181 research outputs found
Cosmic Microwave Background Dipole induced by double inflation
The observed CMBR dipole is generally interpreted as the consequence of the
peculiar motion of the Sun with respect to the reference frame of the CMBR.
This article proposes an alternative interpretation in which the observed
dipole is the result of isocurvature perturbations on scales larger than the
present Hubble radius. These perturbations are produced in the simplest model
of double inflation, depending on three parameters. The observed dipole and
quadrupole can be explained in this model, while severely constraining its
parameters.Comment: Latex, 9 pages, no figure, to appear in Phys. Rev.
Lactitol, a new hydrogenated lactose derivative: intestinal absorption and laxative threshold in normal human subjects
An Erupting Classical Nova in a Globular Cluster of M87
Only one certain classical nova eruption has ever been detected inside a
globular cluster - nova 1860 A.D. (T Sco) in M80. During a survey of M87 we
have detected an erupting star coincident (to within 0.08 pixels) with a
globular cluster of that giant elliptical galaxy. We are able to discount
variables in the foreground or background of M87. The light curve and color of
the erupting star match those expected for a nova at the distance of M87. The
chance superposition of an M87 field nova on the globular cluster is very
unlikely but cannot be completely ruled out.Our detection hints at a globular
cluster nova frequency novae/cluster/year, much higher than
previous observations have suggested
Inelastic Dark Matter
Many observations suggest that much of the matter of the universe is
non-baryonic. Recently, the DAMA NaI dark matter direct detection experiment
reported an annual modulation in their event rate consistent with a WIMP relic.
However, the Cryogenic Dark Matter Search (CDMS) Ge experiment excludes most of
the region preferred by DAMA. We demonstrate that if the dark matter can only
scatter by making a transition to a slightly heavier state (Delta m ~ 100kev),
the experiments are no longer in conflict. Moreover, differences in the energy
spectrum of nuclear recoil events could distinguish such a scenario from the
standard WIMP scenario. Finally, we discuss the sneutrino as a candidate for
inelastic dark matter in supersymmetric theories.Comment: 20 pages, 6 figure
Nuclear Shell Model Calculations of Neutralino-Nucleus Cross Sections for Silicon 29 and Germanium 73
We present the results of detailed nuclear shell model calculations of the
spin-dependent elastic cross section for neutralinos scattering from \si29 and
\ge73. The calculations were performed in large model spaces which adequately
describe the configuration mixing in these two nuclei. As tests of the computed
nuclear wave functions, we have calculated several nuclear observables and
compared them with the measured values and found good agreement. In the limit
of zero momentum transfer, we find scattering matrix elements in agreement with
previous estimates for \si29 but significantly different than previous work for
\ge73. A modest quenching, in accord with shell model studies of other heavy
nuclei, has been included to bring agreement between the measured and
calculated values of the magnetic moment for \ge73. Even with this quenching,
the calculated scattering rate is roughly a factor of 2 higher than the best
previous estimates; without quenching, the rate is a factor of 4 higher. This
implies a higher sensitivity for germanium dark matter detectors. We also
investigate the role of finite momentum transfer upon the scattering response
for both nuclei and find that this can significantly change the expected rates.
We close with a brief discussion of the effects of some of the non-nuclear
uncertainties upon the matrix elements.Comment: 31 pages, figures avaiable on request, UCRL-JC-11408
Weighing the Quiescent Central Black Hole in an Elliptical Galaxy with X-ray Emitting Gas
We present a Chandra study of the hot ISM in the giant elliptical galaxy
NGC4649. In common with other group-centred ellipticals, its temperature
profile rises with radius in the outer parts of the galaxy, from ~0.7keV at
2kpc to ~0.9keV by 20kpc. However, within the central ~2kpc the trend reverses
and the temperature peaks at ~1.1keV within the innermost 200pc. Under the
assumption of hydrostatic equilibrium, we demonstrate that the central
temperature spike arises due to the gravitational influence of a quiescent
central super-massive black hole. We constrain the black hole mass (MBH) to
Msun (90% confidence), in good agreement
with stellar kinematics measurements. This is the first direct measurement of
MBH based on studies of hydrostatic X-ray emitting gas, which are sensitive to
the most massive black holes, and is a crucial validation of both
mass-determination techniques. This agreement clearly demonstrates the gas must
be close to hydrostatic, even in the very centre of the galaxy, which is
consistent with the lack of morphological disturbances in the X-ray image.
NGC4649 is now one of only a handful of galaxies for which MBH has been
measured by more than one method. At larger radii, we were able to decompose
the gravitating mass profile into stellar and dark matter (DM) components.
