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NASA NTRS1981

Observations of faint Haro galaxies

Spectroscopic and photometric data for 23 faint-compact UV-excess galaxy candidates, found by Haro's three-color technique (1956), are presented. Eighteen were found to be emission-line galaxies (magnitudes between 14.4 and 17.9) with redshifts in the range of 1670 to 39,450 km/s; the remaining five appear to be stars. The apparent compactness of the galaxy images is a result of the finite resolution of the Survey plates. Faint Haro galaxies are not distinguishable from the original Haro galaxies in surface brightness or in their range of color and absolute magnitude. The Haro galaxies correspond to roughly two-thirds of Huchra's non-Seyfert Markarian galaxies (1977 a) which have the most negative (U-B) index; the new Haro galaxies have the same V magnitude growth with aperture, the same (B-V) aperture relation, and the same mean surface brightness as the Markarian galaxies.

Kinman, T. D.↗

NASA NTRS1983

The evolution of clusters of galaxies. I - Very rich clusters

A multiple one-body Monte Carlo code is used to investigate the evolution of galaxies in a steady cluster potential under the influence of dynamical friction, two-body relaxation, tidal stripping, and galaxy mergers. The basic assumptions, estimated time scales, method and computer program, and effects of uncertainties in galaxy encounter physics are addressed. Numerical experiments in which the mass initially carried by galaxies and the mass function are varied are reported. It is shown that the formation of a very massive cluster galaxy depends critically on the number of galaxies, the initial division of cluster material between galaxies and a smooth intracluster medium, the mass spectrum of the galaxies, and chance. By the end of all simulations, less than half of the mass in the central regions of the cluster is bound to galaxies. It appears possible to produce any of the Bautz-Morgan classes from very similar initial conditions.

Richstone, D. O.↗

NASA NTRS1984

IRAS observations of Shapley-Ames galaxies

A preliminary discussion of the infrared properties of a representative subsample of galaxies in the Revised Shapley-Ames Catalog (B less than about 13 mag) is presented. Of the 165 galaxies in the sample, 108 predominantly spiral galaxies, are detected in the infrared by IRAS. None of the elliptical galaxies and only about 25 percent of the lenticular galaxies scanned were detected. The range of infrared-to-blue luminosity ratios, a measure of the infrared excess of galaxies, is large, varying from roughly 0.1 to roughly 5. The data suggest that weakly infrared emitting galaxies are cool (100-60 micron color temperatures of about 25 K), while the more infrared luminous ones tend to be warmer (about 50 K). The rate of star formation in barred spiral galaxies is apparently higher than in normal spirals. About 1 solar mass/year of interstellar matter is converted into massive stars in the typical spiral galaxy.

De Jong, T.↗

NASA NTRS1987

CO observations of nearby galaxies and the efficiency of star formation

The CO distributions and total molecular content of 160 galaxies were observed using the 14 meter millimeter telescope of the FCRAO. For the luminous, relatively face-on Sc galaxies, the azimuthally averaged CO distributions are centrally peaked, while for the Sb and Sa galaxies the Co distributions often exhibit central CO holes up to 5 kpc across. None of the Sc galaxies have CO distributions which resemble the Milky Way. A general correlation was found between total CO and IR luminosities in galaxies. The scatter in this relation is highly correlated with dust temperature. No strong correlation of IR luminosities was found with HI masses, and it was thereby concluded that the infrared emission is more directly tied to the molecular content of galaxies. It is suggested that galaxies which have high Star Formation Effiencies (SFEs) produce more stars per unit molecular mass, thereby increasing the average temperature of the dust in the star forming regions. Irregular galaxies and galaxies previously identified as mergers have the highest observed star formation efficiencies. For the mergers, evidence was found that the IR/CO luminosity ratio increases with the merger age estimated by Joseph and Wright (1985).

