533 research outputs found
The star formation histories of early-type galaxies: insights from the rest-frame ultra-violet
Our current understanding of the star formation histories of early-type
galaxies is reviewed, in the context of recent observational studies of their
ultra-violet (UV) properties. Combination of UV and optical spectro-photometric
data indicates that the bulk of the stellar mass in the early-type population
forms at high redshift (z > 2), typically over short timescales (< 1 Gyr).
Nevertheless, early-types of all luminosities form stars over the lifetime of
the Universe, with most luminous (-23 < M(V) < -21) systems forming 10-15% of
their stellar mass after z = 1 (with a scatter to higher value), while their
less luminous (M(V) > -21) counterparts form 30-60% of their mass in the same
redshift range. The large scatter in the (rest-frame) UV colours in the
redshift range 0 < z < 0.7 indicates widespread low-level star formation in the
early-type population over the last 8 billion years. The mass fraction of young
(< 1 Gyr old) stars in luminous early-type galaxies varies between 1% and 6% at
z~0 and is in the range 5-13% at z~0.7. The intensity of recent star formation
and the bulk of the UV colour distribution is consistent with what might be
expected from minor mergers (mass ratios < 1:6) in an LCDM cosmology.Comment: Brief Review, Mod. Phys. Lett.
Strong Balmer lines in old stellar populations: No need for young ages in ellipticals?
Comparing models of Simple Stellar Populations (SSP) with observed line
strengths generally provides a tool to break the age-metallicity degeneracy in
elliptical galaxies. Due to the wide range of Balmer line strengths observed,
ellipticals have been interpreted to exhibit an appreciable scatter in age. In
this paper, we analyze Composite Stellar Population models with a simple mix of
an old metal-rich and an old metal-poor component. We show that these models
simultaneously produce strong Balmer lines and strong metallic lines without
invoking a young population. The key to this result is that our models are
based on SSPs that better match the steep increase of Hbeta in metal-poor
globular clusters than models in the literature. Hence, the scatter of Hbeta
observed in cluster and luminous field elliptical galaxies can be explained by
a spread in the metallicity of old stellar populations. We check our model with
respect to the so-called G-dwarf problem in ellipticals. For a galaxy subsample
covering a large range in UV-V colors we demonstrate that the addition of an
old metal-poor subcomponent does not invalidate other observational constraints
like colors and the flux in the mid-UV.Comment: Accepted for publication in ApJ Main Journal, 9 pages, 5 figure
Origin of Two Distinct Populations in Dwarf Spheroidal Galaxies
We study the chemical and kinematic properties of the first galaxies which
formed at a high redshift, using high resolution cosmological numerical
simulations, and compared them with the recent observational results for the
Sculptor dwarf spheroidal galaxy by Tolstoy et al., who found two distinct
stellar populations: the lower metallicity stars are more spatially extended
and possess a higher velocity dispersion than the higher metallicity stars. Our
calculations reproduce these observations as the result of a steep metallicity
gradient, within a single populations, induced by dissipative collapse of the
gas component. We also predict strong [N/O] enhancements in the lowest
metallicity stars in dwarf spheroidals, due to the preferential retention of
ejected gas from intermediate mass stars, compared to Type II supernovae.Comment: 11 pages, 10 figures, accepted for publication in Ap
Iron as a tracer in galaxy clusters and groups
Available X-ray data are collected and organized concerning the iron and gas
content of galaxy clusters and groups, together with the optical luminosity,
mass and iron abundance of cluster galaxies. Several astrophysical inferences
are then drawn, including the evidence for rich clusters having evolved without
much baryon exchange with their surrondings, and having experienced very
similar star formation histories. Groups are much gas-poor compared to
clusters, and appear instead to have shed a major fraction of their original
cosmic share of baryons, which indicates that galaxy clusters cannot have
formed by assembling groups similar to the present day ones. It is argued that
this favors low- universes, in which the growth of rich clusters is
virtually complete at high redshifts. It is also argued that elemental
abundance ratios in clusters are nearly solar, which is consistent with a
similar proportion of supernovae of Type Ia and Type II having enriched both
the solar neghborhood as well clusters as a whole. Much of the iron in clusters
appears to reside in the intracluster medium rather than inside galaxies. It
appears that the baryon to star conversion in clusters has been nearly as
efficient as currently adopted for the universe as a whole. Yet the metallicity
of the clusters is times higher than the global metallicity adopted
for the nearby universe. It is concluded that the intergalactic medium should
have a metallicity solar if stellar nucleosynthesis has proceeded in
stars within field galaxies with the same efficiency as in stars within
clusters of galaxies.Comment: AASTex Latex, 29 pages, 6 figure
Resolved stellar population of distant galaxies in the ELT era
The expected imaging capabilities of future Extremely Large Telescopes (ELTs)
will offer the unique possibility to investigate the stellar population of
