Expanding the Y Dwarf Census with Spitzer Follow-up of the Coldest CatWISE Solar Neighborhood Discoveries

Abstract

We present Spitzer 3.6$\mu$m and 4.5$\mu$m follow-up of 170 candidate extremely cool brown dwarfs newly discovered via the combination of WISE and NEOWISE imaging at 3$-$5$\mu$m. CatWISE, a joint analysis of archival WISE and NEOWISE data, has improved upon the motion measurements of AllWISE by leveraging a $>$10$\times$ time baseline enhancement, from 0.5 years (AllWISE) to 6.5 years (CatWISE). As a result, CatWISE motion selection has yielded a large sample of previously unrecognized brown dwarf candidates, many of which have archival detections exclusively in the WISE 4.6$\mu$m (W2) channel, suggesting that they could be both exceptionally cold and nearby. Where these objects go undetected in WISE W1 (3.4$\mu$m), Spitzer can provide critically informative detections at 3.6$\mu$m. Of our motion-confirmed discoveries, seventeen have a best-fit Spitzer [3.6]$-$[4.5] color most consistent with spectral type Y. CWISEP J144606.62$-$231717.8 ($\mu \approx 1.3^{\prime \prime }$/yr) is likely the reddest, and therefore potentially coldest, member of our sample with a very uncertain [3.6]$-$[4.5] color of 3.71 $\pm$ 0.44 magnitudes. We also highlight our highest proper motion discovery, WISEA J153429.75$-$104303.3, with $\mu \approx 2.7^{\prime \prime }$/yr. Given that the prior list of confirmed and presumed Y dwarfs consists of just 27 objects, the Spitzer follow-up presented in this work has substantially expanded the sample of identified Y dwarfs. Our new discoveries thus represent significant progress toward understanding the bottom of the substellar mass function, investigating the diversity of the Y dwarf population, and selecting optimal brown dwarf targets for JWST spectroscopy.

accepted for publication in ApJ

References in corpus (14)

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Cited by in corpus (21)

• The CatWISE2020 Catalog
• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project
• Self-consistent Models of Y Dwarf Atmospheres with Water Clouds and Disequilibrium Chemistry
• unTimely: a Full-sky, Time-Domain unWISE Catalog
• WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5: The First Extreme T-type Subdwarfs?
• The Fifth Catalogue of Nearby Stars (CNS5)
• Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs
• Methane Emission From a Cool Brown Dwarf
• WISEA J083011.95+283716.0: A Missing Link Planetary-Mass Object
• The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (aka "The Accident")
• VIRAC2: NIR Astrometry and Time Series Photometry for 500M+ Stars from the VVV and VVVX Surveys
• Physical properties and trigonometric distance of the peculiar dwarf WISE J181005.5$-$101002.3
• An Improved Near-Infrared Spectrum of the Archetype Y Dwarf WISEP J182831.08+265037.8
• Discovery of CWISE J052306.42-015355.4, an Extreme T Subdwarf Candidate
• Physical Parameters and Properties of 20 Cold Brown Dwarfs in JWST
• New Candidates for Planetary-mass Brown Dwarfs in IC 348
• Silicate Precursor Silane detected in Cold Low-Metallicity Brown Dwarf
• Discovery of 16 New Members of the Solar Neighborhood using Proper Motions from CatWISE2020
• Optical constraints on the coldest metal-poor population
• A search for millimeter emission from the coldest and closest brown dwarf with ALMA