Assigned ID: 625 ----- Attempting Submission 1 (Fri Feb 26 21:18:52 GMT 2010) ----- ----- Attempting Submission 1 (Fri Jul 09 19:08:44 GMT 2010) ----- The proposal has a warning that in visit 02 we are not using the most efficient order for the FP-POS positions. I have opted for this order because we checked that the lines we are primarily interested in are not in the gaps for the default setting so I would like to keep the default setting as one of the longer observations. This means having to break up an orbit to change positions either between FP-POS 1&2 (as it is in the proposal) or between 2&4 or 1&4 neither of which is optimal. With this setting all of the changes are during occultation so no time is lost in the observations. Unravelling the Mysteries of the Leo Ring: An Absorption Line Study of an Unusual Gas Cloud We propose an absorption-line study of 3 QSO sight lines behind the Leo Ring with COS. The Leo Ring is a huge (~200 kpc in diameter, HI mass of 2x10^9 solar masses) neutral gas cloud that has been postulated to be either tidal or primordial in origin. Despite over 25 years of investigation, the mystery of its origin remains unsolved. By obtaining the most robust measurement of metallicity to date and constraining the ionized gas content along these sight lines, we will finally be able to determine the origin of the gas. The observations include Ly-alpha plus low and high ionization metal lines in absorption that will be modeled with the photoionization code, CLOUDY. If the gas in this feature is primordial (low metallicity and highly ionized), it provides an interesting challenge for those who model the formation and evolution of galaxies and reveals a unique mode of galaxy formation. Alternatively if the feature is tidal in origin, these observations represent one of the first absorption line studies of tidal gas which has been argued to be a significant component of the enrichment of the intergalactic medium.
We will observe 3 QSOs with the G130M and G160M gratings. For the 2 QSOs with HI detected along the line of sight we will only use G130M while for the third QSO we will observe with both the G130M and G160M gratings. The observation time should allow us to obtain better than a 5-sigma detection in one resolution element. The target acquisition will use a NUV acq/image acquisition with mirror A and the PSA. We propose to observe with the G130M and G160M gratings because they provide the wavelength range to cover the Ly-alpha, CII [1334], CIV[1548], SiII[1260], SiIII[1206], SiIV[1393], and OI[1302] lines. The observation of these lines will allow us to determine the HI column density, metallicity, and ionization of the gas (see scientific justification for details on the model dependent nature of the metallicity and ionization). For two of the three QSOs we can estimate an HI column density from the emission line measurements if we are unable to measure Ly-alpha due to an intervening absorber or, more likely, due to saturation of the line. By setting the G130M grating at lambda = 1300 and the G160M grating at lambda = 1589 none of the lines discussed fall into the gap between detector segments. We set our exposure times to obtain a S/N > 5 per resolution element. The calculation was done assuming a flat continuum in f(lambda) but the times come out almost the same (within a couple hundred seconds) for a FOS based QSO template. This S/N limit translates into a CII equivalent width of ~70 mA, ~1% solar metallicity for a neutral gas column density of N_HI = 10^19 cm^-2. Similar limits on the metallicity can be placed using the OI line. The higher ionization lines of S III, Si IV, and C IV can provide constraints on the ionization of the gas, particularly for a known metallicity. Based on these limits we expect to be able to constrain the ionization of the gas and place limits down to 2 - 3% solar along the two higher column density sight lines. Along the lower column density sight line the metallicity constraints are not as stringent but if an ionized component is detected we can constrain the amount of ionized gas. The presence or absence of gas along this third sight line is important for determining the origins of the ring. QUASAR ABSORPTION LINES AND IGM 12 false 0.0 0.0 false false false false false false SUPPORTED EXT-MEDIUM ABSORPTION LINE SYSTEM - EXTRAGALACTIC HI CLOUD IGM GALEX FUV = 19.9 J2000 10 48 16.2500 +12 07 34.70 J2000 EXT-MEDIUM ABSORPTION LINE SYSTEM - EXTRAGALACTIC HI CLOUD IGM GALEX FUV = 19.4 J2000 10 47 9.8000 +13 04 55.00 J2000 EXT-MEDIUM ABSORPTION LINE SYSTEM - EXTRAGALACTIC HI CLOUD IGM GALEX FUV = 20.1 J2000 10 48 43.4900 +13 06 5.90 J2000 COS/FUV Spectroscopic No No G130M 1300 COS/FUV Spectroscopic No No G160M 1589 COS/FUV Spectroscopic No No G130M 1300 COS/FUV Spectroscopic No No G160M 1589 COS/FUV Spectroscopic No No G130M 1300 COS/FUV Spectroscopic No No G160M 1589 /Users/rosenber/text/proposals/hst/2010/OP-cache/LeoRing_PhaseII-v01.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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