Detection of Missing Baryons in Galaxy Groups with Kinetic Sunyaev-Zel'dovich Effect

We present the detection of the kinetic Sunyaev-Zel'dovich effect (kSZE) signals from groups of galaxies as a function of halo mass down to $\mathrm{log}({M}_{500}/{M}_{\odot })\sim 12.3$ using the Planck cosmic microwave background maps and stacking about 40,000 galaxy systems with known positions, halo masses, and peculiar velocities. The signals from groups of different mass are constrained simultaneously to take care of the projection effects of nearby halos. The total kSZE flux within halos estimated implies that the gas fraction in halos is about the universal baryon fraction, even in low-mass halos, indicating that the "missing baryons" are found. Various tests performed show that our results are robust against systematic effects, such as contamination by infrared/radio sources and background variations, beam size effects, and contributions from halo exteriors. Combined with the thermal Sunyaev-Zel'dovich effect, our results indicate that the "missing baryons" associated with galaxy groups are contained in warm-hot media with temperatures between 10⁵ and 10⁶ K.