Topology of Large-Scale Structure by Galaxy Type: Hydrodynamic Simulations

The topology of large scale structure is studied as a function of galaxy type using the genus statistic. In hydrodynamical cosmological CDM simulations, galaxies form on caustic surfaces (Zeldovich pancakes) then slowly drain onto filaments and clusters. The earliest forming galaxies in the simulations (defined as ``ellipticals") are thus seen at the present epoch preferentially in clusters (tending toward a meatball topology), while the latest forming galaxies (defined as ``spirals") are seen currently in a spongelike topology. The topology is measured by the genus (= number of ``donut" holes - number of isolated regions) of the smoothed density-contour surfaces. The measured genus curve for all galaxies as a function of density obeys approximately the theoretical curve expected for random-phase initial conditions, but the early forming elliptical galaxies show a shift toward a meatball topology relative to the late forming spirals. Simulations using standard biasing schemes fail to show such an effect. Large observational samples separated by galaxy type could be used to test for this effect.Comment: Princeton University Observatory, submitted to The Astrophysical Journal, figures can be ftp'ed from ftp://astro.princeton.edu/cen/TOP

Topology of COBE Microwave Background Fluctuations

We have measured the topology (genus) of the fluctuations in the cosmic microwave background seen in the recently completed (four-year) data set produced by the COBE satellite. We find that the genus is consistent with that expected from a random-phase Gaussian distribution, as might be produced naturally in inflationary models.Comment: 2 pages, one Post-Script figure, MNRAS LaTeX Style (mn.sty), submitted to MNRA

Flexion and Skewness in Map Projections of the Earth

Tissot indicatrices have provided visual measures of local area and isotropy distortions. Here we show how large scale distortions of flexion (bending) and skewness (lopsidedness) can be measured. Area and isotropy distortions depend on the map projection metric, flexion and skewness, which manifest themselves on continental scales, depend on the first derivatives of the metric. We introduce new indicatrices that show not only area and isotropy distortions but flexion and skewness as well. We present a table showing error measures for area, isotropy, flexion, skewness, distances, and boundary cuts allowing us to compare different world map projections. We find that the Winkel-Tripel projection (already adopted for world maps by the National Geographic), has low distortion on most measures and excellent quality overall.Comment: 31 pages, including 27 postscript figures. Accepted to Cartographica. Detailed discussion and code at http://www.physics.drexel.edu/~goldberg/projection

Non-Gaussian Error Distribution of Hubble Constant Measurements

We construct the error distribution of Hubble constant ($H_0$) measurements from Huchra's compilation of 461 measurements of $H_0$ and the WMAP experiment central value $H_0$ = 71 km s$^{-1}$ Mpc$^{-1}$. This error distribution is non-Gaussian, with significantly larger probability in the tails of the distribution than predicted by a Gaussian distribution. The 95.4 % confidence limits are 7.0 $\sigma$ in terms of the quoted errors. It is remarkably well described by either a widened $n = 2$ Student's $t$ distribution or a widened double exponential distribution. These conclusions are unchanged if we use instead the central value $H_0$ = 67 km s$^{-1}$ Mpc$^{-1}$ found from a median statistics analysis of a major subset of $H_0$ measurements used here.Comment: 12 pages, 8 figure

The New Horizon Run Cosmological N-Body Simulations

We present two large cosmological N-body simulations, called Horizon Run 2 (HR2) and Horizon Run 3 (HR3), made using 6000^3 = 216 billions and 7210^3 = 374 billion particles, spanning a volume of (7.200 Gpc/h)^3 and (10.815 Gpc/h)^3, respectively. These simulations improve on our previous Horizon Run 1 (HR1) up to a factor of 4.4 in volume, and range from 2600 to over 8800 times the volume of the Millennium Run. In addition, they achieve a considerably finer mass resolution, down to 1.25x10^11 M_sun/h, allowing to resolve galaxy-size halos with mean particle separations of 1.2 Mpc/h and 1.5 Mpc/h, respectively. We have measured the power spectrum, correlation function, mass function and basic halo properties with percent level accuracy, and verified that they correctly reproduce the LCDM theoretical expectations, in excellent agreement with linear perturbation theory. Our unprecedentedly large-volume N-body simulations can be used for a variety of studies in cosmology and astrophysics, ranging from large-scale structure topology, baryon acoustic oscillations, dark energy and the characterization of the expansion history of the Universe, till galaxy formation science - in connection with the new SDSS-III. To this end, we made a total of 35 all-sky mock surveys along the past light cone out to z=0.7 (8 from the HR2 and 27 from the HR3), to simulate the BOSS geometry. The simulations and mock surveys are already publicly available at http://astro.kias.re.kr/Horizon-Run23/.Comment: 18 pages, 10 figures. Added clarification on Fig 6. Published in the Journal of the Korean Astronomical Society (JKAS). The paper with high-resolution figures is available at http://jkas.kas.org/journals/2011v44n6/v44n6.ht

Transformation of Morphology and Luminosity Classes of the SDSS Galaxies

We present a unified picture on the evolution of galaxy luminosity and morphology. Galaxy morphology is found to depend critically on the local environment set up by the nearest neighbor galaxy in addition to luminosity and the large scale density. When a galaxy is located farther than the virial radius from its closest neighbor, the probability for the galaxy to have an early morphological type is an increasing function only of luminosity and the local density due to the nearest neighbor ($\rho_n$). The tide produced by the nearest neighbor is thought to be responsible for the morphology transformation toward the early type at these separations. When the separation is less than the virial radius, i.e. when $\rho_n > \rho_{\rm virial}$, its morphology depends also on the neighbor's morphology and the large-scale background density over a few Mpc scales ($\rho_{20}$) in addition to luminosity and $\rho_n$. The early type probability keeps increasing as $\rho_n$ increases if its neighbor is an early type. But the probability decreases as $\rho_n$ increases when the neighbor is a late type. The cold gas streaming from the late type neighbor can be the reason for the morphology transformation toward late type. The overall early-type fraction increases as $\rho_{20}$ increases when $\rho_n > \rho_{\rm virial}$. This can be attributed to the hot halo gas of the neighbor which is confined by the pressure of the ambient medium held by the background mass. We have also found that galaxy luminosity depends on $\rho_n$, and that the isolated bright galaxies are more likely to be recent merger products. We propose a scenario that a series of morphology and luminosity transformation occur through distant interactions and mergers, which results in the morphology--luminosity--local density relation.Comment: 14 pages, 7 figures, for higher resolution figures download PDF file at http://astro.kias.re.kr/docs/trans.pdf ; references added and typos in section 3.2 corrected; Final version accepted for publication in Ap