The Las Campanas Infrared Survey - II. Photometric redshifts, comparison with models and clustering evolution

Abstract

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 19<H<20 we find that EROs with R‐H>4 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.

Stellar Population Diagnostics of Elliptical Galaxy Formation

“…Using a much shallower sample than that from the HDF, but one that covers an area ∼ 140 times wider than it, and Firth et al (2002) showed that EROs are much more abundant than previously found in smaller fields and are much more strongly clustered than generic galaxies to the same limiting magnitude K ∼ 19. This made them likely candidates for high-z ETGs, and assuming that ∼ 70% of EROs are indeed ETGs at z > 1, Daddi, Cimatti & Renzini (2000) concluded that most field ellipticals were fully assembled by z ∼ 1.…”

Dusty Infrared Galaxies: Sources of the Cosmic Infrared Background

“…At higher redshifts, correlation lengths r 0 have been measured for different galaxy populations such as the LBGs and EROs. Values of about r 0 =4 h −1 Mpc (Porciani & Giavalisco 2002) and r 0 =11 h −1 Mpc (Daddi et al 2000;Firth et al 2002;Roche et al 2003) are reported with mean redshift of about 3 and 1-1.5 for the LBGs and EROs, respectively. Getting information on the clustering of the infrared galaxies is essential to see how they relate to the other galaxy populations and to understand their formation process.…”

The Clustering of Extremely Red Objects

“…Previous studies have all found that EROs are very strongly clustered (e.g., Daddi et al 2000Daddi et al , 2002Firth et al 2002;Roche et al 2002;Brown et al 2005;Georgakakis et al 2005;Kong et al 2006Kong et al , 2009Kim et al 2011). However, the existing estimates of the clustering strengths, as measured by the scale r 0 where the two-point correlation strength is unity, show a broad range (r 0 = 5.5-17 h −1 Mpc) that makes it difficult to link the higher redshift EROs with local galaxy populations.…”

“…The present range of ERO selection criteria include (but are not limited to) (R − K) Vega > 5.0 (e.g., Brown et al 2005), (I − K) Vega > 4.0 (e.g., Kong et al 2009), (R −H ) Vega > 4.0 (e.g., Firth et al 2002), and (R − [3.6]) Vega > 6.5 (e.g., Wilson et al 2004). The consequences of using different ERO selection criteria have been considered in some studies (e.g., Yan & Thompson 2003;Wilson et al 2004;Conselice et al 2008;Kim et al 2011).…”

“…An additional problem is that the angular correlation function (w(θ )) is usually fit as a fixed power law, which may not correctly represent the data even if it is the only option given the sample sizes (e.g., Firth et al 2002;Georgakakis et al 2005). Furthermore, the uncertainties in the correlation function are frequently assumed to be Poisson with no correlations between data points (e.g., Kong et al 2009;Kim et al 2011).…”