The host galaxy of the short GRB 050709

Ana Nicuesa Guelbenzu, Sylvio Klose, Patricia Schady, Jochen Greiner, D.H. Hartmann, Leslie Hunt, Benjamin Magnelli, Nicola Masetti, Michal Michalowski, Eliana Palazzi, Andrea Rossi, Mark Wieringa, Bringfried Stecklum

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Abstract

The host of the short gamma-ray burst (GRB) 050709 is a morphologically disturbed low-luminous galaxy. At a redshift of z = 0.16, it belongs to one of the cosmologically nearest short-GRB hosts identified to date. Consequently, it represents a promising target for sensitive, spatially resolved observational studies. We have used the Multi Unit Spectroscopic Explorer (MUSE) mounted at the Very Large Telescope to characterize the GRB host galaxy. In addition, we performed deep radio-continuum observations of the host with the Australia Telescope Compact Array (ATCA) and with ALMA at 1.3 mm. Moreover, we made use of archival Spitzer Space Telescope 24 μm and Hubble Space Telescope/F814W imaging data of this galaxy. The spatially resolved MUSE data reveal that the entire host is a source of strong line emission, in particular from Hα and [O III] λ 5007, superimposed on a rather weak stellar continuum. Using the Balmer decrement, we map the internal host-galaxy reddening and derive an extinction-corrected star formation rate based on the flux in the Hα line of 0.15 ± 0.02 M⊙ yr−1. The galaxy is detected neither by ALMA nor by Spitzer, excluding a substantial amount of optically obscured star formation activity. Using the O3N2 metallicity indicator, we measure an average 12 + log (O/H) = 8.40 ± 0.05 (corresponding to ∼0.5 solar). Diagnostic emission line diagrams show that a substantial fraction of all MUSE spaxels that cover the GRB 050709 host galaxy lie close to the star-formation demarcation line. Some spaxels even suggest line emission by shocked gas. The ATCA observations reveal faint diffuse radio emission at the eastern part of the host in excess to that expected from pure star formation, possibly further evidence for nonthermal processes. The kinematics of the Hα-emitting gas suggests a rotationally supported host-galaxy system, apparently in contrast to its irregular photometric morphology. A comparison with the field-galaxy population reveals, however, that the kinematics of the gas in the 050709 host fits into the ensemble of merging galaxies well. Finally, we use the ATCA radio data to set deep constraints on any late-time flux from the GRB afterglow or a potentially associated kilonova radio flare ∼10 years after the burst.
Original languageEnglish
Article numberA117
JournalAstronomy & Astrophysics
Volume650
DOIs
Publication statusPublished - 30 Jun 2021

Funding

Acknowledgements. A.N.G. and S.K. acknowledge financial support by grants DFG Kl 766/16-3, DFG Kl 766/18-1, and DFG RA 2484/1-3. P.S. acknowledges support through the Sofja Kovalevskaja Award from the Alexander von Humboldt Foundation of Germany. M.J.M. acknowledges the support of the National Science Centre, Poland through the SONATA BIS grant 2018/30/E/ST9/00208. The authors thank Thomas Krühler for providing several numerical tools for VLT/MUSE data reduction and for taking care of the VLT/MUSE observations and a first data reduction. A.N.G. and S.K. thank Kris Belczynski, Polish Academy of Sciences, for his interest in this work and very useful discussions. Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA). The Australia Telescope is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. A.N.G. and S.K. thank Catarina Ubach and Sarah Maddison, Swinburne University, Ivy Wong, CSIRO Sydney, and Jamie Stevens, CSIRO Narrabri, for helpful discussions and observing guidance. This paper makes use of the following ALMA data: 2016.1.01333.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The authors thank the anonymous referee for a very careful reading of the manuscript and for very valuable suggestions that helped to improve the content of this paper.

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