Journal Article

Large-scale outflows from <i>z</i>≃ 0.7 starburst galaxies identified via ultrastrong Mg <span class="smallCaps">ii</span> quasar absorption lines

Daniel B. Nestor, Benjamin D. Johnson, Vivienne Wild, Brice Ménard, David A. Turnshek, Sandhya Rao and Max Pettini

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 412, issue 3, pages 1559-1572
Published in print April 2011 | ISSN: 0035-8711
Published online April 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17865.x
Large-scale outflows from z≃ 0.7 starburst galaxies identified via ultrastrong Mg ii quasar absorption lines

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Star formation driven outflows are a critically important phenomenon in theoretical treatments of galaxy evolution, despite the limited ability of observational studies to trace galactic winds across cosmological time-scales. It has been suggested that the strongest Mg ii absorption-line systems detected in the spectra of background quasars might arise in outflows from foreground galaxies. If confirmed, such ‘ultrastrong’ Mg ii (USMg ii) absorbers would represent a method to identify significant numbers of galactic winds over a huge baseline in cosmic time, in a manner independent of the luminous properties of the galaxy. To this end, we present the first detailed imaging and spectroscopic study of the fields of two USMg ii absorber systems culled from a statistical absorber catalogue, with the goal of understanding the physical processes leading to the large velocity spreads that define such systems.

Each field contains two bright emission-line galaxies at similar redshift (Δv≲ 300 km s−1) to that of the absorption. Lower limits on their instantaneous star formation rates (SFRs) from the observed [O ii] and Hβ line fluxes, and stellar masses from spectral template fitting indicate specific SFRs among the highest for their masses at these redshifts. Additionally, their 4000-Å break and Balmer absorption strengths imply they have undergone recent (∼0.01–1 Gyr) starbursts. The concomitant presence of two rare phenomena – starbursts and USMg ii absorbers – strongly implies a causal connection. We consider these data and USMg ii absorbers in general in the context of various popular models, and conclude that galactic outflows are generally necessary to account for the velocity extent of the absorption. We favour starburst-driven outflows over tidally stripped gas from a major interaction, which triggered the starburst as the energy source for the majority of systems. Finally, we discuss the implications of these results and speculate on the overall contribution of such systems to the global SFR density at z≃ 0.7.

Keywords: ISM: jets and outflows; intergalactic medium; quasars: absorption lines; galaxies: starburst

Journal Article.  10515 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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