A Survey of Atomic Carbon [C i] in High-redshift Main-sequence Galaxies

Abstract

We present the first results of an ALMA survey of the lower fine structure line of atomic carbon [C I]( 3 P 1 − 3 P 0 ) in far infrared-selected galaxies on the main sequence at z ∼ 1.2 in the COSMOS field. We compare our sample with a comprehensive compilation of data available in literature for local and high-redshift starbursting systems and quasars. We show that the [C I]( 3 P 1 → 3 P 0 ) luminosity correlates on global scales with the infrared luminosity L IR similarly to low-J CO transitions. We report a systematic variation of L [C I] 3 P1 − 3 P0 /L IR as a function of the galaxy type, with the ratio being larger for main-sequence galaxies than for starbursts and sub-millimeter galaxies at fixed L IR . The L [C I] 3 P1 − 3 P0 /L CO(2−1) and M [C I] /M dust mass ratios are similar for main-sequence galaxies and for local and high-redshift starbursts within a 0.2 dex intrinsic scatter, suggesting that [C I] is a good tracer of molecular gas mass as CO and dust. We derive a fraction of f [C I] = M [C I] /M C ∼ 3 − 13% of the total carbon mass in the atomic neutral phase. Moreover, we estimate the neutral atomic carbon abundance, the fundamental ingredient to calibrate [C I] as a gas tracer, by comparing L [C I] 3 P1 − 3 P0 and available gas masses from CO lines and dust emission. We find lower [C I] abundances in mainsequence galaxies than in starbursting systems and sub-millimeter galaxies, as a consequence of the canonical α CO and gas-to-dust conversion factors. This argues against the application to different galaxy populations of a universal standard [C I] abundance derived from highly biased samples.

Automated Mining of the ALMA Archive in the COSMOS Field (A3COSMOS). I. Robust ALMA Continuum Photometry Catalogs and Stellar Mass and Star Formation Properties for ∼700 Galaxies at z = 0.5–6

“…We do not account for other lines in this work because those are predicted to fall outside the frequency range or are generally much weaker. The line prediction follows empirical luminosity-luminosity correlations: [C ii]-L IR correlation from De Looze et al (2011), with a [C ii] deficit roughly proportional to L −0.335 IR when L IR > 10 10 L which fits the data best; [N ii]-L IR correlation from Zhao et al (2013Zhao et al ( , 2016; CO(1-0)-L IR correlation from Sargent et al (2014); high-J (J upper ≥ 4) CO-L IR correlation from Liu et al (2015); and [C i]-L IR correlation based on the data sets in Liu et al (2015) and Valentino et al (2018). For CO 2 ≤ J upper ≤ 3 lines, we interpolate the line luminosity using the the CO(1-0)-L IR and CO(4-3)-L IR correlations.…”

Direct Measurement of the [C i] Luminosity to Molecular Gas Mass Conversion Factor in High-redshift Star-forming Galaxies

“…To verify the results and demonstrate the application of our new absorption-derived calibration of α [CI] further, we use the recent sample of emission-selected galaxies with positive detections of [C i] compiled by Valentino et al (2018). This sample includes local, intermediate-and high-redshift galaxies and quasars spanning a large redshift range of z ∼ 0 − 5.…”

“…While CO is still the most extensively surveyed species in emission (e.g. Tacconi et al 2013) and typically more abundant than [C i] (Ikeda et al 2002), [C i] has some advantages as a molecular gas tracer, especially at high redshifts Walter et al 2011;Valentino et al 2018).…”

“…The metallicity evolution of α[CI] for a range of radiation field strengths determined from numerical hydrodynamical simulations byGlover & Clark (2016) is shown for comparison. The blue shaded region shows the range of α[CI] estimated for local galaxies(Crocker et al 2019) or high-redshift galaxies(Valentino et al 2018) using the average Galactic conversion factor of αCO,MW = 4.3 M (K km s −1 pc 2 ) −1(Bolatto et al 2013).…”

“…Comparison between α [CI] -and αCO-derived molecular gas masses. The symbols show all the [C i]emitting galaxies selected from the compilation byValentino et al (2018). The colored points show the estimated molecular gas mass assuming a metallicity-dependent conversion factor of αCO = αCO,MW × 10 −1.27 log(Z/Z ) fromGenzel et al (…”