41 research outputs found
Discovery of Nuclear X-ray Sources in SINGS Galaxies
We present the results of a search for nuclear X-ray activity in nearby
galaxies using Chandra archival data in a sample of 62 galaxies from the
Spitzer Infrared Nearby Galaxy Survey (SINGS). We detect 37 nuclear X-ray
sources; seven of these are new detections. Most of the nuclear X-ray sources
are likely to be AGNs. The fraction of galaxies hosting AGNs is thus about 60%,
much higher than that found with optical searches, and demonstrates the
efficacy of X-ray observations to find hidden AGNs in optically normal
galaxies. We find that the nuclear X-ray sources are preferentially present in
earlier type galaxies. Unlike what is observed at high redshift, we do not find
a strong correlation between the AGN luminosity and the 24 micron luminosity of
the host galaxy; we find a strong correlation with the 3.6 micron luminosity
instead. This suggests that at the present epoch the accretion rate depends on
the total mass of the galaxy, as perhaps does the black hole mass.Comment: 35 pages, 10 figures; Accepted for publication in Ap
Spectral optical monitoring of 3C 390.3 in 1995-2007: II. Variability of the spectral line parameters
A study of the variability of the broad emission-line parameters of 3C390.3,
an active galaxy with the double-peaked emission-line profiles, is presented.
We give a detail analysis of variation in the broad Ha and Hb profiles, the
ratios, and the Balmer decrement of different line segments. Studying the
variability of the line profiles we explore the disk structure, that is assumed
to emit the broad double-peaked Ha and Hb emission lines. We divided the
observed spectra in two periods (before and after the outburst in 2002) and
analyzed separately the variation in these two periods. First we analyzed the
spectral emission-line profiles of Ha and Hb, measuring the peak positions.
Then, we divided lines into several segments, and we measured the line-segment
fluxes. The Balmer decrement variation for total Ha and Hb fluxes, as well as
for the line segments has been investigated and discussed. We modeled the line
parameters variation using an accretion disk model. We compared the variability
in the observed line parameters with the disk model predictions and found that
the variation in line profiles and in line segments corresponds to the emission
of a disk-like BLR. But, also there is probably one additional emission
component that contributes to the Ha and Hb line center. We found that the
variation in the line profiles is caused by the variation in the parameters of
the disk-like BLR, first of all in the inner (outer) radius which can well
explain the line parameter variations in the Period I. The Balmer decrement
across the line profile has a bell-like shape, and it is affected not only by
physical processes in the disk, but also by different emitting disk dimension
of the Ha and Hb line. The geometry of the BLR of 3C390.3 seems to be very
complex, and inflows/outflows might be present, but it is evident that the
broad line region with disk-like geometry has dominant emission.Comment: Accepted for publication by A&
Nooru-Mohamed tests performed with a 6 DOF testing machine controlled by Digital Image Correlation
International audienceno abstrac
Nooru-Mohamed tests performed with a 6 DOF testing machine controlled by Digital Image Correlation
International audienceno abstrac
A 3D Displacement Control by Digital Image Correlation for the Multiaxial Testing of Materials with a Stewart Platform
International audienceno abstrac
The Complex, dusty narrow-line region of NGC 4388 : gasâjet interactions, outflows and extinction revealed by near-IR spectroscopy
We present Gemini/GNIRS (Gemini Near-Infrared Spectrograph) spectroscopy of the Seyfert 2 galaxy NGC 4388, with simultaneous coverage from 0.85 to 2.5 ÎŒm. Several spatially extended emission lines are detected for the first time, both in the obscured and unobscured portion of the optical narrow-line region (NLR), allowing us to assess the combined effects of the central continuum source, outflowing gas and shocks generated by the radio jet on the central 280 pc gas. The Hâi and [Feâii] lines allow us to map the extinction affecting the NLR. We found that the nuclear region is heavily obscured, with E(B â V) ⌠1.9 mag. To the NE of the nucleus and up to âŒ150 pc, the extinction remains large, âŒ1 mag or larger, consistent with the system of dust lanes seen in optical imaging. We derived positionâvelocity diagrams for the most prominent lines as well as for the stellar component. Only the molecular gas and the stellar component display a well-organized pattern consistent with disc rotation. Other emission lines are kinematically perturbed or show little evidence of rotation. Extended high-ionization emission of sulphur, silicon and calcium is observed to distances of at least 200 pc both NE and SW of the nucleus. We compared flux ratios between these lines with photoionization models and conclude that radiation from the central source alone cannot explain the observed high-ionization spectrum. Shocks between the radio jet and the ambient gas are very likely an additional source of excitation. We conclude that NGC 4388 is a prime laboratory to study the interplay between all these mechanisms.20 page(s