Nuclear gas dynamics in Arp 220 - sub-kiloparsec scale atomic hydrogen disks

We present new, high angular resolution (~0.22") MERLIN observations of neutral hydrogen (HI) absorption and 21-cm radio continuum emission across the central ~900 parsecs of the ultraluminous infrared galaxy, Arp220. Spatially resolved HI absorption is detected against the morphologically complex and extended 21-cm radio continuum emission, consistent with two counterrotating disks of neutral hydrogen, with a small bridge of gas connecting the two. We propose a merger model in which the two nuclei represent the galaxy cores which have survived the initial encounter and are now in the final stages of merging, similar to conclusions drawn from previous CO studies (Sakamoto, Scoville & Yun 1999). However, we suggest that instead of being coplanar with the main CO disk (in which the eastern nucleus is embedded), the western nucleus lies above it and, as suggested by bridge of HI connecting the two nuclei, will soon complete its final merger with the main disk. We suggest that the collection of radio supernovae (RSN) detected in VLBA studies in the more compact western nucleus represent the second burst of star formation associated with this final merger stage and that free-free absorption due to ionised gas in the bulge-like component can account for the observed RSN distribution. (Abridged)Comment: 26 pages including 8 figures and 1 table; accepted for publication in Ap

Early GRB Optical and Infrared Afterglow Observations with the 2-m Robotic Liverpool Telescope

We present the first optical observations of a Gamma Ray Burst (GRB) afterglow using the 2-m robotic Liverpool Telescope (LT), which is owned and operated by Liverpool John Moores University and situated on La Palma. We briefly discuss the capabilities of LT and its suitability for rapid follow-up observations of early optical and infrared GRB light curves. In particular, the combination of aperture, site, instrumentation and rapid response (robotic over-ride mode aided by telescope's rapid slew and fully-opening enclosure) makes the LT ideal for investigating the nature of short bursts, optically-dark bursts, and GRB blast-wave physics in general. We briefly describe the LT's key position in the RoboNet-1.0 network of robotic telescopes. We present the LT observations of GRB041006 and use its gamma-ray properties to predict the time of the break in optical light curve, a prediction consistent with the observations.Comment: 4 pages, 1 figure, accepted for publication in Il nuovo cimento (4th Workshop Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004

Rapid GRB Follow-up with the 2-m Robotic Liverpool Telescope

We present the capabilities of the 2-m robotic Liverpool Telescope (LT), owned and operated by Liverpool John Moores University and situated at ORM, La Palma. Robotic control and scheduling of the LT make it especially powerful for observations in time domain astrophysics including: (i) rapid response to Targets of Opportunity: Gamma Ray Bursts, novae, supernovae, comets; (ii) monitoring of variable objects on timescales from seconds to years, and (iii) observations simultaneous or coordinated with other facilities, both ground-based and from space. Following a GRB alert from the Gamma Ray Observatories HETE-2, INTEGRAL and Swift we implement a special over-ride mode which enables observations to commence in about a minute after the alert, including optical and near infrared imaging and spectroscopy. In particular, the combination of aperture, site, instrumentation and rapid response (aided by its rapid slew and fully-opening enclosure) makes the LT excellently suited to help solving the mystery of the origin of optically dark GRBs, for the investigation of short bursts (which currently do not have any confirmed optical counterparts) and for early optical spectroscopy of the GRB phenomenon in general. We briefly describe the LT's key position in the RoboNet-1.0 network of robotic telescopes.Comment: 6 pages, 2 figures, to appear in the proceedings of Interacting Binaries: Accretion, Evolution and Outcomes, 4-10 July 2004, Cefalu, Sicily, Italy, eds. Antonelli et a

