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Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs: III. Stellar masses, star formation rates, and metallicities at z > 1

Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs: III. Stellar masses, star formation rates, and metallicities at z > 1
Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs: III. Stellar masses, star formation rates, and metallicities at z > 1

Aims. Long gamma-ray bursts (LGRB) have been proposed as promising tracers of star formation owing to their association with the core-collapse of massive stars. Nonetheless, previous studies we carried out at z < 1 support the hypothesis that the conditions necessary for the progenitor star to produce an LGRB (e.g. low metallicity), were challenging the use of LGRBs as star-formation tracers, at least at low redshift. The goal of this work is to characterise the population of host galaxies of LGRBs at 1 < z < 2, investigate the conditions in which LGRBs form at these redshifts and assess their use as tracers of star formation. Methods. We performed a spectro-photometric analysis to determine the stellar mass, star formation rate, specific star formation rate and metallicity of the complete, unbiased host galaxy sample of the Swift/BAT6 LGRB sample at 1 < z < 2. We compared the distribution of these properties to the ones of typical star-forming galaxies from the MOSDEF and COSMOS2015 Ultra Deep surveys, within the same redshift range. Results. We find that, similarly to z < 1, LGRBs do not directly trace star formation at 1 < z < 2, and they tend to avoid high-mass, high-metallicity host galaxies. We also find evidence for an enhanced fraction of starbursts among the LGRB host sample with respect to the star-forming population of galaxies. Nonetheless we demonstrate that the driving factor ruling the LGRB efficiency is metallicity. The LGRB host distributions can be reconciled with the ones expected from galaxy surveys by imposing a metallicity upper limit of logOH ∼ 8.55. We can determine upper limits on the fraction of super-solar metallicity LGRB host galaxies of ∼20%, 10% at z < 1, 1 < z < 2, respectively. Conclusions. Metallicity rules the LGRB production efficiency, which is stifled at Z≳ 0.7 Z · . Under this hypothesis we can expect LGRBs to trace star formation at z > 3, once the bulk of the star forming galaxy population are characterised by metallicities below this limit. The role played by metallicity can be explained by the conditions necessary for the progenitor star to produce an LGRB. The moderately high metallicity threshold found is in agreement with the conditions necessary to rapidly produce a fast-rotating Wolf-Rayet stars in close binary systems, and could be accommodated by single star models under chemically homogeneous mixing with very rapid rotation and weak magnetic coupling.

Galaxies: abundances, Galaxies: star formation, Gamma-ray burst: general
0004-6361
Palmerio, J. T.
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Vergani, S. D.
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Salvaterra, R.
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Sanders, R. L.
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Japelj, J.
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Vidal-García, A.
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D'Avanzo, P.
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Corre, D.
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Perley, D. A.
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Shapley, A. E.
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Boissier, S.
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Greiner, J.
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Le Floc'h, E.
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Wiseman, P.
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Palmerio, J. T.
fba159b2-0901-4c6d-b0e2-050486c82103
Vergani, S. D.
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Salvaterra, R.
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Sanders, R. L.
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Japelj, J.
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Vidal-García, A.
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D'Avanzo, P.
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Corre, D.
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Perley, D. A.
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Shapley, A. E.
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Boissier, S.
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Greiner, J.
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Le Floc'h, E.
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Wiseman, P.
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Palmerio, J. T., Vergani, S. D., Salvaterra, R., Sanders, R. L., Japelj, J., Vidal-García, A., D'Avanzo, P., Corre, D., Perley, D. A., Shapley, A. E., Boissier, S., Greiner, J., Le Floc'h, E. and Wiseman, P. (2019) Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs: III. Stellar masses, star formation rates, and metallicities at z > 1. Astronomy and Astrophysics, 623, [A26]. (doi:10.1051/0004-6361/201834179).

Record type: Article

Abstract

Aims. Long gamma-ray bursts (LGRB) have been proposed as promising tracers of star formation owing to their association with the core-collapse of massive stars. Nonetheless, previous studies we carried out at z < 1 support the hypothesis that the conditions necessary for the progenitor star to produce an LGRB (e.g. low metallicity), were challenging the use of LGRBs as star-formation tracers, at least at low redshift. The goal of this work is to characterise the population of host galaxies of LGRBs at 1 < z < 2, investigate the conditions in which LGRBs form at these redshifts and assess their use as tracers of star formation. Methods. We performed a spectro-photometric analysis to determine the stellar mass, star formation rate, specific star formation rate and metallicity of the complete, unbiased host galaxy sample of the Swift/BAT6 LGRB sample at 1 < z < 2. We compared the distribution of these properties to the ones of typical star-forming galaxies from the MOSDEF and COSMOS2015 Ultra Deep surveys, within the same redshift range. Results. We find that, similarly to z < 1, LGRBs do not directly trace star formation at 1 < z < 2, and they tend to avoid high-mass, high-metallicity host galaxies. We also find evidence for an enhanced fraction of starbursts among the LGRB host sample with respect to the star-forming population of galaxies. Nonetheless we demonstrate that the driving factor ruling the LGRB efficiency is metallicity. The LGRB host distributions can be reconciled with the ones expected from galaxy surveys by imposing a metallicity upper limit of logOH ∼ 8.55. We can determine upper limits on the fraction of super-solar metallicity LGRB host galaxies of ∼20%, 10% at z < 1, 1 < z < 2, respectively. Conclusions. Metallicity rules the LGRB production efficiency, which is stifled at Z≳ 0.7 Z · . Under this hypothesis we can expect LGRBs to trace star formation at z > 3, once the bulk of the star forming galaxy population are characterised by metallicities below this limit. The role played by metallicity can be explained by the conditions necessary for the progenitor star to produce an LGRB. The moderately high metallicity threshold found is in agreement with the conditions necessary to rapidly produce a fast-rotating Wolf-Rayet stars in close binary systems, and could be accommodated by single star models under chemically homogeneous mixing with very rapid rotation and weak magnetic coupling.

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Accepted/In Press date: 8 January 2019
e-pub ahead of print date: 26 February 2019
Keywords: Galaxies: abundances, Galaxies: star formation, Gamma-ray burst: general

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Local EPrints ID: 429054
URI: http://eprints.soton.ac.uk/id/eprint/429054
ISSN: 0004-6361
PURE UUID: e687b30f-2d66-4606-a41a-b338f76e5090

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Date deposited: 20 Mar 2019 17:30
Last modified: 26 Nov 2021 00:17

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Contributors

Author: J. T. Palmerio
Author: S. D. Vergani
Author: R. Salvaterra
Author: R. L. Sanders
Author: J. Japelj
Author: A. Vidal-García
Author: P. D'Avanzo
Author: D. Corre
Author: D. A. Perley
Author: A. E. Shapley
Author: S. Boissier
Author: J. Greiner
Author: E. Le Floc'h
Author: P. Wiseman

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