3,454 research outputs found
Evidence of an interaction from resolved stellar populations: The curious case of NGC1313
The galaxy NGC1313 has attracted the attention of various studies due to the
peculiar morphology observed in optical bands, although it is classified as a
barred, late-type galaxy with no apparent close-by companions. However, the
velocity field suggests an interaction with a satellite companion. Using
resolved stellar populations, we study different parts of the galaxy to
understand further its morphology. Based on HST/ACS images, we estimated star
formation histories by means of the synthetic CMD method in different areas in
the galaxy. Incompleteness limits our analysis to ages younger than ~100Myr.
Stars in the red and blue He burning phases are used to trace the distribution
of recent star formation. Star formation histories suggest a burst in the
southern-west region. We support the idea that NGC1313 is experiencing an
interaction with a satellite companion, observed as a tidally disrupted
satellite galaxy in the south-west of NGC1313. However, we do not observe any
indication of a perturbation due to the interaction with the satellite galaxy
at other locations across the galaxy, suggesting that only a modest-sized
companion that did not trigger a global starburst was involved.Comment: 10 pages, 4 figures, accepted for publication in MNRA
The Snapshot Hubble U-Band Cluster Survey (SHUCS) II. Star Cluster Population of NGC 2997
We study the star cluster population of NGC 2997, a giant spiral galaxy
located at 9.5 Mpc and targeted by the Snapshot Hubble U-band Cluster Survey
(SHUCS). Combining our U-band imaging from SHUCS with archival BVI imaging from
HST, we select a high confidence sample of clusters in the circumnuclear ring
and disk through a combination of automatic detection procedures and visual
inspection. The cluster luminosity functions in all four filters can be
approximated by power-laws with indices of to . Some deviations
from pure power-law shape are observed, hinting at the presence of a high-mass
truncation in the cluster mass function. However, upon inspection of the
cluster mass function, we find it is consistent with a pure power-law of index
despite a slight bend at M. No
statistically significant truncation is observed. From the cluster age
distributions, we find a low rate of disruption () in both the
disk and circumnuclear ring. Finally, we estimate the cluster formation
efficiency () over the last 100 Myr in each region, finding %
for the disk, % for the circumnuclear ring, and % for the
entire UBVI footprint. This study highlights the need for wide-field UBVI
coverage of galaxies to study cluster populations in detail, though a small
sample of clusters can provide significant insight into the characteristics of
the population.Comment: 31 pages, 9 figures, accepted to the A
Evidence for Environmentally Dependent Cluster Disruption in M83
Using multi-wavelength imaging from the Wide Field Camera 3 on the Hubble
Space Telescope we study the stellar cluster populations of two adjacent fields
in the nearby face-on spiral galaxy, M83. The observations cover the galactic
centre and reach out to ~6 kpc, thereby spanning a large range of environmental
conditions, ideal for testing empirical laws of cluster disruption. The
clusters are selected by visual inspection to be centrally concentrated,
symmetric, and resolved on the images. We find that a large fraction of objects
detected by automated algorithms (e.g. SExtractor or Daofind) are not clusters,
but rather are associations. These are likely to disperse into the field on
timescales of tens of Myr due to their lower stellar densities and not due to
gas expulsion (i.e. they were never gravitationally bound). We split the sample
into two discrete fields (inner and outer regions of the galaxy) and search for
evidence of environmentally dependent cluster disruption. Colour-colour
diagrams of the clusters, when compared to simple stellar population models,
already indicate that a much larger fraction of the clusters in the outer field
are older by tens of Myr than in the inner field. This impression is quantified
by estimating each cluster's properties (age, mass, and extinction) and
comparing the age/mass distributions between the two fields. Our results are
inconsistent with "universal" age and mass distributions of clusters, and
instead show that the ambient environment strongly affects the observed
populations.Comment: 6 pages, 3 figures, MNRAS in pres
Revealing a Ring-like Cluster Complex in a Tidal Tail of the Starburst Galaxy NGC 2146
We report the discovery of a ring-like cluster complex in the starburst
galaxy NGC 2146. The Ruby Ring, so named due to its appearance, shows a clear
ring-like distribution of star clusters around a central object. It is located
in one of the tidal streams which surround the galaxy. NGC 2146 is part of the
Snapshot Hubble U-band Cluster Survey (SHUCS). The WFC3/F336W data has added
critical information to the available archival Hubble Space Telescope imaging
set of NGC 2146, allowing us to determine ages, masses, and extinctions of the
clusters in the Ruby Ring. These properties have then been used to investigate
the formation of this extraordinary system. We find evidence of a spatial and
temporal correlation between the central cluster and the clusters in the ring.
