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Metal-enriched, subkiloparsec gas clumps in the circumgalactic medium of a faint z = 2.5 galaxy.

Crighton, N.H.M. and Hennawi, J.F. and Simcoe, R.A. and Cooksey, K.L. and Murphy, M.T. and Fumagalli, M. and Prochaska, J.X. and Shanks, T. (2015) 'Metal-enriched, subkiloparsec gas clumps in the circumgalactic medium of a faint z = 2.5 galaxy.', Monthly notices of the Royal Astronomical Society., 446 (1). pp. 18-37.


We report the serendipitous detection of a 0.2 L*, Lyα emitting galaxy at redshift 2.5 at an impact parameter of 50 kpc from a bright background QSO sightline. A high-resolution spectrum of the QSO reveals a partial Lyman-limit absorption system (NHi=1016.94±0.10 cm−2) with many associated metal absorption lines at the same redshift as the foreground galaxy. Using photoionization models that carefully treat measurement errors and marginalize over uncertainties in the shape and normalization of the ionizing radiation spectrum, we derive the total hydrogen column density NH=1019.4±0.3cm−2, and show that all the absorbing clouds are metal enriched, with Z = 0.1–0.6 Z⊙. These metallicities and the system's large velocity width (436 km s− 1) suggest the gas is produced by an outflowing wind. Using an expanding shell model we estimate a mass outflow rate of ∼5 M⊙ yr−1. Our photoionization model yields extremely small sizes (<100–500 pc) for the absorbing clouds, which we argue is typical of high column density absorbers in the circumgalactic medium (CGM). Given these small sizes and extreme kinematics, it is unclear how the clumps survive in the CGM without being destroyed by hydrodynamic instabilities. The small cloud sizes imply that even state-of-the-art cosmological simulations require more than a 1000-fold improvement in mass resolution to resolve the hydrodynamics relevant for cool gas in the CGM.

Item Type:Article
Keywords:Galaxies: haloes, Quasars: absorption lines.
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:06 October 2014
Date deposited:18 November 2014
Date of first online publication:10 November 2014
Date first made open access:No date available

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