11,568 research outputs found
Quasars, their host galaxies, and their central black holes
We present the final results from our deep HST imaging study of the hosts of
radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and radio galaxies (RGs).
We describe new WFPC2 R-band observations for 14 objects and model these images
in conjunction with the data already reported in McLure et al (1999). We find
that spheroidal hosts become more prevalent with increasing nuclear luminosity
such that, for nuclear luminosities M_V < -23.5, the hosts of both radio-loud
and radio-quiet AGN are virtually all massive ellipticals. Moreover we
demonstrate that the basic properties of these hosts are indistinguishable from
those of quiescent, evolved, low-redshift ellipticals of comparable mass. This
result kills any lingering notion that radio-loudness is determined by
host-galaxy morphology, and also sets severe constraints on evolutionary
schemes which attempt to link low-z ULIRGs with RQQs. Instead, we show that our
results are as expected given the relationship between black-hole and spheroid
mass established for nearby galaxies, and apply this relation to estimate the
mass of the black hole in each object. The results agree very well with
completely-independent estimates based on nuclear emission-line widths; all the
quasars in our sample have M(bh) > 5 x 10^8 solar masses, while the radio-loud
objects are confined to M(bh) > 10^9 solar masses. This apparent mass-threshold
difference, which provides a natural explanation for why RQQs outnumber RLQs by
a factor of 10, appears to reflect the existence of a minimum and maximum level
of black-hole radio output which is a strong function of black-hole mass.
Finally, we use our results to estimate the fraction of massive
spheroids/black-holes which produce quasar-level activity. This fraction is
\~0.1% at the present day, rising to > 10% at z = 2-3.Comment: Revised version accepted for publication in Monthly Notices of the
Royal Astronomical Society. 46 pages, the final 19 of which comprise an
Appendix. 15 figures in main text. A further 14 4-panel greyscale plots and
14 line plots which appear in the Appendix have been reproduced here with
reduced quality due to space limitations. A full resolution copy of the
manuscript can be obtained via ftp://ftp.roe.ac.uk/pub/jsd/dunlop2002.ps.g
Development of fuel cell electrodes, Electrode improvement and life testing, tasks 1 and 3 Final report, 30 Jun. 1966 - 30 Apr. 1968
Volt-ampere characteristics improvement and life testing of electrodes for hydrogen oxygen fuel cell
Parameter estimation in pair hidden Markov models
This paper deals with parameter estimation in pair hidden Markov models
(pair-HMMs). We first provide a rigorous formalism for these models and discuss
possible definitions of likelihoods. The model being biologically motivated,
some restrictions with respect to the full parameter space naturally occur.
Existence of two different Information divergence rates is established and
divergence property (namely positivity at values different from the true one)
is shown under additional assumptions. This yields consistency for the
parameter in parametrization schemes for which the divergence property holds.
Simulations illustrate different cases which are not covered by our results.Comment: corrected typo
Control of multiferroic domains by external electric fields in TbMnO3
The control of multiferroic domains through external electric fields has been
studied by dielectric measurements and by polarized neutron diffraction on
single-crystalline TbMnO. Full hysteresis cycles were recorded by varying
an external field of the order of several kV/mm and by recording the chiral
magnetic scattering as well as the charge in a sample capacitor. Both methods
yield comparable coercive fields that increase upon cooling.Comment: 12 pages, 6 figure
WFPC2 LRF Imaging of Emission Line Nebulae in 3CR Radio Galaxies
We present HST/WFPC2 Linear Ramp Filter images of high surface brightness
emission lines (either [OII], [OIII], or H-alpha+[NII]) in 80 3CR radio
sources. We overlay the emission line images on high resolution VLA radio
images (eight of which are new reductions of archival data) in order to examine
the spatial relationship between the optical and radio emission. We confirm
that the radio and optical emission line structures are consistent with weak
alignment at low redshift (z < 0.6) except in the Compact Steep Spectrum (CSS)
radio galaxies where both the radio source and the emission line nebulae are on
galactic scales and strong alignment is seen at all redshifts. There are weak
trends for the aligned emission line nebulae to be more luminous, and for the
emission line nebula size to increase with redshift and/or radio power. The
combination of these results suggests that there is a limited but real capacity
for the radio source to influence the properties of the emission line nebulae
at these low redshifts (z < 0.6). Our results are consistent with previous
suggestions that both mechanical and radiant energy are responsible for
