arXiv subjects

P. J. McCarthy

Publications and source records attributed to P. J. McCarthy.

41 records · Page 3Linked to original sources

arXiv1999

NICMOS Imaging of High-Redshift Radio Galaxies

We have obtained near-infrared (1.6 micron) images of 11 powerful 3CR radio galaxies at redshifts 0.8 < z < 1.8 using NICMOS on board HST. The high angular resolution permits a detailed study of galaxy morphology in these systems at rest-frame optical wavelengths, where starlight dominates over the extended, aligned UV continuum. The NICMOS morphologies are mostly symmetric and are consistent with dynamically relaxed, elliptical host galaxies dominated by a red, mature stellar population. The aligned structures are sometimes faintly visible, and nuclear point sources may be present in a few cases which manifest the ``unveiled'' AGN that is obscured from view at optical wavelengths. Our observations are consistent with the hypothesis that the host galaxies of z ~ 1-2 radio galaxies are similar to modern-day gE galaxies. Their sizes are typical of gE galaxies but smaller than present-day cD and brightest cluster galaxies, and their surface brightnesses are higher, as expected given simple luminosity evolution.

astro-ph↗

arXiv1999

Optical and Radio Observations of the Afterglow from GRB990510: Evidence for a Jet

We present multi-color optical and two-frequency radio observations of the bright SAX event, GRB 990510. The well-sampled optical decay, together with the radio observations are inconsistent with simple spherical afterglow models. The achromatic optical steepening and the decay of the radio afterglow both occuring at $t \sim 1$ day are evidence for hydrodynamical evolution of the source, and can be most easily interpreted by models where the GRB ejecta are collimated in a jet. Employing a simple jet model to interpret the observations, we derive a jet opening angle of $θ_o = 0.08$, reducing the isotropic gamma-ray emission of $2.9 \times 10^{53}$ erg by a factor $\sim 300$. If the jet interpretation is correct, we conclude that GRB observations to-date are consistent with an energy for the central source of $E \lsim 10^{52}$ erg.

astro-ph↗

arXiv1999

Emission-Line Galaxies from the NICMOS/HST GRISM Parallel Survey

We present the first results of a survey of random fields with the slitless G141 ($λ_c = 1.5μ, Δλ=0.8μ$) grism on NICMOS. Approximately 64 square arcminutes have been observed at intermediate and high galactic latitudes. The 3$σ$ limiting line and continuum fluxes in each field vary from $7.5 \times 10^{-17}$ to $1 \times 10^{-17} erg/cm^2/sec$ and from H = 20 to 22, respectively. Our median and area weighted $3σ$ limiting line fluxes within a 4 pixel aperture are nearly identical at $4.1 \times 10^{-17} erg/cm^2/sec$ and are 60% deeper than the deepest narrow-band imaging surveys from the ground. We have identified 33 emission-line objects and derive their observed wavelengths, fluxes and equivalent widths. We argue that the most likely line identification is H$α$ and that the redshift range probed is from 0.75 to 1.9. The 2$σ$ rest-frame equivalent width limits range from 9Åto 130Åwith an average of 40Å. The survey probes an effective co-moving volume of $10^5 h_{50}^{-3} Mpc^3$ for $q_0=0.5$. Our derived co-moving number density of emission line galaxies in the range $0.7 < z < 1.9$ is $3.3\times10^{-4} h_{50}^{3} Mpc^{-3}$, very similar to that of the bright Lyman break objects at $z \sim 3$. The objects with detected emission-lines have a median F160W magnitude of 20.4 (Vega scale) and a median H$α$ luminosity of $2.7 \times 10^{42} erg/sec$. The implied star formation rates range from 1 to 324 M_{\odot}/yr, with an average [NII]6583,6548 corrected rate of 21 M_{\odot}/yr for H_0=50 km/s/Mpc and $q_0=0.5$ (34 M_{\odot}/yr for $q_0=0.1$).

astro-ph↗

arXiv1998

A Polarization Study of Radio Galaxies and Quasars selected from the Molonglo Complete Sample

We present total-intensity and linear-polarization observations made with the Very Large Array at $λ$20 and 6 cm of a representative sample of 42 radio galaxies and quasars selected from the Molonglo Complete Sample. The sources have been chosen to be of large size to probe the depolarizing medium on these scales using our present data and later with observations at lower frequencies with the Giant Metrewave Radio Telescope. The $λ$20 and 6 cm data are of similar resolutions and show that depolarization between these two wavelengths is seen largely in only those lobes which are within about 300 kpc of the parent galaxy. Examination of the depolarization of the lobes with arm-length asymmetry shows that depolarization is observed predominantly for the lobe which is closer to the nucleus. There is also a trend for the lobe closer to the nucleus to be brighter, consistent with the scenario that the nearer lobe is interacting with a denser environment which is responsible for the higher depolarization and greater dissipation of energy. We have also examined the depolarization asymmetry of the lobes on opposite sides of the nucleus for galaxies and quasars. This shows that the depolarization asymmetry for quasars is marginally higher than that for galaxies. The depolarization properties of our sample are possibly determined by an asymmetric environment as well as the effects of orientation.

astro-ph↗

arXiv1993

The Environment of Lyman a Absorbers in the Sightline toward 3C273

We present new ground-based data following up on the HST discovery of low-redshift Lya absorption in the sight-line to the quasar 3C273. Narrow-band filter observations show that there are no H II regions within a 12 kpc radius of the line-of-sight to the quasar, at the velocities of three of the absorbers. Broad-band imaging shows that there are no dwarf galaxies at Virgo distances with absolute magnitude above MB~-13.5 and within a radius of 40 kpc. We present fiber spectroscopy of galaxies within a radius of 1 deg, down to an apparent magnitude of B~19. We show that the absorbers are definitely not distributed at random with respect to the galaxies, but also that the absorber-galaxy correlation function is not as strong as the galaxy-galaxy correlation function on large scales. Our data are consistent with the hypothesis that all galaxies more luminous than 1/10 L* have effective cross-sections (for association with absorbers with Log(NH)>13.0), of between 0.5 and 1 Mpc. We also show a clear case of a Lya absorber which has no galaxy brighter than MB=-18 within a projected distance of 4.8 Mpc, and discuss the possibility that Lya absorbers are destroyed in a rich galaxy environment.

astro-ph↗