59 research outputs found
Sizes and Shapes of Young Star Cluster Light Profiles in M83
We measure the radii and two-dimensional light profiles of a large sample of
young, massive star clusters in M83 using archival HST/WFC3 imaging of seven
adjacent fields. We use GALFIT to fit the two-dimensional light profiles of the
clusters, from which we find effective (half-light) radii, core radii, and
slopes of the power-law (EFF) profile (). We find lognormal distributions
of effective radius and core radius, with medians of 2.5 pc and
1.3 pc, respectively. Our results provide strong evidence for a
characteristic size of young, massive clusters. The average effective radius
and core radius increase somewhat with cluster age. Little to no change in
effective radius is observed with increasing galactocentric distance, except
perhaps for clusters younger than 100 Myr. We find a shallow correlation
between effective radius and mass for the full cluster sample, but a stronger
correlation is present for clusters 200-300 Myr in age. Finally, the majority
of the clusters are best fit by an EFF model with index . There is
no strong evidence for change in with cluster age, mass, or
galactocentric distance. Our results suggest that clusters emerge from early
evolution with similar radii and are not strongly affected by the tidal field
of M83. Mass loss due to stellar evolution and/or GMC interactions appear to
dominate cluster expansion in the age range we study.Comment: 34 pages, 11 figures, 3 tables, accepted by MNRAS. Machine-readable
table attached (full version of Table 3). To obtain, download the source file
from the "Other formats" link abov
Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. IV. Stephan's Quintet
We present a spectroscopic survey of 21 young massive clusters and complexes
and one tidal dwarf galaxy candidate (TDG) in Stephan's Quintet, an interacting
compact group of galaxies. All of the selected targets lie outside the main
galaxies of the system and are associated with tidal debris. We find clusters
with ages between a few and 125 Myr and confirm the ages estimated through HST
photometry by Fedotov et al. (2011), as well as their modelled interaction
history of the Quintet. Many of the clusters are found to be relatively
long-lived, given their spectrosopically derived ages, while their high masses
suggest that they will likely evolve to eventually become intergalactic
clusters. One cluster, T118, is particularly interesting, given its age (\sim
125 Myr), high mass (\sim 2\times10^6 M\odot) and position in the extreme outer
end of the young tidal tail. This cluster appears to be quite extended (Reff
\sim 12 - 15 pc) compared to clusters observed in galaxy disks (Reff \sim 3 - 4
pc), which confirms an effect we previously found in the tidal tails of NGC
3256, where clusters are similarly extended. We find that star and cluster
formation can proceed at a continuous pace for at least \sim 150 Myr within the
tidal debris of interacting galaxies. The spectrum of the TDG candidate is
dominated by a young population (\sim 7 Myr), and assuming a single age for the
entire region, has a mass of at least 10^6 M\odot.Comment: 37 pages, 10 Figures, 7 Tabl
Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. III. The Antennae
We present optical spectroscopy of 16 star clusters in the merging galaxies
NGC 4038/39 ("The Antennae") and supplement this dataset with HST imaging. The
age and metallicity of each cluster is derived through a comparison between the
observed Balmer and metal line strengths with simple stellar population models.
We then estimate extinctions and masses using the photometry. We find that all
but three clusters have ages between ~3-200 Myr, consistent with the expected
increase in the star-formation rate due to the merger. Most of the clusters
have velocities in agreement with nearby molecular and HI gas that has been
previously shown to be rotating within the progenitor galaxies, hence
star/cluster formation is still taking place within the galactic disks.
However, three clusters have radial velocities that are inconsistent with being
part of the rotating gas disks, which is surprising given their young
(200-500Myr) ages. Interestingly, we find a stellar association with the same
colors (V-I) near one of these three clusters, suggesting that the cluster and
association were formed concurrently and have remained spatially correlated. We
find evidence for spatially distributed cluster formation throughout the
duration of the merger. The impact of various assumptions about the
star/cluster formation rate on the interpretation of the cluster age
distribution are explored, and we do not find evidence for long term "infant
mortality" as has been previously suggested. Models of galaxy mergers that
include a prescription for star formation can provide an overall good fit to
the observed cluster age distribution.Comment: 15 pages, 11 figures, ApJ in pres
The SAMI Galaxy Survey: energy sources of the turbulent velocity dispersion in spatially-resolved local star-forming galaxies
We investigate the energy sources of random turbulent motions of ionised gas
from H emission in eight local star-forming galaxies from the
Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. These
galaxies satisfy strict pure star-forming selection criteria to avoid
contamination from active galactic nuclei (AGN) or strong shocks/outflows.
