0 Assigned ID: 417 ----- Attempting Submission 1 (Fri Feb 24 14:32:36 GMT 2012) ----- 0 ----- Attempting Submission 1 (Mon Jul 09 00:42:12 GMT 2012) ----- ----- Attempting Submission 2 (Wed Apr 10 23:46:41 GMT 2013) ----- ----- Attempting Submission 3 (Fri Apr 12 08:58:40 GMT 2013) ----- The current FP-POS positions were selected after we discussed with out PC. Most of the Warm-Hot Intergalactic Medium (WHIM) has yet to be found, posing a fundamental challenge to the current theory of cosmological structure formation. A key prediction is that the WHIM resides in the "cosmic web" structures that are traced by galaxy superstructures and served as "signposts" of baryons. Our detection of an OVII K-alpha absorption line located in the Sculptor Wall superstructure of galaxies (z ~ 0.03) in the X-ray spectrum of the blazar H 2356-309 is arguably to date the most promising X-ray detection of gas that could represent the typical WHIM. However, despite the solid statistical significance of our detection (4-sigma) and the consistency of the measurements with both good-quality Chandra and XMM data, further verification is warranted because of the scientific importance of the result and the history of controversial claimed detections in this field. We therefore propose a HST/COS observation of the blazar H 2356-309 sightline. The detection of an HI broad Ly alpha absorber (BLA) will offer an independent confirmation of the Sculptor Wall WHIM absorber at even higher significance than achieved with X-ray data. This sightline also passes through two other galaxy superstructures, therefore offering the best opportunity to perform a comprehensive, joint UV/X-ray study of the WHIM residing in the three galaxy superstructures, the signposts of the cosmic web. We propose a COS observation of the blazar H 2356-309. The main science goal is to detect UV absorption lines produced by ion species in the foreground superstructures, as well as any other locations along the sight line, and perform a joint analysis with high quality X-ray observations. Choice of Gratings; The major ion species we plan to study are listed in the phase I proposal Table 1. We will select COS over the Space Telescope Imaging Spectrograph (STIS) mainly because COS is more sensitive in the far ultraviolet (FUV) band. We will also select the G130M grating of the COS FUV. The resolution of G140L is too low for resolving narrow UV absorption lines. We will use multiple grating central wavelength and FP positions to ensure continuous spectral coverage between 1150 and 1450 A and to dither instrumental features across the spectrum. Our team members have extensive experience in this area. Exposure Time: Recent observations with the HST/COS suggested the spectrum must have a S/N of around 20 per 6 pixel resolution element to detect the BLA. Using the COS Exposure Time Calculator, we estimate an exposure time of 16 ksec., or about 7 orbits after taking into account all the instrumental overheads. With this exposure time, we should be able to detect the BLA down to 30 mA, or H I column density of 5 10^12 cm^-2, at 10-sigma significance. QUASAR ABSORPTION LINES AND IGM 12 false false 0.0 0.0 false false false SUPPORTED GALAXY BL LAC FILAMENT QSO This object was generated by the targetselector and retrieved from the SIMBAD database. V and B magnitude is adopted form SIMBAD, which was reported by 2dF Galaxy Survey ("The 2dF Galaxy Redshift Survey: spectra and redshifts", Colless et al., 2001, MNRAS, 328, 1039 UV flux is taken from previous FUSE measurement (FUSE program data ID P2070701000). GELAX also gave similar flux. No LLS or DLA will block all flux below a certain wavelength since the FUSE data show non-zero flux. 2MASXJ23590793-3037409 1H2351-315 J2000 J2000 B magnitude: 18.4 COS/FUV Spectroscopic No No G130M 1309 COS/FUV Spectroscopic No No G130M 1318 COS/FUV Spectroscopic No No G130M 1327 COS/FUV Spectroscopic No No G130M 1291 COS/FUV Spectroscopic No No G130M 1300 1365636552716 The scheduling data was generated by CASM 21.0. CASM was run in Phase II mode. 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