2,940 research outputs found
A Flaring Megamaser in Mrk 348
We report new observations of the H2O megamaser in the Seyfert 2 galaxy Mrk
348. Following our initial detection in 2000 March using the Effelsberg 100 m
telescope, re-analysis of previous data on this source indicates that the maser
was present but only marginally detectable in late 1997. Monitoring through
late 2000 shows that the maser has again decreased to its original level. The
H2O line is redshifted by ~130 km/s with respect to the systemic velocity, is
extremely broad, with a FWHM of 130 km/s, and has no detectable high velocity
components within 1500 km/s on either side of the strong line. Followup VLBA
observations show that the maser emission emanates entirely from a region >0.25
pc in extent, toward the base of the radio jet.Comment: 4 pages, 2 figures, to appear in Cosmic Masers: from Protostars to
Black Holes, IAU 206, Eds. V. Migenes et al., ASP Conference Serie
HI Observations of the Supermassive Binary Black Hole System in 0402+379
We have recently discovered a supermassive binary black hole system with a
projected separation between the two black holes of 7.3 parsecs in the radio
galaxy 0402+379. This is the most compact supermassive binary black hole pair
yet imaged by more than two orders of magnitude. We present Global VLBI
observations at 1.3464 GHz of this radio galaxy, taken to improve the quality
of the HI data. Two absorption lines are found toward the southern jet of the
source, one redshifted by 370 +/- 10 km/s and the other blueshifted by 700 +/-
10 km/s with respect to the systemic velocity of the source, which, along with
the results obtained for the opacity distribution over the source, suggests the
presence of two mass clumps rotating around the central region of the source.
We propose a model consisting of a geometrically thick disk, of which we only
see a couple of clumps, that reproduces the velocities measured from the HI
absorption profiles. These clumps rotate in circular Keplerian orbits around an
axis that crosses one of the supermassive black holes of the binary system in
0402+379. We find an upper limit for the inclination angle of the twin jets of
the source to the line of sight of 66 degrees, which, according to the proposed
model, implies a lower limit on the central mass of ~7 x 10^8 Msun and a lower
limit for the scale height of the thick disk of ~12 pc .Comment: 20 pages, 7 figures. Accepted on the Astrophysical Journa
Atopic dermatitis: Is innate or adaptive immunity in control? A clinical perspective
Atopic dermatitis (AD) is a chronic inflammatory skin disease with barrier defects and immune dysregulations. The pathogenesis of AD involves the physical barrier as well as epithelial cells, which are considered a vital part of the innate immunity of the skin. The importance of filaggrin mutations in the pathogenesis of AD has also been well-established with reproducible results around the world in multiple studies and ethnic groups. This protein plays an important role in skin barrier functions and further reaffirms barrier defects as one of the primary causes of AD. The main epithelial cells, keratinocytes, function as a major sentinel for the skin in detecting danger signals or microbial pathogens, and trigger downstream immune responses. In AD, these cells express TSLP, IL-33 and IL-25, which lead to downstream systemic production of type 2 cytokines. In spite of major advances in our understanding of the innate immunity of AD, recent success in the systemic therapeutics of AD have focused on targeting the products of the adaptive immunity, particularly cytokines produced by T cells. In addition to type 2 cytokines, type 17 cytokines have also been implicated in the pathogenesis of AD. The current review examines the implications of these cytokines in AD from clinical perspectives
The reproductive ecology of the Antarctic bivalve Aequiyoldia eightsii (Protobranchia: Sareptidae) follows neither Antarctic nor taxonomic patterns
The accepted paradigm for reproduction in Antarctic marine species is one where oogenesis takes 18 months to 2 years, and a bimodal egg-size distribution where two cohorts of eggs are present in female gonads throughout the year. These slow gametogenic traits are driven by low temperature and/or the restriction of resource availability because of extreme seasonality in the marine environment. Here we present data on the reproductive ecology of the common Antarctic bivalve Aequiyoldia eightsii (Jay, 1839) (Protobranchia: Sarepidae) from monthly samples collected between January 2013 and May 2014 at Hangar Cove, Rothera Point on the West Antarctic Peninsula. These data show that A. eightsii is unusual because it does not follow the typical pattern expected for reproduction in Antarctic marine invertebrates, and differs also from closely related nuculanid protobranch bivalves with respect to gametogenic duration and reproductive periodicity. Continuous oogenesis, evidenced by the year-round occurrence of previtellogenic, vitellogenic, and ripe oocytes in female gonads, is supplemented by a seasonal increase in reproductive intensity and spawning in Austral winter (April–May), evidenced by the loss of mature spermatozoa and ripe oocytes from males and females, respectively. The simultaneous occurrence of these contrasting traits in individuals is attributed to a flexible feeding strategy (suspension and deposit feeding) in response to seasonal changes in food supply characteristic of the Antarctic marine environment. Asynchrony between individual females is also notable. We hypothesise that the variability may represent a trade-off between somatic and reproductive growth, and previously reported internal interannual cycles in shell growth
X-ray emission from massive stars in Cyg OB2
We report on the analysis of the Chandra-ACIS data of O, B and WR stars in
the young association Cyg OB2. X-ray spectra of 49 O-stars, 54 B-stars and 3
WR-stars are analyzed and for the brighter sources, the epoch dependence of the
X-ray fluxes is investigated. The O-stars in Cyg\,OB2 follow a well-defined
scaling relation between their X-ray and bolometric luminosities: log(Lx/Lbol)
= -7.2 +/- 0.2. This relation is in excellent agreement with the one previously
derived for the Carina OB1 association. Except for the brightest O-star
binaries, there is no general X-ray overluminosity due to colliding winds in
O-star binaries. Roughly half of the known B-stars in the surveyed field are
detected, but they fail to display a clear relationship between Lx and Lbol.
Out of the three WR stars in Cyg OB2, probably only WR144 is itself responsible
for the observed level of X-ray emission, at a very low log(Lx/Lbol) = -8.8 +/-
0.2. The X-ray emission of the other two WR-stars (WR145 and 146) is most
probably due to their O-type companion along with a moderate contribution from
a wind-wind interaction zone.Comment: Accepted for an ApJS Special Issue devoted to the Chandra Cygnus OB2
Legacy Surve
The Presence and Distribution of HI Absorbing Gas in Sub-galactic Sized Radio Sources
We consider the incidence of HI absorption in intrinsically small
sub-galactic sized extragalactic sources selected from sources classified as
Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources. We
find that the smaller sources (<0.5 kpc) have larger HI column densities than
the larger sources (>0.5 kpc). Both a spherical and an axi-symmetric gas
distribution, with a radial power law density profile, can be used to explain
this anti-correlation between projected linear size and HI column density.
Since most detections occur in objects classified as galaxies, we argue that if
the unified schemes apply to GPS/CSSs a disk distribution for the HI is more
likely. The most favoured explanation for the compact sizes of the GPS/CSSs is
that they are young sources evolving in a power law density medium. For the
GPSs with measured expansion velocities, our derived densities are within an
order of magnitude of those estimated from ram-pressure confinement of the
lobes assuming equipartition. Our results therefore support the youth model.Comment: 12 pages, 8 figures, accepted for publication in A&
- …