Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/238056

Title

Tracing outflows and accretion: a bimodal azimuthal dependence of Mg II absorption

Author(s)

Kacprzak, Glenn G.;  Churchill, Christopher W.;  Nielsen, Nikole M.

Abstract

We report a bimodality in the azimuthal angle distribution of gas around galaxies as traced by Mg II absorption: halo gas prefers to exist near the projected galaxy major and minor axes. The bimodality is demonstrated by computing the mean azimuthal angle probability distribution function using 88 spectroscopically confirmed Mg II-absorption-selected galaxies [Wr (2796) ≥ 0.1 Å] and 35 spectroscopically confirmed non-absorbing galaxies [Wr (2796) < 0.1 Å] imaged with Hubble Space Telescope and Sloan Digital Sky Survey. The azimuthal angle distribution for non-absorbers is flat, indicating no azimuthal preference for gas characterized by Wr (2796) < 0.1 Å. We find that blue star-forming galaxies clearly drive the bimodality while red passive galaxies may exhibit an excess along their major axis. These results are consistent with galaxy evolution scenarios where star-forming galaxies accrete new gas, forming new stars and producing winds, while red galaxies exist passively due to reduced gas reservoirs. We further compute an azimuthal angle dependent Mg II absorption covering fraction, which is enhanced by as much as 20%-30% along the major and minor axes. The Wr (2796) distribution for gas along the major axis is likely skewed toward weaker Mg II absorption than for gas along the projected minor axis. These combined results are highly suggestive that the bimodality is driven by gas accreted along the galaxy major axis and outflowing along the galaxy minor axis. Adopting these assumptions, we find that the opening angle of outflows and inflows to be 100° and 40°, respectively. We find that the probability of detecting outflows is ~60%, implying that winds are more commonly observed.

Publication type

Journal article

Research centre

Swinburne University of Technology

Source

Astrophysical Journal Letters, Vol. 760, no. 1 (Nov 2012), article no. L7

Publication year

2012

FOR Code(s)

0201 Astronomical and Space Sciences

Keyword(s)

Absorption lines;  Galaxy halos;  Intergalactic medium;  Quasars

Publisher

Institute of Physics Publishing

ISSN

2041-8205

Publisher URL

http://dx.doi.org/10.1088/2041-8205/760/1/l7

Copyright

Copyright © 2012 The American Astronomical Society. All rights reserved. The American Astronomical Society does not allow institutions to archive either the accepted manuscript or the published version of the article. However, you can find an earlier version of the full text here: http://arxiv.org/abs/1205.0245

Additional information

The authors acknowledge support from a NASA/STScI grant HST-GO-11667.01-A and NASA's New Mexico Space Grant Consortium.

Peer reviewed