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Galaxy Evolution in the

SDSS Low-z Survey

Huan Lin

Experimental Astrophysics Group

Fermilab

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A Low Redshift Galaxy SurveyJim 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 17.77 < r (Petro) < 19.5

– Photometric redshift selection plus sparse sampling

– 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

● 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

● 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

● 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

Successfulredshifts

Petrosian r Photo-z Model g-r

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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

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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

● 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) – Qzo constant (z) = (0) 10 0.4 P z

● See also similar LF evolution analyses from Baldry et al. on u-band galaxy survey and Yasuda et al. on main sample

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Blue Sequence N=32051

Red Sequence N=22841

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shallow = –0.5

steep = –1.35

Similar M*– 5 log h = –20.55 at z = 0.1

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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● 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