Oral Presentation
Statistical Properties of high-synchrotron peaked blazars
Presenter: Yu-Ling Chang (National Taiwan University)
High synchrotron peaked (HSP) blazars dominate the extragalactic sky at GeV–TeV energies, yet their cosmological evolution and demographic properties have long remained uncertain due to limited and heterogeneous samples. We present a statistical study of HSP blazars using the updated 3HSP-DR2 catalogue, comprising over 2,000 sources, and construct a radio- and X-ray–flux-limited, statistically complete sample by combining ROSAT and Swift OUSXG observations. Using this sample, we investigate number counts, luminosity functions, and evolutionary trends through log N–log S and V/Vₐ analyses. We find that HSP blazars exhibit clear negative cosmological evolution, with a deficit of faint and high-luminosity sources at higher redshifts. The radio and γ-ray luminosity functions are consistent with previous results from smaller complete samples, but show significant disagreement with predictions from the blazar sequence scenario, indicating that selection effects likely drive the apparent sequence. We further show that the fraction of HSPs among BL Lac objects remains approximately constant across radio and γ-ray flux ranges, with extreme HSPs constituting only a small minority of the population. Our results demonstrate that controlling selection effects is essential for interpreting blazar demographics and establish HSP blazars as a negatively evolving population. This work provides a robust statistical framework for future studies of high-energy blazars and their role in γ-ray and multi-messenger astrophysics.
asiaa.sinica.edu.tw