The Homogeneous Properties of Halpha-Selected Galaxies at (0.05<z<0.15)

Details The Homogeneous Properties of Halpha-Selected Galaxies at (0.05<z<0.15) The Homogeneous Properties of Halpha-Selected Galaxies at (0.05<z<0.15)

2010-06-14

arxiv.org/abs/1006.2831v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

accepted by the Astronomical Journal

Scientific paper

We show that the Halpha line (6563 Angstrom) alone is an extremely effective criterion for identifying galaxies that are uniform in color (red), luminosity-weighted age (old), and morphology (bulge-dominated). By combining the Sloan Digital Sky Survey (Data Release 6) with the New York University Value-Added Galaxy Catalog, we have photometric and spectroscopic indices for over 180,000 galaxies at (0.052 (bulge-dominated); and 3) galaxies with n>2 that are also red in (g'-r'). We find that the Halpha-selected galaxies consistently have the smallest color scatter: for example, at z~0.05 the intrinsic scatter in apparent (g'-r') for the Halpha sample is only 0.0287+/-0.0007 compared to 0.0682+/-0.0014 for the Sersic sample. Applying a color-cut to the n>2 sample does decrease the color scatter to 0.0313+/-0.0007, but there remains a measurable fraction of star-forming and/or AGN galaxies (up to 9.3%). All of the EW(Halpha)<0 Angstrom galaxies have n>2, i.e. they are bulge-dominated systems. The spectra for the three samples confirm that the Halpha-selected galaxies have the highest D4000 values and are, on average, nearly twice as old as the Sersic-selected samples. With the advent of multi-object near-infrared spectrographs, Halpha alone can be used to reliably isolate truly quiescent galaxies dominated by evolved stellar populations at any epoch from z~0 up to z~2.

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