TLSS and LRS-J: probing large scale structure near and far

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Tufts, Joseph Rutledge

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The Texas Large Scale Structure Survey (TLSS) is an optical survey of rich galaxy clusters found in the huge superstructures detected in the TONS08 radio source redshift survey. TLSS is consistent with the TONS08 survey in that there is clearly an overdensity of clusters at a redshift 0.26 < z < 0.28 and quite probably a second overdensity at 0.32 < z < 0.34. Moreover, the overdensity of clusters is comparable to that of the radio galaxies confirming, for the first time, that the bias of the radio galaxies can be boosted from it’s canonical value of 1.6 to a value similar to clusters of galaxies (b = 3−4) in superstructure regions. The TLSS survey has confirmed that radio sources are indeed reliable and efficient tracers of very large scale structure. This fact will allow huge volumes of space (out to z ∼ 1) to be probed efficiently for rare superstructures that can be followed up in other passbands including that of LRS-J. LRS-J is a 142 mm f /1 near infrared camera for the 9.2 m Hobby-Eberly Telescope Low Resolution Spectrograph. It covers the wavelength range 0.912 – 1.100 µm with a resolution of Rmax = 1754 at 1.0 µm, and 1.098–1.297 µm at a resolution of Rmax = 1990 at 1.2 µm. The camera was designed as a drop-in replacement for the optical camera and is based on a similar catadioptric Maksutov-type design. The HAWAII-1RG based instrument is fully cryogenic but mates to the warm LRS making use of the existing longslit and multi-object modes as well as the optical collimator. The first instrument to employ both volume phase holographic gratings and a high quantum-efficiency molecular beam epitaxy based HgCdTe array, LRS-J will achieve peak on-sky efficiencies approaching 20%. The LRS-J design is strongly motivated by the desire to observe galaxies at redshifts 1 < z < 2, where the principal strong spectral features used to measure redshifts are shifted into the J-band. LRS-J enables well established optical techniques to be extended into the near-IR allowing measurements of star formation rates of field galaxies, mass determination of z > 1 galaxy clusters, and discovery of z > 7 QSOs by Ly-α emission. LRS/LRS-J is the only near-IR multi-object spectrograph with the sensitivity required to address these key scientific goals.