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

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 clustering-based 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.