58 research outputs found
Galaxy interactions are the dominant trigger for local type 2 quasars
The triggering mechanism for the most luminous, quasar-like active galactic
nuclei (AGN) remains a source of debate, with some studies favouring triggering
via galaxy mergers, but others finding little evidence to support this
mechanism. Here, we present deep Isaac Newton Telescope/Wide Field Camera
imaging observations of a complete sample of 48 optically-selected type 2
quasars the QSOFEED sample (L10; ). Based on visual inspection by eight classifiers, we find clear evidence
that galaxy interactions are the dominant triggering mechanism for quasar
activity in the local universe, with 65 per cent of the type 2
quasar hosts showing morphological features consistent with galaxy mergers or
encounters, compared with only 22 per cent of a stellar-mass- and
redshift-matched comparison sample of non-AGN galaxies a 5
difference. The type 2 quasar hosts are a factor 3.0 more
likely to be morphologically disturbed than their matched non-AGN counterparts,
similar to our previous results for powerful 3CR radio AGN of comparable [OIII]
emission-line luminosity and redshift. In contrast to the idea that quasars are
triggered at the peaks of galaxy mergers as the two nuclei coalesce, and only
become visible post-coalescence, the majority of morphologically-disturbed type
2 quasar sources in our sample are observed in the pre-coalescence phase
(61 per cent). We argue that much of the apparent ambiguity that
surrounds observational results in this field is a result of differences in the
surface brightness depths of the observations, combined with the effects of
cosmological surface brightness dimming.Comment: Accepted for publication in MNRAS. 17 pages, 7 figure
Higher Education and behavior analysis in Europe::Creating a unified approach for the training of autism professionals
Training of behaviour analysts for autism services, has improved notably within a European higher education context. However, regional discrepancies associated with economic, health care, social services, and institutional policies magnify the importance of creating appropriate unified training and consumer protection. Although the European Association for Behaviour Analysis (EABA) has endorsed the Behavior Analyst Certification Board’s (BACB) designations, the absence of European and national regulations, recognition, and accreditation remain significant barriers to quality training and implementation. These challenges are particularly pertinent in light of BACB decision to limit certification to residents in the USA and Canada after 2022. Advances, challenges, and future directions are discussed within the context of higher education in the United Kingdom, the Czech Republic, Greece, Iceland, Italy, Norway, and Sweden. The post-Bologna European agenda for higher education, globalization and opportunities for the training of behaviour analysts within European higher education are outlined
HGCA2.0: An RNA-Seq Based Webtool for Gene Coexpression Analysis in Homo sapiens
Genes with similar expression patterns in a set of diverse samples may be considered coexpressed. Human Gene Coexpression Analysis 2.0 (HGCA2.0) is a webtool which studies the global coexpression landscape of human genes. The website is based on the hierarchical clustering of 55,431 Homo sapiens genes based on a large-scale coexpression analysis of 3500 GTEx bulk RNA-Seq samples of healthy individuals, which were selected as the best representative samples of each tissue type. HGCA2.0 presents subclades of coexpressed genes to a gene of interest, and performs various built-in gene term enrichment analyses on the coexpressed genes, including gene ontologies, biological pathways, protein families, and diseases, while also being unique in revealing enriched transcription factors driving coexpression. HGCA2.0 has been successful in identifying not only genes with ubiquitous expression patterns, but also tissue-specific genes. Benchmarking showed that HGCA2.0 belongs to the top performing coexpression webtools, as shown by STRING analysis. HGCA2.0 creates working hypotheses for the discovery of gene partners or common biological processes that can be experimentally validated. It offers a simple and intuitive website design and user interface, as well as an API endpoint
Do AGN triggering mechanisms vary with radio power? – II. The importance of mergers as a function of radio power and optical luminosity
