Anisotropic Galactic Outflows and Enrichment of the Intergalactic Medium. I: Monte Carlo Simulations

We have developed an analytical model to describe the evolution of anisotropic galactic outflows. With it, we investigate the impact of varying opening angle on galaxy formation and the evolution of the IGM. We have implemented this model in a Monte Carlo algorithm to simulate galaxy formation and outflows in a cosmological context. Using this algorithm, we have simulated the evolution of a comoving volume of size [12h^(-1)Mpc]^3 in the LCDM universe. Starting from a Gaussian density field at redshift z=24, we follow the formation of ~20,000 galaxies, and simulate the galactic outflows produced by these galaxies. When these outflows collide with density peaks, ram pressure stripping of the gas inside the peak may result. This occurs in around half the cases and prevents the formation of galaxies. Anisotropic outflows follow the path of least resistance, and thus travel preferentially into low-density regions, away from cosmological structures (filaments and pancakes) where galaxies form. As a result, the number of collisions is reduced, leading to the formation of a larger number of galaxies. Anisotropic outflows can significantly enrich low-density systems with metals. Conversely, the cross-pollution in metals of objects located in a common cosmological structure, like a filament, is significantly reduced. Highly anisotropic outflows can travel across cosmological voids and deposit metals in other, unrelated cosmological structures.Comment: 32 pages, 9 figures (2 color). Revised version accepted in Ap

Toward the Evidence of the Accretion Disk Emission in the Symbiotic Star RR Tel

In this paper, we argue that in the symbiotic star RR Tel the existence of an accretion disk around the hot companion is strongly implied by the characteristic features exhibited by the Raman-scattered O VI lines around 6830 \AA and 7088 \AA. High degrees of polarization and double-peaked profiles in the Raman-scattered lines and single-peak profiles for other emission lines are interpreted as line-of-sight effects, where the H I scatterers near the giant see an incident double-peaked profile and an observer with a low inclination sees single-peak profiles. It is predicted that different mass concentrations around the accretion disk formed by a dusty wind may lead to the disparate ratios of the blue peak strength to the red counterpart observed in the 6830 and 7088 features. We discuss the evolutionary links between symbiotic stars and bipolar protoplanetary nebulae and conclude that the Raman scattering processes may play an important role in investigation of the physical properties of these objects.Comment: 11 pages, 3 figures, accepted for publication in the ApJ Letter

Is Double Reionization Physically Plausible?

Recent observations of z~6 quasars and the cosmic microwave background imply a complex history to cosmic reionization. Such a history requires some form of feedback to extend reionization over a long time interval, but the nature of the feedback and how rapidly it operates remain highly uncertain. Here we focus on one aspect of this complexity: which physical processes can cause the global ionized fraction to evolve non-monotonically with cosmic time? We consider a range of mechanisms and conclude that double reionization is much less likely than a long, but still monotonic, ionization history. We first examine how galactic winds affect the transition from metal-free to normal star formation. Because the transition is actually spatially inhomogeneous and temporally extended, this mechanism cannot be responsible for double reionization given plausible parameters for the winds. We next consider photoheating, which causes the cosmological Jeans mass to increase in ionized regions and hence suppresses galaxy formation there. In this case, double reionization requires that small halos form stars efficiently, that the suppression from photoheating is strong relative to current expectations, and that ionizing photons are preferentially produced outside of previously ionized regions. Finally, we consider H_2 photodissociation, in which the buildup of a soft ultraviolet background suppresses star formation in small halos. This can in principle cause the ionized fraction to temporarily decrease, but only during the earliest stages of reionization. Finally, we briefly consider the effects of some of these feedback mechanisms on the topology of reionization.Comment: 13 pages, 5 figures, in press at ApJ (reorganized significantly but major conclusions unchanged

Investigation for the puzzling abundance pattern of the neutron-capture elements in the ultra metal-poor star: CS 30322-023

The s-enhanced and very metal-poor star CS 30322-023 shows a puzzling abundance pattern of the neutron-capture elements, i.e. several neutron-capture elements such as Ba, Pb etc. show enhancement, but other neutron-capture elements such as Sr, Eu etc. exhibit deficient with respect to iron. The study to this sample star could make people gain a better understanding of s- and r-process nucleosynthesis at low metallicity. Using a parametric model, we find that the abundance pattern of the neutron-capture elements could be best explained by a star that was polluted by an AGB star and the CS 30322-023 binary system formed in a molecular cloud which had never been polluted by r-process material. The lack of r-process material also indicates that the AGB companion cannot have undergone a type-1.5 supernova, and thus must have had an initial mass below 4.0M$_\odot$, while the strong N overabundance and the absence of a strong C overabundance indicate that the companion's initial mass was larger than 2.0M$_\odot$. The smaller s-process component coefficient of this star illustrates that there is less accreted material of this star from the AGB companion, and the sample star should be formed in the binary system with larger initial orbital separation where the accretion-induced collapse (AIC) mechanism can not work.Comment: 13 pages, 2 figure

