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Galaxy number counts – VI. An H-band survey of the Herschel Deep Field

Metcalfe, N. and Shanks, T. and Weilbacher, P. M. and McCracken, H. J. and Fong, R. and Thompson, D. (2006) Galaxy number counts – VI. An H-band survey of the Herschel Deep Field. Monthly Notices of the Royal Astronomical Society, 370 (3). pp. 1257-1273. ISSN 0035-8711. doi:10.1111/j.1365-2966.2006.10534.x.

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We present H-band infrared (IR) galaxy data to a 3σ limit of H ~ 22.9 and optical–IR colours of galaxies on the William Herschel Deep Field (WHDF). These data were taken from a 7 × 7 arcmin^2 area observed for 14 h with the Ω Prime camera on the 3.5-m Calar Alto telescope. We also present counts derived from the Hubble Deep Field-South (HDF-S) NICMOS camera to the limit of H ~ 29 mag over a 0.95 × 0.95 arcmin^2 area. Following previous papers, we derive H-band number counts, colour–magnitude diagrams and colour histograms for the whole H-selected sample. We review our Pure Luminosity Evolution (PLE) galaxy count models based on the spectral synthesis models of Bruzual & Charlot. We find that our previously assumed forms for the luminosity function (LF) agree well with those recently derived from 2dF Galaxy Redshift Survey (2dFGRS)/Two-Micron All-Sky Survey (2MASS) at B and K, except that the 2dFGRS K LF has an unexpectedly flat slope which, if correct, could affect our interpretation of the faintest H and K counts. We find that these PLE models give an excellent fit to the WHDF H-band count data to H < 22.5 and HDF count data to H < 28. However, if we use the flat 2dFGRS/2MASS near-infrared (NIR) LF, then the predicted count is too flat at H > 21. We confirm that PLE models that assume a Salpeter initial mass function (IMF) for early-type galaxies overestimate the average galaxy redshift in K < 20 galaxy redshift surveys. Models that assume a steep x = 3 IMF continue to give better agreement with the N(z) data than even models based on a Scalo IMF, although they do show an unobserved peak in B−H and I−H colour distributions at faint H magnitudes corresponding to z > 1 early-type galaxies. But this feature may simply reflect a larger scatter in optical–IR colours than in the optical B−R colour of early-type galaxies at this redshift. This scatter is obvious in optical–IR colour–colour diagrams and may be explained by ongoing star formation in an intermediate subpopulation of early-type galaxies. The numbers of EROs detected are a factor of 2–3 lower than predicted by the early-type models that assume the Salpeter IMF and in better agreement with those that assume the x = 3 IMF. The tight sequence of early-type galaxies also shows a subclass which is simultaneously redder in IR bands and bluer in the bluer bands than the classical, passive early-type galaxy; this subclass appears at relatively low redshifts and may constitute an intermediate-age, early-type population. Finally, we have also detected a candidate z > 1 galaxy cluster using our panoramic H-band observations of the WHDF.

Item Type:Article
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URLURL TypeDescription
Metcalfe, N.0000-0001-9034-4402
McCracken, H. J.0000-0002-9489-7765
Additional Information:© 2006 The Authors. Journal compilation © 2006 RAS. Accepted 2006 May 10. Received 2006 May 8; in original form 2005 September 12. Article first published online: 22 Jun. 2006. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). HJMcC and NM acknowledge financial support from PPARC. PMW acknowledges funding from European Commission through the ‘SISCO’ RTN, contract HPRN-CT-2002-00316. The Isaac Newton Telescope (INT) and William Herschel Telescope (WHT) are operated on the island of La Palma by the Isaac Newton Group at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Data-reduction facilities were provided by the UK STARLINK project. We would like to thank Ana Campos for assisting with the observations at Calar Alto.
Funding AgencyGrant Number
Particle Physics and Astronomy Research Council (PPARC)UNSPECIFIED
European CommissionHPRN-CT-2002-00316
Subject Keywords:galaxies: evolution; galaxies: photometry; cosmology: observations
Issue or Number:3
Record Number:CaltechAUTHORS:20110623-151159637
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Official Citation:Metcalfe, N., Shanks, T., Weilbacher, P. M., McCracken, H. J., Fong, R. and Thompson, D. (2006), Galaxy number counts – VI. An H-band survey of the Herschel Deep Field. Monthly Notices of the Royal Astronomical Society, 370: 1257–1273. doi: 10.1111/j.1365-2966.2006.10534.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24189
Deposited On:24 Jun 2011 20:13
Last Modified:09 Nov 2021 16:21

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