The nearby radio galaxy 3C293 is one of a small group of objects where extreme outflows of neutral hydrogen have been detected. However, due to the limited spatial resolution of previous observations, the exact location of the outflow was not able to
be determined. In this letter, we present new higher resolution VLA observations of the central regions of this radio source and detect a fast outflow of HI with a FWZI velocity of Delta v~1200 km/s associated with the inner radio jet, approximately 0.5 kpc west of the central core. We investigate possible mechanisms which could produce the observed HI outflow and conclude that it is driven by the radio-jet. However, this outflow of neutral hydrogen is located on the opposite side of the nucleus to the outflow of ionised gas previously detected in this object. We calculate a mass outflow rate in the range of 8-50 solar masses/yr corresponding to a kinetic energy power injected back into the ISM of 1.38x10^{42} - 1.00x10^{43} erg/s or 0.01 - 0.08 percent of the Eddington luminosity. This places it just outside the range required by some galaxy evolution simulations for negative feedback from the AGN to be effective in halting star-formation within the galaxy.
We present an analysis of deep WSRT observations of the HI in 33 nearby early-type galaxies selected from a sample studied earlier at optical wavelengths with the SAURON integral-field spectrograph. The sample covers both field environments and the V
irgo cluster. Our analysis shows that gas accretion plays a role in the evolution of field early-type galaxies, but less so for those in clusters. For detection limits of a few times 10^6 Msun, HI is detected in about 2/3 of the field galaxies, while <10% of the Virgo objects are detected. In about half of the detections, the HI forms a regularly rotating disc or ring. All HI discs have counterparts of ionised gas and inner HI discs are also detected in molecular gas. The cold ISM is dominated by molecular gas (M_H2/M_HI ~ 10). We conclude that accretion of HI is common for field early-type galaxies, but the amount of material involved is usually small. Cluster galaxies appear not to accrete HI. The few galaxies with a significant young sub-population all have inner gas discs, but for the remaining galaxies there is no trend between stellar population and HI. Some early-type galaxies are very gas rich, but only have an old population. The stellar populations of field galaxies are typically younger than those in Virgo. This is likely related to differences in accretion history. In about 50% of the galaxies we detect a central continuum source. In many objects this emission is from a low-luminosity AGN, in some it is consistent with the observed star formation. Galaxies with HI in the central regions are more likely detected in continuum. This is due to a higher probability for star formation to occur in such galaxies and not to HI-related AGN fuelling. (Abridged)
We present the results of a program of K- and Ks-band imaging of a sample of 2Jy radio galaxies with redshifts 0.03 < z < 0.5, for which the host galaxy morphologies and structural parameters (effective radius, Sersic index and unresolved nuclear poi
nt source contribution) have been determined using GALFIT. Two-thirds of our sample are best modelled as being hosted by massive elliptical galaxies with Sersic indices of n=4-6, with the remainder being better suited either by a mixture of morphological components (usually a bulge plus a small, less luminous, disk component) or by more disky galaxy models with n=1-2. Our measured galaxy sizes are generally in very good agreement with other imaging programs, both space- and ground-based. We also determine a slightly higher average nuclear point source contribution than similar HST-based programs. This is due to our inability to separate the AGN emission from compact circum-nuclear stellar emission, but does not bias our modelling of the remainder of the host galaxies and our results remain robust. We also observe that roughly half of the objects in our sample are either undergoing major or minor merger activity or are clearly morphologically disturbed.
We report the discovery of extremely broad 21-cm HI absorption (FWZI ~1600 km/s) detected with the Westerbork Synthesis Radio Telescope in the radio source 4C37.11 (B2 0402+379). This object has been claimed to host a super-massive binary black hole
(Rodriguez et al. 2006). The main features in the absorption profile are two components, separated by ~1100 km/s. The HI absorption in 4C37.11 is unusual because it is the first case where such broad absorption is found to be centred on the systemic velocity of the host galaxy and not asymmetric and blueshifted as is seen in all other galaxies with broad HI absorption. Given the large width of the absorption, we suggest that a possible explanation for the extreme properties of the HI absorption is that it is the kinematic signature of a binary black hole. If this interpretation is correct, the combined black hole mass derived from the absorption profile is consistent with that derived from the luminosity of the spheroid. If the broad absorption is indeed due to a binary black hole, this finding confirms the importance of the gaseous component in the merging process of supermassive black holes.
We present results of a study of large-scale neutral hydrogen (HI) gas in nearby radio galaxies. We find that the early-type host galaxies of different types of radio sources (compact, FR-I and FR-II) appear to contain fundamentally different large-s
cale HI properties: enormous regular rotating disks and rings are present around the host galaxies of a significant fraction of low power compact radio sources, while no large-scale HI is detected in low power, edge-darkened FR-I radio galaxies. Preliminary results of a study of nearby powerful, edge-brightened FR-II radio galaxies show that these systems generally contain significant amounts of large-scale HI, often distributed in tail- or bridge-like structures, indicative of a recent galaxy merger or collision. Our results suggest that different types of radio galaxies may have a different formation history, which could be related to a difference in the triggering mechanism of the radio source. If confirmed by larger studies with the next generation radio telescopes, this would be in agreement with previous optical studies that suggest that powerful FR-II radio sources are likely triggered by galaxy mergers and collisions, while the lower power FR-I sources are fed in other ways (e.g. through the accretion of hot IGM). The giant HI disks/rings associated with some compact sources could - at least in some cases - be the relics of much more advanced mergers.
