Neutral (HI) gas clouds associated with galaxies are responsible for fuelling the star-formation in the universe.
These stars further inject metals back into the neutral gas clouds both within and outside the galaxy.
The circle continues with metals, radiation and dust from stars influencing the neutral to molecular gas (HI-H2) transition
which further influence the next generation of star-formation. Further, gas abundance and kinematics are influenced
by larger factors such as galactic interactions and mergers.
In my talk, I will focus primarily on my study of high column density neutral gas clouds (Extremely strong Damped Lyman-alpha absorbers, or ESDLAs)
that are observed as absorption signature along the line-of-sight (LOS) of a quasar.
I will further look at the HI-H2 transition and interesting results relevant to diffuse molecular gas.
I will also discuss comparisons between low and high star-forming environment and talk about different samples and techniques
that can be used to study them.
I would like to give my intellectual journey that led to the involvements in gravitational wave science.
My PhD thesis was about the dynamical evolution of dense star clusters including the effects of the binaries and stellar collisions.
The black holes are interesting objects in view of the stellar dynamics in many aspects.
The observational evidence for the supermassive black hole was growing rapidly in late 1980s as the high resolution spectroscopic observations became available,
and the advancement of the speckle interferometry toward the Galactic Center.
My research area expanded to the origin of the supermassive black holes and their interactions with surrounding stars.
In 2000, I was invited to a LISA symposium held in Golm, Germany, where I was first exposed to the gravitational wave experiments.
I felt that the gravitational wave would become an important tool for astronomy and formed a gravitational-wave study group in late 2003.
From 2004, the Korean Gravitational Wave Group (KGWG) organized summer schools every year under the sponsorship
of Asian-Pacific Center for Theoretical Physics (APCTP) and Korea Institute for Science and Technology Information (KISTI) focusing on the general relativity
and gravitational waves and educated ourselves on these topics.
In 2009, KGWG became a member of the LIGO Scientific Collaboration.
While working on the LIGO collaboration, I also continued to study the roles of the black holes in star clusters and found that the black hole merger events
could be more abundant than neutron star binary coalescence in LIGO observations.
The gravitational wave community in Korea is growing and KASI now pursues gravitational wave experiments by developing the measurement techniques
that could enhance the sensitivity significantly.
I will close my talk by giving prospects of gravitational wave astrophysics.