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MASSIVE NEUTRINOS PROMOTE THE SIZE GROWTH OF EARLY-TYPE GALAXIES
Song, Hyunmi,Lee, Jounghun IOP Publishing 2013 The Astrophysical journal Vol.768 No.2
<P>The effect of massive neutrinos on the evolution of early-type galaxies in size and stellar mass is explored by tracing the merging history of galaxy progenitors with the help of robust semi-analytic prescriptions. We show that as the presence of massive neutrinos plays a role in enhancing the mean merger rate per halo as well as the merger-driven increment in halo mass, the high-z progenitors of a massive descendant galactic halo evolve more rapidly in mass-normalized size for a Lambda MDM (Lambda cold dark matter + massive neutrinos) model than for the Lambda CDM (Lambda cold dark matter) case. We provide a physical reason for why the halo mass growth rate and the merger rate are higher in a Lambda MDM cosmology and conclude that if the presence and the role of massive neutrinos are properly taken into account, then it may explain the anomalous compactness of the high-z massive ETGs compared with local giant ellipticals with similar stellar masses.</P>
MODELING THE ALIGNMENT PROFILE OF SATELLITE GALAXIES IN CLUSTERS
Song, Hyunmi,Lee, Jounghun IOP Publishing 2012 The Astrophysical journal Vol.748 No.2
<P>Analyzing the halo and galaxy catalogs from the Millennium Simulations at redshifts z = 0, 0.5, 1, we determine the alignment profiles of cluster galaxies by measuring the average alignments between the major axes of the pseudo inertia tensors from all satellites within a cluster's virial radius and from only those satellites within some smaller radius as a function of the top-hat scale difference. The alignment profiles quantify how well the satellite galaxies retain the memory of the external tidal fields after merging into their host clusters and how fast they lose the initial alignment tendency as the cluster's relaxation proceeds. It is found that the alignment profile drops faster at higher redshifts and on smaller mass scales. This result is consistent with the picture that the faster merging of the satellites and earlier onset of the nonlinear effect inside clusters tend to break the preferential alignments of the satellites with the external tidal fields. Modeling the alignment profile of cluster galaxies as a power law of the density correlation coefficient that is independent of the power spectrum normalization (sigma(8)) and demonstrating that the density correlation coefficient varies sensitively with the density parameter (Omega(m)) and neutrino mass fraction (f(nu)), we suggest that the alignment profile of cluster galaxies might be useful for breaking the Omega(m)-sigma(8) and f(nu)-sigma(8) degeneracies.</P>
Song, Hyunmi,Lee, Jounghun IOP Publishing 2011 The Astrophysical journal Vol.736 No.1
<P>We study the effect of massive neutrinos on the formation and evolution of the first filaments containing the first star-forming halos of mass M similar to 10(6) M-circle dot at z similar to 20. With the help of the extended Press-Schechter formalism, we evaluate analytically the merging rates of the first star-forming halos into zero-dimensional larger halos and one-dimensional first filaments. It is shown that as the neutrino mass fraction f(nu) increases, the halo-to-filament merging rate increases while the halo-to-halo merging decreases sharply. For f(nu) <= 0.04, the halo-to-filament merging rate is negligibly low at all filament mass scales, while for f(nu) >= 0.07 it exceeds 0.1 at the characteristic filament mass scale of similar to 10(9) M-circle dot. The distribution of the redshifts at which the first filaments ultimately collapse along their longest axes is derived and found to have a sharp maximum at z similar to 8. We also investigate the formation and evolution of second-generation filaments which contain the first galaxies of mass 10(9) M-circle dot at z = 8. A similar trend is found: for f(nu) >= 0.07 the rate of clustering of the first galaxies into second-generation filaments exceeds 0.3 at the characteristic mass scale of similar to 10(11) M-circle dot. The longest-axis collapse of these second-generation filaments is found to occur at z similar to 3. The implications of our results on the formation of massive high-z galaxies and the early metal enrichment of the intergalactic medium by supernova-driven outflows, and the possibility of constraining the neutrino mass from the mass distribution of the high-z central black holes, are discussed.</P>
QUASARS AS A TRACER OF LARGE-SCALE STRUCTURES IN THE DISTANT UNIVERSE
Song, Hyunmi,Park, Changbom,Lietzen, Heidi,Einasto, Maret American Astronomical Society 2016 The Astrophysical journal Vol.827 No.2
<P>We study the dependence of the number density and properties of quasars on the background galaxy density using the currently largest spectroscopic data sets of quasars and galaxies. We construct a galaxy number density field smoothed over the variable smoothing scale of between approximately 10 and 20 h(-1) Mpc over the redshift range 0.46 < z < 0.59 using the Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12) Constant MASS galaxies. The quasar sample is prepared from the SDSS-I/II DR7. We examine the correlation of incidence of quasars with the large-scale background density and the dependence of quasar properties such as bolometric luminosity, black hole mass, and Eddington ratio on the large-scale density. We find a monotonic correlation between the quasar number density and large-scale galaxy number density, which is fitted well with a power-law relation, nQ proportional to rho(0.618)(G). We detect weak dependences of quasar properties on the large-scale density such as a positive correlation between black hole mass and density, and a negative correlation between luminosity and density. We discuss the possibility of using quasars as a tracer of large-scale structures at high redshifts, which may be useful for studies of the growth of structures in the high-redshift universe.</P>