Young, Judith S.↗

NASA NTRS1987

Starburst galaxies

The infrared properties of star-forming galaxies, primarily as determined by the Infrared Astronomy Satellite (IRAS), are compared to X-ray, optical, and radio properties. Luminosity functions are reviewed and combined with those derived from optically discovered samples using 487 Markarian galaxies with redshifts and published IRAS 60 micron fluxes, and 1074 such galaxies in the Center for Astrophysics redshift survey. It is found that the majority of infrared galaxies which could be detected are low luminosity sources already known from the optical samples, but non-infrared surveys have found only a very small fraction of the highest luminosity sources. Distributions of infrared to optical fluxes and available spectra indicate that the majority of IRAS-selected galaxies are starburst galaxies. Having a census of starburst galaxies and associated dust allow severl important global calculations. The source counts are predicted as a function of flux limits for both infrared and radio fluxes. These galaxies are found to be important radio sources at faint flux limits. Taking the integrated flux to z = 3 indicates that such galaxies are a significant component of the diffuse X-ray background, and could be the the dominant component depending on the nature of the X-ray spectra and source evolution.

Weedman, Daniel W.↗

NASA NTRS1987

Star formation in Seyfert galaxies

An analysis of the IRAS data for a sample of classical (optically selected) Seyfert galaxies is presented. The IRAS fluxes at 25 micron, 60 micron, and 100 micron are found to be uncorrelated or only very weakly correlated with the UV/Optical continuum flux and the near and mid IR flux at 3.5 and 10 microns. To investigate the possibility that star formation accounts for the far IR flux, the IRAS measurements for the Seyfert galaxies are compared to IRAS observations of a sample of normal spiral galaxies, and a sample of Starburst galaxies. It is shown that the far IR luminosities and far IR colors of Seyfert galaxies are indistinguishable from those of the Starburst galaxies. Besides, normal galaxies are an order of magnitude less luminous than both the Seyfert and the Starburst galaxies. This indicates that star formation produces the bulk of the far infrared emission in Seyfert galaxies.

Espinosa, J. M. Rodriguez↗

NASA NTRS1986

Radio properties of type 1.8 and 1.9 Seyfert galaxies

A number of type 1.8 and 1.9 Seyfert galaxies have been observed at the VLA in order to compare their properties with those of the other types of Seyfert galaxy. The observed types have radio luminosities in the range of 10 to the 39th-40.5th args/s, with the median near 10 to the 40th ergs/s. Most of these galaxies have radio sources with diameters of about 500 pc or less. The ratio of radio luminosity to featureless optical continuum luminosity in the Seyfert 1.8/12.9 galaxies and Seyfert 1.2/1.5 galaxies is intermediate between the values for Seyfert 1 and Seyfert 2 galaxies. The infrared-to-radio ratio decreases along the sequence from Seyfert 1 galaxies, through intermediate Seyfert galaxies, to Seyfert 2 galaxies. This systematic statistical difference in the ratio of two aspect-independent quantities implies that the differences among the Seyfert classes cannot be attributed solely to differences in viewing angle.

Ulvestad, James S.↗

NASA NTRS1988

The far-ultraviolet spectra of early-type galaxies

New and revised ultraviolet energy distributions ar presented based on 97 IUE spectra of 31 early-type galaxies and the bulge of M31. Based on optical spectra and morphology, the sample galaxies are divided into star-forming galaxies, active galaxies, and quiescent galaxies. A well-defined nonlinear relationship between (1550-V) color and Mg2 for the 24 quiescent galaxies is obtained. The ultraviolet spectra of these galaxies can be modeled as a sum of two components: a normal, cool stellar population of main-sequence and giant branch stars that is redder at high Mg2, plus a very blue population having a steeply rising UV flux below 2000 A that increases in strength with metallicity. The UV spectra of star-forming galaxies are significantly flatter than the very blue component of quiescent galxies and are consistent with aging bursts of star formation. Two sample population models are explored for the blue stellar component of quiescent galaxies: postasymptotic giant branch stars and young stars from continuing star formation.

Burstein, David↗

NASA NTRS1988

Spectra of galaxies in the Case Low-Dispersion Sky Survey in the direction of the Bootes void

A sample of 34 galaxies selected from the Case Low-Dispersion Northern Sky Survey in the direction of the Bootes void. Emission-line redshifts were obtained for 33 objects; the spectrum of the thirty-fourth galaxy contains no obvious features. Three of the emission-line galaxies are lcoated within the boundaries of the Bootes void, including one not previously reported. To date, all the galaxies discovered in the void have emission-line spectra. Although more than half the galaxies in the sample are fainter than M(B) = -21.0 mag, all five of the galaxies that were detected by IRAS are brighter than M(B) = 21.5 mag. The relative strengths of the emission lines in most of the galaxies, including those in the void, indicate the lines are excited by photoionization due to young, hot O and B stars. Possible causes for the star formation occurring in these galaxies include interaction with nearby galaxies, star formation induced by nuclear activity, and/or recent development of physical conditions required for star formation.