Using the relatively high spatial and spectral resolution of SAMI, we find that
-- on sub-kpc scales our galaxies display a flat distribution of ionised gas
velocity dispersion as a function of star formation rate (SFR) surface density.
A major fraction of our SAMI galaxies shows higher velocity dispersion than
predictions by feedback-driven models, especially at the low SFR surface
density end. Our results suggest that additional sources beyond star formation
feedback contribute to driving random motions of the interstellar medium (ISM)
in star-forming galaxies. We speculate that gravity, galactic shear, and/or
magnetorotational instability (MRI) may be additional driving sources of
turbulence in these galaxies.Comment: 11 pages, 5 figures, 3 tables. Accepted by MNRA
The SAMI Galaxy Survey: Revising the Fraction of Slow Rotators in IFS Galaxy Surveys
The fraction of galaxies supported by internal rotation compared to galaxies
stabilized by internal pressure provides a strong constraint on galaxy
formation models. In integral field spectroscopy surveys, this fraction is
biased because survey instruments typically only trace the inner parts of the
most massive galaxies. We present aperture corrections for the two most widely
used stellar kinematic quantities and . Our
demonstration involves integral field data from the SAMI Galaxy Survey and the
ATLAS Survey. We find a tight relation for both and
when measured in different apertures that can be used as a linear
transformation as a function of radius, i.e., a first-order aperture
correction. We find that and radial growth curves are
well approximated by second order polynomials. By only fitting the inner
profile (0.5), we successfully recover the profile out to one
if a constraint between the linear and quadratic parameter in the
fit is applied. However, the aperture corrections for and
derived by extrapolating the profiles perform as well as applying
a first-order correction. With our aperture-corrected
measurements, we find that the fraction of slow rotating galaxies increases
with stellar mass. For galaxies with 11, the fraction
of slow rotators is percent, but is underestimated if galaxies
without coverage beyond one are not included in the sample
( percent). With measurements out to the largest aperture radius
the slow rotator fraction is similar as compared to using aperture corrected
values ( percent). Thus, aperture effects can significantly bias
stellar kinematic IFS studies, but this bias can now be removed with the method
outlined here.Comment: Accepted for Publication in the Monthly Notices of the Royal
Astronomical Society. 16 pages and 11 figures. The key figures of the paper
are: 1, 4, 9, and 1
The SAMI Galaxy Survey: gravitational potential and surface density drive stellar populations -- I. early-type galaxies
The well-established correlations between the mass of a galaxy and the
properties of its stars are considered evidence for mass driving the evolution
of the stellar population. However, for early-type galaxies (ETGs), we find
that color and stellar metallicity [Z/H] correlate more strongly with
gravitational potential than with mass , whereas stellar population
age correlates best with surface density . Specifically, for our sample
of 625 ETGs with integral-field spectroscopy from the SAMI Galaxy Survey,
compared to correlations with mass, the color--, [Z/H]--, and
age-- relations show both smaller scatter and less residual trend with
galaxy size. For the star formation duration proxy [/Fe], we find
comparable results for trends with and , with both being
significantly stronger than the [/Fe]- relation. In determining the
strength of a trend, we analyze both the overall scatter, and the observational
uncertainty on the parameters, in order to compare the intrinsic scatter in
each correlation. These results lead us to the following inferences and
interpretations: (1) the color-- diagram is a more precise tool for
determining the developmental stage of the stellar population than the
conventional color--mass diagram; and (2) gravitational potential is the
primary regulator of global stellar metallicity, via its relation to the gas
escape velocity. Furthermore, we propose the following two mechanisms for the
age and [/Fe] relations with : (a) the age-- and
[/Fe]-- correlations arise as results of compactness driven
quenching mechanisms; and/or (b) as fossil records of the
relation in their disk-dominated progenitors.Comment: 9 pages, 4 figures, 1 table Accepted to Ap
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