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The bright end of the galaxy luminosity function at z =7: before the onset of mass quenching?

Bowler, R. A. A. and Dunlop, J. S. and McLure, R. J. and Rogers, A. B. and McCracken, H. J. and Milvang-Jensen, B. and Furusawa, H. and Fynbo, J. P. U. and Taniguchi, Y. and Afonso, J. and Bremer, M. N. and Le Fèvre, O. (2014) The bright end of the galaxy luminosity function at z =7: before the onset of mass quenching? Monthly Notices of the Royal Astronomical Society, 440 (3). pp. 2810-2842. ISSN 0035-8711. doi:10.1093/mnras/stu449.

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We present the results of a new search for bright star-forming galaxies at redshift z ≃ 7 within the UltraVISTA second data release (DR2) and UKIDSS (UKIRT Infrared Deep Sky Survey) UDS (Ultra Deep Survey) DR10 data, which together provide 1.65 deg^2 of near-infrared imaging with overlapping optical and Spitzer data. Using a full photometric redshift analysis, to identify high-redshift galaxies and reject contaminants, we have selected a sample of 34 luminous (−22.7<M_(UV)<−21.2 −22.7<M_(UV)<−21.2) galaxies with 6.5 < z < 7.5. Crucially, the deeper imaging provided by UltraVISTA DR2 confirms all of the robust objects previously uncovered by Bowler et al., validating our selection technique. Our new expanded galaxy sample includes the most massive galaxies known at z ≃ 7, with M^* ≃ 10^(10) M_⊙, and the majority are resolved, consistent with larger sizes (r1/2 ≃ 1–1.5 kpc) than displayed by less massive galaxies. From our final robust sample, we determine the form of the bright end of the rest-frame UV galaxy luminosity function (LF) at z ≃ 7, providing strong evidence that it does not decline as steeply as predicted by the Schechter-function fit to fainter data. We exclude the possibility that this is due to either gravitational lensing, or significant contamination of our galaxy sample by active galactic nuclei (AGN). Rather, our results favour a double power-law form for the galaxy LF at high redshift, or, more interestingly, an LF which simply follows the form of the dark matter halo mass function at bright magnitudes. This suggests that the physical mechanism which inhibits star formation activity in massive galaxies (i.e. AGN feedback or some other form of ‘mass quenching’) has yet to impact on the observable galaxy LF at z ≃ 7, a conclusion supported by the estimated masses of our brightest galaxies which have only just reached a mass comparable to the critical ‘quenching mass’ of M^* ≃ 10^(10).2 M_⊙ derived from studies of the mass function of star-forming galaxies at lower redshift.

Item Type:Article
Related URLs:
URLURL TypeDescription
McCracken, H. J.0000-0002-9489-7765
Milvang-Jensen, B.0000-0002-2281-2785
Fynbo, J. P. U.0000-0002-8149-8298
Taniguchi, Y.0000-0003-2247-3741
Afonso, J.0000-0002-9149-2973
Le Fèvre, O.0000-0001-5891-2596
Additional Information:© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2014 March 4. Received 2014 March 4; in original form 2013 December 20.
Issue or Number:3
Record Number:CaltechAUTHORS:20170629-131638272
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78704
Deposited By: Joy Painter
Deposited On:30 Jun 2017 17:26
Last Modified:15 Nov 2021 17:42

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