Molecular Gas Properties in the Host Galaxy of GRB 080207

• Published in: The Astrophysical journal Vol. 876; no. 2; pp. 91 - 100
• Main Authors: Hatsukade, Bunyo, Hashimoto, Tetsuya, Kohno, Kotaro, Nakanishi, Kouichiro, Ohta, Kouji, Niino, Yuu, Tamura, Yoichi, Tóth, L. Viktor
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 10.05.2019; IOP Publishing
• Subjects: Arrays; Astrophysics; Blackbody; cosmology: observations; Depletion; Dust; Energy distribution; Galaxies; galaxies: high-redshift; galaxies: ISM; Gamma ray bursts; Gamma rays; gamma-ray burst: individual (GRB 080207); Infrared photometry; Kinematics; Line spectra; Metallicity; Molecular gases; Properties (attributes); radio lines: galaxies; Radio telescopes; Rotating disks; Rotation; Star & galaxy formation; Star formation; Star formation rate; Starburst galaxies; Stars & galaxies; Velocity; Velocity distribution
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab1649

We present the results of CO(1-0) and CO(4-3) observations of the host galaxy of a long-duration gamma-ray burst GRB 080207 at z = 2.0858 by using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array. The host is detected in CO(1-0) and CO(4-3), becoming the first case for a gamma-ray burst (GRB) host with more than two CO transitions detected combined with CO(2-1) and CO(3-2) in the literature. Adopting a metallicity-dependent CO-to-H2 conversion factor, we derive a molecular gas mass of Mgas = 8.7 × 1010 M , which places the host in a sequence of normal star-forming galaxies in an Mgas-star formation rate (SFR) plane. A modified blackbody fit to the far-infrared-millimeter photometry results in a dust temperature of 37 K and a dust mass of Mdust = 1.5 × 108 M . The spatially resolved CO(4-3) observations allow us to examine the kinematics of the host. The CO velocity field shows a clear rotation and is reproduced by a rotation-dominated disk model with a rotation velocity of 350 km s−1 and a half-light radius of 2.4 kpc. The CO spectral line energy distribution derived from the four CO transitions is similar to that of starburst galaxies, suggesting a high excitation condition. Comparison of molecular gas properties between the host and normal (main-sequence) galaxies at similar redshifts shows that they share common properties such as gas mass fraction, gas depletion timescale, gas-to-dust ratio, location in the Mgas-SFR (or surface density) relation, and kinematics, suggesting that long-duration GRBs can occur in normal star-forming environments at z ∼ 2.