DR. ANJALI GUPTA

It is well-known that most galaxies are missing most of their baryonic mass. Perhaps more surprisingly, they also seem to be missing most of their metals. Our Milky Way galaxy, like other nearby galaxies, is missing most of its baryons. Cosmological simulations of galaxy formation suggest that the missing baryonic mass should reside in the circum-galactic medium (CGM), in a warm-hot gas phase at temperatures between one million and 10 million K. Although theoretical models predict the existence of the warm-hot gas in the CGM, detecting and characterizing the diffuse CGM has been difficult. At the expected temperatures the baryons are in the form of highly ionized plasma, observable in soft X-rays. A combination of absorption and emission studies at soft X-ray energies is required to fully characterize this warm-hot CGM. Recently, combining the Chandra observations of OVII and OVIII absorption lines and XMM-Newton and Suzaku measurements of the Galactic halo emission measure, we found that there is a huge reservoir of ionized gas around the Milky Way, with the mass of over 2 billion solar masses and the radius of over 100 kpc. I will present Chandra, XMM-Newton and Suzaku observations probing our Milky Way halo in absorption and emission. Our results show that the Milky Way halo contains a huge reservoir of warm-hot gas that may account for a large fraction of missing baryons and metals. I'll review current status of this field, discuss implications of our results to models of galaxy formation and evolution and outline paths for future progress.