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arXiv · 1010.1783

A nearby GRB host prototype for z~7 Lyman-break galaxies: Spitzer-IRS and X-shooter spectroscopy of the host galaxy of GRB031203

D. Watson·J. French·L. Christensen·B. O'Halloran·M. Michałowski·J. Hjorth·D. Malesani·J. P. U. Fynbo·K. D. Gordon·J. M. Castro Cerón
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Abstract

Gamma-ray burst (GRB) host galaxies have been studied extensively in optical photometry and spectroscopy. Here we present the first mid-infrared spectrum of a GRB host, HG031203. It is one of the nearest GRB hosts at z=0.1055, allowing both low and high-resolution spectroscopy with Spitzer-IRS. Medium resolution UV-to-K-band spectroscopy with the X-shooter spectrograph on the VLT is also presented, along with Spitzer IRAC and MIPS photometry, as well as radio and sub-mm observations. These data allow us to construct a UV-to-radio spectral energy distribution with almost complete spectroscopic coverage from 0.3-35 micron of a GRB host galaxy for the first time, potentially valuable as a template for future model comparisons. The IRS spectra show strong, high-ionisation fine structure line emission indicative of a hard radiation field in the galaxy, suggestive of strong ongoing star-formation and a very young stellar population. The selection of HG031203 via the presence of a GRB suggests that it might be a useful analogue of very young star-forming galaxies in the early universe, and hints that local BCDs may be used as more reliable analogues of star-formation in the early universe than typical local starbursts. We look at the current debate on the ages of the dominant stellar populations in z~7 and z~8 galaxies in this context. The nebular line emission is so strong in HG031203, that at z~7, it can reproduce the spectral energy distributions of z-band dropout galaxies with elevated IRAC 3.6 and 4.5 micron fluxes without the need to invoke a 4000A break.

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D. Watson, J. French, L. Christensen, B. O'Halloran, M. Michałowski, J. Hjorth, D. Malesani, J. P. U. Fynbo, K. D. Gordon, J. M. Castro Cerón. 2010-10-08. A nearby GRB host prototype for z~7 Lyman-break galaxies: Spitzer-IRS and X-shooter spectroscopy of the host galaxy of GRB031203. https://doi.org/10.1088/0004-637x/741/1/58

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