The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs

Abstract

We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of color-magnitude and color-color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a $T_{\mathrm{eff}}$ value and judge sample completeness over bins of $T_{\mathrm{eff}}$ and spectral type. Except for types $\ge$ T8 and $T_{\mathrm{eff}}<$ 600K, our census is statistically complete to the 20-pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law ($dN/dM\propto M^{-\alpha }$) with $\alpha =0.6\pm 0.1$. We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200K $<T_{\mathrm{eff}}<$ 1350K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs $\ge$Y0.5 and with $T_{\mathrm{eff}}<$ 400K. We conclude that such frigid objects must exist in substantial numbers, despite the fact that few have so far been identified, and we discuss possible reasons why they have largely eluded detection.

101 pages, 31 figures, accepted for publication in the Astrophysical Journal Supplement Series

References in corpus (88)

• Power-law distributions in empirical data
• The Gaia mission
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The James Webb Space Telescope
• Initial Performance of the NEOWISE Reactivation Mission
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• The UKIDSS Galactic Plane Survey
• The Solar Neighborhood XVII: Parallax Results from the CTIOPI 0.9m Program -- Twenty New Members of the RECONS 10 Parsec Sample
• unWISE: unblurred coadds of the WISE imaging
• No large population of unbound or wide-orbit Jupiter-mass planets
• The CatWISE2020 Catalog
• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• Meeting the Cool Neighbors. IX. The Luminosity Function of M7-L8 Ultracool Dwarfs in the Field
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• Activity and Kinematics of Ultracool Dwarfs Including An Amazing Flare Observation
• Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun
• Spitzer/IRAC Photometry of M, L, and T Dwarfs
• Discovery of a young planetary mass companion to the nearby M dwarf VHS J125601.92-125723.9
• Discovery of 11 New T Dwarfs in the Two Micron All-Sky Survey, Including a Possible L/T Transition Binary
• Discovery of Two Nearby, Peculiar L Dwarfs from the 2MASS Proper Motion Survey: Young or Metal-Rich?
• The UKIRT Hemisphere Survey: Definition and J-band Data Release
• The Solar Neighborhood XXXV: Distances to 1404 M Dwarf Systems Within 25 pc in the Southern Sky
• A search for binary systems among the nearest L dwarfs
• Clouds, Gravity and Metallicity in Blue L dwarfs: The Case of 2MASS J11263991-5003550
• The VISTA ZYJHKs Photometric System: Calibration from 2MASS
• CFBDS J005910.90-011401.3: reaching the T-Y Brown Dwarf transition?
• BANYAN. IV. Fundamental parameters of low-mass star candidates in nearby young stellar kinematic groups - Isochronal Age determination using Magnetic evolutionary models
• A very cool brown dwarf in UKIDSS DR1
• A Cross-Match of 2MASS and SDSS: Newly-Found L and T Dwarfs and an Estimate of the Space Densitfy of T Dwarfs
• SpeX Spectroscopy of Unresolved Very Low Mass Binaries. II. Identification of Fourteen Candidate Binaries with Late-M/Early-L and T Dwarf Components
• The discovery of an M4+T8.5 binary system
• Exploring the substellar temperature regime down to ~550K
• Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer
• Physical and Spectral Characteristics of the T8 and Later-Type Dwarfs
• All-sky Co-moving Recovery Of Nearby Young Members. (ACRONYM) II: The Beta Pictoris Moving Group
• HD3651B: the first directly imaged brown dwarf companion of an exoplanet host star
• Discovery of a T Dwarf Binary with the Largest Known J-Band Flux Reversal
• The Solar Neighborhood. XXI. Parallax Results from the CTIOPI 0.9m Program: 20 New Members of the 25 Parsec White Dwarf Sample
• Discovery of new nearby L and late-M dwarfs at low Galactic latitude from the DENIS database
• LACEwING: A New Moving Group Analysis Code
• A Search for L/T Transition Dwarfs With Pan-STARRS1 and WISE. II. L/T Transition Atmospheres and Young Discoveries
• Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey
• A large spectroscopic sample of L and T dwarfs from UKIDSS LAS: peculiar objects, binaries, and space density
• Wide, Cool and Ultracool Companions to Nearby Stars from Pan-STARRS1
• Primeval very low-mass stars and brown dwarfs. I. Six new L subdwarfs, classification and atmospheric properties
• The Luminosities of the Coldest Brown Dwarfs
• The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 dwarfs with UKIRT
• Space Velocities of L- and T-type Dwarfs
• WISEP J004701.06+680352.1: An intermediate surface gravity, dusty brown dwarf in the AB Dor Moving Group
• An Infrared High Proper Motion Survey Using 2MASS and SDSS: Discovery of M, L and T Dwarfs
• Discovery of a High Proper Motion L Dwarf Binary: 2MASS J15200224-4422419AB
• Signatures of Cloud, Temperature, and Gravity From Spectra of the Closest Brown Dwarfs
• Dynamical Mass of GJ 802B: a brown dwarf in a triple system
• New, nearby bright southern ultracool dwarfs
• The Young L Dwarf 2MASS J11193254-1137466 is a Planetary-Mass Binary
• Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project
• Expanding the Y Dwarf Census with Spitzer Follow-up of the Coldest CatWISE Solar Neighborhood Discoveries
• Discovery of a nearby L-T transition object in the Southern Galactic plane
• Characterization of High Proper Motion Objects from the Wide-field Infrared Survey Explorer
• WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun
• The Gaia Ultra-Cool Dwarf Sample -- II: Structure at the end of the main sequence
• Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs
• Indications of Water Clouds in the Coldest Known Brown Dwarf
• WISEA J041451.67-585456.7 and WISEA J181006.18-101000.5: The First Extreme T-type Subdwarfs?
• Resolved Spectroscopy of M Dwarf/L Dwarf Binaries. II. 2MASS J 17072343-0558249AB
• Discovery of a Low-Luminosity, Tight Substellar Binary at the T/Y Transition
• A Brown Dwarf Census from the SIMP Survey
• FLAMINGOS-2: The Facility Near-Infrared Wide-field Imager & Multi-Object Spectrograph for Gemini
• CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs
• Discovery of a new Y dwarf: WISE J030449.03-270508.3
• WISEA J083011.95+283716.0: A Missing Link Planetary-Mass Object
• NEOWISE-R Observation of the Coolest Known Brown Dwarf
• A Reanalysis of the Fundamental Parameters and Age of TRAPPIST-1
• The very nearby M/T dwarf binary SCR 1845-6357
• Individual, Model-Independent Masses of the Closest Known Brown Dwarf Binary to the Sun
• 2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary
• High Proper Motion Objects from the UKIDSS Galactic Plane Survey
• Improved infrared photometry and a preliminary parallax measurement for the extremely cold brown dwarf CWISEP J144606.62$-$231717.8
• Low-resolution optical spectra of ultracool dwarfs with OSIRIS/GTC
• Optical Spectra of Ultracool Dwarfs with the Southern African Large Telescope
• 49 new T dwarfs identified using methane imaging
• The Lutz-Kelker Paradox
• Proper motions of field L and T dwarfs -II
• WISEA J064750.85-154616.4: a new nearby L/T transition dwarf
• Evidence of a substellar companion to AB Dor C

