Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons™

Open Access. Powered by Scholars. Published by Universities.®

External Galaxies

Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 481 - 491 of 491

Full-Text Articles in Physical Sciences and Mathematics

Determination Of Malmquist Bias And Selection Effects From Monte Carlo Simulations, Wolfram Freudling, Luiz N. Da Costa, Gary Wegner, Riccardo Giovanelli Aug 1995

Determination Of Malmquist Bias And Selection Effects From Monte Carlo Simulations, Wolfram Freudling, Luiz N. Da Costa, Gary Wegner, Riccardo Giovanelli

Dartmouth Scholarship

Maps of the peculiar velocity field derived from distance relations are affected by Malmquist type bias and selection effects. Because of the large number of interdependent effects, they are in most cases difficult to treat analytically. Monte Carlo simulations are used to understand and evaluate these effects. In these simulations the "true" spatial distribution and relevant properties of galaxies as well as selection effects and observational uncertainties are realistically modeled. The results of the simulation can be directly applied to correct observed peculiar velocity maps. The simulation is used to investigate biases in samples of measured peculiar velocities by Lynden-Bell …

Go to article

Discovery Of Extreme-Ultraviolet Radiation From The Seyfert Galaxy Ton S180 (=Euve J0057−223), Stéphane Vennes, Elisha Polomski, Stuart Bowyer, John R. Thorstensen Jul 1995

Discovery Of Extreme-Ultraviolet Radiation From The Seyfert Galaxy Ton S180 (=Euve J0057−223), Stéphane Vennes, Elisha Polomski, Stuart Bowyer, John R. Thorstensen

Dartmouth Scholarship

We report the detection of intense EUV radiation from the Seyfert 1 galaxy Ton S180. The source EUVE J0057-223, discovered in the Extreme-Ultraviolet Explorer all-sky survey, is only 25'' away from its optical counterpart, well within the position error circle. We present a complete broadband energy distribution of Ton S180 using infrared (IRAS), optical, ultraviolet (IUE) and X-ray (ROSAT) flux measurements, and we find that the measured EUV flux, corrected for neutral hydrogen and helium absorption in the Galaxy, suggests the presence of a strong EUV to soft X-ray flux excess. We briefly discuss …

Go to article

Ubvri Photometry Of The Type Ia Sn 1994d In Ngc 4526, Michael W. Richmond, Richard R. Treffers, Alexei V. Filippenko, Schuyler D. Van Dyk, Young Paik, Chien Peng, Laurence A. Marschall, Bentley D. Laaksonen, Bruce Macintosh, Ian S. Mclean May 1995

Ubvri Photometry Of The Type Ia Sn 1994d In Ngc 4526, Michael W. Richmond, Richard R. Treffers, Alexei V. Filippenko, Schuyler D. Van Dyk, Young Paik, Chien Peng, Laurence A. Marschall, Bentley D. Laaksonen, Bruce Macintosh, Ian S. Mclean

Physics and Astronomy Faculty Publications

We present optical photometry for the type Ia SN 1994D in NGC 4526 from 1994 March 7 to June 4 starting 13 days before B-band maximum. The light curves of this SN resemble closely those of the "normal" type Ia events SNe 1989B and 1980N, differing only in a slightly faster decline after maximum in VRI. The optical absolute magnitudes of SN 1994D, however, are significantly brighter than those of its near twins, and brighter than those predicted by Phillips' [ApJ, 413, L105 (1993)] relationship between decline rate and luminosity. Our small amount of IR photometry of SN 1994D …

Go to article

Photoelectric And Ccd Photometry Of E And S0 Galaxies, M. Colless, D. Burstein, G. Wegner, R. P. Saglia May 1993

Photoelectric And Ccd Photometry Of E And S0 Galaxies, M. Colless, D. Burstein, G. Wegner, R. P. Saglia

Dartmouth Scholarship

We present BR photoelectric photometry for 352 E and S0 galaxies that are part of a large survey of the properties and peculiar motions of galaxies in distant clusters. Repeat measurements show our internal errors to be 2 – 3 per cent in B and R and 1 – 2 per cent in B– R. Comparisons of BR and BVR reductions for 10 galaxies also observed in V show small systematic errors due to differences between the spectral energy distributions of stars and galaxies. External comparisons with B– V colours in the literature confirm that these colours are …

Go to article

Moderate-Resolution Spectroscopy Of The Lensed Quasar 2237+0305: A Search For Ca Ii Absorption Due To The Interstellar Medium In The Foreground Lensing Galaxy, P. Hintzen, S. P. Maran, A. G. Michalitsianos, C. B. Foltz, F. H. Chafee, Menas Kafatos Jan 1990

Moderate-Resolution Spectroscopy Of The Lensed Quasar 2237+0305: A Search For Ca Ii Absorption Due To The Interstellar Medium In The Foreground Lensing Galaxy, P. Hintzen, S. P. Maran, A. G. Michalitsianos, C. B. Foltz, F. H. Chafee, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

The gravitational lens system 2237 + 0305 consists of a low-redshift barred spiral galaxy (z = 0.0394) centered on a more distant quasar (z = 1.695). Because the lensing galaxy is nearly face on, spectroscopy of the background quasar affords a unique opportunity to study the interstellar medium in the galaxy's center and buW:. We report moderate-resolution spectroscopy of QS02237 + 0305 yielding a 3u upper limit of 72 rnA forthe rest equivalent width of Ca II K absorption d);le to gas in the intervening galaxy. Since gas in the Milky Way "thick disk" typically produces 220 mA Ca II …

