6,361 research outputs found
Stellar populations in superclusters of galaxies
A catalogue of superclusters of galaxies is used to investigate the influence
of the supercluster environment on galaxy populations, considering galaxies
brighter than M-21+5 h. Empirical spectral synthesis techniques are
applied to obtain the stellar population properties of galaxies which belong to
superclusters and representative values of stellar population parameters are
attributed to each supercluster. We show that richer superclusters present
denser environments and older stellar populations. The galaxy populations of
superclusters classified as filaments and pancakes are statistically similar,
indicating that the morphology of superclusters does not have a significative
influence on the stellar populations. Clusters of galaxies within superclusters
are also examined in order to evaluate the influence of the supercluster
environment on their galaxy properties. Our results suggest that the
environment affects galaxy properties but its influence should operate on
scales of groups and clusters, more than on the scale of superclusters.Comment: 7 pages, 4 figures; accepted to MNRA
Retired galaxies: not to be forgotten in the quest of the star formation -- AGN connection
We propose a fresh look at the Main Galaxy Sample of the Sloan Digital Sky
Survey by packing the galaxies in stellar mass and redshift bins. We show how
important it is to consider the emission-line equivalent widths, in addition to
the commonly used emission-line ratios, to properly identify retired galaxies
(i.e. galaxies that have stopped forming stars and are ionized by their old
stellar populations) and not mistake them for galaxies with low-level nuclear
activity. We find that the proportion of star-forming galaxies decreases with
decreasing redshift in each mass bin, while that of retired galaxies increases.
Galaxies with have formed all their stars at
redshift larger than 0.4. The population of AGN hosts is never dominant for
galaxy masses larger than . We warn about the effects of
stacking galaxy spectra to discuss galaxy properties. We estimate the lifetimes
of active galactic nuclei (AGN) relying entirely on demographic arguments ---
i.e. without any assumption on the AGN radiative properties. We find
upper-limit lifetimes of about 1--5 Gyr for detectable AGN in galaxies with
masses between --. The lifetimes of the AGN-dominated
phases are a few yr. Finally, we compare the star-formation histories of
star-forming, AGN and retired galaxies as obtained by the spectral synthesis
code STARLIGHT. Once the AGN is turned on it inhibits star formation for the
next 0.1 Gyr in galaxies with masses around , 1
Gyr in galaxies with masses around .Comment: accepted for MNRAS figure resolution has been degraded with respect
to what will be published in MNRA
Analysis of the deep chlorophyll maximum across the Azores Front
Physical, chemical and biological observations made in late July and August 1997 across the Azores Front (37ºN, 32ºW to 32ºN, 29ºW) are presented. The objectives of the study were: (1) to analyse horizontal and vertical
profiles of temperature, salinity, density, nutrients and chlorophyll-a (Chl a) of the top 350 m; (2) to identify the
main differences in the deep Chl a Maximum (DCM) and hydrographic structure between the water masses that
pass north and south of the Azores Front; and (3) to estimate phytoplankton primary production in these water
masses. Horizontal and vertical profiles of salinity, temperature, density, nutrients and phytoplankton pigments in
the top 350 m were analysed. The Front separates two distinct water types: the 18 ºC ModeWater (18MW) of subtropical
origin, and the 15 ºC ModeWater (15MW) of sub-polar origin. Differences in the DCM and hydrographic
structure between 18 MW and 15 MW were observed in the contour plots of each section. The average Chl a
concentration between 5 and 200 m depth decreased significantly from 15 MW to 18 MW. The same pattern was
observed for the Chl a concentration at the DCM depth. A vertical one-dimensional model was used to estimate
the phytoplankton primary production in the 15 MW and 18 MW and led to an estimated water column average
gross primary productivity (GPP) between 1.08 and 2.71 mg C
All-sky angular power spectra from cleaned WISESuperCOSMOS galaxy number counts
Aiming to extract cosmological information from linear scales of the
WISESuperCOSMOS photometric redshift catalog, we perform a
characterization of the systematic effects associated with stellar content,
evidencing the presence of contamination and obscuration. We create an
integrated model for these effects (which together we call `usurper
contamination'), devise a method to remove both of them simultaneously and show
its functionality by applying it to a set of mock catalogs. When administered
to WISESuperCOSMOS data, our method shows to improve the measurements
of angular power spectra on scales and the extraction of
cosmological parameters therefrom, even though a significant excess of power
remains at these scales. When ignoring scales , we still find strong
indications of systematics, albeit these can be localized in the southern
equatorial hemisphere. An independent analysis of the northern hemisphere at
agrees with a CDM model with parameters from the Planck
satellite and gives and
at 95% confidence limit when combined with priors
on , and .Comment: 33 pages, 20 figures, 5 tables. Accepted for publication in JCA
Population expansion in the North African Late Pleistocene signalled by mitochondrial DNA haplogroup U6
Background
<br/>
The archaeology of North Africa remains enigmatic, with questions of population continuity versus discontinuity taking centre-stage. Debates have focused on population transitions between the bearers of the Middle Palaeolithic Aterian industry and the later Upper Palaeolithic populations of the Maghreb, as well as between the late Pleistocene and Holocene.
<br/>
Results
Improved resolution of the mitochondrial DNA (mtDNA) haplogroup U6 phylogeny, by the screening of 39 new complete sequences, has enabled us to infer a signal of moderate population expansion using Bayesian coalescent methods. To ascertain the time for this expansion, we applied both a mutation rate accounting for purifying selection and one with an internal calibration based on four approximate archaeological dates: the settlement of the Canary Islands, the settlement of Sardinia and its internal population re-expansion, and the split between haplogroups U5 and U6 around the time of the first modern human settlement of the Near East.
