2,360 research outputs found
Growth and Feedback from the First Black Holes
Regardless of their initial seed mass, any active galactic nuclei observed at
redshifts z > 6 must have grown by several orders of magnitude from their
seeds. In this chapter, we will discuss the physical processes and latest
research on black hole growth and associated feedback after seed formation.
Fueling is initially slowed down by radiative feedback from the black hole
itself and supernova explosions from nearby stars. Its growth however
accelerates once the host galaxy grows past a critical mass.Comment: 30 pages, 6 figures. Preprint of a review volume chapter to be
published in Latif, M., & Schleicher, D.R.G., "Growth and Feedback from the
First Black Holes'', Formation of the First Black Holes, 2018. Copyright
World Scientific Publishing Company,
https://www.worldscientific.com/worldscibooks/10.1142/1065
How Very Massive Metal Free Stars Start Cosmological Reionization
(Abridged) Using ab initio cosmological Eulerian adaptive mesh refinement
radiation hydrodynamical calculations, we discuss how very massive stars start
the process of cosmological reionization. The models include non-equilibrium
primordial gas chemistry and cooling processes and accurate radiation transport
in the Case B approximation using adaptively ray traced photon packages,
retaining the time derivative in the transport equation. Supernova feedback is
modeled by thermal explosions triggered at parsec scales. All calculations
resolve the local Jeans length by at least 16 grid cells at all times and as
such cover a spatial dynamic range of ~10^6. These first sources of
reionization are highly intermittent and anisotropic and first photoionize the
small scales voids surrounding the halos they form in, rather than the dense
filaments they are embedded in. As the merging objects form larger, dwarf sized
galaxies, the escape fraction of UV radiation decreases and the HII regions
only break out on some sides of the galaxies making them even more anisotropic.
In three cases, SN blast waves induce star formation in overdense regions that
were formed earlier from ionization front instabilities. These stars form tens
of parsecs away from the center of their parent DM halo. Approximately 5
ionizing photons are needed per sustained ionization when star formation in
10^6 M_sun halos are dominant in the calculation. As the halos become larger
than ~10^7 M_sun, the ionizing photon escape fraction decreases, which in turn
increases the number of photons per ionization to 15-50, in calculations with
stellar feedback only. Supernova feedback in these more massive halos creates a
more diffuse medium, allowing the stellar radiation to escape more easily and
maintaining the ratio of 5 ionizing photons per sustained ionization.Comment: 16 pages, 15 figures, accepted to ApJ. Final version. High resolution
images and movies available at
http://www.slac.stanford.edu/~jwise/research/Reionizatio
Association of Cystic Medial Necrosis of the Aorta and Undiagnosed Thyroiditis [Scripta Medica]
We have recently seen two patients with cystic medial necrosis of the aorta. The first patient died of a dissecting aneurysm of the thoracic aorta. At autopsy, classical Hashimoto’s thyroiditis was discovered. The second patient died of a rupture of the ascending aorta. At autopsy, chronic thyroiditis was seen with multiple large germinal center and diffuse fibrosis. Neither patient was clinically suspected of thyroid dysfunction although the second patient had had a partial thyroidectomy in the remote past
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