Low Column Density Ly-Alpha Absorbers at z=1.2: High SNR Echelle Spectroscopy of PG 1634+706

Details Low Column Density Ly-Alpha Absorbers at z=1.2: High SNR Echelle Spectroscopy of PG 1634+706 Low Column Density Ly-Alpha Absorbers at z=1.2: High SNR Echelle Spectroscopy of PG 1634+706

Jul 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999hst..prop.8312j&link_type=abstract

HST Proposal ID #8312

Physics

Hst Proposal Id #8312 Quasar Absorption Lines

Scientific paper

We propose to produce the highest signal-to-noise ratio {SNR} Echelle resolution spectrum yet obtained of Ly-Alpha absorbers between z=0.9 and 1.2 by augmenting the planned cycle 7 observations of the luminous quasar PG 1634+706 with five orbits of CVZ observing time with the E230M grating. Our choice of a different central wavelength for our observations will allow the construction of a combined high SNR spectrum covering from 1865 to 3100 Angstroms. Recent theoretical work has shown that the neutral hydrogen column density N_HI of an absorber is tightly correlated with its overdensity, and hence with its dynamical and physical state. However, the mapping between overdensity and N_HI changes as the universe expands. If we wish to study absorbers at z 1 that are physically similar to absorbers at z 3 we must probe a factor 20-50 lower in column density {Dave et al. 1998}. The high SNR spectrum obtained from our observations of PG 1634+706 will allow the accurate measurement of the neutral column densities and line profiles of lines with N_HI as low as 3* 10^12 cm^-2. For the first time it will be possible to study at z 1 the mildly overdense regions of the intergalactic medium that have been observed so successfully at high redshift {z 3} with HIRES and the Keck I telescope.

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