What triggers a radio AGN? The intriguing case of PKSB 1718-649

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 (HI) disk (M(HI) = 1.1x 10^10 M(sun), radius ~ 30 kpc). In particular, we focus on the analysis of 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 HI disk shows that this event may have formed the disk as we see it now, but that it may have not 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 which may represent a population that could be involved in the triggering of 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.Comment: 8 pages, 9 figures, Accepted to A&

Emission lines and optical continuum in low-luminosity radio galaxies

We present spectroscopic observations of a complete sub-sample of 13 low-luminosity radio galaxies selected from the 2Jy sample. The underlying continuum in these sources is carefully modelled in order to make a much-needed comparison between the emission line and continuum properties of FRIs with those of other classes of radio sources. We find that 5 galaxies in the sample show a measurable UV excess: 2 of the these sources are BL Lacs and in the remaining 3 galaxies we argue that the most likely contributor to the UV excess is a young stellar component. Excluding the BL Lacs, we therefore find that \~30% of the sample show evidence for young stars, which is similar to the results obtained for higher luminosity samples. We compare our results with far-infrared measurements in order to investigate the far-infrared-starburst link. The nature of the optical-radio correlations is investigated in light of this new available data and, in contrast to previous studies, we find that the FRI sources follow the correlations with a similar slope to that found for the FRIIs. Finally, we compare the luminosity of the emission lines in the FRI and BL Lac sources and find a significant difference in the [OIII] line luminosities of the two groups. Our results are discussed in the context of the unified schemes.Comment: 18 pages, 31 figures, MNRAS in press, (all enquiries to Clive Tadhunter ([email protected])

Tidal Remnants and Intergalactic HII Regions

We report the discovery of two small intergalactic HII regions in the loose group of galaxies around the field elliptical NGC 1490. The HII regions are located at least 100 kpc from any optical galaxy but are associated with a number of large HI clouds that are lying along an arc 500 kpc in length and that have no optical counterpart on the Digital Sky Survey. The sum of the HI masses of the clouds is almost 10^10 M_sun and the largest HI cloud is about 100 kpc in size. Deep optical imaging reveals a very low surface brightness counterpart to this largest HI cloud, making this one of the HI richest optical galaxies known (M_HI/L_V~200). Spectroscopy of the HII regions indicates that the abundance in these HII regions is only slightly sub-solar, excluding a primordial origin of the HI clouds. The HI clouds are perhaps remnants resulting from the tidal disruption of a reasonably sized galaxy, probably quite some time ago, by the loose group to which NGC1490 belongs. Alternatively, they are remnants of the merger that created the field elliptical NGC1490. The isolated HII regions show that star formation on a very small scale can occur in intergalactic space in gas drawn from galaxies by tidal interactions. Many such intergalactic small star formation regions may exist near tidally interacting galaxies.Comment: To appear in the proceedings of the IAU Symposium #217, Recycling Intergalactic and Interstellar Matter, eds. P.-A. Duc, J. Braine, and E. Brinks, 6 pages with low resolution figures. The full paper with high resolution images can be downloaded from http://www.astron.nl/~morganti/Papers/cloud.ps.g

IC 4200: a gas-rich early-type galaxy formed via a major merger

We present the result of radio and optical observations of the S0 galaxy IC 4200. We find that the galaxy hosts 8.5 billion solar masses of HI rotating on a ~90 deg warped disk extended out to 60 kpc from the centre of the galaxy. Optical spectroscopy reveals a simple-stellar-population-equivalent age of 1.5 Gyr in the centre of the galaxy and V- and R-band images show stellar shells. Ionised gas is observed within the stellar body and is kinematically decoupled from the stars and characterised by LINER-like line ratios.We interpret these observational results as evidence for a major merger origin of IC 4200, and date the merger back to 1-3 Gyr ago.Comment: Accepted for publication in Astronomy & Astrophysics; 18 pages, 13 figures; the tables of Appendix C can be downloaded at http://www.astro.rug.nl/~pserra/IC420

The unfriendly ISM in the radio galaxy 4C12.50 (PKS 1345+12)

