930 research outputs found
What Powers the Compact Radio Emission in Nearby Elliptical and S0 Galaxies?
Many nearby early-type (elliptical and S0) galaxies contain weak
(milli-Jansky level) nuclear radio sources on scales a few hundred parsecs or
less. The origin of the radio emission, however, has remained unclear,
especially in volume-limited samples that select intrinsically less luminous
galaxies. Both active galactic nuclei and nuclear star formation have been
suggested as possible mechanisms for producing the radio emission. This paper
utilizes optical spectroscopic information to address this issue. A substantial
fraction of the early-type galaxies surveyed with the Very Large Array by
Wrobel & Heeschen (1991) exhibits detectable optical emission lines in their
nuclei down to very sensitive limits. Comparison of the observed radio
continuum power with that expected from the thermal gas traced by the optical
emission lines implies that the bulk of the radio emission is nonthermal. Both
the incidence and the strength of optical line emission correlate with the
radio power. At a fixed line luminosity, ellipticals have stronger radio cores
than S0s. The relation between radio power and line emission observed in this
sample is consistent with the low-luminosity extension of similar relations
seen in classical radio galaxies and luminous Seyfert nuclei. A plausible
interpretation of this result is that the weak nuclear sources in nearby
early-type galaxies are the low-luminosity counterparts of more powerful AGNs.
The spectroscopic evidence supports this picture. Most of the emission-line
objects are optically classified as Seyfert nuclei or low-ionization nuclear
emission-line regions (LINERs), the majority of which are likely to be
accretion-powered sources.Comment: LaTex, 16 pages including embedded figures. Accepted for publication
in the Astrophysical Journa
Radio Observations of the Hubble Deep Field South Region III: The 2.5, 5.2 and 8.7 GHz Catalogues and Radio Source Properties
Deep radio observations of a wide region centred on the Hubble Deep Field
South have been performed, providing one of the most sensitive set of radio
observations acquired on the Australia Telescope Compact Array to date. A
central rms of ~10 microJy is reached at four frequencies (1.4, 2.5, 5.2 and
8.7 GHz). In this paper the full source catalogues from the 2.5, 5.2 and 8.7
GHz observations are presented to complement Paper II, along with a detailed
analysis of image quality and noise. We produce a consolidated catalogue by
matching sources across all four frequencies of our survey. Radio spectral
indices are used to investigate the nature of the radio sources and identify a
number of sources with flat or inverted radio spectra, which indicates AGN
activity. We also find several other interesting sources, including a broadline
emitting radio galaxy, a giant radio galaxy and three Gigahertz Peaked Spectrum
sources.Comment: Accepted by AJ. 13 figures and 13 table
On the Origins of Memes by Means of Fringe Web Communities
Internet memes are increasingly used to sway and manipulate public opinion.
This prompts the need to study their propagation, evolution, and influence
across the Web. In this paper, we detect and measure the propagation of memes
across multiple Web communities, using a processing pipeline based on
perceptual hashing and clustering techniques, and a dataset of 160M images from
2.6B posts gathered from Twitter, Reddit, 4chan's Politically Incorrect board
(/pol/), and Gab, over the course of 13 months. We group the images posted on
fringe Web communities (/pol/, Gab, and The_Donald subreddit) into clusters,
annotate them using meme metadata obtained from Know Your Meme, and also map
images from mainstream communities (Twitter and Reddit) to the clusters.
Our analysis provides an assessment of the popularity and diversity of memes
in the context of each community, showing, e.g., that racist memes are
extremely common in fringe Web communities. We also find a substantial number
of politics-related memes on both mainstream and fringe Web communities,
supporting media reports that memes might be used to enhance or harm
politicians. Finally, we use Hawkes processes to model the interplay between
Web communities and quantify their reciprocal influence, finding that /pol/
substantially influences the meme ecosystem with the number of memes it
produces, while \td has a higher success rate in pushing them to other
communities.Comment: A shorter version of this paper appears in the Proceedings of 18th
ACM Internet Measurement Conference (IMC 2018). This is the full versio
“It’s like my life but more, and better!” - Playing with the Cathaby Shark Girls: MMORPGs, young people and fantasy-based social play
This article is available open access through the publisher’s website at the link below. Copyright @ 2011 A B Academic Publishers.Digital technology has opened up a range of new on-line leisure spaces for young people. Despite their popularity, on-line games and Massive Multiplayer Online Role Playing Games in particular are still a comparatively under-researched area in the fields of both Education and more broadly Youth Studies. Drawing on a Five year ethnographic study, this paper considers the ways that young people use the virtual spaces offered by MMORPGs. This paper suggests that MMORPGs represent significant arenas within which young people act out a range of social narratives through gaming. It argues that MMORPG have become important fantasy spaces which offer young people possibilities to engage in what were formally material practices. Although this form of play is grounded in the everyday it also extends material practices and offers new and unique forms of symbolic experimentation, thus I argue that game-play narratives cannot be divorced from the everyday lives of their participants
VLA Observations of a New Population of Blazars
We present the first deep VLA radio images of flat-spectrum radio quasars
(FSRQ) with multiwavelength emission properties similar to those of BL Lacs
with synchrotron X-rays. Our observations of twenty-five of these sources show
that their radio morphologies are similar to those of other radio quasars.
