411 research outputs found
Host Galaxy Evolution in Radio-Loud AGN
We investigate the luminosity evolution of the host galaxies of radio-loud
AGN through Hubble Space Telescope imaging of 72 BL Lac objects, including new
STIS imaging of nine z > 0.6 BL Lacs. With their intrinsically low accretion
rates and their strongly beamed jets, BL Lacs provide a unique opportunity to
probe host galaxy evolution independent of the biases and ambiguities implicit
in quasar studies. We find that the host galaxies of BL Lacs evolve strongly,
consistent with passive evolution from a period of active star formation in the
range 0.5 <~ z <~ 2.5, and inconsistent with either passive evolution from a
high formation redshift or a non-evolving population. This evolution is broadly
consistent with that observed in the hosts of other radio-loud AGN, and
inconsistent with the flatter luminosity evolution of quiescent early types and
radio-quiet hosts. This indicates that active star formation, and hence galaxy
interactions, are associated with the formation for radio-loud AGN, and that
these host galaxies preferentially accrete less material after their formation
epoch than galaxies without powerful radio jets. We discuss possible
explanations for the link between merger history and the incidence of a radio
jet.Comment: 37 pages, 8 figures, accepted for publication in ApJ, for full PDF
incl. figures see
http://www.ph.unimelb.edu.au/~modowd/papers/odowdurry2005.pd
SSGSS: The Spitzer-SDSS-GALEX Spectroscopic Survey
The Spitzer-SDSS-GALEX Spectroscopic Survey (SSGSS) provides a new sample of
101 star-forming galaxies at z < 0.2 with unprecedented multi-wavelength
coverage. New mid- to far-infrared spectroscopy from the Spitzer Space
Telescope is added to a rich suite of previous imaging and spectroscopy,
including ROSAT, Galaxy Evolution Explorer, Sloan Digital Sky Survey, Two
Micron All Sky Survey, and Spitzer/SWIRE. Sample selection ensures an even
coverage of the full range of normal galaxy properties, spanning two orders of
magnitude in stellar mass, color, and dust attenuation. In this paper we
present the SSGSS data set, describe the science drivers, and detail the sample
selection, observations, data reduction, and quality assessment. Also in this
paper, we compare the shape of the thermal continuum and the degree of silicate
absorption of these typical, star-forming galaxies to those of starburst
galaxies. We investigate the link between star formation rate, infrared
luminosity, and total polycyclic aromatic hydrocarbon luminosity, with a view
to calibrating the latter for spectral energy distribution models in
photometric samples and at high redshift. Last, we take advantage of the 5-40
micron spectroscopic and far-infrared photometric coverage of this sample to
perform detailed fitting of the Draine et al. dust models, and investigate the
link between dust mass and star formation history and active galactic nucleus
properties.Comment: 60 pages, 20 figure
Mid-Infrared Spectral Measures of Star-Formation and AGN Activity in Normal Galaxies
We investigate the use of MIR PAH bands, continuum and emission lines as
probes of star-formation and AGN activity in a sample of 100 'normal' and local
(z~0.1) emission-line galaxies. The MIR spectra were obtained with the Spitzer
Space Telescope Infrared Spectrograph (IRS) as part of the Spitzer-SDSS-GALEX
Spectroscopic Survey (SSGSS) which includes multi-wavelength photometry from
the UV to the FIR and optical spectroscopy. The continuum and features were
extracted using PAHFIT (Smith et al. 2007), a decomposition code which we find
to yield PAH equivalent widths up to ~30 times larger than the commonly used
spline methods. Despite the lack of extreme objects in our sample (such as
strong AGNs, low metallicity galaxies or ULIRGs), we find significant
variations in PAH, continuum and emission line properties and systematic trends
between these MIR properties and optically derived physical properties such as
age, metallicity and radiation field hardness. We revisit the diagnostic
diagram relating PAH equivalent widths and [Ne II]12.8micrometers/[O
IV]25.9micrometers line ratios and find it to be in much better agreement with
the standard optical star-formation/AGN classification than when spline
decompositions are used, while also potentially revealing obscured AGNs. The
luminosity of individual PAH components, of the continuum, and with poorer
statistics, of the neon emission lines and molecular hydrogen lines, are found
to be tightly correlated to the total IR luminosity, making individual MIR
components good gauges of the total dust emission in SF galaxies. Like the
total IR luminosity, these individual components can be used to estimate dust
attenuation in the UV and in Halpha lines based on energy balance arguments. We
also propose average scaling relations between these components and dust
