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NASA NTRS1975

Redshift differences of galaxies in nearby groups

It is reported that galaxies in nearby groups exhibit anomalous nonvelocity redshifts. In this discussion, (1) four classes of nearby groups of galacies are analyzed, and no significant nonvelocity redshift effect is found; and (2) it is pointed out that transverse velocities (i.e., velocities transverse to the line of sight of the main galaxy, or center of mass) contribute components to the redshift measurements of companion galaxies. The redshifts of galaxies in nearby groups of appreciable angular size are considerably affected by these velocity projection effects. The transverse velocity contributions average out in rich, isotropic groups, and also in large samples of irregular groups of low membership, as in the four classes referred to in (1), but can introduce apparent discrepancies in small samples (as studied by Arp) of nearby groups of low membership.

Harrison, E. R.↗

NASA NTRS1977

Atmospheric absorption of high frequency noise and application to fractional-octave bands

Pure tone sound absorption coefficients were measured at 1/12 octave intervals from 4 to 100 KHz at 5.5K temperature intervals between 255.4 and 310.9 K and at 10 percent relative humidity increments between 0 percent and saturation in a large cylindrical tube (i.d., 25.4 cm; length, 4.8 m). Special solid-dielectric capacitance transducers, one to generate bursts of sound waves and one to terminate the sound path and detect the tone bursts, were constructed to fit inside the tube. The absorption was measured by varying the transmitter receiver separation from 1 to 4 m and observing the decay of multiple reflections or change in amplitude of the first received burst. The resulting absorption was compared with that from a proposed procedure for computing sound absorption in still air. Absorption of bands of noise was numerically computed by using the pure tone results. The results depended on spectrum shape, on filter type, and nonlinearly on propagation distance. For some of the cases considered, comparison with the extrapolation of ARP-866A showed a difference as large as a factor of 2. However, for many cases, the absorption for a finite band was nearly equal to the pure tone absorption at the center frequency of the band. A recommended prediction procedure is described for 1/3 octave band absorption coefficients.

Shields, F. D.↗

NASA NTRS1985

Detection of Ni 2 lambda 7378 in six Seyfert galaxies

A line due to Ni 2 7378 in the Seyfert galaxies NGC 1068, 2110, 3227, 4151, 5506, and Arp 102 B was detected. The average Ni abundance is about 2 times solar, which is 5 times less than in the filaments of the Crab Nebula. This argues for nucleosynthetic processing in the latter. The Ni 2 line is spatially revolved in NGC 1068, and shows at least a factor of 4 enhancement in the Ni abundance away from the nucleus. The off-nuclear abundance of Ni in NGC 1068 approaches that of the Crab, which strongly suggests that type supernovae enriched the off-nuclear gas clouds.

Halpern, J. P.↗

NASA NTRS1985

CO detections and IRAS observations of bright radio spiral galaxies at cz equal or less than 9000 kilometers per second

CO emission has been detected from 20 of 21 bright radio spirals with strong extended nuclear sources, including the most distant (NGC 7674) and the most luminous (IC 4553 = Arp 220, NGC 6240) galaxies yet detected in CO. All of these galaxies are rich in molecular gas, with M total(H2) = 3 x 10 to the 8th - 2 x 10 to the 10th solar masses. IRAS observations show that they have a strong far-infrared (FIR) excess, with L(FIR)/L(B) approximately equal to 1-35 and L(FIR) (40-400 microns) approximately equal to 10 to the 10th - 10 to the 12th L solar masses. The primary luminosity source for these radio cores appears to be star formation in molecular clouds. A strong correlation is found between the FIR and extended 21 cm continuum flux, implying that the fraction of massive stars formed is independent of the star formation rate. The ratio L(FIR)/M(H2) provides a measure of the current rate of star formation, which is found to be a factor 3-20 larger in these galaxies than for the ensemble of molecular clouds in the Milky Way. At these rates their molecular gas will be depleted in about 10 to the 8th yr.

