NYU Value-Added Galaxy Catalog

Corresponding authors:
Michael R. Blanton and David W. Hogg
Center for Cosmology and Particle Physics
Department of Physics
New York University

Additional authors: David Schlegel (LBL), Douglas Finkbeiner (Princeton University), Nikhil Padmanabhan (Princeton University), Max Tegmark (MIT), Idit Zehavi (University of Arizona), Andreas Berlind (NYU), Ryan Scranton (UPitt), Christy Tremonti (University of Arizona), Jeff Munn (USNO), Gillian Knapp (Princeton University), James Gunn (Princeton University)

1. General description
2. DR6 has arrived!
3. Conditions of use
4. Downloading the data
5. Organization of the data
6. Description of the sample geometry
7. Software tools
8. Datasweeps of full SDSS catalog
9. FAQ

Note any IMPORTANT CHANGES

The NYU Value-Added Galaxy Catalog (NYU-VAGC) is a cross-matched collection of galaxy catalogs maintained for the study of galaxy formation and evolution. It includes carefully constructed large-scale structure samples useful for calculating power spectra, correlation functions, etc.

This catalog is described in a paper published in the Astronomical Journal. Usage of the NYU-VAGC requires citing this paper (as well as the appropriate citations for component catalogs and calibrations).

The latest sample (DR6) consists of 9938 sq deg of photometric imaging and and 6750 sq deg of spectroscopic coverage.

The most useful components of the catalog are:

1. catalog of low-redshift galaxies (10 < d < 150 Mpc/h) [NOT FOR DR6 YET]
2. large-scale structure samples
3. K-corrections

• sending us an email with your email address;
• citing Blanton et al. (2005); and
• citing any other appropriate publications depending on what aspects of the NYU-VAGC you use.

Here we describe how to get to the data, and below we describe how the data is organized.

The public data release data is available through a set of directories conforming to the data model described below. The base URLs are:

• http://sdss.physics.nyu.edu/vagc-dr6/vagc0 for the value-added catalog (corresponds to VAGC_REDUX below)
• http://sdss.physics.nyu.edu/datasweep/dr6/ for the datasweeps of the full SDSS DR6 catalog (only 90G)
• http://sdss.physics.nyu.edu/lss/dr6fix for the large-scale structure samples (corresponds to $LSS_REDUX/dr6fix below)

• they pass the Main sample criteria described by Strauss et al. (2002) AJ, 124, 1810 modified in the following ways:
  • the Petrosian magnitude limit is extended to r=18 (extinction-corrected)
  • the star-magnitude cut in PSF-Model magnitudes is extended down to 0.2 (more inclusive than Main)
  • the bright fiber magnitude limit is extended to g, r, and i magnitudes of 12
  • the small, bright cut is turned off (which allows some binary stars into the catalog)
  These all make this catalog a bit more inclusive than Main (one may want to reapply these cuts using the parameters in Strauss et al. for many purposes).
• They are within 2 arcsec of a Main sample, QSO, or Luminous Red Galaxy target from the target version of the reductions which was fed to the tiling software.
• They are within 2 arcsec of hole drilled in an SDSS plate (which may or may not have yet been observed spectroscopically).

We match all of the objects to the SDSS spectroscopic survey, to the FIRST radio survey, to the 2MASS Point Source Catalog, to the 2MASS extended source catalog, to the Two-degree Field Galaxy Redshift Survey, to the IRAS Point Source Catalog Redshift Survey, to Reference Catalog 3 (RC3.9b), to the GALEX GR1 release, and to the Spitzer SWIRE catalog.

We present all the data in the form of FITS binary tables, FTCL parameter files, and mangle-style polygon files. idlutils contains tools for reading all of these files into IDL structures.

In the $VAGC_REDUX directory are the files:

1. object_catalog.fits: the list of coordinates of every object in the catalog, and their positions (zero-indexed) in the constituent catalogs.
2. object_sdss_imaging.fits: some photometric catalog data for all of the objects in the catalog
   (with full photometric data also available, as well as 2MASS Point Source Catalog and FIRST Catalog data).
3. object_sdss_spectro.fits: spectroscopic catalog data for all of the objects
   (SDSS_SPECTRO_TAG==-1 for objects with no spectroscopic data).
4. object_sdss_tiling.fits: tiling catalog data for all of the objects
   (SDSS_TILING_TAG==-1 for objects with no spectroscopic data).
5. object_twomass.fits: 2MASS Extended Source Catalog data for all the objects
   (TWOMASS_TAG==-1 for objects with no 2MASS data)
6. object_pscz.fits: PSCz catalog data for all the objects
   (PSCZ_TAG==-1 for objects with no PSCz data)
7. object_rc3.fits: RC3 catalog data for all the objects
   (RC3_TAG==-1 for objects with no RC3 data)
8. object_twodf.fits: 2dFGRS catalog data for all the objects
   (TWODF_TAG==-1 for objects with no 2dFGRS data)
9. object_galex.fits: GALEX GR1 catalog data for all the objects
   (GALEX_TAG==-1 for objects with no GALEX data)
10. object_swire.fits: Spitzer SWIRE catalog data for all the objects
    (SWIRE_TAG==-1 for objects with no SWIRE data)

