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Title

Enriched haloes at redshift z=2 with no star formation: implications for accretion and wind scenarios

Author(s)

Bouche, N.;  Murphy, M. T.;  Peroux, C.;  Contini, T.;  Martin, C. L.;  Forster Schreiber, N. M.;  Genzel, R.;  Lutz, D.;  Gillessen, S.;  Tacconi, L.;  Davies, R.;  Eisenhauer, F.

Abstract

[Abridged] In order to understand which process (e.g. galactic winds, cold accretion) is responsible for the cool (T~10^4 K) halo gas around galaxies, we embarked on a program to study the star-formation properties of galaxies selected by their MgII absorption signature in quasar spectra. Specifically, we searched for the H-alpha line emission from galaxies near very strong z=2 MgII absorbers (with rest-frame equivalent width EW>2 \AA) because these could be the sign-posts of outflows or inflows. Surprisingly, we detect H-alpha from only 4 hosts out of 20 sight-lines (and 2 out of the 19 HI-selected sight-lines), despite reaching a star-formation rate (SFR) sensitivity limit of 2.9 M/yr (5-sigma) for a Chabrier initial mass function. This low success rate is in contrast with our z=1 survey where we detected 66%\ (14/21) of the MgII hosts. Taking into account the difference in sensitivity between the two surveys, we should have been able to detect >11.4 of the 20 z=2 hosts whereas we found only 4 galaxies. Interestingly, all the z=2 detected hosts have observed SFR greater than 9 M/yr, well above our sensitivity limit, while at z=1 they all have SFR less than 9 M/yr, an evolution that is in good agreement with the evolution of the SFR main sequence. Moreover, we show that the z=2 undetected hosts are not hidden under the quasar continuum after stacking our data and that they also cannot be outside our surveyed area. Hence, strong MgII absorbers could trace star-formation driven winds in low-mass halos (Mhalo < 10^{10.6} Msun). Alternatively, our results imply that z=2 galaxies traced by strong MgII absorbers do not form stars at a rate expected (3--10 M/yr) for their (halo or stellar) masses, supporting the existence of a transition in accretion efficiency at Mhalo ~ 10^{11} Msun. This scenario can explain both the detections and the non-detections.

Publication type

Journal article

Research centre

Swinburne University of Technology

Source

Monthly Notices of the Royal Astronomical Society, Vol. 419, no. 1 (Jan 2012), pp. 2-13

Publication year

2012

FOR Code(s)

0201 Astronomical and Space Sciences

Keyword(s)

Absorption lines;  Galaxy evolution;  Galaxy formation;  Haloes;  Quasars;  Redshifts

Publisher

Wiley-Blackwell Publishing

ISSN

0035-8711

Publisher URL

http://dx.doi.org/10.1111/j.1365-2966.2011.19500.x

Copyright

Copyright © 2011 The Authors. Journal copyright © 2011 Royal Astronomical Society. The accepted manuscript is reproduced in accordance with the copyright policy of the publisher. The definitive publication is available at www.interscience.wiley.com.

Research Projects

Galaxy formation and femtosecond frequency combs, Australian Research Council grant number DP0877998

Full text

Peer reviewed