24 research outputs found
A Hubble Space Telescope Imaging Study of Four FeLoBAL Quasar Host Galaxies
We study the host galaxies of four Iron Low-Ionization Broad Absorption-line
Quasars (FeLoBALs) using Hubble Space Telescope imaging data, investigating the
possibility that they represent a transition between an obscured AGN and an
ordinary optical quasar. In this scenario, the FeLoBALs represent the early
stage of merger-triggered accretion, in which case their host galaxies are
expected to show signs of an ongoing or recent merger. Using PSF subtraction
techniques, we decompose the images into host galaxy and AGN components at
rest-frame ultraviolet and optical wavelengths. The ultraviolet is sensitive to
young stars, while the optical probes stellar mass. In the ultraviolet we image
at the BAL absorption trough wavelengths so as to decrease the contrast between
the quasar and host galaxy emission. We securely detect an extended source for
two of the four FeLoBALs in the rest-frame optical; a third host galaxy is
marginally detected. In the rest-frame UV we detect no host emission; this
constrains the level of unobscured star formation. Thus, the host galaxies have
observed properties that are consistent with those of non-BAL quasars with the
same nuclear luminosity, i.e., quiescent or moderately starforming elliptical
galaxies. However, we cannot exclude starbursting hosts that have the stellar
UV emission obscured by modest amounts of dust reddening. Thus, our findings
also allow the merger-induced young quasar scenario. For three objects, we
identify possible close companion galaxies that may be gravitationally
interacting with the quasar hosts.Comment: 33 pages, 15 figures. Accepted for publication in MNRA
A catalog of optical to X-ray spectral energy distributions of z~2 quasars observed with Swift. I: First results
We present the Swift optical to X-ray spectral energy distributions (SEDs) of
44 quasars at redshifts z~2 observed by Swift, part of a larger program to
establish and characterize the optical through X-ray SEDs of moderate-redshift
quasars. Here we outline our analysis approach and present preliminary analysis
and results for the first third of the full quasar sample. Not all quasars in
the sample are detected in X-rays; all of the X-ray detected objects so far are
radio loud. As expected for radio loud objects, they are X-ray bright relative
to radio-quiet quasars of comparable optical luminosities, with an average
alpha_ox = 1.39 +/- 0.03 (where alpha_ox is the power-law slope connecting the
monochromatic flux at 2500 Ang and at 2 keV), and display hard X-ray spectra.
We find integrated 3000 Ang - 25 keV accretion luminosities of between
0.7*10^(46) erg s^(-1) and 5.2*10^(47) erg s^(-1). Based on single-epoch
spectroscopic virial black hole mass estimates, we find that these quasars are
accreting at substantial Eddington fractions, 0.1 \le L/LEdd \le 1.Comment: 45 pages (of which, 18 pages main text). Accepted for publication in
MNRA
Constraints on the relative sizes of intervening Mg II-absorbing clouds and quasar emitting regions
Context: A significantly higher incidence of strong (rest equivalent width
W_r > 1 {\AA}) intervening Mg II absorption is observed along gamma-ray burst
(GRB) sight-lines relative to those of quasar sight-lines. A geometrical
explanation for this discrepancy has been suggested: the ratio of the beam size
of the source to the characteristic size of a Mg II absorption system can
influence the observed Mg II equivalent width, if these two sizes are
comparable. Aims: We investigate whether the differing beam sizes of the
continuum source and broad-line region of Sloan Digital Sky Survey (SDSS)
quasars produce a discrepancy between the incidence of strong Mg II absorbers
illuminated by the quasar continuum region and those of absorbers illuminated
by both continuum and broad-line region light. Methods: We perform a
semi-automated search for strong Mg II absorbers in the SDSS Data Release 7
quasar sample. The resulting strong Mg II absorber catalog is available online.
We measure the sight-line number density of strong Mg II absorbers superimposed
on and off the quasar C IV 1550 {\AA} and C III] 1909 {\AA} emission lines.
Results: We see no difference in the sight-line number density of strong Mg II
absorbers superimposed on quasar broad emission lines compared to those
superimposed on continuum-dominated spectral regions. This suggests that the Mg
II-absorbing clouds typically observed as intervening absorbers in quasar
spectra are larger than the beam sizes of both the continuum-emitting regions
and broad line-emitting regions in the centers of quasars, corresponding to a
lower limit of the order of 10^17} cm for the characteristic size of a Mg II
absorbing cloud.Comment: 10 pages, 5 figures. Edit: fixed a missing cross-referenc
The development and validation of a scoring tool to predict the operative duration of elective laparoscopic cholecystectomy
Background: The ability to accurately predict operative duration has the potential to optimise theatre efficiency and utilisation, thus reducing costs and increasing staff and patient satisfaction. With laparoscopic cholecystectomy being one of the most commonly performed procedures worldwide, a tool to predict operative duration could be extremely beneficial to healthcare organisations.
Methods: Data collected from the CholeS study on patients undergoing cholecystectomy in UK and Irish hospitals between 04/2014 and 05/2014 were used to study operative duration. A multivariable binary logistic regression model was produced in order to identify significant independent predictors of long (>â90 min) operations. The resulting model was converted to a risk score, which was subsequently validated on second cohort of patients using ROC curves.
Results: After exclusions, data were available for 7227 patients in the derivation (CholeS) cohort. The median operative duration was 60 min (interquartile range 45â85), with 17.7% of operations lasting longer than 90 min. Ten factors were found to be significant independent predictors of operative durations >â90 min, including ASA, age, previous surgical admissions, BMI, gallbladder wall thickness and CBD diameter. A risk score was then produced from these factors, and applied to a cohort of 2405 patients from a tertiary centre for external validation. This returned an area under the ROC curve of 0.708 (SEâ=â0.013, pââ90 min increasing more than eightfold from 5.1 to 41.8% in the extremes of the score.
Conclusion: The scoring tool produced in this study was found to be significantly predictive of long operative durations on validation in an external cohort. As such, the tool may have the potential to enable organisations to better organise theatre lists and deliver greater efficiencies in care
Visual Analytics of Single Cell Microscopy Data Using a Collaborative Immersive Environment
Understanding complex physiological processes demands the integration of diverse insights derived from visual and quantitative analysis of bio-image data, such as microscopy images. This process is currently constrained by disconnects between methods for interpreting data, as well as by language barriers that hamper the necessary cross-disciplinary collaborations. Using immersive analytics, we leveraged bespoke immersive visualizations to integrate bio-images and derived quantitative data, enabling deeper comprehension and seamless interaction with multi-dimensional cellular information. We designed and developed a visualization platform that combines time-lapse confocal microscopy recordings of cancer cell motility with image-derived quantitative data spanning 52 parameters. The integrated data representations enable rapid, intuitive interpretation, bridging the divide between bio-images and quantitative information. Moreover, the immersive visualization environment promotes collaborative data interrogation, supporting vital cross-disciplinary collaborations capable of deriving transformative insights from rapidly emerging bio-image big data