Search

We present upper limits on the 850 micron and 450 micron fluxes of the warm hyperluminous (bolometric luminosity L_bol > 10^13 L_sun galaxies IRAS P09104+4109 (z=0.442) and IRAS F15307+3252 (z=0.926), derived from measurements using the SCUBA bolometer array on the James Clerk Maxwell Telescope. Hot luminous infrared sources like these are thought to differ from more normal cold ultraluminous infrared (L_bol > 10^12 L_sun) galaxies in that they derive most of their bolometric luminosities from dusty AGNs as opposed to starbursts. Such hot, dusty AGNs at high redshift are thought to be responsible for much of the mass accretion of the Universe that is in turn responsible for the formation of the supermassive black holes seen in the centres of local galaxies. The galaxy IRAS P09104+4109 is also unusual in that it is a cD galaxy in the center of a substantial cooling-flow cluster, not an isolated interacting galaxy like most ultraluminous infrared galaxies. Previously it was known to have large amounts of hot (T > 50 K) dust from IRAS observations. We now show that the contribution of cold dust to the bolometric luminosity is less than 3 per cent. Most ultraluminous infrared galaxies possess large amounts of cold dust, and it is now known that some cooling flow cluster cD galaxies do as well. Yet this object, which is an extreme example of both, does not have enough cold gas to contribute significantly to the bolometric luminosity. We outline physical reasons why this could have happened. We then provide a discussion of stategies for finding hot dusty AGNs, given the limitations on submillimetre surveys implied by this work., MNRAS in press, accepted version, minor revisions

We report on the results of a survey of C18O and C17O toward the 20 most deeply embedded young stars in the Taurus molecular cloud. Most of the sources have been observed in both the J = 1-0 and J = 2-1 transitions of each species. The analysis shows that in general the C17O emission is optically thin, whereas the C18O emission has optical depths between 0.5 and 1.0. The material traced by these lines has an excitation temperature of ~8 K and column density ranging from 3 to 42 × 1021 cm-2. The column density toward a source is found to be inversely correlated with the source's bolometric temperature, Tbol. The correlation between Tbol and source age is reexamined, and the new correlation is used to find the rate at which mass is removed from the circumstellar environment of these sources. We find that the outflows observed toward the sources and infall with a constant mass accretion rate typical of a 10-20 K singular isothermal sphere are individually unlikely to produce the observed reduction in mass over the class I phase. However, a scenario where a highly efficient outflow dominates the beam mass loss during the first 3 × 104 yr and then standard infall dominates the beam mass loss thereafter is plausible.

We present observations of the X-ray transient XTE J1118+480 during its Low/Hard X-ray state outburst in 2000, at radio and sub-millimetre wavelengths with the VLA, Ryle Telescope, MERLIN and JCMT. The high-resolution MERLIN observations reveal all the radio emission (at 5 GHz) to come from a compact core with physical dimensions smaller than 65*d(kpc) AU. The combined radio data reveal a persistent and inverted radio spectrum, with spectral index \~+0.5. The source is also detected at 350 GHz, on an extrapolation of the radio spectrum. Flat or inverted radio spectra are now known to be typical of the Low/Hard X-ray state, and are believed to arise in synchrotron emission from a partially self-absorbed jet. Comparison of the radio and sub-millimetre data with reported near-infrared observations suggest that the synchrotron emission from the jet extends to the near-infrared, or possibly even optical regimes. In this case the ratio of jet power to total X-ray luminosity is likely to be P_J/L_X >> 0.01, depending on the radiative efficiency and relativistic Doppler factor of the jet. Based on these arguments we conclude that during the period of our observations XTE J1118+480 was producing a powerful outflow which extracted a large fraction of the total accretion power., Accepted for publication as a Letter in MNRAS

We present high‐resolution (30‘;0.3 pc) 12CO(2−1), 13CO(2−1), and C18O(2−1) observations of the 7’×5’ region comprising the W3‐Main molecular cloud core. An analysis of velocity channel‐maps of 13CO optical depth and column density reveals seven major clumps, ranging in mass from 180 M⊙ to 965 M⊙. The total H2 mass of the mapped region is ∼6500 M⊙; 58% of the total mass of the mapped region is contained within these seven major clumps, and 26% within just two clumps, one centered on IRS‐4 and the other 30‘ south of that position. The IRS‐4South clump is coincident with a recently discovered peak in submillimeter (350–800 μm) continuum emission, but appears not to be associated with previously identified IRS or radio continuum sources. IRS‐4South is likely the newest center of massive star formation activity in W3‐Main.

We report on submillimeter observations of the star forming region W51 on 11 pc size scales with 0.7 pc resolution. These observations show at least nine emission centers, each of which has enough luminosity to be a potential site for massive star formation. We also detect a region of extended emission surrounding these emission centers. This extended emission component has a steeper submillimeter spectrum, suggesting that it is warmer than the star forming cores.

We have resolved the 450-800 μm emission from the W3(Main) star forming region into three major peaks, using an 8″ beam on the James Clerk Maxwell Telescope (JCMT). One of the submillimeter sources is identified with W3-IRS 5, a well-known candidate protostar. However, to our surprise, we find that none of the submillimeter peaks coincides with any of the prominent compact H II regions in the area. We estimate that the three submillimeter sources together contribute 35%-50% of the total bolometric luminosity of the region and speculate that the contribution of luminous radio-quiet sources to the total luminosity of H II region/molecular cloud complexes may be larger than is often assumed

Observations are presented which show that CO is present in both the troposphere and stratosphere of Neptune, whereas is confined to the Neptune stratosphere with a mean mole fraction in the 0.003-30 mbar pressure level range of 1.0 x 10 exp -9. CO is present in both the stratosphere and in the troposphere with a uniformly mixed model fraction of 1.2 x 10 exp -6. Upper limits of 1.0 x 10 exp -10 and 3.0 x 10 exp -8 mole fractions are derived for HCN and CO respectively on Uranus. The origin of these species in the atmosphere of Neptune and their nondetection in that of Uranus are discussed in detail. It is concluded that the most plausible scenario involves upward convection of CO and N2 from Neptune's deep interior and a failure of chemical equilibrium at deep atmospheric levels, allowing excess CO and presumably N2 to reach the upper atmosphere. Nondetection in Uranus may be explained by the lack of a significant internal heat source in the planet and consequent suppression of vertical convection.