830 research outputs found
High-resolution VLA Imaging of SDSS Stripe 82 at 1.4 GHz
We present a high-resolution radio survey of the Sloan Digital Sky Survey
(SDSS) Southern Equatorial Stripe, a.k.a. Stripe 82. This 1.4 GHz survey was
conducted with the Very Large Array (VLA) primarily in the A-configuration,
with supplemental B-configuration data to increase sensitivity to extended
structure. The survey has an angular resolution of 1.8" and achieves a median
rms noise of 52 microJy/bm over 92 deg^2. This is the deepest 1.4 GHz survey to
achieve this large of an area, filling a gap in the phase space between small,
deep and large, shallow surveys. It also serves as a pilot project for a larger
high-resolution survey with the Expanded Very Large Array (EVLA). We discuss
the technical design of the survey and details of the observations, and we
outline our method for data reduction. We present a catalog of 17,969 isolated
radio components, for an overall source density of ~195 sources/deg^2. The
astrometric accuracy of the data is excellent, with an internal check utilizing
multiply-observed sources yielding an rms scatter of 0.19" in both right
ascension and declination. A comparison to the SDSS DR7 Quasar Catalog further
confirms that the astrometry is well tied to the optical reference frame, with
mean offsets of 0.02" +/- 0.01" in right ascension, and 0.01" +/- 0.02" in
declination. A check of our photometry reveals a small, negative CLEAN-like
bias on the level of 35 microJy. We report on the catalog completeness, finding
that 97% of FIRST-detected quasars are recovered in the new Stripe 82 radio
catalog, while faint, extended sources are more likely to be resolved out by
the resolution bias. We conclude with a discussion of the optical counterparts
to the catalog sources, including 76 newly-detected radio quasars. The full
catalog as well as a search page and cutout server are available online at
http://third.ucllnl.org/cgi-bin/stripe82cutout.Comment: 18 pages, 22, figures. Submitted to AJ, revised to address referee's
comment
Hyperproliferation and Dysregulation ofIL-4 Expression in NF-ATp-Deficient Mice
AbstractNF-ATp is a member of a family of genes that encodes the cytoplasmic component of the nuclear factor of activated T cells (NF-AT). In this study, we show that mice with a null mutation in the NF-ATp gene have splenomegaly with hyperproliferation of both B and T cells. They also display early defects in the transcription of multiple genes encoding cytokines and cell surface receptors, including CD40L and FasL. A striking defect in early IL-4 production was observed after ligation of the TCR complex by treatment with anti-CD3 in vivo. The transcription of other cytokines including IL-13, GM–CSF, and TNFα was also affected, though to a lesser degree. Interestingly, the cytokines IL-2 and IFNγ were minimally affected. Despite this early defect in IL-4 transcription, Th2 development was actually enhanced at later timepoints as evidenced by increased IL-4 production and IgE levels in situations that favor the formation of Th2 cells both in vitro and in vivo. These data suggest that NF-ATp may be involved in cell growth, and that it is important for the balanced transcription of the IL-4 gene during the course of an immune response.BDY
Calibration of the GLAST Burst Monitor detectors
The GLAST Burst Monitor (GBM) will augment the capabilities of GLAST for the
detection of cosmic gamma-ray bursts by extending the energy range (20 MeV to >
300 GeV) of the Large Area Telescope (LAT) towards lower energies by 2
BGO-detectors (150 keV to 30 MeV) and 12 NaI(Tl) detectors (10 keV to 1 MeV).
