The MBHBM^⋆ Project - II. Molecular gas kinematics in the lenticular galaxy NGC 3593 reveal a supermassive black hole

Dieu D. Nguyen , Martin Bureau , Sabine Thater , Kristina Nyland , Mark den Brok , Michele Cappellari , Timothy A. Davis , Jenny E. Greene , Nadine Neumayer , Masatoshi Imanishi , Takuma Izumi , Taiki Kawamuro , Shunsuke Baba , Phuong M. Nguyen , Satoru Iguchi , Takafumi Tsukui , T. N. Lam (1) , Than Ho

1 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics

As part of the Measuring Black Holes in below Milky Way-mass (M^⋆) galaxies (MBHBM^⋆) Project, we present a dynamical measurement of the supermassive black hole (SMBH) mass in the nearby lenticular galaxy NGC 3593, using cold molecular gas ¹²CO(2-1) emission observed at an angular resolution of ≍0${_{.}^{\prime\prime}}$3 (≍10 pc) with the Atacama Large Millimeter/submillimeter Array (ALMA). Our ALMA observations reveal a circumnuclear molecular gas disc (CND) elongated along the galaxy major axis and rotating around the SMBH. This CND has a relatively low-velocity dispersion (≲10 km s^-1) and is morphologically complex, with clumps having higher integrated intensities and velocity dispersions (≲25 km s^-1). These clumps are distributed along the ridges of a two-arm/bi-symmetric spiral pattern surrounded by a larger ring-like structure (radius r ≍ 10 arcsec or ≍350 pc). This pattern likely plays an important role to bridge the molecular gas reservoirs in the CND and beyond (10 ≲ r ≲ 35 arcsec or 350 pc ≲ r ≲ 1.2 kpc). Using dynamical modelling, the molecular gas kinematics allow us to infer an SMBH mass $M_{\rm BH}=2.40_{-1.05}^{+1.87}\times 10^6$ M_⊙ (only statistical uncertainties at the 3σ level). We also detect a massive core of cold molecular gas (CMC) of mass M_CMC = (5.4 ± 1.2) × 10⁶ M_⊙ and effective (half-mass) radius r_CMC,e = 11.2 ± 2.8 pc, co-spatial with a nuclear star cluster (NSC) of mass M_NSC = (1.67 ± 0.48) × 10⁷ M_⊙ and effective radius r_NSC,e = 5.0 ± 1.0 pc (or 0${_{.}^{\prime\prime}}$15 ± 0${_{.}^{\prime\prime}}$03). The mass profiles of the CMC and NSC are well described by Sérsic functions with indices 1-1.4. Our M_BH and M_NSC estimates for NGC 3593 agree well with the recently compiled M_BH-M_NSC scaling relation. Although the M_NSC uncertainty is twice the inferred M_BH, the rapid central rise of the rotation velocities of the CND (as the radius decreases) clearly suggests an SMBH. Indeed, our dynamical models show that even if M_NSC is at the upper end of its allowed range, the evidence for a BH does not vanish, but remains with a lower limit of M_BH > 3 × 10⁵ M_⊙.

Mots clés: galaxies: ISM; galaxies: kinematics and dynamics; galaxies: nuclei; ISM: molecules; (galaxies:) quasars: supermassive black holes; Astrophysics - Astrophysics of Galaxies; Galaxy: disc

Domaines: Planète et Univers [physics]

Dieu D. Nguyen, Martin Bureau, Sabine Thater, Kristina Nyland, Mark den Brok, et al.. The MBHBM^⋆ Project - II. Molecular gas kinematics in the lenticular galaxy NGC 3593 reveal a supermassive black hole. Monthly Notices of the Royal Astronomical Society, 2022, 509, pp.2920-2939. ⟨10.1093/mnras/stab3016⟩. ⟨insu-03713343⟩