145,792 research outputs found
Galaxy Ecosystems: gas contents, inflows and outflows
We use a set of observational data for galaxy cold gas mass fraction and gas
phase metallicity to constrain the content, inflow and outflow of gas in
central galaxies hosted by halos with masses between to
. The gas contents in high redshift galaxies are obtained by
combining the empirical star formation histories of Lu et al. (2014) and star
formation models that relate star formation rate with the cold gas mass in
galaxies. We find that the total baryon mass in low-mass galaxies is always
much less than the universal baryon mass fraction since , regardless of
star formation model adopted. The data for the evolution of the gas phase
metallicity require net metal outflow at , and the metal loading
factor is constrained to be about , or about of the metal yield.
Based on the assumption that galactic outflow is more enriched in metal than
both the interstellar medium and the material ejected at earlier epochs, we are
able to put stringent constraints on the upper limits for both the net
accretion rate and the net mass outflow rate. The upper limits strongly suggest
that the evolution of the gas phase metallicity and gas mass fraction for
low-mass galaxies at is not compatible with strong outflow. We
speculate that the low star formation efficiency of low-mass galaxies is owing
to some preventative processes that prevent gas from accreting into galaxies in
the first place.Comment: 15 pages, 10 figures, submitted to MNRA
Vacua and Exact Solutions in Lower- Limits of EGB
We consider the action principles that are the lower dimensional limits of
the Einstein-Gauss-Bonnet gravity {\it via} the Kaluza-Klein route. We study
the vacua and obtain some exact solutions. We find that the reality condition
of the theories may select one vacuum over the other from the two vacua that
typically arise in Einstein-Gauss-Bonnet gravity. We obtain exact black hole
and cosmological solutions carrying scalar hair, including scalar hairy BTZ
black holes with both mass and angular momentum turned on. We also discuss the
holographic central charges in the asymptotic AdS backgrounds.Comment: Latex, 19 page
Exact Black Hole Formation in Asymptotically (A)dS and Flat Spacetimes
We consider four-dimensional Einstein gravity minimally coupled to a dilaton
scalar field with a supergravity-inspired scalar potential. We obtain an exact
time-dependent spherically symmetric solution describing gravitational collapse
to a static scalar-hairy black hole. The solution can be asymptotically AdS,
flat or dS depending on the value of the cosmological constant parameter
in the potential. As the advanced time increases, the spacetime
reaches equilibrium in an exponential fashion, i.e., with
, where is the mass of the final black
hole and is the second parameter in the potential. Similar to the
Vaidya solution, at , the spacetime can be matched to an (A)dS or flat
vacuum except that at the origin a naked singularity may occur. Moreover, a
limiting case of our solution with gives rise to an (A)dS
generalization of the Roberts solution, thereby making it relevant to critical
phenomena. Our results provide a new model for investigating formation of real
life black holes with . For , it can be instead used
to study non-equilibrium thermalization of certain strongly-coupled field
theory.Comment: Latex, 8 pages, typos corrected and references adde
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