The physical detector response of the GBM instrument for GRBs is determined
with the help of Monte Carlo simulations, which are supported and verified by
on-ground calibration measurements, performed extensively with the individual
detectors at the MPE in 2005. All flight and spare detectors were irradiated
with calibrated radioactive sources in the laboratory (from 14 keV to 4.43
MeV). The energy/channel-relations, the dependences of energy resolution and
effective areas on the energy and the angular responses were measured. Due to
the low number of emission lines of radioactive sources below 100 keV,
calibration measurements in the energy range from 10 keV to 60 keV were
performed with the X-ray radiometry working group of the
Physikalisch-Technische Bundesanstalt (PTB) at the BESSY synchrotron radiation
facility, Berlin.Comment: 2 pages, 1 figure; to appear in the Proc. of the First Int. GLAST
Symp. (Stanford, Feb. 5-8, 2007), eds. S.Ritz, P.F.Michelson, and C.Meegan,
AIP Conf. Pro
On the Nature of Star Formation at Large Galactic Radii
We have compared far-ultraviolet (FUV), near-ultraviolet (NUV), and Halpha
measurements for star forming regions in 21 galaxies, in order to characterise
the properties of their discs at radii beyond the main optical radius (R25). In
our representative sample of extended and non-extended UV discs we find that
half of the extended UV discs also exhibit extended Halpha emission. We find
that extended UV discs fall into two categories, those with a sharp truncation
in the Halpha disc close to the optical edge (R25), and those with extended
emission in Halpha as well as in the ultraviolet. Although most galaxies with
strong Halpha truncations near R25 show a significant corresponding falloff in
UV emission (factor 10--100), the transition tends to be much smoother than in
Halpha, and significant UV emission often extends well beyond this radius,
confirming earlier results by Thilker et al. (2007) and others. After
correcting for dust attenuation the median fraction of total FUV emission from
regions outside of R25 is 1.7%, but it can be as high as 35% in the most
extreme cases. The corresponding fractions of Halpha emission are approximately
half as large on average. This difference reflects both a slightly lower ratio
of Halpha to UV emission in the HII regions in the outer discs, as well as a
lower fraction of star clusters showing HII regions. Most HII regions in the
extended disc have fluxes consistent with small numbers of ionising O-type
stars, and this poor sampling of the upper initial mass function in small
clusters can probably account for the differences in the emission properties,
consistent with earlier conclusions by Zaritsky & Christlein (2007), without
needing to invoke a significant change in the stellar IMF itself. Consistent
Ha/FUV ratios and brightest HII region to total Halpha fluxes in the inner and
extended discs across our whole galaxy sample demonstrate no evidence for a
change in the cluster luminosity function or the IMF in the low gas density
outer disc.Comment: Accepted for publication in MNRAS. 21 Pages, 13 Figures, 2 Table
A kinematic study of the irregular dwarf galaxy NGC 2366 using HI and Halpha observations
Abridged. Context. The metal content of dwarf galaxies and the metal
enrichment of the intergalactic medium both suggest that mass loss from
galaxies is a significant factor for the chemical evolution history of
galaxies, in particular of dwarf galaxies. However, no clear evidence of a
blow-away in local dwarf galaxies has been found so far.
Aims. We therefore performed a detailed kinematic analysis of the neutral and
ionised gas in the nearby star-forming irregular dwarf galaxy NGC 2366 in order
to make predictions about the fate of the gas and to get a more complete
picture of this galaxy.
Methods. A deep Halpha image and Fabry-Perot interferometric data of NGC 2366
were obtained. They were complemented by HI synthesis data from the THINGS
survey. We searched for line-splitting both in Halpha and HI by performing a
Gaussian decomposition. To get an idea whether the expansion velocities are
high enough for a gas blow-away, we used the pseudo-isothermal halo model,
which gives us realistic values for the escape velocities of NGC 2366. The good
data quality also allowed us to discuss some peculiarities of the morphology
and the dynamics in NGC 2366.
Results. A large red-shifted outflow north west of the giant extragalactic
HII region with an expansion velocity of up to 50 km/s is found in Halpha, but
not in HI. Additionally, a blue-shifted component north of the giant
extragalactic HII region was detected both in Halpha and HI with an expansion
velocity of up to 30 km/s. A comparison with the escape velocities of NGC 2366
reveals that the gas does not have enough kinetic energy to leave the
gravitational potential.Comment: 15 pages, 14 figures, accepted for publication by A&
Policing of reproduction by hidden threats in a cooperative mammal
The evolution of cooperation in animal and human societies is associated with mechanisms to suppress individual selfishness. In insect societies, queens and workers enforce cooperation by “policing” selfish reproduction by workers. Insect policing typically takes the form of damage limitation after individuals have carried out selfish acts (such as laying eggs). In contrast, human policing is based on the use of threats that deter individuals from acting selfishly in the first place, minimizing the need for damage limitation. Policing by threat could in principle be used to enforce reproductive suppression in animal societies, but testing this idea requires an experimental approach to simulate reproductive transgression and provoke out-of-equilibrium behavior. We carried out an experiment of this kind on a wild population of cooperatively breeding banded mongooses (Mungos mungo) in Uganda. In this species, each group contains multiple female breeders that give birth to a communal litter, usually on the same day. In a 7-y experiment we used contraceptive injections to manipulate the distribution of maternity within groups, triggering hidden threats of infanticide. Our data suggest that older, socially dominant females use the threat of infanticide to deter selfish reproduction by younger females, but that females can escape the threat of infanticide by synchronizing birth to the same day as older females. Our study shows that reproduction in animal societies can be profoundly influenced by threats that remain hidden until they are triggered experimentally. Coercion may thus extend well beyond the systems in which acts of infanticide are common
ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
We use ALMA to derive the mass, length, and time scales associated with the
nuclear starburst in NGC 253. This region forms ~2 M_sun/yr of stars and
resembles other starbursts in scaling relations, with star formation consuming
the gas reservoir 10 times faster than in galaxy disks. We present observations
of CO, the high effective density transitions HCN(1-0), HCO+(1-0), CS(2-1), and
their isotopologues. We identify ten clouds that appear as peaks in line
emission and enhancements in the HCN-to-CO ratio. These clouds are massive
(~10^7 M_sun) structures with sizes (~30 pc) similar to GMCs in other systems.
