Search results for " Galaxies"
showing 10 items of 289 documents
The history of chemical enrichment in the intracluster medium from cosmological simulations
2017
The distribution of metals in the intracluster medium (ICM) of galaxy clusters provides valuable information on their formation and evolution, on the connection with the cosmic star formation and on the effects of different gas processes. By analyzing a sample of simulated galaxy clusters, we study the chemical enrichment of the ICM, its evolution, and its relation with the physical processes included in the simulation and with the thermal properties of the core. These simulations, consisting of re-simulations of 29 Lagrangian regions performed with an upgraded version of the SPH GADGET-3 code, have been run including two different sets of baryonic physics: one accounts for radiative coolin…
VLBI detection of the HST-1 feature in the M87 jet at 2 cm
2010
A bright feature 80 pc away from the core in the powerful jet of M87 shows highly unusual properties. Earlier radio, optical and X-ray observations have shown that this feature, labeled HST-1, is superluminal, and is possibly connected with the TeV flare detected by HESS in 2005. It has been claimed that this feature might have a blazar nature, due to these properties. To examine the possible blazar-like nature of HST-1, we analyzed lambda 2 cm VLBA archival data from dedicated full-track observations and the 2 cm survey/MOJAVE VLBI monitoring programs obtained between 2000 and 2009. Applying VLBI wide-field imaging techniques, the HST-1 region was imaged at milliarcsecond resolution. Here …
Jet-torus connection in radio galaxies
2017
High-resolution Very-Long-Baseline Interferometry observations of active galactic nuclei have revealed asymmetric structures in the jets of radio galaxies. These asymmetric structures may be due to internal asymmetries in the jet, could be induced by the different conditions in the surrounding ambient medium including the obscuring torus, or a combination of the two. In this paper we investigate the influence of the ambient medium (including the obscuring torus) on the observed properties of jets from radio galaxies. We performed special-relativistic hydrodynamic (RHD) simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code \texttt{Ratpenat}…
A new sample of large angular size radio galaxies
2004
We present in this paper a detailed study of a new sample of large angular size FR I and FR II radio galaxies and compare the properties of the two classes. As expected, a pure morphology based distinction of FR Is and FR IIs corresponds to a break in total radio power. The radio cores in FR Is are also weaker than in FR IIs, although there is not a well defined break power. We find that asymmetry in the structure of the sample members must be the consequence of anisotropies in the medium where the lobes expand, with orientation playing a minor role. Moreover, literature data and our observations at kiloparsec scales suggest that the large differences between the structures of FR I and FR I…
Long-term monitoring of mrk 501 for its very high energy γ emission and a flare in 2011 october
2012
"As one of the brightest active blazars in both X-ray and very high energy γ -ray bands, Mrk 501, is very useful for" "physics associated with jets from active galactic nuclei. The ARGO-YBJ experiment has monitored Mrk 501 for γ - rays above 0.3 TeV since 2007 November. The largest flare since 2005 was observed from 2011 October and lasted until about 2012 April. In this paper, a detailed analysis of this event is reported. During the brightest γ -ray flaring episodes from 2011 October 17 to November 22, an excess of the event rate over 6σ is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the γ -ray flux above 1 TeV by a factor of 6.6 ± 2.2 from its steady…
Dissipative Processes and Their Role in the Evolution of Radio Galaxies
2019
Particle acceleration in relativistic jets to very high energies occurs at the expense of the dissipation of magnetic or kinetic energy. Therefore, understanding the processes that can trigger this dissipation is key to the characterization of the energy budgets and particle acceleration mechanisms at action in active galaxies. Instabilities and entrainment are two obvious candidates to trigger dissipation. On the one hand, supersonic, relativistic flows threaded by helical fields, as expected from the standard formation models of jets in supermassive black-holes, are unstable to a series of magnetohydrodynamical instabilities, such as the Kelvin-Helmholtz, current-driven, or possibly the p…
REM near-IR and optical multiband observations of PKS 2155-304 in 2005 : Erratum
2007
Fernandez Soto, Alberto, Alberto.Fernandez@uv.es
The hyperfine structure in the rotational spectrum of CF+
2012
Context. CF+ has recently been detected in the Horsehead and Orion Bar photo-dissociation regions. The J=1-0 line in the Horsehead is double-peaked in contrast to other millimeter lines. The origin of this double-peak profile may be kinematic or spectroscopic. Aims. We investigate the effect of hyperfine interactions due to the fluorine nucleus in CF+ on the rotational transitions. Methods. We compute the fluorine spin rotation constant of CF+ using high-level quantum chemical methods and determine the relative positions and intensities of each hyperfine component. This information is used to fit the theoretical hyperfine components to the observed CF+ line profiles, thereby employing the h…
A KInetic Database for Astrochemistry (KIDA)
2012
We present a novel chemical database for gas-phase astrochemistry. Named the KInetic Database for Astrochemistry (KIDA), this database consists of gas-phase reactions with rate coefficients and uncertainties that will be vetted to the greatest extent possible. Submissions of measured and calculated rate coefficients are welcome, and will be studied by experts before inclusion into the database. Besides providing kinetic information for the interstellar medium, KIDA is planned to contain such data for planetary atmospheres and for circumstellar envelopes. Each year, a subset of the reactions in the database (kida.uva) will be provided as a network for the simulation of the chemistry of dense…
Minidisk dynamics in accreting, spinning black hole binaries: Simulations in full general relativity
2021
We perform magnetohydrodynamic simulations of accreting, equal-mass binary black holes in full general relativity focusing on the impact of black hole spin on the dynamical formation and evolution of minidisks. We find that during the late inspiral the sizes of minidisks are primarily determined by the interplay between the tidal field and the effective innermost stable orbit around each black hole. Our calculations support that a minidisk forms when the Hill sphere around each black hole is significantly larger than the black hole's effective innermost stable orbit. As the binary inspirals, the radius of the Hill sphere decreases, and minidisk sconsequently shrink in size. As a result, ele…