The Spitzer-HETDEX Exploratory Large Area Survey. II. The Dark Energy Camera and Spitzer/IRAC Multiwavelength Catalog

Abstract

We present the ugriz-band Dark Energy Camera (DECam) plus 3.6 and 4.5 µm IRAC catalogs for the Spitzer /HETDEX Exploratory Large-Area (SHELA) survey. SHELA covers ∼ 24 deg 2 of the Sloan Digital Sky Survey (SDSS) "Stripe 82" region, with seven bandpasses spanning a wavelength range of 0.35 to 4.5 µm. SHELA falls within the footprint of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), which will provide spectroscopic redshifts for ∼ 200,000 Lyα emitters at 1.9 < z < 3.5 and also for ∼ 200,000 [OII] emitters at z < 0.5. SHELA's deep, wide-area multiwavelength images combined with HETDEX's spectroscopic information, will facilitate many extragalactic studies, including measuring the evolution of galaxy stellar mass, halo mass, and environment from 1.5 < z < 3.5. Here we present riz-band selected ugriz-band DECam catalogs that reach a 5σ depth of ∼ 24.5 AB mag (for point sources with an aperture that encloses 70% of the total flux) and cover 17.5 deg 2 of the overall SHELA field. We validate our DECam catalog by comparison to the DECam Legacy Survey (DECaLS) DR5 and the Dark Energy Survey (DES) DR1. We perform IRAC forced photometry with The Tractor image modeling code to measure 3.6 and 4.5 µm fluxes for all objects within our DECam catalog. We demonstrate the utility of our catalog by computing galaxy number counts and estimating photometric redshifts. Our photometric redshifts recover the available z = 0.33 SDSS spectroscopic redshifts with a 1σ scatter in ∆z/(1 + z) of 0.04.

Exploring the high-mass end of the stellar mass function of star-forming galaxies at cosmic noon

“…In the local Universe, recent integral field spectroscopy (IFS) studies (e.g., Sánchez et al 2012, Ma et al 2014, Bundy et al 2015 have confirmed that the most massive galaxies in the nearby Universe have old stellar populations indicative of early growth and rapid quenching at early times (e.g., Pérez et al 2013, Greene et al 2015. Deep, wide-area surveys (e.g., Jannuzi & Dey 1999, de Jong et al 2015, Papovich et al 2016, Wold et al 2019) are necessary to compile large, statistically significant samples of rare systems, such as massive galaxies, overcome cosmic variance, and probe a wide range of environments. As massive galaxies present a challenge to the overall hierarchical structure formation expected in ΛCDM cosmology (e.g., Cowie et al 1996, Fontanot et al 2009), it is imperative that statistically significant samples of massive galaxies are constructed.…”

On the (Lack of) Evolution of the Stellar Mass Function of Massive Galaxies from z = 1.5 to 0.4

“…In addition to the NEWFIRM K-band data, the SHELA survey includes ugriz imaging from the Dark Energy Cam-era over 17.5 deg 2 (DECam; Wold et al (2019)) and deep 3.6 and 4.5 µm imaging from Spitzer/IRAC (Papovich et al 2016). The riz−band selected DECam catalogs reach a 5σ depth of ∼ 24.5 AB mag.…”

“…The riz−band selected DECam catalogs reach a 5σ depth of ∼ 24.5 AB mag. However, we do not use the DE-Cam catalogs and the DECam-selected Spitzer/IRAC forced photometry (Wold et al 2019). In our analysis, we use our new K-band image for detection for the reason we have described in the previous section.…”

“…In our analysis, we use our new K-band image for detection for the reason we have described in the previous section. Following our work in Kawinwanichakij (2018) and Wold et al (2019), we perform "forced photometry" to derive optimal fluxes in the ugriz + [3.6] and [4.5] data for sources detected in the K s catalog. We use the code "The Tractor" (Lang et al 2016b,a) for this process.…”

“…This allows us to measure flux densities (or accurate limits) even for sources below the 5σ depth threshold of the original DECam or IRAC imaging or for sources blended at the resolution of Spitzer/IRAC. We follow identical procedures as those described in Kawinwanichakij (2018) and Wold et al (2019) except we use the NEWFIRM K-band image for detection. With this technique, our forced photometric IRAC catalog is 80% completeness to limiting magnitude of 22.6 AB mag in both 3.6 and 4.5 µm bands, in contrast to 22.3 AB mag for the original published Spitzer/IRACselected catalog (Papovich et al 2016).…”