2,234 research outputs found
Dark Matter and IMF normalization in Virgo dwarf early-type galaxies
In this work we analyze the dark matter (DM) fraction, , and
mass-to-light ratio mismatch parameter, (computed with respect
to a Milky-Way-like IMF), for a sample of 39 dwarf early-type galaxies (dEs) in
the Virgo cluster. Both and are estimated within the
central (one effective radius) galaxy regions, with a Jeans dynamical analysis
that relies on galaxy velocity dispersions, structural parameters, and stellar
M/L ratios from the SMAKCED survey. In this first attempt to constrain,
simultaneously, the IMF normalization and the DM content, we explore the impact
of different assumptions on the DM model profile. On average, for a NFW
profile, the is consistent with a Chabrier-like normalization
(), with . One of the main results of
the present work is that for at least a few systems the is
heavier than the MW-like value (i.e. either top- or bottom-heavy). When
introducing tangential anisotropy, larger and smaller
are derived. Adopting a steeper concentration-mass relation than that from
simulations, we find lower () and larger . A
constant M/L profile with null gives the heaviest
(). In the MONDian framework, we find consistent results to those for
our reference NFW model. If confirmed, the large scatter of for
dEs would provide (further) evidence for a non-universal IMF in early-type
systems. On average, our reference estimates are consistent with those
found for low- () early-type
galaxies (ETGs). Furthermore, we find consistent with values from the
SMAKCED survey, and find a double-value behavior of with stellar mass,
which mirrors the trend of dynamical M/L and global star formation efficiency
with mass.Comment: 11 pages, 3 figures, 1 table, published on MNRAS. Figure 1 has been
updated with respect to version 1, including the range of values found if the
S\'ersic index, n, is varied from 0.5 to 2 (dark-green curves
Fluid physics under reduced gravity : an overview
Problems related to several fluid physics experiments the case of two experiemnts to be performed under reduced gravity, onboard Space- temperatures,lab (1st Mission), are discussed. Special attention is placed on parallel and preparatory work on erth, wich could throw some light on the opportunity, present interest and limitations of these experiments. The need for strong supporting fundamental research and, in particular, a more precise determination of the paremeters involved, is stressed
Analysis and Improvement of Performance through Motor Imagery Study of the Case in Artistic Gymnastics
Childhood conditions influence adult progesterone levels
Background Average profiles of salivary progesterone in women vary significantly at the inter- and intrapopulation level as a function of age and acute energetic conditions related to energy intake, energy expenditure, or a combination of both. In addition to acute stressors, baseline progesterone levels differ among populations. The causes of such chronic differences are not well understood, but it has been hypothesised that they may result from varying tempos of growth and maturation and, by implication, from diverse environmental conditions encountered during childhood and adolescence. Methods and Findings To test this hypothesis, we conducted a migrant study among first- and second-generation Bangladeshi women aged 19–39 who migrated to London, UK at different points in the life-course, women still resident in Bangladesh, and women of European descent living in neighbourhoods similar to those of the migrants in London (total n = 227). Data collected included saliva samples for radioimmunoassay of progesterone, anthropometrics, and information from questionnaires on diet, lifestyle, and health. Results from multiple linear regression, controlled for anthropometric and reproductive variables, show that women who spend their childhood in conditions of low energy expenditure, stable energy intake, good sanitation, low immune challenges, and good health care in the UK have up to 103% higher levels of salivary progesterone and an earlier maturation than women who develop in less optimal conditions in Sylhet, Bangladesh (F9,178 = 5.05, p < 0.001, standard error of the mean = 0.32; adjusted R2 = 0.16). Our results point to the period prior to puberty as a sensitive phase when changes in environmental conditions positively impact developmental tempos such as menarcheal age (F2,81 = 3.21, p = 0.03) and patterns of ovarian function as measured using salivary progesterone (F2,81 = 3.14, p = 0.04). Conclusions This research demonstrates that human females use an extended period of the life cycle prior to reproductive maturation to monitor their environment and to modulate reproductive steroid levels in accordance with projected conditions they might encounter as adults. Given the prolonged investment of human pregnancy and lactation, such plasticity (extending beyond any intrauterine programming) enables a more flexible and finely tuned adjustment to the potential constraints or opportunities of the later adult environment. This research is the first, to our knowledge, to demonstrate a postuterine developmental component to variation in reproductive steroid levels in women
SPIDER - VI. The Central Dark Matter Content of Luminous Early-Type Galaxies: Benchmark Correlations with Mass, Structural Parameters and Environment
We analyze the central dark-matter (DM) content of \sim 4,500 massive (M*
\gsim 10^{10} Msun), low-redshift (z<0.1), early-type galaxies (ETGs), with
high-quality ugrizYJHK photometry and optical spectroscopy from SDSS and
UKIDSS. We estimate the "central" fraction of DM within the K-band effective
radius, \Re, using spherically symmetric isotropic galaxy models. We discuss
the role of systematics. The main results of the present work are the
following: (1) DM fractions increase systematically with both structural
parameters and mass proxies, as in previous studies, and decrease with central
stellar density. 2) All correlations involving DM fractions are caused by two
fundamental ones with galaxy effective radius and central velocity dispersion.
