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

Abstract

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 MCMC = (5.4 ± 1.2) × 106 M⊙ and effective (half-mass) radius rCMC,e = 11.2 ± 2.8 pc, co-spatial with a nuclear star cluster (NSC) of mass MNSC = (1.67 ± 0.48) × 107 M⊙ and effective radius rNSC,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 MBH and MNSC estimates for NGC 3593 agree well with the recently compiled MBH–MNSC scaling relation. Although the MNSC uncertainty is twice the inferred MBH, 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 MNSC is at the upper end of its allowed range, the evidence for a BH does not vanish, but remains with a lower limit of MBH > 3 × 105 M⊙.

ALMA Gas-dynamical Mass Measurement of the Supermassive Black Hole in the Red Nugget Relic Galaxy PGC 11179

“…Our values of ξ are comparable to those for several other ALMA molecular gas-dynamical M BH measurements, which usually range from ∼1 to 2 (e.g., Barth et al 2016b;Davis et al 2017Davis et al , 2018Onishi et al 2017;Smith et al 2019Smith et al , 2021Nguyen et al 2020;Cohn et al 2021;Kabasares et al 2022), although there are also some measurements with ξ < 1 (e.g., Onishi et al 2015;Thater 2019;Nguyen et al 2022). Currently, there are only a couple of measurements that highly resolve the BH SOI (ξ > 10; Boizelle et al 2019;North et al 2019).…”

“…A majority of M BH measurements have been made by modeling stellar orbits, but recently there has been a substantial increase in the number of molecular gas-dynamical determinations with the Atacama Large Millimeter/submillimeter Array (ALMA; e.g., Barth et al 2016a;Davis et al 2017;Boizelle et al 2019Boizelle et al , 2021Nagai et al 2019;North et al 2019;Cohn et al 2021;Smith et al 2021;Kabasares et al 2022;Nguyen et al 2022;Ruffa et al 2023). The rise in the number of molecular gas-dynamical M BH measurements is due to the significant enhancements in sensitivity and angular resolution of ALMA over the previous generation of millimeter/ submillimeter interferometers, coupled with the fact that the cold molecular gas exhibits less turbulent motion than the traditionally used ionized (e.g., Barth et al 2001;Walsh et al 2010Walsh et al , 2013 and warm H 2 molecular gas (e.g., Wilman et al 2005;Neumayer et al 2007;Seth et al 2010;Scharwächter et al 2013) and is thus better suited for dynamical modeling.…”

Simulating supermassive black hole mass measurements for a sample of ultra massive galaxies using ELT/HARMONI high spatial resolution integral-field stellar kinematics

“…As a sanity check, we used the Image Reduction and Analysis Facility (IRAF) ellipse task (Jedrzejewski 1987) to extract radial surface-brightness profiles of the stars in concentric annuli with varying position angles and ellipticities (although keeping both fixed does not change our results (Nguyen et al 2022)). We then fit these stellar radial light surface-brightness profiles with a core-Sérsic function.…”

“…This stellar-mass component will be added in an SMBH or an MMBH with a specific mass as a point source. In this work, we ignored (1) the possible variation in 𝑀/𝐿 inferred from stellar population variation (McConnell et al 2013;Mitzkus et al 2017;Li et al 2017;Nguyen et al 2017Nguyen et al , 2018Nguyen et al , 2019Nguyen et al 2020Nguyen et al , 2021Nguyen et al , 2022Thater et al 2022) due to the lack of spatial resolution of Pan-STARRS observations and (2) the distribution of dark matter halo (Navarro et al 1996) as we concern the stellar kinematics within the FOV of 0. 2 × 0.…”