1,371 research outputs found
Parametrizing growth in dark energy and modified gravity models
It is well-known that an extremely accurate parametrization of the growth
function of matter density perturbations in CDM cosmology, with errors
below , is given by with . In this work, we show that a simple modification of this
expression also provides a good description of growth in modified gravity
theories. We consider the model-independent approach to modified gravity in
terms of an effective Newton constant written as and show
that provides fits to the numerical
solutions with similar accuracy to that of CDM. In the
time-independent case with , simple analytic expressions for
and are presented. In the time-dependent (but
scale-independent) case , we show that has the same time
dependence as . As an example, explicit formalae are provided in the
DGP model. In the general case, for theories with , we obtain a
perturbative expansion for around the General Relativity case
which, for theories, reaches an accuracy below . Finally,
as an example we apply the obtained fitting functions in order to forecast the
precision with which future galaxy surveys will be able to measure the
parameter.Comment: 12 pages, 12 figures. New section on applications to forecasts for
galaxy surveys and new references included. Matches version published in PR
Representative galaxy age-metallicity relationships
The ongoing surveys of galaxies and those for the next generation of
telescopes will demand the execution of high-CPU consuming machine codes for
recovering detailed star formation histories (SFHs) and hence age-metallicity
relationships (AMRs). We present here an expeditive method which provides
quick-look AMRs on the basis of representative ages and metallicities obtained
from colour-magnitude diagram (CMD) analyses. We have tested its perfomance by
generating synthetic CMDs for a wide variety of galaxy SFHs. The representative
AMRs turn out to be reliable down to a magnitude limit with a photometric
completeness factor higher than 85 per cent, and trace the chemical
evolution history for any stellar population (represented by a mean age and an
intrinsic age spread) with a total mass within ~ 40 per cent of the more
massive stellar population in the galaxy.Comment: 12 pages, 11 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
The relative ages of LMC old clusters, and the case of NGC 1841
Using archival HST/WFPC2 imaging of 7 LMC globular clusters, and following
the methods outlined in our previous study, we have reached the tightest
constrain so far on their age dispersion, which cannot be greater than ~ 0.5
Gyr. We also confirm earlier results that their average age is comparable to
that of the metal-poor Galactic globulars. Evidence is also provided that NGC
1841 is younger than the rest of LMC globulars.Comment: 2 pages, 1 figure, requires newpasp.sty. To appear in "New Horizons
in Globular Cluster Astronomy", Giampaolo Piotto, George Meylan, George
Djorgovski and Marco Riello, ed
The red giant branches of Galactic globular clusters in the [(V-I)o,Mv] plane: metallicity indices and morphology
The purpose of this study is to carry out a thorough investigation of the
changes in morphology of the red giant branch (RGB) of Galactic globular
clusters (GGC) as a function of metallicity, in the V,I bands. To this aim, two
key points are developed in the course of the analysis.
(a) Using our photometric V,I database for Galactic globular clusters (the
largest homogeneous data sample to date; Rosenberg et al. 1999) we measure a
complete set of metallicity indices, based on the morphology and position of
the red-giant branch. In particular, we provide here the first calibration of
the S, DV_(1.1) and DV_(1.4) indices in the (V-I,V) plane. We show that our
indices are internally consistent, and we calibrate each index in terms of
metallicity, both on the Zinn & West (1984) and the Carretta & Gratton (1997)
scales. Our new calibrations of the (V-I)o,g, DV_(1.2), (V-I)_(-3.0) and
(V-I)_(-3.5) indices are consistent with existing relations.
(b) Using a grid of selected RGB fiducial points, we define a function in the
{(V-I)o,Mi,[Fe/H]} space which is able to reproduce the whole set of GGC giant
branches in terms of a single parameter (the metallicity). As a first test, we
show that the function is able to predict the correct trend of our observed
indices with metallicity.
