REGULARITY UNDERLYING COMPLEXITY: A REDSHIFT-INDEPENDENT DESCRIPTION OF THE CONTINUOUS VARIATION OF GALAXY-SCALE MOLECULAR GAS PROPERTIES IN THE MASS-STAR FORMATION RATE PLANE

By M. Sargent, E. Daddi, M. B'ethermin, H. Aussel, G. Magdis, H. Hwang, S. Juneau, D. Elbaz, E. D. Cunha. 2013

219 citations recorded by the source corpus.

Star-forming galaxies (SFGs) display a continuous specific star formation rate (sSFR) distribution, which can be approximated by two log-normal functions: one encompassing the galaxy main sequence (MS), and the other a rarer, starbursting population. Starburst (SB) sSFRs can be regarded as the outcome of a physical process (plausibly merging) taking the mathematical form of a log-normal boosting kernel that enhances star formation activity. We explore the utility of splitting the star-forming population into MS and SB galaxies—an approach we term the “2-Star Formation Mode” framework—for understanding their molecular gas properties. Star formation efficiency (SFE) and gas fraction variations among SFGs take a simple redshift-independent form, once these quantities are normalized to the corresponding values for average MS galaxies. SFE enhancements during SB episodes scale supra-linearly with the SFR increase, as expected for mergers. Consequently, galaxies separate more clearly into loci for SBs and normal galaxies in the Schmidt–Kennicutt plane than in (s)SFR versus M⋆ space. SBs with large deviations (>10 fold) from the MS, e.g., local ULIRGs, are not average SBs, but are much rarer events whose progenitors had larger gas fractions than typical MS galaxies. Statistically, gas fractions in SBs are reduced two- to threefold compared to their direct MS progenitors, as expected for short-lived SFR boosts where internal gas reservoirs are depleted more quickly than gas is re-accreted from the cosmic web. We predict variations of the conversion factor αCO in the SFR–M⋆ plane and we show that the higher sSFR of distant galaxies is directly related to their larger gas fractions.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a26ff488908820c5853345dac70b77d82d8ec278

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Citations in the corpus

xCOLD GASS: The Complete IRAM 30 m Legacy Survey of Molecular Gas for Galaxy Evolution Studies (2017, background): “…rate-stellar mass (SFR-M∗) plane can be explained by the availability of cold gas through inflows, the efficiency of the star formation process, and the balancing power of feedback (e.g. Bouché et al. 2010; Lilly et al. 2013; Tacconi et al. 2013, 2017; Sargent et al. 2014; Saintonge et al. 2016).”
PHIBSS: Unified Scaling Relations of Gas Depletion Time and Molecular Gas Fractions (2017, background): “2013, Santini et al. 2014, Sargent et al. 2014, G15, Scoville et al. 2016, 2017).”
The confinement of star-forming galaxies into a main sequence through episodes of gas compaction, depletion and replenishment (2015, methodology): “Already Elbaz et al. (2011), Wuyts et al. (2011), Lada et al. (2012), and Sargent et al. (2014) put forward the idea that the decrease in tdep above the MS may be associated with internal parameters such as the central gas density.”
CO excitation of normal star forming galaxies out to $z=1.5$ as regulated by the properties of their interstellar medium (2014, methodology): “…parameters we can match the gas masses estimates of order of 5–8×1010M⊙ typically inferred for these galaxies using dynamical methods (D10), or converting from dust mass estimates (Magdis et al 2011; 2012), or assuming a local metallicity scaling for theαCO conversion factor (Sargent et al 2014).”
AGN wind scaling relations and the co-evolution of black holes and galaxies (2017, background): “For example, the Sargent et al. (2014) parameterisation results in a depletion timescale a factor of ∼2 shorter than the Genzel et al. (2015) one for galaxies above the MS. Figure 8 shows the star formation against the outflow depletion timescales, tdep(OF) = Mgas/ṀOF.”
COMBINED CO AND DUST SCALING RELATIONS OF DEPLETION TIME AND MOLECULAR GAS FRACTIONS WITH COSMIC TIME, SPECIFIC STAR-FORMATION RATE, AND STELLAR MASS (2014, methodology): “In particular the dependence of the slope on Δ(log(sSFR/sSFR(ms,z,M*)) is in excellent agreement with the findings of Kennicutt (1998), Daddi et al. (2010b), Genzel et al. (2010), Magdis et al. (2012), Sargent et al. (2014) and Tacconi et al. (2013).”
Evolution of density profiles in high-z galaxies: compaction and quenching inside-out (2015, result): “…part of the main sequence are compact, star-forming galaxies (blue nuggets), with higher gas fractions and shorter depletion times, consistent with observations (e.g., Magdis et al. 2012; Sargent et al. 2014; Huang & Kauffmann 2014; Genzel et al. 2015; Silverman et al. 2015; Scoville et al. 2015).”
ISM MASSES AND THE STAR FORMATION LAW AT Z = 1 TO 6: ALMA OBSERVATIONS OF DUST CONTINUUM IN 145 GALAXIES IN THE COSMOS SURVEY FIELD (2015, background): “…for normal SF galaxies and starburst/SMG galaxies; however, in both cases, their ISM masses at high redshift are derived from higher-J CO transitions and they use different highJ to J = 0 line ratios and CO-to-H2 conversion factors for the two classes of galaxies (see also Sargent et al. 2014).”
Evolution of the dust emission of massive galaxies up to z=4 and constraints on their dominant mode of star formation (2014, methodology): “The evolution of 〈U〉we found can be understood from a few simple assumptions on the evolution of the gas metallicity and the (SFE) of galaxies.”
ALMA SPECTROSCOPIC SURVEY IN THE HUBBLE ULTRA DEEP FIELD: SURVEY DESCRIPTION (2016, background): “The goal of the ALMA frequency scan was to reach a sensitivity such that the predicted ‘knee’ of the CO luminosity function could be reached at z ∼ 2 (e.g., Sargent et al. 2014).”