5,806 research outputs found
What produces the extended LINER-type emission in the NUGA galaxy NGC 5850?
(Abridged) The role of low ionization nuclear emission region (LINER)
galaxies within the picture of active galactic nuclei (AGN) has been
controversial. It is still not clear whether they host an AGN in a low
accretion mode, or whether they are not active at all but dominated by
alternative ionization mechanisms, namely shocks, winds/outflows, or
photoionization by a post asymptotic giant branch (p-AGB) stellar population.
The detection of extended LINER-like emission was often taken as evidence of
ionization by stellar components but this has not been undisputed. We performed
optical integral field spectroscopic observations on the central approx. 4 kpc
of NGC 5850 using VIMOS at the VLT, which provides spatially-resolved spectra
for the gas emission and the stellar continuum. We derive and analyse emission
line and kinematic maps. We find the central few kpc of NGC 5850 to be
dominated by extended LINER-like emission. The emission-line ratios that are
sensitive to the ionization parameter increase with radial distance to the
nucleus. Therefore, the extended LINER-like emission in NGC 5850 is dominated
by ionization from distributed ionization sources, probably by stars on the
p-AGB. The LINER-like region is surrounded by emission that is classed as
'composite', likely due to a mixture of a LINER-like ionization pattern and
photoionization by low-level star formation. Two star-forming regions are
present in the 21"x19" field of view. One of them is located approximately in
the ring surrounding the kinematically decoupled core. The second one is close
to the nucleus and is the origin of a region of decreased emission line ratios
oriented radially outwards. We find the interstellar gas to have areas of steep
velocity gradients and a complex kinematic morphology, probably caused by the
lopsided (m=1) distribution of the gas. The inflow of gas toward the center
appears possible.Comment: 18 pages, 17 figures, 2 tables, accepted by 'Astronomy and
Astrophysics
Evidence of Hydronium Formation in Water-Chabazite Zeolite Using Inelastic Neutron Scattering Experiments and ab Initio Molecular Dynamics Simulations
[EN] A combined study of inelastic neutron scattering and ab initio molecular dynamics simulations has been performed in order to study the water-acid site interaction in zeolite chabazite with a ratio Si/Al = 16 that corresponds to 2 protons/uc with two different water coverages with the number of water molecules being lower and higher than that of proton sites. These results have provided a clear picture of the water-acid site interaction, and it has been demonstrated that there are two regimens of water adsorption, which depend on the water loading. (i) At low water coverage (water/acid site similar to 0.5), the main interactions between water and the zeolitic acid sites are established through hydrogen bond and there is no proton transference to water. (ii) At relatively high water loading (water/acid site similar to 3), the clustering of water molecules and hydronioum cations formed by the complete transference of the zeolitic proton to the water molecules has been observed. The formation of water-hydronium clusters interacting with oxygen atoms of the zeolite framework provides the stabilization energy needed for the protonation of water molecules confined in the cavities of chabazite. These results are the experimental evidence obtained from INS of proton transfer from the zeolitic acid site and the hydronium formation and are in agreement with a previous computational study (Phys. Chem. Chem. Phys. 2009, 11, 1702-1712) and very recent solid state NMR spectroscopy studies (J. Am. Chem. Soc. 2019, 141, 3444-3455). The inspection of the low energy bands (translational and optic modes) and librational bands of the experimental results allows obtaining information about the Hbond network of the hydronium-water clusterWe thank MICINN of Spain for funding through Projects RTI2018-101784-B-I00 and SEV-2016-0683. The authors thank the ILL for neutron beam-time allocation (experiment 7-05-456) and the ILL C-Lab for support. A. Moraleda is acknowledged for the synthesis of CHA-16. G.S. and T.L. thank the ILL for the provision of Contract SRH/GRI/AS-15/222 and a Ph.D. contract.Jiménez-Ruiz, M.; Gahle, DS.; Lemishko, T.; Valencia Valencia, S.; Sastre Navarro, GI.; Rey Garcia, F. (2020). Evidence of Hydronium Formation in Water-Chabazite Zeolite Using Inelastic Neutron Scattering Experiments and ab Initio Molecular Dynamics Simulations. The Journal of Physical Chemistry C. 124(9):5436-5443. https://doi.org/10.1021/acs.jpcc.9b11081S54365443124
The Galactic centre mini-spiral in the mm-regime
The mini-spiral is a feature of the interstellar medium in the central ~2 pc
of the Galactic center. It is composed of several streamers of dust and ionised
and atomic gas with temperatures between a few 100 K to 10^4 K. There is
evidence that these streamers are related to the so-called circumnuclear disk