<br/>
Conclusions
<br/>
A Bayesian skyline plot placed the main expansion in the time frame of the Late Pleistocene, around 20 ka, and spatial smoothing techniques suggested that the most probable geographic region for this demographic event was to the west of North Africa. A comparison with U6's European sister clade, U5, revealed a stronger population expansion at around this time in Europe. Also in contrast with U5, a weak signal of a recent population expansion in the last 5,000 years was observed in North Africa, pointing to a moderate impact of the late Neolithic on the local population size of the southern Mediterranean coast
Evidence from 3-a-side soccer games
The aim of this study was to examine the influence of mixing and separating students by sex in the
game performance, as heart rate (HR) demands and rate of perceived exertion (RPE) during 3-a-side small-sided soccer games (SSGs) performed in the context of Physical Education (PE) classes. Twelve students (6 male of 15.33±0.8 years; 1.77±0.10 m; 67.0±4.2 Kg; 21.50±2.5 Kg.m², and; 6 female of 15.00±0.0 years; 1.61±0.01 m; 53.8±9.1 Kg; 19.9±2.3 Kg.m2) performed the SSGs in two conditions: i) separated by sex and ii) mixed-sex.
From single-sex to coeducation conditions results showed significant increases in female RPE and HR (14 to
16.1 and 142 to 163, respectively), but a decrease in the number of wrong passes, goals and shooting accuracy (p < 0.05: 80.5 to 15.2; 3.8 to 1.9 and 1.0 to 0.4, respectively). In the male group, only a single significant increase occurred in the total number of passes between the corresponding two conditions (p = 0.023: 12.5 to 14.1). When comparing the two gender groups in the mixed condition, we registered significantly higher values of the total number of passes and number of wrong passes in males than in females (74%), while the RPE was higher in females (p < 0.05). On the contrary, no significant differences between groups were observed in the separated conditions. These findings suggest a trend toward an increase in the perceived exercise intensity, not completely corroborated by HR data, with less technical proficiency for female students, mainly when playing against their male counterparts. PE teachers should be aware that mixing gender during foot-ball related activities may have a negative impact on female performance, which may impact their motivation and skill acquisition.info:eu-repo/semantics/publishedVersio
Design and development of an inexpensive aquatic swarm robotics system
Swarm robotics is a promising approach characterized by large numbers of relatively small and inexpensive robots. Since such systems typically rely on decentralized control and local communication, they exhibit a number of interesting and useful properties, namely scalability, robustness to individual faults, and flexibility. In this paper, we detail the design and development process of a swarm robotics platform composed of autonomous surface robots, which was designed in order to study the use of robotic swarms in real-world environments. Our aquatic surface robots where manufactured using digital fabrication techniques, such as 3D printing and CNC milling, and all hardware and software has been made available as open-source, thus allowing third-parties to customize and further improve our platform.info:eu-repo/semantics/acceptedVersio
A probabilistic approach to emission-line galaxy classification
We invoke a Gaussian mixture model (GMM) to jointly analyse two traditional
emission-line classification schemes of galaxy ionization sources: the
Baldwin-Phillips-Terlevich (BPT) and vs. [NII]/H
(WHAN) diagrams, using spectroscopic data from the Sloan Digital Sky Survey
Data Release 7 and SEAGal/STARLIGHT datasets. We apply a GMM to empirically
define classes of galaxies in a three-dimensional space spanned by the
[OIII]/H, [NII]/H, and EW(H), optical
parameters. The best-fit GMM based on several statistical criteria suggests a
solution around four Gaussian components (GCs), which are capable to explain up
to 97 per cent of the data variance. Using elements of information theory, we
compare each GC to their respective astronomical counterpart. GC1 and GC4 are
associated with star-forming galaxies, suggesting the need to define a new
starburst subgroup. GC2 is associated with BPT's Active Galaxy Nuclei (AGN)
class and WHAN's weak AGN class. GC3 is associated with BPT's composite class
and WHAN's strong AGN class. Conversely, there is no statistical evidence --
based on four GCs -- for the existence of a Seyfert/LINER dichotomy in our
sample. Notwithstanding, the inclusion of an additional GC5 unravels it. The
GC5 appears associated to the LINER and Passive galaxies on the BPT and WHAN
diagrams respectively. Subtleties aside, we demonstrate the potential of our
methodology to recover/unravel different objects inside the wilderness of
astronomical datasets, without lacking the ability to convey physically
interpretable results. The probabilistic classifications from the GMM analysis
are publicly available within the COINtoolbox
(https://cointoolbox.github.io/GMM\_Catalogue/).Comment: Accepted for publication in MNRA
The galaxy environment in GAMA G3C groups using the Kilo Degree Survey Data Release 3
We aim to investigate the galaxy environment in GAMA Galaxy Groups Catalogue
(G3C) using a volume-limited galaxy sample from the Kilo Degree Survey Data
Release 3. The k-Nearest Neighbour technique is adapted to take into account
the probability density functions (PDFs) of photometric redshifts in our
calculations. This algorithm was tested on simulated KiDS tiles, showing its
capability of recovering the relation between galaxy colour, luminosity and
local environment. The characterization of the galaxy environment in G3C groups
shows systematically steeper density contrasts for more massive groups. The red
galaxy fraction gradients in these groups is evident for most of group mass
bins. The density contrast of red galaxies is systematically higher at group
centers when compared to blue galaxy ones. In addition, distinct group center
definitions are used to show that our results are insensitive to center
definitions. These results confirm the galaxy evolution scenario which
environmental mechanisms are responsible for a slow quenching process as
galaxies fall into groups and clusters, resulting in a smooth observed colour
gradients in galaxy systems.Comment: 14 pages, Accepted to MNRA
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