Journal Article

Constraints on star-forming galaxies at <i>z</i>≥ 6.5 from HAWK-I <i>Y</i>-band imaging of GOODS-South

Samantha Hickey, Andrew Bunker, Matt J. Jarvis, Kuenley Chiu and David Bonfield

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 404, issue 1, pages 212-223
Published in print May 2010 | ISSN: 0035-8711
Published online April 2010 | e-ISSN: 1365-2966 | DOI:
Constraints on star-forming galaxies at z≥ 6.5 from HAWK-I Y-band imaging of GOODS-South

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We present the results of our search for high-redshift Lyman-break galaxies over the GOODS-South field. We use Hubble Space Telescope (HST)-ACS data in B, V, i′ & z′, Very Large Telescope (VLT)-ISAAC J and Ks, Spitzer–Infrared Array Camera (IRAC) 3.6, 4.5, 5.8 and 8.0 μm data in conjunction with the new HAWK-I Y-band science verification data to search for dropout galaxies in the redshift range 6 < z < 9. We survey ≈119 arcmin2 to YAB= 25.7 (5σ), of which 37.5 arcmin2 reaches YAB= 25.9. Candidate z′ and Y dropouts were selected on the basis of a colour cut of (YJ)AB > 0.75 mag and (z′−Y)AB > 1.0 mag, respectively. We find no robust Y-drops (z≈ 9) brighter than JAB < 25.4. In our search for z′-band dropouts (z≈ 6.5– 7.5), we identify four possible candidates, two with z′-drop colours and clear SpitzerIRAC detections and two less likely candidates. We also identify two previously known Galactic T-dwarf stellar contaminants with these colours, and two likely transient objects seen in the Y-band data. The implications if all or none of our candidates is real on the ultraviolet galaxy luminosity functions at z > 6.5 are explored. We find our number of z′-drop candidates to be insufficient based on the expected number of z′ drops in a simple no-evolution scenario from the z= 3 Lyman-break galaxy luminosity function but we are consistent with the observed luminosity function at z≈ 6 (if all our candidates are real). However, if one or both of our best z′-drop candidates are not z > 6.5 galaxies, this would demand evolution of the luminosity function at early epochs, in the sense that the number density of ultraviolet luminous star-forming galaxies at z > 7 is less than at z∼ 6. We show that the future surveys to be conducted with the European Southern Observatory VISTA telescope over the next 5 yr will be able to measure the bulk of the luminosity function for both z′ and Y dropouts and thus provide the strongest constraints on the level of star-formation within the epoch of reionization.

Keywords: galaxies: evolution; galaxies: formation; galaxies: high-redshift; galaxies: starburst; ultraviolet: galaxies

Journal Article.  9371 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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