Suppressed CO emission and high G/D ratios in z=2 galaxies with sub-solar gas-phase metallicity

Coogan, R T, Sargent, M T, Daddi, E, Valentino, F, Strazzullo, V, Béthermin, M, Gobat, R, Liu, D and Magdis, G (2019) Suppressed CO emission and high G/D ratios in z=2 galaxies with sub-solar gas-phase metallicity. Monthly Notices of the Royal Astronomical Society. ISSN 0035-8711

[img] PDF (This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2019 The Royal Astronomical Society Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.) - Published Version
Available under License All Rights Reserved.

Download (2MB)
[img] PDF (This is a pre-copyedited, author-produced PDF of an article accepted for publication in following peer review. The version of record is available online at: https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stz409/531577) - Accepted Version
Download (2MB)

Abstract

We study a population of significantly sub-solar enrichment galaxies at z=1.99, to investigate how molecular gas, dust and star-formation relate in low-metallicity galaxies at the peak epoch of star-formation. We target our sample with several deep ALMA and VLA datasets, and find no individual detections of CO[4-3], CO[1-0] or dust, in stark contrast to the >60% detection rate expected for solar-enrichment galaxies with these MS Halpha SFRs. We find that both low and high density molecular gas (traced by CO[1-0] and CO[4-3] respectively) are affected by the low enrichment, showing sample average (stacked) luminosity deficits >0.5-0.7 dex below expectations. This is particularly pertinent for the use of high-J CO emission as a proxy of instantaneous star-formation rate. Our individual galaxy data and stacked constraints point to a strong inverse dependence ∝Zγ of gas-to-dust ratios (G/D) and CO-to-H2 conversion factors (aco) on metallicity at z∼2, with γG/D<-2.2 and γαCO<-0.8, respectively. We quantify the importance of comparing G/D and aco vs. metallicity trends from the literature on a common, suitably normalised metallicity scale. When accounting for systematic offsets between different metallicity scales, our z∼2 constraints on these scaling relations are consistent with the corresponding relations for local galaxies. However, among those local relations, we favour those with a steep/double power-law dependence of G/D on metallicity. Finally, we discuss the implications of these findings for (a) gas mass measurements for sub-M∗ galaxies, and (b) efforts to identify the characteristic galaxy mass scale contributing most to the comoving molecular gas density at z=2.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QB Astronomy
Depositing User: Mark Sargent
Date Deposited: 28 Jan 2019 11:57
Last Modified: 13 Feb 2019 13:56
URI: http://sro.sussex.ac.uk/id/eprint/81477

View download statistics for this item

📧 Request an update