2,420 research outputs found
Star Formation Across the Taffy Bridge: UGC 12914/15
We present BIMA two-field mosaic CO(1-0) images of the Taffy galaxies (UGC
12914/15), which show the distinct taffy-like radio continuum emission bridging
the two spiral disks. Large amounts of molecular gas (1.4 x 10^{10} Msun, using
the standard Galactic CO-to-H conversion applicable to Galactic disk giant
molecular clouds [GMCs]) were clearly detected throughout the taffy bridge
between the two galaxies, which, as in the more extreme case of HI, presumably
results from a head-on collision between the two galaxies. The highest CO
concentration between the two galaxies corresponds to the H_alpha source in the
taffy bridge near the intruder galaxy UGC 12915. This HII region is also
associated with the strongest source of radio continuum in the bridge, and
shows both morphological and kinematic connections to UGC 12915. The overall CO
distribution of the entire system agrees well with that of the radio continuum
emission, particularly in the taffy bridge. This argues for the star formation
origin of a significant portion of the radio continuum emission. Compared to
the HI morphology and kinematics, which are strongly distorted owing to the
high-speed collision, CO better defines the orbital geometry and impact
parameter of the interaction, as well as the disk properties (e.g., rotation,
orientation) of the progenitor galaxies. Based on the 20cm-to-CO ratio maps, we
conclude that the starburst sites are primarily located in UGC 12915 and the
H_alpha source in the bridge and show that the molecular gas in the taffy
bridge is forming into stars with star formation efficiency comparable to that
of the target galaxy UGC 12914 and similar to that in the Galactic disk.Comment: Minor typo/style corrections to match with the published version (AJ,
Nov. issue). A single .ps.gz file of the entire paper can be downloaded from
http://spider.ipac.caltech.edu/staff/gao/Taffy/all.ps.g
Non-Nuclear Hyper/Ultraluminous X-Ray Sources in the Starbursting Cartwheel Ring Galaxy
We report the Chandra/ACIS-S detection of more than 20 ultraluminous X-ray
sources (ULXs, L_{0.5-10 keV} >~ 3 x 10^{39} ergs/sec) in the Cartwheel
collisional ring galaxy system, of which over a dozen are located in the outer
active star-forming ring. A remarkable hyperluminous X-ray source (HLX,
L_{0.5-10 keV} >~ 10^{41} ergs/sec assuming isotropic radiation), which
dominates the X-ray emission from the Cartwheel ring, is located in the same
segment of the ring as most ULXs. These powerful H/ULXs appear to be coincident
with giant HII region complexes, young star clusters, and radio and
mid-infrared hot-spots: all strong indicators of recent massive star formation.
The X-ray spectra show that H/ULXs have similar properties as those of the {\it
most luminous} ULXs found in the nearest starbursts and galaxy mergers such as
the Antennae galaxies and M82. The close association between the X-ray sources
and the starbursting ring strongly suggests that the H/ULXs are intimately
associated with the production and rapid evolution of short-lived massive
stars. The observations represent the most extreme X-ray luminosities
discovered to date associated with star-forming regions--rivaling the X-ray
luminosities usually associated with active galactic nuclei.Comment: ApJ Letters, accepted (scheduled for the Oct. 20 issue). Full
resolution paper in a single .ps.gz file available at:
http://spider.ipac.caltech.edu/staff/gao/Papers/cartw.ps.g
N-body simulations of galaxies and groups of galaxies with the Marseille GRAPE systems
I review the Marseille GRAPE systems and the N-body simulations done with
them. I first describe briefly the available hardware and software, their
possibilities and their limitations. I then describe work done on interacting
galaxies and groups of galaxies. This includes simulations of the formation of
ring galaxies, simulations of bar destruction by massive compact satellites, of
merging in compact groups and of the formation of brightest members in clusters
of galaxies.Comment: 13 pages, 5 figures, to be published in "Non-linear Dynamics and
Chaos in Astrophysics", eds. J.R. Buchler, S. Gottesman, J. Hunter and H.
