Stripe 82 Massive Galaxy Catalog

 

Instant Gratification:  If you’re interested in a science-ready massive galaxy sample (galaxies only) and just want derived measurements like redshifts and Mstar, download the best_ukwide catalog (contact Kevin Bundy for information about soon-to-appear mass function results using this catalog).  The best redshift estimator is “ZBEST”, which is populated with spectroscopic redshifts where available and the best performing photoz’s for each galaxy when a spec-z doesn’t exist.  The best near-IR Mstar estimates are MASS_IR_BEST.  You can construct rest-frame colors and absolute magnitudes for each galaxy from the 9-element array, ABSMAG_BEST, where the elements corresponds to ugrizYJHK.  You may also be interested in the “birth parameter” B1000_IR_BEST, a proxy for recent star formation.

 

The geometric masks are available on the Footprint page.

 

A Rapid Start:  With a little more time on your hands, you may be interested in the matched observed photometry and other photometric parameters carried in pcat_ukwide.  The synmag PSF-matched photometry after galactic extinction corrections are stored in the XMAG columns (where X designates the filter band).  All of these “synmags” have been scaled to the SDSS ModelMags for each object (i.e., the only difference between RMAG and MODELMAG_R is the extinction correction), so if you want an (r - K) color, simply construct (RMAG - KMAG).

 

Note that UKIDSS total magnitudes are a bit of a mess (see Bundy et al. 2015 for extensive discussion).  I recommend using the XHALLTOT total mag estimates (where X is Y, J, H, or K).

 

The UKWIDE sample is the result of applying a number of cuts on the S82-MGC, including quality flag cuts, veto mask rejection, UKIDSS near-IR detection, and star-galaxy separation.  If you’re interested in objects that may have been thrown out by these cuts, please use the S82-MGC full catalog (pcatd_) and associated files.  Note that I have not extensively tested the S82-MGC photometry for point-sources (could be fine in many cases, but see Annis+2014 for a discussion on PSF problems in the Stripe 82 Coadd).

 

For the Intrepid: I’ve posted the SDSS and UKIDSS parent catalogs from which the S82-MGC is assembled.  These store a lot more photometric information that may of interest to some.  The full set of Mangle polygons describing the survey geometry are available on the Footprint page.

 

You can also find all sets of derived measurement products (masses, redshifts, etc.) for the matched S82-MGC pcatd.  There are estimates regardless of star/galaxy type derived both with and without near-IR data and different measurement sets based on different photo-z sets.  These are the products to use if you want to avoid the neural-network photo-zs for example or you wish to push the highest redshifts.

 

For photo-zs and quantities that depend on them (e.g,. Mstar), one can construct “best” estimates that utilize the best redshift information avilable for each object.  In order of decreasing precision, best values derive from:

  1. Spec-zs (labelled ZSPEC)

  2. redmapper photo-zs (labelled RM)

  3. redmagic photoz-s (labelled ZRED)

  4. neural network (labelled ZREIS)

 

In general, I recommend using near-IR based quantities when possible (labelled with _IR_).

 

UKIDSS:   WFCAM Y-band   WFCAM J-band   WFCAM H-band   WFCAM K-band