Galaxies and Gas in Dark Matter Halos and the Cosmic Web

In the current understanding of galaxy formation, galaxies are believed to form and evolve in dark matter halos. The dark matter halos are collapsed objects that form and grow via gravitational instability of small initial density fluctuation in the cosmic field. They are not only the hosts of galaxies but are tracers of the cosmic web of the Universe. They are thus crucial components for understanding how galaxies form and evolve within the cosmic web. This dissertation is a systematic investigation of the galaxies and gas in the dark matter halos and the cosmic web, using observation data of large galaxy surveys such as the Sloan Digital Sky Survey (SDSS), and of the Cosmic Microwave Background (CMB) survey such as the Planck, together with simulations and modellings for comparison and interpretation. Specifically, we have identified dark matter halos in the low-redshift Universe, and constructed the largest to date all-sky group catalog. We also investigated correlations between many of the galaxy and halo properties, particularly finding, for the first time, an observational proxy of halo age. Then, I developed a series of novel approaches to maximize the detection of the Sunyaev-Zel\u27dovich effect (SZE), and from it explored the gas properties in halos to find that the gas mass fraction even in Milky Way-size halos is about the cosmic mean fraction. The analysis identified the baryons in a warm-hot medium on halo scales. We also show that the thermal SZE can be used to constrain the mean relationship between thermal energy of IGM gas and local total matter density for the first time. We support the reliability of our methods and results with tests where the methods are applied to the mock CMB maps constructed from simulations. Finally, we present comparisons with simulations of the SZE, and discuss the implications for its constraining power of galaxy formation models

Pararhabdepyris Gorbatovskii (Hymenoptera: Bethylidae), new to Korea and the first host record of Allobethylus Kieffer

AbstractPararhabdepyris Gorbatovskii (Hymenoptera: Bethylidae) is newly recognized from South Korea. The genus can be easily recognized from other genera in Scleroderminae by having the head wider than it is long, the antenna with 10 flagellomeres, the clypeus with short projected median lobe, and the metasomal tergite II longer than the combined length of remained tergites. Description and illustrations of diagnostic characteristics of Pararhabdepyris paradoxus Gorbatovskii are provided. In addition, the present paper provides the first host record of Allobethylus Kieffer of Scleroderminae from the world. A revised key to genera and species of South Korean Scleroderminae is also presented

An Analytic Formula for the Supercluster Mass Function

We present an analytic formula for the supercluster mass function which is constructed by modifying the extended Zel'dovich model for the halo mass function. The formula has two characteristic parameters whose best-fit values are determined by fitting to the numerical results from N-body simulations for the standard LambdaCDM cosmology. The parameters are found to be independent of redshifts and robust against variation of the key cosmological parameters. Under the assumption that the same formula for the supercluster mass function is valid for non-standard cosmological models, we show that the relative abundance of the rich superclusters should be a powerful indicator of any deviation of the real universe from the prediction of the standard LambdaCDM model.Comment: accepted for publication in ApJ, 27 pages, 8 figures, significantly revised after the referee's revie

Star formation efficiency across large-scale galactic environments

Environmental effects on the evolution of galaxies have been one of the leading questions in galaxy studies for decades. In this work, we investigate the relationship between the star formation activity of galaxies and their environmental matter density using the cosmological hydrodynamic simulation Simba. The star formation activity indicators we explore include the star formation efficiency (SFE), specific star formation rate (sSFR) and molecular hydrogen mass fraction ($f^*_{H_2}$) and the environment is considered as the large-scale environmental matter density, calculated based on the stellar mass of nearby galaxies on a 1 Mpc/h grid using the cloud in cell (CIC) method. Our sample includes galaxies with $9<\log(M_*/M_{\odot})$ at $0<z<4$, divided into three mass bins to disentangle the effects of mass and environment on the galactic star formation activity. For low- to intermediate-mass galaxies at low-redshifts ($z<1.5$), we find that the star formation efficiency of those in high-density regions are $\sim 0.3$ dex lower than those in low-density regions. However, there is no significant environmental dependence of the star formation efficiency for massive galaxies over all our redshift range, and low- to intermediate-mass galaxies at high redshifts ($z > 1.5$). We present a scaling relation for the depletion time of molecular hydrogen (${t_{depl}}=1/SFE$) as a function of galaxy parameters including environmental density. Our findings provide a framework for quantifying the environmental effects on the star formation activities of galaxies as a function of stellar mass and redshift. The most significant environmental dependence is seen at later cosmic times ($z<1.5$) and towards lower stellar masses ($9<\log(M_*/M_{\odot})<10$). Future large galaxy surveys can use this framework to look for the environmental dependence of the star formation activity and examine our predictions.Comment: 17 pages, 6 figure