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arXiv · 2110.07672

Beyond the Local Volume. I. Surface Densities of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields

Christian Aganze·Adam J Burgasser·Mathew Malkan·Christopher A Theissen·Roberto A Tejada Arevalo·Chih-Chun Hsu·Daniella C Bardalez Gagliuffi·Russell E Ryan Jr·Benne Holwerda
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Abstract

Ultracool dwarf stars and brown dwarfs provide a unique probe of large-scale Galactic structure and evolution; however, until recently spectroscopic samples of sufficient size, depth, and fidelity have been unavailable. Here, we present the identification of 164 M7--T9 ultracool dwarfs in 0.6~deg$^2$ of deep, low-resolution, near-infrared spectroscopic data obtained with the Hubble Space Telescope Wide Field Camera 3 instrument as part of the WFC3 Infrared Spectroscopic Parallel Survey and the 3D-HST survey. We describe the methodology by which we isolate ultracool dwarf candidates from over 200,000 spectra, and show that selection by machine learning classification is superior to spectral index-based methods in terms of completeness and contamination. We use the spectra to accurately determine classifications and spectrophotometric distances, the latter reaching to ~2 kpc for L dwarfs and ~400pc for T dwarfs.

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Christian Aganze, Adam J Burgasser, Mathew Malkan, Christopher A Theissen, Roberto A Tejada Arevalo, Chih-Chun Hsu, Daniella C Bardalez Gagliuffi, Russell E Ryan Jr, Benne Holwerda. 2021-10-14. Beyond the Local Volume. I. Surface Densities of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields. https://doi.org/10.3847/1538-4357/ac35ea

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