Measuring the average molecular gas content of star-forming galaxies at $z=3-4$

Abstract

We study the molecular gas content of 24 star-forming galaxies at $z=3-4$, with a median stellar mass of $10^{9.1}$ M${}_{\odot }$, from the MUSE Hubble Ultra Deep Field (HUDF) Survey. Selected by their Lyman-alpha-emission and H-band magnitude, the galaxies show an average EW $\approx 20$ angstrom, below the typical selection threshold for Lyman Alpha Emitters (EW $>25$ angstrom), and a rest-frame UV spectrum similar to Lyman Break Galaxies. We use rest-frame optical spectroscopy from KMOS and MOSFIRE, and the UV features observed with MUSE, to determine the systemic redshifts, which are offset from Lyman alpha by 346 km s${}^{-1}$, with a 100 to 600 km s${}^{-1}$ range. Stacking CO(4-3) and [CI](1-0) (and higher-$J$ CO lines) from the ALMA Spectroscopic Survey of the HUDF (ASPECS), we determine $3\sigma$ upper limits on the line luminosities of $4.0\times 10^8$ K km s${}^{-1}$pc${}^2$ and $5.6\times 10^8$ K km s${}^{-1}$pc${}^2$, respectively (for a 300 km s${}^{-1}$ linewidth). Stacking the 1.2 mm and 3 mm dust continuum flux densities, we find a $3\sigma$ upper limits of 9 $\mu$Jy and $1.2$ $\mu$Jy, respectively. The inferred gas fractions, under the assumption of a 'Galactic' CO-to-H${}_2$ conversion factor and gas-to-dust ratio, are in tension with previously determined scaling relations. This implies a substantially higher ${\alpha }_{\mathrm{CO}}\ge 10$ and ${\delta }_{\mathrm{GDR}}\ge 1200$, consistent with the sub-solar metallicity estimated for these galaxies ($12+\log (O/H)\approx 7.8\pm 0.2$). The low metallicity of $z\ge 3$ star-forming galaxies may thus make it very challenging to unveil their cold gas through CO or dust emission, warranting further exploration of alternative tracers, such as [CII].

26 pages, 12 figures, 3 tables. Accepted for publication in ApJ

References in corpus (59)

