The Initial Mass Function Based on the Full-sky 20-pc Census of $\sim$3,600 Stars and Brown Dwarfs

• DOI: 10.48550/arxiv.2312.03639
• Publication Date: 2023-01-01
• Authors: Kirkpatrick, J. Davy; Marocco, Federico; Gelino, Christoph...; Raghu, Yadukrishna; Faherty, Jacqueli...; Gagliuffi, Daniel...; Schurr, Steven D.; Apps, Kevin; Schneider, Adam C.; Meisner, Aaron M.; Kuchner, Marc J.; Caselden, Dan; Smart, R. L.; Casewell, S. L.; Raddi, Roberto; Kesseli, Aurora; Andersen, Nikolaj...; Antonini, Edoardo; Beaulieu, Paul; Bickle, Thomas P.; Bilsing, Martin; Chieng, Raymond; Colin, Guillaume; Deen, Sam; Dereveanco, Alexa...; Doll, Katharina; Luca, Hugo A. Dur...; Frazer, Anya; Gantier, Jean Marc; Gramaize, Léopold; Grant, Kristin; Hamlet, Leslie K.; Higashimura, Hiro; Hyogo, Michiharu; Jałowiczor, Peter A.; Jonkeren, Alexander; Kabatnik, Martin; Kiwy, Frank; Martin, David W.; Michaels, Mariann...; Pendrill, William; Machado, Celso Pe...; Pumphrey, Benjamin; Rothermich, Austin; Russwurm, Rebekah; Sainio, Arttu; Sanchez, John; Sapelkin-Tambling...; Schümann, Jörg; Selg-Mann, Karl; Singh, Harshdeep; Stenner, Andres; Sun, Guoyou; Tanner, Christopher; Thévenot, Melina; Ventura, Maurizio; Voloshin, Nikita V.; Walla, Jim; Wedracki, Zbigniew; Adorno, Jose I.; Aganze, Christian; Allers, Katelyn N.; Brooks, Hunter; Burgasser, Adam J.; Calamari, Emily; Connor, Thomas; Costa, Edgardo; Eisenhardt, Peter R.; Gagné, Jonathan; Gerasimov, Roman; Gonzales, Eileen C.; Hsu, Chih-Chun; Kiman, Rocio; Li, Guodong; Low, Ryan; Mamajek, Eric; Pantoja, Blake M.; Popinchalk, Mark; Rees, Jon M.; Stern, Daniel; Suárez, Genaro; Theissen, Christo...; Tsai, Chao-Wei; Vos, Johanna M.; Zurek, David; Worlds, The Backyard; Collaboration, Pl...
• Keywords: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics - Solar and Stellar Astrophysics; Astrophysics of Galaxies (astro-ph.GA); FOS: Physical sciences; Astrophysics - Astrophysics of Galaxies; Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics - Earth and Planetary Astrophysics

A complete accounting of nearby objects -- from the highest-mass white dwarf progenitors down to low-mass brown dwarfs -- is now possible, thanks to an almost complete set of trigonometric parallax determinations from Gaia, ground-based surveys, and Spitzer follow-up. We create a census of objects within a Sun-centered sphere of 20-pc radius and check published literature to decompose each binary or higher-order system into its separate components. The result is a volume-limited census of $\sim$3,600 individual star formation products useful in measuring the initial mass function across the stellar ($<8 M_\odot$) and substellar ($\gtrsim 5 M_{Jup}$) regimes. Comparing our resulting initial mass function to previous measurements shows good agreement above 0.8$M_\odot$ and a divergence at lower masses. Our 20-pc space densities are best fit with a quadripartite power law, $ξ(M) = dN/dM \propto M^{-α}$ with long-established values of $α= 2.3$ at high masses ($0.55 < M < 8.00 M_\odot$) and $α= 1.3$ at intermediate masses ($0.22 < M < 0.55 M_\odot$), but at lower masses we find $α= 0.25$ for $0.05 < M <0.22 M_\odot$ and $α= 0.6$ for $0.01 < M < 0.05 M_\odot$. This implies that the rate of production as a function of decreasing mass diminishes in the low-mass star/high-mass brown dwarf regime before increasing again in the low-mass brown dwarf regime. Correcting for completeness, we find a star to brown dwarf number ratio of, currently, 4:1, and an average mass per object of 0.41 $M_\odot$.<br/>Accepted for publication in The Astrophysical Journal Supplement Series. 123 pages with four ancillary files<br/>