Investigation of the triggering mechanisms of radio active galactic nuclei (radio AGN) is important for improving our general understanding of galaxy evolution. In the first paper in this series, detailed morphological analysis of high-excitation radio galaxies (HERGs) with intermediate radio powers suggested that the importance of triggering via galaxy mergers and interactions increases strongly with AGN radio power and weakly with optical emission-line luminosity. Here, we use an online classification interface to expand our morphological analysis to a much larger sample of 155 active galaxies (3CR radio galaxies, radio-intermediate HERGs, and Type 2 quasars) that covers a broad range in both 1.4 GHz radio power and [O III] λ5007 emission-line luminosity. All active galaxy samples are found to exhibit excesses in their rates of morphological disturbance relative to 378 stellar-mass- and redshift-matched non-active control galaxies classified randomly and blindly alongside them. These excesses are highest for the 3CR HERGs (4.7σ) and Type 2 quasar hosts (3.9σ), supporting the idea that galaxy mergers provide the dominant triggering mechanism for these subgroups. When the full active galaxy sample is considered, there is clear evidence to suggest that the enhancement in the rate of disturbance relative to the controls increases strongly with [O III] λ5007 emission-line luminosity but not with 1.4 GHz radio power. Evidence that the dominant AGN host types change from early-type galaxies at high radio powers to late-type galaxies at low radio powers is also found, suggesting that triggering by secular, disc-based processes holds more importance for lower-power radio AGN
'Glocal' disorder: causes, conduct and consequences of the 2008 Greek unrest
This article examines the unrest that emanated in Athens and rolled out across Greek cities in December 2008 as a case through which to advance understanding of how local, national and international arenas may together shape localised episodes of disorder. We begin by addressing the proximate and structural causes of the unrest, before turning to explore the multifarious character of protest actions, including novel and derivative forms of contestation deployed by protestors, and public debate about the appropriate apportioning of blame amongst the variety of actors involved. Finally, we look at the diverse outcomes of the unrest and their impact upon extant socio-political tensions. For each stage of the lifecycle of the unrest, we evaluate the relevance of international actors, practices and discourses. Our analysis of the Greek unrest of 2008 suggests, first, that the array of intersections between global, national and local dimensions of unrest are more diverse than has heretofore been recognised by pertinent scholarship; and second, that international or transnational factors may play a significant role in the emergence, conduct and consequences of disorder even in instances where national and local dynamics remain predominant
Self-Supervised Clustering on Image-Subtracted Data with Deep-Embedded Self-Organizing Map
Developing an effective automatic classifier to separate genuine sources from
artifacts is essential for transient follow-ups in wide-field optical surveys.
The identification of transient detections from the subtraction artifacts after
the image differencing process is a key step in such classifiers, known as
real-bogus classification problem. We apply a self-supervised machine learning
model, the deep-embedded self-organizing map (DESOM) to this "real-bogus"
classification problem. DESOM combines an autoencoder and a self-organizing map
to perform clustering in order to distinguish between real and bogus
detections, based on their dimensionality-reduced representations. We use 32x32
normalized detection thumbnails as the input of DESOM. We demonstrate different
model training approaches, and find that our best DESOM classifier shows a
missed detection rate of 6.6% with a false positive rate of 1.5%. DESOM offers
a more nuanced way to fine-tune the decision boundary identifying likely real
detections when used in combination with other types of classifiers, for
example built on neural networks or decision trees. We also discuss other
potential usages of DESOM and its limitations
Time-varying double-peaked emission lines following the sudden ignition of the dormant galactic nucleus AT2017bcc
We present a pan-chromatic study of AT2017bcc, a nuclear transient that was
discovered in 2017 within the skymap of a reported burst-like gravitational
wave candidate, G274296. It was initially classified as a superluminous
supernova, and then reclassified as a candidate tidal disruption event. Its
optical light curve has since shown ongoing variability with a structure
function consistent with that of an active galactic nucleus, however earlier
data shows no variability for at least 10 years prior to the outburst in 2017.