Weistrop, Donna↗

NASA NTRS1988

IRAS observations of an optically selected sample of interacting galaxies

IRAS observations of a large, morphologically selected sample of strongly interacting disk-type galaxies have demonstrated that galaxy-galaxy collisions can lead to enhanced infrared emission, but not in all cases. Infrared luminosities of the interacting galaxies span a large range, but are about a factor of 2 higher, on average, than those of isolated disk galaxies. The data suggest the existence of a cutoff in blue luminosity, below which no galaxies show markedly enhanced infrared emission. Only the most strongly interacting systems in the sample show extreme values of infrared excess, suggesting that deep, interpenetrating collisions are necessary to drive infrared emission to extreme levels. Comparisons with optical indicators of star formation show that infrared excess and color temperatures correlate with the level of star-formation activity in the interacting galaxies. All interacting galaxies in our sample that exhibit an infrared excess and have higher than normal color temperatures also have optical indicators of high levels of star formation. It is not necessary to invoke processes other than star formation to account for the enhanced infrared luminosity in this sample of interacting galaxies.

Bushouse, Howard A.↗

NASA NTRS1989

A combined optical/X-ray study of the Galaxy cluster Abell 2256

The dynamics of Abell 2256 is investigated by combining X-ray observations of the intracluster gas with optical observations of the galaxy distribution and kinematics. Magnitudes and positions are presented for 172 galaxies and new redshifts for 75. Abell 2256 is similar to the Coma Cluster in its X-ray luminosity, mass, and galaxy density. Both the X-ray surface brightness and the galaxy surface density distributions exhibit an elliptical morphology. The radial galaxy distribution is steeper than the density profile of the X-ray-emitting gas, yet the galaxy velocity dispersion is higher than the equivalent value for the gas. Under the simplest assumptions that the galaxy velocity distribution is isotropic and the gas is isothermal, the galaxies and gas cannot be in hydrostatic equilibrium in a common gravitational potential. Models consistent with available data have mass-to-light ratios which increase with radius and galaxy orbits that are anisotropic with a radial bias.

Fabricant, Daniel G.↗

NASA NTRS1990

The ratio of molecular to atomic gas in spiral galaxies as a function of morphological type

In order to gain an understanding of the global processes which influence cloud and star formation in disk galaxies, it is necessary to determine the relative amounts of atomic, molecular, and ionized gas both as a function of position in galaxies and from galaxy to galaxy. With observations of the CO distributions in over 200 galaxies now completed as part of the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey (Young et al. 1989), researchers are finally in a position to determine the type dependence of the molecular content of spiral galaxies, along with the ratio of molecular to atomic gas as a function of type. Do late type spirals really have more gas than early types when the molecular gas content is included. Researchers conclude that there is more than an order of magnitude decrease in the ratio of molecular to atomic gas mass as a function of morphological type from Sa-Sd; an average Sa galaxy has more molecular than atomic gas, and an average Sc has less. Therefore, the total interstellar gas mass to blue luminosity ratio, M sub gas/L sub B, increases by less than a factor of two as a function of type from Sa-Sd. The dominant effect found is that the phase of the gas in the cool interstellar medium (ISM) varies along the Hubble sequence. Researchers suggest that the more massive and centrally concentrated galaxies are able to achieve a molecular-dominated ISM through the collection of more gas in the potential. That gas may then form molecular clouds when a critical density is exceeded. The picture which these observations support is one in which the conversion of atomic gas to molecular gas is a global process which depends on large scale dynamics (cf Wyse 1986). Among interacting and merging systems, researchers find considerable scatter in the M(H2)/M(HI) ratio, with the mean ratio similar to that in the early type galaxies. The high global ratio of molecular to atomic gas could result from the removal of HI gas, the enhanced conversion of HI into H2, or both.

