1,209 research outputs found
Infrared Spectroscopy of CO Ro-vibrational Absorption Lines toward the Obscured AGN IRAS 08572+3915
We present high-resolution spectroscopy of gaseous CO absorption in the
fundamental ro-vibrational band toward the heavily obscured active galactic
nucleus (AGN) IRAS 08572+3915. We have detected absorption lines up to highly
excited rotational levels (J<=17). The velocity profiles reveal three distinct
components, the strongest and broadest (delta_v > 200 km s-1) of which is due
to blueshifted (-160 km s-1) gas at a temperature of ~ 270 K absorbing at
velocities as high as -400 km s-1. A much weaker but even warmer (~ 700 K)
component, which is highly redshifted (+100 km s-1), is also detected, in
addition to a cold (~ 20 K) component centered at the systemic velocity of the
galaxy. On the assumption of local thermodynamic equilibrium, the column
density of CO in the 270 K component is NCO ~ 4.5 x 10^18 cm-2, which in fully
molecular gas corresponds to a H2 column density of NH2 ~ 2.5 x 10^22 cm-2. The
thermal excitation of CO up to the observed high rotational levels requires a
density greater than nc(H2) > 2 x 10^7 cm-3, implying that the thickness of the
warm absorbing layer is extremely small (delta_d < 4 x 10-2 pc) even if it is
highly clumped. The large column densities and high radial velocities
associated with these warm components, as well as their temperatures, indicate
that they originate in molecular clouds near the central engine of the AGN.Comment: 13 pages, 7 figures, accepted for publication in PASJ (Vol.65 No.1
2013/02/25
Confronting cold dark matter cosmologies with strong clustering of Lyman break galaxies at
We perform a detailed analysis of the statistical significance of a
concentration of Lyman break galaxies at recently discovered by
Steidel et al. (1997), using a series of N-body simulations with
particles in a (100\himpc)^3 comoving box. While the observed number density
of Lyman break galaxies at implies that they correspond to systems
with dark matter halos of \simlt 10^{12}M_\odot, the resulting clustering of
such objects on average is not strong enough to be reconciled with the
concentration if it is fairly common; we predict one similar concentration
approximately per () fields in three representative cold dark matter
models. Considering the current observational uncertainty of the frequency of
such clustering at , it would be premature to rule out the models, but
the future spectroscopic surveys in a dozen fields could definitely challenge
all the existing cosmological models a posteriori fitted to the universe.Comment: the final version which matchs that published in ApJ Letters (Feb
1998); compared with the previous versions, the predictions for the SCDM
model are slightly changed; Latex, 11 pages, including 3 ps figure
Influence of Random Internal Fields on the Tunneling of OH Defects in NaCl Crystals
Alkali halide crystals doped with certain impurity ions show a low
temperature behaviour, which differs significantly from that of pure crystals.
The origin of these characteristic differences are tunneling centers formed by
atomic or molecular impurity ions. We have investigated the dielectric
susceptibility of hydroxyl ions in NaCl crystals at very low concentrations
(below 30 ppm), where interactions are believed to be negligible. We find that
the temperature dependence of the susceptibility is noticeably different from
what one would expect for isolated defects in a symmetric environment. We
propose that the origin of these deviations are random internal strains arising
from imperfections of the host crystal. We will present the experimental data
and a theoretical model which allows a quantitative understanding on a
microscopic basis.Comment: 3 pages 3 figures, REVTeX, submitted to the proceedings of the
PHONONS 2001 conferenc
Systematic Errors in the Hubble Constant Measurement from the Sunyaev-Zel'dovich effect
The Hubble constant estimated from the combined analysis of the
Sunyaev-Zel'dovich effect and X-ray observations of galaxy clusters is
systematically lower than those from other methods by 10-15 percent. We examine
the origin of the systematic underestimate using an analytic model of the
intracluster medium (ICM), and compare the prediction with idealistic triaxial
models and with clusters extracted from cosmological hydrodynamical
simulations. We identify three important sources for the systematic errors;
density and temperature inhomogeneities in the ICM, departures from
isothermality, and asphericity. In particular, the combination of the first two
leads to the systematic underestimate of the ICM spectroscopic temperature
relative to its emission-weighed one. We find that these three systematics well
reproduce both the observed bias and the intrinsic dispersions of the Hubble
constant estimated from the Sunyaev-Zel'dovich effect.Comment: 26 pages, 7 figures, accepted for publication in ApJ, Minor change
Galaxy clustering constraints on deviations from Newtonian gravity at cosmological scales II: Perturbative and numerical analyses of power spectrum and bispectrum
We explore observational constraints on possible deviations from Newtonian
gravity by means of large-scale clustering of galaxies. We measure the power
spectrum and the bispectrum of Sloan Digital Sky Survey galaxies and compare
the result with predictions in an empirical model of modified gravity. Our
model assumes an additional Yukawa-like term with two parameters that
characterize the amplitude and the length scale of the modified gravity. The
model predictions are calculated using two methods; the second-order
perturbation theory and direct N-body simulations. These methods allow us to
study non-linear evolution of large-scale structure. Using the simulation
results, we find that perturbation theory provides reliable estimates for the
power spectrum and the bispectrum in the modified Newtonian model. We also
construct mock galaxy catalogues from the simulations, and derive constraints
on the amplitude and the length scale of deviations from Newtonian gravity. The
resulting constraints from power spectrum are consistent with those obtained in
our earlier work, indicating the validity of the previous empirical modeling of
gravitational nonlinearity in the modified Newtonian model. If linear biasing
is adopted, the bispectrum of the SDSS galaxies yields constraints very similar
to those from the power spectrum. If we allow for the nonlinear biasing
instead, we find that the ratio of the quadratic to linear biasing
coefficients, b_2/b_1, should satisfy -0.4 < b_2/b_1<0.3 in the modified
Newtonian model.Comment: 12 pages, 7 figure
Extracting Galaxy Cluster Gas Inhomogeneity from X-ray Surface Brightness: A Statistical Approach and Application to Abell 3667
Our previous analysis indicates that small-scale fluctuations in the
intracluster medium (ICM) from cosmological hydrodynamic simulations follow the
lognormal distribution. In order to test the lognormal nature of the ICM
directly against X-ray observations of galaxy clusters, we develop a method of
extracting statistical information about the three-dimensional properties of
the fluctuations from the two-dimensional X-ray surface brightness.
