3,455 research outputs found
A Geometrically Supported Candidate Multiply-Imaged by the Hubble Frontier Fields Cluster Abell 2744
The deflection angles of lensed sources increase with their distance behind a
given lens. We utilize this geometric effect to corroborate the
photometric redshift estimate of a faint near-IR dropout,
triply-imaged by the massive galaxy cluster Abell 2744 in deep Hubble Frontier
Fields images. The multiple images of this source follow the same symmetry as
other nearby sets of multiple images which bracket the critical curves and have
well defined redshifts (up to ), but with larger deflection
angles, indicating that this source must lie at a higher redshift. Similarly,
our different parametric and non-parametric lens models all require this object
be at , with at least 95\% confidence, thoroughly excluding the
possibility of lower-redshift interlopers. To study the properties of this
source we correct the two brighter images for their magnifications, leading to
a SFR of /yr, a stellar mass of , and an age of Myr (95\% confidence). The intrinsic
apparent magnitude is 29.9 AB (F160W), and the rest-frame UV ()
absolute magnitude is . This corresponds to (, adopting ), making
this candidate one of the least luminous galaxies discovered at .Comment: 7 pages, 4 figures, 1 table; V2: very minor changes, ApJ Letters
Accepte
A new physical interpretation of optical and infrared variability in quasars
Changing-look quasars are a recently identified class of active galaxies in
which the strong UV continuum and/or broad optical hydrogen emission lines
associated with unobscured quasars either appear or disappear on timescales of
months to years. The physical processes responsible for this behaviour are
still debated, but changes in the black hole accretion rate or accretion disk
structure appear more likely than changes in obscuration. Here we report on
four epochs of spectroscopy of SDSS J110057.70-005304.5, a quasar at a redshift
of whose UV continuum and broad hydrogen emission lines have faded,
and then returned over the past 20 years. The change in this quasar
was initially identified in the infrared, and an archival spectrum from 2010
shows an intermediate phase of the transition during which the flux below
rest-frame 3400\AA\ has decreased by close to an order of magnitude.
This combination is unique compared to previously published examples of
changing-look quasars, and is best explained by dramatic changes in the
innermost regions of the accretion disk. The optical continuum has been rising
since mid-2016, leading to a prediction of a rise in hydrogen emission line
flux in the next year. Increases in the infrared flux are beginning to follow,
delayed by a 3 year observed timescale. If our model is confirmed, the
physics of changing-look quasars are governed by processes at the innermost
stable circular orbit (ISCO) around the black hole, and the structure of the
innermost disk. The easily identifiable and monitored changing-look quasars
would then provide a new probe and laboratory of the nuclear central engine.Comment: 13 pages, 4 figures, 3 tables. Published in MNRAS. All code and data
links on GitHub, https://github.com/d80b2t/WISE_L
Using a resource effect study pre-pilot to inform a large randomized trial: the Decide2Quit.Org Web-assisted tobacco intervention
Resource effect studies can be useful in highlighting areas of improvement in informatics tools. Before a large randomized trial, we tested the functions of the Decide2Quit.org Web-assisted tobacco intervention using smokers (N=204) recruited via Google advertisements. These smokers were given access to Decide2Quit.org for six months and we tracked their usage and assessed their six months cessation using a rigorous follow-up. Multiple, interesting findings were identified: we found the use of tailored emails to dramatically increase participation for a short period. We also found varied effects of the different functions. Functions supporting seeking social support (Your Online Community and Family Tools), Healthcare Provider Tools, and the Library had positive effects on quit outcomes. One surprising finding, which needs further investigation, was that writing to our Tobacco Treatment Specialists was negatively associated with quit outcomes
The first high-redshift changing-look quasars
We report on three redshift z > 2 quasars with dramatic changes in their C IV emission lines, the first sample of changing-look quasars (CLQs) at high redshift. This is also the first time the changing-look behaviour has been seen in a high-ionization emission line. SDSS J1205+3422, J1638+2827, and J2228 + 2201 show interesting behaviour in their observed optical light curves, and subsequent spectroscopy shows significant changes in the C IV broad emission line, with both line collapse and emergence being displayed on rest-frame time-scales of ∼240–1640 d. These are rapid changes, especially when considering virial black hole mass estimates of M_(BH) > 10⁹M⊙ for all three quasars. Continuum and emission line measurements from the three quasars show changes in the continuum-equivalent width plane with the CLQs seen to be on the edge of the full population distribution, and showing indications of an intrinsic Baldwin effect. We put these observations in context with recent state-change models, and note that even in their observed low-state, the C IV CLQs are generally above ∼5 per cent in Eddington luminosity
The first high-redshift changing-look quasars
We report on three redshift quasars with dramatic changes in their C IV
emission lines, the first sample of changing-look quasars (CLQs) at high
redshift. This is also the first time the changing-look behaviour has been seen
in a high-ionisation emission line. SDSS J1205+3422, J1638+2827, and J2228+2201
show interesting behaviour in their observed optical light curves, and
subsequent spectroscopy shows significant changes in the C IV broad emission
line, with both line collapse and emergence being displayed on rest-frame
timescales of 240-1640 days. These are rapid changes, especially when
considering virial black hole mass estimates of
for all three quasars. Continuum and emission line measurements from the three
quasars show changes in the continuum-equivalent width plane with the CLQs seen
to be on the edge of the full population distribution, and showing indications
of an intrinsic Baldwin effect. We put these observations in context with
recent state-change models, and note that even in their observed low-state, the
C IV CLQs are generally above 5\% in Eddington luminosity.Comment: 12 pages, 7 figures, 4 tables. All data, analysis code and text are
fully available at: github.com/d80b2t/CIV_CLQs. Comments, questions and
suggestions welcome and encourage
Recommended from our members
The Global academic research organization network: Data sharing to cure diseases and enable learning health systems.
