1,156 research outputs found
Interface Transparency of Nb/Pd Layered Systems
We have investigated, in the framework of proximity effect theory, the
interface transparency T of superconducting/normal metal layered systems which
consist of Nb and high paramagnetic Pd deposited by dc magnetron sputtering.
The obtained T value is relatively high, as expected by theoretical arguments.
This leads to a large value of the ratio although Pd does
not exhibit any magnetic ordering.Comment: To be published on Eur. Phys. J.
A Multiwavelength Study of a Sample of 70 μm Selected Galaxies in the COSMOS Field. II. The Role of Mergers in Galaxy Evolution
We analyze the morphological properties of a large sample of 1503 70 μm selected galaxies in the COSMOS field spanning the redshift range 0.01 10^(12) L_☉) being up to ~50%. We also find that the fraction of spirals drops dramatically with L_(IR). Minor mergers likely play a role in boosting the infrared luminosity for sources with low luminosities (L_(IR) 1 being difficult to classify and subject to the effects of bandpass shifting; therefore, these numbers can only be considered lower limits. At z 1, the fraction of major mergers is lower, but is at least 30%-40% for ULIRGs. In a comparison of our visual classifications with several automated classification techniques we find general agreement; however, the fraction of identified mergers is underestimated due to automated classification methods being sensitive to only certain timescales of a major merger. Although the general morphological trends agree with what has been observed for local (U)LIRGs, the fraction of major mergers is slightly lower than seen locally. This is in part due to the difficulty of identifying merger signatures at high redshift. The distribution of the U – V color of the galaxies in our sample peaks in the green valley (= 1.1) with a large spread at bluer and redder colors and with the major mergers peaking more strongly in the green valley than the rest of the morphological classes. We argue that, given the number of major gas-rich mergers observed and the relatively short timescale that they would be observable in the (U)LIRG phase, it is plausible for the observed red sequence of massive ellipticals (<10^(12) M_☉) to have been formed entirely by gas-rich major mergers
X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue
AGN are known to have complex X-ray spectra that depend on both the
properties of the accreting SMBH (e.g. mass, accretion rate) and the
distribution of obscuring material in its vicinity ("torus"). Often however,
simple and even unphysical models are adopted to represent the X-ray spectra of
AGN. In the case of blank field surveys in particular, this should have an
impact on e.g. the determination of the AGN luminosity function, the inferred
accretion history of the Universe and also on our understanding of the relation
between AGN and their host galaxies. We develop a Bayesian framework for model
comparison and parameter estimation of X-ray spectra. We take into account
uncertainties associated with X-ray data and photometric redshifts. We also
demonstrate how Bayesian model comparison can be used to select among ten
different physically motivated X-ray spectral models the one that provides a
better representation of the observations. Despite the use of low-count
spectra, our methodology is able to draw strong inferences on the geometry of
the torus. For a sample of 350 AGN in the 4 Ms Chandra Deep Field South field,
our analysis identifies four components needed to represent the diversity of
the observed X-ray spectra: (abridged). Simpler models are ruled out with
decisive evidence in favour of a geometrically extended structure with
significant Compton scattering. Regarding the geometry of the obscurer, there
is strong evidence against both a completely closed or entirely open toroidal
geometry, in favour of an intermediate case. The additional Compton reflection
required by data over that predicted by toroidal geometry models, may be a sign
of a density gradient in the torus or reflection off the accretion disk.
Finally, we release a catalogue with estimated parameters such as the accretion
luminosity in the 2-10 keV band and the column density, , of the
obscurer.Comment: 28 pages, 18 figures, catalogue available from
https://www.mpe.mpg.de/~jbuchner/agn_torus/analysis/cdfs4Ms_cat/, software
available from https://github.com/JohannesBuchner/BX
Identifying and Repairing Catastrophic Errors in Galaxy Properties Using Dimensionality Reduction
Our understanding of galaxy evolution is derived from large surveys designed to maximize efficiency by only observing the minimum amount needed to infer properties for a typical galaxy. However, for a few percent of galaxies in every survey, these observations are insufficient and derived properties can be catastrophically wrong. Further, it is currently difficult or impossible to determine which objects have failed, so that these contaminate every study of galaxy properties. We develop a novel method to identify these objects by combining the astronomical codes that infer galaxy properties with the dimensionality reduction algorithm t-SNE, which groups similar objects to determine which inferred properties are out of place. This method provides an improvement for the COSMOS catalog, which already uses existing techniques for catastrophic error removal, and therefore should improve the quality of large catalogs and any studies that are sensitive to large redshift errors
Evolution of the Fraction of Clumpy Galaxies at 0.2<z<1.0 in the COSMOS field
Using the Hubble Space Telescope/Advanced Camera for Surveys data in the
COSMOS field, we systematically searched clumpy galaxies at 0.2<z<1.0 and
investigated the fraction of clumpy galaxies and its evolution as a function of
stellar mass, star formation rate (SFR), and specific SFR (SSFR). The fraction
of clumpy galaxies in star-forming galaxies with Mstar > 10^9.5 Msun decreases
with time from ~0.35 at 0.8<z<1.0 to ~0.05 at 0.2<z<0.4 irrespective of the
stellar mass, although the fraction tends to be slightly lower for massive
galaxies with Mstar > 10^10.5 Msun at each redshift. On the other hand, the
fraction of clumpy galaxies increases with increasing both SFR and SSFR in all
the redshift ranges we investigated. In particular, we found that the SSFR
dependences of the fractions are similar among galaxies with different stellar
masses, and the fraction at a given SSFR does not depend on the stellar mass in
each redshift bin. The evolution of the fraction of clumpy galaxies from z~0.9
to z~0.3 seems to be explained by such SSFR dependence of the fraction and the
evolution of SSFRs of star-forming galaxies. The fraction at a given SSFR also
appears to decrease with time, but this can be due to the effect of the
morphological K-correction. We suggest that these results are understood by the
gravitational fragmentation model for the formation of giant clumps in disk
galaxies, where the gas mass fraction is a crucial parameter.Comment: 14 Pages, 13 Figures, 1 Table, Accepted for publication in Ap
Optical and electronic properties of manganese thiophosphate and H2T4 porphyrin metal complexes films
Films of manganese thiophosphate (MnPS3) and Mn(III)T4 porphyrin, obtained from a reaction of a colloidal suspension of MnPS3 nanosheets with an aqueous solution of the porphyrin, have been investigated by means of optical
absorption and X-ray photoemission spectroscopies. Our attention is turned to the (300–850) nm range and to the C and N 1s, Mn, P, S and Cl 2p and Mn 3p core regions. The analysis of the resulting spectra and their comparison with
those reported for the original compounds has allowed us to obtain information both about the interaction between MnPS3 and Mn(III)T4 and the effects produced by the porphyrin metallation
Critical currents of MgB2 thin films depositedin situby sputtering
We have measured the temperature and magnetic field dependencies of the critical current density J(c)(H,T) in MgB2 thin films, in situ deposited by sputtering. Three-dimensional point like normal core pinning was evidenced by measurements of the magnetic dependence of the pinning forces independently from the superconducting and structural quality of the investigated films. The analysis of the experimental data in terms of the collective pinning model has pointed out the presence of a crossover magnetic field from a single vortex to a small vortex bundle pinning regime. A DeltaT(c) pinning mechanism, i.e., a pinning associated with spatial fluctuations of the transition temperature, has been evidenced by the temperature dependence of this crossover field, in agreement with previous observations performed on MgB2 bulk materials
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