Engineering topics

Soifer, B. T.

Publications and source records attributed to Soifer, B. T..

At least 73 records · Page 4

NASA NTRS1988

IRAS 14348-1447, an ultraluminous pair of colliding, gas-rich galaxies - The birth of a quasar?

Ground-baed observations of the object IRAS 14348-1447, which was discovered with the Infrared Astronomical Satellite, show that it is an extremely luminous colliding galaxy system that emits more than 95 percent of its energy at FIR wavelengths. IRAS 14348-1447, which is receeding from the sun at 8 percent of the speed of light, has a bolometric luminosity more than 100 times larger than that of the Galaxy, and is therefore as luminous as optical quasars. New optical, infrared, and spectroscopic measurements suggest that the dominant luminosity source is a dust-enshrouded quasar. The fuel for the intense activity is an enormous supply of molecular gas. Carbon monoxide emission has been detected at a wavelength of 2.6 millimeters by means of a new, more sensitive receiver recently installed on the 12-meter telescope of the National Radio Astronomy Observatory. IRAS 14348-1447 is the most distant and luminous source of carbon monoxide line emission yet detected.

Sanders, D. B.↗

NASA NTRS1988

The IRAS Bright Galaxy Sample. III - 1-10 micron observations and coadded IRAS data for galaxies with L(IR) equal to or greater than 10 to the 11th solar luminosities

This paper presents the results of 1-10-micron observations and coadded IRAS data on 61 galaxies from the Bright Galaxy Sample, with IR luminosities, L(IR), equal to or greater than 10 to the 11th solar luminosities. It was found that an increase in the total L(IR) above 10 to the 11th solar luminosity is correlated with increased emission from hot dust with characteristic temperatures about 800 K. This hot dust contributes a substantial fraction of the 2.2- and 3.7-micron emission, resulting in a greatly increased dispersion in R(3.7/1.6) and R(2.2/1.6) for these high-luminosity galaxies, relative to lower-luminosity galaxies. This excess hot-dust emission appears to 'turn on' at luminosities of about 10 to the 11th solar luminosity. The spatial distribution of the 10-micron emission indicated a substantial extended component for most of the galaxies in this sample, implying that star-formation processes contribute significantly to the luminosities.

Carico, David P.↗

NASA NTRS1988

Aperture synthesis mapping of molecular gas in high-luminosity IRAS galaxies

The Owens Valley millimeter-wave interferometer has been used for high-resolution mapping of the 2.6 mm CO emission from the high-luminosity infrared galaxies NGC 520 (Arp 157), NGC 7469 (Arp 298), and Arp 55. Assuming the same empirical relationship between CO brightness and molecular hydrogen surface mass density as has been found for giant molecular clouds in the Milky Way, it is found that the masses of H2 gas in these concentrations are 10 to the 9th - 10 to the 10th solar masses, typically one-third of the total molecular gas content of these galaxies. The interferometric sizes correspond to radii of 0.8 kpc (NGC 520), 1.4 kpc (NGC 7469), and less than 2.8 kpc (Arp 55). For the same regions the dynamical masses estimated from the CO line width and size of the emission region are only a factor of 3-5 higher. The mean molecular gas surface densities averaged over these regions are in the range 610-825 solar masses/sq pc, a factor of 10 brighter than those obtained for corresponding regions in the nucleus of the Milky Way. The high mass fractions obtained for the interstellar medium in the central regions of these three galaxies strongly suggest that large-scale gravitational instability in the gas may play an important role in the further concentration of the gas in the nucleus and in possibly precipitating a large-scale burst of star formation.

Sanders, D. B.↗

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

Ultraluminous infrared galaxies

The IRAS survey of the local universe has revealed the existence of a class of ultraluminous infrared galaxies with L(8 to 1000 micrometer) greater than 10 to the 12th L sub 0 that are slightly more numerous, and as luminous as optically selected quasars at similar redshift. Optical CCD images of these infrared galaxies show that nearly all are advanced mergers. Millimeter wave CO observations indicate that these interacting systems are extremely rich in molecular gas with total H2 masses 1 to 3 x 10 to the 10th power M sub 0. Nearly all of the ultraluminous infrared galaxies show some evidence in their optical spectra for nonthermal nuclear activity. It is proposed that their infrared luminosity is powered by an embedded active nucleus and a nuclear starburst both of which are fueled by the tremendous reservoir of molecular gas. Once these merger nuclei shed their obscuring dust, allowing the AGN to visually dominate the decaying starburst, they become the optically selected quasars.

