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NASA NTRS1987

Star formation in the Magellanic irregular galaxy NGC 4449

New NIR and FIR maps and J = 1-0 CO spectroscopy of the Magellanic irregular galaxy NGC 4449 are presented. The brighter 150-micron emission is concentrated along the central visual ridge of the galaxy, although there is lower intensity extended emission throughout the visible extent of the object. The maximum FIR emission is coincident, within the uncertainties, with the visual and NIR maxima, identified as the galactic nucleus. It is estimated that the IR luminosity of the 1-kpc-diameter central region in NGC 4449 is comparable to that for a similar-sized region at the center of the Galaxy. A large fraction of the 150-micron emission may arise from warm dust distributed throughout the galaxy and heated by the diffuse radiation field. Active star formation follows the NIR emission in part of the galaxy, but no coincidence is found in another region.

Thronson, Harley A., Jr.↗

NASA NTRS1987

A study of a flux-limited sample of IRAS galaxies

Redshift data and accurate four-color infrared photometry are presented for a complete IRAS sample of galaxies brighter than 2 Jy at 60 microns. A simple power law provides a good fit to the distribution for luminosities from 10 to the 10th to 10 to the 12th solar. There is no indication of an exponential dropoff in the luminosity function at high energies. A flattening of the luminosity function occurs at L less than 10 to the 20th solar. The highest luminosity galaxies typically are found in multiple, possibly interacting, systems and exhibit marginally narrower infrared spectral energy distributions than the isolated spirals which predominate at low luminosities. Infrared-bright galaxies come from a different population than the majority of optically bright galaxies. In particular, galaxies of low blue luminosity are not strong infrared emitters.

Smith, Beverly J.↗

NASA NTRS1987

Isophotal diameters of galaxies at high redshifts

New ultraviolet observations and archival spectra are presented for the bright disk of the galaxy NGC 4736 to derive the ultraviolet surface brightness profile. This is used to predict the appearance of such a galaxy at high redshift. The profiles in red light of 100 galaxies determined by S. Kent (1984) are used with assumed ultraviolet spectra to predict the isophotal diameters of these galaxies as a function of redshift. The results show that, for ground-based imagery, normal spiral galaxies should be resolvable to the largest redshifts (z roughly 1). For space-based imagery, much smaller but brighter galactic disks characterized by extensive star formation will be those resolved at the highest redshifts (z roughly 2.5).

Weedman, Daniel W.↗

NASA NTRS1987

The H I distribution in clouds within galaxies

An interpretation is given for the relatively flat distribution of atomic hydrogen as a function of radius within the visible disks of spiral galaxies and the existence of a correlation between H I surface density and morphological class of spiral galaxy. The H I is mostly contained in constant column density envelopes of molecular clouds. The clouds have a two-dimensional filling factor of unity when a galaxy is viewed face on. The column density of the cloud envelopes depends on the ratio of flux of H2 dissociating radiation in the ambient medium to envelope gas density. The flat H I profiles imply the gas density and pressure follow the ultraviolet ambient flux on kiloparsec scales throughout a given galaxy. Later-type galaxies have larger ultraviolet surface brightnesses, as deduced from the H-alpha surface brightnesses. Therefore, thicker protective H I envelopes develop in late-type spirals.

Shaya, E. J.↗

NASA NTRS1987

Evidence of an infrared luminosity indicator for galaxies

To elucidate the nature of infrared-luminous galaxies discovered with the IRAS satellite, the optical and infrared luminosities of 1161 Markarian galaxies and 2146 'normal' galaxies from the CfA redshift survey are compared. Survival analysis statistical methods that take upper limits fully into account are used. It is found that L(IR)/L(B) is statistically correlated with L(60) in both samples, though they differ in the distribution at low luminosities. The derived correlation shows that L(IR)/L(B) provides an indicator for L(60). Since galaxies selected in unbiased IRAS surveys will have higher L(IR)/L(B) than optically selected galaxies, they are therefore also selected for high L(60).

Feigelson, Eric D.↗

NASA NTRS1987

The IRAS bright galaxy sample. II - The sample and luminosity function

A statistically complete sample of 324 of the brightest infrared galaxies discovered at 60 microns in the IRAS all-sky survey is described. The results show that far-infrared emission is a significant luminosity component in the local universe, representing 25 percent of the luminosity emitted by stars in the same volume. Above 10 to the 11th solar luminosities, the infrared luminous galaxies are the dominant population of objects in the universe, being as numerous as the Seyfert galaxies and more numerous than quasars at higher luminosities. The infrared luminosity appears to be independent of the optical luminosity of galaxies. Most infrared bright galaxies appear to require much of the interstellar matter to be contributing to the observed infrared luminosity. Approximately 60-80 percent of the far-infrared luminosity of the local universe can be attributed, directly or indirectly, to recent or ongoing star formation.