We first create a set of synthetic clusters with lognormal fluctuations.
Performing mock observations of these synthetic clusters, we find that the
resulting X-ray surface brightness fluctuations also follow the lognormal
distribution fairly well. Systematic analysis of the synthetic clusters
provides an empirical relation between the density fluctuations and the X-ray
surface brightness. We analyze \chandra observations of the galaxy cluster
Abell 3667, and find that its X-ray surface brightness fluctuations follow the
lognormal distribution. While the lognormal model was originally motivated by
cosmological hydrodynamic simulations, this is the first observational
confirmation of the lognormal signature in a real cluster. Finally we check the
synthetic cluster results against clusters from cosmological hydrodynamic
simulations. As a result of the complex structure exhibited by simulated
clusters, the empirical relation shows large scatter. Nevertheless we are able
to reproduce the true value of the fluctuation amplitude of simulated clusters
within a factor of two from their X-ray surface brightness alone.
Our current methodology combined with existing observational data is useful
in describing and inferring the statistical properties of the three dimensional
inhomogeneity in galaxy clusters.Comment: 34 pages, 17 figures, accepted for publication in Ap
Imaging Simulations of the Sunyaev-Zel'dovich Effect for ALMA
We present imaging simulations of the Sunyaev-Zel'dovich effect of galaxy
clusters for the Atacama Large Millimeter/submillimeter Array (ALMA) including
the Atacama Compact Array (ACA). In its most compact configuration at 90GHz,
ALMA will resolve the intracluster medium with an effective angular resolution
of 5 arcsec. It will provide a unique probe of shock fronts and relativistic
electrons produced during cluster mergers at high redshifts, that are hard to
spatially resolve by current and near-future X-ray detectors. Quality of image
reconstruction is poor with the 12m array alone but improved significantly by
adding ACA; expected sensitivity of the 12m array based on the thermal noise is
not valid for the Sunyaev-Zel'dovich effect mapping unless accompanied by an
ACA observation of at least equal duration. The observations above 100 GHz will
become excessively time-consuming owing to the narrower beam size and the
higher system temperature. On the other hand, significant improvement of the
observing efficiency is expected once Band 1 is implemented in the future.Comment: 16 pages, 12 figures. Accepted for publication in PASJ. Note added in
proof is include
Photoprocesses in protoplanetary disks
Circumstellar disks are exposed to intense ultraviolet radiation from the
young star. In the inner disks, the UV radiation can be enhanced by more than
seven orders of magnitude compared with the average interstellar field,
resulting in a physical and chemical structure that resembles that of a dense
photon-dominated region (PDR). This intense UV field affects the chemistry, the
vertical structure of the disk, and the gas temperature, especially in the
surface layers of the disk. The parameters which make disks different from
traditional PDRs are discussed, including the shape of the UV radiation field,
grain growth, the absence of PAHs, the gas/dust ratio and the presence of inner
holes. New photorates for selected species, including simple ions, are
presented. Also, a summary of available cross sections at Lyman alpha 1216 A is
made. Rates are computed for radiation fields with color temperatures ranging
from 4000 to 30,000 K, and can be applied to a wide variety of astrophysical
regions including exo-planetary atmospheres. The importance of photoprocesses
is illustrated for a number of representative disk models, including disk
models with grain growth and settling.Comment: A website with the final published version and all photodissociation
cross sections and rates can be found at
http://www.strw.leidenuniv.nl/~ewine/phot
Nonlinear stochastic biasing from the formation epoch distribution of dark halos
We propose a physical model for nonlinear stochastic biasing of one-point
statistics resulting from the formation epoch distribution of dark halos. In
contrast to previous works on the basis of extensive numerical simulations, our
model provides for the first time an analytic expression for the joint
probability function. Specifically we derive the joint probability function of
halo and mass density contrasts from the extended Press-Schechter theory. Since
this function is derived in the framework of the standard gravitational
instability theory assuming the random-Gaussianity of the primordial density
field alone, we expect that the basic features of the nonlinear and stochastic
biasing predicted from our model are fairly generic. As representative
examples, we compute the various biasing parameters in cold dark matter models
as a function of a redshift and a smoothing length. Our major findings are (1)
the biasing of the variance evolves strongly as redshift while its
scale-dependence is generally weak and a simple linear biasing model provides a
reasonable approximation roughly at R\simgt 2(1+z)\himpc, and (2) the
stochasticity exhibits moderate scale-dependence especially on R\simlt
20\himpc, but is almost independent of . Comparison with the previous
numerical simulations shows good agreement with the above behavior, indicating
that the nonlinear and stochastic nature of the halo biasing is essentially
understood by taking account of the distribution of the halo mass and the
formation epoch.Comment: 34 pages, 11 figures, ApJ (2000) in pres
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