Note that the above files only contain the objects in each survey which match entries in object_sdss_imaging. In order to access the other objects from the survey in question, you can look in files of the form:

$VAGC_REDUX/[name]/[name]_catalog.fits

Some derived quantities are also available for each object in subdirectories. Currently these consist of:

1. kcorrect: K-corrections of the ugrizJHK magnitudes (using various collision-corrected redshifts, definitions of magnitude, and bandpasses)
2. cutouts: some cutout images of selected objects
3. quality: eyeball quality checks
4. collisions: a best redshift for each object including correction for collisions, using several methods (these values are useful for some large-scale structure work)
5. velmod_distance: distances corrected for peculiar velocities
6. doublestar: attempt to detect poorly deblended double stars
7. sersic: Sersic radial profile fits
8. lowz: a specially prepared catalog of low-redshift galaxies [NOT FOR DR6 YET]
9. matchspec: attempt to match objects to spectra in a more generous way (connecting objects further than 2 arcsec)
10. parents: properties of parent objects

For the SDSS imaging survey we have an expression for its geometry in terms of spherical polygons.

However, for most people who are worried about the angular selection function, it is best to use a large-scale structure subsample, where the imaging, target, and tiling masks are combined and the flux limit and completeness are tracked as a function of position. In the $LSS_REDUX/dr6fix ("drtwo14" for the DR2 version) directory are the files:

1. lss_combmask.dr6fix.fits: geometry of the sample, with areas around bright stars excised
2. lss_index.dr6fix.fits: positions of all objects in VAGC and which lss_combmask polygon they are in (-1 if outside OR if inside the bright star mask)

1. lss_geometry.dr6fix.fits: file describing geometry of the full large-scale structure sample
2. lss_bsmask.dr6fix.fits: file describing the bright star mask

In addition there are a number of subdirectories. Each subdirectory corresponds to a "pre-redshift" selection criterion; this means that the objects and the area of sky have been selected according to flux limit, completeness, and other properties which do not require knowing the object redshift. Further subdirectories provide complete subsamples based on cuts made after the redshift determination: on redshift, luminosity, intrinsic color, etc. Further details on the large-scale structure samples are available.

We use a large suite of tools in order to create this catalog. The basics are all in idlutils. Public tools for dealing with the spectra are in idlspec2d. Public tools for dealing with the imaging data are in photoop. Our tools for building the NYU-VAGC and the large-scale structure are in vagc. (This last link is a tarball of our vagc v1_10 code; it is very large because it contains a model of the local velocity field.

These are all IDL products, and you need IDL to use them. But you are an astronomer, and probably need IDL anyway (sigh).

A special piece of code that has been useful to use (and is compiled into idlutils) is mangle, a set of tools for dealing with angular masks developed by Andrew Hamilton and Max Tegmark. This code is distributed with idlutils.

There are two catalogs, split into stars and galaxies. For stars, the datasweeps have any stars where the PSF extinction-corrected magnitudes are brigher than the following for at least one band: u < 22.5, g < 22.5, r < 22.5, i < 22, z < 21.5. The catalog is broken down into runs and camcols, and is in files with the names:

calibObj-[run]-[camcol]-star.fits.gz

Similarly, for galaxies , they have any galaxies where the model extinction-corrected magnitudes are brigher than the following for at least one band: u < 21.0, g < 22.0, r < 22.0, i < 20.5, z < 20.1. The names of the files for each run and camcol are:

calibObj-[run]-[camcol]-gal.fits.gz

The meanings of the columns of the FITS files conform to the naming conventions at the Princeton reductions site. Important things to remember are:

1. If you only want one instance of each object, require that (RESOLVE_STATUS&256)>0 be set (as described on the Princeton site).
2. Fluxes are not Galactic extinction corrected, and are in nanomaggies.
3. Radii are generally given in PIXELS (each SDSS pixel is 0.396 arcsec)
4. For stars, the 2MASS PSC magnitudes are included.

NYU Value-Added Galaxy Catalog

Please contact us with comments or questions.