304 research outputs found
Constraining star cluster disruption mechanisms
Star clusters are found in all sorts of environments and their formation and
evolution is inextricably linked to the star formation process. Their eventual
destruction can result from a number of factors at different times, but the
process can be investigated as a whole through the study of the cluster age
distribution. Observations of populous cluster samples reveal a distribution
following a power law of index approximately -1. In this work we use M33 as a
test case to examine the age distribution of an archetypal cluster population
and show that it is in fact the evolving shape of the mass detection limit that
defines this trend. That is to say, any magnitude-limited sample will appear to
follow a dN/dt=1/t, while cutting the sample according to mass gives rise to a
composite structure, perhaps implying a dependence of the cluster disruption
process on mass. In the context of this framework, we examine different models
of cluster disruption from both theoretical and observational standpoints.Comment: To appear in the proceedings of IAU Symposium 266: "Star Clusters:
Basic Galactic Building Blocks Throughout Time And Space", eds. R. de Grijs
and J. Lepin
A detailed study of the enigmatic cluster M82F
We present a detailed study of the stellar cluster M82F, using multi-band
high resolution HST imaging and deep ground based optical slit and integral
field spectroscopy. Using the imaging we create colour maps of the cluster and
surrounding region in order to search for substructure. We find a large amount
of substructure, which we interpret as the result of differential extinction
across the projected face of the cluster. With this interpretation, we are able
to construct a spatially resolved extinction map across the cluster which is
used to derive the intrinsic flux distribution. Fitting cluster profiles (King
and EFF) to the intrinsic images we find that the cluster is 15-30% larger than
previous estimates, and that no strong evidence of mass segregation in this
cluster exists. Using the optical spectra, we find that the age of M82F is
60-80 Myr and from its velocity conclude that the cluster is not physically
associated with a large HII region that it is projected upon, both in agreement
with previous studies. The reconstructed integral field maps show that that
majority of the line emission comes from a nearby HII region. The spatial
dependence of the line widths (implying the presence of multiple
components)measured corresponds to the extinction map derived from photometry,
indicating that the gas/dust clouds responsible for the extinction are also
partially ionised. Even with the wealth of observations presented here, we do
not find a conclusive solution to the problem of the high light-to-mass ratio
previously found for this cluster and its possible top-heavy stellar IMF.Comment: 12 pages, 7 figures, accepted MNRA
Low-frequency wide band-gap elastic/acoustic meta-materials using the K-damping concept
The terms "acoustic/elastic meta-materials" describe a class of periodic
structures with unit cells exhibiting local resonance. This localized resonant
structure has been shown to result in negative effective stiffness and/or mass
at frequency ranges close to these local resonances. As a result, these
structures present unusual wave propagation properties at wavelengths well
below the regime corresponding to band-gap generation based on spatial
periodicity, (i.e. "Bragg scattering"). Therefore, acoustic/elastic
meta-materials can lead to applications, especially suitable in the
low-frequency range. However, low frequency range applications of such
meta-materials require very heavy internal moving masses, as well as additional
constraints at the amplitudes of the internally oscillating locally resonating
structures, which may prohibit their practical implementation. In order to
resolve this disadvantage, the K-Damping concept will be analyzed. According to
this concept, the acoustic/elastic meta-materials are designed to include
negative stiffness elements instead or in addition to the internally resonating
added masses. This concept removes the need for the heavy locally added heavy
masses, while it simultaneously exploits the negative stiffness damping
phenomenon. Application of both Bloch's theory and the classical modal analysis
at the one-dimensional mass-in-mass lattice is analyzed and corresponding
dispersion relations are derived. The results indicate significant advantages
over the conventional mass-in-a mass lattice, such as broader band-gaps and
increased damping ratio and reveal significant potential in the proposed
solution. Preliminary feasibility analysis for seismic meta-structures and low
frequency acoustic isolation-damping confirm the strong potential and