Knezek, Patricia M.↗

NASA NTRS1990

Circumnuclear molecular gas in starburst and Seyfert galaxies

In order to investigate circumnuclear molecular gaseous contents and their relation to the nuclear activity, researchers made a search for circumnuclear (12)CO (J=1-0) emission from 28 starburst-nucleus galaxies (SBNs) and 12 Seyfert galaxies with the recession velocities less than 5000 km/s, using the Nobeyama Radio Observatory 45-m telescope. The full half-power beam width of 17 arcsec covers a region of less than about 5 kpc in diameter for the sample galaxies. The circumnuclear CO emission was detected from twelve SBNs (one is marginal) and four Seyfert galaxies. The main results and conclusions are summarized. Researchers derived the circumnuclear surface density of molecular gas which is corrected for inclination of the galaxies. This analysis shows that the surface density spans a wide range over two orders of magnitude. Further, there is no significant difference in the surface densities between types 1 and 2 Seyfert galaxies. Thus, we may conclude that the circumnuclear molecular content is not a key parameter producing the dichotomy of the Seyfert galaxies. It is also shown that there is no significant difference in the circumnuclear surface densities of molecular gas among the Seyfert, starburst, and normal galaxies. This implies that the circumnuclear gaseous content is not a key parameter determining which activity occurs in nuclei. We may conclude that more centrally condensed (i.e., less than 10 - 100 pc in diameter) gas components play an essential role on the occurrence of nuclear activities. Comparing results with the previous ones, researchers deduced radial distribution of surface density of molecular gases. They cannot obtain evidence for strong central concentration of molecular gas in the sample Seyfert galaxies except for NGC 3227. This is consistent with the previous result by Blitz, Mathieu, and Bally (1986). Comparing the CO emission line profiles with the previous ones taken with the larger beams, researchers discovered circumnuclear components of molecular gases. In particular, they found that molecular gas clouds may be absent in the SE of the nucleus of NGC 7469 where the high-excitation emitting region is discovered by Heckman et al. (1986). It is suggested that the nuclear activity (strong radiation and/or wind) may destruct the molecular clouds in that region.

Taniguchi, Yoshiaki↗

NASA NTRS1990

Morphological type correlation between nearest neighbor pairs of galaxies

Although the morphological type of galaxies is one of the most fundamental properties of galaxies, its origin and evolutionary processes, if any, are not yet fully understood. It has been established that the galaxy morphology strongly depends on the environment in which the galaxy resides (e.g., Dressler 1980). Galaxy pairs correspond to the smallest scales of galaxy clustering and may provide important clues to how the environment influences the formation and evolution of galaxies. Several investigators pointed out that there is a tendency for pair galaxies to have similar morphological types (Karachentsev and Karachentseva 1974, Page 1975, Noerdlinger 1979). Here, researchers analyze morphological type correlation for 18,364 nearest neighbor pairs of galaxies identified in the magnetic tape version of the Center for Astrophysics Redshift Catalogue.

Yamagata, Tomohiko↗

NASA NTRS1990

Stellar kinematics of elliptical galaxies in pairs

In both galaxy pairs Arp 166 and 3C 278 the authors find radially increasing velocity dispersions indicating a perturbed, non-equilibrium state of the galaxies after the tidal interaction. In all galaxies, the increase is most pronounced in the regions which correspond to the centers of the outer isophotes. The authors suggest a scenario in which the galaxies are strongly decelerated on their orbits during the encounter. The deceleration depends on the radial position in the perturbed galaxy and vanishes in the center of the perturbed galaxy (Spitzer, 1958). In addition, the crossing time of the stars near the center is very short, implying that the tidal perturbations can be averaged over several orbital periods (e.g., Binney and Tremaine, 1987). In consequence, the central parts are not affected by the tidal interaction while the outer parts are strongly decelerated. This leads to a displacement of the central parts of the galaxies with respect to their envelopes in an anti-symmetrical way for the two components of each galaxy pair. The motions of the central parts subsequently are opposed by dynamical friction with the surrounding envelopes. Due to dynamical friction, the density of the stars increases in the wakes of the moving central parts (Mulder, 1983). The overdensity of stars in the wakes of the moving central parts efficiently decelerates the motions of the central parts. The reaction of the stars in the overdensity regions leads to an increase of the velocity dispersion mainly along the orbits of the moving central parts. The presented observations, especially the asymmetrical luminosity profiles and the radially increasing velocity dispersions support consistently the above scenario of tidal interaction between galaxies. Further spectroscopic observations are necessary in order to investigate the degree of anisotropy in the kinematically perturbed regions.

