2000000-2000092; galaxies from the RC3 and OpenNGC have IDs 3000000-3023010 and 4000000-4013957, respectively; and sources from DR8 of the Legacy Surveys have IDs >5000000
GALAXY char[29]   Unique galaxy name
PGC int64   Unique number from the Principal Catalogue of Galaxies (-1 if none or not known)
RA float64 degree Right Ascension (J2000)
DEC float64 degree Declination (J2000)
MORPHTYPE char[21]   Visual morphological type (note: heterogeneous and incomplete)
PA_LEDA float32 degree Position angle (astronomical convention, clockwise from North)
D25_LEDA float32 arcmin Diameter at the \(25\,\mathrm{mag}/\mathrm{arcsec}^2\) (optical) surface brightness
BA_LEDA float32   Ratio of the semi-minor axis to the semi-major axis
Z_LEDA float32   Heliocentric redshift from HyperLeda (note: missing values, represented with -1.0, do not imply that no redshift exists)
SB_D25_LEDA float32 Vega \(\mathrm{mag}/\mathrm{arcsec}^2\) Mean surface brightness within D25_LEDA based on the brightness in MAG_LEDA
MAG_LEDA float32 Vega mag Estimated total brightness (note: heterogeneous in both bandpass and aperture; but for most galaxies MAG_LEDA is measured in the B-band)
BYHAND boolean   Flag indicating that one or more quantities (RA, DEC, D25_LEDA, PA_LEDA, BA_LEDA, or MAG_LEDA were changed from their published values)
REF char[13]   Unique reference name: LEDA-20181114, LGDWARFS, RC3, OpenNGC, or DR8
IN_FOOTPRINT boolean   Flag indicating whether the galaxy lies within the Legacy Surveys imaging footprint (~74% of the sample)
IN_FOOTPRINT_GRZ boolean   Union of IN_FOOTPRINT and three-band optical coverage at the central position of the galaxy (~70% of the sample)
GROUP_ID int64   Unique group number
GROUP_NAME char[35]   Unique group name, constructed from the name of its largest member (based on D25_LEDA) and the suffix _GROUP
GROUP_MULT int16   Group multiplicity (i.e., number of members)
GROUP_PRIMARY boolean   Flag indicating the primary (i.e., largest) member
GROUP_RA float64 degree Right Ascencion of the group weighted by D25_LEDA
GROUP_DEC float64 degree Declination of the group weighted by D25_LEDA
GROUP_DIAMETER float32 arcmin Approximate group diameter. For groups with a single galaxy, this quantity equals D25_LEDA. For galaxies with multiple members, we estimate the diameter of the group as the maximum separation of all the pairs of group members (plus their D25_LEDA diameter)
BRICKNAME char[8]   Name of brick, encoding the brick sky position, eg "1126p222" near RA=112.6, Dec=+22.2
DIAM float32 arcmin Placeholder column documented below, but in this catalog populated with D25_LEDA
DIAM_REF char[4]   Placeholder column documented below, but in this catalog populated with the string LEDA
PA float32 degree Placeholder column documented below, but in this catalog populated with PA_LEDA
BA float32   Placeholder column documented below, but in this catalog populated with BA_LEDA
ELLIPSEBIT int32   Placeholder column documented below

Additional products are available on the DR9 files page (coming soon):

File Description
DR9 pipeline ''grz'' files  
GROUP_NAME-ccds-south.fits See the DR9 files page (coming soon)
GROUP_NAME-largegalaxy-blobs.fits.gz See the DR9 files page (coming soon)
GROUP_NAME-largegalaxy-maskbits.fits.fz See the DR9 files page (coming soon)
GROUP_NAME-largegalaxy-outlier-mask.fits.fz See the DR9 files page (coming soon)
GROUP_NAME-largegalaxy-tractor.fits See the DR9 files page (coming soon)
GROUP_NAME-depth-[g,r,z].fits.fz See the DR9 files page (coming soon)
GROUP_NAME-largegalaxy-psf-[g,r,z].fits.fz See the DR9 files page (coming soon)
GROUP_NAME-largegalaxy-[image,invvar,model]-[g,r,z].fits.fz See the DR9 files page (coming soon)
GROUP_NAME-largegalaxy-[image,model,resid]-grz.jpg See the DR9 files page (coming soon)
DR9 pipeline "unWISE" outputs  
GROUP_NAME-[image,invvar,model]-[W1,W2,W3,W4].fits.fz See the DR9 files page (coming soon)
GROUP_NAME-image-W1W2.jpg See the DR9 files page (coming soon)
GROUP_NAME-model-W1W2.jpg See the DR9 files page (coming soon)
SGC pipeline files  
GROUP_NAME-largegalaxy-sample.fits Catalog that corresponds to the data model table, above containing just the galaxies in this galaxy group
GROUP_NAME-coadds.log Logging output for this portion of the pipeline
GROUP_NAME-largegalaxy-coadds.[isdone, isfail] Zero-byte file indicating whether this portion of the pipeline completed successfully (isdone) or failed (isfail)
GROUP_NAME-largegalaxy-ID-ellipse.fits Table containing the ellipse-fitting results for the galaxy with SGA identification number ID, using the data model from the table below
GROUP_NAME-ellipse.log Logging output for this portion of the pipeline
GROUP_NAME-largegalaxy-ellipse.[isdone, isfail] Zero-byte file indicating whether this portion of the pipeline completed successfully (isdone) or failed (isfail)

