Aubrey D. Haschick

Detection of widespread strong methanol masers at 44 GHz

The Haystack Observatory 37-m antenna was used to search for emission from the 44 GHz 7(0)-6(1)A(+) transition of interstellar methanol toward 50 galactic star-forming regions. The line was detected toward half the observed sources. Several of these regions were also observed in the 36 GHz 4(-1)-3(0)E line. In most sources, the detected emission shows one or more narrow components indicating maser action. The spectral appearance and spatial distribution of these methanol masers closely resembles the properties of the well-studied 25 GHz methanol masers: in some cases, distances between individual methanol maser components are of order 1 pc. Unlike the now well-studied 12 GHz methanol masers, these masers appear well separated from OH/H2O maser centers and compact H II regions. 52 refs.

Temperature and density structure of the collapsing core of G10. 6-0. 4

High-resolution aperture synthesis observations of the molecular gas surrounding the ultracompact H II region G10.6-0.4 in the (J,K) = (1,1) and (J,K) = (3,3) inversion lines of NH3 are reported. The ultracompact region is embedded in a dense molecular core whose average n(H2) density over the central 0.1 pc is 4 x 10 to the 6th/cu cm. The H II region is heating the molecular gas. Temperatures in the central 0.1 pc are in the range 95-140 K and scale outward as 1/sq rt R. The molecular core appears to be gravitationally collapsing onto the ultracompact H II region. Rotational gradient measurements suggest that between 1.5 and 0.35 pc the dynamics is consistent with Keplerian rotation and the mass distribution estimated from maps of the column density. 24 references.

Molecular outflows in powerful OH megamasers

High signal-to-noise ratio OH and H I data are presented for five powerful OH megamasers. The OH profiles of the main OH lines of III Zw 35, IR 12112+0305, and IC 4553 show extended blueshifted wings. Two newly detected 1720 MHz OH lines in III Zw 35 and IR 17208-0014 are found to be aligned in velocity with the strongest peak in the main lines. Strong blueshifted wings on the OH and H I lines are direct evidence for molecular outflows from the nuclear regions of active galaxies. These high-velocity regions are consistent with the starburst-driven superwinds observed in some active galaxies. It is found that the velocity extremes of the outflowing OH are consistent with an L(IR) exp 1/2 dependence. A similar dependence is also derived from the H I absorption lines. The accelerated molecular material may be as close as 10 pc from the sites of activity, which is well within the narrow line region of active galactic nuclei. Almost all strong OH megamasers exhibit a two-pronged profile in the 1667 MHz line, due to the excitation of the molecular gas in the nucleus. 57 refs.

Hydroxyl in galaxies. I : surveys with the NRAO 300 ft telescope

Four sessions on the 300 ft telescope during 1984-1987 have been used to search for hydroxyl in galaxies. The surveys of a sample of 321 galaxies has produced a total of seven megamaser detections and four detections of absorption. Three detections of OH megamasers are reported : IR 15065-1107, IR 22025+4205, and IR 22491-1808; the other megamasers have been reported earlier. Detections are reported for three new OH absorption sources : IR 03134-0236, IR 14566-1629, and IR 16577+5900. The observing sample contains sources from a variety of catalogs and represents different selection criteria. The results for the whole sample confirm that FIR luminosity and color criteria used for present surveys are indeed optimized for finding megamasers

IRAS 14070+0525 : an OH gigamaser at z=0.265

OH gigamaser emission has been detected in the luminous FIR galaxy IRAS 14070+0525 at a redshiht of 0.265. The FIR luminosity of IRAS 14070+0525 is 10 12.5 L ⊙ . The OH line luminosity is 1.4 x 10 4 L ⊙ , making it the most luminous known OH emitter. The OH line emission covers a velocity range of approximately 2400 km/s. Two distinct components in the OH emission reveal a powerful outflow component and/or the interactive nature of the system

Formaldehyde emission in galaxies

Nine detections of extragalactic emission in the 4.83 GHz 1 10 -1 11 formaldehyde transition are presented in addition to the only previously known extragalactic emission source in IC 4553. Formaldehyde emission occurs among both OH absorbers and emitters. In contrast with the high-detection rate of extragalactic sources in this survey, there are only a small number of Galactic sources with 4.83 GHz emission. Formaldehyde absorption has been found in one new source. A comparison has been made between the H 2 CO and OH properties of the galaxies. In analogy with the OH megamasers and as proposed for the IC 4553 formaldehyde megamaser emission line, low-gain amplification of radio continuum by foreground clouds in a molecular disk is also suggested for the new formaldehyde megamasers

VLBI observations of the water vapor maser in the nucleus of NGC 3079

The water vapor maser source in the nucleus of NGC 3079 has been observed with a four-station intercontinental VLBI array, which had a resolution of 0.3 mas. VLA observations of NGC 3079 show that the maser source is coincident in angle with the compact continuum radio source in the nucleus of the galaxy to better than 5 mas. The water vapor maser source in NGC 3079 is comparable in size, but apparently 500 times more luminous than the brightest H{sub 2}O maser source in the Galaxy, W49N, based on the assumption of isotropic emission. The small size and apparent high luminosity of this extragalactic source suggests special circumstances for the maser. A model is proposed wherein the maser is an unsaturated amplifier of the nuclear continuum source. 25 refs.

THE 18 CENTIMETER OH-EMISSION OF IC-4553 (ARP-220)

All transitions of hydroxyl have been found in emission in IC 4553 (Arp 220). The line shapes have been decomposed and interpreted in terms of three distinct emission regions: one region at the systemic velocity of the galaxy, and a second at a 334 km/s higher velocity. A third region represents a nuclear outflow with a terminal velocity of approximately 700 km/s. The emission lines for the region I are the strongest and originate in a molecular disk surrounding the nucleus of the galaxy. The infalling foreground region II is thought to be rather extended and has a very prominennt 1612 MHz line. The line ratios of regions I and II are quite different indicating that, although the primary pump for both regions is the infrared radiation field, there are differences in the (secondary) excitation conditions. Regions I and II may represent the two nuclei of the galaxies, which make up the merging IC 4553. The excitation of region III is collisional. 19 references.

Molecular Tori and H2O Megamaser Variability

Five prominent extragalactic water masers have been observed at roughly monthly intervals from 1984 until 1993 to study their temporal characteristics. The observing program at Haystack Observatory comprised five sources: NGC 1068, NGC 3079, NGC 4258, the irregular galaxy IC 10, and IC 133, an H II region complex in M33. The data on two sources, NGC 4258 and IC 10SE, have been presented earlier. All galaxies show strong variability in line strength, line velocity, and line width. The observed variability characteristics support a model with inverted molecular gas located in front of the nuclear source that experiences a variable pump rate and in part amplifies the background continuum. The extragalactic sources have been classified as class I for H II region emission sources in nearby galaxies or class II for mostly powerful emissions from galactic nuclei. In analogy with NGC 4258, the spectral features of class II sources NGC 1068 and NGC 3079 display a drift rate consistent with a compact molecular torus for the emission region.

The detection of the 4(-1)-3(0) E transition of methanol at 36. 2 GHz toward hot H II regions

Using Haystack Observatory at 36.169240 GHz, the 4(-1)-3(0) E transition of methanol toward 26 H II regions has been detected. The strong emission lines have narrow velocity components, thus exhibiting some of the characteristics of maser emission, as well as broader features which are assumed to be thermal in origin. The methanol emission preferably occurs in molecular clouds associated with hot H II regions and has not been detected in cold dark cloud regions or late-type stellar sources. The characteristics of the emission are discussed. 24 refs.