The inferred evolution of the cold gas properties of CANDELS galaxies at 0.5 <z< 3.0

Abstract

We derive the total cold gas, atomic hydrogen, and molecular gas masses of approximately 24 000 galaxies covering four decades in stellar mass at redshifts 0.5 < z < 3.0, taken from the CANDELS survey. Our inferences are based on the inversion of a molecular hydrogen based star formation law, coupled with a prescription to separate atomic and molecular gas. We find that: 1) there is an increasing trend between the inferred cold gas (H I and H 2 ), H I, and H 2 mass and the stellar mass of galaxies down to stellar masses of 10 8 M already in place at z = 3; 2) the molecular fractions of cold gas increase with increasing stellar mass and look-back time; 3) there is hardly any evolution in the mean H I content of galaxies at fixed stellar mass; 4) the cold gas fraction and relative amount of molecular hydrogen in galaxies decrease at a relatively constant rate with time, independent of stellar mass; 5) there is a large population of low-stellar mass galaxies dominated by atomic gas. These galaxies are very gas rich, but only a minor fraction of their gas is molecular; 6) the ratio between star-formation rate (SFR) and inferred total cold gas mass (H I + H 2 ) of galaxies (i.e., star-formation efficiency; SFE) increases with star-formation at fixed stellar masses. Due to its simplicity, the presented approach is valuable to assess the impact of selection biases on small samples of directly-observed gas masses and to extend scaling relations down to stellar mass ranges and redshifts that are currently difficult to probe with direct measurements of gas content.

Slicing the cool circumgalactic medium along the major axis of a star-forming galaxy at z = 0.7

“…G1's star-formation efficiency, defined as SFR/MHI, is relatively high, SFE=3.5 × 10 −10 yr −1 , for the bulk of starforming galaxies (Popping et al 2015). On the other hand, the cool gas fraction, defined as MHI/(MHI + M * ), falls just below average for z = 0.7: fgas ≈ 0.4 (e.g., Popping et al 2015).…”

When the Milky Way turned off the lights: APOGEE provides evidence of star formation quenching in our Galaxy

“…For instance, Papovich et al (2015) inferred that while the gas fraction in M31-type galaxies has decreased to lower than 20% at z ∼ 1.5, it is still high for MW-sized galaxies at ∼40%, consistent with the fraction estimated here. See also Popping et al (2015). Snaith et al (2014;2015; orange curve, left axis), together with the gas fraction evolution in the model (thin black curve and right axis).…”

ALMA + VLT observations of a damped Lyman-α absorbing galaxy: massive, wide CO emission, gas-rich but with very low SFR

“…The corrected PHIBSS sample is seen now to lie closer to the Santini et al (2014) relation but it still lies somewhat below and with a scatter slightly larger than the mass slice would predict. In order to obtain a better evaluation of how the relation based on f mol−gas compares to that of the total gas mass relation, we also include CANDELS galaxies from Popping et al (2015) for which total SFRs are also known. The molecular gas mass for the CANDELS galaxies has not been measured, rather it has been inferred from a suite of optical data and the model presented in Popping et al (2015).…”

“…In order to obtain a better evaluation of how the relation based on f mol−gas compares to that of the total gas mass relation, we also include CANDELS galaxies from Popping et al (2015) for which total SFRs are also known. The molecular gas mass for the CANDELS galaxies has not been measured, rather it has been inferred from a suite of optical data and the model presented in Popping et al (2015). It is seen that for f mol−gas < 0.2 the CANDELS sample follows the Santini et al (2014) relation well, whereas it for larger f mol−gas connects perfectly with the PHIBSS sample.…”