232 research outputs found
Effects of dust scattering albedo and 2175 A bump on ultraviolet colours of normal disc galaxies
We discuss dust properties in the interstellar medium (ISM) of nearby normal
galaxies, by comparing observations in the ultraviolet (UV) with simulations by
a radiative transfer model. The observed UV colours of nearby galaxies show a
reddening relative to their expected intrinsic colours. Some authors argued
that the Milky Way dust cannot reproduce the reddening because of the prominent
2175 \AA absorption bump. Other authors proposed a reduction mechanism of the
bump strength in an {\it attenuation law} derived from the ratio of the
observed intensity to the intrinsic one through an age-selective attenuation
(i.e., young stars are more attenuated selectively). We newly find that the
wavelength dependence of the scattering albedo also has a strong effect on the
UV colour; an albedo decreasing toward shorter wavelengths (except for the
absorption bump range) produces a significant UV reddening. After comparing the
observed UV colours of nearby normal galaxies with those expected from
radiative transfer simulations assumed several dust models, we find two sorts
of dust suitable for these galaxies: (1) dust with a bump and a smaller albedo
for a shorter wavelength (except for the bump range), and (2) dust without any
bump but with an almost constant albedo. If very small carbonaceous grains
responsible for the common unidentified infrared emission band are also the
bump carrier, the former dust is favorable. Finally, we derive mean attenuation
laws of various dust models as a function of the UV attenuation, and derive
some relations between the UV attenuation and observable/theoretical
quantities.Comment: MNRAS in pres
AKARI/IRC Broadband Mid-infrared data as an indicator of Star Formation Rate
AKARI/Infrared Camera (IRC) Point Source Catalog provides a large amount of
flux data at {\it S9W} () and {\it L18W} ()
bands. With the goal of constructing Star-Formation Rate(SFR) calculations
using IRC data, we analyzed an IR selected
GALEX-SDSS-2MASS-AKARI(IRC/Far-Infrared Surveyor) sample of 153 nearby
galaxies. The far-infrared fluxes were obtained from AKARI diffuse maps to
correct the underestimation for extended sources raised by the point-spread
function photometry. SFRs of these galaxies were derived by the spectral energy
distribution fitting program CIGALE. In spite of complicated features contained
in these bands, both the {\it S9W} and {\it L18W} emission correlate with the
SFR of galaxies. The SFR calibrations using {\it S9W} and {\it L18W} are
presented for the first time. These calibrations agree well with previous works
based on Spitzer data within the scatters, and should be applicable to
dust-rich galaxies.Comment: PASJ, in pres
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Latitudinal gradients in butterfly population variability are influenced by landscape heterogeneity
The variability of populations over time is positively associated with their risk of local extinction. Previous work has shown that populations at the high-latitude boundary of speciesâ ranges show higher inter-annual variability, consistent with increased sensitivity and exposure to adverse climatic conditions. However, patterns of population variability at both high- and low-latitude species range boundaries have not yet been concurrently examined. Here, we assess the inter-annual population variability of 28 butterfly species between 1994 and 2009 at 351 and 18 sites in the United Kingdom and Catalonia, Spain, respectively. Local population variability is examined with respect to the position of the speciesâ bioclimatic envelopes (i.e. whether the population falls within areas of the âcoreâ climatic suitability or is a climatically âmarginalâ population), and in relation to local landscape heterogeneity, which may influence these range location â population dynamic relationships. We found that butterfly species consistently show latitudinal gradients in population variability, with increased variability in the more northerly UK. This pattern is even more marked for southerly distributed species with âmarginalâ climatic suitability in the UK but âcoreâ climatic suitability in Catalonia. In addition, local landscape heterogeneity did influence these range location â population dynamic relationships. Habitat heterogeneity was associated with dampened population dynamics, especially for populations in the UK. Our results suggest that promoting habitat heterogeneity may promote the persistence of populations at high-latitude range boundaries, which may potentially aid northwards expansion under climate warming. We did not find evidence that population variability increases towards southern range boundaries. Sample sizes for this region were low, but there was tentative evidence, in line with previous ecological theory, that local landscape heterogeneity may promote persistence in these retracting low-latitude range boundary populations
