Dr Thomas Williams

Abstract:

We apply the Tremaine-Weinberg method to 19 nearby galaxies using stellar mass surface densities and velocities derived from the PHANGS-MUSE survey, to calculate (primarily bar) pattern speeds (ΩP). After quality checks, we find that around half (10) of these stellar-mass-based measurements are reliable. For those galaxies, we find good agreement between our results and previously published pattern speeds, and we use rotation curves to calculate major resonance locations (corotation radii and Lindblad resonances). We also compare these stellar-mass-derived pattern speeds with Hα (from MUSE) and CO(J = 2 - 1) emission from the PHANGS-ALMA survey. We find that in the case of these clumpy interstellar medium (ISM) tracers, this method erroneously gives a signal that is simply the angular frequency at a representative radius set by the distribution of these clumps (Ωclump), and that this Ωclump is significantly different from ΩP (∼20% in the case of Hα, and ∼50% in the case of CO). Thus, we conclude that it is inadvisable to use "pattern speeds"derived from ISM kinematics. Finally, we compare our derived pattern speeds and corotation radii, along with bar properties, to the global parameters of these galaxies. Consistent with previous studies, we find that galaxies with a later Hubble type have a larger ratio of corotation radius to bar length, more molecular-gas-rich galaxies have higher ΩP, and more bulge-dominated galaxies have lower ΩP. Unlike earlier works, however, there are no clear trends between the bar strength and ΩP, nor between the total stellar mass surface density and the pattern speed.

Abstract:

Supermassive black hole (SMBH) masses can be measured by resolving the dynamical influences of the SMBHs on tracers of the central potentials. Modern long-baseline interferometers have enabled the use of molecular gas as such a tracer. We present here Atacama Large Millimeter/submillimeter Array observations of the elliptical galaxy NGC 7052 at 0′′.11 (⁠37pc) resolution in the 12CO(2-1) line and 1.3 mm continuum emission. This resolution is sufficient to resolve the region in which the potential is dominated by the SMBH. We forward model these observations, using a multi-Gaussian expansion of a Hubble Space Telescope F814W image and a spatially constant mass-to-light ratio to model the stellar mass distribution. We infer an SMBH mass of 2.5±0.3×109M⊙ and a stellar I-band mass-to-light ratio of 4.6±0.2M⊙/L⊙,I (3σ confidence intervals). This SMBH mass is significantly larger than that derived using ionized gas kinematics, which however appears significantly more kinematically disturbed than the molecular gas. We also show that a central molecular gas deficit is likely to be the result of tidal disruption of molecular gas clouds due to the strong gradient in the central gravitational potential.

Abstract:

We present high-resolution (synthesized beam size 0′′..′′088 × 0′′..′′083 or 25 × 23 pc²) Atacama Large Millimetre/submillimetre Array ¹²CO(2–1) line and 236 GHz continuum observations, as well as 5 GHz enhanced Multi-Element Radio Linked Interferometer Network (e-MERLIN) continuum observations, of NGC 0708; the brightest galaxy in the low-mass galaxy cluster Abell 262. The line observations reveal a turbulent, rotating disc of molecular gas in the core of the galaxy, and a high-velocity, blueshifted feature ≈0′′..′′4 (≈113 pc) from its centre. The submillimetre continuum emission peaks at the nucleus, but extends towards this anomalous CO emission feature. No corresponding elongation is found on the same spatial scales at 5 GHz with e-MERLIN. We discuss potential causes for the anomalous blueshifted emission detected in this source, and conclude that it is most likely to be a low-mass in-falling filament of material condensing from the hot intracluster medium via chaotic cold accretion, but it is also possible that it is a jet-driven molecular outflow. We estimate the physical properties this structure has in these two scenarios, and show that either explanation is viable. We suggest future observations with integral field spectrographs will be able to determine the true cause of this anomalous emission, and provide further evidence for interaction between quenched cooling flows and mechanical feedback on both small and large scales in this source.