applicability of this concept.Comment: Keywords: Acoustic meta-materials, elastic meta-materials,
low-frequency vibration absorption, seismic meta-structures, noise absorptio
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
The Young Cluster Population of M82 Region B
We present observations obtained with the Advanced Camera for Surveys on
board the Hubble Space Telescope of the "fossil" starburst region B in the
nearby starburst galaxy M82. By comparing UBVI photometry with models, we
derive ages and extinctions for 35 U-band selected star clusters. We find that
the peak epoch of cluster formation occurred ~ 150 Myr ago, in contrast to
earlier work that found a peak formation age of 1.1 Gyr. The difference is most
likely due to our inclusion of U-band data, which are essential for accurate
age determinations of young cluster populations. We further show that the
previously reported turnover in the cluster luminosity function is probably due
to the neglect of the effect of extended sources on the detection limit. The
much younger cluster ages we derive clarifies the evolution of the M82
starburst. The M82-B age distribution now overlaps with the ages of: the
nuclear starburst; clusters formed on the opposite side of the disk; and the
last encounter with M81, some 220 Myr ago.Comment: 11 pages, 4 figures, accepted for publication in ApJ Letter
A spectroscopic census of the M82 stellar cluster population
We present a spectroscopic study of the stellar cluster population of M82,
the archetype starburst galaxy, based primarily on new Gemini-North
multi-object spectroscopy of 49 star clusters. These observations constitute
the largest to date spectroscopic dataset of extragalactic young clusters,
giving virtually continuous coverage across the galaxy; we use these data to
deduce information about the clusters as well as the M82 post-starburst disk
and nuclear starburst environments. Spectroscopic age-dating places clusters in
the nucleus and disk between (7, 15) and (30, 270) Myr, with distribution peaks
at ~10 and ~140 Myr respectively. We find cluster radial velocities in the
range (-160, 220) km/s (wrt the galaxy centre) and line of sight Na I D
interstellar absorption line velocities in (-75, 200) km/s, in many cases
entirely decoupled from the clusters. As the disk cluster radial velocities lie
on the flat part of the galaxy rotation curve, we conclude that they comprise a
regularly orbiting system. Our observations suggest that the largest part of
the population was created as a result of the close encounter with M81 ~220 Myr
ago. Clusters in the nucleus are found in solid body rotation on the bar. The
possible detection of WR features in their spectra indicates that cluster
formation continues in the central starburst zone. We also report the potential
discovery of two old populous clusters in the halo of M82, aged >8 Gyr. Using
these measurements and simple dynamical considerations, we derive a toy model
for the invisible physical structure of the galaxy, and confirm the existence
of two dominant spiral arms.Comment: Accepted for publication in the Astrophysical Journa
Gemini Spectroscopy and HST Imaging of the Stellar Cluster Population in Region B of M82
We present new spectroscopic observations of the stellar cluster population
of region B in the prototype starburst galaxy M82 obtained with the Gillett
Gemini-North 8.1-metre telescope. By coupling the spectroscopy with UBVI
photometry acquired with the Advanced Camera for Surveys (ACS) on the Hubble
Space Telescope (HST), we derive ages, extinctions and radial velocities for
seven young massive clusters (YMCs) in region B. We find the clusters to have
ages between 70 and 200 Myr and velocities in the range 230 to 350 km/s, while
extinctions Av vary between ~1-2.5 mag. We also find evidence of differential
extinction across the faces of some clusters which hinders the photometric
determination of ages and extinctions in these cases. The cluster radial
velocities indicate that the clusters are located at different depths within
the disk, and are on regular disk orbits. Our results overall contradict the
findings of previous studies, where region B was thought to be a bound region
populated by intermediate-age clusters that formed in an independent, offset
starburst episode that commenced 600 Myr-1 Gyr ago. Our findings instead
suggest that region B is optically bright because of low extinction patches,
and this allows us to view the cluster population of the inner M82 disk, which
probably formed as a result of the last encounter with M81. This study forms
part of a series of papers aimed at studying the cluster population of M82
using deep optical spectroscopy and multi-band photometry.Comment: 12 pages, 8 figures; accepted for publication in The Astrophysical
Journa
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