Probing cold gas in a massive, compact star-forming galaxy at z=6

Abstract

Observations of low order CO transitions represent the most direct way to study galaxies' cold molecular gas, the fuel of star formation. Here we present the first detection of CO(2-1) in a galaxy lying on the main-sequence of star-forming galaxies at z>6. Our target, G09-83808 at z=6.03, has a short depletion time-scale of T_dep~50Myr and a relatively low gas fraction of M_gas/M_star=0.30 that contrasts with those measured for lower redshift main-sequence galaxies. We conclude that this galaxy is undergoing a starburst episode with a high star formation efficiency that might be the result of gas compression within its compact rotating disk. Its starburst-like nature is further supported by its high star formation rate surface density, thus favoring the use of the Kennicutt-Schmidt relation as a more precise diagnostic diagram for starbursts. Without further significant gas accretion, this galaxy would become a compact, massive quiescent galaxy at z~5.5. In addition, we find that the calibration for estimating ISM masses from dust continuum emission satisfactorily reproduces the gas mass derived from the CO(2-1) transition (within a factor of ~2). This is in line with previous studies claiming a small redshift evolution in the gas-to-dust ratio of massive, metal-rich galaxies. In the absence of gravitational amplification, this detection would have required of order ~1000h of observing time. The detection of cold molecular gas in unlensed star-forming galaxies at high redshifts is thus prohibitive with current facilities and requires a ten-fold improvement in sensitivity, such as that envisaged for the ngVLA.

Accepted for publication in The Astrophysical Journal

References in corpus (30)

• A simple model to interpret the ultraviolet, optical and infrared emission from galaxies
• The Herschel view of the dominant mode of galaxy growth from z=4 to the present day
• Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
• A Dust-Obscured Massive Maximum-Starburst Galaxy at a Redshift of 6.34
• The Evolution of the Star-forming Interstellar Medium across Cosmic Time
• Galaxy growth in a massive halo in the first billion years of cosmic history
• ISM properties of a Massive Dusty Star-Forming Galaxy discovered at z ~ 7
• The Evolution of the Baryons Associated with Galaxies Averaged over Cosmic Time and Space
• Automated Mining of the ALMA Archive in the COSMOS Field (A3COSMOS): II. Cold Molecular Gas Evolution out to Redshift 6
• The ALPINE-ALMA [CII] survey: Molecular gas budget in the Early Universe as traced by [CII]
• The space density of luminous dusty star-forming galaxies at $z>4$: SCUBA-2 and LABOCA imaging of ultrared galaxies from $Herschel$-ATLAS
• The ALPINE-ALMA [CII] Survey: Obscured Star Formation Rate Density and Main Sequence of star-forming galaxies at z>4
• Turbulent Gas in Lensed Planck-selected Starbursts at redshifts 1-3.5
• Physical Characterization of an Unlensed Dusty Star-Forming Galaxy at $z=5.85$
• Mapping Obscuration to Reionization with ALMA (MORA): 2mm Efficiently Selects the Highest-Redshift Obscured Galaxies
• The most distant, luminous, dusty star-forming galaxies: redshifts from NOEMA and ALMA spectral scans
• Low Gas Fractions Connect Compact Star-Forming Galaxies to their z ~ 2 Quiescent Descendants
• GOODS-ALMA: The slow downfall of star-formation in $z$ = 2-3 massive galaxies
• The emergence of passive galaxies in the early Universe
• GOODS-ALMA 2.0: Starbursts in the main sequence reveal compact star formation regulating galaxy evolution prequenching
• Sub-millimetre compactness as a critical dimension to understand the Main Sequence of star-forming galaxies
• Molecular Line Observations in Two Dusty Star-Forming Galaxies at z = 6.9
• The Number Densities and Stellar Populations of Massive Galaxies at 3 < z < 6: A Diverse, Rapidly Forming Population in the Early Universe
• The NEWFIRM HETDEX Survey: Photometric Catalog and a Conservative Sample of Massive Quiescent Galaxies at z=3-5 over 17.5 deg^2 in the SHELA Field
• Measuring the average molecular gas content of star-forming galaxies at $z=3-4$
• Detection of nitrogen and oxygen in a galaxy at the end of reionization
• The Physical Drivers of the Luminosity-Weighted Dust Temperatures in High-Redshift Galaxies
• NOEMA confirmation of an optically dark ALMA-AzTEC submillimetre galaxy at $z=5.24$. A late-stage starburst prior to quenching
• The Atacama Large Millimeter/submillimeter Array (ALMA) Band-1 Receiver
• Observed cosmic evolution of galaxy dust properties with metallicity and tensions with models

Cited by in corpus (4)

• Cosmological Model Tests with JWST
• Missing Giants: Predictions on Dust-Obscured Galaxy Stellar Mass Assembly Throughout Cosmic Time
• Big Three Dragons: Molecular Gas in a Bright Lyman-Break Galaxy at $z=7.15$
• Cosmic Sands: The Origin of Dusty, Star-forming Galaxies in the Epoch of Reionization