64 research outputs found
The impact of enhanced He and CNONa abundances on globular cluster relative age-dating methods
The impact that unrecognised differences in the chemical patterns of Galactic
globular clusters have on their relative age determinations is studied. The two
most widely used relative age-dating methods, horizontal and vertical, together
with the more recent relative MS-fitting method, were carefully analyzed on a
purely theoretical basis. The BaSTI library was adopted to perform the present
analysis. We find that relative ages derived using the horizontal and vertical
methods are largely dependent on the initial He content and heavy element
distribution. Unrecognized cluster-to-cluster chemical abundance differences
can lead to an error in the derived relative ages as large as ~0.5 (or ~6 Gyr
if an age of 12.8 Gyr is adopted for normalization), and even larger for some
extreme cases. It is shown that the relative MS-fitting method is by far the
age-dating technique for which undetected cluster-to-cluster differences in the
He abundance have less impact. Present results are used in order to pose
constraints on the maximum possible spread in the He and CNONa elements
abundances on the basis of the estimates - taken from the literature - of the
Galactic globular clusters relative age dispersion obtained with the various
relative age-dating techniques. Finally, it is shown that the age-metallicity
relation found for young Galactic globular clusters by the GC Treasury program
is a real age sequence and cannot be produced by variations in the He and/or
heavy element distribution.Comment: 26 pages, 8 figures, accepted for publication in ApJ
The ACS Survey of Galactic Globular Clusters. Vii. Relative Ages
The ACS Survey of Galactic globular clusters is a Hubble Space Telescope Treasury program designed to provide a new large, deep, and homogeneous photometric database. Based on observations from this program, we have measured precise relative ages for a sample of 64 Galactic globular clusters by comparing the relative position of the clusters\u27 main-sequence (MS) turnoffs, using MS fitting to cross-compare clusters within the sample. This method provides relative ages to a formal precision of 2%-7%. We demonstrate that the calculated relative ages are independent of the choice of theoretical model. We find that the Galactic globular cluster sample can be divided into two groups—a population of old clusters with an age dispersion of ~5% and no age-metallicity relation, and a group of younger clusters with an age-metallicity relation similar to that of the globular clusters associated with the Sagittarius dwarf galaxy. These results are consistent with the Milky Way halo having formed in two phases or processes. The first one would be compatible with a rapid (\u3c0.8 Gyr) assembling process of the halo, in which the clusters in the old group were formed. Also these clusters could have been formed before re-ionization in dwarf galaxies that would later merge to build the Milky Way halo as predicted by ΛCDM cosmology. However, the galactocentric metallicity gradient shown by these clusters seems difficult to reconcile with the latter. As for the younger clusters, it is very tempting to argue that their origin is related to their formation within Milky Way satellite galaxies that were later accreted, but the origin of the age-metallicity relation remains unclear
The ACS survey of globular clusters. XIII. Photometric calibration in comparison with Stetson standards
In this study we compare the photometric data of 34 Milky Way globular
clusters, observed within the ACS Treasury Program (PI: Ata Sarajedini) with
the corresponding ground-based data, provided by the Photometric Standard Field
Catalogs of Stetson (2000, 2005). We focus on the transformation between the
HST/ACS F606W to V-band and F814W to I-band only. The goal is to assess the
validity of the filter transformation equations by Sirianni et al.(2005) with
respect to their dependence on metallicity, Horizontal Branch morphology, mass
and integrated (V-I) colour of the various globular clusters. Such a dependence
