The circumnuclear cold gas environments of the powerful radio galaxies 3C 236 and 4C 31.04

Oosterloo

et al. 2017

A&A

222

We present an analysis of the properties of neutral hydrogen (H i) in 248 nearby (0.02 < z < 0.25) radio galaxies with S 1.4 GHz > 30 mJy and for which optical spectroscopy is available. The observations were carried out with the Westerbork Synthesis Radio Telescope as the last large project before the upgrade of the telescope with phased array feed receivers (Apertif). The sample covers almost four orders of magnitude in radio power from log P 1.4 GHz = 22.5 W Hz −1 and 26.2 W Hz −1 . We detect H i in absorption in 27% ± 5.5% of the objects. The detections are found over the full range of radio power. However, the distribution and kinematics of the absorbing H i gas appear to depend on radio power, the properties of the radio continuum emission, and the dust content of the sources. Among the sources where H i is detected, gas with kinematics deviating from regular rotation is more likely found as the radio power increases. In the great majority of these cases, the H i profile is asymmetric with a significant blue-shifted component. This is particularly common for sources with log P 1.4 GHz > 24 W Hz −1 , where the radio emission is small, possibly because these radio sources are young. The same is found for sources that are bright in the mid-infrared, i.e. sources rich in heated dust. In these sources, the H i is outflowing likely under the effect of the interaction with the radio emission. Conversely, in dust-poor galaxies, and in sources with extended radio emission, at all radio powers we only detect H i distributed in a rotating disk. Stacking experiments show that in sources for which we do not detect H i in absorption directly, the H i has a column density that is lower than 3.5 × 10 17 (T spin /c f ) cm −2 . We use our results to predict the number and type of H i absorption lines that will be detected by the upcoming surveys of the Square Kilometre Array precursors and pathfinders (Apertif, MeerKAT, and ASKAP).

Section: H I Morphologies and Kinematics In Different Radio Agnmentioning

confidence: 99%

Kinematics and physical conditions of H i in nearby radio sources

Maccagni

Oosterloo

et al. 2017

A&A

222

“…For example, in 3C 236 (Struve & Conway 2012) several discrete absorbing clouds, not belonging to the rotating H i disk, are observed close to the radio core ( 10 2 pc). Their incoherent structure (kinetic and morphological) suggests they may be involved in the accretion mechanism into the AGN.…”

Section: The H I Absorption and The Origin Of The Atomic Neutral Hydrmentioning

confidence: 99%

What triggers a radio AGN?

Maccagni

Oosterloo

et al. 2014

A&A

We present new Australia Telescope Compact Array (ATCA) observations of the young (<10 2 years) radio galaxy PKS B1718-649.We study the morphology and the kinematics of the neutral hydrogen (H i) disk (M H i = 1.1 × 10 10 M , radius ∼30 kpc). In particular, we focus on analyzing the cold gas in relation to the triggering of the nuclear activity. The asymmetries at the edges of the disk date the last interaction with a companion to more than 1 Gyr ago. The tilted-ring model of the H i disk shows that this event may have formed the disk as we see it now, but that it may not have been responsible for triggering the AGN. The long timescales of the interaction are incompatible with the short ones of the radio activity. In absorption, we identify two clouds with radial motions that may represent a population that could be involved in triggering the radio activity. We argue that PKS B1718-649 may belong to a family of young low-excitation radio AGN where, rather than through a gas-rich merger, the active nuclei (AGN) are triggered by local mechanisms such as accretion of small gas clouds.

“…Atomic neutral hydrogen was revealed as a deep narrow absorption feature near the systemic velocity by van Gorkom et al (1989). The distribution of this gas was studied at high spatial resolution using VLBI techniques by Struve & Conway (2012), who speculate about the radio source interacting with the cold ISM gas. Morganti et al (2005) have discovered a broad and shallow wing, blueshifted up to 1000 km s −1 .…”

Section: Introductionmentioning

confidence: 99%

First look at the giant radio galaxy 3C 236 with LOFAR

Shulevski

Barthel

et al. 2019

A&A

We have examined the giant radio galaxy 3C 236 using LOFAR at 143 MHz down to an angular resolution of 7 , in combination with observations at higher frequencies. We have used the low frequency data to derive spectral index maps with the highest resolution yet at these low frequencies. We confirm a previous detection of an inner hotspot in the north-west lobe and for the first time observe that the south-east lobe hotspot is in fact a triple hotspot, which may point to an intermittent source activity. Also, the spectral index map of 3C 236 shows that the spectral steepening at the inner region of the northern lobe is prominent at low frequencies. The outer regions of both lobes show spectral flattening, in contrast with previous high frequency studies. We derive spectral age estimates for the lobes, as well as particle densities of the IGM at various locations. We propose that the morphological differences between the lobes are driven by variations in the ambient medium density as well as the source activity history. 1 We assume a flat ΛCDM cosmology with H 0 = 67.8 km s −1 Mpc −1 and Ω m = 0.308, taken from the cosmological results of the full-mission Planck observations (Planck Collaboration XIII), and use the cosmol-Article number, page 1 of 10