87 research outputs found
Optical and radio properties of extragalactic radio sources with recurrent jet activity
We present a sample of 74 radio sources with recurrent jet activity. The
sample consists of 67 galaxies, 2 quasars and 5 unidentified sources, selected
from the published data or are newly recognized. The sample's redshift range is
0.002 < z < 0.7 and the size of inner and outer structures varies from 0.02 to
4248 kpc. We analyse the optical and radio properties of the sample and compare
them with the characteristics of ordinary one-off FRII radio sources. With the
help of stellar population modelling, we derive black hole masses and stellar
masses of host galaxies of 35 restarting radio sources, finding that the black
hole masses in restarting radio sources are comparable to those of typical
single-cycle FRII radio sources. The obtained median values of log M are
8.58 and 8.62 M Unlike the black hole masses, the stellar masses in
restarting radio sources tend to be smaller than in the FRII sources. Although
the stellar populations of the hosts of recurrent activity sources are
dominated by old stars, a significant fraction of young stars can be observed
as well. Based on the Sloan Digital Sky Survey photometric observations, we
also analyse the morphology of the host galaxies and obtained significantly
smaller concentration indices for the restarting radio sources when compared to
the classical FRII hosts. This effect can be interpreted as a result of
frequent merger events in the history of host galaxies of restarting radio
sources.Comment: 21 pages, 17 figure
J1420--0545: The radio galaxy larger than 3C236
We report the discovery of the largest giant radio galaxy, J1420-0545: a FR
type II radio source with an angular size of 17.4' identified with an optical
galaxy at z=0.3067. Thus, the projected linear size of the radio structure is
4.69 Mpc (if we assume that H_{0}=71 km\s\Mpc, Omega_{m}=0.27, and
Omega_{\Lambda}=0.73). This makes it larger than 3C236, which is the largest
double radio source known to date. New radio observations with the 100 m
Effelsberg telescope and the Giant Metrewave Radio Telescope, as well as
optical identification with a host galaxy and its optical spectroscopy with the
William Herschel Telescope are reported. The spectrum of J1420-0545 is typical
of elliptical galaxies in which continuum emission with the characteristic
4000A discontinuity and the H and K absorption lines are dominated by evolved
stars. The dynamical age of the source, its jets' power, the energy density,
and the equipartition magnetic field are calculated and compared with the
corresponding parameters of other giant and normal-sized radio galaxies from a
comparison sample. The source is characterized by the exceptionally low density
of the surrounding IGM and an unexpectedly high expansion speed of the source
along the jet axis. All of these may suggest a large inhomogeneity of the IGM.Comment: 20 pages, 5 figures, 3 table
The bright unidentified gamma-ray source 1FGL J1227.9-4852: Can it be associated with an LMXB?
We present an analysis of high energy (HE; 0.1-300 GeV) gamma-ray
observations of 1FGL J1227.9-4852 with the Fermi Gamma-ray Space Telescope,
follow-up radio observations with the Australia Telescope Compact Array, Giant
Metrewave Radio Telescope and Parkes radio telescopes of the same field and
follow-up optical observations with the ESO VLT. We also examine archival
XMM-Newton and INTEGRAL X-ray observations of the region around this source.
