What is galaxy-halo connection?
Galaxies are born and raised in dark matter halos, so,
theoretically, their properties should be tightly
correlated. Thus, it is critical to infer the relation
between their properties from observation, and explain
it with physical model.
What do I want to know?
How are the galaxy properties correlated with halo
What are the physical origins of these correlations?
How can we verify the answers to the above two
Galaxy connection across cosmic time
Why do we want to connect galaxies across cosmic time?
Due to the limited light speed, the more distant we see,
the younger Universe we get. However, observed galaxies
at different cosmic time do not have causal relation.
Consequently, we can only infer the statistical
evolution of galaxies, and models or assumptions must be
adopted. With this connection in hand, we can directly
infer the galaxy evolution process.
What do I want to know?
How to connect galaxies across different redshifts?
- How to verify the connecting method?
- What can we learn from the connected galaxies?
Statistics in astronomy
Why do I value statistics in astronomy?
Unlike experimental physics, we cannot directly observe
the evolution of astronomical objects, or manipulate
them. Thus, the only way to infer the underlying physics
is analysing the data using statistical tools.
What do I want to learn?
How to infer the statistical correlation among
several variables robustly?
How to perform the statistical inference numerically
How to infer the causal relation from statistical
Finding proto-clusters to trace galaxy evolution
What is proto-cluster?
Proto-cluster is the collection of galaxies, halos and
other material at high redshift that will enter in a
common massive dark matter halos. Normally, we require
the descendant halo mass above 10^14 solar mass.
Why is proto-cluster important?
There are two motivations:
We want to connect galaxies across different
redshift to infer their evolution along with
cosmic time. Since proto-clusters are
progenitors of galaxy clusters in local
Universe, their detection can help us to build
Galaxy observation in local Universe reveals
distinct properties for galaxies in field and
cluster environments. Thus, we need to study the
progenitors of local galaxy clusters
How to find proto-clusters?
There are many detection methods proposed, each with
different tracer. In this project, we use the dark
matter halos constructed from the galaxy group finder to
Galaxy Group at high-redshift in incomplete spectroscopic
What is galaxy group?
Galaxy group is a collection of galaxies sharing a
common dark matter halo.
Why do we want to study galaxy group?
In LCDM paradigm, galaxies are formed and evolved in
dark matter halos, so their properties should be tightly
correlated. Thus, by identifying galaxy groups in survey
data, we can directly build the connection between
galaxies and dark matter halos.
What is the challenge of group identification at
At high redshift, galaxy observation is very expensive
due to several reasons. For example, galaxies are
spatially inhomogeneous, so, high completeness in dense
region means a lot of wasting of fiber time in sparse
region. Another reason is that some galaxies at high
redshift do not have prominent spectral features for
reliable redshift calibration. All of these factors will
cause the incompleteness, and it will undermine the
galaxy group finding performance.