14,952 research outputs found
Four hot DOGs eaten up with the EVN
Hot dust-obscured galaxies (hot DOGs) are a rare class of hyperluminous
infrared galaxies recently identified with the Wide-field Infrared Survey
Explorer (WISE) satellite. The majority of the ~1000-member all-sky population
should be at high redshifts (z~2-3), at the peak of star formation in the
history of the Universe. This class most likely represents a short phase during
galaxy merging and evolution, a transition from starburst- to AGN-dominated
phases. For the first time, we observed four hot DOGs with known mJy-level
radio emission using the European VLBI Network (EVN) at 1.7 GHz, in a hope to
find compact radio features characteristic to AGN activity. All four target
sources are detected at ~15-30 mas angular resolution, confirming the presence
of an active nucleus. The sources are spatially resolved, i.e. the flux density
of the VLBI-detected components is smaller than the total flux density,
suggesting that a fraction of the radio emission originates from larger-scale
(partly starburst-related) activity. Here we show the preliminary results of
our e-EVN observations made in 2014 February, and discuss WISE J1814+3412, an
object with kpc-scale symmetric radio structure, in more detail.Comment: 6 pages, 1 figure; appears in the proceedings of the 12th European
VLBI Network Symposium and Users Meeting (7-10 October 2014, Cagliari,
Italy), eds. A. Tarchi, M. Giroletti & L. Feretti. JREF Proceedings of
Science, PoS(EVN 2014)003,
http://pos.sissa.it/archive/conferences/230/003/EVN%202014_003.pd
Four hot DOGs in the microwave
Hot dust-obscured galaxies (hot DOGs) are a rare class of hyperluminous
infrared galaxies identified with the Wide-field Infrared Survey Explorer
(WISE) satellite. The majority of them is at high redshifts (z~2-3), at the
peak epoch of star formation in the Universe. Infrared, optical, radio, and
X-ray data suggest that hot DOGs contain heavily obscured, extremely luminous
active galactic nuclei (AGN). This class may represent a short phase in the
life of the galaxies, signifying the transition from starburst- to
AGN-dominated phases. Hot DOGs are typically radio-quiet, but some of them show
mJy-level emission in the radio (microwave) band. We observed four hot DOGs
using the technique of very long baseline interferometry (VLBI). The 1.7-GHz
observations with the European VLBI Network (EVN) revealed weak radio features
in all sources. The radio is free from dust obscuration and, at such high
redshifts, VLBI is sensitive only to compact structures that are characteristic
of AGN activity. In two cases (WISE J0757+5113, WISE J1603+2745), the flux
density of the VLBI-detected components is much smaller than the total flux
density, suggesting that ~70-90 per cent of the radio emission, while still
dominated by AGN, originates from angular scales larger than probed by the EVN.
The source WISE J1146+4129 appears a candidate compact symmetric object, and
WISE J1814+3412 shows a 5.1-kpc double structure, reminiscent of hot spots in a
medium-sized symmetric object. Our observations support that AGN residing in
hot DOGs may be genuine young radio sources where starburst and AGN activities
coexist.Comment: 8 pages, 4 tables, 1 figure; accepted for publication in the Monthly
Notices of the Royal Astronomical Societ
Two in one? A possible dual radio-emitting nucleus in the quasar SDSS J1425+3231
The radio-emitting quasar SDSS J1425+3231 (z=0.478) was recently found to
have double-peaked narrow [O III] optical emission lines. Based on the analysis
of the optical spectrum, Peng et al. (2011) suggested that this object harbours
a dual active galactic nucleus (AGN) system, with two supermassive black holes
(SMBHs) separated on the kpc scale. SMBH pairs should be ubiquitous according
to hierarchical galaxy formation scenarios in which the host galaxies and their
central black holes grow together via interactions and eventual mergers. Yet
the number of presently-confirmed dual SMBHs on kpc or smaller scales remains
small. A possible way to obtain direct observational evidence for duality is to
conduct high-resolution radio interferometric measurements, provided that both
AGN are in an evolutionary phase when some activity is going on in the radio.
We used the technique of Very Long Baseline Interferometry (VLBI) to image SDSS
J1425+3231. Observations made with the European VLBI Network (EVN) at 1.7 GHz
and 5 GHz frequencies in 2011 revealed compact radio emission at sub-mJy flux
density levels from two components with a projected linear separation of
\sim2.6 kpc. These two components support the possibility of a dual AGN system.
The weaker component remained undetected at 5 GHz, due to its steep radio
spectrum. Further study will be necessary to securely rule out a jet--shock
interpretation of the less dominant compact radio source. Assuming the dual AGN
interpretation, we discuss black hole masses, luminosities, and accretion rates
of the two components, using available X-ray, optical, and radio data. While
high-resolution radio interferometric imaging is not an efficient technique to
search blindly for dual AGN, it is an invaluable tool to confirm the existence
of selected candidates.Comment: 7 pages, 2 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
A single radio-emitting nucleus in the dual AGN candidate NGC 5515
The Seyfert galaxy NGC 5515 has double-peaked narrow-line emission in its
optical spectrum, and it has been suggested that this could indicate that it
has two active nuclei. We observed the source with high resolution Very Long
Baseline Interferometry (VLBI) at two radio frequencies, reduced archival Very
Large Array data, and re-analysed its optical spectrum. We detected a single,
compact radio source at the position of NGC 5515, with no additional radio
emission in its vicinity. The optical spectrum of the source shows that the
blue and red components of the double-peaked lines have very similar
characteristics. While we cannot rule out unambiguously that NGC 5515 harbours
a dual AGN, the assumption of a single AGN provides a more plausible
explanation for the radio observations and the optical spectrum.Comment: 6 pages, 1 figure, accepted for publication in MNRA
Four dual AGN candidates observed with the VLBA
According to hierarchical structure formation models, merging galaxies are
expected to be seen in different stages of their coalescence. However,
currently there are no straightforward observational methods neither to select
nor to confirm a large number of dual active galactic nuclei (AGN) candidates.