The gamma-ray spectrum of 1FGL J1227.9-4852 is best fit with an exponentially
cutoff power-law, reminiscent of the population of pulsars observed by Fermi. A
previously unknown, compact radio source within the 99.7% error circle of 1FGL
J1227.9-4852 is discovered and has a morphology consistent either with an AGN
core/jet structure or with two roughly symmetric lobes of a distant radio
galaxy. A single bright X-ray source XSS J12270-4859, a low-mass X-ray binary,
also lies within the 1FGL J1227.9-4852 error circle and we report the first
detection of radio emission from this source. The potential association of 1FGL
J1227.9-4852 with each of these counterparts is discussed. Based upon the
available data we find the association of the gamma-ray source to the compact
double radio source unlikely and suggest that XSS J12270-4859 is a more likely
counterpart to the new HE source. We propose that XSS J12270-4859 may be a
millisecond binary pulsar and draw comparisons with PSR J1023+0038.Comment: Accepted for publication in MNRAS; 9 pages, 8 figures, 2 table
Response to Merritts et al. (2023): The Anthropocene is complex. Defining it is not
Merritts et al. (2023) misrepresent Paul Crutzenâs Anthropocene concept as encompassing all significant anthropogenic impacts, extending back many millennia. Crutzen's definition reflects massively enhanced, much more recent human impacts that transformed the Earth System away from the stability of Holocene conditions. His concept of an epoch (hence the âceneâ suffix) is more consistent with the strikingly distinct sedimentary record accumulated since the mid-20th century. Waters et al. (2022) highlighted a Great Acceleration Event Array (GAEA) of stratigraphic event markers that are indeed diverse and complex but also tightly clustered around 1950 CE, allowing ultra-high resolution characterization and correlation of a clearly recognisable Anthropocene chronostratigraphic base. The âAnthropocene eventâ offered by Merritts et al., following Gibbard et al. (2021, 2022), is a highly nuanced concept that obfuscates the transformative human impact of the chronostratigraphic Anthropocene. Waters et al. (2022) restricted the meaning of the term âeventâ in geology to conform with usual Quaternary practice and improve its utility. They simultaneously recognized an evidence-based Anthropogenic Modification Episode that is more explicitly defined than the highly interpretive interdisciplinary âAnthropocene eventâ of Gibbard et al. (2021, 2022). The advance of science is best served through clearly developed concepts supported by tightly circumscribed terminology; indeed, improvements to stratigraphy over recent decades have been achieved through increasingly precise definitions, especially for chronostratigraphic units, and not by retaining vague terminology
Anthropogenic- and natural sources of dust in peatland during the Anthropocene
As human impact have been increasing strongly over the last decades, it is crucial to distinguish human-induced dust sources from natural ones in order to define the boundary of a newly proposed epoch - the Anthropocene. Here, we track anthropogenic signatures and natural geochemical anomalies in the Mukhrino peatland, Western Siberia. Human activity was recorded there from cal AD 1958 (±6). Anthropogenic spheroidal aluminosilicates clearly identify the beginning of industrial development and are proposed as a new indicator of the Anthropocene. In cal AD 1963 (±5), greatly elevated dust deposition and an increase in REE serve to show that the geochemistry of elements in the peat can be evidence of nuclear weapon testing; such constituted an enormous force blowing soil dust into the atmosphere. Among the natural dust sources, minor signals of dryness and of the Tunguska cosmic body (TCB) impact were noted. The TCB impact was indirectly confirmed by an unusual occurrence of mullite in the pea
IFN regulatory factor 4 controls post-ischemic inflammation and prevents chronic kidney disease
Ischemia reperfusion injury (IRI) of the kidney results in interferon regulatory factor 4 (IRF4)âmediated counter-regulation of the acute inflammatory response. Beyond that, IRF4 exerts important functions in controlling the cytokine milieu, T-cell differentiation, and macrophage polarization. The latter has been implicated in tissue remodeling. It therefore remains elusive what the role of IRF4 is in terms of long-term outcome following IRI. We hypothesized that an inability to resolve chronic inflammation in Irf4â/â mice would promote chronic kidney disease (CKD) progression. To evaluate the effects of IRF4 in chronic upon acute injury in vivo, a mouse model of chronic injury following acute IRI was employed. The expression of Irf4 increased within 10 days after IRI in renal tissue. Both mRNA and protein levels remained high up to 5 weeks upon IRI, suggesting a regulatory function in the chronic phase. Mice deficient in IRF4 display increased tubular cell loss and defective clearance of infiltrating macrophages. These phenomena were associated with increased expression of pro-inflammatory macrophage markers together with reduced expression of alternatively activated macrophage markers. In addition, IRF4-deficient mice showed defective development of alternatively activated macrophages. Hints of a residual M1 macrophage signature were further observed in human biopsy specimens of patients with hypertensive nephropathy vs. living donor specimens. Thus, IRF4 restricts CKD progression and kidney fibrosis following IRI, potentially by enabling M2 macrophage polarization and restricting a Th1 cytokine response. Deteriorated alternative macrophage subpopulations in Irf4â/â mice provoke chronic intrarenal inflammation, tubular epithelial cell loss, and renal fibrosis in the long course after IRI in mice. The clinical significance of these finding for human CKD remains uncertain at present and warrants further studies
CGCG 292-057 - a radio galaxy with merger-modulated radio activity
We announce the discovery of a unique combination of features in a radio
source identified with the merger galaxy CGCG 292-057. The radio galaxy both
exhibits a highly complex, X-like structure and shows signs of recurrent
activity in the form of double-double morphology. The outer lobes of CGCG
292-057 are characterized by low radio power, P_{1400MHz} \simeq 2 * 10^{24}
W\Hz^{-1}, placing this source below the FRII/FRI luminosity threshold, and are
highly polarized (almost 20 per cent at 1400 MHz) as is typical of X-shaped
radio sources. The host is a LINER-type galaxy with a relatively low black hole
mass and double-peaked narrow emission lines.
