Research interests

Galaxy-Halo Connection

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 properties statistically?
What are the physical origins of these correlations?
How can we verify the answers to the above two questions?

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 fast?
How to infer the causal relation from statistical correlation?

Projects

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 the connection.
- 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 specifically.
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 identify proto-clusters.
[Read more...]

Galaxy Group at high-redshift in incomplete spectroscopic surveys

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 high redshift?
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.