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Register a new userMapping the neutral atomic hydrogen gas outflow in the restarted radio galaxy 3C 236
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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 $sim1000mathrm{,km,s^{-1}}$. This HI outflow is partially recovered by the VLBI observation. In particular, we detect four clouds with masses of $0.28text{-}1.5times 10^4M_odot$ 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 $lesssim 40mathrm{,pc}$, while the fourth is co-spatial to the south-east lobe at a projected distance of $sim270mathrm{,pc}$. Their velocities are between $150$ and $640mathrm{,km,s^{-1}}$ 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.
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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.
We report the detection of very broad HI absorption against the central regions of the radio galaxy 3C293. The absorption profile, obtained with the Westerbork Synthesis Radio Telescope, has a full width at zero intensity of about 1400 km/s and most of this broad absorption (~1000 km/s) is blueshifted relative to the systemic velocity. This absorption represents a fast outflow of neutral gas from the central regions of this AGN. Possible causes for such an outflow are discussed. We favour the idea that the interaction between the radio jet and the rich ISM produces this outflow. Some of the implications of this scenario are considered.
As a rule, both lobes of Fanaroff-Riley (FR) type-II radio sources are terminated with hotspots, but the 3C328 radio galaxy is a specimen of an FR II-like object with a hotspot in only one lobe. A conceivable reason for such asymmetry is that the nucleus of 3C328 was temporarily inactive. There was no energy transfer from it to the lobes during the period of quiescence, and so they began to fade out. However, under the assumption that the axis connecting the two lobes makes an appreciable angle with the sky plane, and hence one is considerably farther from the observer than the other, the lobes are observed at two distinct stages of evolution due to the light-travel lag. While the far-side lobe is still perceived as being of the FR II type with a hotspot, decay of the near-side lobe is already apparent. No jets are visible in the VLA images, but the VLBA observations of the inverted-spectrum core component of 3C328 have revealed that it has a jet of a sub-arcsecond length pointing towards the lobe that shows evidence of decay. Since the jet always points to the near side, its observed orientation is in line with the scenario proposed here. The presence of the jet supports the inference that the nucleus of 3C328 is currently active; however, given the fact that the jet is short (approx. 200 pc in projection), the activity must have restarted very recently. The lower and upper limits of the quiescent period length have been calculated.
We present optical integral field spectroscopy $-$ obtained with the Gemini Multi-Object Spectrograph $-$ of the inner $4.0 times 5.8$ kpc$^2$ of the narrow line radio galaxy 3C 33 at a spatial resolution of 0.58 kpc. The gas emission shows three brightest structures: a strong knot of nuclear emission and two other knots at $approx 1.4$ kpc south-west and north-east of the nucleus along the ionization axis. We detect two kinematic components in the emission lines profiles, with a broader component (with velocity dispersion $sigma > 150$ km s$^{-1}$) being dominant within a $sim$ 1 kpc wide strip (the nuclear strip) running from the south-east to the north-west, perpendicular to the radio jet, and a narrower component ($sigma < 100$ km s$^{-1}$) dominating elsewhere. Centroid velocity maps reveal a rotation pattern with velocity amplitudes reaching $sim pm 350$ km s$^{-1}$ in the region dominated by the narrow component, while residual blueshifts and redshifts relative to rotation are observed in the nuclear strip, where we also observe the highest values of the [N II]/H{alpha}, [S II]/H{alpha} and [O I]/H{alpha} line ratios, and an increase of the gas temperature ($sim 18000$ K), velocity dispersion and electron density ($sim 500$ cm$^{-3}$). We interpret these residuals and increased line ratios as due to a lateral expansion of the ambient gas in the nuclear strip due to shocks produced by the passage of the radio jet. The effect of this expansion in the surrounding medium is very small, as its estimated kinetic power represents only $2.6 - 3.0 times 10^{-5}$ of the AGN bolometric luminosity. A possible signature of inflow is revealed by an increase in the [O I]/H{alpha} ratio values and velocity dispersions in the shape of two spiral arms extending to 2.3 kpc north-east and south-west from the nucleus.
We present JVLA-C observations of the HI gas in JO204, one of the most striking jellyfish galaxies from the GASP survey. JO204 is a massive galaxy in the low-mass cluster Abell 957 at z=0.04243. The HI map reveals an extended 90 kpc long ram-pressure stripped tail of neutral gas, stretching beyond the 30 kpc long ionized gas tail and pointing away from the cluster center. The HI mass seen in emission is (1.32 $ pm 0.13) times 10^{9} rm M_{odot}$, mostly located in the tail. The northern part of the galaxy disk has retained some HI gas, while the southern part has already been completely stripped and displaced into an extended unilateral tail. Comparing the distribution and kinematics of the neutral and ionized gas in the tail indicates a highly turbulent medium. Moreover, we observe associated HI absorption against the 11 mJy central radio continuum source with an estimated HI absorption column density of 3.2 $times 10^{20}$ cm$^{-2}$. The absorption profile is significantly asymmetric with a wing towards higher velocities. We modelled the HI absorption by assuming that the HI and ionized gas disks have the same kinematics in front of the central continuum source, and deduced a wider absorption profile than observed. The observed asymmetric absorption profile can therefore be explained by a clumpy, rotating HI gas disk seen partially in front of the central continuum source, or by ram-pressure pushing the neutral gas towards the center of the continuum source, triggering the AGN activity.
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