These features make this galaxy a primary target for studies of
merger-triggered radio activity.Comment: 7 pages, 5 figures, submitted to MNRA
The pulsating hot subdwarf Balloon 090100001: results of the 2005 multisite campaign
We present the results of a multisite photometric campaign on the pulsating
sdB star Balloon 090100001. The star is one of the two known hybrid hot
subdwarfs with both long- and short-period oscillations. The campaign involved
eight telescopes with three obtaining UBVR data, four B-band data, and one
Stromgren uvby photometry. The campaign covered 48 nights, providing a temporal
resolution of 0.36microHz with a detection threshold of about 0.2mmag in
B-filter data.
Balloon 090100001 has the richest pulsation spectrum of any known pulsating
subdwarf B star and our analysis detected 114 frequencies including 97
independent and 17 combination ones. The strongest mode (f_1) in the 2.8mHz
region is most likely radial while the remaining ones in this region form two
nearly symmetric multiplets: a triplet and quintuplet, attributed to
rotationally split \ell=1 and 2 modes, respectively. We find clear increases of
splitting in both multiplets between the 2004 and 2005 observing campaigns,
amounting to 15% on average. The observed splittings imply that the rotational
rate in Bal09 depends on stellar latitude and is the fastest on the equator. We
use a small grid of models to constrain the main mode (f_1), which most likely
represents the radial fundamental pulsation. The groups of p-mode frequencies
appear to lie in the vicinity of consecutive radial overtones, up to the third
one. Despite the large number of g-mode frequencies observed, we failed to
identify them, most likely because of the disruption of asymptotic behaviour by
mode trapping. The observed frequencies were not, however, fully exploited in
terms of seismic analysis which should be done in the future with a larger grid
of reliable evolutionary models of hot subdwarfs.Comment: accepted for publication in MNRA
Phase Separation in Rapid Solidified Ag-rich Ag-Cu-Zr Alloys
The microstructure and phase formation of rapid solidified Ag-rich Ag-Cu-Zr alloys were investigated. Two types of structure; interconnected- and droplet-type structures, were obtained due to phase separation mechanisms. The former was spinodal decomposition and the later was nucleation and growth mechanism. Depending on the alloy compositions, three crystalline phases; FCC-Ag, AgZr and Cu10Zr7 phases were observed along with an in-situ nanocrystalline/amorphous composite. Vickers hardness testing indicated a significant increase of hardness in the nanocrystalline/amorphous-composite alloy
A method of estimation of the dynamical age of FR II-type radio sources from multifrequency data
We propose a new approach in determining ages of FR II type radio sources. We
apply the assumed dynamical model of Kaiser et al. (1997) to a number of FR II
type radio galaxies observed at different radio frequencies, and fit - for each
frequency separately - the model free parameters to the observed sources'
quantities. Such a procedure, using enlarged in fact a number of observables,
enables us to determine relatively precise ages and other crucial
characteristics of the analyzed sources. The resulting age estimates agree very
well with those obtained by means of `classical' spectral ageing method for
objects not older than 10 Myr, for which good-quality spectral data are
available. The presented method is however also applicable in the case of the
sources older than this, and/or the ones for which the only available
low-resolution radio data do not allow for detailed spectral ageing studies.
Our analysis indicates that the main factor precluding precise age
determination for FR II type radio galaxies regards the poorly known shape of
the initial electron energy distribution injected by the jet terminal shocks to
the expanding lobes/cocoons. We briefly consider this issue, and conclude that
the broad-band single power-law form assumed here may be accurate enough for
the presented estimates, although most likely it does not strictly correspond
to some well-defined realistic particle acceleration process. Instead, it
should be considered as a simplest model approximation of the initial electron
continuum, averaged over a very broad energy range and over the age of the
source, with the effective spectral index which may be different for different
sources.Comment: 15 pages, 9 figures included. Accepted for publication in A&
- âŠ