Engineering topics

Stockton, Alan

Publications and source records attributed to Stockton, Alan.

5 records

DOE OSTI2017

The Circumgalactic Medium of Submillimeter Galaxies. II. Unobscured QSOs within Dusty Starbursts and QSO Sightlines with Impact Parameters below 100 kpc

We present Atacama Large Millimeter/submillimeter Array (ALMA) 870 μm observations of 29 bright Herschel sources near high-redshift QSOs. The observations confirm that 20 of the Herschel sources are submillimeter-bright galaxies (SMGs) and identify 16 new SMG−QSO pairs that are useful to studies of the circumgalactic medium (CGM) of SMGs. Eight out of the 20 SMGs are blends of multiple 870 μm sources. The angular separations for six of the Herschel-QSO pairs are less than 10″, comparable to the sizes of the Herschel beam and the ALMA primary beam. We find that four of these six “pairs” are actually QSOs hosted by SMGs. No additional submillimeter companions are detected around these QSOs, and the rest-frame ultraviolet spectra of the QSOs show no evidence of significant reddening. Black hole accretion and star formation contribute almost equally in bolometric luminosity in these galaxies. The SMGs hosting QSOs show similar source sizes, dust surface densities, and star formation rate surface densities to those of other SMGs in the sample. We find that the black holes are growing ∼3× faster than the galaxies when compared to the present-day black hole/galaxy mass ratio, suggesting a QSO duty cycle of ≲30% in SMGs at z∼3. The remaining two Herschel-detected QSOs are undetected at 870 μm, but each has an SMG “companion” only 9″ and 12″ away (71 and 95 kpc at z = 3). They could be either merging or projected pairs. If the former, they would represent a rare class of “wet−dry” mergers. If the latter, the QSOs would, for the first time, probe the CGM of SMGs at impact parameters below 100 kpc.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

A COMPACT GROUP OF GALAXIES AT Z = 2.48 HOSTING AN AGN-DRIVEN OUTFLOW

We present observations of a remarkable compact group of galaxies at z = 2.48. Four galaxies, all within 40 kpc of each other, surround a powerful high-redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of 3.6 × 10{sup 11}M{sub ⊙} and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the active galactic nucleus (AGN) producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass–metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At ≳50 kpc from the system, we found a fainter extended-emission region that may be a part of a radio-jet-driven outflow.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1999

Infrared Space Observatory (ISO) Data Analysis

Joseph is an ISO Co-Investigator. His Guaranteed Time Observations include both a major programme for which he is the Principal Investigator, and a number of other prgrammes in collaboration with other ISPHOT Co-Investigators, David Sanders, Alan Stockton, and Esther Hu.

Joseph, Robert D.↗

NASA NTRS1997

Two Extremely Red Galaxies

This report concerns one of the major observational studies in the ISO Central Programme, the ISO Normal Galaxy Survey. This is a survey of an unbiased sample of spiral and lenticular galaxies selected from the Revised Shapley-Ames Catalog. It is therefore optically-selected, with a brightness limit of blue magnitude = 12, and otherwise randomly chosen. The original sample included 150 galaxies, but this was reduced to 74 when the allocated observing time was expended because the ISO overheads encountered in flight were much larger than predicted.

Joseph, Robert D.↗

NASA NTRS1997

Deep WFPC2 and Ground-Based Imaging of a Complete Sample of 3C Quasars and Galaxies

We present the results of an HST and ground-based imaging study of a complete 3C sample of zeta approx. equal to 1 sources, comprising 5 quasars and 5 radio galaxies. We have observed all of the sample in essentially line-free bands at rest-frame 0.33 micrometers with WFPC2 and in rest-frame 1 micrometer images from the ground; we have also observed most of the sample in narrow-band filters centered on [O II]. We resolve continuum structure around all of our quasars in the high-resolution WFPC2 images, and in four of the five ground-based K' images. All of the quasars have some optical continuum structure that is aligned with the radio axis. In at least 3 of these cases, some of this optical structure is directly coincident with a portion of the radio structure, including optical counterparts to radio jets in 3C212 and 3C245 and an optical counterpart to a radio lobe in 3C2. These are most likely due to optical synchrotron radiation, and the radio and optical spectral indices in the northern lobe of 3C2 are consistent with this interpretation. The fact that we see a beamed optical synchotron component in the quasars but not in the radio galaxies complicates both the magnitude and the alignment comparisons. Nonetheless, the total optical and K' flux densities of the quasar hosts are consistent with those of the radio galaxies within the observed dispersion in our sample. The distributions of K' flux densities of both radio galaxies and quasar hosts exhibit similar mean and dispersion to that found for other radio galaxies at this redshift, and the average host galaxy luminosity is equivalent to, or a little fainter than, L*. The formal determination of the alignment in the optical and infrared in the two subsamples yields no significant difference between the radio galaxy and quasar subsamples, and the quasars 3C 196 and 3C 336 have aligned continuum and emission-line structure that is probably not due to beamed optical synchrotron emission. Very blue and/or edge-brightened structures are present in some objects within the probable quasar opening angle; these are possibly the result of illumination effects from the active nucleus, i.e., scattered quasar light or photoionization. In 3C 212, we see an optical object that lies 3 min. beyond the radio lobe, but which looks morphologically quite similar to the radio lobe itself. This object is bright in the infrared and has a steep spectral gradient along its length. A striking, semi-circular arc seen associated with 3C 280 may possibly be a tidal tail from a companion, enhanced in brightness by scattering or photoionization. In the near-infrared, most of the radio galaxies have elliptical morphologies with profiles that are well-fit by de Vaucouleurs r(exp 1/4)-laws and colors that are consistent with an old stellar population. All components around the quasars have optical-infrared colors that are redder than or similar to the colors of their respective nuclei; this is more consistent with a stellar origin for the emission than with a dominant scattering contribution. From the correspondence between the total magnitudes in the galaxies and quasars and the detection of aligned components in the quasars, we conclude that this study provides general support for the unification of FR II radio galaxies and quasars. Some of the objects in the sample (e.g, 3C 212) have properties that may be difficult to explain with our current understanding of the nature of FR II radio sources and the alignment effect.

Ridgway, Susan E.↗