David E. Hogg

Asymmetry in High-Precision Global H I Profiles of Isolated Spiral Galaxies

New high signal-to-noise ratio 21 cm H I line profiles have been obtained for 104 galaxies with the Green Bank 43 m telescope. The primary sample is composed of isolated spirals with no known optical companions within a 1° radius and a median ratio of optical diameter to beamwidth of 0.17. An effort was made to ensure linearity of baseline fitting and precise flux density calibration to better than 5%. Two quantitative measures of asymmetry are applied to assess the occurrence of lopsidedness in the global H I profiles. In agreement with previous estimates, half the galaxies show significant H I profile asymmetries. The lopsidedness cannot be explained by pointing offsets but, rather, must result from noncircular motions, confusion with unidentified companions within the telescope beam, or true distortions in the H I distribution.

Interstellar matter in early-type galaxies. I. The catalog

A catalog is given of the currently available measurements of interstellar matter in the 467 early-type galaxies listed in the second edition of the Revised Shapley-Ames Catalog of Bright Galaxies. The morphological type range is E, SO, and Sa. The ISM tracers are emission in the following bands: IRAS 100 micron, X-ray, radio, neutral hydrogen, and carbon monoxide. Nearly two-thirds of the Es and SOs have been detected in one or more of these tracers. Additional observed quantities that are tabulated include: magnitude, colors, radial velocity, central velocity dispersion, maximum of the rotation curve, angular size, 60 micron flux, and supernovae. Qualitative statements as to the presence of dust or emission lines, when available in the literature, are given. Quantities derivative from the observed values are also listed and include masses of H I, CO, X-ray gas, and dust as well as an estimate of the total mass and mass-to-luminosity ratio of the individual galaxies. 204 refs.

Interstellar matter in early-type galaxies. II - The relationship between gaseous components and galaxy types

Interstellar components of early-type galaxies are established by galactic type and luminosity in order to search for relationships between the different interstellar components and to test the predictions of theoretical models. Some of the data include observations of neutral hydrogen, carbon monoxide, and radio continuum emission. An alternative distance model which yields LX varies as LB sup 2.45, a relation which is in conflict with simple cooling flow models, is discussed. The dispersion of the X-ray luminosity about this regression line is unlikely to result from stripping. The striking lack of clear correlations between hot and cold interstellar components, taken together with their morphologies, suggests that the cold gas is a disk phenomenon while the hot gas is a bulge phenomenon, with little interaction between the two. The progression of galaxy type from E to Sa is not only a sequence of decreasing stellar bulge-to-disk ratio, but also of hot-to-cold-gas ratio.

The interaction between hot and cold gas in early-type galaxies

SO and Sa galaxies have approximately equal masses of H I and X-ray emitting gas and are ideal sites for studying the interaction between hot and cold gas. An X-ray observation of the Sa galaxy NGC 1291 with the ROSAT position sensitive proportional counter (PSPC) shows a striking spatial anticorrelation between hot and cold gas where X-ray emitting material fills the large central black hole in the H I disk. This supports a previous suggestion that hot gas is a bulge phenomenon and neutral hydrogen is a disk phenomenon. The X-ray luminosity (1.5 x 10(exp 40) ergs/s) and radial surface brightness distribution (beta = 0.51) is the same as for elliptical galaxies with optical luminosities and velocity dispersions like that of the bulge of NGC 1291. Modeling of the X-ray spectrum requires a component with a temperature of 0.15 keV, similar to that expected from the velocity dispersion of the stars, and with a hotter component where kT = 1.07 keV. This hotter component is not due to emission from stars and its origin remains unclear. PSPC observations are reported for the SO NGC 4203, where a nuclear point source dominates the emission, preventing a study of the radial distribution of the hot gas relative to the H I.