Go to article

Observations Of Two Peculiar Emission Objects In The Large Magellanic Cloud, Menas Kafatos, A. G. Michalitsianos, D. A. Allen, R. E. Stencel Jan 1983

Observations Of Two Peculiar Emission Objects In The Large Magellanic Cloud, Menas Kafatos, A. G. Michalitsianos, D. A. Allen, R. E. Stencel

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ultraviolet and visual wavelength spectra were obtained of two peculiar emission objects, Henize S63 and Sanduleak.'s star in the Large Magellanic Cloud. Previously not observed in the near- or far-ultraviolet, both objects exhibit strong permitted and semiforbidden line emission. Estimates based on the absolute continuum flux of the hot companion star in Hen S63 indicate that it rivals the luminosity of the carbon star primary. The emission-line profile structure in both objects does not suggest Wolf-Rayet type emission. Carbon in Sanduleak.'s star (LMC anonymous) is conspicuously absent, while N v, N IV], and N III] dominate the UV emission-line spectrum. …

Go to article

The High-Energy Spectrum Of Hot Accretion Disks, J. A. Eilek, Menas Kafatos Jan 1983

The High-Energy Spectrum Of Hot Accretion Disks, J. A. Eilek, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

A hot, two-temperature accretion disk can be a strong γ-ray and relativistic particle source. This occurs when the accretion rate is high enough -- M/ M ≥ 3 X 10^-9 α γr^-1 for a canonical Kerr black hole-due to the high ion temperature in the inner disk. We present detailed photon and particle spectra for specific disk models. The predicted γ-ray flux is as high as 10% of the bolometric luminosity in sub-Eddington models. Most of the γ-radiation is continuous, due to the π^0 decay, emitted around 100 MeV but degraded to a few MeV in optically thick models. Spectral …

Go to article

X-Ray Survey Of The Small Magellanic Cloud, F. D. Seward, Melanie Mitchell Feb 1981

X-Ray Survey Of The Small Magellanic Cloud, F. D. Seward, Melanie Mitchell

Computer Science Faculty Publications and Presentations

A region of over 40 square degrees centered on the Small Magellanic Cloud (SMC) has been surveyed with the imaging instruments of the Einstein Observatory. The survey is approximately complete to Lx = 1036 ergs s-1, and the faintest source detected in the SMC, has Lx ≈ 3 x 1035 ergs s-1. Twenty-six sources were clearly seen. Five are identified with objects not associated with the SMC. The only previously known source detected was SMC X-1 which, when in a high state, is the brightest source in the SMC. The second brightest source observed, …

Go to article

Gamma Rays From Penrose Powered Black Holes In Centaurus A, 3c 273, And Ngc 4151, Menas Kafatos Jan 1980

Gamma Rays From Penrose Powered Black Holes In Centaurus A, 3c 273, And Ngc 4151, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Gamma-ray observations of active galaxies have important consequences for theories of the activity in their nuclei. The observations of Cen A, 3C 273, and NGC 4151 are examined under the assumption that Penrose collision processes in the ergospheres of massive black holes power their nuclei. The observed sharp break in the MeV region of the NGC 4151 spectrum cannot be due to the γ-γ pair production process. We attribute this break to the Penrose Compton scattering (PCS), in which γ-rays escape from the ergosphere as a result of Penrose processes involving electrons and lower energy X-ray photons in the ergosphere …

Go to article

150 Ghz Observations Of Three Radio Galaxies, Menas Kafatos, R. W. Hobbs, S. P. Maran, L. W. Brown Jan 1980

150 Ghz Observations Of Three Radio Galaxies, Menas Kafatos, R. W. Hobbs, S. P. Maran, L. W. Brown

Mathematics, Physics, and Computer Science Faculty Articles and Research

Radio galaxies were observed for the first time at 150 GHz. The central sources in Cyg A and 3C Ill were detected, as were the two radio lobes of Cyg A. No emission was found from the central source in 3C 236. Each of these three central sources has been previously discussed as the site of the energy supply for the associated distant components. The millimeter-wavelength emission from the central sources in Cyg A and 3C 111 is probably due in each case to a compact component that is optically thin to synchrotron radiation above about 35 GHz. These components …

Go to article

Magnetohydrodynamic Effects On The Growth Of Condensations In An Expanding Universe & The Formation Of Galaxies, Charles Evans Aug 1979

Magnetohydrodynamic Effects On The Growth Of Condensations In An Expanding Universe & The Formation Of Galaxies, Charles Evans

Masters Theses & Specialist Projects

We review the evidence for existence of a magnetic field of the galaxy and whatever evidence there is of an intergalactic magnetoionic medium. We then consider the magnetohydrodynamics (MHD) of such a medium. The formation of galaxies through purely gravitational means in an expanding universe is then reviewed. Next the role of magnetohydrodynamics in such a universe is analyzed for their effects on galaxy formation. Finally, the importance of MED behavior in the early universe is emphasized from physical considerations and from present day evidence. Appendices discuss isotropic cosmologies, magnetic fields in such a background, the detailed MHD perturbations, and …

Go to article

First Prev