Unless one accounts for the DM, a standard Virial analysis of the stars
dramatically over-estimates the stellar mass of the galaxy. We find the
measured J-band stellar mass-to-light ratio, 1.37+/-0.10 Msun/Lsun, is in good
agreement with simple stellar population model calculations for this object.Comment: 13 pages, 6 figures, accepted for publication in ApJ. Minor revisions
to match published versio
Comparative Approaches to Studying Strategy: Towards an Evolutionary Account of Primate Decision Making
How do primates, humans included, deal with novel problems that arise in interactions with other group members? Despite much research regarding how animals and humans solve social problems, few studies have utilized comparable procedures, outcomes, or measures across different species. Thus, it is difficult to piece together the evolution of decision making, including the roots from which human economic decision making emerged. Recently, a comparative body of decision making research has emerged, relying largely on the methodology of experimental economics in order to address these questions in a cross-species fashion. Experimental economics is an ideal method of inquiry for this approach. It is a well-developed method for distilling complex decision making involving multiple conspecifics whose decisions are contingent upon one another into a series of simple decision choices. This allows these decisions to be compared across species and contexts. In particular, our group has used this approach to investigate coordination in New World monkeys, Old World monkeys, and great apes (including humans), using identical methods. We find that in some cases there are remarkable continuities of outcome, as when some pairs in all species solved a coordination game, the Assurance game. On the other hand, we also find that these similarities in outcomes are likely driven by differences in underlying cognitive mechanisms. New World monkeys required exogenous information about their partnersâ choices in order to solve the task, indicating that they were using a matching strategy. Old World monkeys, on the other hand, solved the task without exogenous cues, leading to investigations into what mechanisms may be underpinning their responses (e.g., reward maximization, strategy formation, etc.). Great apes showed a strong experience effect, with cognitively enriched apes following what appears to be a strategy. Finally, humans were able to solve the task with or without exogenous cues. However, when given the chance to do so, they incorporated an additional mechanism unavailable to the other primates - language - to coordinate outcomes with their partner. We discuss how these results inform not only comparative psychology, but also evolutionary psychology, as they provide an understanding of the evolution of human economic behavior, and the evolution of decision making more broadly
HST/ACS Emission Line Imaging of Low Redshift 3CR Radio Galaxies I: The Data
We present 19 nearby (z<0.3) 3CR radio galaxies imaged at low- and
high-excitation as part of a Cycle 15 Hubble Space Telescope snapshot survey
with the Advanced Camera for Surveys. These images consist of exposures of the
H-alpha (6563 \AA, plus [NII] contamination) and [OIII] 5007 \AA emission lines
using narrow-band linear ramp filters adjusted according to the redshift of the
target. To facilitate continuum subtraction, a single-pointing 60 s line-free
exposure was taken with a medium-band filter appropriate for the target's
redshift. We discuss the steps taken to reduce these images independently of
the automated recalibration pipeline so as to use more recent ACS flat-field
data as well as to better reject cosmic rays. We describe the method used to
produce continuum-free (pure line-emission) images, and present these images
along with qualitative descriptions of the narrow-line region morphologies we
observe. We present H-alpha+[NII] and [OIII] line fluxes from aperture
photometry, finding the values to fall expectedly on the redshift-luminosity
trend from a past HST/WFPC2 emission line study of a larger, generally higher
redshift subset of the 3CR. We also find expected trends between emission line
luminosity and total radio power, as well as a positive correlation between the
size of the emission line region and redshift. We discuss the associated
interpretation of these results, and conclude with a summary of future work
enabled by this dataset.Comment: 18 pages, 12 figures, accepted for publication in ApJ
WFPC2 Observations of Compact Star Cluster Nuclei in Low Luminosity Spiral Galaxies
We have used the Wide Field Planetary Camera 2 aboard the Hubble Space
Telescope to image the compact star cluster nuclei of the nearby, late-type,
low-luminosity spiral galaxies NGC 4395, NGC 4242, and ESO 359-029. We also
analyze archival WFPC2 observations of the compact star cluster nucleus of M33.
A comparative analysis of the structural and photometric properties of these
four nuclei is presented. All of the nuclei are very compact, with luminosity
densities increasing at small radii to the resolution limit of our data. NGC
4395 contains a Seyfert 1 nucleus with a distinct bipolar structure and bright
associated filaments which are likely due to [OIII] emission. The M33 nucleus
has a complex structure, with elongated isophotes and possible signatures of
weak activity, including a jet-like component. The other two nuclei are not
known to be active, but share similar physical size scales and luminosities to
the M33 and NGC 4395 nuclei. The circumnuclear environments of all four of our
program galaxies are extremely diffuse, have only low-to-moderate star
formation, and appear to be devoid of large quantities of dust. The central
gravitational potentials of the galaxies are also quite shallow, making the
origin of these types of `naked' nuclei problematic.Comment: to appear in the July 1999 Astronomical Journal; 38 pages (Latex), 5
tables (postscript), 21 figures (gif); postscript versions of the figures may
be obtained via anonymous ftp at
ftp://ftp.cv.nrao.edu/NRAO-staff/lmatthew/lanl-nucle
Quasar Clustering from SDSS DR5: Dependences on Physical Properties
Using a homogenous sample of 38,208 quasars with a sky coverage of drawn from the SDSS Data Release Five quasar catalog, we study the
dependence of quasar clustering on luminosity, virial black hole mass, quasar
color, and radio loudness. At , quasar clustering depends weakly on
luminosity and virial black hole mass, with typical uncertainty levels for the measured correlation lengths. These weak dependences are
consistent with models in which substantial scatter between quasar luminosity,
virial black hole mass and the host dark matter halo mass has diluted any
clustering difference, where halo mass is assumed to be the relevant quantity
that best correlates with clustering strength. However, the most luminous and
most massive quasars are more strongly clustered (at the level)
than the remainder of the sample, which we attribute to the rapid increase of
the bias factor at the high-mass end of host halos. We do not observe a strong
dependence of clustering strength on quasar colors within our sample. On the
other hand, radio-loud quasars are more strongly clustered than are radio-quiet
quasars matched in redshift and optical luminosity (or virial black hole mass),
consistent with local observations of radio galaxies and radio-loud type 2 AGN.
Thus radio-loud quasars reside in more massive and denser environments in the
biased halo clustering picture. Using the Sheth et al.(2001) formula for the
linear halo bias, the estimated host halo mass for radio-loud quasars is , compared to for
radio-quiet quasar hosts at .Comment: Updated version; accepted for publication in Ap
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