The COSMOS2015 Catalog: Exploring the 1<z<6 Universe with half a million galaxies (1604.02350v1)

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 $\chi^{2}$ 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$\sigma$, 3", AB magnitude). Through a comparison with the zCOSMOS-bright spectroscopic redshifts, we measure a photometric redshift precision of $\sigma_{\Delta z/(1+z_s)}$ = 0.007 and a catastrophic failure fraction of $\eta=0.5$%. At $3<z<6$, using the unique database of spectroscopic redshifts in COSMOS, we find $\sigma_{\Delta z/(1+z_s)}$ = 0.021 and $\eta=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).

• The paper delivers the COSMOS2015 catalog by integrating UltraVISTA-DR2 and SPLASH data, achieving photometric redshift precisions of 0.007–0.021 across z=1–6.
• Enhanced areal coverage and depth enable robust studies of galaxy evolution, with a sample of over 600k galaxies and mass completeness down to 10¹⁰ M☉.
• A robust star-galaxy classification method ensures clean data sets, supporting detailed analysis and future cross-correlation with upcoming surveys.

An Analysis of the COSMOS2015 Catalogue

The COSMOS2015 catalogue paper by Laigle et al. presents a refined and expanded instalment of the COSMOS survey, focusing specifically on analyzing the universe in the redshift range $1 < z < 6$. This comprehensive catalogue includes data for over half a million galaxies across the COSMOS field, powered by the inclusion of near-infrared images from UltraVISTA-DR2, Subaru/Hyper-Suprime-Cam $Y$-band, and IR data from SPLASH. This dataset is particularly optimized for studying galaxy evolution and their environments in the early Universe.

Methodology and Data Collection

Key improvements in the COSMOS2015 catalogue compared to its predecessors lie in its depth and data integration. Near-infrared selection through images from UltraVISTA-DR2 and SPLASH Spitzer allows for a more inclusive detection of galaxies, especially those at higher redshifts. The sources were meticulously detected through an optimized $\chi^{2}$ method integrating $YJHK_{\text{s}}$ and $z^{++}$ images to ensure completeness, especially for blue and high-redshift objects.

The dataset spans a total area of 2 deg$^2$, including about 600,000 objects with precise photometric redshifts and stellar masses. The authors detail calibration efforts to achieve photometric redshifts through the comparison with the vast spectroscopic database of COSMOS, demonstrating a photo-$z$ precision of $\sigma_{\Delta z/(1+z_s)} = 0.007$ at $z < 1.2$ and $\sigma_{\Delta z/(1+z_s)} = 0.021$ at $3 < z < 6$, with a notable catastrophic failure fraction much reduced across earlier COSMOS releases.

Key Results

The catalogue provides significant value in terms of its completeness and the reliability of photometric redshifts across a wide redshift span. With its substantial increase in depth and areal coverage, it offers a critical tool for exploring cosmic deflation, dark energy, and the galaxy-halo connection across critical evolutionary epochs of the Universe.

1. Photometric Redshift and Stellar Mass Calibration: The precise photometric redshifts were refined using a spectroscopic sample, leading to accurate mass assembly histories of galaxies. The catalogue extends its mass completeness to $10^{10} M_\odot$ up to $z = 4$.
2. Environmental and Evolutionary Studies: By reaching deeper magnitudes and covering larger sky areas than previously possible (especially in NIR bands), COSMOS2015 can significantly enhance studies on galaxy-clustering and the environmental influence on galaxy evolution.
3. Star-Galaxy Classification: Utilizing a robust star-galaxy classification method, integrating both NIR and optical data, ensures clean galaxy samples which are critical for further scientific analysis.

Implications and Speculations

The COSMOS2015 expands our capability to analyze the large-scale structure of the universe, understand galaxy formation subtleties, and probe the intricate environment-galaxy dynamics. It sets a foundation for higher fidelity cross-correlation studies with other surveys and is crucial for ongoing simulations and model-testing. The researchers highlight its utility in preparing for upcoming missions like the Euclid satellite mission.

Conclusion

The COSMOS2015 catalogue thus represents a pivotal resource for astrophysicists aiming to understand the universe’s infancy, allowing analyses of galaxy evolution under gravitational and environmental influences. Its unique combination of depth, precision, and wide-field imaging opens up multiple avenues for future cosmological research, supporting efforts for correlating theoretical models with observational data.