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Using realistic host galaxy metallicities to improve the GRB X-ray equivalent total hydrogen column density and constrain the intergalactic medium density

Morris, Simon L; Dalton, Tony

Using realistic host galaxy metallicities to improve the GRB X-ray equivalent total hydrogen column density and constrain the intergalactic medium density Thumbnail


Authors

Tony Dalton



Abstract

It is known that the GRB equivalent hydrogen column density (NHX) changes with redshift and that, typically, NHX is greater than the GRB host neutral hydrogen column density. We have compiled a large sample of data for GRB NHX and metallicity [X/H]. The main aims of this paper are to generate improved NHX for our sample by using actual metallicities, dust corrected where available for detections, and for the remaining GRB, a more realistic average intrinsic metallicity using a standard adjustment from solar. Then, by approximating the GRB host intrinsic hydrogen column density using the measured neutral column (NHI, IC) adjusted for the ionization fraction, we isolate a more accurate estimate for the intergalactic medium (IGM) contribution. The GRB sample mean metallicity is = −1.17 ± 0.09 rms (or 0.07 ± 0.05 Z/Zsol) from a sample of 36 GRB with a redshift 1.76 ≤ z ≤ 5.91, substantially lower than the assumption of solar metallicity used as standard for many fitted NHX. Lower GRB host mean metallicity results in increased estimated NHX with the correction scaling with redshift as Δlog (NHX cm−2) = (0.59 ± 0.04)log(1 + z) + 0.18 ± 0.02. Of the 128 GRB with data for both NHX and NHI, IC in our sample, only six have NHI, IC > NHX when revised for realistic metallicity, compared to 32 when solar metallicity is assumed. The lower envelope of the revised NHX – NHI, IC, plotted against redshift can be fit by log(NHX – NHI, IC cm−2) = 20.3 + 2.4 log(1 + z). This is taken to be an estimate for the maximum IGM hydrogen column density as a function of redshift. Using this approach, we estimate an upper limit to the hydrogen density at redshift zero (n0) to be consistent with n0 = 0.17 × 10−7cm−3.

Citation

Morris, S. L., & Dalton, T. (2020). Using realistic host galaxy metallicities to improve the GRB X-ray equivalent total hydrogen column density and constrain the intergalactic medium density. Monthly Notices of the Royal Astronomical Society, 495(2), 2342-2353. https://doi.org/10.1093/mnras/staa1321

Journal Article Type Article
Acceptance Date May 4, 2020
Online Publication Date May 15, 2020
Publication Date 2020-06
Deposit Date Jul 15, 2020
Publicly Available Date Jul 15, 2020
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 495
Issue 2
Pages 2342-2353
DOI https://doi.org/10.1093/mnras/staa1321
Public URL https://durham-repository.worktribe.com/output/1266475

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Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.






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