Soifer, B. T.↗

NASA NTRS1987

Observable properties of E0 triaxial galaxies - A test for triaxiality

It is shown that most triaxial galaxies oriented in space to appear as E0 galaxies should have observable rotation velocities. By projecting Levison and Richstone's (1987) triaxial models so that they look like E0s, it was found that v/sigma can be as large as 1.0. In a separate argument, the observed distribution of axial ratios of ellipticals was used to show that between 3 percent and 23 percent of E0 galaxies are intrinsically flattened systems. Thus, if elliptical galaxies are triaxial then some E0 galaxies should have observable rotation velocities.

Levison, Harold F.↗

NASA NTRS1988

IRAS galaxies at low galactic and high supergalactic latitudes

Based on IR colors, 371 IRAS point sources with absolute value of b = 2-16 deg (b = galactic latitude) were selected for study at H I 21 cm as potential galaxies: 25 percent (93) of these sources are galaxies with redshifts less than 8000 km/s based on H I spectra. Most of the detected galaxies are at redshifts between 2000 and 7500 km/s. Fifty-five of these lie in an area about 40 deg away from the junction of the Pisces-Perseus and Lynx-Ursa Major superclusters, and show a distribution of systemic velocities very similar to these superclusters. There is an enhanced density of galaxies near 6000 km/s with galactic longitude l about 40 deg and b about 0 deg. The two regions surveyed, centered at l about 192 deg and l about 54 deg, lie outside the plane of the Local Supercluster and do not show any preference for galaxies with low velocity widths.

Dow, M. W.↗

NASA NTRS1988

Linear clusters of galaxies - A194

New measurements for 160 redshifts and previous measurements for 108 other redshifts are presented for galaxies within 5 deg of A194. The galaxy distribution in A194 is shown to be inconsistent with a spherically symmetric King model. A mass-to-light ratio is derived using the virial theorem which is lower than the mean for the groups in the CfA redshift survey (Huchra and Geller, 1982; Geller, 1984). A nonparametric test for galaxy-cluster alignment and a Chi-squared test are used to search for alignment of galaxy major axes with the axis of A194. Evidence for neither luminosity segregation nor significant differences in the velocity or surface distributions of galaxies as a function of morphological type is found.

Chapman, G. N. F.↗

NASA NTRS1986

Galaxies as dynamical probes of cluster structure

The effects of galaxy-cluster tidal forces on the dynamical evolution of member galaxies are investigated by means of numerical simulations. The kinds of normal events in clusters that can have significant immediate or long-term effects on galaxies are reviewed; the principal cluster properties are discussed; and the simulation results are briefly characterized, summarizing the report of Miller (1986). The degree of damage to a galaxy is found to depend strongly on the distance at which it orbits the cluster center and on the 'hardness' of the cluster potential. It is suggested that observations of the internal structure of cluster galaxies can be used to explore the cluster gravitational potential near the center and help locate and identify the nonluminous mass.

Miller, R. H.↗

NASA NTRS1988

The distribution of IRAS galaxies towards the Bootes void

A redshift survey was completed for 342 galaxies detected by the IRAS in the direction of the Bootes void discovered by Kirshner et al. The number density of IRAS galaxies is well determined from the shallower full-sky redshift survey of Strauss et al. Four IRAS galaxies are found within the void as defined by Kirshner et al., of which three are part of a complete sample, implying a density depression of a factor of 4. The underdense region continues to a distance of at least 4000 km/s from the nominal center of the void. Three of the IRAS galaxies studied in this paper were previously unknown. These galaxies have emission-line spectra characteristic of H II regions, and red continuum magnitudes ranging from 16 to 17.5 mag, and thus are bright enough to have been detected in a wide-angle redshift survey as deep as that of Kirshner et al. The luminosity function derived from this sample is in good agreement with that of Lawrence et al.

Strauss, Michael A.↗

NASA NTRS1988

2.2 micron image of 3C 368 at z = 1.13, a galaxy with aligned radio and stellar axes

A K-band IR image of the z = 1.13 radio galaxy 3C 368, one of the brightest examples of the recently discovered phenomenon of alignment between the optical and radio axes of powerful distant radio galaxies, is presented. The observations show that the IR morphology is also elongated and aligned along the optical and radio axes, but is not coincident with the radio emission. Various mechanisms for producing the IR and optical flux and the resultant constraints on the origin of the alignment effect in high-redshift radio galaxies are discussed. The most likely explanation is that the emission is produced mainly by young stars formed by interaction of the radio source with the ISM. The IR flux is then interpreted as dominated by a population of red supergiants. Independent of the origin of the emission, the observed alignment implies that powerful radio galaxies at high redshifts are distant from giant ellipticals, even in the IR. Hence, attempts to derive a cosmological 'standard candle' using studies which combine these two types of galaxies are likely to be invalid.

