119434810
Ly-alpha forests and cooling outflow from dwarf galaxies
We propose that cooling outflows from star-forming dwarf galaxies that are spatially correlated with but unbound to bright galaxies may account for the low column QSO Ly$\alpha$ forests, providing an explanation for both the heavy elements recently detected in them and the large sizes associated with them. Thus, we suggest that structure formations in the early universe on scales where matters collapse gravitationally and the gas forms stars are responsible for the Ly$\alpha$ forests (cf. the mini-halo model). Supernovae shock the interstellar gas to high temperature, and the resulting gas outflows from the dwarfs owing to their shallow potential wells. The gas cools radiatively as the radiative cooling time shortens because of adiabatic expansion. Subsequent thermal instability results in condensation of clouds. The clouds inherit the kinetic energy of the flow and coast to large distances, providing regions of the absorbing gas with sizes of up to hundreds of kpc. We calculate the Ly$\alpha$ absorption line profiles and the neutral column distribution, and show that they are consistent with observations. We suggest that the Ly$\alpha$ forests are caused by the faint blue galaxies found in the deep extragalactic surveys.
121908282
QSO heavy-element absorption line systems and large galactic halos by satellite accretion
Recent observations indicate that the QSO heavy-element absorption line (HEAL) systems are associated with extremely large galactic halos. The origin of the absorbing gas, however, is not well understood. We demonstrate that an extremely large star formation rate is required if the HEAL gas originates from galactic disks. This is clearly incompatible with the observed moderate evolution and the normal colors of the galaxies associated with the Mg II absorption lines (MgALs). Studies of the H I high-velocity clouds, the Magellanic Stream, and recent observations of nearby QSOs suggest that the gas tidally torn out from the LMC/SMC system may be responsible for the MgALs observed in the Galactic halo
119774346
Heavy-element abundances and massive star formation
We investigate the observational consequences that arise for the heavy-element abundances in normal spiral galaxies from variations in the initial mass function (IMF). In particular, we calculate the oxygen yield for a given IMF, using the most recent calculations of supernova nucleosynthesis. Assuming instantaneous recycling of oxygen, we calculate the resultant oxygen abundance. The predicted and observed oxygen abundances in our Galaxy are compared, and we find that the overall abundance is well explained by the IMF determined in the solar neighborhood
54186214
Cooling gas outflows from galaxies
We study steady, radial gas outflows from galaxies in an effort to understand the way tenuous and hot gas is transported to large distances away from galaxies. In particular, we obtain solutions for outflow problems, and study the outflow topology, effects of the galaxy mass, the size of outflow regions, the efficiency of radiative cooling, and the fate of the cooled gas. Under general power-law forms for the cooling function and the gravitational field of galaxies, we show that the outflow solutions are determined by the two-parameter initial conditions. In an analogy with stellar wind or accretion problems, we demonstrate that there exists no transonic flow, but either subsonic or supersonic flows are obtainable. Solutions of the supersonic outflows are studied in detail as they are most likely to carry gas to large distances away from galaxies. We find that if gravity is weak, the outflow is characterized by the ratio of the radiative cooling time to the flow time, $t_c/t_f$. The importance of the galactic gravitational field is characterized by the fractional energy lost radiatively within the flow time in outflows with velocity equal to the circular velocity of the galaxy; if the fraction is small, gravity stops the outflow before the gas has a chance to cool radiatively. In the case the gas does cool radiatively, the cooled gas is most likely to form clouds via various instabilities. The clouds coast farther away from the galaxy because of the finite kinetic energy they inherit. We find that the hot gas in dwarf galaxies can either flow out as galactic winds, or cools radiatively to form clouds. In the latter case, the clouds escape the galaxies. In contrast, massive galaxies like our own tend to confine the gas. We present the surface brightness in various x-ray energy bands. We also estimate the mean
119450767
Gas at Large Distances from Galaxies and QSO Absorption Lines
We present the calculations of steady, spherical gas outflows from galaxies in an effort to understand the effects of the galaxy mass on the flow properties such as the size of the outflow regions, the efficiency of radiative cooling, and the fate of the cooled gas. We show that there exist no transonic flows but either subsonic or supersonic flows are obtainable, in an analogy with the stellar wind or accretion problems. Solutions of the supersonic outflows are studied in detail as they are most likely to carry gas to large distances away from galaxies. In case the gas does cool radiatively, the cooled gas is most likely to form clouds via various instabilities. The clouds coast farther away from the galaxy because of the finite kinetic energy they inherit. Depending on the initial energies, the clouds can either leave the galaxy or fall back ballistically. Applications of the calculations to dwarf and normal galaxies are made, and we argue that normal galaxies like our own should have relatively small gaseous halos formed through this mechanism. We discuss the implications of cold clouds from dwarf galaxies on recent observations of the QSO absorption line systems. For massive galaxies, satellites provide alternative ways to form large gaseous halos. We show how dynamical friction can increase tidal stripping of the gas as the satellite spirals in toward the primary, and that the gas ejected from satellites may account for the QSO heavy element absorption lines.
