7,431 research outputs found
Starburst and post-starburst high-redshift protogalaxies: The feedback impact of high energy cosmic rays
Quenching of star-formation has been identified in many starburst and
post-starburst galaxies, indicating burst-like star-formation histories (SFH)
in the primordial Universe. We have investigated the role of high energy cosmic
rays (CRs) in such environments, particularly how they could contribute to this
burst-like SFH via quenching and feedback. These high energy particles interact
with the baryon and radiation fields of their host via hadronic processes to
produce secondary leptons. The secondary particles then also interact with
ambient radiation fields to generate X-rays through inverse-Compton scattering.
In addition, they can thermalise directly with the semi-ionised medium via
Coulomb processes. Heating at a rate of can be attained by Coulomb processes
in a star-forming galaxy with one core-collapse SN event per decade, and this
is sufficient to cause quenching of star-formation. At high-redshift, a
substantial amount of CR secondary electron energy can be diverted into
inverse-Compton X-ray emission. This yields an X-ray luminosity of above
by redshift which drives a further
heating effect, operating over larger scales. This would be able to halt
inflowing cold gas filaments, strangulating subsequent star-formation. We
selected a sample of 16 starburst and post-starburst galaxies at and determine the star-formation rates they could have sustained.
We applied a model with CR injection, propagation and heating to calculate
energy deposition rates in these 16 sources. Our calculations show that CR
feedback cannot be neglected as it has the strength to suppress star-formation
in these systems. We also show that their currently observed quiescence is
consistent with the suffocation of cold inflows, probably by a combination of
X-ray and CR heating.Comment: 30 pages, 14 figures, 4 tables, accepted for publication in A&A;
abstract abridged. V2: updates to match published version (minor typo
corrections
Average profiles of the solar wind and outer radiation belt during the extreme flux enhancement of relativistic electrons at geosynchronous orbit
We report average profiles of the solar wind and outer radiation belt during the extreme flux enhancement of relativistic electrons at geosynchronous orbit (GEO). It is found that seven of top ten extreme events at GEO during solar cycle 23 are associated with the magnetosphere inflation during the storm recovery phase as caused by the large-scale solar wind structure of very low dynamic pressure (<1.0 nPa) during rapid speed decrease from very high (>650 km/s) to typical (400–500 km/s) in a few days. For the seven events, the solar wind parameters, geomagnetic activity indices, and relativistic electron flux and geomagnetic field at GEO are superposed at the local noon period of GOES satellites to investigate the physical cause. The average profiles support the "double inflation" mechanism that the rarefaction of the solar wind and subsequent magnetosphere inflation are one of the best conditions to produce the extreme flux enhancement at GEO because of the excellent magnetic confinement of relativistic electrons by reducing the drift loss of trapped electrons at dayside magnetopause
Earliest detection of the optical afterglow of GRB 030329 and its variability
We report the earliest detection of an extremely bright optical afterglow of
the gamma-ray burst (GRB) 030329 using a 30cm-telescope at Tokyo Institute of
Technology (Tokyo, JAPAN). Our observation started 67 minutes after the burst,
and continued for succeeding two nights until the afterglow faded below the
sensitivity limit of the telescope (approximately 18 mag). Combining our data
with those reported in GCN Circulars, we find that the early afterglow light
curve of the first half day is described by a broken power-law (t^{- alpha})
function with indices alpha_{1} = 0.88 +/- 0.01 (0.047 < t < t_{b1} days),
alpha_{2} = 1.18 +/- 0.01 (t_{b1} < t < t_{b2} days), and alpha_{3} = 1.81 +/-
0.04 (t_{b2} < t < 1.2 days), where t_{b1} ~ 0.26 days and t_{b2} ~ 0.54 days,
respectively. The change of the power-law index at the first break at t ~ 0.26
days is consistent with that expected from a ``cooling-break'' when the cooling
frequency crossed the optical band. If the interpretation is correct, the decay
index before the cooling-break implies a uniform ISM environment.Comment: 13 pages, 1 table and 2 figures. Accepted to the Astrophysical
Journal Letter
ALMA polarimetric studies of rotating jet/disk systems
We have recently obtained polarimetric data at mm wavelengths with ALMA for
the young systems DG Tau and CW Tau, for which the rotation properties of jet
and disk have been investigated in previous high angular resolution studies.
The motivation was to test the models of magneto-centrifugal launch of jets via
the determination of the magnetic configuration at the disk surface. The
analysis of these data, however, reveals that self-scattering of dust thermal
radiation dominates the polarization pattern. It is shown that even if no
information on the magnetic field can be derived in this case, the polarization
data are a powerful tool for the diagnostics of the properties and the
evolution of dust in protoplanetary disks.Comment: 9 pages, 3 figures, to appear in "Jet Simulations, Experiments and
Theory. Ten years after JETSET, what is next ?", C. Sauty ed., Springer
Natur
Average profiles of the solar wind and outer radiation belt during the extreme flux enhancement of relativistic electrons at geosynchronous orbit
Chandra Discovery of an X-ray Jet and Lobes in 3C 15
We report the Chandra detection of an X-ray jet in 3C 15. The peak of the
X-ray emission in the jet is 4.1'' (a projected distance of 5.1 kpc) from the
nucleus, and coincident with a component previously identified in the radio and
optical jets. We examine four models for the X-ray jet emission: (I) weak
synchrotron cooling in equip., (II) moderate synchrotron cooling in equip.,
(III) weak synchrotron plus SSC cooling, and (IV) moderate synchrotron plus SSC
cooling. We argue that case (II) can most reasonably explain the overall
emission from knot C. Case (III) is also possible, but requires a large
departure from equipartition and for the jet power to be comparable to that of
the brightest quasars. Diffuse X-ray emission has also been detected,
distributed widely over the full extent (63kpc x 25kpc) of the radio lobes. We
compare the total energy contained in the lobes with the jet power estimated
from knot C, and discuss the energetic link between the jet and the lobes. We
argue that the fueling time (t_fuel) and the source age (t_src) are comparable
for case (II), whereas t_fuel << t_src is likely for case (III). The latter may
imply that the jet has a very small filling factor, ~10^{-3}. We consider the
pressure balance between the thermal galaxy halo and non-thermal relativistic
electrons in the radio lobes. Finally, we show that the X-ray emission from the
nucleus is not adequately fitted by a simple absorbed power-law model, but
needs an additional power-law with heavy absorption intrinsic to the source.
