11,195 research outputs found
Physical Properties of Galactic Planck Cold Cores revealed by the Hi-GAL survey
Previous studies of the initial conditions of massive star formation have
mainly targeted Infrared-Dark Clouds (IRDCs) toward the inner Galaxy. This is
due to the fact that IRDCs were first detected in absorption against the bright
mid-IR background, requiring a favourable location to be observed. By
selection, IRDCs represent only a fraction of the Galactic clouds capable of
forming massive stars and star clusters. Due to their low dust temperatures,
IRDCs are bright in the far-IR and millimeter and thus, observations at these
wavelengths have the potential to provide a complete sample of star-forming
massive clouds across the Galaxy. Our aim is to identify the clouds at the
initial conditions of massive star formation across the Galaxy and compare
their physical properties as a function of their Galactic location. We have
examined the physical properties of a homogeneous galactic cold core sample
obtained with the Planck satellite across the Galactic Plane. With the use of
Herschel Hi-GAL observations, we have characterized the internal structure of
them. By using background-subtracted Herschel images, we have derived the H2
column density and dust temperature maps for 48 Planck clumps. Their basic
physical parameters have been calculated and analyzed as a function of location
within the Galaxy. These properties have also been compared with the empirical
relation for massive star formation derived by Kauffmann & Pillai (2010). Most
of the Planck clumps contain signs of star formation. About 25% of them are
massive enough to form high mass stars. Planck clumps toward the Galactic
center region show higher peak column densities and higher average dust
temperatures than those of the clumps in the outer Galaxy. Although we only
have seven clumps without associated YSOs, the Hi-GAL data show no apparent
differences in the properties of Planck cold clumps with and without star
formation.Comment: 22 pages, 11 figures, accepted for publication in A&
An effective theory of accelerated expansion
We work out an effective theory of accelerated expansion to describe general
phenomena of inflation and acceleration (dark energy) in the Universe. Our aim
is to determine from theoretical grounds, in a physically-motivated and model
independent way, which and how many (free) parameters are needed to broadly
capture the physics of a theory describing cosmic acceleration. Our goal is to
make as much as possible transparent the physical interpretation of the
parameters describing the expansion. We show that, at leading order, there are
five independent parameters, of which one can be constrained via general
relativity tests. The other four parameters need to be determined by observing
and measuring the cosmic expansion rate only, H(z). Therefore we suggest that
future cosmology surveys focus on obtaining an accurate as possible measurement
of to constrain the nature of accelerated expansion (dark energy and/or
inflation).Comment: In press; minor changes, results unchange
Factorization and Malleability of RSA Moduli, and Counting Points on Elliptic Curves Modulo N
In this paper we address two different problems related with the factorization of an RSA (Rivest-Shamir-Adleman cryptosystem) modulus N. First we show that factoring is equivalent, in deterministic polynomial time, to counting points on a pair of twisted Elliptic curves modulo N. The second problem is related with malleability. This notion was introduced in 2006 by Pailler and Villar, and deals with the question of whether or not the factorization of a given number N becomes substantially easier when knowing the factorization of another one N′ relatively prime to N. Despite the efforts done up to now, a complete answer to this question was unknown. Here we settle the problem affirmatively. To construct a particular N′ that helps the factorization of N, we use the number of points of a single elliptic curve modulo N. Coppersmith's algorithm allows us to go from the factors of N′ to the factors of N in polynomial time
Cosmological Signatures of Interacting Neutrinos
We investigate signatures of neutrino scattering in the Cosmic Microwave
Background (CMB) and matter power spectra, and the extent to which present
cosmological data can distinguish between a free streaming or tightly coupled
fluid of neutrinos. If neutrinos have strong non-standard interactions, for
example, through the coupling of neutrinos to a light boson, they may be kept
in equilibrium until late times. We show how the power spectra for these models
differ from more conventional neutrino scenarios, and use CMB and large scale
structure data to constrain these models. CMB polarization data improves the
constraints on the number of massless neutrinos, while the Lyman--
power spectrum improves the limits on the neutrino mass. Neutrino mass limits
depend strongly on whether some or all of the neutrino species interact and
annihilate. The present data can accommodate a number of tightly-coupled
relativistic degrees of freedom, and none of the interacting-neutrino scenarios
considered are ruled out by current data -- although considerations regarding
the age of the Universe disfavor a model with three annihilating neutrinos with
very large neutrino masses.Comment: 17 pages, 14 figures, minor changes and references added, published
in Phys. Rev.