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• JWST Observations of the Enigmatic Y Dwarf WISE 1828+2650: I. Limits to a Binary Companion
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• A Search for Predicted Astrometric Microlensing Events by Nearby Brown Dwarfs
• Search for Brown Dwarfs in IC 1396 with Subaru HSC: Interpreting the Impact of Environmental Factors on Sub-stellar Population
• Ultracool dwarfs candidates based on six years of the Dark Energy Survey data
• Probing the Milky Way stellar and brown dwarf initial mass function with modern microlensing observations
• CWISE J014611.20-050850.0AB: The Widest Known Brown Dwarf Binary in the Field
• LSST Survey Strategies and Brown Dwarf Parallaxes
• X-SHYNE: X-Shooter spectra of young exoplanet analogs II. Presentation and analysis of the full library
• Primeval very low-mass stars and brown dwarfs -- VIII. The first age benchmark L subdwarf, a wide companion to a halo white dwarf
• COol Companions ON Ultrawide orbiTS (COCONUTS). III. A Very Red L6 Benchmark Brown Dwarf around a Young M5 Dwarf
• The Sonora Substellar Atmosphere Models VI. Red Diamondback: Extending Diamondback with SPHINX for Brown Dwarf Early Evolution
• Long-term 4.6$\mu$m Variability in Brown Dwarfs and a New Technique for Identifying Brown Dwarf Binary Candidates
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• Near-infrared spectroscopic characterisation of Gaia ultra-cool dwarf candidates; Spectral types and peculiarities
• The Sonora Brown Dwarf Atmosphere and Evolution Models I. Model Description and Application to Cloudless Atmospheres in Rainout Chemical Equilibrium
• The Gaia Ultracool Dwarf Sample -- IV. GTC/OSIRIS optical spectra of Gaia late-M and L dwarfs
• Identifying and characterizing ultracool dwarfs ejected from post-encounter disintegrating systems
• Direct Imaging Discovery of Giant Exoplanet $\beta$ Pictoris d: A Decade-Long Game of Hide-and-Seek
• Atmospheric model-trained machine learning selection and classification of ultracool TY dwarfs
• WISEA J052305.94-015356.1: A New EsdT Candidate
• Silicate Clouds, SiO, and Molecular Trends across the L-T Sequence: A JWST/MIRI LRS Spectral Library of Brown Dwarfs
• Enhanced thermal radiation from a tidally heated exomoon with a single hot spot
• Trigonometric parallaxes of two T dwarfs with Keck and ShaneAO astrometry
• Substellar Hyades Candidates from the UKIRT Hemisphere Survey
• Using Old and New Approaches: Determining Physical Properties of Brown Dwarfs with Empirical Relations and Machine Learning Models