The radio source 4C12.50 has often been suggested to be a prime candidate for the link between ultraluminous infrared galaxies and young radio galaxies. A VLBI study of the neutral hydrogen in the nuclear regions of this object shows that most of the gas detected close to the systemic velocity is associated with an off-nuclear cloud (~50 to 100 pc from the radio core) with a column density of ~10^22 T_spin/100 K) cm^(-2) and an HI mass of a few times 10^5 to 10^6 M_sun. We consider a number of possibilities to explain the results. In particular, we discus the possibility that this cloud indicates the presence of a rich and clumpy interstellar medium in the centre, likely left over from the merger that triggered the activity and that this medium influences the growth of the radio source. The location of the cloud -- at the edge of the northern radio jet/lobe -- suggests that the radio jet might be interacting with a gas cloud. This interaction could be responsible for bending the young radio jet. The velocity profile of the gas is relatively broad (~150$ km/s) and we interpret this as kinematical evidence for interaction of the radio plasma with the cloud. We also consider the model where the cloud is part of a broader circumnuclear structure. Only a limited region of this structure would have sufficient background radio brightness and large enough column depth in neutral gas to obtain detectable HI absorption against the counterjet. The VLBI study of the neutral hydrogen in 4C12.50 suggests that HI detected near the systemic velocity (as it is often the case in radio galaxies) may not necessarily be connected with a circumnuclear disk or torus (as is very often assumed) but instead could be a tracer of the large-scale medium that surrounds the active nucleus and that may influence the growth of the young radio source.Comment: 7 pages, 2 figures. Accepted for publication in A&

A Deep WSRT 1.4 GHz Radio Survey of the Spitzer Space Telescope FLSv Region

The First Look Survey (FLS) is the first scientific product to emerge from the Spitzer Space Telescope. A small region of this field (the verification strip) has been imaged very deeply, permitting the detection of cosmologically distant sources. We present Westerbork Synthesis Radio Telescope (WSRT) observations of this region, encompassing a ~1 sq. deg field, centred on the verification strip (J2000 RA=17:17:00.00, DEC=59:45:00.000). The radio images reach a noise level of ~ 8.5 microJy/beam - the deepest WSRT image made to date. We summarise here the first results from the project, and present the final mosaic image, together with a list of detected sources. The effect of source confusion on the position, size and flux density of the faintest sources in the source catalogue are also addressed. The results of a serendipitous search for HI emission in the field are also presented. Using a subset of the data, we clearly detect HI emission associated with four galaxies in the central region of the FLSv. These are identified with nearby, massive galaxies.Comment: 9 pages, 6 figures (fig.3 in a separate gif file). Accepted for publication in A&A. The full paper and the related material can be downloaded from http://www.astron.nl/wsrt/WSRTsurveys/WFLS

Port cities and urban logistics

Cities and metropolitan areas serve a wide variety of functions. Those cities which have a port function may be subject to significant increases in traffic flows. Thus in recent years port activities have at times been viewed as a problem by those responsible for traffic planning in the city with which the port is connected. This paper considers the port-city interactions over time and highlights how these have changed. A new phase of these interactions may be at hand with significant implications for urban freight movements. Ports’ strategies are constantly evolving and port managers seek to make better use of the port’s assets. One of the main assets is land and here there are some emerging trends that have important implications for the port-city interface. In addition, city authorities are increasingly looking for opportunities to use non-road modes for some of the movements of goods to, from and possibly within their cities. Cities that are connected to a port have some interesting opportunities in this area. These developments imply a new period of more intense port-city interaction

Extended, regular HI structures around early-type galaxies

We discuss the morphology and kinematics of the HI of a sample of 30 southern gas-rich early-type galaxies selected from the HI Parkes All-Sky Survey (HIPASS). This is the largest collection of high-resolution HI data of a homogeneously selected sample. Given the sensitivity of HIPASS, these galaxies represent the most HI-rich early-type galaxies. In two-thirds of the galaxies, we find the HI to be in a large, regular disk- or ring-like structure that in some cases is strongly warped. In the remaining cases we find the HI distributed in irregular tails or clouds offset from the galaxy. The giant, regular HI structures can be up to ~200 kpc in diameter and contain up to 10^10 M_sun of HI. The incidence of irregular HI structures appears to be somewhat higher in elliptical galaxies, but the large, regular structures are observed in both elliptical and S0 galaxies and are not strictly connected to the presence of a stellar disk. If these two types of galaxies are the result of different formation paths, this is not strongly reflected in the characteristics of the HI. The size and the regular kinematics of the HI structures imply that the neutral hydrogen must have settled in these galaxies several Gyr ago. Merging as well as gas accretion from the IGM are viable explanations for the origin of the gas in these galaxies. The average column density of the HI is low so that little star formation is expected to occur and these early-type galaxies can remain gas rich for very long periods of time. The large HI structures likely represent key structures for tracing the origin and evolution of these galaxies.Comment: Accepted for publication in A&A, 13 pages, 6 figures. A version with full resolution figures is available at http://www.astron.nl/~morganti/Papers/hipass.pd