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Pair lines of sight observations of multiphase gas bearing O vi in a galaxy environment

Anshul, Pratyush; Narayanan, Anand; Muzahid, Sowgat; Beckett, Alexander; Morris, Simon L

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Pratyush Anshul

Anand Narayanan

Sowgat Muzahid


Using HST/COS spectra of the twin quasar lines of sight Q 0107–025A & Q 0107–025B, we report on the physical properties, chemical abundances, and transverse sizes of a multiphase medium in a galaxy field at z = 0.399. The angular separation between the quasars corresponds to a physical separation of 520 kpc at the absorber redshift. The absorber towards Q 0107–025B is a partial Lyman limit system (pLLS) with logN(HI)/cm−2≈16.8⁠. The H I column density in the absorber along the other sightline is ≈ 2 orders of magnitude lower. The O VI along both sightlines have comparable column densities and broad b-values (b > 30 km s−1) whereas the low ionization lines are considerably narrower. The low ionization gas is inconsistent with the O VI when modelled assuming photoionization from the same phase. In both lines of sight, O VI and the broad H I coinciding, are best explained through collisional ionization in a cooling plasma with solar metallicity. Ionization models infer 1/10th solar metallicity for the pLLS and solar metallicity for the lower column density absorber along the other sightline. Within ± 250 km s−1 and 2 Mpc of projected distance from the sightlines 12 galaxies are identified, of which five are within 500 kpc. The twin sightlines are at normalized impact parameters of ρ ∼ 1.1Rvir, and ρ ∼ 0.8Rvir from a M* ∼ 1010.7 M⊙, L ∼ 0.07L*, and star formation rate (SFR) < 0.1 M⊙ yr−1 galaxy, potentially probing its CGM (circumgalactic medium). The next closest in normalized separation are a dwarf galaxy with M* ∼ 108.7 M⊙, and SFR ∼ 0.06 M⊙ yr−1, and an intermediate mass galaxy with M* ∼ 1010.0 M⊙, and SFR ∼ 3 M⊙ yr−1. Along both sightlines, O VI could be either tracing narrow transition temperature zones at the interface of low ionization gas and the hot halo of nearest galaxy, or a more spread-out warm component that could be gas bound to the circumgalactic halo or the intragroup medium. The latter scenarios lead to a warm gas mass limit of M ≳ 4.5 × 109 M⊙.


Anshul, P., Narayanan, A., Muzahid, S., Beckett, A., & Morris, S. L. (2021). Pair lines of sight observations of multiphase gas bearing O vi in a galaxy environment. Monthly Notices of the Royal Astronomical Society, 503(3), 3243-3261.

Journal Article Type Article
Acceptance Date Feb 2, 2021
Online Publication Date Feb 13, 2021
Publication Date 2021-05
Deposit Date Aug 23, 2021
Publicly Available Date Aug 23, 2021
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 503
Issue 3
Pages 3243-3261


Published Journal Article (2.7 Mb)

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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