Exploring the 2MASS Extended and Point Source Catalogs with Clustering Redshifts

TL;DR

This paper applies clustering redshift estimation to the 2MASS catalogs, effectively determining redshift distributions for sources without optical data, revealing the extent of the galaxy sample and separating stellar from extragalactic objects.

Contribution

It introduces clustering-based redshift estimation to 2MASS data, overcoming optical biases and characterizing redshift distributions for both extended and point sources.

Findings

Extended sources reach up to z~0.35

Point sources include galaxies up to z~0.7

Approximately 1.6 million extragalactic objects identified

Abstract

The Two-Micron All-Sky Survey (2MASS) has mapped out the low-redshift Universe down to $K_S\sim14$ 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 dataset 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 characterise 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 $z\sim0.35$. % 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 $z\sim0.7$. 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 ten times larger.