The host of GRB 030323 at $\mathsf{\textit{z}=3.372}$: A very high column density DLA system with a low metallicity

Abstract

Abstract. We present photometry and spectroscopy of the afterglow of GRB 030323. VLT spectra of the afterglow show damped Lyα (DLA) absorption and low-and high-ionization lines at a redshift z = 3.3718 ± 0.0005. The inferred neutral hydrogen column density, log N(H i) = 21.90 ± 0.07, is larger than any (GRB-or QSO-) DLA H  column density inferred directly from Lyα in absorption. From the afterglow photometry, we derive a conservative upper limit to the host-galaxy extinction: A V < 0.5 mag. The iron abundance is [Fe/H] = −1.47 ± 0.11, while the metallicity of the gas as measured from sulphur is [S/H] = −1.26 ± 0.20. We derive an upper limit on the H 2 molecular fraction of 2N(H 2 )/(2N(H 2 ) + N(H i)) < ∼ 10 −6 . In the Lyα trough, a Lyα emission line is detected, which corresponds to a star-formation rate (not corrected for dust extinction) of roughly 1 M yr −1 . All these results are consistent with the host galaxy of GRB 030323 consisting of a low metallicity gas with a low dust content. We detect fine-structure lines of silicon, Si *, which have never been clearly detected in QSO-DLAs; this suggests that these lines are produced in the vicinity of the GRB explosion site. Under the assumption that these fine-structure levels are populated by particle collisions, we estimate the H  volume density to be n H i = 10 2 −10 4 cm −3 . HST/ACS imaging 4 months after the burst shows an extended AB(F606W) = 28.0 ± 0.3 mag object at a distance of 0. 14 (1 kpc) from the early afterglow location, which presumably is the host galaxy of GRB 030323.

GRB 100219A with X-shooter – abundances in a galaxy at z =4.7

“…We also detect two fine-structure transitions of Si II and one from C II, as have also been detected in a number of other GRB spectra (first detected by Vreeswijk et al 2004). These transitions are likely produced by UV pumping of the excited levels by the radiation from the GRB itself.…”

A coronagraphic absorbing cloud reveals the narrow-line region and extended Lyman α emission of QSO J0823+0529

“…We detect absorptions from O i * * and Si ii * which are rarely detected in DLAs (see Noterdaeme et al 2015, Neeleman et al 2015 and are more commonly seen in DLAs associated to GRB afterglows (Vreeswijk et al 2004;Chen et al 2005;Fynbo et al 2006). Absorption from the fine structure state of Si ii will be used to constrain the density of the absorbing cloud (see below).…”

An optical spectrum of the afterglow of a γ-ray burst at a redshift of z = 6.295

“…Using the equivalent width ratio of the finestructure transition lines Si II* l ¼ 1,264.7 Å and Si II l ¼ 1,260.4 Å , the electron density n e can be constrained 17 as log½n e ðcm 23 Þ ¼ 2:3^0:7 for a reasonable temperature range of 10 3 K , T , 10 5 K. Combined with the column density and the abundance of Si derived above and assuming a hydrogen ionization fraction of 0.1, we obtain the physical depth of the absorbing system to be 0.4 pc with an uncertainty of a factor of ,10, reflecting the statistical errors and the possible temperature range. These fine-structure lines have been found in GRB afterglow spectra [18][19][20] , whereas they have never been clearly detected in quasar damped Lya systems 18 . This is consistent with a local origin for the absorption such as a metal-enriched molecular cloud in the star-forming region or a dense metal-enriched shell nebula swept-up by a progenitor wind prior to the GRB onset suggested for GRB 021004 (refs 21, 22) and GRB 030226 (ref.…”

“…It may be a damped Lya system associated with the host galaxy, which has been observed in the afterglows of several GRBs at lower redshifts [18][19][20] . The other possibility is the neutral hydrogen in the intergalactic medium (IGM) left over from the pre-reionization era 2 .…”