6,401 research outputs found
M/L, H-alpha Rotation Curves, and HI Measurements for 329 Nearby Cluster and Field Spirals: II. Evidence for Galaxy Infall
We have conducted a study of optical and HI properties of spiral galaxies
(size, luminosity, H-alpha flux distribution, circular velocity, HI gas mass)
to explore the role of gas stripping as a driver of morphological evolution in
clusters. We find a strong correlation between the spiral and S0 fractions
within clusters, and the spiral fraction scales tightly with cluster X-ray gas
luminosity. We explore young star formation and identify spirals that are (1)
asymmetric, with truncated H-alpha emission and HI gas reservoirs on the
leading edge of the disk, on a first pass through the dense intracluster medium
in the cores of rich clusters; (2) strongly HI deficient and stripped, with
star formation confined to the inner 5 kpc/h and 3 disk scale lengths; (3)
reddened, extremely HI deficient and quenched, where star formation has been
halted across the entire disk. We propose that these spirals are in successive
stages of morphological transformation, between infalling field spirals and
cluster S0s, and that the process which acts to remove the HI gas reservoir
suppresses new star formation on a similarly fast timescale. These data suggest
that gas stripping plays a significant role in morphological transformation and
rapid truncation of star formation across the disk.Comment: 24 pages, 12 figures; accepted for publication in AJ;
higher-resolution figures available at http://astronomy.nmsu.edu/nicol
Chandra Observations of Extended X-ray Emission in Arp 220
We resolve the extended X-ray emission from the prototypical ultraluminous
infrared galaxy Arp 220. Extended, faint edge-brightened, soft X-ray lobes
outside the optical galaxy are observed to a distance of 10 to 15 kpc on each
side of the nuclear region. Bright plumes inside the optical isophotes coincide
with the optical line emission and extend 11 kpc from end to end across the
nucleus. The data for the plumes cannot be fit by a single temperature plasma,
and display a range of temperatures from 0.2 to 1 keV. The plumes emerge from
bright, diffuse circumnuclear emission in the inner 3 kpc centered on the
Halpha peak, which is displaced from the radio nuclei. There is a close
morphological correspondence between the Halpha and soft X-ray emission on all
spatial scales. We interpret the plumes as a starburst-driven superwind, and
discuss two interpretations of the emission from the lobes in the context of
simulations of the merger dynamics of Arp 220.Comment: Accepted for publication in ApJ; see also astro-ph/0208477 (Paper 1
A 180 Kpc Tidal Tail in the Luminous Infrared Merger Arp 299
We present VLA HI observations and UH88 deep optical B- and R-band
observations of the IR luminous merger Arp 299 (= NGC 3690 + IC 694). These
data reveal a gas-rich, optically faint tidal tail with a length of over 180
kpc. The size of this tidal feature necessitates an old interaction age for the
merger (~750 Myr since first periapse), which is currently experiencing a very
young star burst (~20 Myr). The observations reveal a most remarkable structure
within the tidal tail: it appears to be composed of two parallel filaments
separated by ~20 kpc. One of the filaments is gas rich with little if any
starlight, while the other is gas poor. We believe that this bifurcation
results from a warped disk in one of the progenitors. The quantities and
kinematics of the tidal HI suggest that Arp 299 results from the collision of a
retrograde Sab-Sb galaxy (IC 694) and a prograde Sbc-Sc galaxy (NGC 3690) that
occurred 750 Myr ago and which will merge into a single object in ~60 Myr. We
suggest that the present IR luminous phase in this system is due in part to the
retrograde spin of IC 694. Finally, we discuss the apparent lack of tidal dwarf
galaxies within the tail.Comment: LaTex, 14 pages, 11 figures, 4 tables, uses emulateapj.sty. Accepted
to AJ for July 1999. For version with full-resolution images see
http://www.cv.nrao.edu/~jhibbard/a299/HIpaper/a299HI.htm
Compilation of extended recursion in call-by-value functional languages
This paper formalizes and proves correct a compilation scheme for
mutually-recursive definitions in call-by-value functional languages. This
scheme supports a wider range of recursive definitions than previous methods.