118856033
Quasinormal modes of black holes absorbing dark energy
Abstract We study perturbations of black holes absorbing dark energy. Due to the accretion of dark energy, the black hole mass changes. We observe distinct perturbation behaviors for absorption of different forms of dark energy onto the black holes. This provides the possibility of extracting information whether dark energy lies above or below the cosmological constant boundary w = − 1 . In particular, we find in the late time tail analysis that, differently from the other dark energy models, the accretion of phantom energy exhibits a growing mode in the perturbation tail. The instability behavior found in this work is consistent with the Big Rip scenario, in which all of the bound objects are torn apart with the presence of the phantom dark energy.
118322963
ON TOPOLOGICAL CHARGED BRANEWORLD BLACK HOLES
We study a class of topological black hole solutions in RSII braneworld scenario in the presence of a localized Maxwell field on the brane. Such a black hole can carry two types of charge, one arising from the extra dimension, the tidal charge, and the other from a localized gauge field confined to the brane. We find that the localized charge on the brane modifies the bulk geometry and in particular the bulk Weyl tensor. The bulk geometry does not depend on different topologies of the horizons. We present the temperature and entropy expressions associated with the event horizon of the braneworld black hole and by using the first law of black hole thermodynamics we calculate the mass of the black hole.
8395378
Reconstruction of Gas Temperature and Density Profiles of the Galaxy Cluster RX J1347.5-1145
We use observations of Sunyaev-Zel'dovich effect and X-ray surface brightness to reconstruct the radial profiles of gas temperature and density under the assumption of a spherically symmetric distribution of the gas. The method of reconstruction, first raised by Silk & White, depends directly on the observations of the Sunyaev-Zel'dovich effect and the X-ray surface brightness, without involving additional assumptions such as the equation of state of the gas or the conditions of hydrostatic equilibrium. We applied this method to the cluster RX J1347.5-1145, which has both the Sunyaev-Zel'dovich effect and X-ray observations with relative high precision. It is shown that it will be an effective method to obtain the gas distribution in galaxy clusters. Statistical errors of the derived temperature and density profiles of gas were estimated according to the observational uncertainties.
121864290
A compact positron annihilation lifetime spectrometer
Using LYSO scintillator coupled on HAMAMATSU R9800 (a fast photomultiplier) to form the small size gamma-ray detectors, a compact lifetime spectrometer has been built for the positron annihilation experiments. The system time resolution FWHM=193 ps and the coincidence counting rate similar to 8 cps/mu Ci were achieved. A lifetime value of 219 +/- 1 ps of positron annihilation in well annealed Si was tested, which is in agreement with the typical values published in the previous lectures.
119330468
Thermodynamical properties of dark energy
We have investigated the thermodynamical properties of dark energy. Assuming that the dark energy temperature T{approx}a{sup -n} and considering that the volume of the Universe enveloped by the apparent horizon relates to the temperature, we have derived the dark energy entropy. For dark energy with constant equation of state w>-1 and the generalized Chaplygin gas, the derived entropy can be positive and satisfy the entropy bound. The total entropy, including those of dark energy, the thermal radiation, and the apparent horizon, satisfies the generalized second law of thermodynamics. However, for the phantom with constant equation of state, the positivity of entropy, the entropy bound, and the generalized second law cannot be satisfied simultaneously.