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The Structure and Kinematics of the Circumgalactic Medium from Far-ultraviolet Spectra of z ≃ 2-3 Galaxies

Steidel, Charles C. and Erb, Dawn K. and Shapley, Alice E. and Pettini, Max and Reddy, Naveen A. and Bogosavljević, Milan and Rudie, Gwen C. and Rakic, Olivera (2010) The Structure and Kinematics of the Circumgalactic Medium from Far-ultraviolet Spectra of z ≃ 2-3 Galaxies. Astrophysical Journal, 717 (1). pp. 289-322. ISSN 0004-637X.

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We present new results on the kinematics and spatial distribution of metal-enriched gas within ~125 kpc of star-forming ("Lyman break") galaxies at redshifts 2 ≲ z ≲ 3. In particular, we focus on constraints provided by the rest-frame far-ultraviolet (far-UV) spectra of faint galaxies, and demonstrate how galaxy spectra can be used to obtain key spatial and spectral information more efficiently than possible with QSO sightlines. Using a sample of 89 galaxies with z = 2.3 ± 0.3 and with both rest-frame far-UV and Hα spectra, we re-calibrate the measurement of accurate galaxy systemic redshifts using only survey-quality rest-UV spectra. We use the velocity-calibrated sample to investigate the kinematics of the galaxy-scale outflows via the strong interstellar (IS) absorption lines and Lyα emission (when present), as well as their dependence on other physical properties of the galaxies. We construct a sample of 512 close (1"-15") angular pairs of z ~ 2-3 galaxies with redshift differences indicating a lack of physical association. Sightlines to the background galaxies provide new information on the spatial distribution of circumgalactic gas surrounding the foreground galaxies. The close pairs sample galactocentric impact parameters 3-125 kpc (physical) at <z> = 2.2, providing for the first time a robust map of cool gas as a function of galactocentric distance for a well-characterized population of galaxies. We propose a simple model of circumgalactic gas that simultaneously matches the kinematics, depth, and profile shape of IS absorption and Lyα emission lines, as well as the observed variation of absorption line strength (H I and several metallic species) versus galactocentric impact parameter. Within the model, cool gas is distributed symmetrically around every galaxy, accelerating radially outward with v_(out)(r) increasing with r (i.e., the highest velocities are located at the largest galactocentric distances r). The inferred radial dependence of the covering fraction of cool gas (which modulates the absorption line strength) is f_c(r) ∝ r^(–γ) with 0.2 ≲ γ ≲ 0.6 depending on transition. We discuss the results of the observations in the context of "cold accretion," in which cool gas is accreting via filamentary streams directly onto the central regions of galaxies. At present, we find little observational evidence for cool infalling material, while evidence supporting the large-scale effects of superwind outflows is strong. This "pilot" study using faint galaxy spectra demonstrates the potential of using galaxies to trace baryons within galaxies, in the circumgalactic medium, and ultimately throughout the intergalactic medium.

Item Type:Article
Related URLs:
URLURL TypeDescription
Steidel, Charles C.0000-0002-4834-7260
Erb, Dawn K.0000-0001-9714-2758
Shapley, Alice E.0000-0003-3509-4855
Pettini, Max0000-0002-5139-4359
Reddy, Naveen A.0000-0001-9687-4973
Rudie, Gwen C.0000-0002-8459-5413
Additional Information:© 2010 American Astronomical Society. Received 2010 February 22; accepted 2010 May 11; published 2010 June 10. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation. This work has been supported by the US National Science Foundation through grants AST-0606912 and AST-0908805 (C.C.S.), and by the David and Lucile Packard Foundation (A.E.S., C.C.S.). C.C.S. acknowledges additional support from the John D. and Catherine T. MacArthur Foundation. D.K.E. is supported by the National Aeronautics and Space Administration under Award No. NAS7-03001 and the California Institute of Technology. We thank Juna Kollmeier and Joop Schaye for interesting and useful conversations, and Patrick Hall, Martin Haehnelt, and the referee for comments that significantly improved the final version of the paper. Kurt Adelberger played a major role in the early days of the survey used in this paper; his intellectual contributions have remained crucial though he has moved on to new challenges in the “real” world. Marc Kassis and the rest of the W. M. Keck Observatory staff keep the instruments and telescopes running effectively, for which we are extremely grateful.We extend thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.
Funding AgencyGrant Number
David and Lucile Packard FoundationUNSPECIFIED
John D. and Catherine T. MacArthur FoundationUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:cosmology: observations; galaxies: evolution; galaxies: high-redshift
Issue or Number:1
Classification Code:PACS: 98.62.Dm; 98.58.Fd; 98.62.Ra; 98.58.Jg; 98.62.Py; 95.85.Mt
Record Number:CaltechAUTHORS:20100709-165047127
Persistent URL:
Official Citation:Charles C. Steidel et al 2010 ApJ 717 289 doi: 10.1088/0004-637X/717/1/289
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18985
Deposited By: Jason Perez
Deposited On:13 Jul 2010 18:39
Last Modified:04 Dec 2019 23:18

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