The COSMOS2015 Catalog: Exploring the 1<z<6 Universe with half a million galaxies

TL;DR

<3-5 sentence high-level summary>The COSMOS2015 paper presents a large, near-infrared–selected catalog spanning 2 deg^2 with precise photometric redshifts and stellar masses for over half a million galaxies, enabled by the combination of UltraVISTA-DR2, HSC $Y$, and SPLASH infrared data and augmented optical data. The authors employ a robust photometric pipeline with PSF homogenization, $ abla$-based detection, and LePhare SED fitting to derive redshifts up to $z\sim6$ and physical properties, including mass completeness down to $\sim10^{10} M_\odot$ to $z\approx 4$. They validate redshifts with extensive spectroscopic samples, achieving $\sigma_{\Delta z/(1+z_s)}$ as low as $0.007$ at $z<1.2$ and $0.021$ for $3<z<6$ with a non-negligible outlier fraction, and demonstrate robust clustering and population demographics. The COSMOS2015 catalog provides a foundational resource for studying galaxy evolution and environmental effects across cosmic time and will support future Euclid-era surveys and spectroscopic planning.

Abstract

We present the COSMOS2015 catalog which contains precise photometric redshifts and stellar masses for more than half a million objects over the 2deg$^{2}$ COSMOS field. Including new $YJHK_{\rm s}$ images from the UltraVISTA-DR2 survey, $Y$-band from Subaru/Hyper-Suprime-Cam and infrared data from the Spitzer Large Area Survey with the Hyper-Suprime-Cam Spitzer legacy program, this near-infrared-selected catalog is highly optimized for the study of galaxy evolution and environments in the early Universe. To maximise catalog completeness for bluer objects and at higher redshifts, objects have been detected on a $χ^{2}$ sum of the $YJHK_{\rm s}$ and $z^{++}$ images. The catalog contains $\sim 6\times 10^5$ objects in the 1.5 deg$^{2}$ UltraVISTA-DR2 region, and $\sim 1.5\times 10^5$ objects are detected in the "ultra-deep stripes" (0.62 deg$^{2}$) at $K_{\rm s}\leq 24.7$ (3$σ$, 3", AB magnitude). Through a comparison with the zCOSMOS-bright spectroscopic redshifts, we measure a photometric redshift precision of $σ_{Δz/(1+z_s)}$ = 0.007 and a catastrophic failure fraction of $η=0.5$%. At $3<z<6$, using the unique database of spectroscopic redshifts in COSMOS, we find $σ_{Δz/(1+z_s)}$ = 0.021 and $η=13.2\% $. The deepest regions reach a 90\% completeness limit of 10$^{10}M_\odot$ to $z=4$. Detailed comparisons of the color distributions, number counts, and clustering show excellent agreement with the literature in the same mass ranges. COSMOS2015 represents a unique, publicly available, valuable resource with which to investigate the evolution of galaxies within their environment back to the earliest stages of the history of the Universe. The COSMOS2015 catalog is distributed via anonymous ftp (ftp://ftp.iap.fr/pub/from_users/hjmcc/COSMOS2015/) and through the usual astronomical archive systems (CDS, ESO Phase 3, IRSA).

Figures (20)

• Figure 1: Schematic of the COSMOS field showing all of the optical (dark blue and turquoise) and NIR (green and orange) observations used. The background image corresponds to the $\chi^{2}$ YKHK$_{\rm s}$-z$^{++}$ detection image (as described in section \ref{['section:prepIm']}). For reference, the region covered by the COSMOS-Advanced Camera for Surveys (ACS) HST data 2007ApJS..172..196K is shown in cyan. ${\cal A}^{\rm COSMOS}$ defines the 2 deg$^{2}$ COSMOS square (dark blue). ${\cal A}^{\rm Uvista}$ (orange area) is the region covered by the UltraVISTA-DR2 observations. We define ${\cal A}^{\rm UD}$ as the light green area, corresponding to the ultra-deep stripes in the UltraVISTA-DR2 observations. ${\cal A}^{\rm Deep}$ is the difference between ${\cal A}^{\rm UVista }$ and ${\cal A}^{\rm UD}$. In our analysis of the performance of the catalog, we limit ourselves to the intersection between ${\cal A}^{\rm UD}$ with ${\cal A}^{\rm COSMOS}$ and ${\cal A}^{\rm Deep}$ with ${\cal A}^{\rm COSMOS}$, after removing the masked objects in the optical bands (${\cal A}^{\rm !OPT}$, not shown on this figure). The effective areas are given in Table \ref{['Tab:coordinates']}.
• Figure 2: Transmission curves for the photometric bands used. The effect of atmosphere, telescope, camera optics, filter, and the detector are included. Note that for clarity the profiles are normalized to a maximum throughput of one: therefore, the relative efficiencies of each telescope and detector system are not shown. Intermediate and narrow bands are not represented, but the region of the spectrum covered by these bands is marked by dashed lines.
• Figure 3: Limiting magnitude at 3$\sigma$ in a 3$\arcsecond$ diameter aperture computed from empty aperture measurements for each band in COSMOS2015, with the exception for NUV filter 2007ApJS..172..468Z. The length of each segment is the FWHM of the filter curves. For the $Y$, $J$, $H$, $K_{\rm s}$ bands; the limiting magnitudes which are specified correspond to ${\cal A}^{\rm UD}$.
• Figure 4: Left: best-fitting stellar PSFs for all bands before and after homogenization (left upper and lower panels respectively), normalized to the target PSF ${\cal F}_{T}$. The vertical black solid line corresponds to the 3$\hbox{$^{\prime\prime}$}$ diameter aperture used for photometric redshifts. The horizontal dashed lines show the 5% relative error. The color map reflects the increase in seeing before homogenization. Right: Median curves of growth (the difference between the magnitude in the $k$th aperture $r_{k}$ with the total magnitude for point-like sources, estimated from the 4$\hbox{$^{\prime\prime}$}$ diameter aperture) as a function of aperture after homogenization for each band. The target Moffat profile with ($\theta$,$\beta$)=(0.8,2.5) is shown in red. The vertical dark dashed lines are the apertures provided in the final public catalog (2$\arcsecond$ and 3$\arcsecond$ diameters).
• Figure 5: Distribution of the difference local seeing and the median image seeing for the selected stars in the $u$ and $IA464$ bands as a function of the position. Note that for these seeing estimations, we did not fit each star individually with a Moffat profile, but we used the Gaussian-profile-based FWHM_WORLD parameter from SExtractor. While the $u$ band is relatively homogenous across the field, $IA464$ shows large positional variations. This is the most extreme case in our catalog.