Browsing by Subject "merger rate"

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    Effects Of Large-Scale Environment On The Assembly History Of Central Galaxies
    (2014-10) Jung, Intae; Lee, Jaehyun; Yi, Sukyoung K.; Jung, Intae
    We examine whether large-scale environment affects the mass assembly history of central galaxies. To facilitate this, we constructed dark matter halo merger trees from a cosmological N-body simulation and calculated the formation and evolution of galaxies using a semi-analytic method. We confirm earlier results that smaller halos show a notable difference in formation time with a mild dependence on large-scale environment. However, using a semi-analytic model, we found that on average the growth rate of the stellar mass of central galaxies is largely insensitive to large-scale environment. Although our results show that the star formation rate (SFR) and the stellar mass of central galaxies in smaller halos are slightly affected by the assembly bias of halos, those galaxies are faint and the difference in the SFR is minute, therefore it is challenging to detect it in real galaxies given the current observational accuracy. Future galaxy surveys, such as the BigBOSS experiment and the Large Synoptic Survey Telescope, which are expected to provide observational data for fainter objects, will provide a chance to test our model predictions.
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    The Estimated Merger Rates of GW150914-like Binary Black Holes from the Astrophysical Argument Perspective and Their Implications
    (2016-05) Liu, Tung Yan; Matzner, Richard A.
    In this paper, we looked at the three possible formation paths for GW150914-like BBH mergers. They are the chemically homogenously evolution(CHE), isolated binaries(IB) scenario, and the dense stellar environment(DSE) scenario. These three models predict consistent merger rates with the inferred merger rate of 2-400 Gpc-3 yr-1 from the detection of GW150914. Although a definite conclusion cannot be drawn on which scenario corresponds to GW150914-like mergers, we found that the IB scenario and CHE scenario are more probable over the DSE scenario. We noticed that strong spin alignment can possibly distinguish isolated binaries scenario from the dense stellar environment scenario, and with both IB and CHE scenario favouring aligned spins, the BBHs formed from CHE scenario mostly merge in z < 1.5, while that of IB can occur at high red-shift. Further studies on comparison between the two conventional models (IB and DES) and CHE model is needed in order to constrain and identify features that can better distinguish the three models.