Radio Galaxy Clustering at z~0.3

Radio galaxies are uniquely useful as probes of large-scale structure as their uniform identification with giant elliptical galaxies out to high redshift means that the evolution of their bias factor can be predicted. As the initial stage in a project to study large-scale structure with radio galaxies we have performed a small redshift survey, selecting 29 radio galaxies in the range 0.19<z<0.45 from a contiguous 40 square degree area of sky. We detect significant clustering within this sample. The amplitude of the two-point correlation function we measure is consistent with no evolution from the local (z<0.1) value. This is as expected in a model in which radio galaxy hosts form at high redshift and thereafter obey a continuity equation, although the signal:noise of the detection is too low to rule out other models. Larger surveys out to z~1 should reveal the structures of superclusters at intermediate redshifts and strongly constrain models for the evolution of large-scale structure.Comment: 7 pages, 3 figures, accepted by ApJ Letter

The Abundances Of Polyacetylenes Toward CRL618

We present a mid-infrared high spectral resolution spectrum of CRL618 in the frequency ranges 778-784 and 1227-1249 cm(-1) (8.01-8.15 and 12.75-12.85 mu m) taken with the Texas Echelon-cross-Echelle Spectrograph (TEXES) and the Infrared Telescope Facility (IRTF). We have identified more than 170 rovibrational lines arising from C2H2, HCN, C4H2, and C6H2. We have found no unmistakable trace of C8H2. The line profiles display a complex structure suggesting the presence of polyacetylenes in several components of the circumstellar envelope (CSE). We derive total column densities of 2.5x10(17), 3.1x10(17), 2.1x10(17), 9.3x10(16) cm(-2), and less than or similar to 5x10(16) cm(-2) for HCN, C2H2, C4H2, C6H2, and C8H2, respectively. The observations indicate that both the rotational and vibrational temperatures in the innermost CSE depend on the molecule, varying from 100 to 350 K for the rotational temperatures and 100 to 500 K for the vibrational temperatures. Our results support a chemistry in the innermost CSE based on radical-neutral reactions triggered by the intense UV radiation field.Spanish Ministerio de Educacion y Ciencia ESP2004-665, AYA2003-2785"Comunidad de Madrid" government S-0505/ESP-0237European Community MCRTN-CT-2004-51230CSICCONACyT SEP-2004-C01-47090UNAMNSF AST-0708074Astronom

The Infrared Nucleus of the Wolf-Rayet Galaxy Henize 2-10

We have obtained near-infrared images and mid-infrared spectra of the starburst core of the dwarf Wolf-Rayet galaxy He 2-10. We find that the infrared continuum and emission lines are concentrated in a flattened ellipse 3-4'' or 150 pc across which may show where a recent accretion event has triggered intense star formation. The ionizing radiation from this cluster has an effective temperature of 40,000 K, corresponding to $30M_\odot$ stars, and the starburst is $0.5-1.5 \times 10^7$ years old.Comment: 17 pages Latex, 7 postscript figures, 1 postscript table, accepted to A

Ionized Gas in the Galactic Center: New Observations and Interpretation

We present new observations of the [Ne II] emission from the ionized gas in Sgr A West with improved resolution and sensitivity. About half of the emission comes from gas with kinematics indicating it is orbiting in a plane tipped about 25\degree\ from the Galactic plane. This plane is consistent with that derived previously for the circumnuclear molecular disk and the northern arm and western arc ionized features. However, unlike most previous studies, we conclude that the ionized gas is not moving along the ionized features, but on more nearly circular paths. The observed speeds are close to, but probably somewhat less than expected for orbital motions in the potential of the central black hole and stars and have a small inward component. The spatial distribution of the emission is well fitted by a spiral pattern. We discuss possible physical explanations for the spatial distribution and kinematics of the ionized gas, and conclude that both may be best explained by a one-armed spiral density wave, which also accounts for both the observed low velocities and the inward velocity component. We suggest that a density wave may result from the precession of elliptical orbits in the potential of the black hole and stellar mass distribution.Comment: 28 pages, 13 figures, ApJ in pres

The radio luminosity function of radio-loud quasars from the 7C Redshift Survey

We present a complete sample of 24 radio-loud quasars (RLQs) from the new 7C Redshift Survey. Every quasar with a low-frequency (151 MHz) radio flux-density S_151 > 0.5 Jy in two regions of the sky covering 0.013 sr is included; 23 of these have sufficient extended flux to meet the selection criteria, 18 of these have steep radio spectra (hereafter denoted as SSQs). The key advantage of this sample over most samples of RLQs is the lack of an optical magnitude limit. By combining the 7C and 3CRR samples, we have investigated the properties of RLQs as a function of redshift z and radio luminosity L_151. We derive the radio luminosity function (RLF) of RLQs and find that the data are well fitted by a single power-law with slope alpha_1=1.9. We find that there must be a break in the RLQ RLF at log_10(L_151 / W Hz^-1 sr^-1) < 27, in order for the models to be consistent with the 7C and 6C source counts. The z-dependence of the RLF follows a one-tailed gaussian which peaks at z=1.7. We find no evidence for a decline in the co-moving space density of RLQs at higher redshifts. A positive correlation between the radio and optical luminosities of SSQs is observed, confirming a result of Serjeant et al. (1998). We are able to rule out this correlation being due to selection effects or biases in our combined sample. The radio-optical correlation and best-fit model RLF enable us to estimate the distribution of optical magnitudes of quasars in samples selected at low radio frequencies. We conclude that for samples with S_151 < 1 Jy one must use optical data significantly deeper than the POSS-I limit (R approx 20), in order to avoid severe incompleteness.Comment: 28 pages with 13 figures. To appear in MNRA

Evidence for a black hole in a radio-quiet quasar nucleus

We present the first milli-arcsecond resolution radio images of a radio-quiet quasar, detecting a high brightness temperature core with data from the VLBA. On maps made with lower-frequency data from MERLIN and the VLA jets appear to emanate from the core in opposite directions, which correspond to radio-emission on arcsecond scales seen with the VLA at higher frequencies. These provide strong evidence for a black-hole--based jet-producing central engine, rather than a starburst, being responsible for the compact radio emission in this radio-quiet quasar.Comment: 10 pages including 1 postscript figure; uses aaspp4.sty. Accepted for publication in Ap. J. Lett. Also available from http://www-astro.physics.ox.ac.uk/research/preprints

Observation of Infrared and Radio Lines of Molecules toward GL2591 and Comparison to Physical and Chemical Models

We have observed rovibrational transitions of acetylene and HCN near 13 microns in absorption toward GL2591. We also observed rotational lines of CS, HCN, H2CO, and HCO+. The combined data are analyzed in terms of models with a cloud envelope with density gradients and discrete regions of hot, dense gas, probably near the infrared source. The abundance of HCN is enhanced by a factor of 400 in the gas producing the infrared absorption, in agreement with chemical models which involve depletion of molecules onto grains and subsequent sublimation when temperatures are raised.Comment: 34 pages, postscript with 14 postscript figure files, uuencoded compressed and tar'ed; unpacks self with csh. In case of problems, contact [email protected]