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The Dusty Co-evolution of Black Holes and Galaxies : A Science Case for a Large Far-IR Space Telescope

The Far-IR Science Interest Group will meet from 3–5 June 20152 with the intention of reaching consensus on the architecture for the Far-IR Surveyor mission. This paper is an except from a larger document which describes one of the architectures to be considered by the community. We present the Cryogenic-Aperture Large Infrared-Submillimeter Telescope Observatory (CALISTO), a 5-meter class, space-borne telescope actively cooled to T∼4 K, emphasizing moderate-resolution spectroscopy in the crucial 35 to 600μm band. CALISTO will enable NASA and the world to study the rise of heavy elements in the Universe’s in the first billion years, chart star formation and black hole growth in dust-obscured galaxies through cosmic time, and conduct a census of forming planetary systems in our region of the Galaxy. CALISTO will capitalize on rapid progress in both format and sensitivity of far-IR detectors. Arrays with a total count of a few ×10 detector pixels will form the heart of a suite of moderate-resolution (R∼500–1000) imaging spectrometers in which each detector reaches the photon background limit. Other instruments are also under consideration, including broad-band imagers and high-spectral-resolution (R>10,000) spectrometers. 1 Motivation for Sensitive Wideband Far-IR Spectroscopy The sensitive CALISTO platform is especially compelling for wideband spectroscopy, as Figure 1 shows and Table 2 presents. CALISTO will obtain full-band spectra of thousands of objects ranging from the first dusty galaxies to the most heavily enshrouded young stars and protoplanetary disks in our own Galaxy, as well as blind discovery of thousands more. These CALISTO spectra will directly address several key goals of modern astrophysics: • Measure the onset of heavy elements and the rise of organic molecules in the Reionization Epoch. See white papers by Cooray et al., and Appleton et al. for more information. • Chart the true history of cosmic star formation and its connection to supermassive black hole growth. More information can be found in a white paper by Armus et al. • Measure clustering and total emission of faint galaxies below the individual detection threshold using tomographic intensity mapping of the far-IR emission lines. • Probe the cycling of matter and energy in the Milky Way and nearby galaxies. • Conduct a census of gas mass and conditions in protoplanetary disks throughout their evolutionary sequence. A white paper by Bergin et al. describes this more fully. 2 Architecture Choice The scientific goals outlined above require excellent spectroscopic sensitivity, both for point sources and mapping, with full coverage between the 28μm cutoff of JWST MIRI and the onset of the ground-based windows at ∼600μm. Accessing the earliest galaxies and most-evolved lowest-mass protoplanetary systems requires a line sensitivity below 10−20 W m−2, large instantaneous bandwidth, and moderate spectral resolving power (R = δλ/λ ≥ 500). The requirement for ultimate sensitivity demands maximum collecting area, low telescope background, and high efficiency. Blind spectroscopic surveys over large fields will also be a part of the program, so the observatory must have enough throughput (AΩ) to make use the large-format array technology now available. These crucial attributes are summarized in Table 1. Collecting area per unit cost is maximized with a monolithic-aperture telescope, particularly since the entire telescope and instruments will be actively cooled. 1JPL and Caltech, bradford@caltech.edu 2http://conference.ipac.caltech.edu/firsurveyor/