341 research outputs found
Evidence for dust accumulation just outside the orbit of Venus
To contribute to the knowledge of dynamics of interplanetary dust we are
searching for structures in the spatial distribution of interplanetary dust
near the orbit of Venus. To this end we study the radial gradient of zodiacal
light brightness, as observed by the zodiacal light photometer on board the
Helios space probes on several orbits from 1975 to 1979. The cleanest data
result from Helios B (= Helios 2) launched in January 1976. With respect to the
general increase of zodiacal light brightness towards the Sun, the data show an
excess brightness of a few percent for positions of the Helios space probe just
outside the orbit of Venus. We consider this as evidence for a dust ring
associated with the orbit of Venus, somewhat similar to that found earlier
along the Earth's orbit.Comment: 7 pages, 8 figures, Astronomy&Astrophysics, accepte
Galaxy size trends as a consequence of cosmology
We show that recently documented trends in galaxy sizes with mass and
redshift can be understood in terms of the influence of underlying cosmic
evolution; a holistic view which is complimentary to interpretations involving
the accumulation of discreet evolutionary processes acting on individual
objects. Using standard cosmology theory, supported with results from the
Millennium simulations, we derive expected size trends for collapsed cosmic
structures, emphasising the important distinction between these trends and the
assembly paths of individual regions. We then argue that the observed variation
in the stellar mass content of these structures can be understood to first
order in terms of natural limitations of cooling and feedback. But whilst these
relative masses vary by orders of magnitude, galaxy and host radii have been
found to correlate linearly. We explain how these two aspects will lead to
galaxy sizes that closely follow observed trends and their evolution, comparing
directly with the COSMOS and SDSS surveys. Thus we conclude that the observed
minimum radius for galaxies, the evolving trend in size as a function of mass
for intermediate systems, and the observed increase in the sizes of massive
galaxies, may all be considered an emergent consequence of the cosmic
expansion.Comment: 14 pages, 13 figures. Accepted by MNRA
High precision spectra at large redshift for dynamical DE cosmologies
The next generation mass probes will investigate DE nature by measuring
non-linear power spectra at various z, and comparing them with high precision
simulations. Producing a complete set of them, taking into account baryon
physics and for any DE state equation w(z), would really be numerically
expensive. Regularities reducing such duty are essential. This paper presents
further n-body tests of a relation we found, linking models with DE state
parameter w(z) to const.-w models, and also tests the relation in hydro
simulations.Comment: PASCOS 2010, the 16th International Symposium on Particles, Strings
and Cosmology, Valencia (Spain), July 19th - 23rd, 201
MaGICC baryon cycle: the enrichment history of simulated disc galaxies
Using cosmological galaxy formation simulations from the MaGICC (Making Galaxies in a Cosmological Context) project, spanning stellar mass from ∼107 to 3 × 1010 M⊙, we trace the baryonic cycle of infalling gas from the virial radius through to its eventual participation in the star formation process. An emphasis is placed upon the temporal history of chemical enrichment during its passage through the corona and circumgalactic medium. We derive the distributions of time between gas crossing the virial radius and being accreted to the star-forming region (which allows for mixing within the corona), as well as the time between gas being accreted to the star-forming region and then ultimately forming stars (which allows for mixing within the disc). Significant numbers of stars are formed from gas that cycles back through the hot halo after first accreting to the star-forming region. Gas entering high-mass galaxies is pre-enriched in low-mass proto-galaxies prior to entering the virial radius of the central progenitor, with only small amounts of primordial gas accreted, even at high redshift (z ∼ 5). After entering the virial radius, significant further enrichment occurs prior to the accretion of the gas to the star-forming region, with gas that is feeding the star-forming region surpassing 0.1 Z⊙ by z = 0. Mixing with halo gas, itself enriched via galactic fountains, is thus crucial in determining the metallicity at which gas is accreted to the disc. The lowest mass simulated galaxy (Mvir ∼ 2 × 1010 M⊙, with M⋆ ∼ 107 M⊙), by contrast, accretes primordial gas through the virial radius and on to the disc, throughout its history. Much like the case for classical analytical solutions to the so-called ‘G-dwarf problem’, overproduction of low-metallicity stars is ameliorated by the interplay between the time of accretion on to the disc and the subsequent involvement in star formation – i.e. due to the inefficiency of star formation. Finally, gas outflow/metal removal rates from star-forming regions as a function of galactic mass are presented
Comparing gene panels for non-retinal indications: A systematic review
IMPORTANCE: The options for genetic testing continue to grow for ocular conditions, including optic atrophy, anterior segment dysgenesis, cataracts, corneal dystrophy, nystagmus, and glaucoma. Gene panels can vary in content and coverage, as we and others have evaluated in inherited retinal disease (IRD).
