Direction-detection spectrometer concepts the CCAT Matt Bradford + others 24 October 2006, in progress

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford2 850 micron counts (stolen from A. Benson talk) Recall: modified IMF and star formation timescale included to reproduce 850 micron counts

Redshift Distribution from GALFORM model -- similar to Chapman 350 um window 13% of sources 450 um window: 21% of sources Models provide approach to CCAT population z distribution: Apply to C+ 350 & 450 microns window are likely to access 31% of the 850 micron populatio n in C+

C+ 158 microns redshifted for CCAT spectrograph Recall: a 1 mJy 850 micron source is a ULIRG, independent of redshift CCAT spectroscopic sensitivities: 5 sig, 1h W/m2: 1.8e-19 (350) 1.2e-19 (450)

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford5 Options for far-IR through mm spectrometers  Grating spectrometer is the best choice for point sources  1 st order  octave of instantaneous bandwidth  Good efficiency  But only moderate resolution  Fabry-Perot naturally accommodates spectral mapping  But scanning time results in sensitivity penalty, esp for searching  Fourier transform spectrometer (FTS) couples the full band to a single detector  Sensitivity penalty  Heterodyne receivers provide the highest spectral resolution  But suffer from quantum noise NEP QN ~ h [  1/2 vs. NEP BG ~ h [n (n+1)  1/2  Also offer limited bandwidth:  10 GHz IF bandwidth at 1 THz gives  ~ 100

C+ 158 microns redshifted for CCAT spectrograph Source densities: 1 mJy (850) source densities: 1.2e4 per square degree -> means one per ,350) CCAT beams Based on 1 hour sensitivities 1 mJy population is likely to be candidates for spectroscopy Wideband spectroscopic follow-up

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford7 350, 450  m windows w/ R~ Examples of submillimeter-wave broadband systems: ZEUS for the JCMT / APEX Cornell -- Stacey et al. Grating Detector Array LP Filter 1 LP Filter 2 BP Filter Wheel M2 M3 M4 M6 4 He Cold Finger Entrance Beam f/12 Scatter Filter 3 He Dual Stage Refrigerator M1 4 He Cryostat M5: Primary Entrance slit

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford8 A new R~1000 echelle spectrometer for CCAT AMULE -- Atacama MUltiband Longslit Echelle Design: Grating 816 micron pitch Assuming 128 spectral element array -- e.g mm pixels -- f/2.5 spectrometer, slightly oversampled Angular deviation off the grating 18 deg total. collimator must be oversized by 12 cm ! --> 30 cm diameter collimator --> grating 30 cm by 40 cm, to accommodate spatial throughput

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford9 AMULE is large So grating and collimator large fraction of 1 meter in all dimensions times larger than ZEUS Reimaging optics size will depend on the size of the slit, but also grows relative to ZEUS: --scales as telescope f# x #of beams: Relative to ZEUS, AMULE will have 8/12 x 128/32 = 2.7 times larger reimaging optics. Requires 35 cm (+ overhead) window if reimaged from telescope focus inside cryostat (but can be shaped like a slit) Optics envelope inside cryostat approaching 1 meter in all dimensions. Large but doable. 30 cm 40 cm 35 cm

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford10 How about an imaging Fabry-Perot (BIG Imaging Fabry-Perot Interferometer (BIFI)) SPIFI demonstrates concept, at JCMT & the South Pole 5x5 spatial array, two scanning FPs provide R up to 10,000 at microns 60 mK ADR-cooled focal plane

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford11 CO 3-2 M. Dumke et al. 2001, ALMA will resolve out extended emission in nearby galaxies CO 7-6 Bradford et al. 2003, ALMA Primary beam at 810 GHz And Herschel under- resolves it Herschel beam at 810 GHz 16x16 array on CCAT

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford12 How about an imaging Fabry-Perot (BIG Imaging Fabry-Perot Interferometer (BIFI)) BIFI will be much larger than SPIFI due to the large throughput Limitation is beam divergence in the high-res FP. D col ~ 1.5 (R x n beams ) 1/2 1-D field size for 20 cm beam High- order FP spacing (mm) w/ F=60 Order-sorter also requires collimated 2.2cm (or slow) beam Field size (1-D) driven by 20 cm beam 3 min x 3 min field

CCAT instrumentation workshop: Caltech Mar 2005Matt Bradford13 BIFI will be much larger than SPIFI due to the huge throughput 8 x 20 cm = 160 cm collimator focus Full field at f/8: 20 cm window! Collimated beam + overheads: 25 cm dia (and etalon must be near pupil) Etalon spacing is modest: few cm even for 650  m Faster final focal ratio (2-3) to accommodate large array Array is as large as 10 cm Factor of two in all dimensions of the optical train

WaFIRS is an ideal broad-band point source architecture. -- possibility for multi-object spectroscopy Currently 4-5 cm delta z per module But could be smaller, far from limits: -- stiffness of plates -- detector illumination -- feed (f lambda from the telescope)

WaFIRS is an ideal broad-band point source architecture. -- possibility for multi-object spectroscopy 50 cm for > 10 modules