Relativistic supernova 2009bb exploded close to an atomic gas cloud^⋆

¹ Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, ul. Słoneczna 36, 60-286 Poznań, Poland
e-mail: michal.michalowski@amu.edu.pl
² Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Royal Observatory, Blakford Hill, EH9 3HJ Edinburgh, UK
³ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281-S9, 9000 Gent, Belgium
⁴ Department of Physics and Astrophysics, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
⁵ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁶ Max-Planck-Institut für Extraterrestrische Physik, Giessenbach-straße, 85748 Garching bei München, Germany
⁷ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁸ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁹ National Centre for Radio Astrophysics, TIFR, Ganeshkhind, 411007 Pune, India
¹⁰ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
¹¹ Visitor Scientist at Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000 Zagreb, Croatia
¹² INAF – Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monteporzio Catone, Italy
¹³ ASI Science Data Centre, Via Galileo Galilei, 00044 Frascati (RM), Italy
¹⁴ Hulu LLC., 100084 Beijing, PR China
¹⁵ PITT PACC, Department of Physics and Astronomy, University of Pittsburgh, 15260, Pittsburgh, PA, USA
¹⁶ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁷ Centre for Astrophysics Research, University of Hertfordshire, College Lane, AL10 9AB Hatfield, UK
¹⁸ Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu – CNRS – Université Paris Diderot, CE-Saclay, pt courrier 131, 91191 Gif-sur-Yvette, France
¹⁹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²⁰ INAF-OAS Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
²¹ Technical University of Denmark, Department of Physics, Fysikvej, building 309, 2800 Kgs., Lyngby, Denmark
²² Physics Department, University of Calabria, 87036 Arcavacata di Rende, Italy
²³ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
²⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
²⁵ GEPI, Observatoire de Paris, PSL Research University, CNRS, Place Jules Janssen, 92190 Meudon, France

Received: 24 November 2017
Accepted: 12 July 2018

Abstract

Context. The host galaxies of gamma-ray bursts (GRBs) have been claimed to have experienced a recent inflow of gas from the intergalactic medium. This is because their atomic gas distribution is not centred on their optical emission and because they are deficient in molecular gas given their high star formation rates (SFRs). Similar studies have not been conducted for host galaxies of relativistic supernovae (SNe), which may have similar progenitors.

Aims. The potential similarity of the powering mechanisms of relativistic SNe and GRBs allowed us to make a prediction that relativistic SNe are born in environments similar to those of GRBs, that is, ones which are rich in atomic gas. Here we embark on testing this hypothesis by analysing the properties of the host galaxy NGC 3278 of the relativistic SN 2009bb. This is the first time the atomic gas properties of a relativistic SN host are provided and the first time resolved 21 cm-hydrogen-line (H I) information is provided for a host of an SN of any type in the context of the SN position.

Methods. We obtained radio observations with the Australia Telescope Compact Array (ATCA) covering the H I line, and optical integral field unit spectroscopy observations with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). Moreover, we analysed archival carbon monoxide (CO) and multi-wavelength data for this galaxy.

Results. The atomic gas distribution of NGC 3278 is not centred on the optical galaxy centre, but instead around a third of atomic gas resides in the region close to the SN position. This galaxy has a few times lower atomic and molecular gas masses than predicted from its SFR. Its specific SFR (sSFR ≡ SFR/M_*) is approximately two to three times higher than the main-sequence value, placing it at the higher end of the main sequence, towards starburst galaxies. SN 2009bb exploded close to the region with the highest SFR density and the lowest age, as evident from high Hα EW, corresponding to the age of the stellar population of ~5.5 Myr. Assuming this timescale was the lifetime of the progenitor star, its initial mass would have been close to ~36 M_⊙.

Conclusions. As for GRB hosts, the gas properties of NGC 3278 are consistent with a recent inflow of gas from the intergalactic medium, which explains the concentration of atomic gas close to the SN position and the enhanced SFR. Super-solar metallicity at the position of the SN (unlike for most GRBs) may mean that relativistic explosions signal a recent inflow of gas (and subsequent star formation), and their type (GRBs or SNe) is determined either (i) by the metallicity of the inflowing gas, so that metal-poor gas results in a GRB explosion and metal-rich gas (for example a minor merger with an evolved galaxy or re-accretion of expelled gas) results in a relativistic SN explosion without an accompanying GRB, or (ii) by the efficiency of gas mixing (efficient mixing for SN hosts leading to a quick disappearance of metal-poor regions), or (iii) by the type of the galaxy (more metal-rich galaxies would result in only a small fraction of star formation being fuelled by metal-poor gas).