Chambers, K. C.↗

NASA NTRS1988

Energy densities and temperature associated with the diffuse X-ray background, galaxies and large scale structures

Model independent evidence indicating numerical coincidences between energy densities and temperatures which indicate possible connections between the diffuse X-ray background and the formation of galaxies and large scale structures is presented. A consideration of characteristic temperatures associated with galaxies, peculiar velocities of galaxies, and voids suggests characteristic energies of emission. Barring complications induced by magnetic fields, these temperatures may also be associated with components of the X-ray background. Thermal bremsstrahlung emmission associated with the formation of large scale structures may be the dominant contributor to the high energy X-ray background, 5 to 200 keV. Thermal bremsstrahlung emission produced by galaxies at the epoch of their formation may contribute significantly to the low energy X-ray background, 0.1 to 3 keV. It is concluded that an important, if not dominant fraction of the X-ray background, was probably emitted by hot gas associated with the formation of large scale structures and galaxies.

Daly, Ruth A.↗

NASA NTRS1988

A statistical study of properties of Seyfert and starburst galaxies

Spectral and morphological data for 282 Seyfert and emission-line galaxies spanning radio to X-ray wavelengths are compiled. The data include a large number of optical emission-line measurements which have not been reported previously. These data are intended to provide a convenient summary of the relevant properties of these galaxies, as well as a data base to search for correlations among the various parameters in order to obtain a better understanding of the active galaxy phenomenon. The paper presents the data and analyzes the distributions of various properties of Seyfert 1 and Seyfert 2 galaxies and starburst galaxies. It is found that Seyferts 2s have a higher 60 micron/forbidden O III 5007 A flux ratio than Seyfert 1s. This result, combined with the fact that Seyfert 2s are more heavily reddened, indicate that they have a higher dust content. It is also found that starburst nuclei are comparable to Seyfert 2s in far-infrared and 20 cm luminosities, although their optical spectra are markedly different.

Dahari, Oved↗

NASA NTRS1988

Hard X-ray observations of ultraluminous infrared galaxies

X-ray flux upper limits of 2-10 keV for ultraluminous infrared galaxies were drawn from the HEAO A-1 data base. The hard X-ray luminosities of these sources are much weaker relative to their total luminosities than would be expected for Seyfert 1 galaxies or quasi-stellar objects. Because of the low level of interstellar extinction for hard X-rays, this result suggests that the ultraluminous galaxies are not powered by embedded QSOs that are otherwise similar to other QSOs. Three other possibilities are: (1) the infrared galaxies may contain a form of X-ray-quiet active nucleus; (2) the X-ray sources in active nuclei may not turn on until after the circumnuclear gas has cleared; or (3) the bulk of the infrared luminosity in these galaxies may be generated by intense circumnuclear star formation.

Rieke, G. H.↗

NASA NTRS1988

Peculiar velocities of cD galaxies - MX spectroscopy of Abell 1795

Spectroscopic observations of galaxies in the Abell 1795 field have been obtained using the MX multiple-object spectrograph on the Steward Observatory 2.3 m telescope. Redshifts are presented for 46 galaxies, including 41 cluster members. It is found that the A1795 cD galaxy is not at rest in the cluster gravitational potential well; it has a peculiar radial velocity, cz, of 365 km/s, and the hypothesis that the mean cluster velocity is as large as the cD's velocity can be rejected at the 99.5 percent confidence level. This conclusion is supported by spectroscopic data for the 'cooling flow' gas found in the central region of the cluster; this gas, except for the portion coincident with the cD nucleus, lies at the velocity derived for the cluster mean. It is suggested that current models of the formation of cD galaxies are unlikely to account for the large peculiar velocities of the cD galaxies in A1795 and A2670 unless substantial subclustering is still present. However, the available data show no evidence for velocity subclustering in either A1795 or A2670.

Hill, John M.↗

NASA NTRS1987

UV, optical and infrared properties of star forming galaxies

The UVOIR properties of galaxies with extreme star formation rates are examined. These objects seem to fall into three distinct classes which can be called (1) extragalactic H II regions, (2) clumpy irregulars, and (3) starburst galaxies. Extragalactic H II regions are dominated by recently formed stars and may be considered 'young' galaxies if the definition of young is having the majority of total integrated star formation occurring in the last billion years. Clumpy irregulars are bursts of star formation superposed on an old population and are probably good examples of stochastic star formation. It is possible that star formation in these galaxies is triggered by the infall of gas clouds or dwarf companions. Starburst galaxies are much more luminous, dustier and more metal rich than the other classes. These objects show evidence for shock induced star formation where shocks may be caused by interaction with massive companions or are the result of an extremely strong density wave.

Huchra, John P.↗

NASA NTRS1988

A catalog of IRAS observations of large optical galaxies

A catalog is presented of IRAS observations of 85 galaxies with blue-light isophotal diameters greater than 8 arcmin. The observations, data processing, and data measurement techniques are described, and total IRAS flux densities and integrated infrared emission properties of the sample are reported. Infrared brightness profiles of the detected galaxies and infrared surface brightness contour maps of the galaxies for which structural features were resolved are displayed. A classification scheme based on the degree of central concentration and spatial structure of the 60 micron emission of the best-resolved galaxies is proposed. The 60 micron and blue-light isophotal diameters of the largest galaxies are compared.

Rice, W.↗