Prior HST usage does not count towards the page total. The Scientific Justication is 3 pages, and the total without the prior usage is 7.5 pages. 1031762645 Assigned ID: 832 ----- Attempting Submission 1 (Fri Apr 11 21:09:50 GMT 2014) ----- We propose to measure the emission from the gas associated with known extragalactic UV absorbers to constrain the physical conditions and physical size of the gas. This will be accomplished through the co-addition of numerous ( >75) COS QSO lines of sight, shifted in wavelength so the absorbers are coincident. The COS aperture admits light from the surrounding sky that can be separated from the point source signal to measure diffuse emission. No single observation has the sensitivity to detect these signals, but large coadditions can, unless the gas is extremely low density. We have custom extraction procedures for this project, and our intimate understanding of CalCOS, the optical performance of COS, and FUV detector systematics (scattered light, dark rate, gain sag, detector walk, etc.), are essential to its success. Our team consists of COS IDT members, the COS PI and optical designer of COS, STScI COS calibration team members, and IGM/CGM experts. We will look for emission from HI Lya 1216A and OVI 1032A. Emission and absorption measures on a unique line of sight would normally allow for a determination of the volume density and physical size. However, since this study will produce a net emission measure from many co-added lines of sight, it will provide an average, but unique, physical insight into the nature of the gas, and in particular, indicate what fraction of this previously undetected gas is circumgalactic versus truly intergalactic in nature. We will also search for extended diffuse emission from gas not associated with absorption systems. We will also assist in testing and enabling many cutting edge additions to CalCOS which will benefit future COS users. QUASAR ABSORPTION LINES AND IGM Default Medium false true false false false SUPPORTED