659 research outputs found
Outflows of hot molecular gas in ultra-luminous infra-red galaxies mapped with VLT-SINFONI
We present the detection and morphological characterization of hot molecular
gas outflows in nearby ultra-luminous infrared galaxies, using the near-IR
integral-field spectrograph SINFONI on the VLT. We detect outflows observed in
the 2.12 micron H 1-0 S(1) line for three out of four ULIRGs analyzed;
IRAS 12112+0305, 14348-1447, and 22491-1808. The outflows are mapped on scales
of 0.7-1.6 kpc, show typical outflow velocities of 300-500 km/s, and appear to
originate from the nuclear region. The outflows comprise hot molecular gas
masses of ~6-8x10 M(sun). Assuming a hot-to-cold molecular gas mass ratio
of 6x10, as found in nearby luminous IR galaxies, the total (hot+cold)
molecular gas mass in these outflows is expected to be ~1x10 M(sun). This
translates into molecular mass outflow rates of ~30-85 M(sun)/yr, which is a
factor of a few lower than the star formation rate in these ULIRGs. In
addition, most of the outflowing molecular gas does not reach the escape
velocity of these merger systems, which implies that the bulk of the outflowing
molecular gas is re-distributed within the system and thus remains available
for future star formation. The fastest H outflow is seen in the
Compton-thick AGN of IRAS 14348-1447, reaching a maximum outflow velocity of
~900 km/s. Another ULIRG, IRAS 17208-0014, shows asymmetric H line
profiles different from the outflows seen in the other three ULIRGs. We discuss
several alternative explanations for its line asymmetries, including a very
gentle galactic wind, internal gas dynamics, low-velocity gas outside the disk,
or two superposed gas disks. We do not detect the hot molecular counterpart to
the outflow previously detected in CO(2-1) in IRAS 17208-0014, but we note that
our SINFONI data are not sensitive enough to detect this outflow if it has a
small hot-to-cold molecular gas mass ratio of < 9x10.Comment: Accepted for publication in A&A (11 pages, 10 figures
Entropy maximization and the busy period of some single-server vacation models
In this paper, information theoretic methodology for system modeling is applied to investigate the probability density function of the busy period in M/G/1 vacation models operating under the N-, T- and D-policies. The information about the density function is limited to a few mean value constraints (usually the first moments). By using the maximum entropy methodology one obtains the least biased probability density function satisfying the system's constraints. The analysis of the three controllable M/G/1 queueing models provides a parallel numerical study of the solution obtained via the maximum entropy approach versus “classical” solutions. The maximum entropy analysis of a continuous system descriptor (like the busy period) enriches the current body of literature which, in most cases, reduces to discrete queueing measures (such as the number of customers in the system)
The busy period and the waiting time analysis of a MAP/M/c queue with finite retrial group
We concentrate on the analysis of the busy period and the waiting time distribution of a multi-server retrial queue in which primary arrivals occur according to a Markovian arrival process (MAP). Since the study of a model with an infinite retrial group seems intractable, we deal with a system having a finite buffer for the retrial group. The system is analyzed in steady state by deriving expressions for (a) the Laplace–Stieltjes transforms of the busy period and the waiting time; (b) the probabiliy generating functions for the number of customers served during a busy period and the number of retrials made by a customer; and (c) various moments of quantites of interest. Some illustrative numerical examples are discussed
Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
We present sub-arcsecond 7.513 m imaging- and spectro-polarimetric
observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio
CANARIAS. At all wavelengths, we find:
(1) A 90 60 pc extended polarized feature in the northern ionization
cone, with a uniform 44 polarization angle. Its polarization
arises from dust and gas emission in the ionization cone, heated by the active
nucleus and jet, and further extinguished by aligned dust grains in the host
galaxy. The polarization spectrum of the jet-molecular cloud interaction at
24 pc from the core is highly polarized, and does not show a silicate
feature, suggesting that the dust grains are different from those in the
interstellar medium.
