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

Kirkpatrick, J. Davy and Gelino, Christopher R. and Faherty, Jacqueline K. and Meisner, Aaron M. and Caselden, Dan and Schneider, Adam C. and Marocco, Federico and Cayago, Alfred J. and Smart, R. L. and Eisenhardt, Peter R. and Kuchner, Marc J. and Wright, Edward L. and Cushing, Michael C. and Allers, Katelyn N. and Bardalez Gagliuffi, Daniella C. and Burgasser, Adam J. and Gagné, Jonathan and Logsdon, Sarah E. and Martin, Emily C. and Ingalls, James G. and Lowrance, Patrick J. and Abrahams, Ellianna S. and Aganze, Christian and Gerasimov, Roman and Gonzales, Eileen C. and Hsu, Chih-Chun and Kamraj, Nikita and Kiman, Rocio and Rees, Jon and Theissen, Christopher and Ammar, Kareem and Andersen, Nikolaj Stevnbak and Beaulieu, Paul and Colin, Guillaume and Elachi, Charles A. and Goodman, Samuel J. and Gramaize, Léopold and Hamlet, Leslie K. and Hong, Justin and Jonkeren, Alexander and Khalil, Mohammed and Martin, David W. and Pendrill, William and Pumphrey, Benjamin and Rothermich, Austin and Sainio, Arttu and Stenner, Andres and Tanner, Christopher and Thévenot, Melina and Voloshin, Nikita V. and Walla, Jim and Wędracki, Zbigniew (2021) The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs. Astrophysical Journal Supplement Series, 253 (1). Art. No. 7. ISSN 0067-0049.

