1,912 research outputs found
Pressure dependence of phase transitions in the quasi one-dimensional metal-insulator transition system beta-Na1/3V2O5
The pressure dependence of phase transitions in the quasi one-dimensional
vanadium oxide -NaVO has been studied by magnetic
susceptibility and electrical resistivity measurements. The pressure dependence
of the various transition temperatures is quite differently. The transition at
T=240 K, previously reported and attributed to ordering on Na sites, and a
second transition at K, reported here for the first time and
attributed to a further increase of order on Na sites, are almost independent
of pressure. On the other hand, the metal-insulator (MI) transition at
K shifts to lower temperatures, while the magnetic transition at
K shifts to higher temperatures with increasing pressure. We discuss
the different pressure dependencies of and in terms of
increasing interchain coupling and the MI transition to be of Peierls type.Comment: 5 pages, 5 figure
Post-Impact Thermal Evolution of Porous Planetesimals
Impacts between planetesimals have largely been ruled out as a heat source in
the early Solar System, by calculations that show them to be an inefficient
heat source and unlikely to cause global heating. However, the long-term,
localized thermal effects of impacts on planetesimals have never been fully
quantified. Here, we simulate a range of impact scenarios between planetesimals
to determine the post-impact thermal histories of the parent bodies, and hence
the importance of impact heating in the thermal evolution of planetesimals. We
find on a local scale that heating material to petrologic type 6 is achievable
for a range of impact velocities and initial porosities, and impact melting is
possible in porous material at a velocity of > 4 km/s. Burial of heated
impactor material beneath the impact crater is common, insulating that material
and allowing the parent body to retain the heat for extended periods (~
millions of years). Cooling rates at 773 K are typically 1 - 1000 K/Ma,
matching a wide range of measurements of metallographic cooling rates from
chondritic materials. While the heating presented here is localized to the
impact site, multiple impacts over the lifetime of a parent body are likely to
have occurred. Moreover, as most meteorite samples are on the centimeter to
meter scale, the localized effects of impact heating cannot be ignored.Comment: 38 pages, 9 figures, Revised for Geochimica et Cosmochimica Acta
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The relation of cosmic environment and morphology with the star formation and stellar populations of AGN and non-AGN galaxies
In this work, we study the relation of cosmic environment and morphology with
the star-formation (SF) and the stellar population of galaxies. Most
importantly, we examine if this relation differs for systems with active and
non-active supermassive black holes. For that purpose, we use 551 X-ray
detected active galactic nuclei (AGN) and 16,917 non-AGN galaxies in the
COSMOS-Legacy survey, for which the surface-density field measurements are
available. The sources lie at redshift of , probe X-ray
luminosities of and have stellar
masses, . Our results show that isolated AGN
(field) have lower SFR compared to non AGN, at all L spanned by our sample.
However, in denser environments (filaments, clusters), moderate L AGN () and non-AGN galaxies have similar SFR.
We, also, examine the stellar populations and the morphology of the sources in
different cosmic fields. For the same morphological type, non-AGN galaxies tend
to have older stellar populations and are less likely to have undergone a
recent burst in denser environments compared to their field counterparts. The
differences in the stellar populations with the density field are, mainly,
driven by quiescent systems. Moreover, low L AGN present negligible
variations of their stellar populations, in all cosmic environments, whereas
moderate L AGN have, on average, younger stellar populations and are more
likely to have undergone a recent burst, in high density fields. Finally, in
the case of non-AGN galaxies, the fraction of bulge-dominated (BD) systems
increases with the density field, while BD AGN are scarce in denser
environments. Our results are consistent with a scenario in which a common
mechanism, such as mergers, triggers both the SF and the AGN activity.Comment: Accepted for publication in A&A. 10 pages, 5 figures, 3 table
The selective effect of environment on the atomic and molecular gas-to-dust ratio of nearby galaxies in the Herschel Reference Survey
We combine dust, atomic (HI) and molecular (H) hydrogen mass
measurements for 176 galaxies in the Herschel Reference Survey to investigate
the effect of environment on the gas-to-dust mass ()
ratio of nearby galaxies. We find that, at fixed stellar mass, the average
ratio varies by no more than a factor of 2
when moving from field to cluster galaxies, with Virgo galaxies being slightly
more dust rich (per unit of gas) than isolated systems. Remarkably, once the
molecular and atomic hydrogen phases are investigated separately, we find that
\hi-deficient galaxies have at the same time lower
ratio but higher ratio than \hi-normal systems. In
other words, they are poorer in atomic but richer in molecular hydrogen if
normalized to their dust content. By comparing our findings with the
predictions of theoretical models, we show that the opposite behavior observed
in the and ratios is
fully consistent with outside-in stripping of the interstellar medium (ISM),
and is simply a consequence of the different distribution of dust, \hi\ and
H across the disk. Our results demonstrate that the small environmental
variations in the total ratio, as well as in the
gas-phase metallicity, do not automatically imply that environmental mechanisms
are not able to affect the dust and metal content of the ISM in galaxies.Comment: 11 pages, 6 figures, 2 tables. Accepted for publication in MNRA
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Earth’s carbon deficit caused by early loss through irreversible sublimation
