Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey

TL;DR

This paper reports the discovery of fifteen new T dwarfs in the UKIDSS survey, analyzes their properties, and estimates the sub-stellar mass function, providing insights into the population and characteristics of T dwarfs.

Contribution

The study presents fifteen new T dwarfs discovered in UKIDSS, characterizes their spectral types and properties, and estimates the T dwarf population and mass function in the survey volume.

Findings

Discovered 15 new T dwarfs with spectral types T2.5-T7.5.

Estimated at least 17±4 T4 or later dwarfs in the survey volume.

Sub-stellar mass function exponent consistent with -1.0 to 0.

Abstract

We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between ~24-93pc, identified in the first three main data releases of the UKIRT Infrared Deep Sky Survey. This brings the total number of T dwarfs discovered in the Large Area Survey (to date) to 28. These discoveries are confirmed by near infrared spectroscopy, from which we derive spectral types on the unified scheme of Burgasser et al. (2006). Seven of the new T dwarfs have spectral types of T2.5-T4.5, five have spectral types of T5-T5.5, one is a T6.5p, and two are T7-7.5. We assess spectral morphology and colours to identify T dwarfs in our sample that may have non-typical physical properties (by comparison to solar neighbourhood populations). The colours of the full sample of LAS T dwarfs show a possible trend to bluer Y-J with decreasing effective temperature beyond T8. By accounting for the main sources of incompleteness (selection, follow-up and spatial) as well as the effects of unresolved binarity and Malmquist bias, we estimate that there are 17+-4 >=T4 dwarfs in the J<=19 volume of the LAS second data release. Comparing this to theoretical predictions is most consistent with a sub-stellar mass function exponent alpha between -1.0 and 0. This is consistent with the latest 2MASS/SDSS constraint (which is based on lower number statistics), and is significantly lower than the alpha~1.0 suggested by L dwarf field populations, possibly a result of the lower mass range probed by the T dwarf class.