2,012 research outputs found
Quasar Radio-Loudness and the Elliptical Core Problem
The dichotomy between radio-loud and radio-quiet QSOs is not simply one of
host morphology. While spiral galaxies almost exclusively host radio-quiet
QSOs, ellipticals can host either radio-louds or radio-quiets. We find that a
combination of accretion rate and host scale determines which type of QSO a
given elliptical galaxy will host. QSOs with high x-ray luminosities (above
10^44.5 erg/s at 0.5 keV) are mostly radio-loud. But those with low
luminosities divide fairly neatly in size (measured by the half-light radius,
r_e). Those larger than about 10 kpc are radio-loud, while smaller ones are
radio-quiet. It has recently been found that core and coreless ellipticals are
also divided near this limit. This implies that for low-luminosity QSOs,
radio-louds are found in core ellipticals, while radio-quiets are in coreless
ellipticals and spirals. This segregation also shows up strongly for
low-redshift objects, and in general, there is a loss over time of coreless,
radio-loud QSOs. Since the presence or absence of a core may be tied to the
galactic merger history, we have an evolutionary explanation for the
differences between radio-loud and radio-quiet QSOs.Comment: 8 pages, 4 figures. To be published in MNRA
Nearby quasar remnants and ultra-high energy cosmic rays
As recently suggested, nearby quasar remnants are plausible sites of
black-hole based compact dynamos that could be capable of accelerating
ultra-high energy cosmic rays (UHECRs). In such a model, UHECRs would originate
at the nuclei of nearby dead quasars, those in which the putative underlying
supermassive black holes are suitably spun-up. Based on galactic optical
luminosity, morphological type, and redshift, we have compiled a small sample
of nearby objects selected to be highly luminous, bulge-dominated galaxies,
likely quasar remnants. The sky coordinates of these galaxies were then
correlated with the arrival directions of cosmic rays detected at energies EeV. An apparently significant correlation appears in our data. This
correlation appears at closer angular scales than those expected when taking
into account the deflection caused by typically assumed IGM or galactic
magnetic fields over a charged particle trajectory. Possible scenarios
producing this effect are discussed, as is the astrophysics of the quasar
remnant candidates. We suggest that quasar remnants be also taken into account
in the forthcoming detailed search for correlations using data from the Auger
Observatory.Comment: 2 figures, 4 tables, 11 pages. Final version to appear in Physical
Review
August 16, 2012 Executive Committee Meeting Minutes
Minutes of the August 16, 2012 Executive Committee meeting, Board of Trustees
September 11, 2015 Meeting Minutes
Minutes of the September 11, 2015 Board of Trustees meeting
March 11, 2016 Executive Committee Meeting
Minutes of the March 11, 2016 Executive Committee Meeting, Board of Trustees
April 21, 2006 Meeting Minutes
Minutes of the April 21, 2006 Board of Trustees meeting
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