10,750 research outputs found
Investigating the Structure of the Windy Torus in Quasars
Thermal mid-infrared emission of quasars requires an obscuring structure that
can be modeled as a magneto-hydrodynamic wind in which radiation pressure on
dust shapes the outflow. We have taken the dusty wind models presented by
Keating and collaborators that generated quasar mid-infrared spectral energy
distributions (SEDs), and explored their properties (such as geometry, opening
angle, and ionic column densities) as a function of Eddington ratio and X-ray
weakness. In addition, we present new models with a range of magnetic field
strengths and column densities of the dust-free shielding gas interior to the
dusty wind. We find this family of models -- with input parameters tuned to
accurately match the observed mid-IR power in quasar SEDs -- provides
reasonable values of the Type 1 fraction of quasars and the column densities of
warm absorber gas, though it does not explain a purely luminosity-dependent
covering fraction for either. Furthermore, we provide predictions of the
cumulative distribution of E(B-V) values of quasars from extinction by the wind
and the shape of the wind as imaged in the mid-infrared. Within the framework
of this model, we predict that the strength of the near-infrared bump from hot
dust emission will be correlated primarily with L/L_Edd rather than luminosity
alone, with scatter induced by the distribution of magnetic field strengths.
The empirical successes and shortcomings of these models warrant further
investigations into the composition and behaviour of dust and the nature of
magnetic fields in the vicinity of actively accreting supermassive black holes.Comment: 11 pages, 6 figures, accepted for publication in MNRA
Cosmic Pathways for Compact Groups in the Milli-Millennium Simulation
We detected 10 compact galaxy groups (CGs) at in the semi-analytic
galaxy catalog of Guo et al. (2011) for the milli-Millennium Cosmological
Simulation (sCGs in mGuo2010a). We aimed to identify potential canonical
pathways for compact group evolution and thus illuminate the history of
observed nearby compact groups. By constructing merger trees for sCG
galaxies, we studied the cosmological evolution of key properties, and compared
them with Hickson CGs (HCGs). We found that, once sCG galaxies come
within 1 (0.5) Mpc of their most massive galaxy, they remain within that
distance until , suggesting sCG "birth redshifts". At stellar masses
of sCG most-massive galaxies are within . In several cases, especially in the two 4- and 5-member
systems, the amount of cold gas mass anti-correlates with stellar mass, which
in turn correlates with hot gas mass. We define the angular difference between
group members' 3D velocity vectors, , and note that
many of the groups are long-lived because their small values of
indicate a significant parallel component. For
triplets in particular, values range between
and so that galaxies are coming together along
roughly parallel paths, and pairwise separations do not show large pronounced
changes after close encounters. The best agreement between sCG and HCG physical
properties is for galaxy values, but HCG values are higher overall,
including for SFRs. Unlike HCGs, due to a tail at low SFR and , and a
lack of galaxies, only a few sCG galaxies
are on the star-forming main sequence.Comment: Style fixes to better match ApJ published version. Uses likeapj1.1
style files: 17 pages, 13 figures, 2 tables. LaTex style files available at
https://github.com/qtast/likeapj/releases/lates
Observation of the Ettingshausen effect in quantum Hall systems
Evidence of the Ettingshausen effect in the breakdown regime of the integer
quantum Hall effect has been observed in a GaAs/AlGaAs two-dimensional electron
system. Resistance of micro Hall bars attached to both edges of a current
channel shows remarkable asymmetric behaviors which indicate an electron
temperature difference between the edges. The sign of the difference depends on
the direction of the electric current and the polarity of the magnetic field.
The results are consistent with the recent theory of Akera.Comment: 4 pages, 6 figures, submitted to Phys. Rev.
Deep ALMA imaging of the merger NGC1614 - Is CO tracing a massive inflow of non-starforming gas?
Observations of the molecular gas over scales of 0.5 to several kpc provide
crucial information on how gas moves through galaxies, especially in mergers
and interacting systems, where it ultimately reaches the galaxy center,
accumulates, and feeds nuclear activity. Studying the processes involved in the
gas transport is an important step forward to understand galaxy evolution.
