The Initial Mass Function Based on the Full-sky 20 pc Census of ∼3600 Stars and Brown Dwarfs

April 2024 • 2024ApJS..271...55K

Authors • Kirkpatrick, J. Davy • Marocco, Federico • Gelino, Christopher R. • Raghu, Yadukrishna • Faherty, Jacqueline K. • Bardalez Gagliuffi, Daniella C. • 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 • Stevnbak Andersen, Nikolaj • Antonini, Edoardo • Beaulieu, Paul • Bickle, Thomas P. • Bilsing, Martin • Chieng, Raymond • Colin, Guillaume • Deen, Sam • Dereveanco, Alexandru • Doll, Katharina • Durantini Luca, Hugo A. • 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, Marianne N. • Pendrill, William • Pessanha Machado, Celso • Pumphrey, Benjamin • Rothermich, Austin • Russwurm, Rebekah • Sainio, Arttu • Sanchez, John • Sapelkin-Tambling, Fyodor Theo • Schümann, Jörg • Selg-Mann, Karl • Singh, Harshdeep • Stenner, Andres • Sun, Guoyou • Tanner, Christopher • Thévenot, Melina • Ventura, Maurizio • Voloshin, Nikita V. • Walla, Jim • Wędracki, 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, Christopher • Tsai, Chao-Wei • Vos, Johanna M. • Zurek, David • The Backyard Worlds: Planet 9 Collaboration

Abstract • 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 ∼3600 individual star formation products useful in measuring the initial mass function across the stellar (<8M _⊙) and substellar (≳5M _Jup) regimes. Comparing our resulting initial mass function to previous measurements shows good agreement above 0.8M _⊙ and a divergence at lower masses. Our 20 pc space densities are best fit with a quadripartite power law, $\xi (M)={dN}/{dM}\propto {M}^{-\alpha }$ , with long-established values of α = 2.3 at high masses (0.55 < M < 8.00M _⊙), and α = 1.3 at intermediate masses (0.22 < M < 0.55M _⊙), but at lower masses, we find α = 0.25 for 0.05 < M < 0.22M _⊙, and α = 0.6 for 0.01 < M < 0.05M _⊙. 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 _⊙.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2024ApJS..271...55K
• DATA http://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJS/271/55
• DATA http://archive.eso.org/bin/ads2eso?2024ApJS..271...55K
• DATA https://archive.gemini.edu/searchform/publication=2024ApJS..271...55K
• PREPRINT http://arxiv.org/abs/2312.03639
• ELECTR https://doi.org/10.3847%2F1538-4365%2Fad24e2