Michele Cappellari

Abstract:

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. We report a tight linear relation between the H i circular velocity measured at 6 R e and the stellar velocity dispersion measured within 1 R e for a sample of 16 early-type galaxies with stellar mass between 1010 and 1011 M ⊙ . The key difference from previous studies is that we only use spatially resolved v circ (H i) measurements obtained at large radius for a sizeable sample of objects. We can therefore link a kinematical tracer of the gravitational potential in the dark-matter dominated outer regions of galaxies with one in the inner regions, where baryons control the distribution of mass. We find that v circ (H i)= 1.33 σ e with an observed scatter of just 12 per cent. This indicates a strong coupling between luminous and dark matter from the inner- to the outer regions of early-type galaxies, analogous to the situation in spirals and dwarf irregulars. The v circ (H i)-σ e relation is shallower than those based on v circ measurements obtained from stellar kinematics and modelling at smaller radius, implying that v circ declines with radius - as in bulge-dominated spirals. Indeed, the value of v circ (H i) is typically 25 per cent lower than the maximum v circ derived at ~0.2 R e from dynamical models. Under the assumption of power-law total density profiles ρ ∝ r -γ , our data imply an average logarithmic slope 〈γ〉 = 2.18 ± 0.03 across the sample, with a scatter of 0.11 around this value. The average slope and scatter agree with recent results obtained from stellar kinematics alone for a different sample of early-type galaxies.

Abstract:

We present the results of a high-resolution, 5 GHz, Karl G. Jansky Very Large Array study of the nuclear radio emission in a representative subset of the ATLAS3D survey of early-type galaxies (ETGs). We find that 51 ± 4 per cent of the ETGs in our sample contain nuclear radio emission with luminosities as low as 1018 W Hz-1. Most of the nuclear radio sources have compact (≲25-110 pc) morphologies, although ~10 per cent display multicomponent core+jet or extended jet/lobe structures. Based on the radio continuum properties, as well as optical emission line diagnostics and the nuclear X-ray properties, we conclude that the majority of the central 5 GHz sources detected in the ATLAS3D galaxies are associated with the presence of an active galactic nucleus (AGN). However, even at subarcsecond spatial resolution, the nuclear radio emission in some cases appears to arise from low-level nuclear star formation rather than an AGN, particularly when molecular gas and a young central stellar population is present. This is in contrast to popular assumptions in the literature that the presence of a compact, unresolved, nuclear radio continuum source universally signifies the presence of an AGN. Additionally, we examine the relationships between the 5 GHz luminosity and various galaxy properties including the molecular gas mass and - for the first time - the global kinematic state. We discuss implications for the growth, triggering, and fuelling of radio AGNs, as well as AGN-driven feedback in the continued evolution of nearby ETGs.