These correlations are independent of each other, so that ETGs populate a
central-DM plane (DMP), i.e. a correlation among fraction of total-to-stellar
mass, effective radius, and velocity dispersion, whose scatter along the
total-to-stellar mass axis amounts to \sim 0.15 dex. (3) In general, under the
assumption of an isothermal or a constant M/L profile for the total mass
distribution, a Chabrier IMF is favoured with respect to a bottom-heavier
Salpeter IMF, as the latter produces negative (i.e. unphysical) DM fractions
for more than 50% of the galaxies in our sample. For a Chabrier IMF, the DM
estimates agree with \LambdaCDM toy-galaxy models based on contracted DM-halo
density profiles. We also find agreement with predictions from hydrodynamical
simulations. (4) The central DM content of ETGs does not depend significantly
on the environment where galaxies reside, with group and field ETGs having
similar DM trends. (Abridged)Comment: 20 pages, 13 figures, 2 tables, accepted for publication on MNRAS,
version including revisions after the referee's report and feedbacks from
communit
Highly Functionalized SWCNTs with a Dopamine Derivative as a Support for Pd Nanoparticles: A Recyclable Catalyst for the Reduction of Nitro Compounds and the Heck Reaction
Single-walled carbon nanotubes (SWCNTs) were functionalized with a dopamine derivative in which the amine group was converted to azide (dopamine azide). The direct reaction of SWCNTs and dopamine azide in o-dichlorobenzene at high temperature (160 °C) led to very highly functionalized CNTs (≈60 wt.%). Surprisingly, despite this high degree of functionalization, Raman spectroscopy detected a low disruption of the π-network of the carbonaceous support. This finding was justified by the rehybridization from sp3 to sp2 of the sidewall carbon atoms of CNTs involved in the functionalization process. Further characterization by means of different techniques such as X-ray photoelectron spectroscopy (XPS) analysis and transmission electron microscopy (TEM) allowed to shed some light on the chemical composition and morphology of the obtained material. Moreover, the estimation of the total content of phenolic units and their reducing potential after CNTs functionalization was also assessed using Folin and Ciocalteu and 2,2-diphenyl-1-picryl hydrazide (DPPH) assays. The functionalization of CNTs was exploited to immobilize palladium(II) species that were subsequently reduced with NaBH4 leading to the formation of Pd nanoparticles (NPs). The so obtained hybrid material was used as a recyclable heterogeneous catalyst for the reduction of nitro compounds and the Heck reaction
Stellar mass-to-light ratio gradients in galaxies: correlations with mass
We analyze the stellar mass-to-light ratio (M/L) gradients in a large sample
of local galaxies taken from the Sloan Digital Sky Survey, spanning a wide
range of stellar masses and morphological types. As suggested by the well known
relationship between M/L ratios and colors, we show that M/L gradients are
strongly correlated with colour gradients, which we trace to the effects of age
variations. Stellar M/L gradients generally follow patterns of variation with
stellar mass and galaxy type that were previous found for colour and metallicty
gradients. In late-type galaxies M/L gradients are negative, steepening with
increasing mass. In early-type galaxies M/L gradients are shallower while
presenting a two-fold trend: they decrease with mass up to a characteristic
mass of \M* \sim 10^10.3 M_sun and increase at larger masses. We compare our
findings with other analyses and discuss some implications for galaxy formation
and for dark matter estimates.Comment: 9 pages, 3 figures, 3 tables, accepted for publication on MNRA
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