Such a high column density is consistent with the presence of a dense, dusty
torus which obscures the quasar nucleus.Comment: 14 pages, 8 figures, accepted for publication in A&
Suzaku observation of TeV blazar the 1ES 1218+304: clues on particle acceleration in an extreme TeV blazar
We observed the TeV blazar 1ES 1218+304 with the X-ray astronomy satellite
Suzaku in May 2006. At the beginning of the two-day continuous observation, we
detected a large flare in which the 5-10 keV flux changed by a factor of ~2 on
a timescale of 5x10^4 s. During the flare, the increase in the hard X-ray flux
clearly lagged behind that observed in the soft X-rays, with the maximum lag of
2.3x10^4 s observed between the 0.3-1 keV and 5-10 keV bands. Furthermore we
discovered that the temporal profile of the flare clearly changes with energy,
being more symmetric at higher energies. From the spectral fitting of
multi-wavelength data assuming a one-zone, homogeneous synchrotron self-Compton
model, we obtain B~0.047 G, emission region size R = 3.0x10^16 cm for an
appropriate beaming with a Doppler factor of delta = 20. This value of B is in
good agreement with an independent estimate through the model fit to the
observed time lag ascribing the energy-dependent variability to differential
acceleration timescale of relativistic electrons provided that the gyro-factor
\xi is 10^5.Comment: 11 pages, 3 figures, Accepted for publication in ApJ
X-ray Emitting GHz-Peaked Spectrum Galaxies: Testing a Dynamical-Radiative Model with Broad-Band Spectra
In a dynamical-radiative model we recently developed to describe the physics
of compact, GHz-Peaked-Spectrum (GPS) sources, the relativistic jets propagate
across the inner, kpc-sized region of the host galaxy, while the electron
population of the expanding lobes evolves and emits synchrotron and
inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the
expanding lobes, and photoionized by the active nucleus, are responsible for
the radio spectral turnover through free-free absorption (FFA) of the
synchrotron photons. The model provides a description of the evolution of the
spectral energy distribution (SED) of GPS sources with their expansion,
predicting significant and complex high-energy emission, from the X-ray to the
gamma-ray frequency domain. Here, we test this model with the broad-band SEDs
of a sample of eleven X-ray emitting GPS galaxies with Compact-Symmetric-Object
(CSO) morphology, and show that: (i) the shape of the radio continuum at
frequencies lower than the spectral turnover is indeed well accounted for by
the FFA mechanism; (ii) the observed X-ray spectra can be interpreted as
non-thermal radiation produced via IC scattering of the local radiation fields
off the lobe particles, providing a viable alternative to the thermal,
accretion-disk dominated scenario. We also show that the relation between the
hydrogen column densities derived from the X-ray (N_H) and radio (N_HI) data of
the sources is suggestive of a positive correlation, which, if confirmed by
future observations, would provide further support to our scenario of
high-energy emitting lobes.Comment: 29 pages, 3 figures, 6 tables; to appear in ApJ. A few clarifications
included, according to referee's suggestion
Relationship of Associated Cardiovascular Risk Factors and Chronic Kidney Disease with Participants Enrolled in the National Kidney Foundation of Hawai\u27i Kidney Early Detection Screening (KEDS) Program
Objective The objective of this study was to further examine the relationship of associated cardiovascular risk factors and chronic kidney disease (CKD) with a large cross-sectional sample of Native Hawaiians, Japanese, Chinese, Filipino, and White participants who were enrolled in the National Kidney Foundation of Hawai\u27i Kidney Early Detection Screening (KEDS) program.
Methods Data for this cross-sectional study was collected between 2006 and 2009 from the National Kidney Foundation of Hawaii (NKFH). Nine hundred and fifteen participants who attended the NKFH KEDS program were 18 years and older, and residents of the State of Hawaii. Data included demographic information, clinical risk factors, anthropometric measurements, and lab values. Microalbuminuria was used as an indicator for CKD. Descriptive analysis using frequencies, means, and standard deviations, chi-square tests, and ANOVA were conducted to examine the differences in cardiovascular disease (CVD) risk factors and normal and abnormal microalbuminuria groups. A multivariate hierarchical logistic regression model was used to identify the CV risk factors associated with abnormal microalbuminuria. The Hosmer and Lemeshow Goodness of Fit test and R-2-type indices examined the fit of the regression model to the data. Results Significant results related to microalbuminuria included BMI (p=0.004), glucose (p=.004), and Japanese ethnicity (p=.008).
Conclusion The findings support the need to address CVD risk factors in NKFH KEDS program.
Keywords: chronic kidney disease, CVD risk factors, microalbuminuria, Asians, Native Hawaiians Pacific Islander
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