is expected due to the fact that the transformation equations are based on the
observations of only one globular cluster, i.e., NGC 2419. Surprisingly, the
correlation between offset and metallicity is found to be weak, with a low
level significance. The correlation between offset and Horizontal Branch
structure, as well as total cluster mass is still weaker. Based on the
available data we do not find the photometric offset to be linked to multiple
stellar populations, e.g., as found in NGC 0288, NGC 1851, and NGC 5139. The
results of this study show that there are small systematic offsets between the
transformed ACS- and observed ground based photometry, and that these are only
weakly correlated, if at all, with various cluster parameters and their
underlying stellar populations. As a result, investigators wishing to transform
globular cluster photometry from the Sirianni et al.(2005) ground-based V, I
system onto the Stetson (2000) system simply need to add 0.040 (+/-0.012) to
the V-band magnitudes and 0.047 (+/-0.011) to the I-band magnitudes. This in
turn means that the transformed ACS (V-I) colours match the ground-based values
from Stetson (2000) to within ~0.01 mag.Comment: 28 pages, 14 figures, accepted for publication in ApJ
Photometric type Ia supernova surveys in narrow band filters
We study the characteristics of a narrow band type Ia supernova survey
through simulations based on the upcoming Javalambre Physics of the
accelerating universe Astrophysical Survey (J-PAS). This unique survey has the
capabilities of obtaining distances, redshifts, and the SN type from a single
experiment thereby circumventing the challenges faced by the resource-intensive
spectroscopic follow-up observations. We analyse the flux measurements
signal-to-noise ratio and bias, the supernova typing performance, the ability
to recover light curve parameters given by the SALT2 model, the photometric
redshift precision from type Ia supernova light curves and the effects of
systematic errors on the data. We show that such a survey is not only feasible
but may yield large type Ia supernova samples (up to 250 supernovae at
per month of search) with low core collapse contamination ( per
cent), good precision on the SALT2 parameters (average ,
and ) and on the distance modulus (average
, assuming an intrinsic scatter
), with identified systematic uncertainties
. Moreover, the
filters are narrow enough to detect most spectral features and obtain excellent
photometric redshift precision of , apart from 2 per
cent of outliers. We also present a few strategies for optimising the survey's
outcome. Together with the detailed host galaxy information, narrow band
surveys can be very valuable for the study of supernova rates, spectral feature
relations, intrinsic colour variations and correlations between supernova and
host galaxy properties, all of which are important information for supernova
cosmological applications.Comment: 20 pages, 12 tables and 26 figures. Version accepted by MNRAS, with
results slightly different from previous on
Evidence for Blue Straggler Stars Rejuvenating the Integrated Spectra of Globular Clusters
Integrated spectroscopy is the method of choice for deriving the ages of
unresolved stellar systems. However, hot stellar evolutionary stages, such as
hot horizontal branch stars and blue straggler stars (BSSs), can affect the
integrated ages measured using Balmer lines. Such hot, "non-canonical" stars
may lead to overestimations of the temperature of the main sequence turn-off,
and therefore underestimations of the integrated age of a stellar population.
Using an optimized Hbeta index in conjunction with HST/WFPC2 color-magnitude
diagrams (CMDs), we show that Galactic globular clusters exhibit a large
scatter in their apparent "spectroscopic" ages, which does not correspond to
that in their CMD-derived ages. We find for the first time that the specific
frequency of BSSs, defined within the same aperture as the integrated spectra,
shows a clear correspondence with Hbeta in the sense that, at fixed
metallicity, higher BSS ratios lead to younger "apparent" spectroscopic ages.
