110 research outputs found
Globular Cluster Formation in M82
We present high resolution mid-infrared (mid-IR; 11.7 and 17.65 micron) maps
of the central 400 pc region of the starburst galaxy M82. Seven star forming
clusters are identified which together provide ~ 15% of the total mid-IR
luminosity of the galaxy. Combining the mid-IR data with thermal radio
measurements and near- and mid-IR line emission, we find that these young
stellar clusters have inferred masses and sizes comparable to globular
clusters. At least 20% of the star formation in M82 is found to occur in
super-star clusters.Comment: 12 pages including three color figures; accepted for publication in
Ap
Mid-IR FORCAST/SOFIA Observations of M82
We present 75"x75" size maps of M82 at 6.4 micron, 6.6 micron, 7.7 micron,
31.5 micron, and 37.1 micron with a resolution of ~4" that we have obtained
with the mid-IR camera FORCAST on SOFIA. We find strong emission from the inner
60" (~1kpc) along the major axis, with the main peak 5" west-southwest of the
nucleus and a secondary peak 4" east-northeast of the nucleus. The detailed
morphology of the emission differs among the bands, which is likely due to
different dust components dominating the continuum emission at short mid-IR
wavelengths and long mid-IR wavelengths. We include Spitzer-IRS and
Herschel/PACS 70 micron data to fit spectral energy distribution templates at
both emission peaks. The best fitting templates have extinctions of A_V = 18
and A_V = 9 toward the main and secondary emission peak and we estimated a
color temperature of 68 K at both peaks from the 31 micron and 37 micron
measurement. At the emission peaks the estimated dust masses are on the order
of 10^{4} M_sun.Comment: ApJL in press (ApJ, 749, L19), article also available at at
http://stacks.iop.org/2041-8205/749/L1
Comparative theory, China, and the future of East Asian regionalism(s)
Despite the development of an increasingly sophisticated literature on comparative regional integration drawing from a variety of cases, the European experience remains the most often used benchmark against which other integrative processes are judged; there is still an often implicit expectation that 'successful' processes of regionalism will end up looking something like the European Union. While it is correct to move away from such a 'Euro-dominance', the theoretical lessons learned continue to have salience when applied to emerging and competing forms of integrative processes in East Asia. in particular, when economic considerations dominate regional relations at times of economic crises then integrative logics and strategies come to the fore. In more 'normal' times when geo-strategic considerations reassert themselves, then the consensus over region building and the very nature of the region itself is weakened and cooperation is replaced by competing visions and the over-supply of region
Why nations lead or lag in energy transitions
Policy-driven change hinges on institutions that support insulation or compensationaRussia’s invasion of Ukraine has disrupted energy markets, producing price spikes reminiscent of the 1970s. Many suggest that the crisis may accelerate transitions away from fossil fuels and reduce greenhouse gas (GHG) emissions. Yet, governments have responded very differently to the price shock. Though some are prioritizing clean energy, others are doubling down on fossil fuel production. Why do countries respond so differently to the same problem? Access to domestic fossil fuel resources is only part of the story. Countries also vary in the political sources that enable transformational change in energy and climate policy (1, 2). We draw on two historical episodes illustrating variation in energy transitions across countries—the 1970s oil shocks, and policies to address climate change—to offer important lessons on the political opportunities and constraints for policy-makers across different countries to accelerate the transition to clean energy
Where Are The M Dwarf Disks Older Than 10 Million Years?
We present 11.7-micron observations of nine late-type dwarfs obtained at the
Keck I 10-meter telescope in December 2002 and April 2003. Our targets were
selected for their youth or apparent IRAS 12-micron excess. For all nine
sources, excess infrared emission is not detected. We find that stellar wind
drag can dominate the circumstellar grain removal and plausibly explain the
dearth of M Dwarf systems older than 10 Myr with currently detected infrared
excesses. We predict M dwarfs possess fractional infrared excess on the order
of L_{IR}/L_{*}\sim10^{-6} and this may be detectable with future efforts.Comment: 24 pages, 2 figures, accepted to Ap
AAOmega spectroscopy of 29 351 stars in fields centered on ten Galactic globular clusters
Galactic globular clusters have been pivotal in our understanding of many
astrophysical phenomena. Here we publish the extracted stellar parameters from
a recent large spectroscopic survey of ten globular clusters. A brief review of
the project is also presented. Stellar parameters have been extracted from
individual stellar spectra using both a modified version of the Radial Velocity
Experiment (RAVE) pipeline and a pipeline based on the parameter estimation
method of RAVE. We publish here all parameters extracted from both pipelines.
