Abstract
We have exploited the large area coverage of the combined UKIDSS Ultra Deep Survey (UDS) and Subaru/XMM-Newton Deep Survey (SXDS) to search for bright Lyman-break galaxies (LBGs) at z >= 5. Using the available optical+near-infrared photometry to efficiently exclude low-redshift contaminants, we identify nine z >= 5 LBG candidates brighter than z'=25(AB) within the 0.6 square degree overlap region between the UDS early data release (EDR) and the optical coverage of the SXDS. Accounting for selection incompleteness, we estimate the corresponding surface density of z >= 5 LBGs with z' ~5x10^10 Msun which, if confirmed, places them amongst the most massive galaxies currently known at z >= 5. It is found that Lambda CDM structure formation can produce sufficient numbers of dark matter halos at z >= 5 to accommodate our estimated number density of massive LBGs for plausible values of sigma_8 and the ratio of stellar to dark matter. Moreover, it is found that recent galaxy formation models can also account for the existence of such massive galaxies at z >= 5. Finally, no evidence is found for the existence of LBGs with stellar masses in excess of ~3x10^11 Msun at this epoch, despite the large co-moving volume surveyed.
Highlights
The increasing availability of survey fields with deep multiwavelength data has led to so-called “dropout” techniques becoming established for photometrically identifying high-redshift galaxies
In this paper we have presented the results of a study aimed at exploiting the large co-moving volume of the Subaru/XMM-Newton Deep Survey (SXDS)/Ultra Deep Survey (UDS) data-set to identify the most massive Lyman-break galaxies (LBGs) at z ≥ 5
Our main conclusions can be summarised as follows: (i) We have identified a robust sample of nine bright (z′ ≤ 25) LBG candidates with photometric redshifts in the range
Summary
The increasing availability of survey fields with deep multiwavelength data has led to so-called “dropout” techniques becoming established for photometrically identifying high-redshift galaxies. Of the many hundreds of i−drop galaxies identified in the deep HST fields, only one has z850 ≤ 25 (SBM03#3, spectroscopically confirmed at z = 5.78; Bunker et al 2003) This is an important shortcoming because accurately determining the number density of massive galaxies at high-redshift (z ≥ 5) has the potential to place important new constraints on galaxy formation models, only 1 Gyr after the Big Bang. It is clear that what is required is a combination of both depth and large area coverage In this respect, the study of z ≃ 6 LBGs in the Subaru Deep Field (SDF; Maihara et al 2001) by Shimasaku et al (2005) is perhaps the most notable. When referring to the i and z−band filters, i′ and z′ refer to the Subaru filters, whereas i814 and z850 are the equivalent HST filters
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