The final DR9 data model for the ellipse-fitting results is coming soon. The current data model is:

Name Type Units Description
SGA_ID int64   See the data model (the first table on this page)
GALAXY char[?]   See the data model (the first table on this page)
RA float64 degree See the data model (the first table on this page)
DEC float64 degree See the data model (the first table on this page)
PGC int64   See the data model (the first table on this page)
PA_LEDA float32 degree See the data model (the first table on this page)
BA_LEDA float32   See the data model (the first table on this page)
D25_LEDA float32 arcmin See the data model (the first table on this page)
BANDS char[1][3]   List of bandpasses fitted
REFBAND char[1]   Reference band
REFPIXSCALE float32 arcsec/pixel Pixel scale in the reference band
SUCCESS boolean   Flag indicating success or failure
FITGEOMETRY boolean   Flag indicating whether the ellipse geometry was allowed to vary with semi-major axis (here, always False)
INPUT_ELLIPSE boolean   Flag indicating whether ellipse parameters were passed from an external file (here, always False)
LARGESHIFT boolean   Flag indicating that the light-weighted center (from the ellipse moments) is different from the Tractor position by more than 10 pixels in either dimension
RA_X0 float64 degree Right ascension (J2000) at pixel position X0
DEC_Y0 float64 degree Declination (J2000) at pixel position Y0
X0 float32 pixel Light-weighted position along the x-axis (from ellipse moments)
Y0 float32 pixel Light-weighted position along the y-axis (from ellipse moments)
EPS float32   Ellipticity (\(e=1-b/a\), where \(b/a\) is the semi-minor to semi-major axis ratio) see this FAQ for details (from ellipse moments)
PA float32 degree Position angle (astronomical convention, clockwise from North; from ellipse moments)
THETA float32 degree Position angle measured clockwise from the x-axis, given by [\((270-PA)\) mod 180] (from ellipse moments)
MAJORAXIS float32 pixel Light-weighted length of the semi-major axis (from ellipse moments)
MAXSMA float32 pixel Maximum semi-major axis length used for the ellipse-fitting and curve-of-growth measurements (taken to be two times MAJORAXIS)
INTEGRMODE char[6]   photutils.isophote.Ellipse.fit_image integration mode
SCLIP int16   photutils.isophote.Ellipse.fit_image sigma-clipping threshold
NCLIP int16   Number of photutils.isophote.Ellipse.fit_image sigma-clipping iterations
PSFSIZE_[G,R,Z] float32 arcsec Mean width of the point-spread function over the full mosaic (derived from the PSFSIZE_[G,R,Z] columns in the Tractor catalogs)
PSFDEPTH_[G,R,Z] float32 mag Mean \(5\hbox{-}\sigma\) depth over the full mosaic (derived from the PSFDEPTH_[G,R,Z] columns in the Tractor catalogs)
MW_TRANSMISSION_[G,R,Z] float32   Galactic transmission fraction (taken from the corresponding Tractor catalog at the central coordinates of the galaxy)
REFBAND_WIDTH float32 pixel Width of the optical mosaics in REFBAND
REFBAND_HEIGHT float32 pixel Height of the optical mosaics in REFBAND (always equal to REFBAND_WIDTH)
[G,R,Z]_SMA float32 pixel  
[G,R,Z]_EPS float32    
[G,R,Z]_EPS_ERR float32    
[G,R,Z]_PA float32 degree  
[G,R,Z]_PA_ERR float32 degree  
[G,R,Z]_INTENS float32 \(\mathrm{nanomaggies}/\mathrm{arcsec}^2\)  
[G,R,Z]_INTENS_ERR float32 \(\mathrm{nanomaggies}/\mathrm{arcsec}^2\)  
[G,R,Z]_X0 float32 pixel  
[G,R,Z]_X0_ERR float32 pixel  
[G,R,Z]_Y0 float32 pixel  
[G,R,Z]_Y0_ERR float32 pixel  
[G,R,Z]_A3 float32    
[G,R,Z]_A3_ERR float32    
[G,R,Z]_A4 float32    
[G,R,Z]_A4_ERR float32    
[G,R,Z]_RMS float32 \(\mathrm{nanomaggies}/\mathrm{arcsec}^2\)  
[G,R,Z]_PIX_STDDEV float32 \(\mathrm{nanomaggies}/\mathrm{arcsec}^2\)  
[G,R,Z]_STOP_CODE int16    
[G,R,Z]_NDATA int16    
[G,R,Z]_NFLAG int16    
[G,R,Z]_NITER int16    
[G,R,Z]_COG_SMA float32 pixel  
[G,R,Z]_COG_MAG float32 mag  
[G,R,Z]_COG_MAGERR float32 mag  
[G,R,Z]_COG_PARAMS_MTOT float32 mag  
[G,R,Z]_COG_PARAMS_M0 float32 mag  
[G,R,Z]_COG_PARAMS_ALPHA1 float32    
[G,R,Z]_COG_PARAMS_ALPHA2 float32    
[G,R,Z]_COG_PARAMS_CHI2 float32    
RADIUS_SB[23,23.5,24,24.5,25,25.5,26] float32    
RADIUS_SB[23,23.5,24,24.5,25,25.5,26]_ERR float32    
[G,R,Z]_MAG_SB[23,23.5,24,24.5,25,25.5,26] float32    
[G,R,Z]_MAG_SB[23,23.5,24,24.5,25,25.5,26]_ERR float32