corrected, Halpha derived star-formation rates.Comment: Accepted for publication in Ap
A powerful intervention: general practitioners' use of sickness certification in depression
<b>Background</b> Depression is frequently cited as the reason for sickness absence, and it is estimated that sickness certificates are issued in one third of consultations for depression. Previous research has considered GP views of sickness certification but not specifically in relation to depression. This study aimed to explore GPs views of sickness certification in relation to depression.<p></p>
<b>Methods</b> A purposive sample of GP practices across Scotland was selected to reflect variations in levels of incapacity claimants and antidepressant prescribing. Qualitative interviews were carried out between 2008 and 2009.<p></p>
<b>Results</b> A total of 30 GPs were interviewed. A number of common themes emerged including the perceived importance of GP advocacy on behalf of their patients, the tensions between stakeholders involved in the sickness certification system, the need to respond flexibly to patients who present with depression and the therapeutic nature of time away from work as well as the benefits of work. GPs reported that most patients with depression returned to work after a short period of absence and that it was often difficult to predict which patients would struggle to return to work.<p></p>
<b>Conclusions</b>
GPs reported that dealing with sickness certification and depression presents distinct challenges. Sickness certificates are often viewed as powerful interventions, the effectiveness of time away from work for those with depression should be subject to robust enquiry
The HST Survey of BL Lacertae Objects. II. Host Galaxies
We have used the HST WFPC2 camera to survey 132 BL Lac objects comprising
seven complete radio-, X-ray-, and optically-selected samples. We obtained
useful images for 110 targets spanning the redshift range 0 < z < 1.3. In two
thirds of the BL Lac images, host galaxies are detected, including nearly all
for z < 0.5 (58 of 63). The highest redshift host galaxy detected is in a BL
Lac object at z=0.664. In 58 of the 72 resolved host galaxies, a de Vaucouleurs
profile is significantly preferred, at >99% confidence, over a pure exponential
disk; the two fits are comparable in the remaining 14 cases. These results
limit the number of disk systems to at most 8% of BL Lacs (at 99% confidence),
and are consistent with all BL~Lac host galaxies being ellipticals. The
detected host galaxies are luminous ellipticals with a median absolute
K-corrected magnitude of M_R= -23.7 +- 0.6 mag, at least one magnitude brighter
than M* and comparable to brightest cluster galaxies. The galaxy morphologies
are generally smooth and undisturbed, with small or negligible ellipticities
(<0.2). There is no correlation between host galaxy and observed nuclear
magnitude or estimated jet power corrected for beaming. If black hole mass is
correlated linearly with bulge mass in general, this implies a large range in
Eddington ratio. Present data strongly support the unification picture with FR
I galaxies constituting the bulk of the parent population of BL Lac objects.Comment: Accepted for publication on ApJ. 38 pages, 8 figure
Turing learning: : A metric-free approach to inferring behavior and its application to swarms
We propose Turing Learning, a novel system identification method for
inferring the behavior of natural or artificial systems. Turing Learning
simultaneously optimizes two populations of computer programs, one representing
models of the behavior of the system under investigation, and the other
representing classifiers. By observing the behavior of the system as well as
the behaviors produced by the models, two sets of data samples are obtained.
The classifiers are rewarded for discriminating between these two sets, that
is, for correctly categorizing data samples as either genuine or counterfeit.
Conversely, the models are rewarded for 'tricking' the classifiers into
categorizing their data samples as genuine. Unlike other methods for system
identification, Turing Learning does not require predefined metrics to quantify
the difference between the system and its models. We present two case studies
with swarms of simulated robots and prove that the underlying behaviors cannot
be inferred by a metric-based system identification method. By contrast, Turing
Learning infers the behaviors with high accuracy. It also produces a useful
by-product - the classifiers - that can be used to detect abnormal behavior in
the swarm. Moreover, we show that Turing Learning also successfully infers the
behavior of physical robot swarms. The results show that collective behaviors
can be directly inferred from motion trajectories of individuals in the swarm,
which may have significant implications for the study of animal collectives.