distant galaxies from the photometry of the stars in very crowded fields. Using
simulated images and photometric analysis we explore here two representative
science cases aimed at recovering the characteristics of the stellar
populations in the inner regions of distant galaxies. Specifically: case A) at
the center of the disk of a giant spiral in the Centaurus Group, (mu B~21,
distance of 4.6 Mpc); and, case B) at half of the effective radius of a giant
elliptical in the Virgo Cluster (mu~19.5, distance of 18 Mpc). We generate
synthetic frames by distributing model stellar populations and adopting a
representative instrumental set up, i.e. a 42 m Telescope operating close to
the diffraction limit. The effect of crowding is discussed in detail showing
how stars are measured preferentially brighter than they are as the confusion
limit is approached. We find that (i) accurate photometry (sigma~0.1,
completeness >90%) can be obtained for case B) down to I~28.5, J~27.5 allowing
us to recover the stellar metallicity distribution in the inner regions of
ellipticals in Virgo to within ~0.1 dex; (ii) the same photometric accuracy
holds for the science case A) down to J~28.0, K~27.0, enabling to reconstruct
of the star formation history up to the Hubble time via simple star counts in
diagnostic boxes. For this latter case we discuss the possibility of deriving
more detailed information on the star formation history from the analysis of
their Horizontal Branch stars. We show that the combined features of high
sensitivity and angular resolution of ELTs may open a new era for our knowledge
of the stellar content of galaxies of different morphological type up to the
distance of the Virgo cluster.Comment: 21 pages, 17 figures, PASP accepted in pubblicatio
The Long-Term Experiment Platform for the Study of Agronomical and Environmental Effects of the Biochar: Methodological Framework
In this communication, a wide overview of historical Long-Term Experimental Platforms (LTEP) regarding changes in soil organic matter is presented for the purpose of networking, data sharing, experience sharing and the coordinated design of experiments in the area of Earth system science. This serves to introduce a specific platform of experiments regarding biochar application to soil (LTEP-BIOCHAR) and its use for agronomic and environmental purposes (e.g., carbon sequestration, soil erosion, soil biodiversity) in real conditions and over a significative timeframe for pedosphere dynamics. The methodological framework, including the goals, geographical scope and eligibility rules of such a new platform, is discussed. Currently, the LTEP-BIOCHAR is the first of its kind, a community-driven resource dedicated to biochar, and displays around 20 long-term experiments from Europe, the Middle East and Africa. The selected field experiments take place under dynamically, meteorologically and biologically different conditions. The purposes of the platform are (1) listing the field experiments that are currently active, (2) uncovering methodological gaps in the current experiments and allowing specific metadata analysis, (3) suggesting the testing of new hypotheses without unnecessary duplications while establishing a minimum standard of analysis and methods to make experiments comparable, (4) creating a network of expert researchers working on the agronomical and environmental effects of biochar, (5) supporting the design of coordinated experiments and (6) promoting the platform at a wider international level
Assessment of seasonal changes in water chemistry of the ridracoli water reservoir (Italy): Implications for water management
The Ridracoli artificial basin is the main water reservoir of the Emilia-Romagna region (Northeast Italy). The reservoir was made by construction of a dam on the Bidente River in 1982. It is used as the main drinking water supply of the region and for hydropower production. The physical and chemical parameterseters (temperature, pH, electrical conductivity, and dissolved oxygen) of shallow water are continuously monitored whereas vertical depth profiles of water chemical data (major anions and cations, as well as heavy metals) are available on a bimonthly base. The dataset used in this research is related to the years 2015 and 2016. Data show that the reservoir is affected by an alternation of water stratification and mixing processes due to seasonal change in water temperature, density, and the reservoir water level. In late summer and winter months, the water column is stratified with anoxic conditions at the bottom. During the spring, on the other hand, when storage is at its maximum, water recirculation and mixing occur. The reservoir is characterized by a dynamic system in which precipitation, dissolution, and adsorption processes at the bottom affect water quality along the reservoir depth column. The temperature stratification and anoxic conditions at the reservoir bottom influence the concentration and mobility of some heavy metals (i.e., Fe and Mn) and, consequently, the quality of water that reaches the treatment and purification plant. This study is relevant for water resource management of the reservoir. Assessing the seasonal changes in water quality along the reservoir water column depth is fundamental to plan water treatment operations and optimize their costs. The reservoir assessment allows one to identify countermeasures to avoid or overcome the high concentrations of heavy metals and the stratification problem (i.e., artificial mixing of the water column, new water intakes at different depths operating at different times of the year, blowers, etc.)
