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:
- https://github.com/moustakas/SGA
- https://github.com/moustakas/legacyhalos
- https://github.com/legacysurvey/legacypipe
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 |