The evolution of the dust temperatures of galaxies in the SFR–M∗ plane up to z similar to 2
Abstract
We study the evolution of the dust temperature of galaxies in the
SFR− M∗ plane up to z ~ 2 using
far-infrared and submillimetre observations from the Herschel Space
Observatory taken as part of the PACS Evolutionary Probe (PEP) and Herschel
Multi-tiered Extragalactic Survey (HerMES) guaranteed time key programmes.
Starting from a sample of galaxies with reliable star-formation rates (SFRs), stellar
masses (M∗) and redshift estimates, we grid the
SFR− M∗parameter space in several redshift ranges and
estimate the mean dust temperature (Tdust) of each
SFR–M∗ − z bin. Dust temperatures are
inferred using the stacked far-infrared flux densities (100–500 μm) of
our SFR–M∗ − z bins. At all redshifts, the
dust temperature of galaxies smoothly increases with rest-frame infrared luminosities
(LIR), specific SFRs (SSFR; i.e.,
SFR/M∗), and distances with respect to the main sequence
(MS) of the SFR− M∗ plane (i.e.,
Δlog (SSFR)MS = log [SSFR(galaxy)/SSFRMS(M∗,z)]).
The Tdust − SSFR and
Tdust − Δlog (SSFR)MS
correlations are statistically much more significant than the
Tdust − LIR one. While the
slopes of these three correlations are redshift-independent, their normalisations evolve
smoothly from z = 0 and z ~ 2. We convert these
results into a recipe to derive Tdust from SFR,
M∗ and z, valid out to
z ~ 2 and for the stellar mass and SFR range covered by our stacking
analysis. The existence of a strong
Tdust − Δlog (SSFR)MS
correlation provides us with several pieces of information on the dust and gas content of
galaxies. Firstly, the slope of the
Tdust − Δlog (SSFR)MS
correlation can be explained by the increase in the star-formation efficiency (SFE;
SFR/Mgas) with Δlog (SSFR)MS
as found locally by molecular gas studies. Secondly, at fixed
Δlog (SSFR)MS, the constant dust temperature observed in
galaxies probing wide ranges in SFR and M∗ can be explained by
an increase or decrease in the number of star-forming regions with comparable SFE enclosed
in them. And thirdly, at high redshift, the normalisation towards hotter dust temperature
of the Tdust − Δlog (SSFR)MS
correlation can be explained by the decrease in the metallicities of galaxies or by the
increase in the SFE of MS galaxies. All these results support the hypothesis that the
conditions prevailing in the star-forming regions of MS and far-above-MS galaxies are
different. MS galaxies have star-forming regions with low SFEs and thus cold dust, while
galaxies situated far above the MS seem to be in a starbursting phase characterised by
star-forming regions with high SFEs and thus hot dust.
Domains
Astrophysics [astro-ph]
Origin : Publication funded by an institution
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