Hot and Cold Gas in Early-Type Spirals: NGC 3623, NGC 2775, and NGC 1291

We have studied the distribution of cool, warm, and hot interstellar matter in three of the nearest bright Sa galaxies. New X-ray data for NGC 1291, the object with the most prominent bulge, confirm earlier results that the ISM in the bulge is dominated by hot gas. NGC 3623 has a lesser amount of hot gas in the bulge but has both molecular gas and ionized hydrogen in the central regions. NGC 2775 has the least prominent bulge; its X-ray emission is consistent with an origin in X-ray binary stars, and there is a strict upper limit on the amount of molecular present in the bulge. All three galaxies have a ring of neutral hydrogen in the disk. NGC 3623 and NGC 2775 each have in addition a molecular ring coincident with the hydrogen ring. We conclude that even within the morphological class Sa there can be significant differences in the gas content of the bulge, with the more massive bulges being likely to contain hot, X-ray–emitting gas. We discuss the possibility that the X-ray gas is part of a cooling flow in which cool gas is produced in the nucleus.

The Amorphous Galaxy NGC 2777: H I Evidence for Tidal Interaction with a Faint Companion

NGC 2777 is an amorphous galaxy possessing the classic signature of an A-type spectrum with superposed emission lines. There is no optical evidence for an interaction, but observations of the neutral hydrogen in this system reveal an H I bridge between NGC 2777 and U3, a companion that is 3 mag fainter. Far-infrared observations indicate that the current rate of massive star formation in NGC 2777 is low, but the optical spectra indicate that it must have been significantly higher in the recent past. We were unable to detect CO in either galaxy. We also consider a sample of 10 amorphous galaxies, all showing A-type absorption spectra: nine from the Revised Shapley-Ames Catalog, plus NGC 2777. All show optical/H I interaction and/or peculiar velocity fields, supporting the view that amorphous characteristics are the result of interaction. For some of the galaxies, the interacting companion is much fainter than the amorphous system, which indicates that previous concerns raised by the existence of isolated amorphous galaxies may have been premature.

A search for CO emission in cooling flows

The NRAO 12 m telescope was used to search for CO emission from the centers of two elliptical galaxies and four clusters of galaxies rich in 10 to the 7th-10 to the 8th K gas. No CO emission was detected, and the 3(delta) upper limits are 1-2 x 10 to the 8th solar masses for elliptical galaxies and 1-6 x 10 to the 10th solar masses for the clusters. The cooling-flow model for the evolution of the hot gas predicts the rate at which cool gas, and eventually stars, are produced. If this model is correct, measurements indicate that the ratio of the CO mass to the star-formation rate is at least a half order of magnitude less than in the Galaxy; star formation occurs rapidly and efficiently. 28 references.

Resolution of the Radio Source γ2 Vel

The WC star γ2 Vel has been resolved at radio wavelengths with the VLA. At a frequency of 4860 MHz, the flux density observed at a given antenna separation is independent of the position angle of the baseline, implying that the wind is spherical. The data at three frequencies suggest that the electron density decreases with distance more rapidly than r-2 for distances greater than 3 x 1015 cm. The wind is isothermal with temperature 5600 ± 500 K, and the mass loss rate is (8.6 ± 1.0) x 10-5 M0 yr-1.

SELECTING AND SCHEDULING OBSERVING PROPOSALS AT NRAO TELESCOPES

The process by which proposals for the use of the NRAO1 telescopes are selected is described. The demands of modern astronomical research have required new procedures to accommodate projects which require large amounts of observing time or which study transient phenomena, and to facilitate the coordination of programs with NRAO telescopes and telescopes at other observatories.

Radio Emission from WR Stars

In principle radio observations of WR stars offer the best possibility of determining the rate of mass loss, since for a simple model of the extended atmosphere the mass loss rate depends primarily on quantities--the flux density, the velocity, and the distance--which are observable (Barlow 1979). Until now, detections of Wolf-Rayet stars have been limited by the sensitivity and resolution of available telescopes. The advent of the Very Large Array makes a search for emission from a large number of these stars feasible.