Kandrup, Annals of the New York Academy of Science
Turbulent molecular gas and star formation in the shocked intergalactic medium of Stephan's Quintet
We report on single-dish radio CO observations towards the inter-galactic
medium (IGM) of the Stephan's Quintet (SQ) group of galaxies. Extremely bright
mid-IR H2 rotational line emission from warm molecular gas has been detected by
Spitzer in the kpc-scale shock created by a galaxy collision. We detect in the
IGM CO(1-0), (2-1) and (3-2) line emission with complex profiles, spanning a
velocity range of 1000 km/s. The spectra exhibit the pre-shock recession
velocities of the two colliding gas systems (5700 and 6700 km/s), but also
intermediate velocities. This shows that much of the molecular gas has formed
out of diffuse gas accelerated by the galaxy-tidal arm collision. A total H2
mass of 5x10^9 Msun is detected in the shock. The molecular gas carries a large
fraction of the gas kinetic energy involved in the collision, meaning that this
energy has not been thermalized yet. The turbulent kinetic energy of the H2 gas
is at least a factor of 5 greater than the thermal energy of the hot plasma
heated by the collision. The ratio between the warm H2 mass derived from
Spitzer IRS spectroscopy and the H2 mass derived from CO fluxes is ~0.3 in the
IGM of SQ, which is 10-100 times higher than in star-forming galaxies. In the
shocked region, the ratio of the PAH-to-CO surface luminosities, commonly used
to measure the star formation efficiency of the H2 gas, is lower (up to a
factor 75) than the observed values in star-forming galaxies. We suggest that
turbulence fed by the galaxy-tidal arm collision maintains a high heating rate
within the H2 gas. This interpretation implies that the velocity dispersion on
the scale of giant molecular clouds in SQ is one order of magnitude larger than
the Galactic value. The high amplitude of turbulence may explain why this gas
is not forming stars efficiently. [abridged version]Comment: Revised abstract and small editing to match published version. 15
pages, 5 figures. Accepted for publication in Ap
Powerful H Line-cooling in Stephan's Quintet : I - Mapping the Significant Cooling Pathways in Group-wide Shocks
We present results from the mid-infrared spectral mapping of Stephan's
Quintet using the Spitzer Space Telescope. A 1000 km/s collision has produced a
group-wide shock and for the first time the large-scale distribution of warm
molecular hydrogen emission is revealed, as well as its close association with
known shock structures. In the main shock region alone we find 5.0
M of warm H spread over 480 kpc and
additionally report the discovery of a second major shock-excited H
feature. This brings the total H line luminosity of the group in excess of
10 erg/s. In the main shock, the H line luminosity exceeds, by a
factor of three, the X-ray luminosity from the hot shocked gas, confirming that
the H-cooling pathway dominates over the X-ray. [Si II]34.82m
emission, detected at a luminosity of 1/10th of that of the H, appears to
trace the group-wide shock closely and in addition, we detect weak
[FeII]25.99m emission from the most X-ray luminous part of the shock.
Comparison with shock models reveals that this emission is consistent with
regions of fast shocks (100 < < 300 km/s) experiencing depletion of
iron and silicon onto dust grains. Star formation in the shock (as traced via
ionic lines, PAH and dust emission) appears in the intruder galaxy, but most
strikingly at either end of the radio shock. The shock ridge itself shows
little star formation, consistent with a model in which the tremendous H
power is driven by turbulent energy transfer from motions in a post-shocked
layer. The significance of the molecular hydrogen lines over other measured
sources of cooling in fast galaxy-scale shocks may have crucial implications
for the cooling of gas in the assembly of the first galaxies.Comment: 23 pages, 15 figures, Accepted to Ap
Teaching with Feminist Judgments: A Global Conversation
This conversational-style essay is an exchange among fourteen professorsârepresenting thirteen universities across five countriesâwith experience teaching with feminist judgments. Feminist judgments are âshadowâ court decisions rewritten from a feminist perspective, using only the precedent in effect and the facts known at the time of the original decision. Scholars in Canada, England, the U.S., Australia, New Zealand, Scotland, Ireland, India, and Mexico have published (or are currently producing) written collections of feminist judgments that demonstrate how feminist perspectives could have changed the legal reasoning or outcome (or both) in important legal cases. This essay begins to explore the vast pedagogical potential of feminist judgments. The contributors to this conversation describe how they use feminist judgments in the classroom; how students have responded to the judgments; how the professors achieve specific learning objectives through teaching with feminist judgments; and how working with feminist judgmentsâwhether studying them, writing them, or bothâcan help students excavate the multiple social, political, economic, and even personal factors that influence the development of legal rules, structures, and institutions. The primary takeaway of the essay is that feminist judgments are a uniquely enriching pedagogical tool that can broaden the learning experience. Feminist judgments invite future lawyers, and indeed any reader, to re-imagine what the law is, what the law can be, and how to make the law more responsive to the needs of all people
Familiarity and liking of vegetables: Is it important for vegetable consumption?
The results presented in this paper are part of the early findings from a large European study, VeggiEAT involving the UK, Denmark, France and Italy with the aim of improving vegetable consumption in young people and older people. The results presented here are from UK young people (aged 12â14) focusing on familiarity and liking of vegetables and looking at their vegetable consumption and awareness of what constitutes a healthy diet. The study adds to the literature on vegetable familiarity, liking and consumption in this age group. Early exposure of young children to a variety of vegetables is very important and parents/carers and school nurses need to understand the importance of this in terms of the foods offered and available early within a child`s life and the potential influence of this on vegetable consumption over their lifetime
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