Chemodynamics of Lyman alpha emitters, Lyman break galaxies and elliptical galaxies

We report an ultra-high-resolution simulation that follows evolution from the earliest stages of galaxy formation through the period of dynamical relaxation. The bubble structures of gas revealed in our simulation ($< 3\times 10^8$ years) resemble closely the high-redshift Lyman $\alpha$ emitters (LAEs). After $10^9$ years these bodies are dominated by stellar continuum radiation and look like the Lyman break galaxies (LBGs) known as the high-redshift star-forming galaxies at which point the abundance of elements appears to be solar. After $1.3\times10^{10}$ years, these galaxies resemble present-day ellipticals. The comparisons of simulation results with the observations of elliptical galaxies allow us to conclude that LAEs and LBGs are infants of elliptical galaxies or bulge systems in the nearby universe.Comment: To appear in the proceedings of the CRAL-Conference Series I "Chemodynamics: from first stars to local galaxies", Lyon 10-14 July 2006, France, Eds. Emsellem, Wozniak, Massacrier, Gonzalez, Devriendt, Champavert, EAS Publications Serie

Mergers of accreting stellar-mass black holes

We present post-Newtonian $N$-body simulations on mergers of accreting stellar-mass black holes (BHs), where such general relativistic effects as the pericenter shift and gravitational wave (GW) emission are taken into consideration. The attention is concentrated on the effects of the dynamical friction and the Hoyle-Lyttleton mass accretion by ambient gas. We consider a system composed of ten BHs with initial mass of $30~M_\odot$. As a result, we show that mergers of accreting stellar-mass BHs are classified into four types: a gas drag-driven, an interplay-driven, a three body-driven, or an accretion-driven merger. We find that BH mergers proceed before significant mass accretion, even if the accretion rate is $\sim10$ Eddington accretion rate, and then all BHs can merge into one heavy BH. Using the simulation results for a wide range of parameters, we derive a critical accretion rate ($\dot{m}_{\rm c}$), below which the BH growth is promoted faster by mergers. Also, it is found that the effect of the recoil by the GW emission can reduce $\dot{m}_{\rm c}$ especially in gas number density higher than $10^8~{\rm cm}^{-3}$, and enhance the escape probability of merged BHs. Very recently, a gravitational wave event, GW150914, as a result of the merger of a $\sim 30~M_\odot$ BH binary has been detected (Abbott et al. 2016). Based on the present simulations, the BH merger in GW150914 is likely to be driven by three-body encounters accompanied by a few $M_\odot$ of gas accretion, in high-density environments like dense interstellar clouds or galactic nuclei.Comment: 13 pages, 16 figures. Accepted for publication in MNRA

Large-Scale Structure of Short-Lived Lyman\alpha Emitters

Recently discovered large-scale structure of Ly\alpha Emitters (LAEs) raises a novel challenge to the cold dark matter (CDM) cosmology. The structure is extended over more than 50 Mpc at redshift z=3.1, and exhibits a considerably weak angular correlation. Such properties of LAE distributions appear to be incompatible with the standard biased galaxy formation scenario in the CDM cosmology. In this paper, by considering the possibility that LAEs are short-lived events, we attempt to build up the picture of LAEs concordant with the CDM cosmology. We find that if the lifetime of LAEs is as short as (6.7 \pm 0.6) \times 10^7 yr, the distributions of simulated galaxies successfully match the extension and morphology of large-scale structure of LAEs at z=3.1, and also the weak angular correlation function. This result implies that LAEs at z=3.1 do not necessarily reside in high density peaks, but tends to be located in less dense regions, in a different way from the expectation by the standard biased galaxy formation scenario. In addition, we make a prediction for the angular correlation function of LAEs at redshifts higher than 3. It is found that the prediction deviates from that by the standard biased galaxy formation scenario even at redshifts 4 < z < 6.Comment: 5 pages, 4 figures, accepted for publication in MNRA