Introduction:Global data sharing is essential. This is the premise of the Academic Research Organization (ARO) Council, which was initiated in Japan in 2013 and has since been expanding throughout Asia and into Europe and the United States. The volume of data is growing exponentially, providing not only challenges but also the clear opportunity to understand and treat diseases in ways not previously considered. Harnessing the knowledge within the data in a successful way can provide researchers and clinicians with new ideas for therapies while avoiding repeats of failed experiments. This knowledge transfer from research into clinical care is at the heart of a learning health system. Methods:The ARO Council wishes to form a worldwide complementary system for the benefit of all patients and investigators, catalyzing more efficient and innovative medical research processes. Thus, they have organized Global ARO Network Workshops to bring interested parties together, focusing on the aspects necessary to make such a global effort successful. One such workshop was held in Austin, Texas, in November 2017. Representatives from Japan, Taiwan, Singapore, Europe, and the United States reported on their efforts to encourage data sharing and to use research to inform care through learning health systems. Results:This experience report summarizes presentations and discussions at the Global ARO Network Workshop held in November 2017 in Austin, TX, with representatives from Japan, Korea, Singapore, Taiwan, Europe, and the United States. Themes and recommendations to progress their efforts are explored. Standardization and harmonization are at the heart of these discussions to enable data sharing. In addition, the transformation of clinical research processes through disruptive innovation, while ensuring integrity and ethics, will be key to achieving the ARO Council goal to overcome diseases such that people not only live longer but also are healthier and happier as they age. Conclusions:The achievement of global learning health systems will require further exploration, consensus-building, funding aligned with incentives for data sharing, standardization, harmonization, and actions that support global interests for the benefit of patients
Hyperarousal symptoms after traumatic and nontraumatic births
Background: Measurement is critical in postnatal posttraumatic stress disorder (PTSD) because symptoms may be influenced by normal postnatal phenomena such as physiological changes and fatigue. Objective: This study examined: (1) whether hyperarousal symptoms differ between women who have traumatic or nontraumatic births; (2) whether the construct of hyperarousal is coherent in postnatal women; and (3) whether hyperarousal symptoms are useful for identifying women who have traumatic births or PTSD. Methods: A survey of PTSD symptoms in 1,078 women recruited via the community or Internet who completed an online or paper questionnaire measuring childbirth-related PTSD symptoms between 1 and 36 months after birth. Women who had a traumatic birth as defined by DSM-IV criterion A (n = 458) were compared with women who did not have a traumatic birth (n = 591). Results: A one-factor dimension of hyperarousal was identified that included all five hyperarousal items. Diagnostic criteria of two or more hyperarousal symptoms in the previous week were reported by 75.3% of women with traumatic birth and 50.5% of women with nontraumatic births. The difference in mean hyperarousal symptoms between groups was substantial at 0.76 of a standard deviation (Hedge’s g, CI = 0.64, 0.89). A larger difference was observed between women with and without diagnostic PTSD (g = 1.64, CI 1.46, 1.81). However, receiver operating characteristic analyses showed hyperarousal symptoms have poor specificity and alternative ways of calculating symptoms did not improve this. Comparison with other PTSD symptoms found re-experiencing symptoms were most accurate at identifying women with traumatic births. Conclusions: Results suggest hyperarousal symptoms are associated with traumatic birth and are a coherent construct in postnatal women. However, they have poor specificity and should only be used as part of diagnostic criteria, not as a sole indicator
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