Deep COS Spectra of the Two Brightest Quasars that Probe the He II Post-Reionization Era

Deep COS Spectra of the Two Brightest Quasars that Probe the He II Post-Reionization Era We propose to obtain deep observations of the two brightest (known) He II quasars (HE2347-4342 and HS1700+6416) using the short-wavelength mode (G130M/1222) on the Cosmic Origins Spectrograph. These are among the few percent of z ~ 3 quasars that have visible flux at the He II Ly-alpha break, owing to unusually low integrated H I column densities along their sight lines. With the new grating mode, we can obtain high-resolution spectra at short (far-ultraviolet) wavelengths (1067-1363 A) that cover the He II post-reionization epoch at 2.5 < z_{HeII} < 2.75. During this time, helium ionization fronts overlap and the intergalactic medium (IGM) becomes transparent in the 4 ryd continuum. These high-S/N, high-resolution spectra are needed to resolve individual He II absorption lines, to compare with H I (Lya) and metal-line absorbers (C IV, Si IV), and constrain QSO lifetimes and ionization-front overlap with QSO transverse-proximity surveys (Jacobsen et al. 2003; Furlanetto & Lidz 2011). The He II post-reionization epoch is of astronomical and cosmological interest for several reasons: (1) The ionizing continua are changing rapidly, affecting QSO metal-line absorber ratios; (2) Photoelectric heating from He II changes the IGM temperature and equation of state; (3) He II-ionizing QSOs transverse to sight line constrain QSO lifetimes and ionization fronts; (4) Jeans smoothing from this extra heating may affect low-mass galaxy formation. We will conduct a detailed study of the end of the helium reionization epoch using the two FUV-brightest He II quasars. Most of the data will be taken in G130M/1222 to obtain coverage of the He II Gunn-Peterson trough and He II Ly-alpha forest at good resolution. Some G140L data will be taken for continuum fitting, using cenwave 1105 to avoid possible flux and wavelength calibration issues across the two segments. Accurate SDSS coordinates or prior HST observation allow us to use ACQ/IMAGE only to acquire our targets (to S/N=40 for the given time). The targets do not come close to violating overlight safety, and GALEX imaging directly verifies no nearby UV-bright objects. All FP-POS are used for the G130M observations to maximize S/N. QUASAR ABSORPTION LINES AND IGM Default false true false false false SUPPORTED GALAXY HIGH REDSHIFT GALAXY LYMAN ALPHA CLOUD QUASAR Position verified to be accurate to <0.4" by prior COS acquisition (program 11528). J2000 J2000 3.5E-15 erg/cm2/s/A at 1150 Angstroms (previous COS G130M) GALAXY HIGH REDSHIFT GALAXY LYMAN ALPHA CLOUD QUASAR J2000 J2000 3.0E-15 erg/cm2/s/A at 1150 (previous COS/G140L observation) COS/FUV Spectroscopic No No G130M 1222 COS/NUV Imaging No No MIRRORA COS/FUV Spectroscopic No No G130M 1222 COS/NUV Imaging No No MIRRORA The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. 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