of molecular gas and are ionized by photons from massive, hot stars in the
central parsec. We attempt to constrain the emission mechanisms and physical
properties of the ionized gas and dust of the mini-spiral region with the help
of our multiwavelength data sets. Our observations were carried out at 1.3 mm
and 3 mm with the mm interferometric array CARMA in California in March and
April 2009, with the MIR instrument VISIR at ESO's VLT in June 2006, and the
NIR Br-gamma with VLT NACO in August 2009. We present high resolution maps of
the mini-spiral, and obtain a spectral index of 0.5 for Sgr A*, indicating an
inverted synchrotron spectrum. We find electron densities within the range
0.8-1.5x10^4 cm-3 for the mini-spiral from the radio continuum maps, along with
a dust mass contribution of ~0.25 solar masses from the MIR dust continuum, and
extinctions ranging from 1.8-3 at 2.16 micron in the Br-gamma line. We observe
a mixture of negative and positive spectral indices in our 1.3 mm and 3 mm
observations of the extended emission of the mini-spiral, which we interpret as
evidence that there are a range of contributions to the thermal free-free
emission by the ionized gas emission and by dust at 1.3 mm.Comment: 9 pages, 11 figures, accepted to A&
Evidences of the Cerium Oxide-Catalysed DPF Regeneration in a Real Diesel Engine Exhaust
The active phase Ce0.5Pr0.5O2 has been loaded on commercial substrates (SiC DPF and cordierite honeycomb monolith) to perform DPF regeneration experiments in the exhaust of a diesel engine. Also, a powder sample has been prepared to carry out soot combustion experiments at laboratory. Experiments performed in the real diesel exhaust demonstrated the catalytic activity of the Ce–Pr mixed oxide for the combustion of soot, lowering the DPF regeneration temperature with regard to a counterpart catalyst-free DPF. The temperature for active regeneration of the Ce0.5Pr0.5O2-containing DPF when the soot content is low is in the range of 500–550 °C. When the Ce0.5Pr0.5O2-containing DPF is saturated with a high amount of soot, pressure drop and soot load at the filter reach equilibrium at around 360 °C under steady state engine operation due to passive regeneration. The uncoated DPF reached this equilibrium at around 440 °C. Comparing results at real exhaust with those at laboratory allow concluding that the Ce0.5Pr0.5O2-catalysed soot combustion in the real exhaust is not based on the NO2-assisted mechanism but is most likely occurring by the active oxygen-based mechanism.The authors thank the financial support of Generalitat Valenciana (Project Prometeo 2009/047), Spanish Ministry of Science and Innovation (project CIT-420000-2009-48) and EU (FEDER funding)
Experimental Indicators of Accretion Processes in Active Galactic Nuclei
Bright Active Galactic Nuclei are powered by accretion of mass onto the super
massive black holes at the centers of the host galaxies. For fainter objects
star formation may significantly contribute to the luminosity. We summarize
experimental indicators of the accretion processes in Active Galactic Nuclei
(AGN), i.e., observable activity indicators that allow us to conclude on the
nature of accretion. The Galactic Center is the closest galactic nucleus that
can be studied with unprecedented angular resolution and sensitivity.
Therefore, here we also include the presentation of recent observational
results on Sagittarius A* and the conditions for star formation in the central
stellar cluster. We cover results across the electromagnetic spectrum and find
that the Sagittarius A* (SgrA*) system is well ordered with respect to its
geometrical orientation and its emission processes of which we assume to
reflect the accretion process onto the super massive black hole.Comment: 16 pages, 4 figures, conference proceeding: Accretion Processes in
Cosmic Sources - APCS2016 - 5-10 September 2016, Saint Petersburg, Russi
Beating the confusion limit: The necessity of high angular resolution for probing the physics of Sagittarius A* and its environment: Opportunities for LINC-NIRVANA (LBT), GRAVITY (VLTI) and and METIS (E-ELT)
The super-massive 4 million solar mass black hole (SMBH) SgrA* shows variable
emission from the millimeter to the X-ray domain. A detailed analysis of the
infrared light curves allows us to address the accretion phenomenon in a
statistical way. The analysis shows that the near-infrared flux density
excursions are dominated by a single state power law, with the low states of
SgrA* limited by confusion through the unresolved stellar background. We show
that for 8-10m class telescopes blending effects along the line of sight will
result in artificial compact star-like objects of 0.5-1 mJy that last for about
3-4 years. We discuss how the imaging capabilities of GRAVITY at the VLTI,
LINC-NIRVANA at the LBT and METIS at the E-ELT will contribute to the
investigation of the low variability states of SgrA*.Comment: 19 pages, 5 figure, Conf. Proc. SPIE Astronomical Telescopes +
Instrumentation 1 - 6 July 2012. Amsterdam No. 8445-
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