• The NumPy array: a structure for efficient numerical computation
• A simple model to interpret the ultraviolet, optical and infrared emission from galaxies
• Dust Masses, PAH Abundances, and Starlight Intensities in the SINGS Galaxy Sample
• Constraining the Low-Mass Slope of the Star Formation Sequence at 0.5<z<2.5
• Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
• The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lya Emitters from z=3.1 to 5.7 in the 1 deg^2 Field: Luminosity Functions and AGN
• The Chandra Deep Field-South Survey: 7 Ms Source Catalogs
• The Stellar, Gas and Dynamical Masses of Star-Forming Galaxies at z~2
• xCOLD GASS: the complete IRAM-30m legacy survey of molecular gas for galaxy evolution studies
• An ALMA survey of Sub-millimeter Galaxies in the Extended Chandra Deep Field South: Physical properties derived from ultraviolet-to-radio modelling
• The Evolution of the Star-forming Interstellar Medium across Cosmic Time
• The MUSE Hubble Ultra Deep Field Survey: I. Survey description, data reduction and source detection
• The Universal Relation of Galactic Chemical Evolution: The Origin of the Mass-Metallicity Relation
• New fully empirical calibrations of strong-line metallicity indicators in star forming galaxies
• CO excitation of normal star forming galaxies out to z=1.5 as regulated by the properties of their interstellar medium
• The ALPINE-ALMA [CII] Survey: data processing, catalogs, and statistical source properties
• ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Survey Description
• The Herschel Dwarf Galaxy Survey: I. Properties of the low-metallicity ISM from PACS spectroscopy
• Galaxies with Wolf-Rayet signatures in the low-redshift Universe - A survey using the Sloan Digital Sky Survey
• UVUDF: Ultraviolet Through Near-infrared Catalog and Photometric Redshifts of Galaxies in the Hubble Ultra Deep Field
• The MUSE Hubble Ultra Deep Field Survey: II. Spectroscopic redshifts and comparisons to color selections of high-redshift galaxies
• The Ly-alpha Properties of Faint Galaxies at z2-3 with Systemic Redshifts and Velocity Dispersions from Keck-MOSFIRE
• Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas
• Tracing the reionization epoch with ALMA: [CII] emission in z~7 galaxies
• ALMA uncovers the [CII] emission and warm dust continuum in a z = 8.31 Lyman break galaxy
• The ALMA Spectroscopic Survey Large Program: The Infrared Excess of z=1.5-10 UV-selected Galaxies and the Implied High-Redshift Star Formation History
• The Rest-Frame Submillimeter Spectrum of High-Redshift, Dusty, Star-Forming Galaxies
• The Evolution of the Baryons Associated with Galaxies Averaged over Cosmic Time and Space
• A Consistent Study of Metallicity Evolution at 0.8 < z < 2.6
• 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 ALMA Spectroscopic Survey in the HUDF: CO Excitation and Atomic Carbon in Star-Forming Galaxies at $z=1-3$
• Missing [CII] emission from early galaxies
• The Origins of [CII] Emission in Local Star-forming Galaxies
• The Herschel Dwarf Galaxy Survey: II. Physical conditions, origin of [CII] emission, and porosity of the multiphase low-metallicity ISM
• ALMA Observation of 158 micron [CII] Line and Dust Continuum of a z=7 Normally Star-forming Galaxy in the Epoch of Reionization
• The ALMA Spectroscopic Survey in the HUDF: Multi-band constraints on line luminosity functions and the cosmic density of molecular gas
• Gas Fraction and Depletion Time of Massive Star Forming Galaxies at z~3.2: No Change in Global Star Formation Process out to z>3
• ALMA reveals metals yet no dust within multiple components in CR7
• The MUSE Hubble Ultra Deep Field Survey VI: The Faint-End of the Lya Luminosity Function at 2.91 < z < 6.64 and Implications for Reionisation
• Molecular gas content in strongly-lensed z~1.5-3 star-forming galaxies with low IR luminosities
• ALMA [CII] detection of a redshift 7 lensed galaxy behind RXJ1347.1-1145
• A Detailed Study of Gas and Star Formation in a Highly Magnified Lyman Break Galaxy at z=3.07
• The ALMA Spectroscopic Survey in the HUDF: Deep 1.2 mm continuum number counts
• ALMA Reveals Weak [NII] Emission in "Typical" Galaxies and Intense Starbursts at z=5-6
• The ALMA Spectroscopic Survey in the HUDF: The Cosmic Dust and Gas Mass Densities in Galaxies up to $z\sim 3$
• The Absence of [CII] 158$\mu$m Emission in Spectroscopically-Confirmed Galaxies at $z>8$
• VLA-ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (VLASPECS): Total Cold Gas Masses and CO Line Ratios for z=2-3 "Main Sequence" Galaxies
• Dust and Gas in Star Forming Galaxies at z~3 - Extending Galaxy Uniformity to 11.5 Billion Years
• The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The nature of the faintest dusty star-forming galaxies
• CO emission in distant galaxies on and above the main sequence
• High gas fraction in a CO-selected main-sequence galaxy at $z>3$
• The MUSE Hubble Ultra Deep Field Survey. XV. The mean rest-UV spectra of Ly-alpha emitters at z>3
• The cosmic abundance of cold gas in the local Universe
• ORIGIN: Blind detection of faint emission line galaxies in MUSE datacubes
• GOODS-ALMA: Using IRAC and VLA to probe fainter millimeter galaxies
• ALMA reveals the molecular gas properties of 5 star-forming galaxies across the main sequence at 3 < z < 3.5
• Suppressed CO emission and high G/D ratios in z=2 galaxies with sub-solar gas-phase metallicity
• The ALMA Spectroscopic Survey in the HUDF: Constraining the Molecular Content at $\log (M_{\ast }/M_{\odot })\sim 9.5$ with CO stacking of MUSE detected $z\sim 1.5$ Galaxies

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• The MUSE Hubble Ultra Deep Field surveys: Data release II
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