Research Topics
(Note: this site is always under construction.)
Previous Researches
IGM and galaxy evolution at the epoch of the reionization
[Link to Recent Poster]
with Paul Shapiro (UT) and Collaborators
Propagating the ionization photon at the epoch of the reionization can significantly affect the baryon evolution.
For example, it can suppress galaxy formation in early dark matter halos through the gas photoevaporation.
Carefully treating this effect will have of important consequence on the early galaxy formation and high-z IGM distribution.
With P. Shapiro and his group in University of Texas Austin, I am working the detail physical process how the propagating ionization
front modifies the gas evolution at the EoR using high resolution Gadget simulations that add a new algorithm for the transport and
shielding of ionizing radiation. I also participate in large international team that implemented the hybrid MPI/GPU cosmological
radiation-hydro-gravity code RAMSES-CUDATON, used to simulate reionization of the local Universe centered on the Milky Way on
supercomputer Titan in 2013 and 2014 under the DOE Incite Program at Oak Ridge.
This radiation-hydrodynamics coupled simulation demonstrates the progressive ionization and heating of the Intergalactic medium and
shows a strong self-regulation and complete suppression of star formation in low mass haloes after reionization.
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First supermassive black hole formation
[Link to Recent Poster]
[Link to Recent Talk]
with Isaac Shlosman (UKY), Mitchell C. Begelman (UC Boulder)
Currently, two options appear viable in forming the SMBHs at high redshifts: the hierarchical assembly versus a direct collapse.
We, first, implement the series of idealized numerical simulations to study the gas collapse in the midst of dark matter halos using an AMR code ENZO.
We find that the infalling gas leads to the formation a transient disk-like configuration at the center which is subject to a runaway collapse to very high densities, supplemented by a catastrophic loss of its angular momentum through the bar-within-bar mechanism.
We are carrying on the detail study the physical processes that play a role on the runaway collapse and trying to apply to realistic cosmological condition that can make a prediction the formation of the first SMBH.
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AGORA high-resolution galaxy simulation comparison project
with Kentaro Nagamine(Osaka/UNLV), Robert Thompson(UWC/Arizona), Keita Todoroki (Kansas)
I participate in the AGORA project on the behalf of Kentaro Nagamine's UNLV gadget group.
I have particularly worked on incorporating the Grackle non-equilibrium chemistry cooling code into the Gadget N-body/Hydrodynamic cosmological simulation code.
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Galaxy formation in cluster environment at high-z
[Link to Recent Poster]
with Isaac Shlosman(UKY), Emilio Romano-Diaz(AlfA) Raphael Sadoun (Utah)
Using a high-resolution simulation with constrained realization method, we study the detail properties of high-z galaxies in the cluster environment.
In this project, we try to answer some outstanding questions in high-z galaxy formation such as high-z galaxy morphology, galaxy mass growth history, temperature and metalicity evolution of IGM and so on.
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Simulating observational galaxy properties at high-z
with Kentaro Nagamine(UNLV/Osaka), Jason Jaacks (UNLV/UT), Hidenobu Yajima (PSU/Edinburgh) Robert Thompson (Arizona)
Using cosmological smoothed particle hydrodynamics simulations based on the concordance LCDM model, we demonstrate that the Galaxy Stellar Mass Functions (GSMFs) and UV Luminosity Functions (UV LFs) shows very steep low-mass end slopes of (a < -2) for high-z galaxies.
This finding suggests that the galaxy stellar mass evolution is significantly fast at high-z.
Applying Authentic Radiative Transfer (ART) code to cosmological simulations, we study the escape fraction of the ionizing photon and find that the low mass galaxies play major role on the reionizaition.
We also study the properties of Damped Lyα system using cosmological simulation and radiative transfer calculation.
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Gas physics in cosmological simulation
with Kentaro Nagamine (UNLV)
Due to the resolution limitation, current cosmological simulations use simplified phenomenological relationships to implement SF and its feedback.
In order to improve this situation, we are developing improved models in cosmological N-body/Hydrodynamics simulation, GADGET.
First, we implemented metal enrichment, metal cooling, and evolution of mean atomic weight.
Owing to the additional metal cooling, global SFR is enhanced.
Second, we developed a new SF model that takes the effect of molecular hydrogen formation into account.
Our new model suppresses the early SF and shifts the peak of the cosmic SF history toward low redshift, more consistently with the recent observations.
Third, we have developed a new wind model which reproduces multi-phase outflows with variable wind speed depending on the galaxy SFR.
The new wind model does not overheats IGM, while significantly suppresses SFR and spreads metals into IGM, because large fractions of galactic winds in this model are warm and cold gas and contain considerable metals.
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Resonant dynamics in dark matter halo and satellite interaction
with Martin D. Weinberg, Neal Katz (UMass)
Interactions between bar-dark matter halo and satellite-primary galaxy play an important role in explaining observed present day galaxy characteristics.
Galaxy evolution by these interactions mostly occurs through resonance coupling of orbits.
Current N-body simulations are possibly inadequate to resolve the appropriate resonant dynamics, resonant dynamics is easily distorted or erased by astronomically unrealistic noise sources, such as Poisson noise and two-body relaxation.
Failure of reproducing resonant dynamics in N-body simulation possibly causes (or enhances) the "small scale" CDM crises.
We are investigating galaxy evolution due to satellite-dark matter halo interaction in detail using both state-of-the-art N-body simulations and linear perturbation theory calculation to determine the validity of the simulation and to understand what processes really drive galaxy evolution.
According to our study, the resonant dynamics plays an important role in galaxy evolution.
We find the resonant torque, the angular momentum transfer from time dependent host halo potential to satellite particles, enhances satellite mass loss.
Third, we expect that owing to global excitation by resonant interaction, the satellite halo interaction can cause the halo cusp evolution.
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"If you torture the data enough, it will confess anything!"
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