The latter are about 4 Myr younger than the central cluster, which has an age
of 7 Myr. This result is supported by the H alpha emission which is strongly
coincident with the ring, and weaker at the position of the central cluster.
From the derived total H alpha luminosity of the system we constrain the star
formation rate density to be quite high, e.g. ~ 0.47 Msun/yr/kpc^2. The Ruby
Ring is the product of an intense and localised burst of star formation,
similar to the extended cluster complexes observed in M51 and the Antennae, but
more impressive because is quite isolated. The central cluster contains only 5
% of the total stellar mass in the clusters that are determined within the
complex. The ring-like morphology, the age spread, and the mass ratio support a
triggering formation scenario for this complex. We discuss the formation of the
Ruby Ring in a "collect & collapse" framework. The predictions made by this
model agree quite well with the estimated bubble radius and expansion velocity
produced by the feedback from the central cluster, making the Ruby Ring an
interesting case of triggered star formation.Comment: 11 pages, 7 figures, 1 table; Accepted for publication in MNRA
The effect of spatial resolution on optical and near-IR studies of stellar clusters: implications for the origin of the red excess
Recent ground-based near-IR (NIR) studies of stellar clusters in nearby galaxies have suggested that young clusters remain embedded for 7–10 Myr in their progenitor molecular cloud, in conflict with optical-based studies which find that clusters are exposed after 1–3 Myr. Here, we investigate the role that spatial resolution plays in this apparent conflict. We use a recent catalogue of young (5000 M⊙) clusters in the nearby spiral galaxy, M83, along with Hubble Space Telescope (HST) imaging in the optical and NIR, and ground-based NIR imaging, to see how the colours (and hence estimated properties such as age and extinction) are affected by the aperture size employed, in order to simulate studies of differing resolution. We find that the NIR is heavily affected by the resolution, and when aperture sizes >40 pc are used, all young/blue clusters move redwards in colour space, which results in their appearance as heavily extincted clusters. However, this is due to contamination from nearby sources and nebular emission, and is not an extinction effect. Optical colours are much less affected by resolution. Due to the larger effect of contamination in the NIR, we find that, in some cases, clusters will appear to show NIR excess when large (>20 pc) apertures are used. Our results explain why few young (<6 Myr), low-extinction (A V <1 mag) clusters have been found in recent ground-based NIR studies of cluster populations, while many such clusters have been found in higher resolution HST-based studies. Additionally, resolution effects appear to (at least partially) explain the origin of the NIR excess that has been found in a number of extragalactic young massive clusters
Leaf pigments in cauliflower cultivated with different water conditions and silicon applications
Environmental factors and crop management can influence the characteristics of plant morphology and physiology, altering photosynthetic efficiency and mass accumulation. The study aimed to analyze the contents of leaf pigments in cauliflower cultivated under different conditions of water availability and silicon (Si) applications. The experiment was carried out in a protected environment in the city of Maringá-PR. A randomized block design, in a 3x4 factorial scheme, with three replacement conditions [40, 70 and 100% of crop evapotranspiration (ETc)] and four Si doses (0, 50, 100 and 150 kg ha-1), with four repetitions. The cauliflower cultivation, cultivar Sharon, was carried out in dystroferric RED NITOSOL. Daily evapotranspiration was determined with a constant level water table lysimeter and water replacement was performed with drip irrigation. Si was applied in split doses in three applications (initial, intermediate and final phases). At flowering, leaf tissue from the upper third of the plant was collected, with pigment extraction performed with pure acetone and determination in a spectrophotometer. At harvest, the leaf area of ​​the plants was determined. Data were subjected to analysis of variance and regression analysis. Cauliflower crop under water-deficient reduces leaf area development and alters chloroplast pigments dynamics. Silicon use in the soil increases leaf development, chlorophyll a and b contents, and reduces carotenoids concentration. Under water stress conditions, silicon addition to the soil improves cauliflower performance
The relation between surface star formation rate density and spiral arms in NGC 5236 (M83)
For a long time the consensus has been that star formation rates are higher
in the interior of spiral arms in galaxies, compared to inter-arm regions.