HE 0435-1223: a wide separation quadruple QSO and gravitational lens
We report the discovery of a new gravitationally lensed QSO, at a redshift z
= 1.689, with four QSO components in a cross-shaped arrangement around a bright
galaxy. The maximum separation between images is 2.6 arcsec, enabling a
reliable decomposition of the system. Three of the QSO components have g =
19.6, while component A is about 0.6 mag brighter. The four components have
nearly identical colours, suggesting little if any dust extinction in the
foreground galaxy. The lensing galaxy is prominent in the i band, weaker in r
and not detected in g. Its spatial profile is that of an elliptical galaxy with
a scale length of 12 kpc. Combining the measured colours and a mass
model for the lens, we estimate a most likely redshift range of 0.3 < z < 0.4.
Predicted time delays between the components are \la 10 days. The QSO shows
evidence for variability, with total g band magnitudes of 17.89 and 17.71 for
two epochs separated by months. However, the relative fluxes of the
components did not change, indicating that the variations are intrinsic to the
QSO rather than induced by microlensing.Comment: 7 pages, submitted to Astronomy and Astrophysic
BL Lacertae identifications in a ROSAT-selected sample of Fermi unidentified objects
The optical spectroscopic followup of 27 sources belonging to a sample of 30
high-energy objects selected by positionally cross correlating the first
Fermi/LAT Catalog and the ROSAT All-Sky Survey Bright Source Catalog is
presented here. It has been found or confirmed that 25 of them are BL Lacertae
objects (BL Lacs), while the remaining two are Galactic cataclysmic variables
(CVs). This strongly suggests that the sources in the first group are
responsible for the GeV emission detected with Fermi, while the two CVs most
likely represent spurious associations. We thus find an 80% a posteriori
probability that the sources selected by matching GeV and X-ray catalogs belong
to the BL Lac class. We also show suggestions that the BL Lacs selected with
this approach are probably high-synchrotron-peaked sources and in turn good
candidates for the detection of ultra-high-energy (TeV) photons from them.Comment: 16 pages, 9 figures, 4 tables, one appendix, accepted for publication
on A&A, main journal. Tables 1-3 and Figures 2-6 will only be published in
the electronic edition of the journa
The Gaia-ESO Survey: dynamics of ionized and neutral gas in the Lagoon nebula (M8)
We present a spectroscopic study of the dynamics of the ionized and neutral
gas throughout the Lagoon nebula (M8), using VLT/FLAMES data from the Gaia-ESO
Survey. We explore the connections between the nebular gas and the stellar
population of the associated star cluster NGC6530. We characterize through
spectral fitting emission lines of H-alpha, [N II] and [S II] doublets, [O
III], and absorption lines of sodium D doublet, using data from the
FLAMES/Giraffe and UVES spectrographs, on more than 1000 sightlines towards the
entire face of the Lagoon nebula. Gas temperatures are derived from line-width
comparisons, densities from the [S II] doublet ratio, and ionization parameter
from H-alpha/[N II] ratio. Although doubly-peaked emission profiles are rarely
found, line asymmetries often imply multiple velocity components along the line
of sight. This is especially true for the sodium absorption, and for the [O
III] lines. Spatial maps for density and ionization are derived, and compared
to other known properties of the nebula and of its massive stars 9 Sgr,
Herschel 36 and HD 165052 which are confirmed to provide most of the ionizing
flux. The detailed velocity fields across the nebula show several expanding
shells, related to the cluster NGC6530, the O stars 9 Sgr and Herschel 36, and
the massive protostar M8East-IR. The origins of kinematical expansion and
ionization of the NGC6530 shell appear to be different. We are able to put
constrains on the line-of-sight (relative or absolute) distances between some
of these objects and the molecular cloud. The large obscuring band running
through the middle of the nebula is being compressed by both sides, which might
explain its enhanced density. We also find an unexplained large-scale velocity
gradient across the entire nebula. At larger distances, the transition from
ionized to neutral gas is studied using the sodium lines.Comment: 26 pages, 31 figures, accepted on Astronomy and Astrophysics journa
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