12CO, 13CO and C18O1-0 high-sensitivity ALMA observations were used to assess
properties of the large-scale molecular gas reservoir and its connection to the
circumnuclear molecular ring in NGC1614. The role of excitation and abundances
were studied in this context. Spatial distributions of the 12CO and 13CO
emission show significant differences. 12CO traces the large-scale molecular
gas reservoir, associated with a dust lane that harbors infalling gas. 13CO
emission is - for the first time - detected in the large-scale dust lane. Its
emission peaks between dust lane and circumnuclear molecular ring. A
12CO-to-13CO1-0 intensity ratio map shows high values in the ring region (~30)
typical for the centers of luminous galaxy mergers and even more extreme values
in the dust lane (>45). This drop in ratio is consistent with molecular gas in
the dust lane being in a diffuse, unbound state while being funneled towards
the nucleus. We find a high 16O-to-18O abundance ratio in the starburst region
(>900), typical of quiescent disk gas - by now, the starburst is expected to
have enriched the nuclear ISM in 18O relative to 16O. The massive inflow of gas
may be partially responsible for the low 18O/16O abundance since it will dilute
the starburst enrichment with unprocessed gas from greater radii. The
12CO-to-13CO abundance is consistent with this scenario. It suggests that the
nucleus of NGC1614 is in a transient phase of evolution where starburst and
nuclear growth are fuelled by returning gas from the minor merger event.Comment: 10 pages, 9 figures, accepted for publication in A&
Seeking large-scale magnetic fields in a pure-disk dwarf galaxy NGC 2976
It is still unknown how magnetic field-generation mechanisms could operate in
low-mass dwarf galaxies. Here, we present a detailed study of a nearby
pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this
galaxy possesses a clearly defined disk. For the purpose of our studies, we
performed deep multi-frequency polarimetric observations of NGC 2976 with the
VLA and Effelsberg radio telescopes. Additionally, we supplement them with
re-imaged data from the WSRT-SINGS survey. The magnetic field morphology
discovered in NGC 2976 consists of a southern polarized ridge. This structure
does not seem to be due to just a pure large-scale dynamo process (possibly
cosmic-ray driven) at work in this object, as indicated by the RM data and
dynamo number calculations. Instead, the field of NGC 2976 is modified by past
gravitational interactions and possibly also by ram pressure inside the M 81
galaxy group environment. The estimates of total (7 muG) and ordered (3 muG)
magnetic field strengths, as well as degree of field order (0.46), which is
similar to those observed in spirals, suggest that tidally generated magnetized
gas flows can further enhance dynamo action in the object. NGC 2976 is
apparently a good candidate for the efficient magnetization of its
neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic
field into the intergalactic space up to a distance of about 5 kpc. Tidal
interactions (and possibly also ram pressure) can lead to the formation of
unusual magnetic field morphologies (like polarized ridges) in galaxies out of
the star-forming disks, which do not follow any observed component of the
interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to
provide ordered magnetic fields far out of their main disks.Comment: 16 page
Conscious sedation: is this provision equitable? Analysis of sedation services provided within primary dental care in England, 2012-2014.
Aim: Patients receiving primary dental care may occasionally require conscious sedation as an adjunct to care. It is one of a range of options to support anxious patients or those undergoing difficult procedures. The aim of this study was to examine patterns of conscious sedation within primary dental care in relation to patient demography, deprivation status, geography (local authority, region) and type of care (Band) within England to examine equity in distribution of service provision. Materials and Methods: Descriptive analysis of cross-sectional primary dental care data, obtained from national claims held by the National Health Service (NHS) Business Services Authority, on patients who had received one or more courses of care involving sedation. Results: Just under 137,000 episodes of care involving sedation are provided for over 120,000 patients per year, the majority of which are for adults. Four out of ten (41%) patients were children, with 6-12-year-olds forming the largest group; 6% were aged under six years. Eleven per cent of patients had more than one course of care involving sedation, with adults aged 25-34 years having the highest rate: 1.17 (s.d.: 0.887) in 2012/2013 and 1.16 (s.d.: 0.724) in 2013/2014. There was a clear social gradient, whereby the most deprived quintile had the highest volume of patients that had received sedation at least once in primary dental care in both years (31.5%). Whilst there was a clear social gradient amongst children and young adults who received sedation, the gradient flattened among middle-aged and was flat amongst older adults. The majority of courses of care involving sedation were associated with Band 2 claims for care (88.6% in 2012/2013; 88.8 in 2013/2014). Whilst one or more patients in all higher tier local authorities received care involving sedation, there were marked geographic inequalities. Discussion: Patients receive sedation in support of NHS primary dental care across the life course and social spectrum. Whilst the pattern of uptake of care parallels the social gradient in younger age groups overall, there are clear geographical inequalities in provision. As sedation is only one of a series of adjuncts to care which may be provided across different sectors of the health system, a wider systems analysis should be undertaken as the findings raise important issues about equitable access to appropriate care. Furthermore, there should be a greater emphasis on prevention to reduce the need for care. The implications for child oral health, access and quality are discussed
Luminous, pc-scale CO 6-5 emission in the obscured nucleus of NGC1377
High resolution submm observations are important in probing the morphology,
column density and dynamics of obscured active galactic nuclei (AGNs). With
high resolution (0.06 x 0.05) ALMA 690 GHz observations we have found bright
(TB >80 K) and compact (FWHM 10x7 pc) CO 6-5 line emission in the nucleus of
the extremely radio-quiet galaxy NGC1377. The integrated CO 6-5 intensity is
aligned with the previously discovered jet/outflow of NGC1377 and is tracing
the dense (n>1e4 cm-3), hot gas at the base of the outflow. The velocity
structure is complex and shifts across the jet/outflow are discussed in terms
of jet-rotation or separate, overlapping kinematical components. High velocity
gas (deltaV +-145 km/s) is detected inside r<2-3 pc and we suggest that it is
emerging from an inclined rotating disk or torus of position angle PA=140+-20
deg with a dynamical mass of approx 3e6 Msun. This mass is consistent with that
of a supermassive black hole (SMBH), as inferred from the M-sigma relation. The
gas mass of the proposed disk/torus constitutes <3% of the nuclear dynamical
mass. In contrast to the intense CO 6-5 line emission, we do not detect dust
continuum with an upper limit of S(690GHz)<2mJy. The corresponding, 5 pc, H2
column density is estimated to N(H2)<3e23 cm-2, which is inconsistent with a
Compton Thick (CT) source. We discuss the possibility that CT obscuration may
be occuring on small (subparsec) or larger scales. From SED fitting we suggest
that half of the IR emission of NGC1377 is nuclear and the rest (mostly the
far-infrared (FIR)) is more extended. The extreme radio quietness, and the lack
of emission from other star formation tracers, raise questions on the origin of
the FIR emission. We discuss the possibility that it is arising from the
dissipation of shocks in the molecular jet/outflow or from irradiation by the
nuclear source along the poles.Comment: 7 pages, 5 figures, submitted to Astronomy and Astrophysic
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