Sanders, D. B.↗

NASA NTRS1986

Detection of forbidden Ni II lambda 7378 in six Seyfert galaxies

A line due to Ni 2 7378 in the Seyfert galaxies NGC 1068, 2110, 3227, 4151, 5506, and Arp 102 B was detected. The average Ni abundance is about 2 times solar, which is 5 times less than in the filaments of the Crab Nebula. This argues for nucleosynthetic processing in the latter. The Ni 2 line is spatially resolved in NGC 1068, and shows at least a factor of 4 enhancement in the Ni abundance away from the nucleus. The off-nuclear abundance of Ni in NGC 1068 approaches that of the Crab, which strongly suggests that type supernovae enriched the off-nuclear gas clouds.

Halpern, J. P.↗

NASA NTRS1986

An apparent gravitational lens with an image separation of 2.6 arc min

Observations are reported which confirm Paczynski's 1986 speculation that the previously known (Arp and Hazard, 1980) pair of 19th magnitude quasars 1146+111B,C are actually two images of a single object produced by a gravitational lens. The image split is 157 arcsec, more than 20 times greater than any previously reported, thus indicating an exceptionally massive lensing object. The data supporting the lens hypothesis are remarkably similar, high signal-to-noise, moderate resolution spectra of the two components. Both spectra show strong Mg II 2798-angstrom emission at z = 1.012 plus or minus 0.001 with indistinguishable redshifts (delta v = 126 plus or minus 309 km/s), widths (FWHM = 64 plus or minus 4 angstroms) and detailed profile shapes. Both spectra also show broad troughs at 6180 angstroms and several weaker continuum features. Neither object exhibits the O II 3727-A forbidden line which is frequently strong in Mg II emission objects. If the foreground galaxy clustering apparent in a deep R band charge-coupled device image proves insufficient to explain the large image splitting, other possibilities such as massive dark objects (e.g. a black hole of about 10 to the 15th solar masses) or a cosmic string may be indicated.

Turner, E. L.↗

NASA NTRS1986

6 CM OH absorption in megamaser galaxies

Absorption in the 2Pi sub 1/2 J = 1/2 Lambda doublet transitions of OH, 182 K above the ground state, is detected in the megamaser galaxies IC 4553 (Arp 220), MK 231, MK 273, MGC 3690, and IRAS 17208-0014. The 4660, 4751, and 4766 MHz lines have intensity ratios moderately deviating from the LTE values (1:2:1). The OH rotational temperatures appear to be close to the temperature of the dust, approx. 60 K. The common characteristics of these galaxies (absence of 6 cm inversion, the optical depths, the infrared properties, the systematic trends in the line parameters, and the rotational temperatures) all suggest that the same pump process is responsible for the 18 cm line inversion in the five megamaser sources. The inversion is probably not due to an excitation mechanism involving collisions with HI or H2. While excitation via photodissociation of H2O cannot entirely be ruled out, the most likely mechanism is considered to be to be a combination of the intense FIR field (populating higher excited OH rotational states) and the non-thermal radiation from the nuclei of the parent galaxies (affecting the excitation within the Lambda -doublets). According to an LVG model of the OH excitation of IC4553, the OH-cloud(s) have to be located close, within 200 to 300 pc, to the center of the galaxy. The excitation of the individual 18 cm lines depends critically on the effective background radiation field and hence on the galactocentric distance of the masing clump. With increasing distance first the 1720 MHz and then the 18 cm main line inversion is quenched, while 1612 MHz inversion is obtained up to approx. 600 pc. The 1612 MHz satellite line is predicted to be more intense than the 1720 MHz line. A critical test for our excitation model is to observe the 2 Pi 3/2 J = 5/2 Lambda-doublet transitions which are predicted to be detectable in absorption.

Henkel, C.↗

NASA NTRS1987

Starburst-driven superwinds from infrared galaxies

New data is presented that indicate that strong far infrared galaxies commonly have largescale emission line nebulae whose properties are suggestive of mass outflows (superwinds), presumably driven by the high supernova rate associated with the central starburst. These data include longslit spectra of M82 which show that the radial variation of the gas pressure in the emission line nebula is in excellent agreement with a previous wind model. The M82 nebula also has a LINER spectrum, consistent with shock heating. Morphologically and spectroscopically similar emission line nebulae were found in NGC253, and Arp 220 and NGC6240. A longslit spectroscopic investigation was conducted of 20 additional very powerful far-infrared galaxies and found that they generally have spatially extended emission line nebulae whose spectra closely resemble that of the M82 nebula. If the superwind interpretation is correct, it could have many important consequences in extragalactic astronomy.

