Speaker
Description
Identifying the origin of TeV-PeV neutrinos requires understanding both how much target material is available for hadronic interactions and where high-energy emission originates in blazar jets. While excess neutrino emission toward the Galactic Center suggests that dense gas environments play an important role, the association of a high-energy neutrino with the blazar TXS 0506+056 indicates that relativistic jets can also accelerate cosmic rays. In both cases, the key quantities governing neutrino production, namely target density and particle acceleration power, remain poorly constrained.
We present a new observational approach based on the ALMA Calibrator Source Catalogue, a large and homogeneous dataset of bright blazars and background continuum sources, which allows us to probe both ingredients in a unified way. First, absorption-line measurements toward ALMA calibrators reveal diffuse molecular gas, including CO-dark components missed by conventional emission-line surveys, and thus provide direct constraints on the target density for cosmic-ray interactions. Second, using a statistically significant sample of ALMA-Fermi matched blazars, we find a strong correlation between millimeter and gamma-ray luminosities, indicating that millimeter emission traces the average jet power and particle acceleration efficiency. Taken together, these results demonstrate that ALMA calibrator observations provide a unique framework for linking target environments and jet energetics in the study of gamma rays and high-energy neutrinos.