Star Forming Objects in the Tidal Tails of Compact Groups
A search for star forming objects belonging to tidal tails has been carried
out in a sample of deep Halpha images of 16 compact groups of galaxies. A total
of 36 objects with Halpha luminosity larger than 10^38 erg s-1 have been
detected in five groups. The fraction of the total Halpha luminosity of their
respective parent galaxies shown by the tidal objects is always below 5% except
for the tidal features of HCG95, whose Halpha luminosity amounts to 65% of the
total luminosity. Out of this 36 objects, 9 star forming tidal dwarf galaxy
candidates have been finally identified on the basis of their projected
distances to the nuclei of the parent galaxies and their total Halpha
luminosities. Overall, the observed properties of the candidates resemble those
previously reported for the so-called tidal dwarf galaxies.Comment: 5 gif figures. Accepted for publication in Astrophysical Journa
The Local Universe as Seen in Far-Infrared and in Far-Ultraviolet: A Global Point of View on the Local Recent Star Formation
We select far-infrared (FIR-60 microns) and far-ultraviolet (FUV-1530 A)
samples of nearby galaxies in order to discuss the biases encountered by
monochromatic surveys (FIR or FUV). Very different volumes are sampled by each
selection and much care is taken to apply volume corrections to all the
analyses. The distributions of the bolometric luminosity of young stars are
compared for both samples: they are found to be consistent with each other for
galaxies of intermediate luminosities but some differences are found for high
(>5 10^{10} L_sun) luminosities. The shallowness of the IRAS survey prevents us
from securing comparison at low luminosities (<2 10^9 L_sun). The ratio of the
total infrared (TIR) luminosity to the FUV luminosity is found to increase with
the bolometric luminosity in a similar way for both samples up to 5 10^{10}
L_sun. Brighter galaxies are found to have a different behavior according to
their selection: the L_TIR/L_FUV ratio of the FUV-selected galaxies brighter
than 5 10^{10} L_sun reaches a plateau whereas L_TIR/L_FUV continues to
increase with the luminosity of bright galaxies selected in FIR. The
volume-averaged specific star formation rate (SFR per unit galaxy stellar mass,
SSFR) is found to decrease toward massive galaxies within each selection. The
SSFR is found to be larger than that measured for optical and NIR-selected
sample over the whole mass range for the FIR selection, and for masses larger
than 10^{10} M_sun for the FUV selection. Luminous and massive galaxies
selected in FIR appear as active as galaxies with similar characteristics
detected at z ~ 0.7.Comment: 32 pages, 9 figures, to be published in the Astrophysical Journal
Supplement series dedicated to GALEX result
The GALEX UV luminosity function of the cluster of galaxies Abell 1367
We present the GALEX NUV (2310 A) and FUV (1530 A) galaxy luminosity
functions of the nearby cluster of galaxies A1367 in the magnitude range -20.3<
M_AB < -13.3. The luminosity functions are consistent with previous (~ 2 mag
shallower) estimates based on the FOCA and FAUST experiments, but display a
steeper faint-end slope than the GALEX luminosity function for local field
galaxies. Using spectro-photometric optical data we select out star-forming
systems from quiescent galaxies and study their separate contributions to the
cluster luminosity function. We find that the UV luminosity function of cluster
star-forming galaxies is consistent with the field. The difference between the
cluster and field LF is entirely due to the contribution at low luminosities
(M_AB >-16 mag) of non star-forming, early-type galaxies that are significantly
over dense in clusters.Comment: 4 pages, 4 figures, 1 table. Accepted for publication in
Astrophysical Journal Letter
UV to IR SEDs of UV selected galaxies in the ELAIS fields: evolution of dust attenuation and star formation activity from z=0.7 to z=0.2
We study the ultraviolet to far-infrared (hereafter UV-to-IR) SEDs of a
sample of intermediate redshift (0.2 < z < 0.7) UV-selected galaxies from the
ELAIS-N1 and ELAIS-N2 fields by fitting a multi-wavelength dataset to a library
of GRASIL templates. Star formation related properties of the galaxies are
derived from the library of models by using the Bayesian statistics. We find a
decreasing presence of galaxies with low attenuation and low total luminosity
as redshift decreases, which does not hold for high total luminosity galaxies.
