432 research outputs found
Prospects for ACT: simulations, power spectrum, and non-Gaussian analysis
A new generation of instruments will reveal the microwave sky at high
resolution. We focus on one of these, the Atacama Cosmology Telescope, which
probes scales 1000<l<10000, where both primary and secondary anisotropies are
important. Including lensing, thermal and kinetic Sunyaev-Zeldovich (SZ)
effects, and extragalactic point sources, we simulate the telescope's
observations of the CMB in three channels, then extract the power spectra of
these components in a multifrequency analysis. We present results for various
cases, differing in assumed knowledge of the contaminating point sources. We
find that both radio and infrared point sources are important, but can be
effectively eliminated from the power spectrum given three (or more) channels
and a good understanding of their frequency dependence. However, improper
treatment of the scatter in the point source frequency dependence relation may
introduce a large systematic bias. Even if all thermal SZ and point source
effects are eliminated, the kinetic SZ effect remains and corrupts measurements
of the primordial slope and amplitude on small scales. We discuss the
non-Gaussianity of the one-point probability distribution function as a way to
constrain the kinetic SZ effect, and we develop a method for distinguishing
this effect from the CMB in a window where they overlap. This method provides
an independent constraint on the variance of the CMB in that window and is
complementary to the power spectrum analysis.Comment: 22 pages, 11 figures. Submitted to New Astronomy. High resolution
figures provided at
http://www.princeton.edu/~khuffenb/pubs/prospects-act.htm
Magnetic Fields in the 3C 129 Cluster
We present multi-frequency VLA observations of the two radio galaxies 3C 129
and 3C 129.1 embedded in a luminous X-ray cluster. These radio observations
reveal a substantial difference in the Faraday Rotation Measures (RMs) toward
3C 129.1 at the cluster center and 3C 129 at the cluster periphery. After
deriving the density profile from available X-ray data, we find that the RM
structure of both radio galaxies can be fit by a tangled cluster magnetic field
with strength 6 microGauss extending at least 3 core radii (450 kpc) from the
cluster center. The magnetic field makes up a small contribution to the total
pressure (5%) in the central regions of the cluster. The radio morphology of 3C
129.1 appears disturbed on the southern side, perhaps by the higher pressure
environment. In contrast with earlier claims for the presence of a moderately
strong cooling flow in the 3C 129 cluster, our analysis of the X-ray data
places a limit on the mass deposition rate from any such flow of <1.2 Msun/yr.Comment: in press at MNRA
The Cosmic Microwave Background & Inflation, Then & Now
Boomerang, Maxima, DASI, CBI and VSA significantly increase the case for
accelerated expansion in the early universe (the inflationary paradigm) and at
the current epoch (dark energy dominance), especially when combined with data
on high redshift supernovae (SN1) and large scale structure (LSS). There are
``7 pillars of Inflation'' that can be shown with the CMB probe, and at least
5, and possibly 6, of these have already been demonstrated in the CMB data: (1)
a large scale gravitational potential; (2) acoustic peaks/dips; (3) damping due
to shear viscosity; (4) a Gaussian (maximally random) distribution; (5)
secondary anisotropies; (6) polarization. A 7th pillar, anisotropies induced by
gravity wave quantum noise, could be too small. A minimal inflation parameter
set, \omega_b,\omega_{cdm}, \Omega_{tot}, \Omega_Q,w_Q,n_s,\tau_C, \sigma_8},
is used to illustrate the power of the current data. We find the CMB+LSS+SN1
data give \Omega_{tot} =1.00^{+.07}_{-.03}, consistent with (non-baroque)
inflation theory. Restricting to \Omega_{tot}=1, we find a nearly scale
invariant spectrum, n_s =0.97^{+.08}_{-.05}. The CDM density, \Omega_{cdm}{\rm
h}^2 =.12^{+.01}_{-.01}, and baryon density, \Omega_b {\rm h}^2 =
>.022^{+.003}_{-.002}, are in the expected range. (The Big Bang nucleosynthesis
estimate is 0.019\pm 0.002.) Substantial dark (unclustered) energy is inferred,
\Omega_Q \approx 0.68 \pm 0.05, and CMB+LSS \Omega_Q values are compatible with
the independent SN1 estimates. The dark energy equation of state, crudely
parameterized by a quintessence-field pressure-to-density ratio w_Q, is not
well determined by CMB+LSS (w_Q < -0.4 at 95% CL), but when combined with SN1
the resulting w_Q < -0.7 limit is quite consistent with the w_Q=-1 cosmological
constant case.Comment: 20 pages, 8 figures, in Theoretical Physics, MRST 2002: A Tribute to
George Libbrandt (AIP), eds. V. Elias, R. Epp, R. Myer
Deep Chandra and multicolor HST observations of the jets of 3C 371 and PKS 2201+044
This paper presents multiwavelength imaging and broad-band spectroscopy of
the relativistic jets in the two nearby radio galaxies 3C 371 and PKS 2201+044,
acquired with Chandra, HST, VLA, and Merlin. Radio polarization images are also
available. The two sources stand out as "intermediate'' between FRIs and FRIIs;
their cores are classified as BL Lacs, although broad and narrow optical
emission lines were detected at times. The multiwavelength images show jet
morphologies with the X-ray emission peaking closer to the nucleus than the
longer wavelengths. The jets are resolved at all wavelengths in a direction
perpendicular to the jet axis. The jets SEDs are consistent with a single
spectral component from radio to X-rays, interpreted as synchrotron emission.