We formalize our technique as a translation scheme to a lambda-calculus
featuring in-place update of memory blocks, and prove the translation to be
correct.Comment: 62 pages, uses pi
An X-ray Imaging Study of the Stellar Population in RCW49
We present the results of a high-resolution X-ray imaging study of the
stellar population in the Galactic massive star-forming region RCW49 and its
central OB association Westerlund 2. We obtained a 40 ks X-ray image of a
17'x17' field using the Chandra X-ray Observatory and deep NIR images using the
Infrared Survey Facility in a concentric 8'3x8'3 region. We detected 468 X-ray
sources and identified optical, NIR, and Spitzer Space Telescope MIR
counterparts for 379 of them. The unprecedented spatial resolution and
sensitivity of the X-ray image, enhanced by optical and infrared imaging data,
yielded the following results: (1) The central OB association Westerlund 2 is
resolved for the first time in the X-ray band. X-ray emission is detected from
all spectroscopically-identified early-type stars in this region. (2) Most
(86%) X-ray sources with optical or infrared identifications are cluster
members in comparison with a control field in the Galactic Plane. (3) A loose
constraint (2--5 kpc) for the distance to RCW49 is derived from the mean X-ray
luminosity of T Tauri stars. (4) The cluster X-ray population consists of
low-mass pre--main-sequence and early-type stars as obtained from X-ray and NIR
photometry. About 30 new OB star candidates are identified. (5) We estimate a
cluster radius of 6'--7' based on the X-ray surface number density profiles.
(6) A large fraction (90%) of cluster members are identified individually using
complimentary X-ray and MIR excess emission. (7) The brightest five X-ray
sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra.Comment: 19 pages, 17 figures, 4 tables. ApJ in pres
Reconstructing Quantum Geometry from Quantum Information: Spin Networks as Harmonic Oscillators
Loop Quantum Gravity defines the quantum states of space geometry as spin
networks and describes their evolution in time. We reformulate spin networks in
terms of harmonic oscillators and show how the holographic degrees of freedom
of the theory are described as matrix models. This allow us to make a link with
non-commutative geometry and to look at the issue of the semi-classical limit
of LQG from a new perspective. This work is thought as part of a bigger project
of describing quantum geometry in quantum information terms.Comment: 16 pages, revtex, 3 figure
Quantum Histories and Quantum Gravity
This paper reviews the histories approach to quantum mechanics. This
discussion is then applied to theories of quantum gravity. It is argued that
some of the quantum histories must approximate (in a suitable sense) to
classical histories, if the correct classical regime is to be recovered. This
observation has significance for the formulation of new theories (such as
quantum gravity theories) as it puts a constraint on the kinematics, if the
quantum/classical correspondence principle is to be preserved. Consequences for
quantum gravity, particularly for Lorentz symmetry and the idea of "emergent
geometry", are discussed.Comment: 35 pages (29 pages main body), two figure
Highly Damped Quasinormal Modes of Kerr Black Holes: A Complete Numerical Investigation
We compute for the first time very highly damped quasinormal modes of the
(rotating) Kerr black hole. Our numerical technique is based on a decoupling of
the radial and angular equations, performed using a large-frequency expansion
for the angular separation constant_{s}A_{l m}. This allows us to go much
further in overtone number than ever before. We find that the real part of the
quasinormal frequencies approaches a non-zero constant value which does not
depend on the spin s of the perturbing field and on the angular index l:
\omega_R=m\varpi(a). We numerically compute \varpi(a). Leading-order
corrections to the asymptotic frequency are likely to be of order 1/\omega_I.
The imaginary part grows without bound, the spacing between consecutive modes
being a monotonic function of a.Comment: 5 pages, 3 figure
Oxidation of graphene on metals
We use low-energy electron microscopy to investigate how graphene is removed
from Ru(0001) and Ir(111) by reaction with oxygen. We find two mechanisms on
Ru(0001). At short times, oxygen reacts with carbon monomers on the surrounding
Ru surface, decreasing their concentration below the equilibrium value. This
undersaturation causes a flux of carbon from graphene to the monomer gas. In
this initial mechanism, graphene is etched at a rate that is given precisely by
the same non-linear dependence on carbon monomer concentration that governs
growth. Thus, during both growth and etching, carbon attaches and detaches to
graphene as clusters of several carbon atoms. At later times, etching
accelerates. We present evidence that this process involves intercalated
oxygen, which destabilizes graphene. On Ir, this mechanism creates observable
holes. It also occurs mostly quickly near wrinkles in the graphene islands,
depends on the orientation of the graphene with respect to the Ir substrate,
and, in contrast to the first mechanism, can increase the density of carbon
monomers. We also observe that both layers of bilayer graphene islands on Ir
etch together, not sequentially.Comment: 15 pages, 10 figures. Manuscript revised to improve discussion,
following referee comments. Accepted for publication in Journal of Physical
Chemistry C, Feb. 11, 201
Conserved Quantities in Background Independent Theories
We discuss the difficulties that background independent theories based on
quantum geometry encounter in deriving general relativity as the low energy
limit. We follow a geometrogenesis scenario of a phase transition from a
pre-geometric theory to a geometric phase which suggests that a first step
towards the low energy limit is searching for the effective collective
excitations that will characterize it. Using the correspondence between the
pre-geometric background independent theory and a quantum information
processor, we are able to use the method of noiseless subsystems to extract
such coherent collective excitations. We illustrate this in the case of locally
evolving graphs.Comment: 11 pages, 3 figure
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