NASA Hubble Space Telescope Daily Report #4946

HUBBLE SPACE TELESCOPE DAILY REPORT #4946

Continuing to Collect World Class Science

PERIOD COVERED: 5am October 6 – 5am October 7, 2009 (DOY 279/09:00z-280/09:00z)

OBSERVATIONS SCHEDULED

COS/FUV 11592

Testing the Origin(s) of the Highly Ionized High-Velocity Clouds: A Survey of Galactic Halo Stars at z>3 kpc

Cosmological simulation predicts that highly ionized gas plays an important role in the formation and evolution of galaxies and their interplay with the intergalactic medium. The NASA HST and FUSE missions have revealed high-velocity CIV and OVI absorption along extragalactic sightlines through the Galactic halo. These highly ionized high-velocity clouds (HVCs) could cover 85% of the sky and have a detection rate higher than the HI HVCs. Two competing, equally exciting, theories may explain the origin of these highly ionized HVCs: 1) the “Galactic” theory, where the HVCs are the result of feedback processes and trace the disk-halo mass exchange, perhaps including the accretion of matter condensing from an extended corona; 2) the “Local Group” theory, where they are part of the local warm-hot intergalactic medium, representing some of the missing baryonic matter of the Universe. Only direct distance determinations can discriminate between these models. Our group has found that some of these highly ionized HVCs have a Galactic origin, based on STIS observations of one star at z<5.3 kpc. We propose an HST FUV spectral survey to search for and characterize the high velocity NV, CIV, and SiIV interstellar absorption toward 24 stars at much larger distances than any previous searches (4
SCHEDULED SUCCESSFUL
FGS GSAcq 7 7
FGS REAcq 7 7
OBAD with Maneuver 5 5

SIGNIFICANT EVENTS: (None)