Hydrogen Clouds before Reionization: a Lognormal Model Approach

We study the baryonic gas clouds (the IGM) in the universe before the reionization with the lognormal model which is shown to be dynamcially legitimate in describing the fluctuation evolution in quasilinear as well as nonlinear regimes in recent years. The probability distribution function of the mass field in the LN model is long tailed and so plays an important role in rare events, such as the formation of the first generation of baryonic objects. We calculate density and velocity distributions of the IGM at very high spatial resolutions, and simulate the distributions at resolution of 0.15 kpc from z=7 to 15 in the LCDM cosmological model. We performed a statistics of the hydrogen clouds including column densities, clumping factors, sizes, masses, and spatial number density etc. One of our goals is to identify which hydrogen clouds are going to collapse. By inspecting the mass density profile and the velocity profile of clouds, we found that the velocity outflow significantly postpones the collapsing process in less massive clouds, in spite of their masses are larger than the Jeans mass. Consequently, only massive (> 10^5 M_sun) clouds can form objects at higher redshift, and less massive (10^4-10^5) collapsed objects are formed later. For example, although the mass fraction in clouds with sizes larger than the Jeans length is already larger than 1 at z=15, there is only a tiny fraction of mass (10^{-8}) in the clouds which are collapsed at that time. If all the ionizing photons, and the 10^{-2} metallicity observed at low redshift are produced by the first 1% mass of collapsed baryonic clouds, the majority of those first generation objects would not happen until z=10.Comment: Paper in AAStex, 12 figure

More evidence for an intracluster planetary nebulae population in the Virgo cluster

We surveyed a 50 sq arcmin region in the Virgo cluster core to search for intergalactic planetary nebulae, and found 11 candidates in the surveyed area. The measured fluxes of these unresolved sources are consistent with these objects being planetary nebulae from an intracluster population of stars. We compute the cumulative luminosity function of these 11 planetary nebula candidates. If we assume that they belong to the Virgo cluster, their cumulative luminosity function is in good agreement with planetary nebula luminosity function simulations. This comparison allows us to estimate the surface mass density of the intracluster stellar population at the surveyed field in the cluster core.Comment: ApJ Letters, in press. A .ps file is also available at: http://www.usm.uni-muenchen.de:8001/people/mendez/preprints/preprints.htm

Intracluster stars in the Virgo cluster core

We have investigated the properties of the diffuse light in the Virgo cluster core region, based on the detection of intracluster planetary nebulae (PNe) in four fields. We eliminate the bias from misclassified faint continuum objects, using improved Monte Carlo simulations, and the contaminations by high redshift Ly$\alpha$ galaxies, using the Ly$\alpha$ luminosity function in blank fields. Recent spectroscopic observations confirm that our photometric PN samples are well-understood. We find that the diffuse stellar population in the Virgo core region is inhomogeneous on scales of 30'-90': there exist significant field-to-field variations in the number density of PNe and the inferred amount of intracluster light, with some empty fields, some fields dominated by extended Virgo galaxy halos, and some fields dominated by the true intracluster component. There is no clear trend with distance from M87. The mean surface luminosity density, its rms variation, and the mean surface brightness of diffuse light in our 4 fields are $\Sigma_B = 2.7 x 10^{6}$ L$_{B\odot}$ arcmin$^{-2}$, ${rms} = 2.1 \times 10^{6}$ L$_{B\odot}$ arcmin$^{-2}$, and $\bar{\mu}_{B}=29.0$ mag arcsec$^{-2}$ respectively. Our results indicate that the Virgo cluster is a dynamically young environment, and that the intracluster component is associated at least partially with local physical processes like galaxy interactions or harassment. We also argue, based on kinematic evidence, that the so-called 'over-luminous' PNe in the halo of M84 are dynamically associated with this galaxy, and must thus be brighter than and part of a different stellar population from the normal PN population in elliptical galaxies.Comment: 31 pages, 6 figure. In press on the Astronomical Journa

Poor health status and distress in cardiac patients: The role of device therapy vs. underlying heart disease

AimsImplantable cardioverter defibrillator (ICD) therapy, which includes the risk of shocks, is considered the primary culprit of reductions in patient reported outcomes (PROs; e.g. health status and distress), thereby negating the role of underlying disease severity. We examined the relative influence of living with an ICD vs. congestive heart failure (CHF) on PROs and compared (i) ICD patients without CHF (ICD only), (ii) CHF patients without an ICD (CHF-only), and (iii) CHF patients with an ICD (ICD + CHF).Methods and resultsSeparate cohorts of ICD and CHF patients (N = 435; 75% men) completed PROs at baseline, 6 and 12 months. Groups differed on physical health status only at baseline (F(2,415) = 7.15, P = 0.001) and on anxiety at 12 months (F(2,415) = 4.04, P = 0.01); ICD + CHF patients had the most impaired physical health status but the lowest anxiety level followed by the ICD only and CHF only patients. Congestive heart failure only patients had the most impaired mental health status and reported the highest level of anxiety as compared to the ICD only (P < 0.001) and ICD + CHF groups (P = 0.009), while the two latter groups did not differ. The effect sizes ranged from very small (0.03) to moderate-large (0.69). Groups did not differ in depression scores.ConclusionCongestive heart failure patients reported worse PROs as compared to ICD patients, although the magnitude of the differences was relatively small. This suggests that the well being of patients is not necessarily negatively influenced by the implantation of an ICD, and that underlying heart disease may have at least an equal if not greater influence on PROs

Mass Transfer by Stellar Wind

I review the process of mass transfer in a binary system through a stellar wind, with an emphasis on systems containing a red giant. I show how wind accretion in a binary system is different from the usually assumed Bondi-Hoyle approximation, first as far as the flow's structure is concerned, but most importantly, also for the mass accretion and specific angular momentum loss. This has important implications on the evolution of the orbital parameters. I also discuss the impact of wind accretion, on the chemical pollution and change in spin of the accreting star. The last section deals with observations and covers systems that most likely went through wind mass transfer: barium and related stars, symbiotic stars and central stars of planetary nebulae (CSPN). The most recent observations of cool CSPN progenitors of barium stars, as well as of carbon-rich post-common envelope systems, are providing unique constraints on the mass transfer processes.Comment: Chapter 7, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe