Day 1743

Monday.

2008.02808

The Supersonic Project: to cool or not to cool supersonically induced gas objects (SIGOs)?

Chiou, et al

Supersonically Induced Gas Objects (SIGOs) primarily form in the early Universe, outside of dark matter halos due to the presence of a relative stream velocity between baryons and dark matter. These structures may be the progenitors of globular clusters. Since SIGOs are made out of pristine gas, we investigate the effect of atomic cooling on their properties. We run a set of four simulations by using the moving-mesh code {\sc arepo}, with and without baryon-dark matter relative velocity and with and without the effects of atomic cooling. We show that SIGO's density, temperature, and prolateness are determined by gravitational interactions rather than cooling. The cold gas fraction in SIGOs is much higher than that of dark matter halos. Specifically, we show that the SIGO's characteristic low temperature and extreme high gas density forges a nurturing site for the earliest star formation sites.

2008.02960

A semi-analytic model of pairwise velocity distribution between dark matter haloes

Shirasaki, Huff, Markovic, Rhodes

We study the probability distribution function (PDF) of relative velocity between two different dark matter halos (i.e. pairwise velocity) with a set of high-resolution cosmological $N$-body simulations. We investigate the pairwise velocity PDFs over a wide range of halo masses of $10^{12.5-15}\, h^{-1}M_{\odot}$ and redshifts of $0<z<1$. At a given set of masses, redshift and the separation length between two halos, our model requires three parameters to set the pairwise velocity PDF, whereas previous non-Gaussian models in the literature assume four or more free parameters. At the length scales of $r=5-40\, [h^{-1}\, \mathrm{Mpc}]$, our model predicts the mean and dispersion of the pairwise velocity for dark matter halos with their masses of $10^{12.5-13.5} \, [h^{-1}M_{\odot}]$ at $0.3 < z < 1$ with a 5%-level precision, while the model precision reaches a 20% level (mostly a 10% level) for other masses and redshifts explored in the simulations. We demonstrate that our model of the pairwise velocity PDF provides an accurate mapping of the two-point clustering of massive-galaxy-sized halos at the scales of $O(10)\, h^{-1}\mathrm{Mpc}$ between redshift and real space for a given real-space correlation function. For a mass-limited halo sample with their masses greater than $10^{13.5}\, h^{-1}M_{\odot}$ at $z=0.55$, our model can explain the monopole and quadropole moments of the redshift-space two-point correlations with a precision better than 5% at the scales of $5-40$ and $10-30\, h^{-1}\mathrm{Mpc}$, respectively. Our model of the pairwise velocity PDF will give a detailed explanation of statistics of massive galaxies at the intermediate scales in redshift surveys, including the non-linear redshift-space distortion effect in two-point correlation functions and the measurements of the kinematic Sunyaev-Zel'dovich effect.

2008.03099

Feedback between Sgr A and B: AGN-Sstarburst connection in the Galactic Centre

Sofue

Propagation of fast-mode magneto-hydrodynamic (MHD) compression waves is traced in the Galactic Centre. MHD waves produced by the active Galactic nucleus (Sgr A) focus on the molecular clouds such as Sgr B in the central molecular zone, which will trigger star formation, or possibly starburst. MHD waves newly excited by the starburst propagate backward, and focus on the nucleus (Sgr A), where implosive waves compress the nuclear gas to promote fueling the nucleus and may trigger nucleus activity. Echoing focusing of MHD waves between Sgr A (active galactic nucleus: AGN) and Sgr B (starburst) trigger each other at high efficiency by minimal energy requirement. It also solves the problem of angular momentum for AGN fueling, as the focusing waves do not require global gas flow.

2008.03291

Nuclear and dark matter heating in massive white dwarf stars

Horowitz

Recently, Cheng et al. identified a number of massive white dwarfs (WD) that appear to have an additional heat source providing a luminosity near $\approx 10^{-3}L_\odot$ for multiple Gyr. In this paper we explore heating from electron capture and pycnonuclear reactions. We also explore heating from dark matter annihilation. WD stars appear to be too small to capture enough dark matter for this to be important. Finally, if dark matter condenses to very high densities inside a WD this could ignite nuclear reactions. We calculate the enhanced central density of a WD in the gravitational potential of a very dense dark matter core. While this might start a supernova, it seems unlikely to provide modest heating for a long time. We conclude that electron capture, pycnonuclear, and dark matter reactions are unlikely to provide significant heating in the massive WD that Cheng considers.