Heckman, Timothy M.↗

NASA NTRS1987

Extragalactic OH megamasers in strong IRAS sources

From the OH and HI survey of the strongest far infrared IRAS sources, 3 new powerful OH megamasers were discovered in Arp 143, IRAS 1510+0724 and in the uncatalogued IRAS source, IRAS 17208-0014. The HI line, the OH 1667 and 1665 MHz main lines and the 21 cm continuum observations were made with Nancy radio telescope. The optical spectra and images were obtained at the European Southern Observatory. The spectra are displayed in figures together with the main IR and OH properties of the 8 megamasers detected up to now, including IC 4553, NGC 3690 and Mrk 231, Mrk 273 and III ZW35.

Bottinelli, L.↗

NASA NTRS1987

The relation between star formation and active nuclei

Three questions relevant to the relation between an active nucleus and surrounding star formation are discussed. The infrared stellar CO absorption bands can be used to identify galaxies with large populations of young, massive stars and thus can identify strong starburst unambiguously, such as in NGC 6240, and can help identify composite active/starburst systems such as Arp 220. An active nucleus is probably not required for LINER spectral characteristics; dusty starburst galaxies, particularly if they are nearly edge-on, can produce LINER spectra through the shock heating of their interstellar media by supernovae combined with the obscuration of their nuclei in the optical. The Galactic Center would be an ideal laboratory for studying the interaction of starbursts and active nuclei, if both could be demonstrated to occur there. Failure to detect a cusp in the stellar distribution raises questions about the presence of an active nucleus, which should be answered by additional observations in the near future.

Rieke, G. H.↗

NASA NTRS1987

Spectrophotometery of Brackett lines in very luminous IRAS galaxies

Observation of the Brackett-alpha and Brackett-gamma hydrogen recombination lines were made in a sample of galaxies chosen from the IRAS catalog to have high luminosities at infrared wavelengths. Most have strong Brackett line emission indicating large numbers of high mass stars; the formation of these stars may hence be the underlying source for the galaxies' luminosities. However, there are at least two exceptions that may not be explained in this manner: NGC 6240 and Arp 220. Additional evidence indicates that each of these exceptions may be more closely related to Seyfert-type galaxies or other active galactic nuclei.

Depoy, D. L.↗

NASA NTRS1986

Enhancement of features in galaxy images

Several image-enhancement techniques useful for morphological analysis of galactic or cometary images are described and compared. Such techniques can be used to search for, and investigate the properties of dust lanes, stellar disks or rings, jets, shells, tidal distortions, etc. Applications of the techniques are illustrated on CCD images of the peculiar galaxy Arp 230; this object has a rich morphology, indicative of a merger of two disk galaxies.

Djorgovski, S.↗

NASA NTRS1987

The effects of interactions on spiral galaxies. II - Disk star-formation rates

H-alpha emission-line and IRAS far-IR observations of interacting spiral and irregular galaxies are here used to assess the influence of interactions on their global star-formation rates. Two samples of interacting galaxies were observed: a complete sample of close pairs, and an Arp atlas sample of peculiar systems. When compared to a control sample of single galaxies, both samples of interacting systems exhibit systematically higher levels of H-alpha and infrared emission on average, and a larger dispersion in emission properties. Emission levels in the very active system are much more strongly correlated with the properties of the interaction than with the internal properties of the galaxies themselves. Strong disk emission is almost always accompanied by unusually strong nuclear activity. Simple star-formation burst models can reproduce the observed H-alpha equivalent widths and broadband colors of most of the galaxies. The bursts are relatively short (few times 10 million yr) and rarely involve more than 1-2 percent of a galaxy's total mass.

