1207.6115 (D. Thomas et al.)

Stellar velocity dispersions and emission line properties of SDSS-III/BOSS galaxies    [PDF]

D. Thomas, O. Steele, C. Maraston, J. Johansson, A. Beifiori, J. Pforr, G. Strombaeck, C. A. Tremonti, D. Wake, D. Bizyaev, A. Bolton, H. Brewington, J. R. Browstein, J. Comparat, J. P. Kneib, E. Malanushenko, V. Malanushenko, D. Oravetz, K. Pan, J. K. Parejko, D. P. Schneider, A. Shelden, A. Simmons, S. Snedden, M. Tanaka, B. A. Weaver, R. Yan

We perform a spectroscopic analysis of 492,450 galaxy spectra from the first two years of observations of the Sloan Digital Sky Survey-III/Baryonic Oscillation Spectroscopic Survey (BOSS) collaboration. This data set is released in the ninth SDSS data release in July 2012, the first public data release of BOSS spectra. We show that the typical signal-to-noise ratio of BOSS spectra, despite being low, is sufficient to measure stellar velocity dispersion and emission line fluxes for individual objects. We show that the typical velocity dispersion of a BOSS galaxy is ~240 km/s. The typical error in the velocity dispersion measurement 14 per cent, and 93 per cent of BOSS galaxies have velocity dispersions with an accuracy of better than 30 per cent. The distribution in velocity dispersion is redshift independent between redshifts 0.15 and 0.7, which reflects the survey design targeting massive galaxies with an approximately uniform mass distribution in this redshift interval. The majority of BOSS galaxies lack detectable emission lines. We analyse the emission line properties for a subsample below z=0.45. For this subset we show that the emission line properties are strongly redshift dependent and that there is a clear correlation between observed frame colours and emission line properties. In general, the fraction of star forming galaxies decreases and the fraction of AGN increases with increasing redshift, mostly owing to selection effects. Within in the low-z sample (LOWZ), the majority of emission-line galaxies have some AGN component, the fraction of purely star forming galaxies at z>0.15 only being a few per cent. The fraction of star-forming galaxies among the emission-line galaxies within the high-z sample (CMASS), instead, is ~20 per cent. We show that these objects typically have blue observed g-r colours and are well separated in the g-r vs r-i target selection diagram.

View original: http://arxiv.org/abs/1207.6115