However, their range of extended powers is more similar to that of BL Lacertae
objects (BL Lacs) and extends down to the low values typical of FR I radio
galaxies. Five out of our nine lobe-dominated sources have extended radio
powers in the range typical of both FR I and FR II radio galaxies, but their
extended radio structure is clearly FR II-like. Therefore, we have not yet
found a large population of radio quasars hosted by FR Is. Two thirds of our
sources have a core-dominated radio morpholgy and thus X-rays likely dominated
by the jet. We find that their ratios of radio core to total X-ray luminosity
are low and in the regime indicative of synchrotron X-rays. This result shows
that also blazars with strong emission lines can produce jets of high-energy
synchrotron emission and undermines at least in part the ``blazar sequence''
scenario which advocates that particle Compton cooling by an external radiation
field governs the frequency of the synchrotron emission peak.Comment: 26 pages, 33 figures. Accepted for publication in Ap
Chandra Observations of 3C Radio Sources with z<0.3: Nuclei, Diffuse Emission, Jets and Hotspots
We report on our Chandra Cycle 9 program to observe half of the 60
(unobserved by Chandra) 3C radio sources at z<0.3 for 8 ksec each. Here we give
the basic data: the X-ray intensity of the nuclei and any features associated
with radio structures such as hot spots and knots in jets. We have measured
fluxes in soft, medium and hard bands and are thus able to isolate sources with
significant intrinsic column density. For the stronger nuclei, we have applied
the standard spectral analysis which provides the best fit values of X-ray
spectral index and column density. We find evidence for intrinsic absorption
exceeding a column density of 10^{22} cm^{-2} for one third of our sources.Comment: 12 pages, 37 figures (the complete version of the paper with all
figures is available on line, see appendix for details), ApJ accepte
Gas Accretion and Giant Lyman-alpha Nebulae
Several decades of observations and discoveries have shown that high-redshift
AGN and massive galaxies are often surrounded by giant Lyman-alpha nebulae
extending in some cases up to 500 kpc in size. In this review, I discuss the
properties of the such nebulae discovered at z>2 and their connection with gas
flows in and around the galaxies and their halos. In particular, I show how
current observations are used to constrain the physical properties and origin
of the emitting gas in terms of the Lyman-alpha photon production processes and
kinematical signatures. These studies suggest that recombination radiation is
the most viable scenario to explain the observed Lyman-alpha luminosities and
Surface Brightness for the large majority of the nebulae and imply that a
significant amount of dense, ionized and cold clumps should be present within
and around the halos of massive galaxies. Spectroscopic studies suggest that,
among the giant Lyman-alpha nebulae, the one associated with radio-loud AGN
should have kinematics dominated by strong, ionized outflows within at least
the inner 30-50 kpc. Radio-quiet nebulae instead present more quiescent
kinematics compatible with stationary situation and, in some cases, suggestive
of rotating structures. However, definitive evidences for accretion onto
galaxies of the gas associated with the giant Lyman-alpha emission are not
unambiguously detected yet. Deep surveys currently ongoing using other bright,
non-resonant lines such as Hydrogen H-alpha and HeII1640 will be crucial to
search for clearer signatures of cosmological gas accretion onto galaxies and
AGN.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dave', to be published by
Springe
Youth transitions as ‘wiki-transitions’ in youth policies platforms
The version of a journal article that has been accepted for publication in a journal.
This is an Accepted Manuscript of an article published by Taylor & Francis in European Societies on 22/11/2019 available online: http://www.tandfonline.com/10.1080/14616696.2019.1690158.In recent years, a number of youth-focused online platforms have emerged which, in different ways, seek to support young people across Europe in building pathways to independent adulthood. In this article, we draw on data from Edgeryders, a recent youth policy research project, to reflect on the extent to which online discussion platforms are useful instruments for understanding the challenges youth face in their transitions to independent adulthood across Europe. Noting the collaborative emphasis articulated by both the project designers and participants, we ask how we might make sense of the data – and the meanings conveyed by that data – produced by online projects. We propose the notion of ‘wiki-transitions’ as a means of theorising young people’s use of online space to support their transitions to adulthood
The transformation of transport policy in Great Britain? 'New Realism' and New Labour's decade of displacement activity
In a 1999 paper, Goodwin announced ‘the transformation of transport policy in Great Britain’. His central point was that consensus was emerging among policy makers and academics based on earlier work including Transport: The New Realism, which rejected previous orthodoxy that the supply of road space could and should be continually expanded to match demand. Instead a combination of investment in public transport, walking and cycling opportunities and – crucially – demand management should form the basis of transport policy to address rising vehicle use and associated increases in congestion and pollution / carbon emissions. This thinking formed the basis of the 1997 Labour government’s ‘sustainable transport’ policy, but after 13 years in power ministers neither transformed policy nor tackled longstanding transport trends. Our main aim in this paper is to revisit the concept of New Realism and re-examine its potential utility as an agent of change in British transport policy. Notwithstanding the outcome of Labour’s approach to transport policy, we find that the central tenets of the New Realism remain robust and that the main barriers to change are related to broader political and governance issues which suppress radical policy innovation
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