In addition the dust attenuation of low mass galaxies increases as redshift
decreases, and this trend seems to disappear for galaxies with M* > 10^11
M_sun. This result is consistent with a mass dependent evolution of the dust to
gas ratio, which could be driven by a mass dependent efficiency of star
formation in star forming galaxies. The specific star formation rates (SSFR)
decrease with increasing stellar mass at all redshifts, and for a given stellar
mass the SSFR decreases with decreasing redshift. The differences in the slope
of the M*--SSFR relation found between this work and others at similar redshift
could be explained by the adopted selection criteria of the samples which, for
a UV selected sample, favours blue, star forming galaxies.Comment: 21 figures, accepted for publication in Ap
Purification and characterization of a variant of human prothrombin: prothrombin Segovia
A dysprothrombin designated prothrombin Segovia was isolated from the plasma of an individual with normal prothrombin antigen and prothrombin activity lesser than 25% of the control prothrombin activity. Activation by prothrombinase complex showed a lower amidolytic than clotting activity, which suggests a lesser generation of active intermediates than normal prothrombin. When prothrombin Segovia was activated by prothrombinase complex in the absence of factor Va, no thrombin formation was found by functional activities. SDS-PAGE analysis of the molecules derived by activation with prothrombinase complex, Taipan snake venom and Echis carinatus venom showed an accumulation of molecules not cleaved at bond Arg320-Ile321. This was more evident with Echis carinatus venom, which only acts on this bond. Our data suggest that the alteration of prothrombin Segovia impairs the scission of bond Arg320-Ile321
Star formation in the nearby universe: the ultraviolet and infrared points of view
This work presents the main ultraviolet (UV) and far-infrared (FIR)
properties of two samples of nearby galaxies selected from the GALEX (\AA, hereafter NUV) and IRAS (m) surveys respectively.
They are built in order to get detection at both wavelengths for most of the
galaxies. Star formation rate (SFR) estimators based on the UV and FIR
emissions are compared. Systematic differences are found between the SFR
estimators for individual galaxies based on the NUV fluxes corrected for dust
attenuation and on the total IR luminosity. A combined estimator based on NUV
and IR luminosities seems to be the best proxy over the whole range of values
of SFR. Although both samples present similar average values of the birthrate
parameter b, their star-formation-related properties are substantially
different: NUV-selected galaxies tend to show larger values of for lower
masses, SFRs and dust attenuations, supporting previous scenarios for the star
formation history (SFH). Conversely, about 20% of the FIR-selected galaxies
show high values of , SFR and NUV attenuation. These galaxies, most of them
being LIRGs and ULIRGs, break down the downsizing picture for the SFH, however
their relative contribution per unit volume is small in the local Universe.
Finally, the cosmic SFR density of the local Universe is estimated in a
consistent way from the NUV and IR luminosities.Comment: 43 pages, 13 figures, accepted for publication in Astrophysical
Journal Supplement Serie
Obscured phylogeny and possible recombinational dormancy in Escherichia coli
<p>Abstract</p> <p>Background</p> <p><it>Escherichia coli </it>is one of the best studied organisms in all of biology, but its phylogenetic structure has been difficult to resolve with current data and analytical techniques. We analyzed single nucleotide polymorphisms in chromosomes of representative strains to reconstruct the topology of its emergence.</p> <p>Results</p> <p>The phylogeny of <it>E. coli </it>varies according to the segment of chromosome analyzed. Recombination between extant <it>E. coli </it>groups is largely limited to only three intergroup pairings.</p> <p>Conclusions</p> <p>Segment-dependent phylogenies most likely are legacies of a complex recombination history. However, <it>E. coli </it>are now in an epoch in which they no longer broadly share DNA. Using the definition of species as organisms that freely exchange genetic material, this recombinational dormancy could reflect either the end of <it>E. coli </it>as a species, or herald the coalescence of <it>E. coli </it>groups into new species.</p
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