The physical properties of star-forming galaxies in the low-redshift Universe

Abstract

We present a comprehensive study of the physical properties of ∼ 105 galaxies with measurable star formation in the Sloan Digital Sky Survey (SDSS). By comparing physical information extracted from the emission lines with continuum properties, we build up a picture of the nature of star‐forming galaxies at z < 0.2. We develop a method for aperture correction using resolved imaging and show that our method takes out essentially all aperture bias in the star formation rate (SFR) estimates, allowing an accurate estimate of the total SFRs in galaxies. We determine the SFR density to be 1.915+0.02−0.01 (random)+0.14−0.42 (systematic) h7010−2 M⊙ yr−1 Mpc−3 at z= 0.1 (for a Kroupa initial mass function) and we study the distribution of star formation as a function of various physical parameters. The majority of the star formation in the low‐redshift Universe takes place in moderately massive galaxies (1010–1011 M⊙), typically in high surface brightness disc galaxies. Roughly 15 per cent of all star formation takes place in galaxies that show some sign of an active nucleus. About 20 per cent occurs in starburst galaxies. By focusing on the SFR per unit mass we show that the present to past average SFR, the Scalo b‐parameter, is almost constant over almost three orders of magnitude in mass, declining only at M* > 1010 M⊙. The volume averaged b parameter is 0.408+0.005−0.002 (random)+0.029−0.090 (systematic)h−170. We use this value to constrain the star formation history of the Universe. For the concordance cosmology the present‐day Universe is forming stars at at least 1/3 of its past average rate. For an exponentially declining cosmic star formation history this corresponds to a time‐scale of 7+0.7−1.5 Gyr. In agreement with other work we find a correlation between b and morphological type, as well as a tight correlation between the 4000‐Å break (D4000) and b. We discuss how D4000 can be used to estimate b parameters for high‐redshift galaxies.

Redshift evolution of stellar mass versus gas fraction relation in 0 <z< 2 regime: observational constraint for galaxy formation models

“…This estimate was found to be comparable with the one obtained from stellar absorption features (Kauffmann et al 2003). Further, SFRs were derived by fitting the fluxes of no less than five emission lines (Brinchmann et al 2004). In this study, we only use the data of the normal star-forming galaxies of their sample.…”

Star Forming Dwarf Galaxies

“…Over long time scales it is controlled by feedback processes [111] and environmental influences. Starburst galaxies are rare and, in the present epoch, do not significantly influence the evolution of star forming dwarfs as a type [12,35,90]. On the individual level however, starbursts may significantly alter the conditions momentarily although it seems unlikely that a major fraction of the gas can be permanently expelled as a consequence of the supernovae winds and thus transform a gas rich galaxy to a gas poor.…”

“…A galaxy with b >3 can be regarded as a mild starburst galaxy while one with b > 10 is of the 'classical' starburst type. In the study of star forming galaxies in the SDSS, Brinchmann et al [12] concluded that about 20% of star formation takes place in galaxies with b=2-3. It is a matter of taste if one wants to call this a starburst but the starburst concept gets very watered-down if all galaxies with b>2 are to be regarded as starbursts.…”

A new sample of X-ray selected narrow emission-line galaxies

“…those that have the best available spectra). We have restricted our selection to objects having spectral fitting performed by the MPA-JHU group (called the galspec measurements and described in Brinchmann et al 2004;Kauffmann et al 2003b;Tremonti et al 2004).This catalogue has the advantage of including emission line fluxes corrected for Galactic reddening. In addition, through fitting of the observed spectrum with galaxy spectra models, the derived products provide estimates of emission line strengths after subtraction of stellar absorption line components.…”