Sanders, D. B.↗

NASA NTRS1987

Interferometric CO observations of the ultraluminous IRAS galaxies ARP 220, IC 694/NGC 3690, NGC 6420 and NGC 7469

High resolution CO observations of the IRAS galaxies Arp 220, IC 694/NGC 3690, NGC 6240 and NGC 7469 were made with the Millimeter Wave Interferometer of the Owen Valley Radio Observatory. These yield spatial information on scales of 1 to 5 kpc and allow the separation of compact condensations from the more extended emission in the galaxies. In the case of the obviously interacting system IC 694/NGC 3690 the contributions of each component can be discerned. For that galaxy, and also for Arp 220, the unusually high lumonisities may be produced by nonthermal processes rather than by intense bursts of star formation.

Sargent, A. I.↗

NASA NTRS1987

The luminosity function of the brightest galaxies in the IRAS survey

Results from a study of the far infrared properties of the brightest galaxies in the IRAS survey are described. There is a correlation between the infrared luminosity and the infrared to optical luminosity ratio and between the infrared luminosity and the far infrared color temperature in these galaxies. The infrared bright galaxies represent a significant component of extragalactic objects in the local universe, being comparable in space density to the Seyferts, optically identified starburst galaxies, and more numerous than quasars at the same bolometric luminosity. The far infrared luminosity in the local universe is approximately 25% of the starlight output in the same volume.

Soifer, B. T.↗

NASA NTRS1987

Near-infrared observations of IRAS minisurvey galaxies

Near infrared photometry at J, H, and K was obtained for 82 galaxies from the IRAS minisurvey. The near infrared colors of these galaxies cover a larger range in J-H and H-K than do normal field spiral galaxies, and evidence is presented of a tighter correlation between the near and far infrared emission in far infrared bright galaxies than exists between the far infrared and the visible emission. These results suggest the presence of dust in the far infrared bright galaxies, with hot dust emission contributing to the 2.2 micron emission, and extinction by dust affecting both the near infrared colors and the visible luminosities. In addition, there is some indication that the infrared emission in many of the minisurvey galaxies is coming from a strong nuclear component.

Carico, David P.↗

NASA NTRS1987

The most luminous far-infrared extragalactic sources

Extremely luminous far-infrared sources are difficult to explain as active sites of star formation, because their ratios of optical-to-infrared luminosities are extremely low. It is shown that brief intervals during which interacting galaxies collide can account for extremely high (more than 10 to the 11th) solar luminosities. The small fraction of the population that exhibits extreme luminosity also roughly equals the fraction of spiral galaxies expected to be observed undergoing collisions at any given time. A number of potential tests that would distinguish the model from others is proposed.

Harwit, M.↗

NASA NTRS1987

Compact molecular gas structure in the interacting galaxy pair Arp 299 (IC 694-NGC 3690)

High-resolution (about 5-arcsec) CO observations of the interacting galaxy pair Arp 299 (IC 694-NGC 3690) show that about 40 percent of the total molecular gas content is concentrated in two compact regions each of mass 1.4 x 10 to the 9th solar mass. One component lies at the nucleus of IC 694, while the other spans the region of overlap between the two galaxies. The properties of the latter component are consistent with its being a region of greatly enhanced star formation. However, the unusually high L(FIR)/M(H2) ration for IC 694, together with the presence of a flat-spectrum radio source, suggest that its remarkable luminosity may be largely produced by nonthermal processes.

Sargent, A. I.↗

NASA NTRS1987

Detection of CO(1-0) emission and optical imaging of the Seyfert galaxy/QSO Markarian 231

The detection of CO(J = 1-0) emission and optical imaging of the luminous infrared galaxy Markarian 231 are reported. The galaxy is extremely rich in molecular gas with MT(H2) approximately equal to 1.4 x 10 to the 10th solar masses, approximately 5 times the molecular gas content of the Galaxy. Markarian 231 is the most luminous object in the local universe (z approximately equal to or less than 0.1), with a far-infrared luminosity (lambda = 40-400 microns) of 2.1 x 10 to the 12th solar luminosities. THe CO detection yields a L(FIR)/M(H2) ratio of 150. A deep optical CCD image shows two striking tidal tails with total extent of about 75 kpc. The CCD image strongly suggests that Markarian 231 is an advanced merger system. If the molecular gas is highly concentrated in the nuclear region it may fuel an intense starburst and possibly feed the accretion onto an embedded QSO. The trigger for the intense activity observed in Markarian 231 appears to be the collision of two gas-rich spiral galaxies.

