1,794 research outputs found
The PdBI Arcsecond Whirlpool Survey (PAWS). I. A Cloud-Scale/Multi-Wavelength View of the Interstellar Medium in a Grand-Design Spiral Galaxy
The PdBI (Plateau de Bure Interferometer) Arcsecond Whirlpool Survey (PAWS)
has mapped the molecular gas in the central ~9kpc of M51 in its 12CO(1-0) line
emission at cloud-scale resolution of ~40pc using both IRAM telescopes. We
utilize this dataset to quantitatively characterize the relation of molecular
gas (or CO emission) to other tracers of the interstellar medium (ISM), star
formation and stellar populations of varying ages. Using 2-dimensional maps, a
polar cross-correlation technique and pixel-by-pixel diagrams, we find: (a)
that (as expected) the distribution of the molecular gas can be linked to
different components of the gravitational potential, (b) evidence for a
physical link between CO line emission and radio continuum that seems not to be
caused by massive stars, but rather depend on the gas density, (c) a close
spatial relation between the PAH and molecular gas emission, but no predictive
power of PAH emission for the molecular gas mass,(d) that the I-H color map is
an excellent predictor of the distribution (and to a lesser degree the
brightness) of CO emission, and (e) that the impact of massive (UV-intense)
young star-forming regions on the bulk of the molecular gas in central ~9kpc
can not be significant due to a complex spatial relation between molecular gas
and star-forming regions that ranges from co-spatial to spatially offset to
absent. The last point, in particular, highlights the importance of galactic
environment -- and thus the underlying gravitational potential -- for the
distribution of molecular gas and star formation.Comment: 52 pages, 14 figures, 2 tables, (several minor typos corrected)
accepted by ApJ, high resolution version available, see
http://www.mpia.de/PAWS/pub/paws_schinnerer.pdf ; for more information on
PAWS, further papers and the data, see http://www.mpia.de/PAW
Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
We demonstrate the usability of mm-wavelength imaging data obtained from the
APEX-SZ bolometer array to derive the radial temperature profile of the hot
intra-cluster gas out to radius r_500 and beyond. The goal is to study the
physical properties of the intra-cluster gas by using a non-parametric
de-projection method that is, aside from the assumption of spherical symmetry,
free from modeling bias. We use publicly available X-ray imaging data from the
XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data
from the APEX-SZ experiment at 150 GHz to de-project the density and
temperature profiles for the relaxed cluster Abell 2204. We derive the gas
density, temperature and entropy profiles assuming spherical symmetry, and
obtain the total mass profile under the assumption of hydrostatic equilibrium.
For comparison with X-ray spectroscopic temperature models, a re-analysis of
the recent Chandra observation is done with the latest calibration updates.
Using the non-parametric modeling we demonstrate a decrease of gas temperature
in the cluster outskirts, and also measure the gas entropy profile. These
results are obtained for the first time independently of X-ray spectroscopy,
using SZE and X-ray imaging data. The contribution of the SZE systematic
uncertainties in measuring T_e at large radii is shown to be small compared to
the Chandra systematic spectroscopic errors. The upper limit on M_200 derived
from the non-parametric method is consistent with the NFW model prediction from
weak lensing analysis.Comment: Replaced with the published version; A&A 519, A29 (2010
Observational Evidence Against Long-Lived Spiral Arms in Galaxies
We test whether the spiral patterns apparent in many large disk galaxies
should be thought of as dynamical features that are stationary in a co-rotating
frame for > t_{dyn}, as implied by the density wave approach for explaining
spiral arms. If such spiral arms have enhanced star formation (SF),
observational tracers for different stages of the SF sequence should show a
spatial ordering, from up-stream to downstream in the corotating frame: dense
HI, CO, tracing molecular hydrogen gas, 24 micron emission tracing enshrouded
SF and UV emission tracing unobscured young stars. We argue that such a spatial
ordering should be reflected in the angular cross-correlation (CC, in polar
coordinates) using all azimuthal positions among pairs of these tracers; the
peak of the CC should be offset from zero, in different directions inside and
outside the corotation radius. Recent spiral SF simulations by Dobbs & Pringle,
show explicitly that for the case of a stationary spiral arm potential such
angular offsets between gas and young stars of differing ages should be
observable as cross-correlation offsets. We calculate the angular
cross-correlations for different observational SF sequence tracers in 12 nearby
spiral galaxies, drawing on a data set with high quality maps of the neutral
gas HI, THINGS), molecular gas (CO, HERACLES) along with 24 micron emission
(Spitzer, SINGS); we include FUV images (GALEX) and 3.6 m emission
(Spitzer, IRAC) for some galaxies, tracing aging stars and longer timescales.
In none of the resulting tracer cross-correlations for this sample do we find
systematic angular offsets, which would be expected for a stationary dynamical
spiral pattern of well-defined pattern speed. This result indicates that spiral
density waves in their simplest form are not an important aspect of explaining
spirals in large disk galaxies.Comment: 13 pages, 16 figure
Elastic Constants of Quantum Solids by Path Integral Simulations
Two methods are proposed to evaluate the second-order elastic constants of
quantum mechanically treated solids. One method is based on path-integral
simulations in the (NVT) ensemble using an estimator for elastic constants. The
other method is based on simulations in the (NpT) ensemble exploiting the
relationship between strain fluctuations and elastic constants. The strengths
and weaknesses of the methods are discussed thoroughly. We show how one can
reduce statistical and systematic errors associated with so-called primitive
estimators. The methods are then applied to solid argon at atmospheric
pressures and solid helium 3 (hcp, fcc, and bcc) under varying pressures. Good
agreement with available experimental data on elastic constants is found for
helium 3. Predictions are made for the thermal expectation value of the kinetic
energy of solid helium 3.Comment: 9 pages doublecolumn, 6 figures, submitted to PR
The QCD/SM Working Group: Summary Report
This Report documents the results obtained by the Working Group on Quantum
ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV
Colliders'', Les Houches, France, 21 May - 1 June 2001. The account of
uncertainties in Parton Distribution Functions is reviewed. Progresses in the
description of multiparton final states at Next-to-Leading Order and the
extension of calculations for precision QCD observables beyond this order are
summarized. Various issues concerning the relevance of resummation for
observables at TeV colliders is examined. Improvements to algorithms of jet
reconstruction are discussed and predictions for diphoton and photon pi-zero
production at the LHC are made for kinematic variables of interest regarding
searches for a Higgs boson decaying into two photons. Finally, several
improvements implemented in Monte-Carlo event generators are documented
- …