45,652 research outputs found
Eddington limited starbursts in the central 10pc of AGN, and the Torus in NGC1068
We present results from a survey of nearby AGN using the near infrared
adaptive optics integral field spectrograph SINFONI. These data enable us to
probe the distribution and kinematics of the gas and stars at spatial
resolutions as small as 0.085arcsec. We find strong evidence for recent but
short lived starbursts residing in very dense nuclear disks. On scales of less
than 10pc these would have reached Eddington-limited luminosities when active,
perhaps accounting for their short duration. In addition, for NGC1068 at a
resolution of 6pc, we present direct observations of molecular gas close around
the AGN which we identify with the obscuring torus.Comment: Conference proceedings to appear in "The Central Engine of Active
Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San Francisco: ASP
The existence and detection of optically dark galaxies by 21cm surveys
One explanation for the disparity between Cold Dark Matter (CDM) predictions
of galaxy numbers and observations could be that there are numerous dark
galaxies in the Universe. These galaxies may still contain baryons, but no
stars, and may be detectable in the 21cm line of atomic hydrogen. The results
of surveys for such objects, and simulations that do/do not predict their
existence, are controversial. In this paper we use an analytical model of
galaxy formation, consistent with CDM, to firstly show that dark galaxies are
certainly a prediction of the model. Secondly, we show that objects like
VIRGOHI21, a dark galaxy candidate recently discovered by us, while rare are
predicted by the model. Thirdly, we show that previous 'blind' HI surveys have
placed few constraints on the existence of dark galaxies. This is because they
have either lacked the sensitivity and/or velocity resolution or have not had
the required detailed optical follow up. We look forward to new 21cm blind
surveys (ALFALFA and AGES) using the Arecibo multi-beam instrument which should
find large numbers of dark galaxies if they exist
Are There Magnetars in High Mass X-ray Binaries? The Case of SuperGiant Fast X-Ray Transients
In this paper we survey the theory of wind accretion in high mass X-ray
binaries hosting a magnetic neutron star and a supergiant companion.
We concentrate on the different types of interaction between the inflowing
wind matter and the neutron star magnetosphere that are relevant when accretion
of matter onto the neutron star surface is largely inhibited; these include the
inhibition through the centrifugal and magnetic barriers. Expanding on earlier
work, we calculate the expected luminosity for each regime and derive the
conditions under which transition from one regime to another can take place. We
show that very large luminosity swings (~10^4 or more on time scales as short
as hours) can result from transitions across different regimes.
The activity displayed by supergiant fast X-ray transients, a recently
discovered class of high mass X-ray binaries in our galaxy, has often been
interpreted in terms of direct accretion onto a neutron star immersed in an
extremely clumpy stellar wind. We show here that the transitions across the
magnetic and/or centrifugal barriers can explain the variability properties of
these sources as a results of relatively modest variations in the stellar wind
velocity and/or density. According to this interpretation we expect that
supergiant fast X-ray transients which display very large luminosity swings and
host a slowly spinning neutron star are characterized by magnetar-like fields,
irrespective of whether the magnetic or the centrifugal barrier applies.
Supergiant fast X-ray transients might thus provide a new opportunity to
detect and study magnetars in binary systems.Comment: Accepted for publication in ApJ. 16 pages, 6 figure
The Arecibo Galaxy Environment Survey VII : A Dense Filament With Extremely Long HI Streams
We present completed observations of the NGC 7448 galaxy group and background
volume as part of the blind neutral hydrogen Arecibo Galaxy Environment Survey
(AGES). Our observations cover a region spanning 5x4 degrees, over a redshift
range of approximately -2,000 < cz < 20,000 km/s. A total of 334 objects are
detected, mostly in three overdensities at cz 7,500, cz 9,600 and
cz 11,400 km/s. The galaxy density is extremely high (15 per square
degree) and many (24%) show signs of extended HI emission, including some
features as much as 800 kpc in projected length. We describe the overall
characteristics of this environment : kinematics, typical galaxy colours and
mass to light ratios, and substructure. To aid in the cataloguing of this data
set, we present a new FITS viewer (FRELLED : Fits Realtime Explorer of Low
Latency in Every Dimension). This incorporates interactive source cataloguing
tools which increase our source extraction speed by approximately a factor of
50.Comment: 15 pages, 13 figures, accepted for publication in MNRA
A photometric analysis of Abell 1689: two-dimensional multi-structure decomposition, morphological classification, and the Fundamental Plane
We present a photometric analysis of 65 galaxies in the rich cluster Abell
1689 at , using the Hubble Space Telescope Advanced Camera for Surveys
archive images in the rest-frame -band. We perform two-dimensional
multi-component photometric decomposition of each galaxy adopting different
models of the surface-brightness distribution. We present an accurate
morphological classification for each of the sample galaxies. For 50 early-type
galaxies, we fit both a de Vaucouleurs and S\'ersic law; S0s are modelled by
also including a disc component described by an exponential law. Bars of SB0s
are described by the profile of a Ferrers ellipsoid. For the 15 spirals, we
model a S\'ersic bulge, exponential disc, and, when required, a Ferrers bar
component. We derive the Fundamental Plane by fitting 40 early-type galaxies in
the sample, using different surface-brightness distributions. We find that the
tightest plane is that derived by S\'ersic bulges. We find that bulges of
spirals lie on the same relation. The Fundamental Plane is better defined by
the bulges alone rather than the entire galaxies. Comparison with local samples
shows both an offset and rotation in the Fundamental Plane of Abell 1689.Comment: 53 pages, 71 figures, MNRAS in pres
Teaching Media Production: Understanding Unconscious Bias in Creative Idea Development
Drawing on initial findings based on observations, surveys and interviews with a range of new entrants and established television professionals, carried out during an 18 month period working with a talent development scheme, we discuss the perspectives these findings have given us on teaching practices within our own
institutions and how we are seeking to bring these insights into changing these practices. In particular we discuss the way that the presence of unconscious bias and assumed consensus within the idea development process can reinforce structural inequalities,
militating against the aims of broadcasters to produce a truly diverse range of programmes. We propose that it is equally important for media educators to be aware of the presence of unconscious bias and of ways of tackling it in relation to creative idea development within the academy. We discuss both the barriers and potential solutions for an inclusive approach to the
idea development process
Doppler lidar observations of sensible heat flux and intercomparisons with a ground-based energy balance station and WRF model output
This is an open access article - Copyright @ 2009 E. Schweizerbart'sche VerlagsbuchhandlungDuring the Convective and Orographically induced Precipitation Study (COPS), a scanning Doppler lidar was deployed at Achern, Baden-WĂŒttemberg, Germany from 13th June to 16th August 2007. Vertical velocity profiles ('rays') through the boundary layer were measured every 3 seconds with vertical profiles of horizontal wind velocity being derived from performing azimuth scans every 30 minutes. During Intense Observation Periods radiosondes were launched from the site. In this paper, a case study of convective boundary layer development on 15th July 2007 is investigated. Estimates of eddy dissipation rate are made from the vertically pointing lidar data and used as one input to the velocity-temperature co-variance equation to estimate sensible heat flux. The sensible heat flux values calculated from Doppler lidar data are compared with a surface based energy balance station and output from the Weather Research and Forecasting (WRF) model.Funding is obtained from NER
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