The Lambda cold dark matter (LCDM) model is now the standard cosmological model. It correctly predicts the cosmic background radiation and the large-scale distribution of galaxies. However, there are still several remaining challenges to the model. In this talk, I will present our recent work on two of the challenges: abundance of pseudo-bulge galaxies and the cusp-core controversy in dwarf galaxies.
In the first part, I will introduce our work on pseudo-bulges and classical bulges using the new bulge indicator ΔΣ1, which measures relative central stellar-mass surface density within 1 kpc. Structural parameters show fairly linear log-log relations vs. ΔΣ1, while stellar-population parameters show a highly non-linear "elbow" in which specific star-formation rate remains roughly flat with increasing central density and then falls rapidly at the elbow. The wide range of star-formation rates in classical bulges helps to explain why bulge classifications using different parameters have sometimes disagreed in the past. However, no matter which criteria we choose to classify the bulge types, there are still relatively high fraction of massive pseudo-bulges.
In the second part, I will introduce our recent work on direct measurements of the dark matter halos of dwarf galaxies. We justify the present and future deep+wide photometric weak gravitational lensing surveys including HSC, LSST and WFIRST would have the statistical capability of measuring the lensing signal of dwarf galaxies at logM∗/M⊙~8 with high signal-to-noise out to z=0.1. However, further work will be required to develop optimized strategies for extracting dwarfs samples from these surveys, determining redshifts, and accurately measuring lensing on small radial scales. Dwarf lensing will be a new and powerful tool to constrain the halo masses and inner density slopes of dwarf galaxies and to distinguish between baryonic feedback and modified dark matter scenarios.
Yifei Luo is currently a PhD student in the Department of Astronomy and Astrophysics at University of California Santa Cruz, working on galaxy evolution and observational cosmology. Yifei got his Bachelor of Science in Astronomy at Nanjing University. After that he worked at the National Astronomical Observatories, Chinese Academy of Sciences as a research assistant for a year. Yifei has been working on various fields including weak gravitational lensing, the link between galaxy structure and quenching processes and the co-evolution between galaxy and dark matter.