Most attempts involve the better understanding of double-peaked narrow emission
line sources, to distinguish the objects where the emission lines originate
from narrow-line kinematics or jet-driven outflows from those which might
harbour dual AGN. We observed four such candidate sources with the Very Long
Baseline Array (VLBA) at 1.5 GHz with 10 milli-arcsecond angular
resolution where spectral profiles of AGN optical emission suggested the
existence of dual AGN. In SDSS J210449.13-000919.1 and SDSS J23044.82-093345.3,
the radio structures are aligned with the optical emission features, thus the
double-peaked emission lines might be the results of jet-driven outflows. In
the third detected source SDSS J115523.74+150756.9, the radio structure is less
extended and oriented nearly perpendicular to the position angle derived from
optical spectroscopy. The fourth source remained undetected with the VLBA but
it has been imaged with the Very Large Array at arcsec resolution a few months
before our observations, suggesting the existence of extended radio structure.
In none of the four sources did we detect two radio-emitting cores, a
convincing signature of duality.Comment: 35 pages, 3 figures, 2 tables, accepted for publication in Ap
The radio structure of 3C 316, a galaxy with double-peaked narrow optical emission lines
The galaxy 3C\,316 is the brightest in the radio band among the
optically-selected candidates exhibiting double-peaked narrow optical emission
lines. Observations with the Very Large Array (VLA), Multi-Element Remotely
Linked Interferometer Network (e-MERLIN), and the European VLBI Network (EVN)
at 5\,GHz have been used to study the radio structure of the source in order to
determine the nature of the nuclear components and to determine the presence of
radio cores. The e-MERLIN image of 3C 316 reveals a collimated coherent
east-west emission structure with a total extent of about 3 kpc. The EVN image
shows seven discrete compact knots on an S-shaped line. However, none of these
knots could be unambiguously identified as an AGN core. The observations
suggest that the majority of the radio structure belongs to a powerful radio
AGN, whose physical size and radio spectrum classify it as a compact
steep-spectrum source. Given the complex radio structure with radio blobs and
knots, the possibility of a kpc-separation dual AGN cannot be excluded if the
secondary is either a naked core or radio quiet.Comment: 12 pages, 3 figures, 2 tables. Accepted for publication in the MNRA
Coexistence in a One-Dimensional Cyclic Dominance Process
Cyclic (rock-paper-scissors-type) population models serve to mimic complex
species interactions. Focusing on a paradigmatic three-species model with
mutations in one dimension, we observe an interplay between equilibrium and
non-equilibrium processes in the stationary state. We exploit these insights to
obtain asymptotically exact descriptions of the emerging reactive steady state
in the regimes of high and low mutation rates. The results are compared to
stochastic lattice simulations. Our methods and findings are potentially
relevant for the spatio-temporal evolution of other non-equilibrium stochastic
processes.Comment: 4 pages, 4 figures and 2 pages of Supplementary Material. To appear
in Physical Review
Three-fold way to extinction in populations of cyclically competing species
Species extinction occurs regularly and unavoidably in ecological systems.
The time scales for extinction can broadly vary and inform on the ecosystem's
stability. We study the spatio-temporal extinction dynamics of a paradigmatic
population model where three species exhibit cyclic competition. The cyclic
dynamics reflects the non-equilibrium nature of the species interactions. While
previous work focusses on the coarsening process as a mechanism that drives the
system to extinction, we found that unexpectedly the dynamics to extinction is
much richer. We observed three different types of dynamics. In addition to
coarsening, in the evolutionary relevant limit of large times, oscillating
traveling waves and heteroclinic orbits play a dominant role. The weight of the
different processes depends on the degree of mixing and the system size. By
analytical arguments and extensive numerical simulations we provide the full
characteristics of scenarios leading to extinction in one of the most
surprising models of ecology
The use of happiness research for public policy
Research on happiness tends to follow a "benevolent dictator" approach where politicians pursue people's happiness. This paper takes an antithetic approach based on the insights of public choice theory. First, we inquire how the results of happiness research may be used to improve the choice of institutions. Second, we show that the policy approach matters for the choice of research questions and the kind of knowledge happiness research aims to provide. Third, we emphasize that there is no shortcut to an optimal policy maximizing some happiness indicator or social welfare function since governments have an incentive to manipulate this indicator
Educating Future Environmental Health Professionals
Future environmental health problems will require a new generation of educated and trained professionals. Efforts to enhance the environmental public health workforce have been promoted by several organizations. While progress has been measured by these organizations, many environmental health academic programs are experiencing budget reductions and lower enrollments. One of the reasons for this trend is the so-called higher education crisis. We argue that training is not equivalent to education in the environmental health sciences, albeit the two terms are often used interchangeably. Organizations involved with the education, training, and credentialing of environmental health professionals must work together to ensure the viability and effectiveness of environmental health academic programs
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