PROPERTIES OF THE INTERSTELLAR MEDIUM IN STAR-FORMING GALAXIES AT z ∼ 1.4 REVEALED WITH ALMA

Abstract

We conducted observations of 12CO(J = 5–4) and dust thermal continuum emission toward 20 star-forming galaxies on the main sequence at z ∼ 1.4 using ALMA to investigate the properties of the interstellar medium. The sample galaxies are chosen to trace the distributions of star-forming galaxies in diagrams of stellar mass versus star formation rate and stellar mass versus metallicity. We detected CO emission lines from 11 galaxies. The molecular gas mass is derived by adopting a metallicity-dependent CO-to-H2 conversion factor and assuming a CO(5–4)/CO(1–0) luminosity ratio of 0.23. Masses of molecular gas and its fractions (molecular gas mass/(molecular gas mass + stellar mass)) for the detected galaxies are in the ranges of (3.9–12) × 1010 M ⊙ and 0.25–0.94, respectively; these values are significantly larger than those in local spiral galaxies. The molecular gas mass fraction decreases with increasing stellar mass; the relation holds for four times lower stellar mass than that covered in previous studies, and the molecular gas mass fraction decreases with increasing metallicity. Stacking analyses also show the same trends. Dust thermal emissions were clearly detected from two galaxies and marginally detected from five galaxies. Dust masses of the detected galaxies are (3.9–38) × 107 M ⊙. We derived gas-to-dust ratios and found they are 3–4 times larger than those in local galaxies. The depletion times of molecular gas for the detected galaxies are (1.4–36) × 108 yr while the results of the stacking analysis show ∼3 × 108 yr. The depletion time tends to decrease with increasing stellar mass and metallicity though the trend is not so significant, which contrasts with the trends in local galaxies.

A Radio-to-mm Census of Star-forming Galaxies in Protocluster 4C23.56 at Z = 2.5: Gas Mass and Its Fraction Revealed with ALMA

“…For the DM mass estimation included within r e , we adopt a nominal value of 0.25 M dyn (Daddi et al 2010). 26 We used the line widths listed in Table 1, which are likely the upper limits of FWHM that yield the highest S/N when integrating across the velocity range (following Seko et al 2016; M. Lee et al 2017, in preparation). Since we cannot constrain the inclination of the galaxy from the measurement,substantial uncertainties are included in the estimation of true line width.…”

“…Instead of performing a Gaussian fit for CO(3-2), we compute and choose an integrating range for CO(3-2) to obtained the maximum S/N in the peak flux in the velocityintegrated image following the description in Seko et al (2016). The map was checked by eye afterward for unexpected cases, such as extremelybroad-line widths to integrate, because some galaxies have unusual spectra that are not well-fitted with a single Gaussian, in addition toinhomogeneous spatial distributions and the velocity gradients (see Figures 4-7 for the morphology andspectrum, M. Lee et al 2017, in preparation).…”

xCOLD GASS: The Complete IRAM 30 m Legacy Survey of Molecular Gas for Galaxy Evolution Studies

“…Because the COLD GASS sample is large and unbiased, it serves as the perfect reference for studies of particular galaxy populations (e.g., active galactic nucleus [AGN] hosts, interacting galaxies, early-type galaxies) and has been extensively used as such (e.g., Fumagalli et al 2012;Bothwell et al 2014;Kirkpatrick et al 2014;Shimizu et al 2015;Stanway et al 2015;Alatalo et al 2016;Amorín et al 2016;Yesuf et al 2017). It is also an ideal z=0 reference point for studies of molecular gas at higher redshifts (e.g., Combes et al 2013;Troncoso et al 2014;Genzel et al 2015;Seko et al 2016;Tacconi et al 2017) and provides powerful constraints for theoretical models and numerical simulations (e.g., Lagos et al 2011;Genel et al 2014;Lagos et al 2015;Popping et al 2015;Davé et al 2017).…”

Evolutionary Phases of Gas-rich Galaxies in a Galaxy Cluster at z = 1.46

“…Since star-forming galaxies in high-z galaxy clusters should grow to massive earlytype galaxies in the local Universe, the cluster galaxies' gas content allows us to better understand the quenching mechanisms of galaxies in dense environments. However, most of the observations of molecular gas at high redshifts have been limited to the galaxies in general fields (e.g., Carilli & Walter 2013;Walter et al 2014;Genzel et al 2015;Silverman et al 2015;Decarli et al 2016;Seko et al 2016;Tacconi et al 2017). Although several studies have surveyed molecular gas in galaxy (proto-)clusters at z ≈ 1-3, CO emissions are detected from at most a few member galaxies in each cluster (Aravena et al 2012;Casasola et al 2013;Ivison et al 2013;Tadaki et al 2014;Dannerbauer et al 2017).…”