"The Development of Replicated Optical Integral Field Spectrographs and their Application to the Study of Lyman-alpha Emission at Moderate Redshifts"
In the upcoming era of extremely large ground-based astronomical telescopes, the design of wide-field spectroscopic survey instrumentation has become increasingly complex due to the linear growth of instrument pupil size with telescope diameter at a constant spectral resolving power. The upcoming VIRUS instrument for the Hobby-Eberly Telescope (HET) Dark Energy Experiment (HETDEX) represents one of the first uses of large-scale replication to break this relationship by dividing the telescope's field of view between 150 simple fiber integral field spectrographs. While large-scale replication presents unique challenges, it has clear advantages for obtaining the total information grasp of a traditional monolithic instrument at a fraction of the cost and engineering complexity.
In this dissertation talk, I present the HET's second generation facility Low Resolution Spectrograph (LRS2), which is based on the VIRUS unit design and replaces the venerable Marcario Low Resolution Spectrograph after its recent decommissioning in preparation for the HET wide field upgrade. I discuss the design, operational concept, construction, and laboratory testing of LRS2, which highlights the benefits of leveraging the large engineering investment, economies of scale, and laboratory and observatory infrastructure associated with the massively replicated VIRUS instrument. LRS2 will provide integral field spectroscopy for a seeing-limited field of 12 x 6 arcsec with broad wavelength coverage from 370 nm to 1 micron spread between two independent dual-channel spectrographs at a moderate spectral resolving power R~2000.
I also present the results of investigations into the spectrally resolved Lyman-alpha emission of 2.0 < z < 3.5 Lyman-alpha emitting galaxies (LAEs) from the HETDEX Pilot Survey, in which the low column density of neutral hydrogen gas is suggested to be the primary regulator of Lyman-alpha escape for this galaxy population. Looking forward, I present a model of LRS2's sensitivity and apply it to the science case of conducting one of the first systematic integral field surveys of extended Lyman-alpha emission at moderate redshifts. LRS2 is expected to reach a Lyman-alpha surface brightness limit of ~5 x 10^-18 erg/s/cm^2/arcsec^2 at 5 sigma significance, which is competitive with similar future instruments on other 10 meter-class telescopes. This science case illustrates the power of LRS2 as a workhorse survey follow-up instrument for HETDEX.
University of Texas at Austin