Related papers: Optical Detection of the Hidden Nuclear Engine in …
The detection of polarized continuum and line emission from the nucleus of NGC 4258 by Wilkes et al. (1995) provides an intriguing application of the unified model of Seyfert nuclei to a galaxy in which there is known to be an edge-on,…
NGC 4258 is an SABbc Seyfert galaxy, located at a distance of $7.2 \pm 0.3$ Mpc. This object is well known by its nearly edge-on molecular nuclear disc, located between 0.16 and 0.28 pc from the nucleus, whose H$_2$O maser emission allows a…
It has been claimed that the megamaser observations of the nucleus of NGC 4258 show that a massive black hole is present in its center (Miyoshi et al. 1995, Greenhill et al. 1995). We show that the evidence of ejection of gas, radio plasma,…
XMM-Newton observed the Seyfert 1.9 galaxy NGC 4258 in December 2000. At energies above 2 keV a hard nuclear point source is resolved that can be fitted by a highly absorbed power-law spectrum (NH = (8.0+-0.4)x10^22 cm^-2, photon index…
In 2006 June, the obscured low luminosity active galactic nucleus in the nearby Seyfert 1.9 galaxy NGC 4258 was observed with Suzaku for ~ 100 ks. Utilizing the XIS and the HXD, the nucleus emission was detected over 2 to 40 keV range, with…
[abridged] We present an X-ray study of the low-luminosity active galactic nucleus (AGN) in NGC4258 using data from Suzaku, XMM-Newton, and the Swift/BAT survey. We find that signatures of X-ray reprocessing by cold gas are very weak in the…
There is now dynamical evidence for massive dark objects at the center of several galaxies, but suggestions that these are supermassive black holes are based only on indirect astrophysical arguments. The recent unprecedented measurement of…
In order to determine whether unified models of active galactic nuclei apply to low-luminosity objects, we have undertaken a spectropolarimetric survey of of LINERs and Seyfert nuclei at the Keck Observatory. The 14 objects observed have a…
We present new mid-infrared (N-band) images of a sample of eight nearby Seyfert galaxies. In all of our targets, we detect a central unresolved source, which in some cases has been identified for the first time. In particular, we have…
We present a deep X-ray observation of the low-luminosity active galactic nucleus in NGC4258 (M106) using ASCA. The soft X-ray spectrum <2keV is dominated by thermal emission from optically-thin plasma with kT~0.5keV. The hard X-ray…
Emission-line variability data for Seyfert 1 galaxies provide strong evidence for the existence of supermassive black holes in the nuclei of these galaxies, and that the line-emitting gas is moving in the gravitational potential of that…
We present the analysis of an optical data cube of the central region of NGC 1448, obtained with the Multi Unit Spectroscopic Explorer (MUSE). Chandra X-ray data indicate that the active galactic nucleus (AGN) is not located at the apparent…
NGC 4395 is one of the least luminous and nearest known type 1 Seyfert galaxies, and it also lacks a bulge. We present an HST I-band image of its nuclear region and Keck high-resolution (8 km/s) echelle spectra containing the Ca II…
We report on the nuclear X-ray properties of the radio galaxy NGC 6251 observed with XMM-Newton. NGC 6251 is a well-known radio galaxy with intermediate FRI/II radio properties. It is optically classified as a Seyfert 2 and hosts a…
We present the first results from an XMM-Newton observation of the FRI galaxy NGC 4261, which harbors a supermassive black hole and a low-ionization nuclear emission-line region (LINER). Here we focus on the X-ray properties of the nucleus,…
The recent observations of high-velocity maser emissions in NGC 4258 by Myoshi et al provide strong evidence for a central object of mass 3.6 10**7 solar masses in the nucleus of this galaxy based on a kinematic argument. However, they…
The clumpy maser disks observed in some galactic nuclei mark the outskirts of the accretion disk that fuels the central black hole and provide a potential site of nuclear star formation. Unfortunately, most of the gas in maser disks is…
We determine the mass of the black hole at the center of the spiral galaxy NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These models are constrained by high spatial resolution imaging and long-slit spectroscopy of…
Improved analysis of ultraviolet and optical monitoring data on the Seyfert 1 galaxy NGC 3783 provides evidence for the existence of a supermassive, (8.7+/-1.1)x10^6 M_sun, black hole in this galaxy. By using recalibrated spectra from the…
Active Galactic Nuclei are objects associated with the presence of an accretion disc around supermassive black holes found in the very central region of galaxies with a well-defined bulge. In the optical range of the spectrum, a possible…