Results 1 - 10 of 6380
Results 1 - 10 of 6380. Search took: 0.026 seconds
|Sort by: date | relevance|
[en] The first international conference on the central region of our galaxy was held at UCLA during July 25-29, 1988. Radio, infrared, X-, and γ-ray astronomers, benefitting from recent technological advances, confronted theorists, as well as each other, with impressive new imagery in each of these domains. Traditionally hidden by an impenetrable veil of dust, the galactic center is now largely transpasrent, particularly in the near-IR, where the extinction toward the galactic center is an order of magnitude less than at optical wavelengths. On the large scale, one observes a large reservoir of molecular gas, some of which is exhibiting complex, noncircular motions. Some of the kinematical behavior is best explained in terms of energetic explosions occurring about 107 years ago. The radio continuum reveals numerous filaments of ionized gas, and strong, poloidal magnetic fields are implied, quite unlike the field anywhere else in the galaxy. On small scales, much effort is going into the attempt to identify a unique objedct at the nucleus that may or may not be a massive black hole (a mass of 3x106 Msun has been defended). Candidates exist for a compact mass concentration, and for a strong central luminosity source, but they are not necessarily one and the same, and there are problems identifying any of the candidates with a massive accreting object at the center. Surrounding the dynamical center of the galaxy is the prominent radio source Sgr A, which includes a warm, turbulent circumnuclear disk on 5 to 10 pc scales, streamers of ionized gas which may represent flows of material into the central potential well, and a background shell of nonthermal radio emission, probably a superimposed supernova remnant. This summary describes some of the current research activity on the galactic center, with particular attention to the implications of X- and γ-ray observations. (orig.)
[en] The models of galactic nuclei providing the large fluxes of high energy neutrinos (Esub(ν) > or approximately = I TeV) are studied. The models of cocooned black hole and a black hole with the accretion provided by stellar tidal disruption are found most plausible for high energy neutrino production. It is demonstrated that in these models the particles can be accelerated to high energies, and at the same time the density of ambient gas and/or X-ray photons is sufficient for effective neutrinos production through the pion decays. It is found the ratio of neutrino to gamma-ray fluxes can convincingly distinguish the structureless magnetoid and the black hole as the models of galactic nuclei. The implication of high energy neutrinos for the search for antimatter in the Universe is discussed
[en] We report on the discovery and observations of the extremely luminous optical transient CSS100217:102913+404220 (CSS100217 hereafter). Spectroscopic observations showed that this transient was coincident with a galaxy at redshift z = 0.147 and reached an apparent magnitude of V ∼ 16.3. After correcting for foreground Galactic extinction we determine the absolute magnitude to be MV = -22.7 approximately 45 days after maximum light. Over a period of 287 rest-frame days, this event had an integrated bolometric luminosity of 1.3 x 1052 erg based on time-averaged bolometric corrections of ∼15 from V- and R-band observations. Analysis of the pre-outburst Sloan Digital Sky Survey (SDSS) spectrum of the source shows features consistent with a narrow-line Seyfert 1 galaxy. High-resolution Hubble Space Telescope and Keck follow-up observations show that the event occurred within 150 pc of the nucleus of the galaxy, suggesting a possible link to the active nuclear region. However, the rapid outburst along with photometric and spectroscopic evolution are much more consistent with a luminous supernova. Line diagnostics suggest that the host galaxy is undergoing significant star formation. We use extensive follow-up of the event along with archival Catalina Sky Survey NEO search and SDSS data to investigate the three most likely sources of such an event: (1) an extremely luminous supernova, (2) the tidal disruption of a star by the massive nuclear black hole, and (3) variability of the central active galactic nucleus (AGN). We find that CSS100217 was likely an extremely luminous Type IIn supernova and occurred within the range of the narrow-line region of an AGN. We discuss how similar events may have been missed in past supernova surveys because of confusion with AGN activity.
[en] The papers in these conference proceedings are organized into the following categories: invited talks, the stellar cluster, the circumnuclear ring, thermal and nonthermal emission, astrometry, relationship to external galaxies, astrophysical models, and galactic center arc and lobes. Separate abstracts were prepared for 39 papers in these proceedings
[en] Detailed photographic UBV photometry of the double UV-excess galaxy Kazarian 163 performed on 2.6-m Biurakan telescope plates yields integrated magnitudes and colors for the object as a whole, the two main components, and their nuclei. The two-color diagram demonstrates that the blueness of the galaxy is dictated by the bright S-component nucleus, whose colors U - B = -0.63 mag, B - V = +0.42 mag are typical of active Seyfert nuclei. Having very different photometric parameters, the N component resembles a normal E galaxy. 8 references
[en] Since the early decades of theoretical studies of galactic dynamics the barred galaxies have been considered to possess some of the fundamental keys to the spiral structure problem. The author discusses two galaxies that may be of interest when comparing dynamical theories with observations: NGC 1365 and NGC 1512. (Auth.)
[en] Two main modes of star formation are know to control the growth of galaxies: a relatively steady one in disk-like galaxies, defining a tight star formation rate (SFR)-stellar mass sequence, and a starburst mode in outliers to such a sequence which is generally interpreted as driven by merging. Such starburst galaxies are rare but have much higher SFRs, and it is of interest to establish the relative importance of these two modes. PACS/Herschel observations over the whole COSMOS and GOODS-South fields, in conjunction with previous optical/near-IR data, have allowed us to accurately quantify for the first time the relative contribution of the two modes to the global SFR density in the redshift interval 1.5 < z < 2.5, i.e., at the cosmic peak of the star formation activity. The logarithmic distributions of galaxy SFRs at fixed stellar mass are well described by Gaussians, with starburst galaxies representing only a relatively minor deviation that becomes apparent for SFRs more than four times higher than on the main sequence. Such starburst galaxies represent only 2% of mass-selected star-forming galaxies and account for only 10% of the cosmic SFR density at z ∼ 2. Only when limited to SFR > 1000 Msun yr-1, off-sequence sources significantly contribute to the SFR density (46% ± 20%). We conclude that merger-driven starbursts play a relatively minor role in the formation of stars in galaxies, whereas they may represent a critical phase toward the quenching of star formation and morphological transformation in galaxies.