(2) A southern polarized feature at 9.6 pc from the core. Its
polarization arises from a dust emission component extinguished by a large
concentration of dust in the galaxy disc. We cannot distinguish between dust
emission from magnetically aligned dust grains directly heated by the jet close
to the core, and aligned dust grains in the dusty obscuring material
surrounding the central engine. Silicate-like grains reproduce the polarized
dust emission in this feature, suggesting different dust compositions in both
ionization cones.
(3) An upper limit of polarization degree of 0.3 per cent in the core. Based
on our polarization model, the expected polarization of the obscuring dusty
material is 0.1 per cent in the 813 m wavelength range. This
low polarization may be arising from the passage of radiation through aligned
dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA
On First Passage Times in Discrete Skeletons and Uniformized Versions of a Continuous-Time Markov Chain
In this paper, the aim is to study similarities and differences between a continuous-time Markov chain and its uniformized Markov chains and discrete skeletons in terms of first passage times when the taboo subset of states is assumed to be accessible from a class of communicating states. Under the assumption of a finite communicating class, we characterize the first-passage times in terms of either continuous or discrete phase-type random variables. For illustrative purposes, we show how first passage times in uniformized Markov chains and discrete skeletons can be used to approximate the random duration of an outbreak in the SIS epidemic model
Near-Infrared Polarimetric Adaptive Optics Observations of NGC 1068: A torus created by a hydromagnetic outflow wind
We present J' and K' imaging linear polarimetric adaptive optics observations
of NGC 1068 using MMT-Pol on the 6.5-m MMT. These observations allow us to
study the torus from a magnetohydrodynamical (MHD) framework. In a 0.5" (30 pc)
aperture at K', we find that polarisation arising from the passage of radiation
from the inner edge of the torus through magnetically aligned dust grains in
the clumps is the dominant polarisation mechanism, with an intrinsic
polarisation of 7.0%2.2%. This result yields a torus magnetic field
strength in the range of 482 mG through paramagnetic alignment, and
139 mG through the Chandrasekhar-Fermi method. The measured
position angle (P.A.) of polarisation at K is found to be similar to the
P.A. of the obscuring dusty component at few parsec scales using infrared
interferometric techniques. We show that the constant component of the magnetic
field is responsible for the alignment of the dust grains, and aligned with the
torus axis onto the plane of the sky. Adopting this magnetic field
configuration and the physical conditions of the clumps in the MHD outflow wind
model, we estimate a mass outflow rate 0.17 M yr at 0.4
pc from the central engine for those clumps showing near-infrared dichroism.
The models used were able to create the torus in a timescale of 10
yr with a rotational velocity of 1228 km s at 0.4 pc. We conclude
that the evolution, morphology and kinematics of the torus in NGC 1068 can be
explained within a MHD framework.Comment: 14 pages, 4 figures, Accepted by MNRA
Noisy Kondo impurities
The anti-ferromagnetic coupling of a magnetic impurity carrying a spin with
the conduction electrons spins of a host metal is the basic mechanism
responsible for the increase of the resistance of an alloy such as
CuFe at low temperature, as originally suggested by
Kondo . This coupling has emerged as a very generic property of localized
electronic states coupled to a continuum . The possibility to design artificial
controllable magnetic impurities in nanoscopic conductors has opened a path to
study this many body phenomenon in unusual situations as compared to the
initial one and, in particular, in out of equilibrium situations. So far,
measurements have focused on the average current. Here, we report on
\textit{current fluctuations} (noise) measurements in artificial Kondo
impurities made in carbon nanotube devices. We find a striking enhancement of
the current noise within the Kondo resonance, in contradiction with simple
non-interacting theories. Our findings provide a test bench for one of the most
important many-body theories of condensed matter in out of equilibrium
situations and shed light on the noise properties of highly conductive
molecular devices.Comment: minor differences with published versio
- …