Furthermore, Turing Learning could prove useful whenever a behavior is not
easily characterizable using metrics, making it suitable for a wide range of
applications.Comment: camera-ready versio
Intercultural communication in the context of Saudi Arab tertiary education
© Springer Science+Business Media Singapore 2015. This chapter is a case study of intercultural communication in a tertiary educational setting in Saudi Arabia. Given the fact that educational institutions adopt Western models of education and employ foreign professors, this study aims at shedding light on the patterns of communication in the classroom. The elements of Hofstede\u27s five dimensional model, namely, uncertainty avoidance, individualism/collectivism, and power distance dimensions were applied for the purpose of analysis. The study involved in-depth interviews with 17 female students of a private university in the Eastern Province. While assessing the perception of the students about the communication patterns, it provides recommendations on improving the educational experience of local students taught by Western professors. Ultimately, the findings will contribute in promoting a culturally responsible education characterized by critical thinking skills, individual creativity, and movement out of comfort zones, which will prepare students for the globalized job market\u27s challenges
The HST Survey of BL~Lacertae Objects. IV. Infrared Imaging of Host Galaxies
The HST NICMOS Camera 2 was used for H-band imaging of 12 BL Lacertae objects
taken from the larger sample observed with the WFPC2 in the R band (Urry et al.
2000; Scarpa et al. 2000). Ten of the 12 BL Lacs are clearly resolved, and the
detected host galaxies are large, bright ellipticals with average H-band
absolute magnitude M=-26.2+-0.45 mag and effective radius 10+-5 kpc. The
rest-frame integrated color of the host galaxies is on average R-H=2.3+-0.3,
consistent with the value for both radio galaxies and normal, non-active
elliptical galaxies, and indicating the dominant stellar population is old. The
host galaxies tend to be bluer in their outer regions than in their cores, with
average color gradient Delta(R-H)/Delta(log r)=-0.2 mag, again consistent with
results for normal non-active elliptical galaxies. The infrared Kormendy
relation, derived for the first time for BL Lac host galaxies, is m(e) =
3.8*log(R)+14.8 (where m(e) is the surface brightness at the effective radius
R), fully in agreement with the relation for normal ellipticals. The close
similarity between BL Lac host galaxies and normal ellipticals suggests the
active nucleus has surprisingly little effect on the host galaxy. This supports
a picture in which all elliptical galaxies harbor black holes which can be
actively accreting for some fraction of their lifetime.Comment: Accepted for publication on ApJ. 25 pages, 7 figure
On the selection of AGN neutrino source candidates for a source stacking analysis with neutrino telescopes
The sensitivity of a search for sources of TeV neutrinos can be improved by
grouping potential sources together into generic classes in a procedure that is
known as source stacking. In this paper, we define catalogs of Active Galactic
Nuclei (AGN) and use them to perform a source stacking analysis. The grouping
of AGN into classes is done in two steps: first, AGN classes are defined, then,
sources to be stacked are selected assuming that a potential neutrino flux is
linearly correlated with the photon luminosity in a certain energy band (radio,
IR, optical, keV, GeV, TeV). Lacking any secure detailed knowledge on neutrino
production in AGN, this correlation is motivated by hadronic AGN models, as
briefly reviewed in this paper.
The source stacking search for neutrinos from generic AGN classes is
illustrated using the data collected by the AMANDA-II high energy neutrino
detector during the year 2000. No significant excess for any of the suggested
groups was found.Comment: 43 pages, 12 figures, accepted by Astroparticle Physic
Response to the editorial by Dr Geraghty
This article is written in response to the linked editorial by Dr Geraghty about the adaptive Pacing, graded Activity and Cognitive behaviour therapy; a randomised Evaluation (PACE) trial, which we led, implemented and published. The PACE trial compared four treatments for people diagnosed with chronic fatigue syndrome. All participants in the trial received specialist medical care. The trial found that adding cognitive behaviour therapy or graded exercise therapy to specialist medical care was as safe as, and more effective than, adding adaptive pacing therapy or specialist medical care alone. Dr Geraghty has challenged these findings. In this article, we suggest that Dr Geraghty’s views are based on misunderstandings and misrepresentations of the PACE trial; these are corrected
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