TMT's Guide Through Thermal-Infrared Darkness

MICHI is a possible 2nd generation instrument for the Thirty Meter Telescope (TMT). The Mid-Ifrared Camera with High spectral resolution and IFU. It is the result of a collaboration initiated by astronomers in the USA and Japan, and has now expanded to include representatives from all the partner countries of the TMT consortium.

MICHI is optimized to cover the thermal-IR region (~3-13 μm ), and capable of operation up to ~26 μm. It combines diffraction-limited broad and narrow band imaging with low- and high-spectral resolution (R~1,000 and ~120,000) across the wavelengths of optimization, and an integral field unit (N band only).

We are preparing for the next generation instrumentation call for proposals, expected in early 2017. In these pages you can find a little about who we are, the science we plan with MICHI, the instrument summary, some pictures of our development work, and some comments about the possible site location of the TMT and the implications this has to MICHI. For more information, please contact either Mitsuhiko Honda or Chris Packham.

Applying TMT's power to elusive thermal-IR mysteries.

Helping TMT capture the fine details and dynamics of the dusty universe.

Helping TMT capture the fine details and dynamics of the dusty universe…

The TMT's aperture will enable thermal IR, high resolution spectroscopic studies to progress from the current level, where most studies concentrate on the brightest 5-10 object of a given class, to a plane where comparative study of a hundred objects with good signal-to-noise is entirely practical. For example, a typical solar mass T Tauri star can be studied in a volume that extends past Orion as opposed to just reaching Taurus - permuting study of cluster star formation, not just formation in small aggregates. Objects ~3 magnitudes fainter become accessible, comparable to the gain between the Bright Star Catalog (~9,000 objects) and the HD Catalog (~360,000 objects including the extensions). Surveys that require 10 hours of integration time per target on 8-meter telescopes, will only require 3 minutes for the same signal-to-noise ratio.

MICHI studies will be critical to completing the picture of planetary system formation. While other facilities will be better for characterizing the diversity of planetary system, MICHI provided a uniquely powerful tool for probing planet formation environments for clues to the physical origin of this diversity. Higher excitation energy tracers, common in the MIR, will provide a direct view of the inner disc regions (<5 AU regions) where terrestrial and giant planets form.

Through observations of gas in discs, the interstellar medium, comments, and other environments, MICHI offers the opportunity to investigate the abundance of prebiotic compounds that led to emergence of life on Earth.

The Decadal Survey stressed the importance of extragalactic supermassive black holes (SMBH) to both astrophysics and cosmology. These is a clear connection between the SMBH and galaxy properties, as shown through the famous M_BH vs. M_bulge and M_BH vs. σ relationships, demonstrating that the galaxy bulge mass (M_bulge) and the stellar velocity dispersion (σ) are tightly correlated with (M_BH), despite being on widely different spatial scales. This correlation strongly implies some form of co evolution between the SMBH growth and the galaxy bulge, but the precise nature of this relationship remains uncertain. Understanding this relationship will help to address two crucial questions in cosmology:

• Which formed first, the SMBH or the galaxy?
• How did SMBHs form so soon after the big bang?

The SMBH will often show a level of 'activity' arising through accretion of gas and dust, leading to an Active Galactic Nuclei (AGN). The study of AGN has recently been invigorated through high-spatial resolution observations of the torus in 8-m class telescopes. These observations have shown a complex, clumpy, and probabilistic unification scheme, with tentative hints that the torus structure is (partially) dependent on the level of AGN activity. Possible other effects could be the level of radio emission (radio loud/quiet AGN) and that of the host galaxy, as well the precise fueling of AGN. The complex interplay between the host galaxy and AGN remains poorly constrained, and is a goal of the Decadal Survey.

The TMT will have sufficient point-source sensitivity to permit direct detection of gas giants, achieving a 'tipping' point in sensitivity to achieve this exciting goal. In a gas is in thermal equilibrium with irradiation by the central star, MICHI will be capable of detecting such giants at a distance of a few AU from nearby (~10 pc) early type (AFG type) stars. If a young (~1 Gyr) planet's temperature is determined by its own internal heating (Burrows et al. 2004), detectability is easier. MICHI observations of gas giants holds the promise of the characterization ~5 times closer to the central star than MIR space-based facilities due to the superior spatial resolution.

MIR molecular absorption bands and lines (i.e. NH3 and CH4) can be detected with low- and high-angular resolution spectroscopy, and in particular, the 10.5 μm NH3 absorption band is a unique indicator of low temperature (< 1,000 K) planets, only accessible in the MIR. Such information has extremely valuable information on planetary atmospheres.

Existing near- and mid-IR observations of planet forming regions, protoplanetary and debris discs, have revealed astonishing pictures of pleat forming discs such as spirals, gaps, holes and, dips, which strongly imply that planets are forming there. Further, the volition of dust, the key ingredient of planets, such as grain growth and crystallization have been observed. However, these are challenging observations from 8-m class observatories. The spatial resolution and sensitivity of MICHI will be crucial to dramatically increase the number of available sources, conduct statistically significant surveys, and probe the disc chemistry.

Based on the science drivers, we summarize important required capatibilities for MICHI may include:

• Imaging in the N (7.3-13.5 μm) band
• Low-dispersion spectroscopy in the N, M, and N bands with R~ a few hundred
• High-strehl imaging at the L, M, N bands with R ~100,000
• Thermal IR AO system, which enables high-strehl, high-sensitivity imaging and lower dispersion.
• Cold internal chopper to enable high-sensitivity imaging and lower dispersion spectroscopy
• Integral field spectroscopic capability with the low-dispersion (R~250 to 1000) and ~2“ x 5” FOV
• Polarimetry in both imaging and low-dispersion spectroscopic modes (TBC)