Galaxy Evolution
in the
SDSS Low-z Survey
Huan Lin
Experimental Astrophysics Group
Fermilab
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A Low Redshift Galaxy Survey
Jim Annis, Huan Lin, Mariangela Bernardi
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Science Goals
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Cluster Finding
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Luminosity Function
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Velocity Dispersion Function
Sample Selection
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Southern Equatorial Survey spectroscopy program
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Aimed at z < 0.15 galaxies with 17.77 < r (Petro) < 19.5
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Photometric redshift selection plus sparse sampling
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Improved photo-z’s using catalog-level coadded magnitudes
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Low-z
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Southern Survey and Special
Spectroscopic Programs
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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
http://www-sdss.fnal.gov/targetlink/southernEqSurvey/
See Ivan Baldry’s page and catalogs at
http://mrhanky.pha.jhu.edu/~baldry/sdss-southern/
Will be further documented in DR4 paper and web site
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Catalog-Coadded Magnitudes
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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
rP=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 rPSF – rmodel  0.24, same
as for MAIN sample but using coadded magnitudes
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Redshift Completeness
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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
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Targets w/
fibers
Successful
redshifts
Petrosian r
Photo-z
Model g-r
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Galaxy Templates
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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 bestfitting 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
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Cumulative
distributions of
magnitude residuals for
galaxy template fits
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r-band LFs of Red and Blue
Sequence Galaxies
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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 
0.4 P z
o (z) = (0) 10
See also similar LF evolution analyses from Baldry et al. on uband galaxy survey and Yasuda et al. on main sample
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Red
Sequence
N=22841
Blue
Sequence
N=32051
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shallow
 = –0.5
Similar M*– 5 log h = –20.55
at z = 0.1
steep
 = –1.35
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increasing
redshift
increasing
redshift
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increasing
redshift
increasing
redshift
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Evolution
of M* with
redshift
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number
density
increases
at higher
z
M* brighter at higher z
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luminosity
density
increases
at higher z
M* brighter at higher z
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Luminosity
Density
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Luminosity
Density
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Summary
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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
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