We estimate the mass of the intermediate-mass black hole at the heart of the dwarf elliptical galaxy NGC 404 using Atacama Large Millimeter/submillimeter Array( ALMA) observations of the molecular interstellar medium at an unprecedented linear resolution of ≈0.5pc, in combination with existing stellar kinematic information. These ALMA observations reveal a central disc/torus of molecular gas clearly rotating around the black hole. This disc is surrounded by a morphologically and kinematically complex flocculent distribution of molecular clouds, that we resolve in detail. Continuum emission is detected from the central parts of NGC404, likely arising from the Rayleigh–Jeans tail of emission from dust around the nucleus, and potentially from dusty massive star-forming clumps at discrete locations in the disc. Several dynamical measurements of the black hole mass in this system have been made in the past, but they do not agree. We show here that both the observed molecular gas and stellar kinematics independently require a ≈5×105M black hole once we include the contribution of the molecular gas to the potential. Our best estimate comes from the high-resolution molecular gas kinematics, suggesting the black hole mass of this system is 5.5+4.1 −3.8×105 M (at the 99% confidence level), in good agreement with our revised stellar kinematic measurement and broadly consistent with extrapolations from the black hole mass–velocity dispersion and black hole mass – bulge mass relations. This highlights the need to accurately determine the mass and distribution of each dynamically important component around intermediate-mass black holes when attempting to estimate their masses.

中文翻译：

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用亚秒差距分辨率的 ALMA 观测揭示矮星系 NGC 404 中心的中等质量黑洞

我们使用阿塔卡马大型毫米波/亚毫米波阵列 (ALMA) 以前所未有的线性分辨率 ≈0.5pc 对分子星际介质进行观测，并结合使用，估计了矮椭圆星系 NGC 404 中心的中等质量黑洞的质量。现有的恒星运动信息。这些 ALMA 观测揭示了一个明显围绕黑洞旋转的分子气体的中心圆盘/圆环。这个圆盘被分子云的形态学和运动学复杂的絮状分布所包围，我们对此进行了详细解析。从 NGC404 的中心部分检测到连续发射，可能来自于核周围尘埃发射的瑞利-金斯尾，也可能来自盘中离散位置的多尘大质量恒星形成团块。过去曾对该系统中的黑洞质量进行过多次动力学测量，但结果不一致。我们在这里表明，一旦我们包括分子气体对势能的贡献，观察到的分子气体和恒星运动学都独立地需要一个 ≈5×105M 的黑洞。我们最好的估计来自高分辨率分子气体运动学，表明该系统的黑洞质量为 5.5+4.1 -3.8×105 M（在 99% 的置信水平），与我们修正的恒星运动学测量结果非常一致，并且广泛地与黑洞质量-速度色散和黑洞质量-膨胀质量关系的推断一致。