The Las Campanas Infrared Survey. III. TheH‐Band Imaging Survey and the Near‐Infrared and Optical Photometric Catalogs

Abstract

Listen

Translate article

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 σ detection limit in a 4 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 σ detection thresholds in a 4 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 σ detection thresholds in a 4 diameter aperture of V ~ 26.8, R ~ 26.2, I ~ 25.3, and z' ~ 23.7 mag. We perform object detection in all bandpasses and identify ≳ 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, I-H ≳ 3, at z ≳ 1. We find that (1) the differential number counts N(m) for the H-band-detected objects has a slope of d log N(m)/dm = 0.45 ± 0.01 mag^(-2) at H ≾ 19 and 0.27 ± 0.01 mag^(-2) at H ≳ 19, with a mean surface density ≈7200 deg^(-2) mag^(-1) at H = 19. In addition, we find that (2) the differential number counts for the H-band-detected red objects has a very steep slope, d log N(m; I - H ≳ 3)/dm = 0.84 ± 0.06 mag^(-2) at H ≾ 20 and 0.32 ± 0.07 mag^(-2) at H ≳ 20, with a mean surface density ≈3000 deg^(-2) mag^(-1) at H = 20. Finally, we find that (3) galaxies with red optical to near-IR colors (I-H > 3) constitute ≈20% of the H-band-detected galaxies at H ≾ 21, but only ≈2% at H ≾ 19. 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 V-I colors.