681 research outputs found
Evolution of column density distributions within Orion~A
We compare the structure of star-forming molecular clouds in different
regions of Orion A to determine how the column density probability distribution
function (N-PDF) varies with environmental conditions such as the fraction of
young protostars. A correlation between the N-PDF slope and Class 0 protostar
fraction has been previously observed in a low-mass star-formation region
(Perseus) by Sadavoy; here we test if a similar correlation is observed in a
high-mass star-forming region. We use Herschel data to derive a column density
map of Orion A. We use the Herschel Orion Protostar Survey catalog for accurate
identification and classification of the Orion A young stellar object (YSO)
content, including the short-lived Class 0 protostars (with a 0.14 Myr
lifetime). We divide Orion A into eight independent 13.5 pc regions; in
each region we fit the N-PDF distribution with a power-law, and we measure the
fraction of Class 0 protostars. We use a maximum likelihood method to measure
the N-PDF power-law index without binning. We find that the Class 0 fraction is
higher in regions with flatter column density distributions. We test the
effects of incompleteness, YSO misclassification, resolution, and pixel-scale.
We show that these effects cannot account for the observed trend. Our
observations demonstrate an association between the slope of the power-law
N-PDF and the Class 0 fractions within Orion A. Various interpretations are
discussed including timescales based on the Class 0 protostar fraction assuming
a constant star-formation rate. The observed relation suggests that the N-PDF
can be related to an "evolutionary state" of the gas. If universal, such a
relation permits an evaluation of the evolutionary state from the N-PDF
power-law index at much greater distances than those accesible with protostar
counts. (abridged)Comment: A&A Letter, accepte
Astrophysical and Cosmological Constraints on Neutrino masses
We review some astrophysical and cosmological properties and implications of
neutrino masses and mixing angles. These include: constraints based on the
relic density of neutrinos, limits on their masses and lifetimes, BBN limits on
mass parameters, neutrinos and supernovae, and neutrinos and high energy cosmic
rays.Comment: 23 pages, latex, 9 eps figures, added reference
Electroweak Baryogenesis in a Supersymmetric U(1)' Model
We construct an anomaly free supersymmetric U(1)' model with a secluded
U(1)'-breaking sector. We study the one-loop effective potential at finite
temperature, and show that there exists a strong enough first order electroweak
phase transition for electroweak baryogenesis (EWBG) because of the large
trilinear term in the tree-level Higgs potential. Unlike in
the MSSM, the lightest stop can be very heavy. We consider the non-local EWBG
mechanism in the thin wall regime, and find that within uncertainties the
observed baryon number can be generated from the lepton contribution,
with the secluded sector playing an essential role. The chargino and neutralino
contributions and the implications for the Z' mass and electric dipole moments
are briefly discussed.Comment: RevTex, 4 pages, 2 figures, references added, version to appear in
PR
The interior spacetimes of stars in Palatini f(R) gravity
We study the interior spacetimes of stars in the Palatini formalism of f(R)
gravity and derive a generalized Tolman-Oppenheimer-Volkoff and mass equation
for a static, spherically symmetric star. We show that matching the interior
solution with the exterior Schwarzschild-De Sitter solution in general gives a
relation between the gravitational mass and the density profile of a star,
which is different from the one in General Relativity. These modifications
become neglible in models for which is a decreasing function of R however. As a result, both Solar System
constraints and stellar dynamics are perfectly consistent with .Comment: Published version, 6 pages, 1 figur
High-fidelity view of the structure and fragmentation of the high-mass, filamentary IRDC G11.11-0.12
Star formation in molecular clouds is intimately linked to their internal
mass distribution. We present an unprecedentedly detailed analysis of the
column density structure of a high-mass, filamentary molecular cloud, namely
IRDC G11.11-0.12 (G11). We use two novel column density mapping techniques:
high-resolution (FWHM=2", or ~0.035 pc) dust extinction mapping in near- and
mid-infrared, and dust emission mapping with the Herschel satellite. These two
completely independent techniques yield a strikingly good agreement,
highlighting their complementarity and robustness. We first analyze the dense
gas mass fraction and linear mass density of G11. We show that G11 has a top
heavy mass distribution and has a linear mass density (M_l ~ 600 Msun pc^{-1})
that greatly exceeds the critical value of a self-gravitating, non-turbulent
cylinder. These properties make G11 analogous to the Orion A cloud, despite its
low star-forming activity. This suggests that the amount of dense gas in
molecular clouds is more closely connected to environmental parameters or
global processes than to the star-forming efficiency of the cloud. We then
examine hierarchical fragmentation in G11 over a wide range of size-scales and
densities. We show that at scales 0.5 pc > l > 8 pc, the fragmentation of G11
is in agreement with that of a self-gravitating cylinder. At scales smaller
than l < 0.5 pc, the results agree better with spherical Jeans' fragmentation.