The SEDs show a progressive softening from the inner to the outer regions of
the jet, indicating that the electron break energy moves to lower energies with
distance from the core. Overall, the X-ray and multiwavelength properties of
the jets of 3C 371 and PKS 2201+044 appear intermediate between those of FRIs
and FRIIs.Comment: Accepted for publication in ApJ; 28 pages (emulateapj5), 17 figure
Relativistic jet models for two low-luminosity radio galaxies: evidence for backflow?
We show that asymmetries in total intensity and linear polarization between
the radio jets and counter-jets in two lobed Fanaroff-Riley Class I (FR I)
radio galaxies, B2 0206+35 (UGC 1651) and B2 0755+37 (NGC 2484), can be
accounted for if these jets are intrinsically symmetrical, with decelerating
relativistic outflows surrounded by mildly relativistic backflows. Our
interpretation is motivated by sensitive, well-resolved Very Large Array
imaging which shows that both jets in both sources have a two-component
structure transverse to their axes. Close to the jet axis, a centrally-darkened
counter-jet lies opposite a centrally-brightened jet, but both are surrounded
by broader collimated emission that is brighter on the counter-jet side. We
have adapted our previous models of FR I jets as relativistic outflows to
include an added component of symmetric backflow. We find that the observed
radio emission, after subtracting contributions from the extended lobes, is
well described by models in which decelerating outflows with parameters similar
to those derived for jets in plumed FR I sources are surrounded by backflows
containing predominantly toroidal magnetic fields. These return to within a few
kpc of the galaxies with velocities of roughly 0.25c and radiate with a
synchrotron spectral index close to 0.55. We discuss whether such backflow is
to be expected in lobed FR I sources and suggest ways in which our hypothesis
can be tested by further observations.Comment: 22 pages, 17 figures, accepted for publication in MNRA
A Measurement of the Angular Power Spectrum of the CMB Temperature Anisotropy from the 2003 Flight of Boomerang
We report on observations of the Cosmic Microwave Background (CMB) obtained
during the January 2003 flight of Boomerang . These results are derived from
195 hours of observation with four 145 GHz Polarization Sensitive Bolometer
(PSB) pairs, identical in design to the four 143 GHz Planck HFI polarized
pixels. The data include 75 hours of observations distributed over 1.84% of the
sky with an additional 120 hours concentrated on the central portion of the
field, itself representing 0.22% of the full sky. From these data we derive an
estimate of the angular power spectrum of temperature fluctuations of the CMB
in 24 bands over the multipole range (50 < l < 1500). A series of features,
consistent with those expected from acoustic oscillations in the primordial
photon-baryon fluid, are clearly evident in the power spectrum, as is the
exponential damping of power on scales smaller than the photon mean free path
at the epoch of last scattering (l > 900). As a consistency check, the
collaboration has performed two fully independent analyses of the time ordered
data, which are found to be in excellent agreement.Comment: 11 pages, 7 figures, 3 tables. High resolution figures and data are
available at http://cmb.phys.cwru.edu/boomerang/ and
http://oberon.roma1.infn.it/boomerang/b2
Resolution enhancement of multichannel microwave imagery from the Nimbus-7 SMMR for maritime rainfall analysis
A restoration of the 37, 21, 18, 10.7, and 6.6 GHz satellite imagery from the scanning multichannel microwave radiometer (SMMR) aboard Nimbus-7 to 22.2 km resolution is attempted using a deconvolution method based upon nonlinear programming. The images are deconvolved with and without the aid of prescribed constraints, which force the processed image to abide by partial a priori knowledge of the high-resolution result. The restored microwave imagery may be utilized to examined the distribution of precipitating liquid water in marine rain systems
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