نتایج جستجو برای: active galaxy
تعداد نتایج: 491329 فیلتر نتایج به سال:
The idea that some of the unusual features in the X-ray spectra of Narrow-Line Seyfert 1 galaxies (NLS1s) are due to the steep X-ray continuum is tested by comparing photoionization model calculations with various observed properties of Seyfert 1 galaxies. A meaningful comparison must involve the careful use of the “right” X-ray ionization parameter, designated here U(oxygen). When this is done...
We are conducting the first systematic 3D spectroscopic imaging survey to quantify the properties of the atomic gas (Hi) in a distance-limited sample of 28 Seyfert galaxies and a sample of 28 inactive control galaxies with well-matched optical properties (the VHIKINGS survey). This study aims to address the role of the host galaxy in nuclear activity and confront outstanding controversies in op...
Deep Chandra X-ray exposures provide an efficient route for locating optically faint active galactic nuclei (AGN) at high redshifts. We use deep multicolor optical data to search for z > 5 AGN in the 2 Ms X-ray exposure of the Chandra Deep Field-North. Of the 423 X-ray sources bright enough (z < 25.2) for a color-color analysis, at most one lies at z = 5 − 6 and none at z > 6. The z > 5 object ...
X-ray transience is the most extreme form of variability observed in AGN or normal in-active galaxies. While factors of 2-3 on timescales of days to years are quite commen among AGN, X-ray transients appear only once and vanish from the X-ray sky years later. The ROSAT All-Sky Survey was the tool to discover these sources. X-ray transience in AGN or galaxies can be caused by dramatic changes in...
A sub-parsec scale radio counterjet has been detected in the nucleus of the closest radio galaxy, Centaurus A (NGC 5128), with VLBI imaging at 2.3 and 8.4 GHz. This is one of the first detections of a VLBI counterjet, and provides new constraints on the kinematics of the radio jets emerging from the nucleus of Centaurus A. A bright, compact core is seen at 8.4 GHz, along with a jet extending al...
Any connection between central activity and the large-scale dynamics of disk galaxies requires an efficient mechanism to remove angular momentum from the orbiting material. The only viable means of achieving inflow from kiloparsec scales is through gravitational stresses created by bars and/or mergers. The inflow of gas in bars today appears to stall at a radius of few hundred parsec, however, ...
Broad infrared spectra (7–200 μm) of four NLS1 galaxies, obtained with the imaging photo-polarimeter (ISOPHOT) on board the Infrared Space Observatory (ISO), are presented. The infrared luminosities and temperatures, opacities and sizes of the emitting dust components are derived. A comparison between the observed infrared spectra and the optical emission line fluxes of a sample of 16 NLS1 gala...
Galaxy interactions are studied in terms of the starburst-Seyfert connection. The starburst requires a high rate of gas supply. Since the efficiency for supplying the gas is high in a galaxy interaction, although the companion is not necessarily discernible, Seyfert galaxies with circumnuclear starbursts are expected to be interacting. Since the large amounts of circumnuclear gas and dust obscu...
We have computed new estimates of the local rates of supernovae (SNe) adding the updated log of Evans’ visual search to our SN search database. In this way, we have accumulated the largest SN statistics ever assembled for this purpose. The new SN rates are corrected on an empirical basis for the bias in the inner regions of galaxies and that in inclined spirals. We also tested an alternative ap...
We present multi–filter far infrared photometry of active and inactive galaxies obtained with ISOPHOT. We find that the far infrared and submillimeter spectrum of the active galaxies can be described by a single modified black–body at a color temperature of 31.5 ± 2.8K. The ratio of infrared luminosity to gas mass, LIR/Mgas, where the latter quantity has been obtained from 1.3 mm observations w...
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