5,433 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
The ALICE Inner Tracking System Off-line Software
Presentation for CHEP2000An overall view of the ALICE Inner Tracking System Off-line Software is presented. Besides the general scheme, some preliminary results concerning geometry, material budget, track reconstruction and particle identification are also shown
SPIDER - IV. Optical and NIR color gradients in Early-type galaxies: New Insights into Correlations with Galaxy Properties
We present an analysis of stellar population gradients in 4,546 Early-Type
Galaxies with photometry in along with optical spectroscopy. A new
approach is described which utilizes color information to constrain age and
metallicity gradients. Defining an effective color gradient, ,
which incorporates all of the available color indices, we investigate how
varies with galaxy mass proxies, i.e. velocity dispersion,
stellar (M_star) and dynamical (M_dyn) masses, as well as age, metallicity, and
alpha/Fe. ETGs with M_dyn larger than 8.5 x 10^10, M_odot have increasing age
gradients and decreasing metallicity gradients wrt mass, metallicity, and
enhancement. We find that velocity dispersion and alpha/Fe are the main drivers
of these correlations. ETGs with 2.5 x 10^10 M_odot =< M_dyn =< 8.5 x 10^10
M_odot, show no correlation of age, metallicity, and color gradients wrt mass,
although color gradients still correlate with stellar population parameters,
and these correlations are independent of each other. In both mass regimes, the
striking anti-correlation between color gradient and alpha-enhancement is
significant at \sim 4sigma, and results from the fact that metallicity gradient
decreases with alpha/Fe. This anti-correlation may reflect the fact that star
formation and metallicity enrichment are regulated by the interplay between the
energy input from supernovae, and the temperature and pressure of the hot X-ray
gas in ETGs. For all mass ranges, positive age gradients are associated with
old galaxies (>5-7 Gyr). For galaxies younger than \sim 5 Gyr, mostly at
low-mass, the age gradient tends to be anti-correlated with the Age parameter,
with more positive gradients at younger ages.Comment: Accepted for Publication in the Astronomical Journa
Characterizing the nature of Fossil Groups with XMM
We present an X-ray follow-up, based on XMM plus Chandra, of six Fossil Group
(FG) candidates identified in our previous work using SDSS and RASS data. Four
candidates (out of six) exhibit extended X-ray emission, confirming them as
true FGs. For the other two groups, the RASS emission has its origin as either
an optically dull/X-ray bright AGN, or the blending of distinct X-ray sources.
Using SDSS-DR7 data, we confirm, for all groups, the presence of an r-band
magnitude gap between the seed elliptical and the second-rank galaxy. However,
the gap value depends, up to 0.5mag, on how one estimates the seed galaxy total
flux, which is greatly underestimated when using SDSS (relative to Sersic)
magnitudes. This implies that many FGs may be actually missed when using SDSS
data, a fact that should be carefully taken into account when comparing the
observed number densities of FGs to the expectations from cosmological
simulations. The similarity in the properties of seed--FG and non-fossil
ellipticals, found in our previous study, extends to the sample of X-ray
confirmed FGs, indicating that bright ellipticals in FGs do not represent a
distinct population of galaxies. For one system, we also find that the velocity
distribution of faint galaxies is bimodal, possibly showing that the system
formed through the merging of two groups. This undermines the idea that all
selected FGs form a population of true fossils.Comment: 9 pages, 3 figures. Submitted 01/12/2011 to MNRAS, referee report
received 21/02/2012, accepted 22/02/201
I paesaggi agrari tradizionali dellâalbero: il significato moderno di forme dâuso del suolo del passato
Italy represents one of the most suitable
environment for fruit trees and vines and since the origin
of their domestication and introduction in extremely
varying environments, depending on the species
adaptability and local culture, a complex mosaic of
landscapes has been originated by Nature, farmers or
gardeners. In the study of the landscape it must be
considered that the relationship between fruit trees or
vines and landscapes represents a precious aspect of
the Italian culture and has been studied by History,
represented in Art and Literature, analyzed by science
like Architecture and Agronomy, but at first has been
created by Agriculture. Owing to the evolution of the
relationship land and farmers, the development of
agricultural practices, the change of marked requirements
and objectives, different agricultural landscapes
have been created, each having an unique
meaning and functions. Nonetheless, the physiognomy
of tree cropping systems has changed rapidly
starting from half of the past century because of the
introduction of new genetic resources, the change in
the meaning of the productâs quality, the industrialization
of the agronomic technique. These recent developments
have turned out in loss of landscape diversity,
biodiversity erosion, environment resources depletion.
