ON STAR FORMATION RATES AND STAR FORMATION HISTORIES OF GALAXIES OUT TOz∼ 3

Abstract

We compare multi-wavelength star formation rate (SFR) indicators out to z ∼ 3 in the GOODS-South field. Our analysis uniquely combines U -to-8µm photometry from FIREWORKS, MIPS 24 µm and PACS 70, 100, and 160 µm photometry from the PEP survey, and Hα spectroscopy from the SINS survey. We describe a set of conversions that lead to a continuity across SFR indicators. A luminosityindependent conversion from 24 µm to total infrared luminosity yields estimates of L IR that are in the median consistent with the L IR derived from PACS photometry, albeit with significant scatter. Dust correction methods perform well at low to intermediate levels of star formation. They fail to recover the total amount of star formation in systems with large SF R IR /SF R UV ratios, typically occuring at the highest SFRs (SF R UV +IR 100 M ⊙ /yr) and redshifts (z 2.5) probed. Finally, we confirm that Hα-based SFRs at 1.5 < z < 2.6 are consistent with SF R SED and SF R UV +IR provided extra attenuation towards HII regions is taken into account (A V,neb = A V,continuum /0.44). With the cross-calibrated SFR indicators in hand, we perform a consistency check on the star formation histories inferred from SED modeling. We compare the observed SFR-M relations and mass functions at a range of redshifts to equivalents that are computed by evolving lower redshift galaxies backwards in time. We find evidence for underestimated stellar ages when no stringent constraints on formation epoch are applied in SED modeling. We demonstrate how resolved SED modeling, or alternatively deep UV data, may help to overcome this bias. The age bias is most severe for galaxies with young stellar populations, and reduces towards older systems. Finally, our analysis suggests that SFHs typically vary on timescales that are long (at least several 100 Myr) compared to the galaxies' dynamical time.

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

“…This result contrasts what was found for galaxies that are individually detected in the far-IR images which show no strong evidence of a systematic trend (see Figure 2). This suggests that the fainter, non-detected galaxies have SEDs that are not consistent with their more luminous counterparts (Muzzin et al 2010;Wuyts et al 2011). Nevertheless, this discrepancy is not dominant, but comparable to the level of scatter between surveys noted earlier (0.2 dex).…”

“…We estimate bolometric infrared luminosities (L IR ≡ L 8-1000 μm ) by fitting an IR spectral template to the stacked 24-160 μm photometry. The template introduced by Wuyts et al (2008), hereafter referred to as the W08 template, was constructed by averaging the logarithm of the spectral template library from Dale & Helou Furthermore, Wuyts et al (2011) find that at 0 < z < 3 this luminosity-independent conversion yields consistent L IR estimates from 24 μm when compared to L IR derived from PACS photometry from the Herschel PEP survey . For our stacking analysis, we smooth the W08 template by the redshift distribution of the galaxies in each mass-redshift bin prior to fitting.…”

“…The launch of the Herschel Space Observatory (Pilbratt et al 2010) expanded observational studies in the far-IR with improved data quality at longer wavelengths. Combinations of Spitzer and Herschel data make it possible to constrain IR spectral energy distributions (SEDs) for large enough samples of galaxies to complement modern optical/near-IR galaxy surveys (e.g., Elbaz et al 2011;Wuyts et al 2011).…”

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

“…The stellar mass was estimated from SED fitting. The SFR estimate was based on the sum of the observed UVand IR-luminosities for the z ∼ 1.2 samples (Wuyts et al 2011), and the extinction-corrected Hα luminosities for the z ∼ 2.2 samples (Kennicutt 1998a;Förster Schreiber et al 2009;Mancini et al 2011;Wuyts et al 2011). Their sample follows the main sequence of star-forming galaxies at the redshift.…”

The Alma Spectroscopic Survey in the Hubble Ultra Deep Field: Molecular Gas Reservoirs in High-Redshift Galaxies

“…These extreme sources might contribute significantly to the star formation budget in the universe at > z 4, but their role declines with cosmic time (Casey et al 2014). Indeed, the bulk of star formation up toz 2 is observed in galaxies along the so-called "main sequence" (Elbaz et al 2007Noeske et al 2007;Daddi et al 2010aDaddi et al , 2010bGenzel et al 2010;Wuyts et al 2011;Whitaker et al 2012), a tight (scatter rms ∼0.3 dex) relation between the SFR and the stellar mass, M * . Addressing the molecular gas content of main-sequence galaxies beyond the local universe has become feasible only in recent years.…”