However, recent studies have found that the star formation inside the arms is
not more efficient than elsewhere in the galaxy. Previous studies have based
their conclusion mainly on integrated light. We use resolved stellar
populations to investigate the star formation rates throughout the nearby
spiral galaxy NGC 5236. We aim to investigate how the star formation rate
varies in the spiral arms compared to the inter-arm regions, using optical
space-based observations of NGC 5236. Using ground-based H\alpha images we
traced regions of recent star formation, and reconstructed the arms of the
galaxy. Using HST/ACS images we estimate star formation histories by means of
the synthetic CMD method. Arms based on H\alpha images showed to follow the
regions where stellar crowding is higher. Star formation rates for individual
arms over the fields covered were estimated between 10 to 100 Myr, where the
stellar photometry is less affected by incompleteness. Comparison between arms
and inter-arm surface star formation rate densities (\Sigma) suggested
higher values in the arms (\sim0.6 dex). Over a small fraction of one arm we
checked how the \Sigma changes for the trailing and leading part. The
leading part of the arm showed to have a higher \Sigma in the age range
10-100 Myr. Predictions from the density wave theory of a rapid increase in the
star formation at the edge where the stars and the gas enter the density wave
are confirmed. The \Sigma presents a steep decrease with distance from
the center of the arms through the inter-arm regions.Comment: 10 pages, 11 figures. Accepted for publication in Astronomy and
Astrophysic
Stellar Clusters in M83: Formation, evolution, disruption and the influence of environment
We study the stellar cluster population in two adjacent fields in the nearby,
face-on spiral galaxy, M83, using WFC3/HST imaging. The clusters are selected
through visual inspection to be centrally concentrated, symmetric, and resolved
on the images, which allows us to differentiate between clusters and likely
unbound associations. We compare our sample with previous studies and show that
the differences between the catalogues are largely due to the inclusion of
large numbers of diffuse associations within previous catalogues. The
luminosity function of the clusters is well approximated by a power-law with
index, -2, over most of the observed range, however a steepening is seen at M_V
= -9.3 and -8.8 in the inner and outer fields, respectively. Additionally, we
show that the cluster population is inconsistent with a pure power-law mass
distribution, but instead exhibits a truncation at the high mass end. If
described as a Schechter function, the characteristic mass is 1.6 and 0.5 *
10^5 Msun, for the inner and outer fields, respectively, in agreement with
previous estimates of other cluster populations in spiral galaxies. Comparing
the predictions of the mass independent disruption (MID) and mass dependent
disruption (MDD) scenarios with the observed distributions, we find that both
models can accurately fit the data. However, for the MID case, the fraction of
clusters destroyed (or mass lost) per decade in age is dependent on the
environment, hence, the age/mass distributions of clusters are not universal.
In the MDD case, the disruption timescale scales with galactocentric distance
(being longer in the outer regions of the galaxy) in agreement with analytic
and numerical predictions. Finally, we discuss the implications of our results
on other extragalactic surveys, focussing on the fraction of stars that form in
clusters and the need (or lack thereof) for infant mortality.Comment: 19 pages, 20 figures, MNRAS in pres
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