Thus, the specific frequency of BSSs in globular clusters sets a fundamental
limit on the accuracy for which spectroscopic ages can be determined for
globular clusters, and maybe for other stellar systems like galaxies. The
observational implications of this result are discussed.Comment: 5 pages, 2 figures, 1 table. Accepted for publication in ApJ
The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
We present new Hubble Space Telescope photometry of the massive globular
cluster M54 (NGC 6715) and the superposed core of the tidally disrupted
Sagittarius (Sgr) dSph galaxy as part of the ACS Survey of Galactic Globular
Clusters. Our deep (F606W~26.5), high-precision photometry yields an
unprecedentedly detailed color-magnitude diagram showing the extended blue
horizontal branch and multiple main sequences of the M54+Sgr system. The
distance and reddening to M54 are revised usingboth isochrone and main-sequence
fitting to (m-M)_0=17.27 and E(B-V)=0.15. Preliminary assessment finds the
M54+Sgr field to be dominated by the old metal-poor populations of Sgr and the
globular cluster. Multiple turnoffs indicate the presence of at least two
intermediate-aged star formation epochs with 4 and 6 Gyr ages and [Fe/H]=-0.4
to -0.6. We also clearly show, for the first time, a prominent, 2.3 Gyr old Sgr
population of near-solar abundance. A trace population of even younger (0.1-0.8
Gyr old), more metal-rich ([Fe/H]\sim0.6) stars is also indicated. The Sgr
age-metallicity relation is consistent with a closed-box model and multiple
(4-5) star formation bursts over the entire life of the satellite, including
the time since Sgr began disrupting.Comment: Accepted to ApJ Letter; 11 pages, 2 figures; figure 1 uploaded as
jpg; paper in ApJ format with full-resolution figures available at:
http://www.astro.ufl.edu/~ata/public_hstgc/paperIV/paperIV.p
Nutritional ecology of European rabbit (Oryctolagus cuniculus): Factors affecting chemical composition of gastric content
[EN] Nutritional ecology seeks to unravel the extensive web of nutritional links that directs animals in their interactions with their ecological and social environments. European rabbit (Oryctolagus cuniculus) populations its endemic locations are declining and it is considered a keystone species of the Mediterranean ecosystem prompteing the interest in its conservation. The main aim of this study was to determine the nutritional composition of the diet of European rabbits through the relative and absolute chemical composition of the gastric content. To address this objective, gastric content was collected from 80 European rabbits in a Mediterranean area for the analysis of its chemical composition. To this end, gastric content was analyzed for dry matter (DM), organic matter (OM), ash, crude protein (CP), highly digestible nonnitrogenous nutrients (HDNN), neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin. The rabbits were divided into two groups: EMPTY and FULL, depending on the level of stomach filling, directly related to food intake. Our results revealed a positive correlation between the rabbits weight with DM in the gastric content, total gastric content with DM in the gastric content, and DM in gastric content with all chemical parameters analysed. The mean relative values obtained were 8.8%, 25.5%, 40.4% and 25.4%, for ash, CP, NDF and HDNN, respectively. Moreover, EMPTY rabbits had both a proportional (+19%, p = 0.002 and -40%; p = 0.004, on NDF and HDNN, respectively) and absolute (-38%, p = 0.014, -52%; p = 0.012, -52%; p = 0.011 and +83%; p = 0.008 for OM, ash, HDNN, and lignin, respectively) different proportion of nutrients in gastric contents than FULL animals. Since there is a connection between this availability and the fitness of this species, understanding the chemical composition of the rabbit's diet can be utilised to delve into its biology. Our study provides information that will help elucidate the factors affecting the chemical composition of the gastric content of European rabbits to assist land use planners and conservationists in identifying sites for conservation in Mediterranean ecosystems.Regional Ministry of Innovation, Universities, Science and Digital Society of the Generalitat Valenciana, Grant/Award Number: GV/2021/115MarÃn-GarcÃa, PJ.; Llobat, L.; Aguayo-Adán, JA.; Franch, J.; Cambra López, M.; Blas Ferrer, E.; Pascual Amorós, JJ.... (2023). Nutritional ecology of European rabbit (Oryctolagus cuniculus): Factors affecting chemical composition of gastric content. Journal of Animal Physiology and Animal Nutrition. 107(6):1495-1501. https://doi.org/10.1111/jpn.1384914951501107
An ionized superbubble powered by a protocluster at z = 6.5