OBJECTIVE: To describe gene panel testing options for inherited eye disease phenotypes and their differences. This review is important for making diagnostic decisions.
EVIDENCE REVIEW: A licensed, certified genetic counselor (RP) used Concert Genetics and the search terms optic atrophy, corneal dystrophy, cataract, glaucoma, anterior segment dysgenesis, microphthalmia/anophthalmia, and nystagmus to identify available testing options performed by CLIA-certified commercial genetic testing laboratories. Other co-authors were surveyed with respect to genetic panels used for the indications of interest. Ophthalmic panels were then compared using Concert Genetics in addition to their own websites.
FINDINGS: Panels from each clinical category were included and summarized. This comparison highlighted the differences and similarities between panels so that clinicians can make informed decisions.
CONCLUSIONS: Access to genetic testing is increasing. The diagnostic yield of genetic testing is increasing. Each panel is different, so phenotyping or characterizing clinical characteristics that may help predict a specific genotype, as well as pre-test hypotheses regarding a genotype, should shape the choice of panels
Impact of Supernova feedback on the Tully-Fisher relation
Recent observational results found a bend in the Tully-Fisher Relation in
such a way that low mass systems lay below the linear relation described by
more massive galaxies. We intend to investigate the origin of the observed
features in the stellar and baryonic Tully-Fisher relations and analyse the
role played by galactic outflows on their determination. Cosmological
hydrodynamical simulations which include Supernova feedback were performed in
order to follow the dynamical evolution of galaxies. We found that Supernova
feedback is a fundamental process in order to reproduce the observed trends in
the stellar Tully-Fisher relation. Simulated slow rotating systems tend to have
lower stellar masses than those predicted by the linear fit to the massive end
of the relation, consistently with observations. This feature is not present if
Supernova feedback is turned off. In the case of the baryonic Tully-Fisher
relation, we also detect a weaker tendency for smaller systems to lie below the
linear relation described by larger ones. This behaviour arises as a result of
the more efficient action of Supernovae in the regulation of the star formation
process and in the triggering of powerful galactic outflows in shallower
potential wells which may heat up and/or expel part of the gas reservoir.Comment: 10 pages, 9 figures, accepted for publication in A&
MaGICC discs: matching observed galaxy relationships over a wide stellar mass range
We use the same physical model to simulate four galaxies that match the relation between stellar and total mass, over a mass range that includes the vast majority of disc galaxies. The resultant galaxies, part of the Making Galaxies in a Cosmological Context (MaGICC) program, also match observed relations between luminosity, rotation velocity, size, colour, star formation rate, HI mass, baryonic mass, and metallicity. Radiation from massive stars and supernova energy regulate star formation and drive outflows, balancing the complex interplay between cooling gas, star formation, large scale outflows, and recycling of gas in a manner which correctly scales with the mass of the galaxy. Outflows also play a key role in simulating galaxies with exponential surface brightness profiles, flat rotation curves and dark matter cores. Our study implies that large scale outflows are the primary driver of the dependence of disc galaxy properties on mass. We show that the amount of outflows invoked in our model is required to meet the constraints provided by observations of OVI absorption lines in the circum-galactic-media of local galaxies
Fingerprints of the hierarchical building up of the structure on the gas kinematics of galaxies
Recent observational and theoretical works have suggested that the
Tully-Fisher Relation might be generalised to include dispersion-dominated
systems by combining the rotation and dispersion velocity in the definition of
the kinematical indicator. Mergers and interactions have been pointed out as
responsible of driving turbulent and disordered gas kinematics, which could
generate Tully-Fisher Relation outliers. We intend to investigate the gas
kinematics of galaxies by using a simulated sample which includes both, gas
disc-dominated and spheroid-dominated systems. Cosmological hydrodynamical
simulations which include a multiphase model and physically-motivated Supernova
feedback were performed in order to follow the evolution of galaxies as they
are assembled. Both the baryonic and stellar Tully-Fisher relations for gas
disc-dominated systems are tight while, as more dispersion-dominated systems
are included, the scatter increases. We found a clear correlation between
and morphology, with dispersion-dominated systems
exhibiting the larger values (). Mergers and interactions can affect the
rotation curves directly or indirectly inducing a scatter in the Tully-Fisher
Relation larger than the simulated evolution since . Kinematical
indicators which combine rotation velocity and dispersion velocity can reduce
the scatter in the baryonic and the stellar mass-velocity relations. Our
findings also show that the lowest scatter in both relations is obtained if the
velocity indicators are measured at the maximum of the rotation curve.
