GTC Osiris spectroscopic identification of a faint L subdwarf in the UKIRT Infrared Deep Sky Survey

TL;DR

This paper reports the discovery and spectroscopic analysis of the faintest known L subdwarf in the UKIRT Infrared Deep Sky Survey, expanding the catalog of such objects and providing initial estimates of their space density.

Contribution

It presents the first identification of an L subdwarf in UKIRT data, including spectroscopic confirmation and spectral classification, along with a preliminary space density estimate.

Findings

Identified the faintest L subdwarf to date.

Spectroscopic features consistent with mid-L subdwarfs.

Estimated space density of mid-L subdwarfs as 1.5x10^(-4) pc^(-3).

Abstract

We present the discovery of an L subdwarf in 234 square degrees common to the UK Infrared Telescope (UKIRT) Infrared Deep Sky Survey Large Area Survey Data Release 2 and the Sloan Digital Sky Survey Data Release 3. This is the fifth L subdwarf announced to date, the first one identified in the UKIRT Infrared Deep Sky Survey, and the faintest known. The blue optical and near-infrared colors of ULAS J135058.86+081506.8 and its overall spectra energy distribution are similar to the known mid-L subdwarfs. Low-resolution optical (700-1000 nm) spectroscopy with the Optical System for Imaging and low Resolution Integrated Spectroscopy spectrograph on the 10.4 m Gran Telescopio de Canarias reveals that ULAS J135058.86+081506.8 exhibits a strong KI pressure-broadened line at 770 nm and a red slope longward of 800 nm, features characteristics of L-type dwarfs. From direct comparison with the four known L subdwarfs, we estimate its spectral type to be sdL4-sdL6 and derive a distance in the interval 94-170 pc. We provide a rough estimate of the space density for mid-L subdwarfs of 1.5x10^(-4) pc^(-3).