Exploring the 2MASS extended and point source catalogues with clustering redshifts

Abstract

The Two-Micron All-Sky Survey (2MASS) has mapped out the low-redshift Universe down to KS ~ 14 mag. As its near-infrared photometry primarily probes the featureless Rayleigh- Jeans tail of galaxy spectral energy distributions, colour-based redshift estimation is rather uninformative. Until now, redshift estimates for this data set have relied on optical follow-up suffering from selection biases. Here, we use the newly developed technique of clusteringbased redshift estimation to infer the redshift distribution of the 2MASS sources regardless of their optical properties. We characterize redshift distributions of objects from the Extended Source Catalogue as a function of near-infrared colours and brightness and report some observed trends.We also apply the clustering redshift technique to dropout populations, sources with non-detections in one or more near-infrared bands, and present their redshift distributions. Combining all extended sources, we confirm with clustering redshifts that the distribution of this sample extends up to z ~ 0.35. We perform a similar analysis with the Point Source Catalogue and show that it can be separated into stellar and extragalactic contributions with galaxies reaching z ~ 0.7. We estimate that the Point Source Catalogue contains 1.6 million extragalactic objects: as many as in the Extended Source Catalogue but probing a cosmic volume 10 times larger.