Asnakew Bewketu Belete
Chalmers Institute of Technology
Molecular gas kinematics in the nuclear region of nearby Seyfert galaxies with ALMA
It now seems that active galactic nuclei (AGN) feeding and feedback are common ingredients of massive galaxies from low to high redshift. The study of the distribution, morphology and kinematics of ionized and cold molecular gas in the nuclear and circumnuclear regions of AGN helps to identify the mechanism(s) that drives gas from the disk towards the nucleus, to characterise and hence to quantify the impact of the AGN on the host galaxy over its lifetime. We present the analysis of the molecular gas in the nuclear regions of three Seyfert galaxies, NGC 4968, NGC 4845, and MCG-06-30-15, with the help of ALMA observations of the CO(2-1) emission line. The aim is to determine the kinematics of the gas in the central (~ 1 kpc) region, and thereby to probe AGN nuclear fueling and feedback. Circular motions dominate the kinematics of the molecular gas in the central discs, mainly in NGC 4845 and MCG-06-30-15, however there is a clear evidence of non-circular motions in the central (~ 1 kpc) region of NGC 4845 and NGC 4968. The strongest non-circular motion is detected in the inner disc of NGC 4968, mainly along the minor kinematic axis, with velocity ~ 115 km s-1. The observed could be due to the nuclear barred structure, the gas streaming in elliptical orbits aligned along the bar. In the NGC 4968 galaxy, the torques exerted on the gas by the bar are positive in the centre, within the gas nuclear ring, and negative outside, indicating that that the gas is transiently trapped in the inner Lindblad resonance. The positive torque in the centre could be due to an ionised outflow driven by the AGN; however it seems that the AGN is not strongly disrupting the structure of the circumnuclear region. The comparison of the CO intensity maps with the map of the cold dust emission shows the absence of CO in the centre of NGC 4968, which could be a sign of molecular gas removal by an ionised outflow in the centre, and that the dust distribution and the CO emission in and around the centre of NGC 4845. We discuss the possibility that the observed pattern in the kinematics be due to the presence of the AGN but despite the high spectral and spatial resolution of ALMA this issue cannot be finally addressed Finally, we present for this scientific case the possibility of further exploration through higher spatial resolution observations in the submillimetre and in the far-infrared regime. The need of far-IR spectroscopy and interferometry is explored in particular through the use of far- and mid-infrared molecular and ionic fine structure lines that may trace outflowing and infalling gas. Outflowing gas will be identified through P-Cygni line shapes and absorption blue-shifted wings in the molecular lines with high dipolar moments, and through emission line wings of fine-structure lines of the ionised gas.