We show herein that a proto-cluster of Ly α emitting galaxies, spectroscopically confirmed at redshift 6.5, produces a remarkable number of ionizing continuum photons. We start from the Ly α fluxes measured in the spectra of the sources detected spectroscopically. From these fluxes, we derive the ionizing emissivity of continuum photons of the protocluster, which we compare with the ionizing emissivity required to reionize the protocluster volume. We find that the sources in the protocluster are capable of ionizing a large bubble, indeed larger than the volume occupied by the protocluster. For various calculations, we have used the model AMIGA, in particular to derive the emissivity of the Lyman continuum photons required to maintain the observed volume ionized. Besides, we have assumed the ionizing photons escape fraction given by AMIGA at this redshift
The ACS Survey of Galactic Globular Clusters. IX. Horizontal Branch Morphology and the Second Parameter Phenomenon
The horizontal branch (HB) morphology of globular clusters (GCs) is most
strongly influenced by metallicity. The second parameter phenomenon
acknowledges that metallicity alone is not enough to describe the HB morphology
of all GCs. In particular, the outer Galactic halo contains GCs with redder HBs
at a given metallicity than are found inside the Solar circle. Thus, at least a
second parameter is required to characterize HB morphology. Here we analyze the
median color difference between the HB and the red giant branch (RGB), d(V-I),
measured from HST ACS photometry of 60 GCs within ~20 kpc of the Galactic
Center. Analysis of this homogeneous data set reveals that, after the influence
of metallicity has been removed, the correlation between d(V-I) and age is
stronger than that of any other parameter considered. Expanding the sample to
include HST photometry of the 6 most distant Galactic GCs lends additional
support to the correlation between d(V-I) and age. This result is robust with
respect to the adopted metallicity scale and the method of age determination,
but must bear the caveat that high quality, detailed abundance information is
not available for a significant fraction of the sample. When a subset of GCs
with similar metallicities and ages are considered, a correlation between
d(V-I) and central luminosity density is exposed. With respect to the existence
of GCs with anomalously red HBs at a given metallicity, we conclude that age is
the second parameter and central density is most likely the third. Important
problems related to HB morphology in GCs, notably multi-modal distributions and
faint blue tails, remain to be explained. (Abridged)Comment: Accepted for publication in ApJ; 49 pages, 19 figure
Near-IR narrow-band imaging with CIRCE at the Gran Telescopio Canarias: Searching for Lyα-emitters at z ∼ 9.3
Context. Identifying very high-redshift galaxies is crucial for understanding the formation and evolution of galaxies. However, many questions still remain, and the uncertainty on the epoch of reionization is large. In this approach, some models allow a double-reionization scenario, although the number of confirmed detections at very high z is still too low to serve as observational proof. Aims: The main goal of this project is studying whether we can search for Lyman-α emitters (LAEs) at z ∼ 9 using a narrow-band (NB) filter that was specifically designed by our team and was built for this experiment. Methods: We used the NB technique to select candidates by measuring the flux excess due to the Lyα emission. The observations were taken with an NB filter (full width at half minimum of 11 nm and central wavelength λc = 1.257 μm) and the CIRCE near-infrared camera for the Gran Telescopio Canarias. We describe a data reduction procedure that was especially optimized to minimize instrumental effects. With a total exposure time of 18.3 h, the final NB image covers an area of ∼6.7 arcmin2, which corresponds to a comoving volume of 1.1 × 103 Mpc3 at z = 9.3. Results: We pushed the source detection to its limit, which allows us to analyze an initial sample of 97 objects. We detail the different criteria we applied to select the candidates. The criteria included visual verifications in different photometric bands. None of the objects resembled a reliable LAE, however, and we found no robust candidate down to an emission-line flux of 2.9 × 10−16 erg s−1 cm−2, which corresponds to a Lyα luminosity limit of 3 × 1044 erg s−1. We derive an upper limit on the Lyα luminosity function at z ∼ 9 that agrees well with previous constraints. We conclude that deeper and wider surveys are needed to study the LAE population at the cosmic dawn
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