Dust extinction in high-z galaxies with gamma-ray burst afterglow spectroscopy: the 2175 Å feature at z = 2.45

Á. Elíasdóttir; J. P. U. Fynbo; J. Hjorth; C. Ledoux; D. J. Watson; A. C. Andersen; D. Malesani; P. M. Vreeswijk; J. X. Prochaska; J. Sollerman; A. O. Jaunsen

doi:10.1088/0004-637X/697/2/1725

Dust extinction in high-z galaxies with gamma-ray burst afterglow spectroscopy: the 2175 Å feature at z = 2.45

Á. Elíasdóttir, J. P. U. Fynbo, J. Hjorth, C. Ledoux, D. J. Watson, A. C. Andersen, D. Malesani, P. M. Vreeswijk, J. X. Prochaska, J. Sollerman, A. O. Jaunsen

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Abstract

We report the clear detection of the 2175 Å dust absorption feature in the optical afterglow spectrum of the gamma-ray burst (GRB) GRB 070802 at a redshift of z = 2.45. This is the highest redshift for a detected 2175 Å dust bump to date, and it is the first clear detection of the 2175 Å bump in a GRB host galaxy, while several tens of optical afterglow spectra without the bump have been recorded in the past decade. The derived extinction curve gives AV = 0.8-1.5 depending on the assumed intrinsic slope. Of the three local extinction laws, a Large Magellanic Cloud (LMC) type extinction gives the best fit to the extinction curve of the host of GRB 070802. Besides the 2175 Å bump we find that the spectrum of GRB 070802 is characterized by unusually strong low-ionization metal lines and possibly a high metallicity for a GRB sightline ([Si/H] = –0.46 ± 0.38, [Zn/H] = –0.50 ± 0.68). In particular, the spectrum of GRB 070802 is unique for a GRB spectrum in that it shows clear C I absorption features, leading us to propose a correlation between the presence of the bump and C I. The gas-to-dust ratio for the host galaxy is found to be significantly lower than that of other GRB hosts with N(H I)/AV = (2.4 ± 1.0) × 1021 cm–2 mag–1, which lies between typical Milky Way and LMC values. Our results are in agreement with the tentative conclusion reached by Gordon et al. that the shape of the extinction curve, in particular the presence of the bump, is affected by the UV flux density in the environment of the dust. Based on observations collected under progs. ID 079.D–0429(B) and 177.D–0591(P,Q), using the FORS2 instrument installed at the Cassegrain focus of the Very Large Telescope (VLT), Unit 1 - Antu, operated by the European Southern Observatory (ESO) on Cerro Paranal, Chile.

Original language	English
Journal	Astrophysical Journal
Volume	697
Issue number	2
Pages (from-to)	1725-1740
Number of pages	15
ISSN	0004-637X
DOIs	https://doi.org/10.1088/0004-637X/697/2/1725
Publication status	Published - 2009

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10.1088/0004-637X/697/2/1725

http://adsabs.harvard.edu/abs/2009ApJ...697.1725E

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Elíasdóttir, Á., Fynbo, J. P. U., Hjorth, J., Ledoux, C., Watson, D. J., Andersen, A. C., Malesani, D., Vreeswijk, P. M., Prochaska, J. X., Sollerman, J., & Jaunsen, A. O. (2009). Dust extinction in high-z galaxies with gamma-ray burst afterglow spectroscopy: the 2175 Å feature at z = 2.45. Astrophysical Journal, 697(2), 1725-1740. https://doi.org/10.1088/0004-637X/697/2/1725

@article{6dff64f069fd11de8bc9000ea68e967b,

title = "Dust extinction in high-z galaxies with gamma-ray burst afterglow spectroscopy: the 2175 {\AA} feature at z = 2.45",

abstract = "We report the clear detection of the 2175 {\AA} dust absorption feature in the optical afterglow spectrum of the gamma-ray burst (GRB) GRB 070802 at a redshift of z = 2.45. This is the highest redshift for a detected 2175 {\AA} dust bump to date, and it is the first clear detection of the 2175 {\AA} bump in a GRB host galaxy, while several tens of optical afterglow spectra without the bump have been recorded in the past decade. The derived extinction curve gives AV = 0.8-1.5 depending on the assumed intrinsic slope. Of the three local extinction laws, a Large Magellanic Cloud (LMC) type extinction gives the best fit to the extinction curve of the host of GRB 070802. Besides the 2175 {\AA} bump we find that the spectrum of GRB 070802 is characterized by unusually strong low-ionization metal lines and possibly a high metallicity for a GRB sightline ([Si/H] = –0.46 ± 0.38, [Zn/H] = –0.50 ± 0.68). In particular, the spectrum of GRB 070802 is unique for a GRB spectrum in that it shows clear C I absorption features, leading us to propose a correlation between the presence of the bump and C I. The gas-to-dust ratio for the host galaxy is found to be significantly lower than that of other GRB hosts with N(H I)/AV = (2.4 ± 1.0) × 1021 cm–2 mag–1, which lies between typical Milky Way and LMC values. Our results are in agreement with the tentative conclusion reached by Gordon et al. that the shape of the extinction curve, in particular the presence of the bump, is affected by the UV flux density in the environment of the dust. Based on observations collected under progs. ID 079.D–0429(B) and 177.D–0591(P,Q), using the FORS2 instrument installed at the Cassegrain focus of the Very Large Telescope (VLT), Unit 1 - Antu, operated by the European Southern Observatory (ESO) on Cerro Paranal, Chile.",