Moreover, the rotation velocity estimated at the maximum of the gas rotation
curve is found to be the best proxy for the potential well regardless of
morphology.Comment: 16 pages, 10 figures, accepted for publication in A&
Reproducing the Stellar Mass/Halo Mass Relation in Simulated LCDM Galaxies: Theory vs Observational Estimates
We examine the present-day total stellar-to-halo mass (SHM) ratio as a
function of halo mass for a new sample of simulated field galaxies using fully
cosmological, LCDM, high resolution SPH + N-Body simulations.These simulations
include an explicit treatment of metal line cooling, dust and self-shielding,
H2 based star formation and supernova driven gas outflows. The 18 simulated
halos have masses ranging from a few times 10^8 to nearly 10^12 solar masses.
At z=0 our simulated galaxies have a baryon content and morphology typical of
field galaxies. Over a stellar mass range of 2.2 x 10^3 to 4.5 x 10^10 solar
masses, we find extremely good agreement between the SHM ratio in simulations
and the present-day predictions from the statistical Abundance Matching
Technique presented in Moster et al. (2012). This improvement over past
simulations is due to a number systematic factors, each decreasing the SHM
ratios: 1) gas outflows that reduce the overall SF efficiency but allow for the
formation of a cold gas component 2) estimating the stellar masses of simulated
galaxies using artificial observations and photometric techniques similar to
those used in observations and 3) accounting for a systematic, up to 30 percent
overestimate in total halo masses in DM-only simulations, due to the neglect of
baryon loss over cosmic times. Our analysis suggests that stellar mass
estimates based on photometric magnitudes can underestimate the contribution of
old stellar populations to the total stellar mass, leading to stellar mass
errors of up to 50 percent for individual galaxies. These results highlight the
importance of using proper techniques to compare simulations with observations
and reduce the perceived tension between the star formation efficiency in
galaxy formation models and in real galaxies.Comment: Submitted to ApJ 9 pages, 5 figure
Simulations of the galaxy population constrained by observations from z=3 to the present day: implications for galactic winds and the fate of their ejecta
We apply Monte Carlo Markov Chain (MCMC) methods to large-scale simulations of galaxy formation in a LambdaCDM cosmology in order to explore how star formation and feedback are constrained by the observed luminosity and stellar mass functions of galaxies. We build models jointly on the Millennium and Millennium-II simulations, applying fast sampling techniques which allow observed galaxy abundances over the ranges 7<log(M*/Msun)<12 and z=0 to z=3 to be used simultaneously as constraints in the MCMC analysis. When z=0 constraints alone are imposed, we reproduce the results of previous modelling by Guo et al. (2012), but no single set of parameters can reproduce observed galaxy abundances at all redshifts simultaneously, reflecting the fact that low-mass galaxies form too early and thus are overabundant at high redshift in this model. The data require the efficiency with which galactic wind ejecta are reaccreted to vary with redshift and halo mass quite differently than previously assumed, but in a similar way as in some recent hydrodynamic simulations of galaxy formation. We propose a specific model in which reincorporation timescales vary inversely with halo mass and are independent of redshift. This produces an evolving galaxy population which fits observed abundances as a function of stellar mass, B- and K-band luminosity at all redshifts simultaneously. It also produces a significant improvement in two other areas where previous models were deficient. It leads to present day dwarf galaxy populations which are younger, bluer, more strongly star-forming and more weakly clustered on small scales than before, although the passive fraction of faint dwarfs remains too high
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