Sanders, D. B.↗

NASA NTRS1987

The IRAS view of the extragalactic sky

The IR-observable characteristics of the extragalactic sky are reviewed, summarizing the results of recent studies based on the IRAS survey, which covers over 96 percent of the sky to about 500 mJy at 12, 25, and 60 microns and to about 1.5 Jy at 100 microns. The numerical and morphological data are described; possible mechanisms for the IR emission are discussed; and the object classes are considered separately. Consideration is given to spiral and disk galaxies, barred and ring galaxies, irregular and dwarf galaxies, blue compact galaxies, elliptical and S0 galaxies, AGN observations (BL Lacs and OVV quasars, Seyfert galaxies, and quasars), highly luminous IR galaxies, and the cosmological implications of the IRAS findings. Diagrams, graphs, and tables are provided.

Soifer, B. T.↗

NASA NTRS1986

Millimeter interferometry of the molecular gas in ARP 20

The Owens Valley Millimeter Wave Interferometer has been used to map the 2.6-mm CO emission in the ultraluminous infrared galaxy Arp 220. Approximately 70 percent of the CO emission from the galaxy originates from an unresolved region less than 4 arcsec x 6 arcsec in size (corresponding to 1500 pc diameter) centered on the near-infrared nucleus. The mass of gas within this region is 10 to the 10th solar mass, which is about 30 times greater than that in an equivalent area of the Galaxy. This concentration could result in efficient star formation via cloud-cloud collisions and provide a significant accretion flow onto a compact, central object.

Scoville, N. Z.↗

NASA NTRS1986

Near-infrared observations of IRAS minisurvey galaxies

Near-infrared photometry was obtained for 82 galaxies from the Infrared Astronomy Satellite (IRAS) minisurvey, a sample of infrared selected galaxies. The near-infrared colors of these galaxies are similar to those of normal field spiral galaxies, but cover a larger range in J - H and H - K. There is evidence of a tighter correlation between the near and far infrared emission than exists between far-infrared and the visible emission. These results suggest that hot dust emission contributes to the 2.2 micron luminosity, and extinction by dust affects both the near-infrared colors and the visible luminosities. In addition, there is an indication that the far-infrared emission in many of the minisurvey galaxies is coming from a strong nuclear component.

Carico, David P.↗

NASA NTRS1986

Research in planetary astronomy at Palomar Observatory

The goals of this program are three fold. The ring systems in the outer solar system were studied. New comets and asteroids in the solar system were surveyed. The volatile surface coverings of the primitive bodies in the outer solar system were studied via infrared spectroscopy.

Soifer, B. T.↗

NASA NTRS1986

Discovery of an infrared-loud quasar

The IRAS source 13349 + 2438 is a quasar with a redshift of z = 0.107, broad (15,000 km/s) emission lines and a luminosity of 2.7 x 10 to the 12th solar luminosity, emitted mostly between 4.8 and 12 microns. The object, a weak radio source, is the first previously unidentified quasar selected through its infrared emission and is the prototype radio-quiet, infrared-bright quasar. A dusty interstellar medium may be responsible for the infrared emission as well as for quenching the visual emission and attenuating the radio emission from the central energy source.

Beichman, C. A.↗

NASA NTRS1986

Molecular gas in high-luminosity IRAS galaxies

The paper reports observations of CO(J = 1-0) emission from an unbiased sample of the highest-luminosity IRAS galaxies with the aim of measuring their molecular gas content and determining whether star formation is a viable energy source for these high luminosities. All of the observed galaxies are rich in molecular gas with H2 masses in the range (4 x 10 to the 9th)-(4 x 10 to the 10th) solar masses. Their primary luminosity source appears to be star formation in molecular clouds. The majority, if not all, of the most luminous IRAS galaxies (L-FIR greater than 10 to the 11th solar luminosities) appear to be strongly interacting systems; those with the highest L-FIR/M(H2) ratios are mergers or close contact pairs.

Sanders, D. B.↗

NASA NTRS1986

IRAS observations of the nuclear bulge of M31

IRAS observations of the nuclear bulge of M31 are reported. The 12-micron and 25-micron emission is attributed to circumstellar dust emission from late-type stars, while the 60 and 100-micron emission is attributed to interstellar dust emission. The total input rate of circumstellar gas and dust into the interstellar medium is estimated to be 0.015 solar masses/yr. The mass of dust in the interstellar medium estimated from the far-infared flux is about 1500 solar masses. The color temperature of the far-infrared-emitting dust is 45 K. The time required to accumulate the observed mass in interstellar dust is about 10 million yr. Either supernova-generated winds or star formation can deplete this gas without violating the observations.

Soifer, B. T.↗