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NASA NTRS1976

Optical and infrared spectrophotometry of 18 Markarian galaxies

Slit spectra, spectrophotometric scans, and infrared broad-band observations are presented for 18 Markarian galaxies with emission lines. Eight of the program galaxies can be classified as Seyfert galaxies. Arguments are given that thermal, nonthermal, and stellar radiation components are present. Broadly speaking, one group of Seyfert galaxies is characterized both by the presence of a high-density region of gas and by a continuum dominated by nonthermal radiation. The continua of the remaining program Seyferts, which do not have a high-density region of gas, are dominated by thermal radiation from dust and a stellar continuum. The 10 galaxies which are not Seyfert galaxies are shown to be examples of extragalactic H II regions; there is evidence for thermal emission from dust being present at 10 microns in four of these galaxies.

Neugebauer, G.↗
NASA NTRS1978

On the rotation of elliptical galaxies

The tensor virial theorem is applied to models of early-type galaxies. First the theorem is applied to rotating elliptical galaxies whose constant-density surfaces are similar ellipsoids. A relationship is obtained between the observed rotations and the forms of generally triaxial galaxies. By applying the results of Robert (1962) to the evaluation of the components of the Chandrasekhar tensor which occurs in this relationship, it is found that the form of a galaxy that lacks global velocity anisotropy uniquely determines the ratio of its rotational and random kinetic energies independently of the radial density profile of that galaxy. A distribution of three-dimensional prolate spheroids is derived which accounts for the observed distribution of ellipticities reported by Sandage, Freeman, and Stokes (1970). This is then used to derive curves giving the expected frequency of occurrence of galaxies of given rotational velocities for each of a number of different apparent elongations on the sky. It is found that if elliptical galaxies are prolate, there should be little correlation between apparent ellipticity and rotation velocity.

Binney, J.↗
NASA NTRS1979

A photometric determination of twists in three early-type galaxies

Detailed photometric data have been obtained for three early-type galaxies by using the Cerro Tololo 1.5-m telescope and an SEC television camera. The aim of this photometry is to gain further accurate information on the occurrence of twists in such galaxies; i.e., on any variations with radius of the position angle of the major axes of the isophotes. The results of the photometry are: (1) the finding of no detectable twist within the bulge of the S0 galaxy NGC 5102; (2) confirmation of a substantial twist (about 10 deg) in the inner portion of the E3 galaxy IC 1459; and (3) determination of a moderate twist (about 5 deg) within the E4 galaxy NGC 4697, possibly too small to have been previously detected. If such moderate twists should turn out to be common in elliptical galaxies, the suspicion of triaxiality for most such galaxies would be enhanced.

Williams, T. B.↗
NASA NTRS1979

VV 5-32-63/64 - The 'supermassive double galaxy' in Abell 1775 revisited

Spectroscopy is presented for galaxies in A 1775, the cluster containing VV 5-32-63/64, an apparent double galaxy which has long been considered a gravitationally bound system with supermassive components (10 to the 13th solar masses). However, this model has run afoul of recent radio observations, which detected an extremely long straight radio tail emanating from the eastern galaxy in the pair. The present observations indicate that if both galaxies are members of the same cluster, the cluster radial-velocity dispersion (1522 km/sec) is large enough to account for the velocity difference between the two VV galaxies (1650 km/sec). It is therefore suggested that the VV galaxies are not gravitationally bound and need not be supermassive. The large velocity dispersion measured for A 1775 also strains suggested velocity dispersion vs X-ray luminosity relations for clusters of galaxies, as A 1775 has not yet been detected at X-ray wavelengths.

