Dr. Pengfei Li

Humboldt fellow

PhD in Astronomy, August 2020, Case Western Reserve University, U.S.

Master in Theoretical High-Energy Nuclear Physics, July 2015, Peking University, China.

Research interests: dynamics of galaxies, galaxy clusters, dark matter, cosmology, alternative theories

Major collaborations: SPARC, eROSITA, and SDSS-V (Black Hole Mapper)

Publication list at ADS

Follow me on Twitter: @PengfeiLi0606

Dwarf Galaxies and the Galactic Halo
Postdoctoral Researcher
Office: LH/1-10
Phone: +49 331 7499 662

für Astrophysik Potsdam (AIP)
An der Sternwarte 16
14482 Potsdam

The largest known sample of dark matter halos

During my PhD, my research focus on testing and constraining various dark matter models. I studied the rotation curves of 175 late-type galaxies from the Spitzer Photometry & Accurate Rotation Curves (SPARC) database. The SPARC sample is a good representative of late-type galaxies, ranging from dwarfs to large spirals, gas-poor to gas-rich galaxies. With this sample, I built the largest known sample of dark matter halos insofar with 2100 rotation curve fits using seven popular halo models (read the paper here). Using this halo catalogue, I found the volume density of dark matter halos is almost constant for low-mass and high-mass galaxies (read the paper here). I also established an empirical relation between halo mass and HI line width. HI line width is an easy observable, so I used the empirical relation to derive the halo mass for the HIPASS sample and measured the dark matter halo mass function (read the paper here). My halo catalogue can be used as a source for the halo mass, and compared with simulations.

In addition, using the SPARC sample, I found that the statistically established RAR (radial acceleration relation) also applies to individual galaxies once the uncertainties on galaxy distance, disk inclinations and stellar mass-to-light ratios are properly considered. The RAR is a tight relation that states the observed total acceleration exactly corresponds to the acceleration from baryonic distributions. My finding implies that the total dynamics "knows" accurately the baryonic distributions, so the distribution of dark matter particles and baryons must be strongly correlated (read the paper here).

Interplay between dark matter and baryons

In the two years after my PhD, I invented a new approach to fitting rotation curves by incorporating the interplay between dark matter and baryons (read the paper here). Baryonic disks are supposed to affect the structure of dark matter halos, which has long been ignored when fitting rotation curves. As a result, the best-fit dark matter halos are generally not in dynamical equilibrium with embedded baryons. I numerically calculated the halo response to the gravitational potential of barons, and implemented it into rotation curve fitting. This way, we fit compressed halos to observed rotation curves, and it guarantees the dynamical equilibrium of the final configuration. With the new approach, I found that the initial NFW halos become more cuspy that are problematic even for massive galaxies.

The interplay between dark matter and baryons also suggests that one cannot build galaxies by setting up each component (baryonic disk and dark matter halo) separately. This simple configuration cannot stay in dynamical equilibrium and thereby does not exist in reality. Once the mutual gravitational interaction is considered, the semi-empirically built galaxies systematically deviate from observed relations (read the paper here).

Dynamics of galaxy clusters from galaxy kinematics

Since I joined AIP, I started working on the dynamics of galaxy clusters. I propose to use galaxy kinematics to trace the gravitational potential of clusters (read the paper here). This is the third tracer besides X-ray gas (hydrostatic equilibrium) and passing photons (gravitational lensing). I joined the eROSITA collaboration and SDSS-V collaboration. eROSITA is an X-ray space telescope for all-sky survey, providing more extended observations with respect to Chandra, XMM-Newton and ROSAT. It has observed ~20k galaxy clusters and groups with the first formal data release expected in May/June 2023. SDSS-V is the latest generation, which aims for all-sky survey. Its Black Hole Mapper provides the optical observations covering almost all the eROSITA field. Its first dataset (DR18) has been released in January 2023. I combine the optical data from SDSS-V and X-ray data from eROSITA to investigate the dynamical status of galaxy clusters, study the formation and evolution, and test dark matter models as well as alternative theories of gravity.


Latest refereed publications, retrieved from NASA ADS:

Li, P., McGaugh, S. S., Lelli, F., Schombert, J. M., Pawlowski, M. S., 2022
Astronomy and Astrophysics, 665, A143; published September 2022
Participating AIP sections and groups: Dwarf Galaxies and the Galactic Halo
Pawlowski, M. S., Kanehisa, K. J., Taibi, S., Li, P., 2022
Astronomy and Astrophysics, 664, L6; published August 2022
Participating AIP sections and groups: Dwarf Galaxies and the Galactic Halo