2,601 research outputs found
Testing An Identification Algorithm for Extragalactic OB Associations Using a Galactic Sample
We have used a Galactic sample of OB stars and associations to test the
performance of an automatic grouping algorithm designed to identify
extragalactic OB associations. The algorithm identifies the known Galactic OB
associations correctly when the search radius (78 pc) is defined by the
observed stellar surface density. Galactic OB associations identified with a 78
pc search radius have diameters that are 3 times larger than OB
associations identified with a 22 pc search radius in M33. Applying the smaller
search radius to the Galactic data matches both the sizes and the number of
member stars between the two galaxies quite well. Thus, we argue that this and
similar algorithms should be used with a constant physical search radius,
rather than one which varies with the stellar surface density. Such an approach
would allow the identification of differences in the giant molecular cloud
populations and star formation efficiency under most circumstances.Comment: accepted to AJ; 16 pages, aas latex, 9 postscript figures; available
at http://www.physics.mcmaster.ca/Wilson_Preprints/index.htm
Extreme CO Isotopic Abundances in the ULIRG IRAS 13120-5453: An Extremely Young Starburst or Top-Heavy Initial Mass Function
We present ALMA CO (J=1-0, 3-2 and 6-5), CO (J=1-0) and
CO (J=1-0) observations of the local Ultra Luminous Infrared Galaxy,
IRAS 13120-5453 (dubbed "The Yo-yo"). The morphologies of the three isotopic
species differ, where CO shows a hole in emission towards the center. We
measure integrated brightness temperature line ratios of CO/CO
60 (exceeding 200) and CO/CO 1 in the central
region. Assuming optical thin emission, CO is more abundant than
CO in several regions. The abundances within the central 500 pc are
consistent with enrichment of the ISM via a young starburst (7Myr), a
top-heavy initial mass function or a combination of both.Comment: 7 pages, 3 figures, accepted for publication in ApJ
Situating emotional experience
Psychological construction approaches to emotion suggest that emotional experience is situated and dynamic. Fear, for example, is typically studied in a physical danger context (e.g., threatening snake), but in the real world, it often occurs in social contexts, especially those involving social evaluation (e.g., public speaking). Understanding situated emotional experience is critical because adaptive responding is guided by situational context (e.g., inferring the intention of another in a social evaluation situation vs. monitoring the environment in a physical danger situation). In an fMRI study, we assessed situated emotional experience using a newly developed paradigm in which participants vividly imagine different scenarios from a first-person perspective, in this case scenarios involving either social evaluation or physical danger. We hypothesized that distributed neural patterns would underlie immersion in social evaluation and physical danger situations, with shared activity patterns across both situations in multiple sensory modalities and in circuitry involved in integrating salient sensory information, and with unique activity patterns for each situation type in coordinated large-scale networks that reflect situated responding. More specifically, we predicted that networks underlying the social inference and mentalizing involved in responding to a social threat (in regions that make up the “default mode” network) would be reliably more active during social evaluation situations. In contrast, networks underlying the visuospatial attention and action planning involved in responding to a physical threat would be reliably more active during physical danger situations. The results supported these hypotheses. In line with emerging psychological construction approaches, the findings suggest that coordinated brain networks offer a systematic way to interpret the distributed patterns that underlie the diverse situational contexts characterizing emotional life
Two Populations of Young Massive Star Clusters in Arp 220
We present new optical observations of young massive star clusters in Arp
220, the nearest ultraluminous infrared galaxy, taken in UBVI with the Hubble
Space Telescope ACS/HRC camera. We find a total of 206 probable clusters whose
spatial distribution is centrally concentrated toward the nucleus of Arp 220.
We use model star cluster tracks to determine ages, luminosities, and masses
for 14 clusters with complete UBVI indices or previously published
near-infrared data. We estimate rough masses for 24 additional clusters with I
< 24 mag from BVI indices alone. The clusters with useful ages fall into two
distinct groups: a ``young'' population (< 10 Myr) and an intermediate-age
population (~300 Myr). There are many clusters with masses clearly above 10^6
Msun and possibly even above 10^7 Msun in the most extreme instances. These
masses are high enough that the clusters being formed in the Arp 220 starburst
can be considered as genuine young globular clusters. In addition, this study
allows us to extend the observed correlation between global star formation rate
and maximum cluster luminosity by more than an order of magnitude in star
formation rate.Comment: 30 pages, 8 figures; figs 1-3 in color; accepted to Ap
Primary interoceptive cortex activity during simulated experiences of the body
Studies of the classic exteroceptive sensory systems (e.g., vision, touch) consistently demonstrate that
vividly imagining a sensory experience of the world – simulating it – is associated with increased
activity in the corresponding primary sensory cortex. We hypothesized, analogously, that simulating
internal bodily sensations would be associated with increased neural activity in primary interoceptive
cortex. An immersive, language-based mental imagery paradigm was used to test this hypothesis (e.g.,
imagine your heart pounding during a roller coaster ride, your face drenched in sweat during a
workout). During two neuroimaging experiments, participants listened to vividly described situations
and imagined “being there” in each scenario. In Study 1, we observed significantly heightened activity
in primary interoceptive cortex (of dorsal posterior insula) during imagined experiences involving
vivid internal sensations. This effect was specific to interoceptive simulation: it was not observed
during a separate affect focus condition in Study 1, nor during an independent Study 2 that did not
involve detailed simulation of internal sensations (instead involving simulation of other sensory
experiences). These findings underscore the large-scale predictive architecture of the brain and reveal
that words can be powerful drivers of bodily experiences
Magnetic Fields in Star-Forming Molecular Clouds I. The First Polarimetry of OMC-3 in Orion A
The first polarimetric images of the OMC-3 region of the Orion A filamentary
molecular cloud are presented. Using the JCMT, we have detected polarized
thermal emission at 850 microns from dust along a 6' length of the dense
filament. The polarization pattern is highly ordered and is aligned with the
filament throughout most of the region. The plane-of-sky magnetic field
direction is perpendicular to the measured polarization. The mean percentage
polarization is 4.2% with a 1 sigma dispersion of 1%. This region is part of
the integral-shaped filament, and active star formation is ongoing along its
length. The protostellar outflow directions do not appear to be consistently
correlated with the direction of the plane-of-sky field or the filament
structure itself. Depolarization toward the filament center, previously
detected in many other star-forming cores and protostars, is also evident in
our data. (abstract abridged)Comment: 9 pages plus 2 figures (1 colour); accepted for publication in the
March 10, 2000 issue (vol. 531 #2) of The Astrophysical Journa
A new view on the ISM of galaxies: far-infrared and submillimetre spectroscopy with Herschel
The FIR/submm window is amongst the least explored spectral regions of the
electromagnetic spectrum. It is, however, a key to study the general properties
of the interstellar medium of galaxies, as it contains important spectral line
diagnostics from the neutral, ionized and molecular ISM. The Herschel Space
Observatory, successfully launched on 14 May 2009, is the first observatory to
cover the entire FIR/submm range between 57 and 672 mum. We discuss the main
results from the ISO era on FIR spectroscopy of galaxies and the enormous
science potential of the Herschel mission through a presentation of its
spectroscopic extragalactic key programs.Comment: 10 pages, 4 figures, accepted for publication in New Astronomy
Review
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