Hintzen, P.↗
NASA NTRS1982

The impact of IUE observations on our knowledge about galaxies and quasars

Observations of extragalactic objects with IUE are discussed. Elliptical galaxies show the presence of very hot stars which are probably highly evolved horizontal branch objects, although the observations are not adequate to rule out young OB stars. Spiral and irregular galaxies often show evidence of young OB stars although the nucleus of M31 is very similar to elliptical galaxies. Several narrow emission line galaxies appear to have nonthermal continua. Observations of Seyfert galaxies permit detailed studies of the continua and line ratios such as L alpha to H beta to be made. Unlike quasars, there is evidence for dust based on the 2175 A feature. The problem of understanding Seyfert galaxy spectra is no easier than that for quasars although observed variability in the broad lines may present useful clues. Observations of high redshift quasars with IUE allow spectra to be obtained down to rest wavelengths of a few hundred Angstroms and provide information about the amount of ionizing flux. Observations of low redshift quasars can be used to test whether the myriads of absorption lines seen below L alpha in high redshift quasars are indeed produced by intergalactic clouds and halos of intervening galaxies.

Oke, J. B.↗
NASA NTRS1982

Ultraviolet photometry from the Orbiting Astronomical Observatory. XL - The energy distributions of spiral and irregular galaxies

Measurements of the total light of 40 spiral and irregular galaxies are presented. The photometry covers the wavelength range 1550-4250 A and is calibrated on an absolute basis. On the average later-type galaxies are not only bluer at short wavelengths than ellipticals but significantly bluer than visual colors would imply. This reflects a recent history of more vigorous formation of massive stars. The shape of the upper part of the initial mass function apparently varies more among early-type galaxies, producing a wide scatter in their energy distributions. In at least some galaxies interstellar dust appears to have little influence upon the emerging radiation. The local volume luminosity spectrum due to galaxies turns up steeply at short wavelengths, and is shaped largely by contributions from late-type galaxies. The observed ultraviolet background cannot be produced by normal galaxies, although the large corrections implied by theoretical evolutionary models may account for the measurements.

Code, A. D.↗
NASA NTRS1982

Large-scale superclusters surrounding the giant galaxy void in Bootes

The overdensity of galaxies observed by Kirshner et al. (1981) on both redshift sides of the galaxy void in Bootes is found to coincide in redshift space with similar overdensities of clusters and superclusters of galaxies in the northern hemisphere. The main contributors to these overdensities are the rich Hercules and Corona Borealis superclusters. It is suggested that large-scale density enhancements of galaxies associated with the Hercules and Corona Borealis superclusters may extend to more than about 100-150/h Mpc in projection and surround the giant volume of galaxy depletion in Bootes. Previous observational evidence, together with the results presented here, suggests that galaxy voids may generally be associated with surrounding galaxy excesses.

Bahcall, N. A.↗
NASA NTRS1982

0351+026 - A QSO spawned by interacting galaxies

The results of a detailed investigation into the nature of the H I-rich quasi-stellar object 0351+026 are presented. An improved H I profile reveals the presence of two distinct components. A high-quality CCD image clearly shows the presence of two galaxies. The brighter galaxy hosts the QSO while the less luminous companion has a prominent, apparently stellar nucleus. Moreover, this image also shows streamers of nebulosity emanating from the two galaxies and has an overall morphology which is highly reminiscent of that seen in other strongly interacting galaxies. Optical spectroscopy of the system shows that the forbidden O III emission lies between the two nuclei and there is strong evidence of stellar absorption lines in both the host and companion galaxies. Overall, the data suggest that this system represents a violent encounter between two low-luminosity H I-rich galaxies. The possibility exists that this collision has triggered the QSO activity in the brighter galaxy.

Bothun, G. D.↗
NASA NTRS1983

Observations of neutral hydrogen in radio-loud and interacting galaxies

The results of a survey of H I in radio-loud and interacting galaxies is presented. Four cases of H I absorption and five of emission are reported. The interesting features found for individual galaxies are described, and the systematic properties are discussed. Column densities of absorbing gas generally exceed those expected for a 'Milky Way' H I disk by more than an order of magnitude. The absorbing gas must have a flattened, disklike morphology oriented roughly parallel to the optical disk of the galaxy. Turbulent noncircular gas motions are evidently present, which are shown to be almost certainly induced by galaxy-galaxy interactions. The set of galaxies in which H I absorption has been detected is dominated by morphologically peculiar objects. It is concluded that the detection of H I seen in absorption against a nuclear radio source permits direct determination of the sense of radial flow of extranuclear material, and is direct evidence that potential 'food' for a compact object in the nucleus exists in the galaxy.