We calibrate the metallicity and convert this to [Fe/H] for each star and,
furthermore, we compare the velocities and velocity dispersions of the Galactic
stars in each field to the Besan\c{c}on Galaxy model. We find that the model
does not correspond well with the data, indicating that the model is probably
of little use for comparisons with pencil beam survey data such as this.Comment: 6 pages, 5 figures, 4 tables. Accepted for publication in A&A. Data
described in tables will be available on CDS (at
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/530/A31) once publishe
Locating the Youngest HII Regions in M82 with 7 mm Continuum Maps
We present 7mm Very Large Array continuum images of the starburst galaxy M82.
On arcsecond scales, two-thirds of the 7mm continuum consists of free-free
emission from HII regions. In the subarcsecond resolution map, we identify 14
compact sources, including 9 bright HII regions with N_Lyc > 10^51 sec^-1. Four
of the HII regions have rising spectra, implying emission measures > 10^8 cm^-6
pc. Except for one compact source with peculiar features, all other compact
radio sources are found in dust lanes and do not have optical or near-infrared
continuum counterparts. Four regions of extended, high brightness (EM > 10^7
cm-6 pc) radio emission are found in our high resolution map, including some as
large as ~2", or 30 pc, representing either associations of small HII regions,
or sheetlike structures of denser gas. The good correlation between 7 mm
emission and Spitzer IRAC 8 micron continuum-removed PAH feature suggests that
PAH emission may track the recently formed OB stars. We find an excellent
correlation between molecular gas and star formation, particularly dense gas
traced by HCN, down to the ~ 45 pc scale in M82. We also find star formation
efficiencies (SFEs) of 1-10% on the same scale, based on CO maps. The highest
SFE are found in regions with the highest dense gas fractions.Comment: 18 pages, 10 figures. Accepted for publication in A
Red supergiants as potential Type IIn supernova progenitors: Spatially resolved 4.6 micron CO emission around VY CMa and Betelgeuse
We present high-resolution 4.6micron CO spectra of the circumstellar
environments of two RSGs that are potential SN progenitors: Betelgeuse and VY
CMa. Around Betelgeuse, 12CO emission within 3arcsec follows a mildly clumpy
but otherwise spherical shell, smaller than its 55arcsec shell in KI
lambda7699. In stark contrast, 4.6micron CO emission around VY CMa is
coincident with bright KI in its clumpy asymmetric reflection nebula, within
5arcsec of the star. Our CO data reveal redshifted features not seen in KI
spectra of VY CMa, indicating a more isotropic distribution of gas punctuated
by randomly distributed asymmetric clumps. The relative CO and KI distribution
in Betelgeuse arises from ionization effects within a steady wind, whereas in
VY CMa, KI is emitted from skins of CO cloudlets resulting from episodic mass
ejections 500--1000 yr ago. In both cases, CO and KI trace potential pre-SN
circumstellar matter: we conclude that an extreme RSG like VY CMa might produce
a Type IIn event like SN1988Z if it were to explode in its current state, but
Betelgeuse will not. VY CMa demonstrates that LBVs are not necessarily the only
progenitors of SNe IIn, but it underscores the requirement that SNe IIn suffer
enhanced episodic mass loss shortly before exploding.Comment: 16 pages, AJ accepte
Evolving Starburst Modeling of FIR/sub-mm/mm Line Emission. II. Application to M 82
We present starburst models for far-infrared/sub-millimeter/millimeter
(FIR/sub-mm/mm) line emission of molecular and atomic gas in an evolving
starburst region, which is treated as an ensemble of non-interacting hot
bubbles which drive spherical shells of swept-up gas into a surrounding uniform
gas medium. These bubbles and shells are driven by stellar winds and supernovae
within massive star clusters formed during an instantaneous starburst. The
underlying stellar radiation from the evolving clusters affects the properties
and structure of photodissociation regions (PDRs) in the shells, and hence the
spectral energy distributions (SEDs) of the molecular and atomic line emission
from these swept-up shells and the associated parent giant molecular clouds
(GMCs) contains a signature of the stage of evolution of the starburst. The
physical and chemical properties of the shells and their structure are computed
using a a simple well known similarity solution for the shell expansion, a
stellar population synthesis code, and a time-dependent PDR chemistry model.
The SEDs for several molecular and atomic lines (CO and its isotope
CO, HCN, HCO, C, O, and C) are computed using a non-local
thermodynamic equilibrium (non-LTE) line radiative transfer model. By comparing
our models with the available observed data of nearby infrared bright galaxies,
especially M 82, we constrain the models and in the case of M 82, we provide
estimates for the ages (5 - 6 Myr, 10 Myr) of recent starburst activity. We
also derive a total H gas mass of 2 - 3.4 10
M for the observed regions of the central 1 kpc starburst disk of M
82.Comment: Accepted for publication in the ApJ, 56 pages, 14 figures, 3 table
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