Compared to disk galaxy GMCs, they show high line widths (~20-40 km/s) given
their size, with implied Mach numbers ~90. The clouds also show high surface
(~6,000 M_sun/pc^2) and volume densities (n_H2~2,000 cm^-3). Given these,
self-gravity can explain the line widths. This short free fall time (~0.7 Myr)
helps explain the more efficient star formation in NGC 253. We also consider
the starburst region as a whole. The geometry is confused by the high
inclination, but simple models support a non-axisymmetric, bar-like geometry
with a compact, clumpy region of high gas density embedded in an extended CO
distribution. Even for the whole region, the surface density still exceeds that
of a disk galaxy GMC. The orbital time (~10 Myr), disk free fall time (<~ 3
Myr), and disk crossing time (<~ 3 Myr) are each much shorter than in a normal
spiral galaxy disk. Some but not all aspects of the structure correspond to
predictions from assuming vertical dynamical equilibrium or a marginally stable
rotating disk. Finally, the CO-to-H2 conversion factor implied by our cloud
calculations is approximately Galactic, contrasting with results showing a low
value for the whole starburst region. The contrast provides resolved support
for the idea of mixed molecular ISM phases in starburst galaxies.Comment: Accepted for publication in the Astrophysical Journal. 31 pages, 16
Figure
The relative and absolute timing accuracy of the EPIC-pn camera on XMM-Newton, from X-ray pulsations of the Crab and other pulsars
Reliable timing calibration is essential for the accurate comparison of
XMM-Newton light curves with those from other observatories, to ultimately use
them to derive precise physical quantities. The XMM-Newton timing calibration
is based on pulsar analysis. However, as pulsars show both timing noise and
glitches, it is essential to monitor these calibration sources regularly. To
this end, the XMM-Newton observatory performs observations twice a year of the
Crab pulsar to monitor the absolute timing accuracy of the EPIC-pn camera in
the fast Timing and Burst modes. We present the results of this monitoring
campaign, comparing XMM-Newton data from the Crab pulsar (PSR B0531+21) with
radio measurements. In addition, we use five pulsars (PSR J0537-69, PSR
B0540-69, PSR B0833-45, PSR B1509-58 and PSR B1055-52) with periods ranging
from 16 ms to 197 ms to verify the relative timing accuracy. We analysed 38
XMM-Newton observations (0.2-12.0 keV) of the Crab taken over the first ten
years of the mission and 13 observations from the five complementary pulsars.
All the data were processed with the SAS, the XMM-Newton Scientific Analysis
Software, version 9.0. Epoch folding techniques coupled with \chi^{2} tests
were used to derive relative timing accuracies. The absolute timing accuracy
was determined using the Crab data and comparing the time shift between the
main X-ray and radio peaks in the phase folded light curves. The relative
timing accuracy of XMM-Newton is found to be better than 10^{-8}. The strongest
X-ray pulse peak precedes the corresponding radio peak by 306\pm9 \mus, which
is in agreement with other high energy observatories such as Chandra, INTEGRAL
and RXTE. The derived absolute timing accuracy from our analysis is \pm48 \mus.Comment: 16 pages, 9 figures. Accepted for publication on A&
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