61,829 research outputs found
SDSS photometry of Asteroids in Cometary Orbits
Aiming at exploring the relationship between asteroids in cometary orbits and
other minor body populations from the observational point of view, I explore
the large photometric database of the Sloan Digital Sky Survey - Moving Objects
Catalog.
The sample of interest was carefully selected analyzing colors and orbital
properties within the data in the catalog. I computed the spectral slope for
each object and compared with published spectroscopic results of other
Asteroids in Cometary Orbits, as well as with other populations of asteroids in
the outer region of the Main belt and Trojans.
Using this extended database I find that Asteroids in Cometary Orbits with
Tisserand parameter below 2.9, and especially below 2.8, are most likely of
primitive origin. The population of objects with Tisserand parameter larger
than 2.9 is a mixture of populations ranging from the inner to the outer Main
belt.Comment: Accepted for publication: 13/11/201
Quasar H II Regions During Cosmic Reionization
Cosmic reionization progresses as HII regions form around sources of ionizing
radiation. Their average size grows continuously until they percolate and
complete reionization. We demonstrate how this typical growth can be calculated
around the largest, biased sources of UV emission, such as quasars, by further
developing an analytical model based on the excursion set formalism. This
approach allows us to calculate the sizes and growth of the HII regions created
by the progenitors of any dark matter halo of given mass and redshift with a
minimum of free parameters. Statistical variations in the size of these
pre-existing HII regions are an additional source of uncertainty in the
determination of very high redshift quasar properties from their observed HII
region sizes. We use this model to demonstrate that the transmission gaps seen
in very high redshift quasars can be understood from the radiation of only
their progenitors and associated clustered small galaxies. The fit sets a lower
limit on the redshift of overlap at z = 5.8 +/- 0.1. This interpretation makes
the transmission gaps independent of the age of the quasars observed. If this
interpretation were correct it would raise the prospects of using radio
interferometers currently under construction to detect the epoch of
reionization.Comment: 6 pages, 3 figures, accepted by MNRAS, revised to match published
versio
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