The spectrum shows complex profiles in the broad Balmer lines: a central
component with a broad blue wing, and a boxy component with time-variable blue
and red shoulders. The H emission profile is well modelled using a
circular accretion disc component, and a blue-shifted double Gaussian which may
indicate a partially obscured outflow. Weak narrow lines, together with the
previously flat light curve, suggest that this object represents a dormant
galactic nucleus which has recently been re-activated. Our time-series
modelling of the Balmer lines suggests that this is connected to a disturbance
in the disc morphology, and we speculate this could involve a sudden violent
event such as a tidal disruption event involving the central supermassive black
hole. Although we find that the redshifts of AT2017bcc () and G274296
() are inconsistent, this event adds to the growing diversity of both
nuclear transients and multi-messenger contaminants.Comment: Submitted to MNRA
Searching for electromagnetic counterparts to gravitational-wave merger events with the prototype Gravitational-wave Optical Transient Observer (GOTO-4)
We report the results of optical follow-up observations of 29 gravitational-wave (GW) triggers during the first half of the LIGO–Virgo Collaboration (LVC) O3 run with the Gravitational-wave Optical Transient Observer (GOTO) in its prototype 4-telescope configuration (GOTO-4). While no viable electromagnetic (EM) counterpart candidate was identified, we estimate our 3D (volumetric) coverage using test light curves of on- and off-axis gamma-ray bursts and kilonovae. In cases where the source region was observable immediately, GOTO-4 was able to respond to a GW alert in less than a minute. The average time of first observation was 8.79 h after receiving an alert (9.90 h after trigger). A mean of 732.3 square degrees were tiled per event, representing on average 45.3 per cent of the LVC probability map, or 70.3 per cent of the observable probability. This coverage will further improve as the facility scales up alongside the localization performance of the evolving GW detector network. Even in its 4-telescope prototype configuration, GOTO is capable of detecting AT2017gfo-like kilonovae beyond 200 Mpc in favourable observing conditions. We cannot currently place meaningful EM limits on the population of distant (D^L=1.3 Gpc) binary black hole mergers because our test models are too faint to recover at this distance. However, as GOTO is upgraded towards its full 32-telescope, 2 node (La Palma & Australia) configuration, it is expected to be sufficiently sensitive to cover the predicted O4 binary neutron star merger volume, and will be able to respond to both northern and southern triggers
Processing GOTO data with the Rubin Observatory LSST Science Pipelines I: Production of coadded frames
The past few decades have seen the burgeoning of wide field, high cadence surveys, the most formidable of which will be the Legacy Survey of Space and Time (LSST) to be conducted by the Vera C. Rubin Observatory. So new is the field of systematic time-domain survey astronomy, however, that major scientific insights will continue to be obtained using smaller, more flexible systems than the LSST. One such example is the Gravitational-wave Optical Transient Observer (GOTO), whose primary science objective is the optical follow-up of Gravitational Wave events. The amount and rate of data production by GOTO and other wide-area, high-cadence surveys presents a significant challenge to data processing pipelines which need to operate in near real-time to fully exploit the time-domain. In this study, we adapt the Rubin Observatory LSST Science Pipelines to process GOTO data, thereby exploring the feasibility of using this "off-the-shelf" pipeline to process data from other wide-area, high-cadence surveys. In this paper, we describe how we use the LSST Science Pipelines to process raw GOTO frames to ultimately produce calibrated coadded images and photometric source catalogues. After comparing the measured astrometry and photometry to those of matched sources from PanSTARRS DR1, we find that measured source positions are typically accurate to sub-pixel levels, and that measured L-band photometries are accurate to ∼50 mmag at mL∼16 and ∼200 mmag at mL∼18. These values compare favourably to those obtained using GOTO's primary, in-house pipeline, GOTOPHOTO, in spite of both pipelines having undergone further development and improvement beyond the implementations used in this study. Finally, we release a generic "obs package" that others can build-upon should they wish to use the LSST Science Pipelines to process data from other facilities
Multiwavelength observations of the extraordinary accretion event AT2021lwx
We present observations from X-ray to mid-infrared wavelengths of the most
energetic non-quasar transient ever observed, AT2021lwx. Our data show a single
optical brightening by a factor to a luminosity of erg
s, and a total radiated energy of erg, both greater
than any known optical transient. The decline is smooth and exponential and the
ultra-violet - optical spectral energy distribution resembles a black body with
temperature K. Tentative X-ray detections indicate a secondary
mode of emission, while a delayed mid-infrared flare points to the presence of
dust surrounding the transient. The spectra are similar to recently discovered
optical flares in known active galactic nuclei but lack some characteristic
features. The lack of emission for the previous seven years is inconsistent
with the short-term, stochastic variability observed in quasars, while the
extreme luminosity and long timescale of the transient disfavour the disruption
of a single solar-mass star. The luminosity could be generated by the
disruption of a much more massive star, but the likelihood of such an event
occurring is small. A plausible scenario is the accretion of a giant molecular
cloud by a dormant black hole of solar masses. AT2021lwx thus
represents an extreme extension of the known scenarios of black hole accretion.Comment: 11 pages, 5 figures, Accepted for publication in MNRA
- …