589,661 research outputs found
New age-metallicity diagnostic diagram for the Washington photometric system
The age calibration of the Washington deltaT1 index is mainly used to
estimate ages of star clusters older than 1 Gyr, no age-metallicity degeneracy
effect is considered. We have profusely exploited synthetic T1 versus C-T1
colour magnitude diagrams aiming at exploring the intrinsic behaviour of the
deltaT1 index. The analysis shows that deltaT1 varies with age and metal
content as well. In general, the dependence on age weakens for ages greater
than ~ 6 Gyr, and results even less sensitive to age as the metallicity
decreases. For ages younger than ~ 5 Gyr deltaT1 shows a strong correlation
with both age and metallicity. The deltaC index -defined as deltaT1 for the C
passband- is also a combined measurement of age and metallicity. We introduce a
new age-metallicity diagnostic diagram, deltaT1 versus deltaC - deltaT1, which
has shown the ability of unambiguously providing age and metallicity estimates,
simultaneously. The new procedure allows to derive ages from 1 up to 13 Gyr and
metallicities [Fe/H] from -2.0 up to +0.5 dex, and is independent of the
cluster reddening and distance modulus. It does solve the constraints found in
the deltaT1 index and surpasses the performance of the standard giant branch
metallicity method. All these features make the diagnostic diagram a powerful
tool for estimating accurate ages as well as metallicities.Comment: 14 pages, 7 figures, accepted for publication in MNRA
The usage of Stromgren photometry in studies of Local Group Dwarf Spheroidal Galaxies - Application to Draco: a new catalogue of Draco members and a study of the metallicity distribution function and radial gradients
In this paper we demonstrate how Stromgren uvby photometry can be efficiently
used to: 1. Identify red giant branch stars that are members in a dwarf
spheroidal galaxy. 2. Derive age-independent metallicities for the same stars
and quantify the associated errors. Stromgren uvby photometry in a 11 x 22
arcmin field centered on the Draco dwarf spheroidal galaxy was obtained using
the Isaac Newton Telescope on La Palma. Members of the Draco dSph galaxy were
identified using the surface gravity sensitive c_1 index which discriminates
between red giant and dwarf stars. Thus enabling us to distinguish the (red
giant branch) members of the dwarf spheroidal galaxy from the foreground dwarf
stars in our galaxy. The method is evaluated through a comparison of our
membership list with membership classifications in the literature based on
radial velocities and proper motions. The metallicity sensitive m_1 index was
used to derive individual and age-independent metallicities for the members of
the Draco dSph galaxy. The derived metallicities are compared to studies based
on high resolution spectroscopy and the agreement is found to be very good. We
present metallicities for 169 members of the red giant branch in the Draco
dwarf spheroidal galaxy (the largest sample to date). The metallicity
distribution function for the Draco dSph galaxy shows a mean [Fe/H] = -1.74 dex
with a spread of 0.24 dex. The correlation between metallicity and colour for
the stars on the red giant branch is consistent with a dominant old, and coeval
population. There is a possible spatial population gradient over the field with
the most metal-rich stars being more centrally concentrated than the metal-poor
stars.Comment: Accepted for publication in A&A. 26 pages, 27 figures (some at
reduced resolution). High resolution version available at
http://www.astro.lu.se/~daniel/draco/faria.p
The Age, Metallicity and Alpha-Element Abundance of Galactic Globular Clusters from Single Stellar Population Models
Establishing the reliability with which stellar population parameters can be
measured is vital to extragalactic astronomy. Galactic GCs provide an excellent
medium in which to test the consistency of Single Stellar Population (SSP)
models as they should be our best analogue to a homogeneous (single) stellar
population. Here we present age, metallicity and -element abundance
measurements for 48 Galactic globular clusters (GCs) as determined from
integrated spectra using Lick indices and SSP models from Thomas, Maraston &
Korn, Lee & Worthey and Vazdekis et al. By comparing our new measurements to
independent determinations we are able to assess the ability of these SSPs to
derive consistent results -- a key requirement before application to
heterogeneous stellar populations like galaxies.
