4,473 research outputs found
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
A Principal Component Analysis approach to the Star Formation History of elliptical galaxies in Compact Groups
(Abridged) Environmental differences in the stellar populations of early-type
galaxies are explored using principal component analysis (PCA), focusing on
differences between elliptical galaxies in Hickson Compact Groups (HCGs) and in
the field. The method is model-independent and relies on variations between the
observed spectra. The projections (PC1,PC2) reveal a difference with respect to
environment, with a wider range in PC1 and PC2 in the group sample. We define a
spectral parameter (zeta=0.36PC1-PC2) which simplifies this result to a single
number: field galaxies have a very similar value of zeta, whereas HCG galaxies
span a wide range in this parameter. We obtain a strong correlation between the
values of zeta and the mass fraction in younger stars, so that some group
galaxies present a higher fraction of them. PCA is more sensitive than other
methods based on a direct analysis of observables such as the structure of the
surface brightness profile or the equivalent width of absorption lines. The
latter do not reveal any significant variation between field and compact group
galaxies. Our results imply that the presence of young stars only amounts to a
fraction of a percent in its contribution to the total variance.Comment: 9 pages, 8 figures. Accepted for publication in MNRA
Nanocarriers for topical delivery of resveratrol.
Purpose: The aim of the present work was to develop a nanocarrier-based formulation for topical delivery of resveratrol.
Methods: Trans-resveratrol (t-res) was encapsulated in liposomes, ethosomes or transferosomes, by a modified hand-shaking method followed by extrusion. All the formulations were characterised in terms of mean diameter, size distribution (I.P.), t-res loading, t-res stability upon encapsulation during storage. The nanocarriers containing t-res were then introduced in cellulose-based gel to allow their final administration on the skin and the viscoelastic properties of the resulting formulation were investigated. Finally, we studied the inhibition of reactive oxygen species (ROS) in human keratinocyte (HaCaT) cell line stimulated with H2O2 for 24 h and then incubated with the t-res containing nanocarriers.
Results: All the t-res containing carriers were characterised by a very high (close to 100%) encapsulation efficiency, a negligible t-res release at 4°C and stability of resveratrol in its trans form. The carriers only slightly influenced the viscoelastic characteristics of cellulose-based gels. Nanocarriers encapsulating t-res reduced, in a concentration-dependent manner, ROS production induced by H2O2 and this effect was higher when using t-res-encapsulating nanocarrier, with the higher effect observed in the case of ethosomes.
Conclusions: In this work nanocarriers with high encapsulation efficiency, high physical stability and negligible t-res release during storage at 4°C were prepared. To allow their final administration on the skin, the nanocarrier can be easilisy loaded in cellulose-based gels without altering its rheological properties. Moreover, the use of t-res-encapsulating ethosomes led to an efficient antioxidant activity. Further ex vivo and in vivo studies will clarify the role of the different carrier when administered on the skin
On the Nature of Fossil Galaxy Groups: Are they really fossils ?
We use SDSS-DR4 photometric and spectroscopic data out to redshift z~0.1
combined with ROSAT All Sky Survey X-ray data to produce a sample of
twenty-five fossil groups (FGs), defined as bound systems dominated by a
single, luminous elliptical galaxy with extended X-ray emission. We examine
possible biases introduced by varying the parameters used to define the sample
and the main pitfalls are discussed. The spatial density of FGs, estimated via
the V/V_ MAX} test, is 2.83 x 10^{-6} h_{75}^3 Mpc^{-3} for L_x > 0.89 x 10^42
h_{75}^-2 erg/s consistent with Vikhlinin et al. (1999), who examined an X-ray
overluminous elliptical galaxy sample (OLEG). We compare the general properties
of FGs identified here with a sample of bright field ellipticals generated from
the same dataset. These two samples show no differences in the distribution of
neighboring faint galaxy density excess, distance from the red sequence in the
color-magnitude diagram, and structural parameters such as a and internal
color gradients. Furthermore, examination of stellar populations shows that our
twenty-five FGs have similar ages, metallicities, and -enhancement as
the bright field ellipticals, undermining the idea that these systems represent
fossils of a physical mechanism that occurred at high redshift. Our study
reveals no difference between FGs and field ellipticals, suggesting that FGs
might not be a distinct family of true fossils, but rather the final stage of
mass assembly in the Universe.Comment: 18 pages, Accepted to A
The SDSS-UKIDSS Fundamental Plane of Early-type Galaxies
We derive the Fundamental Plane (FP) relation for a sample of 1430 early-type
galaxies in the optical (r band) and the near-infrared (K band), by combining
SDSS and UKIDSS data. With such a large, homogeneous dataset, we are able to
assess the dependence of the FP on the waveband. Our analysis indicates that
the FP of luminous early-type galaxies is essentially waveband independent,
with its coefficients increasing at most by 8% from the optical to the NIR.
This finding fits well into a consistent picture where the tilt of the FP is
not driven by stellar populations, but results from other effects, such as
non-homology. In this framework, the optical and NIR FPs require more massive
galaxies to be slightly more metal rich than less massive ones, and to have
highly synchronized ages, with an age variation per decade in mass smaller than
a few percent.Comment: 7 pages, 2 figures, accepted for publication on Ap
Evidence for tidal interaction and merger as the origin of galaxy morphology evolution in compact groups
We present the results of a morphological study based on NIR images of 25
galaxies, with different levels of nuclear activity, in 8 Compact Groups of
Galaxies (CGs). We perform independently two different analysis: a isophotal
study and a study of morphological asymmetries. The results yielded by the two
analysis are highly consistent. For the first time, it is possible to show that
deviations from pure ellipses are produced by inhomogeneous stellar mass
distributions related to galaxy interactions and mergers. We find evidence of
mass asymmetries in 74% of the galaxies in our sample. In 59% of these cases,
the asymmetries come in pairs, and are consistent with tidal effects produced
by the proximity of companion galaxies. The symmetric galaxies are generally
small in size or mass, inactive, and have an early-type morphology. In 20% of
the galaxies we find evidence for cannibalism. In 36% of the early-type
galaxies the color gradient is positive (blue nucleus) or flat. Summing up
these results, as much as 52% of the galaxies in our sample could show evidence
of an on going or past mergers. Our observations suggest that galaxies in CGs
merge more frequently under ``dry'' conditions. The high frequency of
interacting and merging galaxies observed in our study is consistent with the
bias of our sample towards CGs of type B, which represents the most active
phase in the evolution of the groups. In these groups we also find a strong
correlation between asymmetries and nuclear activity in early-type galaxies.
This correlation allows us to identify tidal interactions and mergers as the
cause of galaxy morphology transformation in CGs.[abridge]Comment: 64 pages, 35 figures. Accepted for publication in Ap
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