Researches
Quasar is an active galactic nucleus of very high luminosity. A quasar consists of a supermassive black hole surrounded by an orbiting accretion disk of gas. As gas in the accretion disk falls toward the black hole, energy is released in the form of electromagnetic radiation. Quasar's variabilities are over the whole electromagnetic spectrum, e.g., radio, infrared, UV/optical, X-ray, with different timescales. My interests are in the quasar variability and variability-related sciences.
AGN unification model
Damped random walk model for Quasar
1. Quasar variability
Our ideas are using multi-epoch and multi-wavelength modern survey data to investigate the spectroscopic [1], [2], [3], [4], and photometric variability [5], [6] to understand the relationships between different parameters and the physics of quasars.
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2. Supermassive black hole binary
Most (if not all) massive galaxies contain a supermassive black hole in their central region. When galaxies merge, their central BHs would potentially merge too, which would produce the loudest gravitational wave (GW) signals. Therefore, searching for the SMBH binaries will not only help to understand the evolution of galaxies and the "final-pc" problem, but also to find candidates for GW. What I am interested in is using different methods, e.g., the radial velocity shift [1], SED [2], periodic light curve [3, 4], to find sub-pc SMBH binary candidates.
Radial velocity shift
Simulation of binary merger
Changing-look (CL) is a rare phenomenon of active galactic nuclei (AGNs) that exhibit emerging or disappearing broad lines accompanied by continuum variations on astrophysically short timescales (≲1 yr to a few decades). Previous studies have only found Balmer-line (broad Hα and/or Hβ) CLAGNs. Our work discovered the first MgII CLAGN [1]. Then, we also discovered the largest high-redshift CLAGNs in broad UV lines [2]. In addition, we found that the CL phenomenon can be naturally produced by the photoionization model [3].
The first MgII CLAGN
CL sequence simulated by photoionization model
4. Intermediate mass black hole (IMBH)
Supermassive black holes (SMBH) as massive as ∼1–10 billion solar masses were already formed when the universe was only a few hundred Myr old. However, how they formed is still a mystery. Finding the black seeds at high redshift will be greatly beneficial for understanding the formation history of the SMBHs. We discovered the most distant (z = 0.82) spectroscopically confirmed IMBH with the variability method [1].
Variability selected IMBH at z = 0.82
A Python code to fit the spectrum of quasars [1]. This code is the only public python code for quasar decomposition. The flexibility and accuracy have been tested with the largest quasar sample size [2]. The code is wildly used in AGN field.
Fit to a quasar spectrum
It is a python improved ICCF code [1] to measure the time lag between AGN continuum and emission-line light curves in reverberation mapping projects. Compared with the old PyCCF code, we added the significance test for the measured lags and allow more interpolation methods (e.g., DRW or more complicated CARMA model).
NGC 5548
