A HIGHLY CONSISTENT FRAMEWORK FOR THE EVOLUTION OF THE STAR-FORMING “MAIN SEQUENCE” FROM z ∼ 0-6

Abstract

Using a compilation of 25 studies from the literature, we investigate the evolution of the star-forming galaxy (SFG) Main Sequence (MS) in stellar mass and star formation rate (SFR) out to z ∼ 6. After converting all observations to a common set of calibrations, we find a remarkable consensus among MS observations (∼ 0.1 dex 1σ interpublication scatter). By fitting for time evolution of the MS in bins of constant mass, we deconvolve the observed scatter about the MS within each observed redshift bins. After accounting for observed scatter between different SFR indicators, we find the width of the MS distribution is ∼ 0.2 dex and remains constant over cosmic time. Our best fits indicate the slope of the MS is likely time-dependent, with our best fit log SFR(M * , t) = (0.84 ± 0.02 − 0.026 ± 0.003 × t) log M * −(6.51 ± 0.24 − 0.11 ± 0.03 × t), with t the age of the Universe in Gyr. We use our fits to create empirical evolutionary tracks in order to constrain MS galaxy star formation histories (SFHs), finding that (1) the most accurate representations of MS SFHs are given by delayed-τ models, (2) the decline in fractional stellar mass growth for a "typical" MS galaxy today is approximately linear for most of its lifetime, and (3) scatter about the MS can be generated by galaxies evolving along identical evolutionary tracks assuming an initial 1σ spread in formation times of ∼ 1.4 Gyr.

THE SFR–M* RELATION AND EMPIRICAL STAR FORMATION HISTORIES FROM ZFOURGE AT 0.5 < z < 4*

“…Curves for the Schreiber et al (2015) relations come from their parameterization evaluated at the central redshift of each bin shown here (see their Section 4.1). Similarly, the curves for Speagle et al (2014) correspond to parameterizations from their Table 9: "All" and "Mixed" for the all-and star-forming galaxy samples shown here. We also note that the redshift bins of the Karim et al (2011) relations are different than those indicated at the top: 0.6 < z < 0.8, 1.0 < z < 1.2, 1.6 < z < 2.0, 2.0 < z < 2.5, and 2.5 < z < 3.0 respectively.…”

“…Another type of lookback study involves using the observed correlation between stellar mass and star formation rate, hereafter referred to as the SFR-M * relation (e.g., Brinchmann et al 2004;Noeske et al 2007;Gilbank et al 2011;Whitaker et al 2012;Speagle et al 2014). By tracing along this evolving star formation sequence it is possible to predict how galaxies should evolve due to star formation (e.g., Leitner 2012;Speagle et al 2014).…”

“…By tracing along this evolving star formation sequence it is possible to predict how galaxies should evolve due to star formation (e.g., Leitner 2012;Speagle et al 2014). In general some disagreement between this approach and the number density selection (NDS) is expected since the former does not include growth due to mergers; indeed, Drory & Alvarez (2008) use this difference to derive the merger rate.…”

SDSS-IV MaNGA-resolved Star Formation and Molecular Gas Properties of Green Valley Galaxies: A First Look with ALMA and MaNGA

“…They are randomly selected to be massive galaxies that lie below the star-forming main-sequence relation with different separations from the main sequence, ΔsSFR, defined as the offset in log(sSFR) relative to the mainsequence value (i.e., log(sSFR)-log(sSFR MS )). Previous studies have revealed significant differences in the slope and normalization of the main sequence (e.g., see Speagle et al 2014). The selection of the star-forming population, the method determining the star formation rate and stellar mass, as well as the IMF, have a strong effect in determining the properties of the main sequence.…”

CONFIRMING THE EXISTENCE OF A QUIESCENT GALAXY POPULATION OUT TO z = 3: A STACKING ANALYSIS OF MID-, FAR-INFRARED, AND RADIO DATA

“…The IR-bright QG candidates have similar or higher SFR H compared to SFGs, and are significantly higher than the IR-faint counterparts. For comparison, the SFR-M å measured in Speagle et al (2014) is plotted as gray lines, with the 1−3× observed dispersion (σ SFR =0.3) shown as dark-to-light shades. IR-faint QG candidates have SFRs at least 2-3 dispersions (0.6-0.9 dex) below those of SFGs out to z∼2, and at z=2-3 the difference is smaller.…”