Madejsky, Rainer↗

NASA NTRS1990

Multi-color imaging of selected southern interacting galaxies

The authors present preliminary results from a study of selected Arp-Madore Southern Hemisphere peculiar galaxies. Broadband charge coupled device (CCD) images (BVRI) of a subset of these galaxies allow us to study each galaxy's optical morphology, color, and (in a crude manner) degree of nuclear activity, and to compare them with similar data we possess on other active galaxies. Many of these galaxies have optical morphologies closely resembling those of powerful radio galaxies (Smith and Heckman 1989), yet their radio emission is unremarkable. Accurate positions for subsequent spectroscopic studies have been determined along with broad band photometry and morphology studies. Detailed observations of these comparatively bright, low-redshift, well-resolved interacting systems should aid our understanding of the role interactions play in triggering galaxy activity. This work is the initial effort in a long term project to study the role played by the dynamics of the interaction in the production and manifestations of activity in galaxies, and the frequency of galaxy mergers.

Smith, Eric P.↗

NASA NTRS1990

Radio line and continuum observations of quasar-galaxy pairs and the origin of low reshift quasar absorption line systems

There are a number of known quasars for which our line of sight to the high redshift quasar passes within a few Holmberg radii of a low redshift galaxy. In a few of these cases, spectra of the quasar reveal absorption by gas associated with the low redshift galaxy. A number of these pairs imply absorption by gas which lies well outside the optical disk of the associated galaxy, leading to models of galaxies with 'halos' or 'disks' of gas extending to large radii. The authors present observations of 4 such pairs. In three of the four cases, they find that the associated galaxy is highly disturbed, typically due to a gravitational interaction with a companion galaxy, while in the fourth case the absorption can be explained by clouds in the optical disk of the associated galaxy. They are led to an alternative hypothesis concerning the origin of the low redshift absorption line systems: the absorption is by gas clouds which have been gravitationally stripped from the associated galaxy. These galaxies are rapidly evolving, and should not be used as examples of absorption by clouds in halos of field spirals. The authors conclude by considering the role extended gas in interacting systems plays in the origin of higher redshift quasar absorption line systems.

Carilli, C. L.↗

NASA NTRS1990

Gas flows in S-E binary systems of galaxies

Tidal interaction between the galaxies in binary systems leads to important consequences. Some peculiarities in galactic morphology as well as the transfer of matter from one galaxy to another may be due to this factor. In particular, gas flows in intergalactic space may be formed. Such flows enriching one component with gas from the other may play a substantial role in the evolution of mixed (S-E) pairs. One can mention several facts corroborating the possibility of the gas transfer from the spiral to the elliptical galaxy. High HI content (10(exp 7) to 10(exp 9) solar mass) is detected in nearly 40 E galaxies (Bottinelli and Gougenheim, 1979; Knapp et al., 1985). Such galaxies are often members of pairs or of multiple systems including an S galaxy, which may be the source of gas (Smirnov and Komberg, 1980). Moreover, the gas kinematics and its distribution also indicate an external origin for this gas (Knapp et al., 1985). In many cases there is an outer gaseous disk. The directions of the disk and of stellar rotation don't always coincide (van Gorkom et al., 1985; Varnas et al., 1987). The galaxy colors in S-E pairs are correlated (the Holmberg effect): bluer ellipticals have spiral components that are usually bluer (Demin et al., 1984). The fraction of E galaxies with emission lines (N sub em) in S-E pairs showing traces of tidal interaction is twice as large (N sub em approx. equals 0.24) as in pairs without interaction (N sub em approx. equals 0.12) (Sotnikova, 1988b). Since the presence of emission lines in a galaxy spectrum strongly depends on gas content, this fact also leads to the conclusion that ellipticals in interacting S-E pairs are enriched with gas. These facts may be considered as a serious indication of the existence of gas transfer. Hence, investigation of this process is of interest.

Sotnikova, N. YA.↗