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Relationship between the Metallicity of the Circumgalactic Medium and Galaxy Orientation

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posted on 2024-07-26, 14:53 authored by Stephanie Pointon, Glenn KacprzakGlenn Kacprzak, Nikole NielsenNikole Nielsen, Sowgat Muzahid, Michael MurphyMichael Murphy, Christopher W. Churchill, Jane C. Charlton
We investigate the geometric distribution of gas metallicities in the circumgalactic medium (CGM) around 47, z < 0.7 galaxies from the "Multiphase Galaxy Halos" Survey. Using a combination of quasar spectra from Hubble Space Telescope (HST)/COS and from Keck/HIRES or Very Large Telescope/UVES, we measure column densities of, or determine limits on, CGM absorption lines. We then use a Markov Chain Monte Carlo approach with Cloudy to estimate the metallicity of cool (T similar to 10(4) K) CGM gas. We also use HST images to determine host-galaxy inclination and quasar-galaxy azimuthal angles. Our sample spans a H I column density range of 13.8 cm(-2) < log N-H I < 19.9 cm(-2). We find (1) while the metallicity distribution appears bimodal, a Hartigan dip test cannot rule out a unimodal distribution (0.4 sigma). (2) CGM metallicities are independent of halo mass, spanning three orders of magnitude at a fixed halo mass. (3) The CGM metallicity does not depend on the galaxy azimuthal and inclination angles regardless of H I column density, impact parameter, and galaxy color. (4) The ionization parameter does not depend on azimuthal angle. We suggest that the partial Lyman limit metallicity bimodality is not driven by a spatial azimuthal bimodality. Our results are consistent with simulations where the CGM is complex and outflowing, accreting, and recycled gas are well-homogenized at z < 0.7. The presence of lowmetallicity gas at all orientations suggests that cold streams of accreting filaments are not necessarily aligned with the galaxy plane at low redshifts or intergalactic transfer may dominate. Finally, our results support simulations showing that strong metal absorption can mask the presence of low-metallicity gas in integrated line-of-sight CGM metallicities.

Funding

The physics of gas flows around galaxies at cosmic noon

Australian Research Council

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ARC Centre of Excellence for Quantum Computation and Communication Technology

Australian Research Council

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PDF (Published version)

ISSN

1538-4357

Journal title

Astrophysical Journal

Volume

883

Issue

1

Article number

article no.78

Pagination

78-

Publisher

American Astronomical Society

Copyright statement

Copyright © 2019 The American Astronomical Society. All rights reserved. The published version is reproduced in accordance with the copyright policy of the publisher.

Language

eng

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