Yong-Ik Byun

We have obtained V-band images of 45 nearby elliptical galaxies and bulges using the original Planetary Camera of the Hubble Space Telescope. The majority of the sample is at distances of 10-20 Mpc. This represents a substantial increase in the number of galaxies that have been studied at a resolution of a few parsecs. At this resolution, many galaxies reveal previously unknown central disks, dust clouds, and nuclear components. We find that galaxies have two types of brightness profiles. The fi

Abstract
\nIn a companion Letter (Arnouts et al.) we present new measurements of the galaxy luminosity function at 1500 Å out to z~1 using Galaxy Evolution Explorer VIMOS-VLT Deep Survey observations (1039 galaxies with NUV<=24.5 and z>0.2) and at higher z using existing data sets. In this Letter we use the same sample to study evolution of the FUV luminosity density rho1500. We detect evolution consistent with a (1+z)2.5+/-0.7 rise to z~1 and (1+z)0.5+/-0.4 for z>1. The lumino

We have used the first matched set of GALEX and SDSS data to investigate the properties of a sample of 74 nearby galaxies with far-ultraviolet luminosities chosen to overlap the luminosity range of typical high-z Lyman Break Galaxies (LBGs). GALEX deep surveys have shown that ultraviolet-luminous galaxies (UVLGs) similar to these are the fastest evolving component of the UV galaxy population. Model fits to the combined GALEX and SDSS photometry yield typical FUV extinctions similar to LBGs. The

We present a set of structural parameters for the central parts of 57 early-type galaxies observed with the Planetary Camera of the Hubble Space Telescope. These parameters are based on a new empirical law that successfully characterizes the centers of early-type galaxies. This empirical law assumes that the surface brightness profile is a combination of two power laws with different slopes γ and β for the inner and outer regions. Conventional structural parameters such as core radius and centra

We describe a method of bulge-to-disk decomposition which utilizes a full two-dimensional image of a galaxy. It provides much better estimates of the structural parameters for each component than the widely used conventional procedure which involves a χ<SUP>2</SUP> decomposition on elliptically averaged profiles. The performances of the conventional one-dimensional method and the present two-dimensional technique are compared by using a set of realistic model galaxy images. We show that the conv

In order to find the best observable diagnostics for the amount of internal extinction within spiral galaxies, we have constructed realistic models for disk galaxies with immersed dust layers. The radiative transfer including both scattering and absorption has been computed for a range of model galaxies in various orientations. Standard galaxy surface photometry techniques were then applied to the numerical data to illustrate how different observables such as total magnitude, color and luminosit

We introduce new methods for robust high-precision photometry from well-sampled images of a non-crowded field with a strongly varying point-spread function. For this work, we used archival imaging data of the open cluster M37 taken by MMT 6.5 m telescope. We find that the archival light curves from the original image subtraction procedure exhibit many unusual outliers, and more than 20% of data get rejected by the simple filtering algorithm adopted by early analysis. In order to achieve better p

Recently it has been suggested that some bulges are really disks (Kormendy 1993). He argues that some bulges are not spheroidal components of steep luminosity distribution like elliptical galaxies but actually parts of flat disks, whose central luminosity profiles are steeper than the inward extrapolation of an exponential fit to the outer parts. The existence of disk-like bulges strongly supports the idea of disk secular evolution.