Recovering the Structure and Dynamics of the Local Universe

Abstract

Cosmicflows is an ambitious program to map the velocity and density fields of the nearby universe. The current dissertation is a part of the Cosmicflows-4 project with the aim of measuring distances of more than 10,000 spiral galaxies in the local universe up to ~15,000 km/s. New HI linewidth information has come primarily from the Arecibo Legacy Fast ALFA Survey. Photometry of the sample galaxies has been carried out in optical (SDSS ugriz) and infrared (WISE W1 and W2) bands. Inclinations have been determined using an online graphical interface accessible to a collaboration of citizen scientists. Galaxy distances are measured based on the correlation between the rotation rate of spirals and their absolute luminosity, known as the Tully-Fisher Relation (TFR). I present the calibration of the TFR using a sub-sample of ~600 spirals located in 20 galaxy clusters. Correlations among observables such as color, surface brightness, and relative HI content are explored in attempts to reduce the scatter about the TFR with the goal of obtaining more accurate distances. I address the color-dependent discrepancies between measured distances at different wavebands. I study the dependency of the global intrinsic extinction in spiral galaxies on their morphologies, sizes, and spatial inclinations, using a subsample of ~2,200 galaxies with optical and infrared photometry information. I present two models for dust obscuration, a parametric model and a non-parametric model based on the Gaussian process formalism. An average dust attenuation curve is derived in the wavelengths range 0.36 to 4.5 microns. Finally, an algorithm to find nearby galaxy groups within 3,500 \kms (~45 Mpc) is presented. This algorithm is based on the observed scaling correlations that relate luminosity, velocity dispersion and dimensions of galaxy groups. Applying these scaling relations, in an iterative process, galaxies with almost the same radial velocities and in close angular proximity fall into groups. The most remarkable result of the study emerges from the construction of the halo mass function from the sample. At ~10^12 solar mass, there is a jog from the expectation Sheth-Tormen function, such that halo counts drop by a factor ~3 in all lower mass bins.