TheHerschelview of the dominant mode of galaxy growth fromz= 4 to the present day

Abstract

We present an analysis of the deepest Herschel images in four major extragalactic fields GOODS-North, GOODS-South, UDS, and COSMOS obtained within the GOODS-Herschel and CANDELS-Herschel key programs. The star formation picture provided by a total of 10 497 individual far-infrared detections is supplemented by the stacking analysis of a mass complete sample of 62 361 starforming galaxies from the Hubble Space Telescope (HST) H band-selected catalogs of the CANDELS survey and from two deep ground-based K s band-selected catalogs in the GOODS-North and the COSMOS-wide field to obtain one of the most accurate and unbiased understanding to date of the stellar mass growth over the cosmic history. We show, for the first time, that stacking also provides a powerful tool to determine the dispersion of a physical correlation and describe our method called "scatter stacking", which may be easily generalized to other experiments. The combination of direct UV and far-infrared UV-reprocessed light provides a complete census on the star formation rates (SFRs), allowing us to demonstrate that galaxies at z = 4 to 0 of all stellar masses (M * ) follow a universal scaling law, the so-called main sequence of star-forming galaxies. We find a universal close-to-linear slope of the log 10 (SFR)-log 10 (M * ) relation, with evidence for a flattening of the main sequence at high masses (log 10 (M * /M ) > 10.5) that becomes less prominent with increasing redshift and almost vanishes by z 2. This flattening may be due to the parallel stellar growth of quiescent bulges in star-forming galaxies, which mostly happens over the same redshift range. Within the main sequence, we measure a nonvarying SFR dispersion of 0.3 dex: at a fixed redshift and stellar mass, about 68% of star-forming galaxies form stars at a universal rate within a factor 2. The specific SFR (sSFR = SFR/M * ) of star-forming galaxies is found to continuously increase from z = 0 to 4. Finally we discuss the implications of our findings on the cosmic SFR history and on the origin of present-day stars: more than two-thirds of present-day stars must have formed in a regime dominated by the "main sequence" mode. As a consequence we conclude that, although omnipresent in the distant Universe, galaxy mergers had little impact in shaping the global star formation history over the last 12.5 billion years.

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

“…In agreement with recent results, we find that SFRs are roughly proportional to stellar mass at low masses (10 10.2 M e ), but that this trend flattens at higher masses (see also Whitaker et al 2014;Lee et al 2015;Schreiber et al 2015;Tasca et al 2015). Furthermore, although the evolution of the SFR-M * relation is still predominantly in normalization, the slope at high masses (M *  10 10.2 M e ) is also changing.…”

“…Papovich et al (2015) find similar results in their analysis of the progenitors of galaxies with present-day masses of the Milky Way and M31 galaxies. Finally, we have repeated this comparison using the SFR-M * parameterizations provided by Whitaker et al (2014) and Schreiber et al (2015) and in both cases we find similar disagreements. This suggests that the discrepancies between the star formation rates and mass evolution that were previously reported by Leja et al (2015) have not been completely resolved using the more up-to-date data sets.…”

“…Unfortunately however, imaging used to probe obscured star formation (typically far-IR and radio) rarely ever reach complementary depths. Thus, many studies over the past several years have turned to measuring SFRs from stacked data in order to compensate for this disparity (e.g., Dunne et al 2009;Rodighiero et al 2010;Karim et al 2011;Whitaker et al 2014;Schreiber et al 2015). However it is important to keep in mind that the interpretation of stacked results may be complicated by the fact that the intrinsic distribution of SFRs may not be unimodal or symmetric.…”

“…Note, due to the large redshift bins used by Tasca et al (2015) we show weighted averages of their measurements here. 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.…”

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

“…These values are 0.1-0.3 dex lower than of those of Viero et al (2013), which may be due to our inclusion of 24 μm sources not already selected in the UltraVISTA catalog (see Section 3) in the stacking procedure. Interestingly, the L IR estimates of Schreiber et al (2015) are ∼0.6 dex lower than that of Viero et al (2013), despite both stacking UVJ-selected QGs. The discrepancy is likely due to the different stacking algorithms used.…”