The host galaxy of GRB 990712

We present a comprehensive study of the z = 0.43 host galaxy of GRB 990712, involving ground-based photometry, spectroscopy, and HST imaging. The broad-band UBVRIJHKs photometry is used to determine the global spectral energy distribution (SED) of the host galaxy. Comparison with that of known galaxy types shows that the host is similar to a moderately reddened starburst galaxy with a young stellar population. The estimated internal extinction in the host is A V = 0.15 ′ 0.1 and the star-formation rate (SFR) from the UV continuum is 1.3 ′ 0.3 M O . yr - 1 (not corrected for the effects of extinction). Other galaxy template spectra than starbursts failed to reproduce the observed SED. We also present VLT spectra leading to the detection of Hα from the GRB host galaxy. A SFR of 2.8 ′ 0.7 M O . yr - 1 is inferred from the Ha line flux, and the presence of a young stellar population is supported by a large equivalent width. Images from HST/STIS show that the host has two separate knots, which could be two distinct star-forming regions.

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