The actual physiognomy of the Italian countryside,
from the plan to the most represented mountain
areas, is characterized by modern and traditional agricultural
landscapes, not even distinguished, frequently
overlaid. They represent the âformsâ of the todayâs
arboriculture visible in the historic and contemporary
gardens, in the remnants of the coltura promiscua, in
the polycultural growing systems, as well as in the
specialized orchards. The contemporary landscape of
fruit trees and vines witnesses its history, characters
and functions particularly in terms of biological and
environmental diversity maintenance. This review is
focused on the traditional fruit tree and vineâs landscapes
still well rooted in the Italian agricultural landscape,
but differently conserved, managed and perceived.
The aim of the historical excursus is to go
through their development phases and to underline
the changing functions. A survey of the multifunctionality
recognisable in the traditional agricultural landscape,
in particular their role in the preservation of
environmental resources, agro-ecosystems functionality,
landscape diversity and cultural memory justifies
the interest in the preservation and valorisation of
these productive landscapes and of the traditional
agricultural techniques, thank to which they are maintained.
The preserving strategies adopted in the
European countries as well as the modern study
approaches based on multidisciplinary methodologies
are also analysed
SPIDER X - Environmental effects in central and satellite early-type galaxies through the stellar fossil record
A detailed analysis of how environment affects the star formation history of
early-type galaxies (ETGs) is undertaken via high signal to noise ratio stacked
spectra obtained from a sample of 20,977 ETGs (morphologically selected) from
the SDSS-based SPIDER survey. Two major parameters are considered for the
study: the central velocity dispersion (sigma), which relates to local drivers
of star formation, and the mass of the host halo, which relates to
environment-related effects. In addition, we separate the sample between
centrals (the most massive galaxy in a halo) and satellites. We derive trends
of age, metallicity, and [alpha/Fe] enhancement, with sigma. We confirm that
the major driver of stellar population properties in ETGs is velocity
dispersion, with a second-order effect associated to the central/satellite
nature of the galaxy. No environmental dependence is detected for satellite
ETGs, except at low sigma - where satellites in groups or in the outskirts of
clusters tend to be younger than those in the central regions of clusters. In
contrast, the trends for centrals show a significant dependence on halo mass.
Central ETGs in groups (i.e. with a halo mass >10^12.5 M_Sun) have younger
ages, lower [alpha/Fe], and higher internal reddening, than "isolated" systems
(i.e. centrals residing in low-mass, <10^12.5 M_Sun, halos). Our findings imply
that central ETGs in groups formed their stellar component over longer time
scales than "isolated" centrals, mainly because of gas-rich interactions with
their companion galaxies.Comment: 22 pages, 19 figures, accepted for publication in MNRA
The puzzling interpretation of NIR indices: The case of NaI2.21
We present a detailed study of the Na I line strength index centered in the
-band at , {\AA} (NaI2.21 hereafter) relying on different samples of
early-type galaxies. Consistent with previous studies, we find that the
observed line strength indices cannot be fit by state-of-art scaled-solar
stellar population models, even using our newly developed models in the NIR.
The models clearly underestimate the large NaI2.21 values measured for most
early-type galaxies. However, we develop a Na-enhanced version of our newly
developed models in the NIR, which - together with the effect of a bottom-heavy
initial mass function - yield NaI2.21 indices in the range of the observations.
Therefore, we suggest a scenario in which the combined effect of [Na/Fe]
enhancement and a bottom-heavy initial mass function are mainly responsible for
the large NaI2.21 indices observed for most early-type galaxies. To a smaller
extent, also [C/Fe] enhancement might contribute to the large observed NaI2.21
values.Comment: 13 pages, 4 figures, accepted for publication in MNRA
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