Science Case Study


The prime driver for the ARGOS ground layer adaptive optics system is to greatly enhance the science that can be carried out with existing facility instruments, and in particular with LUCI. This can be enabled by improving the resolution and sensitivity for both imaging and multiobject spectroscopy over a very wide field of view. In particular, the combination of GLAO with a wide-field MOS will be a unique facility.
The direct benefits to the LBT are afforded by an improvement of factor tow to three in the spatial resolution. Indeed, ARGOS can be considered as a "seeing enhancer" for the existing facility instruments, which enables us to address much more of the primary science that has been identified in science cases.

The reasons are as follows:

  • Observations can be made much faster, saving a significant amount of observing time.
  • Demanding science programs that would normally require the best seeing conditions can be carried out during most nights.
The science case study addresses these issues in greater detail. It describes the gains that can be achieved with GLAO; and the requirements on the design are justified. A specific detailed comparison is given for a highlight science case: the dynamics and stellar populations in high redshift galaxies.

Questions ranked around this topic are:

  • How did galaxies assemble over time, and what is the role of mergers?
  • How did galaxies grow their stellar mass?
  • How did galaxies acquire their morphology and how did the Hubble sequence arise?
  • How did galaxies get their angular momentum?


In order to answer these fundamental questions, robust measures are needed for mass, age, star formation rate, gas phase metallicity and ionization state, dust obscuration, sizes, and morphologies for complete samples of z ~ 1–4 galaxies. This epoch is crucial as it corresponds to the peak of (dust-enshrouded) star formation and quasar activity, as well as the assembly of a significant fraction of the present-day galaxies. Spectroscopic investigations at z ~ 1–4 remain challenging, however, since the key spectral diagnostics (Hα, Hβ, [NII], [OIII], [OII], [SII] emission lines, continuum emission, stellar absorption features, and Balmer/4,000 Å breaks) that are emitted in the rest-frame optical are redshifted to the near IR, between 1 and 2.5 μm. Due to the technological challenges to build multiplexed near-IR cryogenic spectrographs, there is a lack of such capabilities on 8-m-class telescopes. LUCI will therefore play a very important role in answering the above scientific questions. This highlight science case is accomplished by a number of short science cases contributed by the LBT community, which illustrate the breadth of science that can be addressed with the GLAO system. These include a mixture of cases, some of which specifically require GLAO for the science itself while others need AO over a smaller field, but still make use of the wide-field GLAO capability in order to measure the corrected PSF. In all cases, the improved resolution enables a better scientific analysis and interpretation, and yields gains in observing time of a factor of four to nine.

Additionally, the science case study outlines the gains in science capability with GLAO:
  • Increased point source sensitivity
  • Increased slit coupling efficiency
  • Reduced crowding noise
  • Enhanced spatial resolution
The science case study also contains a detailed comparison with the spectroscopic capabilities of JWST and ground-based facilities. While ARGOS and LUCI are not expected to compete effectively with JWST in terms of resolution or sensitivity, the simulation results show that ARGOS will make the LBT spectroscopically competitive with JWST between the OH lines and at wavelengths shorter 2.2 μm. In comparison with other existing or planned facilities, LUCI and its wide-field MOS has several strong competitors. ARGOS therefore will be a crucial enhancement to LUCI to give it an edge over other instruments.
Go to Editor View