X-Spec: A Multi-Object Wideband Survey Spectrograph for CCAT
Abstract
We are developing a multi-object dispersive survey spectrograph for CCAT. X-Spec is optimized for rest-frame far-IR / submm atomic and molecular transitions in high-z galaxies, and it will conduct multi-galaxy spectral survey up to 10x faster than ALMA. Detected lines will provide redshifts for and interstellar gas conditions in tens of thousands of galaxies ranging from the early universe (z > 6) to the present day. X-Spec will be particularly sensitive to the 158-micron ionized carbon fine-structure transition [CII], and the initial instrument will target the 650-um, 850-um, and 1-mm atmospheric windows, corresponding to 3.5 to 9 for [CII]. By following up high-z candidate objects, X-Spec surveys of [CII] will reveal the early evolution of galaxies' energy sources and interstellar gas conditions. CCAT/X-Spec can also probe below individually-detected sources by using fluctuation analyses; the spatial-spectral fluctuations mm and submm bands are dominated by [CII], and can be used to measure the growth of large-scale structure and the global properties of galaxies in the reionization epoch. X-Spec will have at least 15 independent spectrometer backend 'pixels', each covering 195-520 GHz instantaneously at R=400-700, in both polarizations with photon-background-limited sensitivity. It will use lithographically-patterned filterbank chips formed with superconducting transmission line. The detectors are titanium-nitride kinetic inductance detectors (KIDs), and each spectrometer chip will have ~500 KIDs integrated with the filterbank in a package a few square cm in size. Each chip has a bandwidth of ~ 1:1.6 and is single-polarization, so coverage of the full 195-520 GHz range in dual-pol requires 4 chips and ~2000 detectors. With the compact size and inexpensive mass production, much larger spectrometer formats (100-300 pixels) will be possible as detector readout technology progresses. To optimize on-source observation efficiency, a 2-axis rotary positioning system for each pixel will steer to an arbitrary position in a circular patch of sky; this system will steer to target galaxies, compensate for field rotation, and enable beam modulation (chopping) at ~1-2 Hz for sky subtraction.
- Publication:
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American Astronomical Society Meeting Abstracts #221
- Pub Date:
- January 2013
- Bibcode:
- 2013AAS...22115009B