The usage of this function will improve the current determinations of
metallicity and distances within the Local Group, since it allows to easily map
[(V-I)o,Mi] coordinates into {[Fe/H],Mi} ones. To this aim the ``synthetic''
RGB distribution is generated both for the currently used Lee et al. (1990)
distance scale, and for the most recent results on the RR Lyr distance scale.Comment: 14 pages, 11 PS figures, accepted for publication in Astronomy &
Astrophysics, main journa
Taxation in times of the Principate
Octavius Augustus' reformatory work covered all scopes of the administration and government. To make that enormous transformation possible it was also necessary to introduce changes in the tax system.La obra reformadora de Octavio Augusto abarcó todos los ámbitos de la administración y gobierno. Para hacer posible toda esa ingente transformación era necesario también introducir cambios en el sistema fiscal
BIM: a technology acceptance model in Peru
The purpose of this paper is to empirically study factors that facilitate the adoption of building information modelling (BIM) among practitioners using the unified theory of technology acceptance model (TAM). The factors identified in the TAM were examined using a quantitative approach. The empirical investigation has been conducted using a survey questionnaire. The data set has been obtained from 73 architects and engineers in Peru. Results show that Perceived Usefulness (PU) is the most important determinant of Behavioural Intention (BI), while Perceived Ease of Use (PEOU) is found to have no significant effect on BI. The findings provide an excellent backdrop in the development of policy and a roadmap for BIM implementation in Peru. The original contribution and value of the paper is the use of TAM to provide empirical evidence on factors that facilitate BIM adoption in Peru
Regional devolopment and solidarity in Spain: the relationship between the E.C. and the internal solidarity funds.
This paper will analyse the importance that the Regional Solidarity Funds have acquired in the financial systems of those Autonomous Communities able to benefit from them, and the influence that these Funds have had in their development. In addition, the special role that Structural Funds have had in order to bring the Autonomous Communities’ development in line with the average level of the European Member States will be referred to. Then, the different EC tools that are connected with regional development will be described and analysed; next, the Spanish regions that have benefited from these tools since Spain joined the European Union in 1986 will be studied. The Internal Solidarity Funds and their relationship with the EC Structural Funds will also be analysed. The effects of these mechanisms will be examined from three different points of view. First of all, the impact of these resources on the regional financial system will be considered; secondly, the coordination between the EC Structural Funds and the Internal Solidarity Funds, and the impact of this relationship will be analysed; and finally, whether or not these mechanisms are efficient enough to achieve the aim of regional unity will be determined, and their influence in different areas of production will also be observed. Key words: Fiscal Federalism, Spanish Autonomous Communities, Structural Funds, Inter-regional Solidarity. JEL Codes: H7, H77.
The age-metallicity relationship in the Fornax spheroidal dwarf galaxy
We produce a comprehensive field star age-metallicity relationship (AMR) from
the earliest epoch until ~ 1 Gyr ago for three fields in the Fornax dSph galaxy
by using VI photometric data obtained with FORS1 at the VLT. We find that the
innermost one does not contains dominant very old stars (age > 12 Gyr), whereas
the relatively outer field does not account for representative star field
populations younger than ~ 3 Gyr. When focusing on the most prominent stellar
populations, we find that the derived AMRs are engraved by the evidence of a
outside-in star formation process. The studied fields show bimodal metallicity
distributions peaked at [Fe/H] = (-0.95 +- 0.15) dex and (-1.15 or -1.25 +-
0.05) dex, respectively, but only during the first half of the entire galaxy
lifetime. Furthermore, the more metal-rich population appears to be more
numerous in the outer fields, while in the innermost Fornax field the
contribution of both metallicity populations seems to be similar. We also find
that the metallicity spread ~ 6 Gyr ago is remarkable large, while the
intrinsic metallicity dispersion at ~ 1-2 Gyr results smaller than that for the
relatively older generations of stars. We interpret these outcomes as a result
of a possible merger of two galaxies that would have triggered a star formation
bursting process that peaked between ~ 6 and 9 Gyr ago, depending on the
position of the field in the galaxy.Comment: 7 pages, 5 figures, MNRAS, in pres
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