1 Galaxy Evolution in the SDSS Low-z Survey Huan Lin Experimental Astrophysics Group Fermilab

2 A Low Redshift Galaxy Survey Jim Annis, Huan Lin, Mariangela Bernardi ● Science Goals – Cluster Finding – Luminosity Function – Velocity Dispersion Function ● Sample Selection – Southern Equatorial Survey spectroscopy program – Aimed at z < 0.15 galaxies with < r (Petro) < 19.5 – Photometric redshift selection plus sparse sampling – Improved photo-z’s using catalog-level coadded magnitudes

3 Low-z

4 Southern Survey and Special Spectroscopic Programs ● Mostly on Stripe 82, including u-selected galaxies, low-z galaxies, deep LRGs, faint quasars, spectra of everything, stellar programs, … ● See the Southern Equatorial Survey plates page at ● See Ivan Baldry’s page and catalogs at ● Will be further documented in DR4 paper and web site

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7 Catalog-Coadded Magnitudes ● Magnitudes catalog-coadded from 62 Stripe 82 imaging runs: asinh mag  flux  average  standard mag ● Average of 10 runs per object  over factor of 3 improvement in S/N: e.g., at spectroscopic sample limit r P =19.5, median Petrosian mag error is 0.07 mag for an individual run (measured from empirical run-to-run scatter), but only 0.02 mag for catalog coadd ● Star/galaxy separation criterion r PSF – r model  0.24, same as for MAIN sample but using coadded magnitudes

8 Redshift Completeness ● Redshift sample defined using spectro1d redshift confidence zConf > 0.7 ● Redshift completeness (fraction of galaxies with redshifts) somewhat complicated due to variety of samples involved ● Compute redshift completeness on a grid of bins in the most relevant variables: Petrosian r-band magnitude, photometric redshift, and g-r model color ● Redshift success rate (fraction of fibers with successful redshift) is much simpler: overall > 90% and a weak function of magnitude, photo-z, and color

9 Targets w/ fibers Successful redshifts Petrosian rPhoto-zModel g-r

10 Galaxy Templates ● Two galaxy templates derived from ugriz magnitudes of Stripe 82 galaxies, using variant of Csabai et al. technique, iterating from CWW E and Im SEDs ● ugriz magnitudes of each galaxy used to find the best- fitting linear combination (in flux) of the two galaxy templates ● This simple model works well, with 68% residuals of 0.03 mag or less for all filters except u (~0.1 mag) ● r-band k-corrections and rest-frame g-r colors derived from best-fitting template

11 Cumulative distributions of magnitude residuals for galaxy template fits

12 r-band LFs of Red and Blue Sequence Galaxies ● Red and blue sequences fit by double gaussian model, as in Baldry et al. (2004), but using rest-frame g-r color ● Red/blue division using simple cut in the plane of rest g-r color vs. r-band absolute magnitude ● Evolving LF model (Lin et al. 1999), fit using standard maximum likelihood techniques o M*(z) = M*(0) – Qz o constant  o  (z) =  (0) P z ● See also similar LF evolution analyses from Baldry et al. on u- band galaxy survey and Yasuda et al. on main sample

13 Blue Sequence N=32051 Red Sequence N=22841

14 shallow  = –0.5 steep  = –1.35 Similar M*– 5 log h = –20.55 at z = 0.1

15 increasing redshift

16 increasing redshift

17 Evolution of M* with redshift

18 number density increases at higher z M* brighter at higher z

19 luminosity density increases at higher z M* brighter at higher z

20 Luminosity Density

21 Luminosity Density

22 Summary ● Linear trend of M* vs. z, with constant , is reasonable model, though with deviation at lowest redshifts ● Red and blue sequences both show significant brightening of M* at higher z (Q = 1.9, 1.5), amounting to 0.6 and 0.45 magnitudes from z = 0 to z = 0.3 ● Red and blue sequences show opposite number density evolution trends, so that luminosity density trends are different: constant for red, factor of 1.8 increase for blue from z = 0 to z = 0.3 ● r-band luminosity densities and trends consistent with higher-redshift CNOC2 results