CO and Fine-Structure Lines Reveal Low Metallicity in a Stellar-Mass-Rich Galaxy at z ~ 1?

Abstract

We present detections of the CO(4-3) and [C I] 609 $\mu$m spectral lines, as well as the dust continuum at 480.5 GHz (rest-frame), in 3C 368, a Fanaroff-Riley class II (FR-II) galaxy at redshift (z) 1.131. 3C 368 has a large stellar mass, ~ 3.6 x 10${}^{11}$ M${}_{\odot }$, and is undergoing an episode of vigorous star formation, at a rate of ~ 350 M${}_{\odot }$/yr, and active galactic nucleus (AGN) activity, with radio-emitting lobes extended over ~ 73 kpc. Our observations allow us to inventory the molecular-gas reservoirs in 3C 368 by applying three independent methods: (1) using the CO(4-3)-line luminosity, excitation state of the gas, and an ${\alpha }_{CO}$ conversion factor, (2) scaling from the [C I]-line luminosity, and (3) adopting a gas-to-dust conversion factor. We also present gas-phase metallicity estimates in this source, both using far-infrared (FIR) fine-structure lines together with radio free-free continuum emission and independently employing the optical [O III] 5007 A and [O II] 3727 A lines (R${}_{23}$ method). Both methods agree on a sub-solar gas-phase metallicity of ~ 0.3 Z${}_{\odot }$. Intriguingly, comparing the molecular-gas mass estimated using this sub-solar metallicity, M${}_{gas}$ ~ 6.4 x 10${}^{10}$ M${}_{\odot }$, to dust-mass estimates from multi-component spectral energy distribution (SED) modeling, M${}_{dust}$ ~ 1.4 x 10${}^8$ M${}_{\odot }$, yields a gas-to-dust ratio within ~ 15% of the accepted value for a metallicity of 0.3 Z${}_{\odot }$. The derived gas-mass puts 3C 368 on par with other galaxies at z ~ 1 in terms of specific star-formation rate and gas fraction. However, it does not explain how a galaxy can amass such a large stellar population while maintaining such a low gas-phase metallicity. Perhaps 3C 368 has recently undergone a merger, accreting pristine molecular gas from an external source.

arXiv comment10 pages, 5 figures, 2 tables, accepted for publication in the Astrophysical Journal

References in corpus (36)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters
• The chemical composition of the Sun
• The CO-to-H2 Conversion Factor
• Using Strong Lines to Estimate Abundances in Extragalactic HII Regions and Starburst Galaxies
• Cool Gas in High Redshift Galaxies
• High molecular gas fractions in normal massive star forming galaxies in the young Universe
• Gas-to-Dust mass ratios in local galaxies over a 2 dex metallicity range
• Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
• The Stellar, Gas and Dynamical Masses of Star-Forming Galaxies at z~2
• A 158 Micron [CII] Line Survey of Galaxies at z ~ 1 to 2: An Indicator of Star Formation in the Early Universe
• Evolution of Interstellar Medium, Star Formation, and Accretion at High Redshift
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• The far-infrared/radio correlation as probed by Herschel
• The CI lines as tracers of molecular gas, and their prospects at high redshifts
• HST, radio and infrared observations of 28 3CR radio galaxies at redshift z ~ 1: I. Old stellar populations in central cluster galaxies
• Gas and Dust in the Cloverleaf Quasar at Redshift 2.5
• Blind detections of CO J = 1--0 in 11 H-ATLAS galaxies at z = 2.1--3.5 with the GBT/Zpectrometer
• ALMA observations of atomic carbon in z~4 dusty star-forming galaxies
• A Survey of Atomic Carbon [C I] in High-redshift Main-Sequence Galaxies
• Detection of the 158 micron [CII] Transition at z=1.3: Evidence for a Galaxy-Wide Starburst
• High-J CO Versus Far-Infrared Relations in Normal and Starburst Galaxies
• The Origins of [CII] Emission in Local Star-forming Galaxies
• CI emission in Ultra Luminous Infrared Galaxies as a molecular gas mass tracer
• The CO Luminosity Density at High-z (COLDz) Survey: A Sensitive, Large Area Blind Search for Low-J CO Emission from Cold Gas in the Early Universe with the Karl G. Jansky Very Large Array
• Radio synchrotron spectra of star-forming galaxies
• A Total Molecular Gas Mass Census in z~2-3 Star-forming Galaxies: Low-J CO Excitation Probes of Galaxies' Evolutionary States
• Star formation in z>1 3CR host galaxies as seen by Herschel
• New places and phases of CO-poor/CI-rich molecular gas in the Universe
• Improved collision strengths and line ratios for forbidden [O III] far-infrared and optical lines
• Deep spectroscopy of distant 3CR radio galaxies: the data
• Total Molecular Gas Masses of Planck - Herschel Selected Strongly Lensed Hyper Luminous Infrared Galaxies
• Deep radio observations of 3C324 and 3C368: evidence for jet-cloud interactions
• Disentangling star formation and AGN activity in powerful infrared luminous radio galaxies at 1<z<4
• Resolving Star Formation on Sub-Kiloparsec Scales in the High-Redshift Galaxy SDP.11 Using Gravitational Lensing
• Suppressed CO emission and high G/D ratios in z=2 galaxies with sub-solar gas-phase metallicity
• CO-Dark Star Formation and Black Hole Activity in 3C 368 at z = 1.131: Coeval Growth of Stellar and Supermassive Black Hole Masses

Cited by in corpus (4)

• The properties of the interstellar medium of galaxies across time as traced by the neutral atomic carbon [CI]
• A comprehensive view of the interstellar medium in a quasar host galaxy at z~6.4
• Calibrating Mg II-based black-hole mass estimators using Low-to-High-Luminosity Active Galactic Nuclei
• Uncovering the absorbed atomic Universe with the [OI]63um line