No abstract

The Las Campanas Infrared Survey, based on broadband optical and near-infrared photometry, is designed to robustly identify a statistically significant and representative sample of evolved galaxies at redshifts z > 1. We have completed an H-band imaging survey over 1.1 deg 2 of sky in six separate fields. The average 5 detection limit in a 4 00 diameter aperture is H $ 20:8. Here we describe the design of the survey, the observation strategies, data-reduction techniques, and object identification procedures. We present sample near-infrared and optical photometric catalogs for objects identified in two survey fields. The optical images of the Hubble Deep Field-South region obtained from the literature reach 5 detection thresholds in a 4 00 diameter aperture of U $ 24:6, B $ 26:1, V $ 25:6, R $ 25:1, and I $ 24:2 mag. The optical images of the Chandra Deep Field-South region obtained from our own observations reach 5 detection thresholds in a 4 00 diameter aperture of V $ 26:8, R $ 26:2, I $ 25:3, and z 0 $ 23:7 mag. We perform object detection in all bandpasses and identify e 54,000 galaxies over 1408 arcmin 2 of sky in the two fields. Of these galaxies, $14,000 are detected in the H band and $2000 have the colors of evolved galaxies, IÀHe3, at ze1. We find that (1) the differential number counts NðmÞ for the H-band-detected objects has a slope of d log NðmÞ=dm ¼ 0:45 AE 0:01 mag À2 at Hd19 and 0:27 AE 0:01 mag À2 at He19, with a mean surface density %7200 deg À2 mag À1 at H ¼ 19. In addition, we find that (2) the differential number counts for the H-banddetected red objects has a very steep slope, d log Nðm; I À He3Þ=dm ¼ 0:84 AE 0:06 mag À2 at Hd20 and 0:32 AE 0:07 mag À2 at He20, with a mean surface density %3000 deg À2 mag À1 at H ¼ 20. Finally, we find that (3) galaxies with red optical to near-IR colors (IÀH > 3) constitute %20% of the H-band-detected galaxies at Hd21, but only %2% at Hd19. We show that red galaxies are strongly clustered, which results in a strong field-to-field variation in their surface density. Comparisons of observations and predictions based on various formation scenarios indicate that these red galaxies are consistent with mildly evolving early-type galaxies at z $ 1, although with a significant amount of ongoing star formation, as indicated by the large scatter in their VÀI colors.

The Las Campanas Infrared (LCIR) Survey, using the Cambridge Infra‐Red Survey Instrument (CIRSI), reaches H∼21 over nearly 1 deg2. In this paper we present results from 744 arcmin2 centred on the Hubble Deep Field South for which UBVRI optical data are publicly available. Making conservative magnitude cuts to ensure spatial uniformity, we detect 3177 galaxies to H=20.0 in 744 arcmin2 and a further 842 to H=20.5 in a deeper subregion of 407 arcmin2. We compare the observed optical–infrared (IR) colour distributions with the predictions of semi‐analytic hierarchical models and find reasonable agreement. We also determine photometric redshifts, finding a median redshift of ∼0.55. We compare the redshift distributions N(z) of E, Sbc, Scd and Im spectral types with models, showing that the observations are inconsistent with simple passive‐evolution models while semi‐analytic models provide a reasonable fit to the total N(z) but underestimate the number of z∼1 red spectral types relative to bluer spectral types. We also present N(z) for samples of extremely red objects (EROs) defined by optical–IR colours. We find that EROs with R‐H>4 and H<20.5 have a median redshift zm∼1 while redder colour cuts have slightly higher zm. In the magnitude range 194 comprise ∼18 per cent of the observed galaxy population, while in semi‐analytic models they contribute only ∼4 per cent. We also determine the angular correlation function w(θ) for magnitude, colour, spectral type and photometric redshift‐selected subsamples of the data and use the photometric redshift distributions to derive the spatial clustering statistic ξ(r) as a function of spectral type and redshift out to z∼1.2. Parametrizing ξ(r) by ξ(rc,z)=[rc/r∗(z)]‐1.8, where rc is in comoving coordinates, we find that r∗(z) increases by a factor of 1.5–2 from z=0 to z∼1.2. We interpret this as a selection effect – the galaxies selected at z∼1.2 are intrinsically very luminous, about 1–1.5 mag brighter than L∗. When galaxies are selected by absolute magnitude, we find no evidence for evolution in r∗ over this redshift range. Extrapolated to z=0, we find r∗(z=0)∼6.5 h‐1 Mpc for red galaxies and r∗(z=0)∼2–4 h‐1 Mpc for blue galaxies. We also find that, while the angular clustering amplitude of EROs with R‐H>4 or I‐H>3 is up to four times that of the whole galaxy population, the spatial clustering length r∗(z=1) is ∼7.5–10.5 h‐1 Mpc, which is only a factor of ∼1.7 times r∗(z=1) for R‐H<4 and I‐H<3 galaxies lying in a similar redshift and luminosity range. This difference is similar to that observed between red and blue galaxies at low redshifts.

We have identified a population of faint red galaxies from a 0.62 deg 2 region of the Las Campanas Infrared Survey whose properties are consistent with their being the progenitors of early-type galaxies. The optical and IR colors, number-magnitude relation, and angular clustering together indicate modest evolution and increased star formation rates among the early-type field population at redshifts between 1 and 2. The counts of red galaxies with H magnitudes between 17 and 20 rise with a slope that is much steeper than that of the total H sample. The surface density of red galaxies drops from roughly 3000 deg. The VϪI colors are approximately 1.5 mag bluer on average than a pure old population and H p 20 H 1 5 span a range of more than 3 mag. The strength of the angular clustering of the red galaxies is an order of magnitude larger than that of the full galaxy sample. The colors, and photometric redshifts derived from them, indicate that the red galaxies have redshift distributions adequately described by Gaussians with centered, with the exception that galaxies having VϪ and IϪ are primarily in the z p 1 I ! 1.6 H 1 3 1 . 5 Շ z Շ 2 range. We invert the angular correlation functions using these n(z) and find comoving correlation lengths of h Ϫ1 Mpc at , comparable to, or larger than, those found for early-type galaxies at lower redshifts. r Ӎ 9-10 z Ӎ 1 0 A simple photometric evolution model reproduces the counts of the red galaxies, with only an ∼30% decline in the underlying space density of early-type galaxies at . The colors indicate characteristic star formation z ∼ 1.2 rates of ∼1 yr Ϫ1 per 10 10. We suggest on the basis of the colors, counts, and clustering that these red M M , ,galaxies are the bulk of the progenitors of present-day early-type galaxies.