author = "{\'A}. El{\'i}asd{\'o}ttir and Fynbo, {J. P. U.} and J. Hjorth and C. Ledoux and Watson, {D. J.} and Andersen, {A. C.} and D. Malesani and Vreeswijk, {P. M.} and Prochaska, {J. X.} and J. Sollerman and Jaunsen, {A. O.}",

note = "Keywords: dust; extinction; galaxies: abundances; galaxies: distances and redshifts; galaxies: ISM; gamma rays: bursts",

year = "2009",

doi = "10.1088/0004-637X/697/2/1725",

language = "English",

volume = "697",

pages = "1725--1740",

journal = "Astrophysical Journal",

issn = "0004-637X",

publisher = "Institute of Physics Publishing, Inc",

number = "2",

}

TY - JOUR

T1 - Dust extinction in high-z galaxies with gamma-ray burst afterglow spectroscopy

T2 - the 2175 Å feature at z = 2.45

AU - Elíasdóttir, Á.

AU - Fynbo, J. P. U.

AU - Hjorth, J.

AU - Ledoux, C.

AU - Watson, D. J.

AU - Andersen, A. C.

AU - Malesani, D.

AU - Vreeswijk, P. M.

AU - Prochaska, J. X.

AU - Sollerman, J.

AU - Jaunsen, A. O.

N1 - Keywords: dust; extinction; galaxies: abundances; galaxies: distances and redshifts; galaxies: ISM; gamma rays: bursts

PY - 2009

Y1 - 2009

N2 - We report the clear detection of the 2175 Å dust absorption feature in the optical afterglow spectrum of the gamma-ray burst (GRB) GRB 070802 at a redshift of z = 2.45. This is the highest redshift for a detected 2175 Å dust bump to date, and it is the first clear detection of the 2175 Å bump in a GRB host galaxy, while several tens of optical afterglow spectra without the bump have been recorded in the past decade. The derived extinction curve gives AV = 0.8-1.5 depending on the assumed intrinsic slope. Of the three local extinction laws, a Large Magellanic Cloud (LMC) type extinction gives the best fit to the extinction curve of the host of GRB 070802. Besides the 2175 Å bump we find that the spectrum of GRB 070802 is characterized by unusually strong low-ionization metal lines and possibly a high metallicity for a GRB sightline ([Si/H] = –0.46 ± 0.38, [Zn/H] = –0.50 ± 0.68). In particular, the spectrum of GRB 070802 is unique for a GRB spectrum in that it shows clear C I absorption features, leading us to propose a correlation between the presence of the bump and C I. The gas-to-dust ratio for the host galaxy is found to be significantly lower than that of other GRB hosts with N(H I)/AV = (2.4 ± 1.0) × 1021 cm–2 mag–1, which lies between typical Milky Way and LMC values. Our results are in agreement with the tentative conclusion reached by Gordon et al. that the shape of the extinction curve, in particular the presence of the bump, is affected by the UV flux density in the environment of the dust. Based on observations collected under progs. ID 079.D–0429(B) and 177.D–0591(P,Q), using the FORS2 instrument installed at the Cassegrain focus of the Very Large Telescope (VLT), Unit 1 - Antu, operated by the European Southern Observatory (ESO) on Cerro Paranal, Chile.

AB - We report the clear detection of the 2175 Å dust absorption feature in the optical afterglow spectrum of the gamma-ray burst (GRB) GRB 070802 at a redshift of z = 2.45. This is the highest redshift for a detected 2175 Å dust bump to date, and it is the first clear detection of the 2175 Å bump in a GRB host galaxy, while several tens of optical afterglow spectra without the bump have been recorded in the past decade. The derived extinction curve gives AV = 0.8-1.5 depending on the assumed intrinsic slope. Of the three local extinction laws, a Large Magellanic Cloud (LMC) type extinction gives the best fit to the extinction curve of the host of GRB 070802. Besides the 2175 Å bump we find that the spectrum of GRB 070802 is characterized by unusually strong low-ionization metal lines and possibly a high metallicity for a GRB sightline ([Si/H] = –0.46 ± 0.38, [Zn/H] = –0.50 ± 0.68). In particular, the spectrum of GRB 070802 is unique for a GRB spectrum in that it shows clear C I absorption features, leading us to propose a correlation between the presence of the bump and C I. The gas-to-dust ratio for the host galaxy is found to be significantly lower than that of other GRB hosts with N(H I)/AV = (2.4 ± 1.0) × 1021 cm–2 mag–1, which lies between typical Milky Way and LMC values. Our results are in agreement with the tentative conclusion reached by Gordon et al. that the shape of the extinction curve, in particular the presence of the bump, is affected by the UV flux density in the environment of the dust. Based on observations collected under progs. ID 079.D–0429(B) and 177.D–0591(P,Q), using the FORS2 instrument installed at the Cassegrain focus of the Very Large Telescope (VLT), Unit 1 - Antu, operated by the European Southern Observatory (ESO) on Cerro Paranal, Chile.

U2 - 10.1088/0004-637X/697/2/1725

DO - 10.1088/0004-637X/697/2/1725

M3 - Journal article

SN - 0004-637X

VL - 697

SP - 1725

EP - 1740

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2

ER -

Dust extinction in high-z galaxies with gamma-ray burst afterglow spectroscopy: the 2175 Å feature at z = 2.45

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