Heckman, T. M.↗
NASA NTRS1983

Blue compact dwarf galaxies. II - Near-infrared studies and stellar populations

An IR photometric survey was performed of 36 blue compact dwarf galaxies (BCDG) where intense bursts of star formation have been observed. The survey covered the J, H, and K lines, with all readings taken at the level of a few mJy. Although the near-IR fluxes observed in the galaxies are due to K and M giants, the bursts have calculated ages of less than 50 million yr. However, the BCDG galaxies surveyed are not young, with the least chemically evolved galaxy observed, I Zw 18, featuring 50 pct of its stars formed prior to its last burst, but with a missing mass that is not accounted for by H I interferometric observations. It is concluded that the old stars must be more spatially extended than the young stars, and a mixture of OB stars with the K and M giants is projected as capable of displaying the colors observed. The star formation processes in the BCDG galaxies is defined as dependent on the total mass of the galaxies, with low mass galaxies having a high ratio of star formation, compared to their previous rates.

Thuan, T. X.↗
NASA NTRS1983

Dust in galaxies

The manifestations of dust in the Galaxy, in normal galaxies, active nuclei galaxies (ANGs), and in QSOs are discussed. Findings on the composition, abundance, size distribution, and global properties of the Galaxy's dust obtained with absorption and emission studies are reviewed. The properties of dust in other galaxies, the variation of those properties among galaxies, and the effect of the dust on the appearance of galaxies are considered, discussing the LMC, M51, and M82 as examples. Evidence for the existence of dust in the nuclei of ANGs and in QSOs is examined with regard to reddening, dust emission and absorption, and polarization. The question of the existence of intergalactic dust is briefly addressed.

Stein, W. A.↗
NASA NTRS1983

The environment of D and cD galaxies

The Dressler (1980) morphological sample of galaxies in clusters is used in an investigation of bright galaxy spatial distribution, which has established that such galaxies with luminous extended halos as the D or cD lie on significant cluster galaxy distribution peaks irrespective of whether they are the brightest cluster member. The mean distance of bright D and cD galaxies from local density peaks is of the order of their halo scales, and the positions of bright galaxies of other morphological types are consistent with their being drawn at random from each morphological population. It is noted that local density peaks with associated d ocD galaxies have a mean density 2-3 times greater than peaks without a D or cD.

Beers, T. C.↗
NASA NTRS1985

IRAS observations of active galaxies

The IRAS survey gives an unbiased view of the infrared properties of the active galaxies. Seyfert galaxies occupy much the same area in color-color plots as to normal infrared bright galaxies, but extend the range towards flatter 60 to 25 mm slopes. Statistically the Seyfert 1 galaxies can be distinguished from the Seyfert 2 galaxies, lying predominantly closer to the area with constant slopes between 25 and 200 mm. The infrared measurements of the Seyfert galaxies cannot distinguish between the emission mechanisms in these objects although they agree with the currently popular ideas; they do provide a measure of the total luminosity of the Seyferts. The quasar's position in the color-color diagrams continue the trend of the Seyferts. The quasar 3C48 is shown to be exceptional among the radio loud quasars in that it has a high infrared luminosity which dominates the power output of the quasar and is most likely associated with the underlying host galaxy.