We find that metallicity determinations are extremely robust, showing good
agreement for all models examined here, including a range of enhancement
methods. Ages and -element abundances are accurate for a subset of our
models, with the caveat that the range of these parameters in Galactic GCs is
limited. We are able to show that the application of published Lick index
response functions to models with fixed abundance ratios allows us to measure
reasonable -element abundances from a variety of models. We also
examine the age-metallicity and [/Fe]-metallicity relations predicted
by SSP models, and characterise the possible effects of varied model horizontal
branch morphology on our overall results.Comment: 22 pages, 19 figures, accepted for publication in MNRA
On the Interpretation of the Age Distribution of Star Clusters in the Small Magellanic Cloud
We re-analyze the age distribution (dN/dt) of star clusters in the Small
Magellanic Cloud (SMC) using age determinations based on the Magellanic Cloud
Photometric Survey. For ages younger than 3x10^9 yr the dN/dt distribution can
be approximated by a power-law distribution, dN/dt propto t^-beta, with
-beta=-0.70+/-0.05 or -beta=-0.84+/-0.04, depending on the model used to derive
the ages. Predictions for a cluster population without dissolution limited by a
V-band detection result in a power-law dN/dt distribution with an index of
~-0.7. This is because the limiting cluster mass increases with age, due to
evolutionary fading of clusters, reducing the number of observed clusters at
old ages. When a mass cut well above the limiting cluster mass is applied, the
dN/dt distribution is flat up to 1 Gyr. We conclude that cluster dissolution is
of small importance in shaping the dN/dt distribution and incompleteness causes
dN/dt to decline. The reason that no (mass independent) infant mortality of
star clusters in the first ~10-20 Myr is found is explained by a detection bias
towards clusters without nebular emission, i.e. cluster that have survived the
infant mortality phase. The reason we find no evidence for tidal (mass
dependent) cluster dissolution in the first Gyr is explained by the weak tidal
field of the SMC. Our results are in sharp contrast to the interpretation of
Chandar et al. (2006), who interpret the declining dN/dt distribution as rapid
cluster dissolution. This is due to their erroneous assumption that the sample
is limited by cluster mass, rather than luminosity.Comment: 8 pages, 4 figures, accepted for publication in Ap
Peer effects and academics’ industry involvement : the moderating role of age on professional imprinting
This study explores the interaction between professional imprinting and age in the context of
industry-science collaboration. Specifically, we examine the impact of localized and personal peer effects on academics’ involvement with industry and how these effects are moderated by the career age of the scientist. We suggest that both localized and personal peer effects drive industry involvement but that the effects from such imprinting are more pronounced for younger researchers, suggesting that professional imprinting takes place in the early stages of a scientist’s academic career. Based on a sample of 330 German academics in the field of biotechnology and publication data from the Science Citation Index Expanded (SCIE), we find that scientists with industry-oriented co-authors are more likely to be involved with industry (personal peer effect). Moreover, we find that the scientist’s involvement increases with the orientation of the scientist’s department towards industry (localized peer effect).
Only the latter effect turns out to be moderated by scientist’s age. While personal peer effects are independent of the scientist’s age, localized peer effects emerge for younger researchers
Galaxy And Mass Assembly (GAMA): Stellar-to-Dynamical Mass Relation I. Constraining the Precision of Stellar Mass Estimates
In this empirical work, we aim to quantify the systematic uncertainties in
stellar mass estimates made from spectral energy distribution (SED)
fitting through stellar population synthesis (SPS), for galaxies in the local
Universe, by using the dynamical mass estimator as an
SED-independent check on stellar mass. We first construct a statistical model
of the high dimensional space of galaxy properties; size , velocity
dispersion , surface brightness , mass-to-light ratio
, rest-frame colour, S\'ersic index and dynamical mass
; accounting for selection effects and covariant errors. We
disentangle the correlations among galaxy properties and find that the
variation in is driven by , S\'ersic index and
colour. We use these parameters to calibrate an SED-independent
estimator, . We find the random scatter of the relation
to be and for
quiescent and star-forming galaxies respectively. Finally, we inspect the
residuals as a function of SPS parameters (dust, age, metallicity, star
formation rate) and spectral indices (H, H, . For
quiescent galaxies, of the scatter can be explained by the
uncertainty in SPS parameters, with dust and age being the largest sources of
uncertainty. For star-forming galaxies, while age and metallicity are the
leading factors, SPS parameters account for only of the scatter.
These results leave us with remaining unmodelled scatters of
and for quiescent and star-forming galaxies respectively.
This can be interpreted as a conservative limit on the precision in
that can be achieved via simple SPS-modelling.Comment: Accepted for publication in the Astrophysical Journal on 14 June 202
- …