The Age of Cluster Galaxies from Continuum Colors
We determine the age of 1,104 early-type galaxies in eight rich clusters ( to ) using a new continuum color technique. We find that
galaxies in clusters divide into two populations, an old population with a mean
age similar to the age of the Universe (12 Gyrs) and a younger population with
a mean age of 9 Gyrs. The older population follows the expected relations for
mass and metallicity that imply a classic monolithic collapse origin. Although
total galaxy metallicity is correlated with galaxy mass, it is uncorrelated
with age. It is impossible, with the current data, to distinguish between a
later epoch of star formation, longer duration of star formation or late bursts
of star formation to explain the difference between the old and young
populations. However, the global properties of this younger population are
correlated with cluster environmental factors, which implies secondary
processes, post-formation epoch, operate on the internal stellar population of
a significant fraction of cluster galaxies. In addition, the mean age of the
oldest galaxies in a cluster are correlated with cluster velocity dispersion
implying that galaxy formation in massive clusters begins at earlier epochs
than less massive clusters.Comment: 35 pages, 10 figures, accepted by Ap
Analytic solution of Chemical Evolution Models with Type Ia SNe
Context: In the last years, a significant number of works have focused on
finding analytic solutions for the chemical enrichment models of galactic
systems, including the Milky Way. Some of these solutions, however, cannot
account for the enrichment produced by Type Ia SNe due to the presence of the
delay time distributions (DTDs) in the models.
Aims: We present a new analytic solution for the chemical evolution model of
the Galaxy. This solution can be used with different prescriptions of the DTD,
including the single and double degenerate scenarios, and allows the inclusion
of an arbitrary number of pristine gas infalls.
Methods: We integrate the chemical evolution model by extending the
instantaneous recycling approximation with the contribution of Type Ia SNe. For
those DTDs that lead to non-analytic integrals, we describe them as a
superposition of Gaussian, exponential and 1/t functions using a restricted
least-squares fitting method.
Results: We obtain the exact solution for a chemical model with Type Ia SNe
widely used in previous works. This solution can reproduce the expected
chemical evolution of the alpha and iron-peak elements in less computing time
than numerical integration methods. We compare the pattern in the [Si/Fe] vs.
[Fe/H] plane observed by APOGEE DR17 with that predicted by the model. We find
the low alpha sequence can be explained by a delayed gas infall. We exploit the
applicability of our solution by modelling the chemical evolution of a
simulated Milky Way-like galaxy from its star formation history. The
implementation of our solution is released as a python package.
Conclusions: Our solution constitutes a promising tool for the Galactic
Archaeology and is able to model the observed trends in alpha element
abundances versus [Fe/H] in the solar neighbourhood. We infer the chemical
information of a simulated galaxy modelled without Chemistry.Comment: Accepted for publication in A&A. 22 pages, 16 figures. ChEAP code
available at https://bitbucket.org/pedroap/cheap/src/master
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