Neugebauer, G.↗
NASA NTRS1985

Optical multicolors - A poor person's z machine for galaxies

The feasibility, limits, accuracy, and uncertainties of using optical broadband colors in the form of two-color plots to measure the redshifts of faint galaxies are explored. Comparison of redshifts from slit spectra and 4-m photographic UBVI photometry of 100 faint galaxies confirms that colors do yield redshifts. These galaxies of 17-23 mag in B span a wide range of intrinsic color and are thus unlike previous samples of faint galaxies that were largely radio or cluster galaxies of early (red) type. For redshifts less than 0.35, two-thirds of the color redshifts agree with the spectroscopic values to within + or - 0.04 in z; for higher redshifts to z of 0.6, the errors increase to + or - 0.06. These accuracies were achieved for blue as well as red galaxies, and ensure that multicolors can serve as a poor person's redshift machine to study distant galaxies in clusters and the field.

Koo, D. C.↗
NASA NTRS1985

X-ray emission from E and S0 galaxies with compact nuclear radio sources

The imaging proportional counter on the Einstein Observatory has been used to search for X-ray emission from 13 nearby E and S0 galaxies with compact nuclear radio sources. Five galaxies with X-ray luminosity of about 10 to the 41st ergs/s were detected, and one of them was resolved. These galaxies and a few similar ones observed by others are compared to a sample of radio-quiet E and S0 galaxies. The radio-emitting galaxies have consistently greater X-ray luminosities per unit of optical luminosity than most radio-quiet galaxies. Possible emission mechanisms and models for the resolved source, for the most powerful source, and for the class of E/S0 galaxies with active nuclei are discussed.

Dressel, L. L.↗
NASA NTRS1986

Metallicity and the level of the ultraviolet rising branch in elliptical galaxies

This final report concerns a project to study the systematics of the ultraviolet flux level in elliptical galaxies. Prior to the inception of this work, the systematic behavior of the ultraviolet flux level was basically unknown and ultraviolet fluxes were observed to vary greatly from galaxy to galaxy. There was a suggestion, however, that there might be a dependence of ultraviolet flux on galaxy metallicity, but the correlation was based on just six galaxies. IUE spectra of elliptical galaxies have been reanalyzed and placed on a consistent, homogenous flux system. The major conclusion is a confirmation of the original hypothesis: galaxies with stronger Mg2 lines show enhanced ultraviolet flux.

Faber, S. M.↗
NASA NTRS1985

Boxy isophotes, discs and dust lanes in elliptical galaxies

CCD images of 42 elliptical and S0 galaxies are examined for low-contrast structures or subtle distortions of the isophotes from perfect ellipses. 75 percent of the galaxies have isophotes completely describable as concentric ellipses to within the photometry errors. 'Boxy' isophotes, stellar discs, and dust lanes are detected in the remaining 25 percent of the sample. The boxy elliptical galaxies appear dynamically indistinguishable from normal ellipticals and are therefore different from boxy bulges, which rotate rapidly. Most of the galaxies with faint discs, however, appear dynamically similar to S0 galaxies. Nearly edge-on dust lanes are found in four galaxies, which suggests that dust lanes may commonly occur in elliptical galaxies.

Lauer, T. R.↗
NASA NTRS1986

The X-ray properties of normal galaxies

X-ray observations with the Einstein satellite have shown that normal galaxies of all morphological types are spatially extended sources of X-ray emission with luminosities in the range of L(x) of about 10 to the 39th to 10 to the 41st erg/s. Although this is only a small fraction of the total energy output of a normal galaxy, X-ray observations are uniquely suited to study phenomena that are otherwise elusive. In X-rays one can study directly the end products of stellar evolution (SNRs and compact remnants). X-ray observations have led to the discovery of gaseous outflows linked to starburst nuclear activity in spiral galaxies and to the detection of a hot interstellar medium in early-type galaxies. Through X-ray observations it is possible to set constraints on structural galaxy parameters, such as the mass of elliptical galaxies, and perhaps get new insight on the origin of cosmic rays and the properties of the magnetic fields of spiral galaxies.

Fabbiano, G.↗