Showing papers by "Mark J. Reid published in 1996"

Formaldehyde Absorption at z = 0.685 toward the “Einstein Ring” B0218+357

Abstract: We report VLA observations of absorption in the 211 → 212 transition of formaldehyde (H2CO) at a redshift of 0.68466 toward the Einstein ring gravitational lens system B0218+357. We observe the H2CO line at 8.6 GHz only toward the stronger of the two compact images of this system. The column densities of H2CO and other molecules previously observed at millimeter wavelengths, as well as their relative abundances, are comparable to the values one finds for molecular clouds within the Milky Way. We argue that the material seen in absorption has a molecular hydrogen column density between 5 × 1021 and 5 × 1022 cm-2.

Neutral Hydrogen 21cm Absorption at Redshift 0.673 towards 1504+377

Abstract: We detect the 21 cm line of neutral hydrogen in absorption at a redshift of 0673 towards the 1 Jy radio source 1504+377 The 1504+377 radio source is located toward the center of what appears to be an inclined disk galaxy at z = 0674 The 21 cm absorption line shows multiple velocity components over a velocity range of about 100 km sec$^{-1}$, with a total HI column density: N(HI) = $38\times10^{19}\times({{T_s}\over{f}})$ cm$^{-2}$ The velocity-integrated optical depth of this system is the largest yet seen for redshifted HI 21 cm absorption line systems (Carilli 1995) The 21 cm absorption line is coincident in redshift with a previously detected broad molecular absorption line system (Wiklind and Combes 1996) We do not detect HI 21 cm absorption associated with the narrow molecular absorption line system at z = 067150, nor do we detect absorption at these redshifts by the 18 cm lines of OH, nor by the 2 cm transition of H$_2$CO There is no evidence for a bright optical AGN in 1504+377, suggesting significant obscuration through the disk -- a hypothesis supported by the strong absorption observed The 1504+377 system resembles the ``red quasar'' PKS 1413+135, which has been modeled as a optically obscured AGN with a very young radio jet in the center of a gas rich disk galaxy (Perlman et al 1996) The presence of very bright radio jets at the centers of these two disk galaxies presents a challenge to unification schemes for extragalactic radio sources and to models for the formation of radio loud AGN

Maser Spot Shape Persistence: Evidence for the Kinematic Interpretation of Proper Motions

Abstract: Intrinsic morphologies of interstellar OH maser-emitting gas condensations have been measured, for the first time, at two distinct epochs. The shapes and orientations of these maser condensations, in the vicinity of the ultracompact H II region W3(OH), are remarkably persistent from one epoch to the next despite significant position shifts. These observations provide the first direct evidence that the motions measured are due to actual physical movement of discrete clumps of maser-emitting matter, rather than to some sort of nonkinematic effect, such as traveling excitation phenomena or chance realignments of coherency paths through the masing gas. The kinematic assumption is crucial to astrophysical applications of maser proper-motion measurements, including distance determinations and studies of source dynamics. The shapes of the OH maser spots in W3(OH) show a tendency to be elongated in a direction parallel to the shock front delineated by radio continuum maps of the H II region, supporting the picture in which masers are formed in compressed gas behind the shock front.