Mapping the neutral atomic hydrogen gas outflow in the restarted radio galaxy 3C 236

The energetic feedback that is generated by radio jets in active galactic nuclei (AGNs) has been suggested to be able to produce fast outflows of atomic hydrogen (HI) gas that can be studied in absorption at high spatial resolution. We have used the Very Large Array (VLA) and a global very-long-baseline-interferometry (VLBI) array to locate and study in detail the HI outflow discovered with the Westerbork Synthesis Radio Telescope (WSRT) in the re-started radio galaxy 3C 236. We confirm, from the VLA data, the presence of a blue-shifted wing of the HI with a width of $\sim1000\mathrm{\,km\,s^{-1}}$. This HI outflow is partially recovered by the VLBI observation. In particular, we detect four clouds with masses of $0.28\text{-}1.5\times 10^4M_\odot$ with VLBI that do not follow the regular rotation of most of the HI. Three of these clouds are located, in projection, against the nuclear region on scales of $\lesssim 40\mathrm{\,pc}$, while the fourth is co-spatial to the south-east lobe at a projected distance of $\sim270\mathrm{\,pc}$. Their velocities are between $150$ and $640\mathrm{\,km\,s^{-1}}$ blue-shifted with respect to the velocity of the disk-related HI. These findings suggest that the outflow is at least partly formed by clouds, as predicted by some numerical simulations and originates already in the inner (few tens of pc) region of the radio galaxy. Our results indicate that all of the outflow could consist of many clouds with perhaps comparable properties as the ones detected, distributed also at larger radii from the nucleus where the lower brightness of the lobe does not allow us to detect them. However, we cannot rule out the presence of a diffuse component of the outflow. The fact that 3C 236 is a low excitation radio galaxy, makes it less likely that the optical AGN is able to produce strong radiative winds leaving the radio jet as the main driver for the HI outflow.Comment: 13 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

Causal relevance of conditionals: semantics or pragmatics?

In this paper we argue that the antecedent of a (non-analytic) conditional is causally relevant to the consequent, … at least if standard background conditions hold. Natural counterexamples to the causal relevance analysis are argued to be cases where the standardly assumed background condition(s) do not hold

Natural kinds and dispositions: A causal analysis

Objects have dispositions. Dispositions are normally analyzed by providing a meaning to disposition ascriptions like ‘This piece of salt is soluble’. Philosophers like Carnap, Goodman, Quine, Lewis and many others have proposed analyses of such disposition ascriptions. In this paper we will argue with Quine (‘Natural Kinds’, 1970) that the proper analysis of ascriptions of the form ‘x is disposed to m (when C)’, where ‘x’ denotes an object, ‘m’ a manifestation, and ‘C’ a condition, goes like this: (i) ‘x is of natural kind k’, and (ii) the generic ‘ks are m (when C)’ is true. For the analysis of the generic, we propose an analysis in terms of causal powers: ‘ks (when C) have the causal power to m’. The latter, in turn, is analyzed in a very precise way, making use of Pearl’s probabilistic graphical causal models. We will show how this natural kind-analysis improves on standard conditional analyses of dispositions by avoiding the standard counterexamples, and that it gives rise to precise observable criteria under which the disposition ascription is true