5,806 research outputs found
Assembly Bias of Dwarf-sized Dark Matter Haloes
Previous studies indicate that assembly bias effects are stronger for lower
mass dark matter haloes. Here we make use of high resolution re-simulations of
rich clusters and their surroundings from the Phoenix Project and a large
volume cosmological simulation, the Millennium-II run, to quantify assembly
bias effects on dwarf-sized dark matter haloes. We find that, in the regions
around massive clusters, dwarf-sized haloes ([10^9,10^{11}]\ms) form earlier
( in redshift) and possess larger ()
than the field galaxies. We find that this environmental dependence is largely
caused by tidal interactions between the ejected haloes and their former hosts,
while other large scale effects are less important. Finally we assess the
effects of assembly bias on dwarf galaxy formation with a sophisticated
semi-analytical galaxy formation model. We find that the dwarf galaxies near
massive clusters tend to be redder () and have three times
as much stellar mass compared to the field galaxies with the same halo mass.
These features should be seen with observational data.Comment: 8 pages, 8 figures, accepted by MNRA
Jet-dominated quiescent states in black hole X-ray binaries: the case of V404 Cyg
The dynamical and radiative properties of the quiescent state (X-ray
luminosity ) of black hole X-ray transients
(BHXTs) remains unclear, mainly because of low-luminosity and poor data
quantity. We demonstrate that, the simultaneous multi-wavelength (including
radio, optical, ultraviolet and X-ray bands) spectrum of V404 Cyg in its bright
quiescent state can be well described by the radiation from the companion star
and more importantly, the compact jet. Neither the outer thin disc nor the
inner hot accretion flow is important in the total spectrum. Together with
several additional recent findings, i.e. the power-law X-ray spectrum and the
constant X-ray spectral shape (or constant photon index) in contrast to the
dramatic change in the X-ray luminosity, we argue the quiescent state spectrum
of BHXTs is actually jet-dominated. Observational features consistent with this
jet model are also discussed as supporting evidences.Comment: accepted for the publication in MNRAS Letters, 5 pages, 2 figure
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