Excessive Seepage Losses at Westwood Lake Dam

Excessive seepage losses at Westwood Lake Darn in east-central Indiana were apparent in 1974 during first filling of the lake when seepage areas developed downstream of the dam and abutments. Several remedial studies were performed which included additional test borings, field and laboratory tests, installation of observation wells, and a review of the site geology and hydrology. Data and observations from these studies were used to develop semi-quantitative assessments of seepage loss rates as related to lake levels. These analyses served as a basis for design of a major repair which consisted of blanketing a significant portion of the lake bottom with on-site, low-plasticity clays and clayey silts. The blanketing was completed in 1984 and postrepair filling required about two years. Subsequent monitoring and observations indicate that the lake level is holding at or within 1.5 ft of the original design normal pool

The Cold and Hot Gas Content of Fine-Structure E and S0 Galaxies

We investigate trends of the cold and hot gas content of early-type galaxies with the presence of optical morphological peculiarities, as measured by the fine-structure index (Sigma). HI mapping observations from the literature are used to track the cold-gas content, and archival ROSAT PSPC data are used to quantify the hot-gas content. We find that E and S0 galaxies with a high incidence of optical peculiarities are exclusively X-ray underluminous and, therefore, deficient in hot gas. In contrast, more relaxed galaxies with little or no signs of optical peculiarities span a wide range of X-ray luminosities. That is, the X-ray excess anticorrelates with Sigma. There appears to be no similar trend of cold-gas content with either fine-structure index or X-ray content. The fact that only apparently relaxed E and S0 galaxies are strong X-ray emitters is consistent with the hypothesis that after strong disturbances such as a merger hot-gas halos build up over a time scale of several gigayears. This is consistent with the expected mass loss from stars.Comment: 12 pages, latex, 5 figures. Accepted for publication in A

Direct measurement of the jet geometry in Seyfert galaxies

We demonstrate that, by combining optical, radio and X-ray observations of a Seyfert, it is possible to provide a direct measurement of the angle $\beta$ between the direction of the radio jet and the normal to the plane of the spiral host galaxy. To do so, we make the assumptions that the inner radio jet is perpendicular to the X-ray observed inner accretion disk, and that the observed jet (or the stronger component, if the jet is two-sided) is physically closer to Earth than the plane of the galaxy. We draw attention to the possibility of measurement producing a result which is not self-consistent, in which case for that galaxy, one of the assumptions must fail.Comment: 11 pages, 1 figure, accepted for publication in The Astrophysical Journal Letter

Distribution and Kinematics of the Circum-nuclear Molecular Gas in the Seyfert 1 Galaxy NGC 3227

We present new interferometric observations of the 12CO(1-0), 12CO(2-1) and HCN (1-0) molecular line emission in NGC 3227 obtained with the IRAM Plateau de Bure interferometer (PdBI). We achieved an unprecedented angular resolution in the 12CO(2-1) line of about 0.6'' corresponding to only about 80pc at a distance of 17.3Mpc. The mapped 12CO emission is concentrated in the inner 8'' and accounts for 20% of the total 30m CO line flux. The 12CO emission is resolved into an asymmetric nuclear ring with a diameter of about 3''. The HCN line emission is mostly unresolved at our resolution of ~2.4'' and contains all of the single dish flux. We have decomposed the observed molecular gas motions into a circular and non-circular component revealing that about 80% of the gas in the circum-nuclear region exhibits pure circular rotation. We find evidence for bar streaming onto the nuclear ring and a redshifted emission knot on the ring perimeter. In the central arcsecond the gas shows apparent counter rotation. This behavior can be best explained by a warping of the inner molecular gas disk rather than gas motion in a nuclear bar potential. We detected molecular gas at a distance from the nucleus of only ~13pc with a velocity of about 75 km/s with respect to the systemic velocity and find that within the central arcsecond the rotation curve is rising again. This is the first time that millimetric CO-line emission has been detected interferometrically at such small distances to the nucleus of a Seyfert galaxy. These measurements indicate a lower limit on the enclosed mass of about 2x10^7 M_solar in the inner 15pc.Comment: accepted for Ap.J. April issue, 54 pages, 22 figure