# The Quasar Proximity Effect and the Intergalactic Medium at Low Redshift

Author/​Artist:
Eltvedt, Alice [Browse]
Format:
Senior thesis
Language:
English
In this work, I determine the quasar (QSO) proximity effect at low redshift (z<0.85) using the largest high resolution data catalog from the Hubble Space Telescope Cosmic Origins Spectrograph. I analyze the recent data from the HST/COS survey of 82 low redshift UV- bright Active Galactic Nuclei (AGN), published by Danforth et al. (2016), and detect the proximity effect through a lack of Ly absorption lines at column densities of logN$$_{HI}$$>~14.5-15. The proximity effect is not present for weaker column density lines of 13<~logN$$_{HI}$$<~14.5-15. I conduct an analysis of these observations to find more detailed trends within the proximity zone, such as a lack of additional thermal broadening in the absorption lines with respect to the broadening seen in the area outside of the proximity zone. After highlighting the lack of current data at these lower redshifts I discuss multiple models predicting the quasar proximity effect, structure formation, quasar lifetime constraints, the neutral hydrogen column density distribution, and the evolution of ionization in the intergalactic medium (IGM), especially at redshifts of z<2.