The evolving star formation rate:M_⋆relation and sSFR sincez≃ 5 from the VUDS spectroscopic survey

Abstract

We study the evolution of the star formation rate (SFR) -stellar mass (M ) relation and specific star formation rate (sSFR) of star-forming galaxies (SFGs) since a redshift z 5.5 using 2435 (4531) galaxies with highly reliable spectroscopic redshifts in the VIMOS Ultra-Deep Survey (VUDS). It is the first time that these relations can be followed over such a large redshift range from a single homogeneously selected sample of galaxies with spectroscopic redshifts. The log(SFR) − log(M ) relation for SFGs remains roughly linear all the way up to z = 5, but the SFR steadily increases at fixed mass with increasing redshift. We find that for stellar masses M ≥ 3.2 × 10 9 M the SFR increases by a factor of ∼13 between z = 0.4 and z = 2.3. We extend this relation up to z = 5, finding an additional increase in SFR by a factor of 1.7 from z = 2.3 to z = 4.8 for masses M ≥ 10 10 M . We observe a turn-off in the SFR-M relation at the highest mass end up to a redshift z ∼ 3.5. We interpret this turn-off as the signature of a strong on-going quenching mechanism and rapid mass growth. The sSFR increases strongly up to z ∼ 2, but it grows much less rapidly in 2 < z < 5. We find that the shape of the sSFR evolution is not well reproduced by cold gas accretion-driven models or the latest hydrodynamical models. Below z ∼ 2 these models have a flatter evolution (1 + z) Φ with Φ = 2−2.25 compared to the data which evolves more rapidly with Φ = 2.8 ± 0.2. Above z ∼ 2, the reverse is happening with the data evolving more slowly with Φ = 1.2 ± 0.1. The observed sSFR evolution over a large redshift range 0 < z < 5 and our finding of a non-linear main sequence at high mass both indicate that the evolution of SFR and M is not solely driven by gas accretion. The results presented in this paper emphasize the need to invoke a more complex mix of physical processes including major and minor merging to further understand the co-evolution of the SFR and stellar mass growth.

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.…”

“…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. Similar to Lee et al (2015) and Tasca et al (2015) we find that the transition mass at which this flattening occurs evolves with redshift; this is true whether or not quenched galaxies are included. Full parameterizations of the SFR-M * relation with respect to redshift, Ψ(z, M * ), for both all and star-forming galaxies are presented in Section 3.3 and shown in Figures 7 and 8.…”

“…There is excellent agreement at the overlapping redshifts between our measurements and those of Lee et al (2015) and Gavazzi et al (2015). We do observe a roughly uniform offset of ≈0.5 dex with Tasca et al (2015) which may be the result of a different parameterization used to measure the turnover mass.…”

“…Recent results from Gavazzi et al (2015) show that this evolution extends to z ∼ 2.5 and that extrapolating to to z = 0 coincides with a break observed in the local SFR-M * relation. Results from the VUDS spectroscopic survey have also found a redshift dependence for the turnover mass (Tasca et al 2015). However, because we include all galaxies in the analysis presented here the observed evolution of M 0 may be a consequence of the increasing population of massive quenched galaxies at low-z.…”

“…All sequences shown here have been converted to a Chabrier (2003) IMF. 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).…”