Carbon is an essential element for life, but its behavior during Earth’s accretion is not well understood. Carbonaceous grains in meteoritic and cometary materials suggest that irreversible sublimation, and not condensation, governs carbon acquisition by terrestrial worlds. Through astronomical observations and modeling, we show that the sublimation front of carbon carriers in the solar nebula, or the soot line, moved inward quickly so that carbon-rich ingredients would be available for accretion at 1 astronomical unit after the first million years. On the other hand, geological constraints firmly establish a severe carbon deficit in Earth, requiring the destruction of inherited carbonaceous organics in the majority of its building blocks. The carbon-poor nature of Earth thus implies carbon loss in its precursor material through sublimation within the first million years
The bolometric and UV attenuation in normal spiral galaxies of the Herschel Reference Survey
The dust in nearby galaxies absorbs a fraction of the
UV-optical-near-infrared radiation produced by stars. This energy is
consequently re-emitted in the infrared. We investigate the portion of the
stellar radiation absorbed by spiral galaxies from the HRS by modelling their
UV-to-submillimetre spectral energy distributions. Our models provide an
attenuated and intrinsic SED from which we find that on average 32 % of all
starlight is absorbed by dust. We define the UV heating fraction as the
percentage of dust luminosity that comes from absorbed UV photons and find that
this is 56 %, on average. This percentage varies with morphological type, with
later types having significantly higher UV heating fractions. We find a strong
correlation between the UV heating fraction and specific star formation rate
and provide a power-law fit. Our models allow us to revisit the IRX-AFUV
relations, and derive these quantities directly within a self-consistent
framework. We calibrate this relation for different bins of NUV-r colour and
provide simple relations to relate these parameters. We investigated the
robustness of our method and we conclude that the derived parameters are
reliable within the uncertainties which are inherent to the adopted SED model.
This calls for a deeper investigation on how well extinction and attenuation
can be determined through panchromatic SED modelling.Comment: 14 pages, 7 figures. Accepted for publication in Astronomy &
Astrophysic
The slippery slope of dust attenuation curves: Correlation of dust attenuation laws with star-to-dust compactness up to z = 4
Aims. We investigate dust attenuation of 122 heavily dust-obscured galaxies
detected with the Atacama Large Millimeter Array (ALMA) and Herschel in the
COSMOS field. We search for correlations between dust attenuation recipes and
the variation of physical parameters, mainly the effective radii of galaxies,
their star formation rates (SFR), and stellar masses, and aim to understand
which of the commonly used laws best describes dust attenuation in dusty
star-forming galaxies at high redshift. Methods. We make use of the extensive
photometric coverage of the COSMOS data combined with highly-resolved dust
continuum maps from ALMA. We use CIGALE to estimate various physical properties
of these dusty objects, mainly their SFR, their stellar masses and their
attenuation. We infer galaxy effective radii (Re) using GALFIT in the Y band of
HSC and ALMA continuum maps. We use these radii to investigate the relative
compactness of the dust continuum and the extension of the rest-frame
UV/optical Re(y)/Re(ALMA). Results. We find that the physical parameters
calculated from our models strongly depend on the assumption of dust
attenuation curve. As expected, the most impacted parameter is the stellar
mass, which leads to a change in the "starburstiness" of the objects. We find
that taking into account the relative compactness of star-to-dust emission
prior to SED fitting is crucial, especially when studying dust attenuation of
dusty star-forming galaxies. Shallower attenuation curves did not show a clear
preference of compactness with attenuation, while the Calzetti attenuation
curve preferred comparable spatial extent of unattenuated stellar light and
dust emission. The evolution of the Re(UV)/Re(ALMA) ratio with redshift peeks
around the cosmic noon in our sample of DSFGs, showing that this compactness is
correlated with the cosmic SFR density of these dusty sources.Comment: 18 pages, 13 figures, accepted for publication in A&A. Abstract
abridged for arXiv submissio
Towards understanding the relation between the gas and the attenuation in galaxies at kpc scales
[abridged]
Aims. The aim of the present paper is to provide new and more detailed
relations at the kpc scale between the gas surface density and the face-on
optical depth directly calibrated on galaxies, in order to compute the
attenuation not only for semi-analytic models but also observationally as new
and upcoming radio observatories are able to trace gas ever farther in the
Universe.
Methods. We have selected a sample of 4 nearby resolved galaxies and a sample
of 27 unresolved galaxies from the Herschel Reference Survey and the Very
Nearby Galaxies Survey, for which we have a large set of multi-wavelength data
from the FUV to the FIR including metallicity gradients for resolved galaxies,
along with radio HI and CO observations. For each pixel in resolved galaxies
and for each galaxy in the unresolved sample, we compute the face-on optical
depth from the attenuation determined with the CIGALE SED fitting code and an
assumed geometry. We determine the gas surface density from HI and CO
observations with a metallicity-dependent XCO factor.
Results. We provide new, simple to use, relations to determine the face-on
optical depth from the gas surface density, taking the metallicity into
account, which proves to be crucial for a proper estimate. The method used to
determine the gas surface density or the face-on optical depth has little
impact on the relations except for galaxies that have an inclination over 50d.
Finally, we provide detailed instructions on how to compute the attenuation
practically from the gas surface density taking into account possible
information on the metallicity.
Conclusions. Examination of the influence of these new relations on simulated
FUV and IR luminosity functions shows a clear impact compared to older oft-used
relations, which in turn could affect the conclusions drawn from studies based
on large scale cosmological simulations.Comment: 24 pages, 21 figures, accepted for publication in A&
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