250 research outputs found
How well do we know the age and mass distributions of the star cluster system in the Large Magellanic Cloud?
[ABRIDGED] The LMC star cluster system offers the unique opportunity to
independently check the accuracy of age and mass determinations based on a
number of complementary techniques, including isochrone analysis. Using our
sophisticated tool for star cluster analysis based on broad-band spectral
energy distributions (SEDs), we reanalyse the Hunter et al. (2003) LMC cluster
photometry. Our main aim is to set the tightest limits yet on the accuracy of
ABSOLUTE age determinations based on broad-band SEDs, and therefore on the
usefulness of such an approach. Our broad-band SED fits yield reliable ages,
with statistical absolute uncertainties within Delta[log(Age/yr)] = 0.4
overall. The systematic differences we find with respect to previous age
determinations are caused by conversions of the observational photometry to a
different filter system. The LMC's cluster formation rate (CFR) has been
roughly constant outside of the well-known age gap between ~3 and 13 Gyr, when
the CFR was a factor of ~5 lower. We derive the characteristic cluster
disruption time-scale, log(t_4^dis/yr) = 9.9 +- 0.1, where t_dis = t_4^dis
(M_cl/10^4 Msun)^0.62. This long characteristic disruption time-scale implies
that we are observing the INITIAL cluster mass function (CMF). We conclude that
the youngest mass and luminosity-limited LMC cluster subsets show shallower
slopes than the slope of alpha = -2 expected (at least below masses of a few x
10^3 Msun), which is contrary to dynamical expectations. This may imply that
the initial CMF slope of the LMC cluster system as a whole is NOT well
represented by a power-law, although we cannot disentangle the unbound from the
bound clusters at the youngest ages.Comment: 14 pages, 8 figures, resubmitted to MNRAS after responding to referee
repor
Clustering of Local Group distances: publication bias or correlated measurements? III. The Small Magellanic Cloud
Aiming at providing a firm mean distance estimate to the Small Magellanic
Cloud (SMC), and thus to place it within the internally consistent Local Group
distance framework we recently established, we compiled the current-largest
database of published distance estimates to the galaxy. Based on careful
statistical analysis, we derive mean distance estimates to the SMC using
eclipsing binary systems, variable stars, stellar population tracers, and star
cluster properties. Their weighted mean leads to a final recommendation for the
mean SMC distance of mag, where the
uncertainty represents the formal error. Systematic effects related to
lingering uncertainties in extinction corrections, our physical understanding
of the stellar tracers used, and the SMC's complex geometry---including its
significant line-of-sight depth, its irregular appearance which renders
definition of the galaxy's center uncertain, as well as its high inclination
and possibly warped disk---may contribute additional uncertainties possibly
exceeding 0.15--0.20 mag.Comment: 17 pages, 2 figures (emulateapj format); AJ, in pres
Clustering of Local Group distances: publication bias or correlated measurements? II. M31 and beyond
The accuracy of extragalactic distance measurements ultimately depends on
robust, high-precision determinations of the distances to the galaxies in the
local volume. Following our detailed study addressing possible publication bias
in the published distance determinations to the Large Magellanic Cloud (LMC),
here we extend our distance range of interest to include published distance
moduli to M31 and M33, as well as to a number of their well-known dwarf galaxy
companions. We aim at reaching consensus on the best, most homogeneous, and
internally most consistent set of Local Group distance moduli to adopt for
future, more general use based on the largest set of distance determinations to
individual Local Group galaxies available to date. Based on a careful,
statistically weighted combination of the main stellar population tracers
(Cepheids, RR Lyrae variables, and the magnitude of the tip of the red-giant
branch), we derive a recommended distance modulus to M31 of mag---adopting as our calibration an LMC distance modulus of
mag---and a fully internally consistent set of
benchmark distances to key galaxies in the local volume, enabling us to
establish a robust and unbiased, near-field extragalactic distance ladder.Comment: AJ, in press; 32 pages in AASTeX preprint format, 6 postscript
figures. For online database, see http://astro-expat.info/Data/pubbias.htm
Near-infrared integral-field spectroscopy of violent starburst environments
Near-infrared (NIR) integral-field spectroscopy (IFS) of violent starburst
environments at high spatial (and spectral) resolution has the potential to
revolutionise our ideas regarding the local interactions between the
newly-formed massive stars and the interstellar medium (ISM) of their host
galaxies. To illustrate this point, I present NIR IFS analysis of the central
starburst region of NGC 1140, obtained with CIRPASS on Gemini-South. While
strong [FeII] emission is found throughout the galaxy, higher-order Brackett
emission is predominantly associated with the northern starburst region. Based
on the spatial distributions of the [FeII] versus Brackett line emission, I
conclude that a galaxy-wide starburst was induced several x 10^7 yr ago, with
more recent starburst activity concentrated around the northern starburst
region. I look forward and discuss the exciting prospects that IFS at higher
spatial (and spectral) resolution will allow us trace (i) the massive outflows
("superwinds") expected to originate in the dense, young massive star clusters
commonly found in intense starburst environments, and (ii) their impact on the
galaxy's ISM.Comment: Submitted to "Adaptive Optics-Assisted Integral-Field Spectroscopy",
Rutten R.G.M., Benn C.R., Mendez J., eds., May 2005, La Palma (Spain), New
Astr. Re
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