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 $\log (M_{500}/{\rm M_\odot}) \sim 12.3$, using the {\it Planck} CMB 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 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 $10^5$ and $10^6\,{\rm K}$.