One possible explanation for the change in fragmentation characteristics is the
size-scale-dependent collapse time-scale that results from the finite size of
real molecular clouds: at scales l < 0.5 pc, fragmentation becomes sufficiently
rapid to be unaffected by global instabilities.Comment: 8 pages, 8 figures, accepted to A&
The Musca cloud: A 6 pc-long velocity-coherent, sonic filament
Filaments play a central role in the molecular clouds' evolution, but their
internal dynamical properties remain poorly characterized. To further explore
the physical state of these structures, we have investigated the kinematic
properties of the Musca cloud. We have sampled the main axis of this
filamentary cloud in CO and CO (2--1) lines using APEX
observations. The different line profiles in Musca shows that this cloud
presents a continuous and quiescent velocity field along its 6.5 pc of
length. With an internal gas kinematics dominated by thermal motions (i.e.,
) and large-scale velocity gradients, these results
reveal Musca as the longest velocity-coherent, sonic-like object identified so
far in the ISM. The transonic properties of Musca present a clear departure
from the predicted supersonic velocity dispersions expected in the Larson's
velocity dispersion-size relationship, and constitute the first observational
evidence of a filament fully decoupled from the turbulent regime over
multi-parsec scales.Comment: 12 pages, 6 figures; Accepted for publication in A&
Relationship between the column density distribution and evolutionary class of molecular clouds as viewed by ATLASGAL
We present the first study of the relationship between the column density
distribution of molecular clouds within nearby Galactic spiral arms and their
evolutionary status as measured from their stellar content. We analyze a sample
of 195 molecular clouds located at distances below 5.5 kpc, identified from the
ATLASGAL 870 micron data. We define three evolutionary classes within this
sample: starless clumps, star-forming clouds with associated young stellar
objects, and clouds associated with HII regions. We find that the N(H2)
probability density functions (N-PDFs) of these three classes of objects are
clearly different: the N-PDFs of starless clumps are narrowest and close to
log-normal in shape, while star-forming clouds and HII regions exhibit a
power-law shape over a wide range of column densities and log-normal-like
components only at low column densities. We use the N-PDFs to estimate the
evolutionary time-scales of the three classes of objects based on a simple
analytic model from literature. Finally, we show that the integral of the
N-PDFs, the dense gas mass fraction, depends on the total mass of the regions
as measured by ATLASGAL: more massive clouds contain greater relative amounts
of dense gas across all evolutionary classes.Comment: Accepted for publication in A&A (25th June 15) 23 pages, 12 figures.
Additional appendix figures will appear in the journal version of this pape
Conformal Window of Gauge Theories with Four-Fermion Interactions and Ideal Walking
We investigate the effects of four-fermion interactions on the phase diagram
of strongly interacting theories for any representation as function of the
number of colors and flavors. We show that the conformal window, for any
representation, shrinks with respect to the case in which the four-fermion
interactions are neglected. The anomalous dimension of the mass increases
beyond the unity value at the lower boundary of the new conformal window. We
plot the new phase diagram which can be used, together with the information
about the anomalous dimension, to propose ideal models of walking technicolor.
We discover that when the extended technicolor sector, responsible for giving
masses to the standard model fermions, is sufficiently strongly coupled the
technicolor theory, in isolation, must have an infrared fixed point for the
full model to be phenomenologically viable. Using the new phase diagram we show
that the simplest one family and minimal walking technicolor models are the
archetypes of models of dynamical electroweak symmetry breaking. Our
predictions can be verified via first principle lattice simulations.Comment: RevTeX4, 22 pages, 16 figure
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