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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_(eff) value and judge sample completeness over bins of T_(eff) and spectral type. Except for types ≥T8 and T_(eff) < 600 K, 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∝M^(−α)) with α = 0.6 ± 0.1. We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200 K < T_(eff) < 1350 K, 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 ≥Y0.5 and with T_(eff) < 400 K. 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kirkpatrick, J. Davy0000-0003-4269-260X
Faherty, Jacqueline K.0000-0001-6251-0573
Meisner, Aaron M.0000-0002-1125-7384
Caselden, Dan0000-0001-7896-5791
Schneider, Adam C.0000-0002-6294-5937
Marocco, Federico0000-0001-7519-1700
Smart, R. L.0000-0002-4424-4766
Kuchner, Marc J.0000-0002-2387-5489
Wright, Edward L.0000-0001-5058-1593
Cushing, Michael C.0000-0001-7780-3352
Allers, Katelyn N.0000-0003-0580-7244
Bardalez Gagliuffi, Daniella C.0000-0001-8170-7072
Burgasser, Adam J.0000-0002-6523-9536
Gagné, Jonathan0000-0002-2592-9612
Logsdon, Sarah E.0000-0002-9632-9382
Martin, Emily C.0000-0002-0618-5128
Ingalls, James G.0000-0003-4714-1364
Lowrance, Patrick J.0000-0001-8014-0270
Abrahams, Ellianna S.0000-0002-9879-1183
Gonzales, Eileen C.0000-0003-4636-6676
Hsu, Chih-Chun0000-0002-5370-7494
Kamraj, Nikita0000-0002-3233-2451
Kiman, Rocio0000-0003-2102-3159
Theissen, Christopher0000-0002-9807-5435
Andersen, Nikolaj Stevnbak0000-0003-4714-3829
Colin, Guillaume0000-0002-7630-1243
Goodman, Samuel J.0000-0003-2236-2320
Gramaize, Léopold0000-0002-8960-4964
Hamlet, Leslie K.0000-0002-7389-2092
Jonkeren, Alexander0000-0003-3743-3320
Pumphrey, Benjamin0000-0001-9692-7908
Rothermich, Austin0000-0003-4083-9962
Sainio, Arttu0000-0003-4864-5484
Thévenot, Melina0000-0001-5284-9231
Additional Information:© 2021. The American Astronomical Society. Received 2020 October 11; revised 2020 November 12; accepted 2020 November 22; published 2021 February 23. This publication makes use of data products from WISE, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech), funded by the National Aeronautics and Space Administration (NASA). Work in this paper is based on observations made with the Spitzer Space Telescope, which is operated by JPL/Caltech, under a contract with NASA. Support for this work was provided to J.D.K. by NASA through a Cycle 14 award issued by JPL/Caltech. Some of the data presented here were obtained at the W. M. Keck observatory, which is operated as a scientific partnership among Caltech, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Results here are partly based on observations obtained at the Hale Telescope, Palomar Observatory, as part of a continuing collaboration between Caltech, NASA/JPL, Yale University, and the National Astronomical Observatories of China. We would like to thank SURF students Tea Freedman-Susskind, Emily Zhang, Yerong Xu, and Feiyang Liu for help with the spectroscopic observation of WISE 2126+2530 from Palomar. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research has made use of IRSA, which is operated by JPL/Caltech, under contract with NASA. This research has also made use of the SIMBAD database, operated at CDS, Strasbourg, France. Federico Marocco acknowledges support from grant #80NSSC20K0452 under the NASA Astrophysics Data Analysis Program. Alfred Cayago gratefully acknowledges financial support through the Fellowships and Internships in Extremely Large Data Sets (FIELDS) Program, a National Aeronautics and Space Administration (NASA) science/technology/engineering/math (STEM) grant administered by the University of California, Riverside. Emily Martin is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1801978. Eileen Gonzales acknowledges support from an LSSTC Data Science Fellowship. Christopher Theissen acknowledges support for this work through NASA Hubble Fellowship grant HST-HF2-51447.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. The Backyard Worlds: Planet 9 team thanks Zooniverse volunteers who have participated in the project. Backyard Worlds research was supported by NASA grant 2017-ADAP17-0067 and by the NSF under grants AST-2007068, AST-2009177, and AST-2009136. CatWISE is led by JPL/Caltech, with funding from NASA's Astrophysics Data Analysis Program. This research was partly carried out at JPL/Caltech, under contract with NASA. We thank the referee for a quick report despite difficulties imposed by the current pandemic. Facilities: Spitzer(IRAC) - Spitzer Space Telescope satellite, WISE - , Gaia - , IRSA - , CTIO:2MASS - , FLWO:2MASS - , Blanco(NEWFIRM - , ARCoIRIS) - , SO:Kuiper(2MASS), Gemini:South(FLAMINGOS-2) - , Magellan:Baade(PANIC - , FIRE) - , FLWO:2MASS - , Hale(WIRC - , DBSP) - , SOAR(OSIRIS) - , DCT(NIHTS), Keck:II(NIRES) - , IRTF(SpeX) - , HST(WFC3). - Software: IDL (, MOPEX/APEX (, mpfit (Markwardt 2009), WiseView (Caselden et al. 2018).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
University of California, RiversideUNSPECIFIED
NSF Astronomy and Astrophysics FellowshipAST-1801978
Large Synoptic Survey Telescope CorporationUNSPECIFIED
NASA Hubble FellowshipHST-HF2-51447.001-A
Heising-Simons Foundation51 Pegasi b Fellowship
Subject Keywords:Stellar mass functions; Trigonometric parallax; Brown dwarfs; Solar neighborhood; Absolute magnitude; Stellar effective temperatures; L dwarfs; T dwarfs; Y dwarfs; Stellar classification; Binary stars; Two-color diagrams
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Stellar mass functions (1612); Trigonometric parallax (1713); Brown dwarfs (185); Solar neighborhood (1509); Absolute magnitude (10); Stellar effective temperatures (1597); L dwarfs (894); T dwarfs (1679); Y dwarfs
Record Number:CaltechAUTHORS:20210413-125137820
Persistent URL:
Official Citation:J. Davy Kirkpatrick et al 2021 ApJS 253 7
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108716
Deposited By: Tony Diaz
Deposited On:13 Apr 2021 21:56
Last Modified:19 Apr 2021 22:33

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