Kennicutt, Robert C., Jr.↗

NASA NTRS1987

The spatial distribution and population of novae in M31

Results from an H-alpha survey for novae in the bulge of M31 are reported, and the spatial distribution of the nova population is analyzed. It is shown that in M31's central bulge the distribution of novae follows that of the light to within about 10 arcsec of the nucleus, refuting the notion that there is a nova 'hole' near the center of the galaxy. The Hubble-Arp nova sample is reanalyzed, concluding that the novae observed in the central 30 arcmin x 15 arcmin region belong almost exclusively to the bulge population. This result is compared to the observed cataclysmic variable distribution in the Galaxy, concluding that M31's spheroidal nova population is still compatible with the thin disk distribution of cataclysmic variables measured in the solar neighborhood. Possible explanations for the high specific nova rate of the bulge are discussed.

Ciardullo, Robin↗

NASA NTRS1988

The enhancement of infrared emission in interacting galaxies

Selected infrared properties, based on IRAS observations, of two categories of interacting galaxy pairs from the Arp-Madore Catalogue of Southern Peculiar Galaxies and Associations are examined. For pairs of comparably sized galaxies, a strong tendency exists for pairs with the highest far-IR color temperatures to have the smallest separation. This finding implies that galaxy interactions significantly enhance the intensity or the efficiency of star formation. No trend of far-IR color temperature varying with pair separation is found for pairs consisting of a galaxy with a small companion. There are 10 times as many pairs in the sample that contain one IRAS far-IR galaxy as there are pairs for which both galaxies were detected by IRAS, thus strengthening previous conclusions that the effect of a perturbation depends strongly on the detailed geometry of the interaction.

Telesco, C. M.↗

NASA NTRS1988

Ultraviolet observations of selected astronomical sources

The results of the 9th and 10th IUE episode programs listed are summarized. Observations and basic data reductions were completed for 4 extragalactic programs which were allocated a total of 9 US1 shifts, and 2 stellar investigations which used 10 US2 shifts. Use was made of the Goddard RDAF to obtain better signal to noise ratio spectra using the Gaussian extraction routines. Highlights include the first IUE observations of H1821+643, the second brightest quasar in the sky, and the discovery of accretion disk emission line profiles in the elliptical Seyfert galaxy Arp 102B. Both of these observations were accompanied by nearly simultaneous optical spectrophotometry. As a result of the stellar programs, large amplitude variability associated with the rotation period of the Ap stars 78 Vir and 53 Cam was found.

Halpern, Jules P.↗

NASA NTRS1988

The twin-nucleus merging galaxy Markarian 266 (NGC 5256)

Optical imaging in continuum and line wavelengths, spatially resolved optical spectroscopy, and 21 cm radio imaging of Markarian 266 are presented. The galaxy has faint extended plumes of luminosity, which indicate that it is a recent merger. There are extended regions of blue luminosity suggestive of recent star formation, and remarkable structure in forbidden O III line emission. Spectroscopic data show the velocities and densities in the ionized gas. Radio observations taken with the VLA show that both nuclei are resolved radio sources, and that there is a third radio source between them which has no optical counterpart; 21-cm absorption is seen against the brighter optical nucleus, indicating possible infall. These results are discussed in terms of galaxy mergers, nuclear activation, and ionized gas. Mkn 266 has many similarities to Arp 220 and appears to be a somewhat lower-luminosity version of the IRAS ultraluminous galaxies.

Hutchings, J. B.↗

NASA NTRS1988

Novae as distance indicators

It is shown that nova shells are characteristically prolate with equatorial bands and polar caps. Failure to take this geometry into consideration can lead to large errors in expansion parallaxes for individual novae. Extinction in the bulge of M31 is investigated by projecting Arp's and Rosino's novae onto a composite B - 6200 A color map of the bulge. Of the 86 novae, 32 project onto a smooth background with no underlying structure due to the presence of a dust cloud along the line of sight. The distribution of maximum magnitudes versus fade rates for these 'unreddened' novae is indistinguishable from the distribution for the entire set of novae. It is concluded that novae suffer very little extinction from the filamentary and patchy distribution of dust seen in the bulge of M31.

Ford, Holland C.↗