The MBHBM_⋆ Project. I. Measurement of the Central Black Hole Mass in Spiral Galaxy NGC 3504 Using Molecular Gas Kinematics

Abstract

We present a dynamical-mass measurement of the supermassive black hole (SMBH) in the nearby double-barred spiral galaxy NGC 3504 as part of the Measuring Black Holes in Below Milky Way (M ⋆) mass galaxies (MBHBM ⋆) Project. Our analysis is based on Atacama Large Millimeter/submillimeter Array (ALMA) Cycle-5 observations of the 12 CO(2 − 1) emission line. These observations probe NGC 3504's circumnuclear gas disk (CND). Our dynamical model of the CND simultaneously constrains a black hole (BH) mass of 1.6 +0.6 −0.4 × 10 7 M ⊙ , which is consistent with the empirical BH-galaxy scaling relations, and a mass-to-light ratio in H-band of 0.44 ± 0.12 (M ⊙ /L ⊙). This measurement also relies on our new distant estimation to the galaxy of 32.4 ± 2.1 Mpc using the surface brightness fluctuation method (SBF), which is much further than the existing distant estimates. Additionally, our observations detect a central deficit in the 12 CO(2 − 1) integrated intensity map with a diameter of 6.3 pc at the putative position of the SMBH. However, we find a dense gas tracer CS(5 − 4) peaks at the galaxy center, filling in the 12 CO(2 − 1)-attenuated hole. Holes like this one are observed in other galaxies, and our observations suggest these may be caused by changing excitation conditions rather than a true absence of molecular gas around the nucleus.

Revealing the intermediate-mass black hole at the heart of the dwarf galaxy NGC 404 with sub-parsec resolution ALMA observations

“…Left panel: M BH -σ e relation (grey data points and black dashed line) from the compilation of van den Bosch (2016). We show the BH mass measured for NGC 404 here as a large blue data point, and highlight other measurements using the molecular gas technique with red data points (Davis et al 2013b;Onishi et al 2015;Barth et al 2016a,b;Onishi et al 2017;Davis et al 2017Davis et al , 2018Combes et al 2019;Smith et al 2019;Nagai et al 2019;North et al 2019;Boizelle et al 2019;Nguyen et al 2020). In yellow we show the BH masses of low-mass galaxies measured in Nguyen et al (2019).…”

“…The red dashed line shows the stellar contribution with Γ = 0.89 (as found by Nguyen et al 2017), that would provide a good fit to the total mass enclosed if one did not know about the presence of molecular gas (that contributes significantly to the enclosed mass, especially at larger radii). Smith et al 2019;North et al 2019;Combes et al 2019;Boizelle et al 2019;Nagai et al 2019;Nguyen et al 2020). In this Section, we employ this technique to obtain an independent measurement of the mass of the IMBH in NGC 404.…”

“…This tool allows input guesses for the true gas distribution and kinematics and, assuming the gas is in circular rotation, produces a simulated data cube that can be compared to the observed data cube (taking into account the effects of beamsmearing, spatial and velocity binning, disc thickness, gas velocity dispersion, etc.). This tool has been applied to estimate BH masses in various other works (Onishi et al 2017;Davis et al 2017Davis et al , 2018Smith et al 2019;North et al 2019;Nguyen et al 2020), each of which has iteratively improved the technique. We highlight the important aspects of this fitting procedure below.…”

WISDOM project – VII. Molecular gas measurement of the supermassive black hole mass in the elliptical galaxy NGC 7052

“…Barth et al 2016a,b;Boizelle et al 2019;Nagai et al 2019;Thater et al 2020). Notably, using this method, robust constraints have even been placed on a few SMBH masses in dwarf galaxies (Nguyen et al 2020;Davis et al 2020).…”

WISDOM project – VI. Exploring the relation between supermassive black hole mass and galaxy rotation with molecular gas

“…Other groups have also used the same method to constrain SMBH masses (e.g. Onishi et al 2015;Barth et al 2016a,b;Boizelle et al 2019;Nagai et al 2019;Ruffa et al 2019;Nguyen et al 2020). In addition to measuring SMBH masses, the same data can be used to investigate the physical state of the molecular gas and study giant molecular clouds (Utomo et al 2015;Liu et al in preparation).…”