31 research outputs found
Statistical multifrequency study of narrow-line Seyfert 1 galaxies
High-energy {\gamma}-rays, which are produced by powerful relativistic jets,
are usually associated with blazars and radio galaxies. In the current active
galactic nuclei (AGN) paradigm, such jets are almost exclusively launched from
massive elliptical galaxies. Recently, however, Fermi/LAT detected
{\gamma}-rays from a few narrow-line Seyfert 1 galaxies and thus confirmed the
presence of relativistic jets in them. Since NLS1 galaxies are assumed to be
young evolving AGN, they offer a unique opportunity to study the production of
relativistic jets in late-type galaxies. Our aim is to estimate by which
processes the emission of various kinds is produced in NLS1 galaxies and to
study how emission properties are connected to other intrinsic AGN properties.
We have compiled the so far largest multiwavelength database of NLS1 sources.
This allowed us to explore correlations between different wavebands and source
properties using, for example, Pearson and Spearman correlations and principal
component analysis. We did this separately for radio-loud and radio-quiet
sources. Multiwavelength correlations suggest that radio-loud sources host
relativistic jets that are the predominant sources of radio, optical, and X-ray
emission. The origin of infrared emission remains unclear. Radio-quiet sources
do not host a jet, or the jet is very weak. In them, radio and infrared
emission is more likely generated via star formation processes, and the optical
and X-ray emission originate in the inner parts of the AGN. We also find that
the black hole mass correlates significantly with radio loudness, which
suggests that NLS1 galaxies with more massive black holes are more likely to be
able to launch powerful relativistic jets.Comment: 29 pages, 7 figures, accepted for publication in Astronomy &
Astrophysic
Cluster Galaxy Morphologies: The Relationship among Structural Parameters, Activity and the Environment
We use an approach to estimate galaxy morphologies based on an ellipticity
(e) vs. Bulge-to-Total ratio (B/T) plane. We have calibrated this plane by
comparing with Dressler's classifications. With the aid of our calibration, we
have classified 635 galaxies in 18 Abell clusters (0.02 < z < 0.08). Our
approach allowed us to recover the Kormendy's relation. We found that
ellipticals and Spirals are slightly brighter than S0 in R band. As S0 bulges
are brighter than spirals bulges, we believe that ram pressure is not the main
mechanism to generate S0s. In our sample, cluster radio galaxies morphologies
cover the range S0-E-cD and their bulges have absolutes magnitudes distributed
within -21 mag < M < -24.5 mag. If we believe Ferrarese & Merrit's relation,
these radio sources have 10^8-10^9 M black hole mass.Comment: Originally published in the proceedings of the conference "The
Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", AIP
Conference Proceedings, Volume 1201 edited by Sebastian Heinz and Eric
Wilcots. This version contains slight modification
Discovery of a pseudobulge galaxy launching powerful relativistic jets
Supermassive black holes launching plasma jets at close to the speed of light, producing gamma-rays, have ubiquitously been found to be hosted by massive elliptical galaxies. Since elliptical galaxies are generally believed to be built through galaxy mergers, active galactic nuclei (AGN) launching relativistic jets are associated with the latest stages of galaxy evolution. We have discovered a pseudobulge morphology in the host galaxy of the gamma-ray AGN PKS 2004-447. This is the first gamma-ray emitter radio-loud AGN found to have been launched from a system where both the black hole and host galaxy have been actively growing via secular processes. This is evidence of an alternative black hole-galaxy co-evolutionary path to develop powerful relativistic jets, which is not merger driven
Discovery of a Pseudobulge Galaxy Launching Powerful Relativistic Jets
Supermassive black holes launching plasma jets at close to the speed of light, producing gamma-rays, have ubiquitously been found to be hosted by massive elliptical galaxies. Since elliptical galaxies are generally believed to be built through galaxy mergers, active galactic nuclei (AGN) launching relativistic jets are associated with the latest stages of galaxy evolution. We have discovered a pseudobulge morphology in the host galaxy of the gamma-ray AGN PKS 2004-447. This is the first gamma-ray emitter radio-loud AGN found to have been launched from a system where both the black hole and host galaxy have been actively growing via secular processes. This is evidence of an alternative black hole-galaxy co-evolutionary path to develop powerful relativistic jets, which is not merger driven.</p
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Persistent Asymmetric Structure of Sagittarius A* on Event Horizon Scales
The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3 mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3 mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over 4 years. Closure phases, the sum of visibility phases along a closed triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180-degree rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons along the line of sight.Astronom
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230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy γ-ray state in 2012
We report on 230 GHz (1.3 mm) VLBI observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona and Cedar Flat in California. For the first time, we have acquired 230 GHz VLBI interferometric phase information on M87 through measurement of closure phase on the triangle of long baselines. Most of the measured closure phases are consistent with 0◦ as expected by physically-motivated models for 230 GHz structure such as jet models and accretion disk models. The brightness temperature of the event-horizon-scale structure is ∼ 1 × 1010 K derived from the compact flux density of ∼ 1 Jy and the angular size of ∼ 40 µas ∼ 5.5 Rs, which is broadly consistent with the peak brightness of the radio cores at 1-86 GHz located within ∼ 102 Rs. Our observations occurred in the middle of an enhancement in very-high-energy (VHE) γ-ray flux, presumably originating in the vicinity of the central black hole. Our measurements, combined with results of multi-wavelength observations, favor a scenario in which the VHE region has an extended size of ∼20-60 Rs.Astronom