5,887 research outputs found
The star cluster - field star connection in nearby spiral galaxies. II. Field star and cluster formation histories and their relation
Recent studies have started to cast doubt on the assumption that most stars
are formed in clusters. Observational studies of field stars and star cluster
systems in nearby galaxies can lead to better constraints on the fraction of
stars forming in clusters. We aim to constrain the amount of star formation
happening in long-lived clusters for four galaxies through the homogeneous
study of field stars and star clusters. Using HST/ACS-WFPC2 images of the
galaxies NGC45, NGC1313, NGC5236 and NGC7793, we estimate star formation
histories by means of the synthetic CMD method. Masses and ages of star
clusters are estimated using simple stellar population model fitting. Comparing
observed and modeled luminosity functions we estimate cluster formation rates.
By randomly sampling the stellar IMF, we construct artificial star clusters and
quantify how stochastic effects influence cluster detection, integrated colors
and age estimates. Star formation rates appear to be constant over the past
10-100 Myr. The number of clusters identified per galaxy varies, with few
massive (>10^5Msun) and few old (>1Gyr) clusters. The galaxies NGC5236 and
NGC1313 show high star and cluster formation rates compare to NGC7793 and
NGC45. Stochastic sampling of the SIMF has a strong impact on estimation of
ages, colors and completeness for clusters with masses <10^4Msun, while for
high masses the effect is less pronounced. Stochasticity also makes size
measurements highly uncertain at young ages, making it difficult to distinguish
between clusters and stars based on sizes. The ratio of star formation
happening in clusters compared to the global star formation () appears
to vary for different galaxies. We find no obvious relation between
and the star formation rate density within the range probed here. The
values do, however, appear to correlate with the specific U-band luminosity
(T_L (U)).Comment: 18 pages, 17 figures. A&A accepte
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
No Evidence for Significant Age Spreads in Young Massive LMC Clusters
Recent discoveries have put the picture of stellar clusters being simple
stellar populations into question. In particular, the color-magnitude diagrams
of intermediate age (1-2 Gyr) massive clusters in the Large Magellanic Cloud
(LMC) show features that could be interpreted as age spreads of 100-500 Myr. If
multiple generations of stars are present in these clusters then, as a
consequence, young (<1 Gyr) clusters with similar properties should have age
spreads of the same order. In this paper we use archival Hubble Space Telescope
(HST) data of eight young massive LMC clusters (NGC 1831, NGC 1847, NGC 1850,
NGC 2004, NGC 2100, NGC 2136, NGC 2157 and NGC 2249) to test this hypothesis.
We analyzed the color-magnitude diagrams of these clusters and fitted their
star formation history to derive upper limits of potential age spreads. We find
that none of the clusters analyzed in this work shows evidence for an extended
star formation history that would be consistent with the age spreads proposed
for intermediate age LMC clusters. Tests with artificial single age clusters
show that the fitted age dispersion of the youngest clusters is consistent with
spreads that are purely induced by photometric errors. As an additional result
we determined a new age of NGC 1850 of ~100 Myr, significantly higher than the
commonly used value of about 30 Myr, although consistent with early HST
estimates.Comment: 19 pages, 33 figures, accepted for publication in A&
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 studies of stellar clusters in nearby galaxies
have suggested that young clusters remain embedded for 7-10Myr in their
progenitor molecular cloud, in conflict with optical based studies which find
that clusters are exposed after 1-3Myr. Here, we investigate the role that
spatial resolution plays in this apparent conflict. We use a recent catalogue
of young (~\msun) clusters in the nearby spiral
galaxy, M83, along with Hubble Space Telescope (HST) imaging in the optical and
near-IR, and ground based near-IR 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 near-IR is heavily affected by the resolution, and when aperture sizes
~pc are used, all young/blue clusters move red-ward 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 affect of contamination in the near-IR, we find that, in some cases,
clusters will appear to show near-IR excess when large (~pc) apertures are
used. Our results explain why few young (~Myr), low extinction (\av <
1~mag) clusters have been found in recent ground based near-IR 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 near-IR excess that has been found
in a number of extragalactic YMCs.Comment: 8 pages, 5 figures, accepted for publication in MNRA
An intelligent approach to design and development of personalized meta search: Recommendation of scientific articles
In this article we present a method to recommend articles scientists taking into account their degree of generality or specificity. In terms of methodology, two approaches are presented to recommend articles based on Topic Modeling. The first of these is based on the divergence of topics that are given in the documents, while the second is based on the similarity between these topics. After a validation process it was demonstrated that the proposed methods are more efficient than the traditional methods
Some remarks on Petty projection of log-concave functions
In this note we study the Petty projection of a log-concave function, which
has been recently introduced in [9]. Moreover, we present some new inequalities
involving this new notion, partly complementing and correcting some results
from [9].Comment: 11 Page
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