Ultradeep Ks Imaging in the GOODS-N

TL;DR

This paper introduces an ultradeep Ks-band image of the GOODS-N region, along with a novel IRAC catalog construction method using high-resolution Ks data as priors, enabling detailed galaxy and AGN studies.

Contribution

The paper presents a new iterative method for constructing IRAC catalogs using Ks images as priors, improving flux estimation accuracy over traditional methods.

Findings

Deep Ks-band image reaching 24.45 AB magnitude at 5 sigma

New iterative IRAC catalog construction method validated with multi-epoch data

Effective color-based selection of AGNs and galaxies at various redshifts

Abstract

We present an ultradeep Ks-band image that covers 0.5*0.5 deg^2 centered on the Great Observatories Origins Deep Survey-North (GOODS-N). The image reaches a 5 \sigma depth of Ks(AB) = 24.45 in the GOODS-N region, which is as deep as the GOODS-N Spitzer Infrared Array Camera (IRAC) 3.6 \mu m image. We present a new method of constructing IRAC catalogs that uses the higher spatial resolution Ks image and catalog as priors and iteratively subtracts fluxes from the IRAC images to estimate the IRAC fluxes. Our iterative method is different from the \chi^2 approach adopted by other groups. We verified our results using data taken in two different epochs of observations, as well as by comparing our colors with the colors of stars and with the colors derived from model spectral energy distributions (SEDs) of galaxies at various redshifts. We make available to the community our WIRCam Ks-band image and catalog (94951 objects in 0.25 deg^2), the Interactive Data Language (IDL) pipeline used for reducing the WIRCam images, and our IRAC 3.6 to 8.0 \mu m catalog (16950 objects in 0.06 deg^2 at 3.6 \mu m). With this improved Ks and IRAC catalog and a large spectroscopic sample from our previous work, we study the color-magnitude and color-color diagrams of galaxies. We compare the effectiveness of using Ks and IRAC colors to select active galactic nuclei (AGNs) and galaxies at various redshifts. We also study a color selection of z = 0.65--1.2 galaxies using the Ks, 3.6 \mu m, and 4.5 \mu m bands.