generating alignment between the radio source and emission line gas.Comment: 80 pages, 54 figures. Accepted for publication in ApJ
Untangling the Conceptual Isssues Raised in Reydon and Scholz’s Critique of Organizational Ecology and Darwinian Populations
Reydon and Scholz raise doubts about the Darwinian status of organizational ecology by arguing that Darwinian principles are not applicable to organizational populations. Although their critique of organizational ecology’s typological essentialism is correct, they go on to reject the Darwinian status of organizational populations. This paper claims that the distinction between replicators and interactors, raised in modern philosophy of biology but not discussed by Reydon and Scholz, points the way forward for organizational ecologists. It is possible to conceptualise evolving Darwinian populations providing the inheritance mechanism is appropriately specified. By this approach, adaptation and selection are no longer dichotomised, and the evolutionary significance of knowledge transmission is highlightedPeer reviewe
Bycatch of lined seahorses (Hippocampus erectus) in a Gulf of Mexico shrimp trawl fishery
Bycatch studies have largely ignored population level effects on fish species of little commercial interest. Here we analyze bycatch of the lined seahorse (Hippocampus erectus) in the bait-shrimp trawl fishery in Hernando Beach, Florida, providing the first fisheries data for this species. Based on catch per unit of effort (CPUE), size, sex, and reproductive status of trawled H. erectus, 1) approximately 72,000 seahorses were caught annually by this fleet, from a population of unknown size, 2) trawling affected population cohorts differentially because of temporal and spatial variation in CPUE and population size, and 3) a greater proportion of females than males was removed in trawling. Our findings suggest that trawling may affect seahorse populations through direct mortality, social disruption, and habitat damage. However, the lack of specific abundance or catchability estimates for H. erectus means that the precise impact of trawling on this fish remains uncertain. This paper focuses attention on the need for research and monitoring of small fishes that are caught incidentally in nonselective gear
The worldwide costs of marine protected areas
Declines in marine harvests, wildlife, and habitats have prompted calls at both the 2002 World Summit on Sustainable Development and the 2003 World Parks Congress for the establishment of a global system of marine protected areas (MPAs). MPAs that restrict fishing and other human activities conserve habitats and populations and, by exporting biomass, may sustain or increase yields of nearby fisheries. Here we provide an estimate of the costs of a global MPA network, based on a survey of the running costs of 83 MPAs worldwide. Annual running costs per unit area spanned six orders of magnitude, and were higher in MPAs that were smaller, closer to coasts, and in high-cost, developed countries. Models extrapolating these findings suggest that a global MPA network meeting the World Parks Congress target of conserving 20–30% of the world’s seas might cost between 19 billion annually to run and would probably create around one million jobs. Although substantial, gross network costs are less than current government expenditures on harmful subsidies to industrial fisheries. They also ignore potential private gains from improved fisheries and tourism and are dwarfed by likely social gains from increasing the sustainability of fisheries and securing vital ecosystem services
Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters
We present new (B,I) photometry for the globular cluster systems in eight
Brightest Cluster Galaxies (BCGs), obtained with the ACS/WFC camera on the
Hubble Space Telescope. In the very rich cluster systems that reside within
these giant galaxies, we find that all have strongly bimodal color
distributions All the BCGs show population gradients, with much higher relative
numbers of red clusters within 5 kpc of their centers, consistent with their
having formed at later times than the blue, metal-poor population. A striking
new feature of the color distributions emerging from our data is that for the
brightest clusters (M_I < -10.5) the color distribution becomes broad and less
obviously bimodal. we suggest that it may be a characteristic of many BCGs.
Furthermore, the blue (metal-poor) clusters become progressively redder with
increasing luminosity, following a mass/metallicity scaling relation Z ~
M^0.55. We argue that these GCS characteristics are consistent with a
hierarchical-merging formation picture in which the metal-poor clusters formed
in protogalactic clouds or dense starburst complexes with gas masses in the
range 10^7 - 10^10 M_Sun, but where the more massive clusters on average formed
in bigger clouds with deeper potential wells where more pre-enrichment could
occur.Comment: 48 pages, 24 Figures, PDF, Submitted to Astrophys.J. and refereed.
For complete pdf file with better figures, see:
http://physwww.mcmaster.ca/%7Eharris/Preprints.htm
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