CCAT Science and Facility Requirements Terry Herter + CCAT Science Steering Committee 13-Jul-2005
Why the submillimeter? A timely convergence of science, technology, and opportunity. Many astronomical object emit most of their energy in the FIR/sub-mm e.g. star forming regions, the outer solar system, local and redshifted galaxies Many molecular species have spectral lines in the sub-mm Sub-mm technology is progressing such that Large (bolometer) format arrays can be constructed (> 10,000 pixels) Sensitive, very high resolution (heterodyne) spectrographs are now possible at short (200 – 450 mm) sub-mm wavelengths Opportunity The Atacama site provides low water vapor overburden and physical proximity to ALMA enabling unique science and natural synergies with ALMA A large, first-rate (unique) sub-mm telescope which does excellent science can be built at a cost affordable by a university consortium
Galaxies peak in FIR/sub-mm Flux density vs. wavelength for an interacting galaxy system (Arp220) for redshifts of 1, 2, 4, and 8. Note the strong “negative K-correction” from about 500 mm. Interacting Galaxies – Top: CO contours overlaid over optical image. Bottom: Spitzer multi-color infrared image.
Sub-mm is rich in spectral lines Spectrum Orion KL region in the 350 mm window showing a few of the molecular species accessible in the sub-mm (Comito et al. 2005). This is a very small portion (~1%) of the available window The spectral resolution is 2 MHz resolution (R ~ 410,000). Orion Molecular Cloud – Top: Optical image. Bottom: 350 mm map. The arrow points to the location where the spectrum was taken.
Sub-mm Atmospheric Transmission Atmospheric transmission for different amounts of precipitable water vapor. The horizontal red bars represent the adopted bandpasses and the average transmission for 0.25 mm PWV.
Time Available to Observe Ref. Sairecabur Chajnantor l n Time to CL PWV available # CL (mm) (GHz) (hr) hrs/yr fields 200 1500 1248 0.26 281 84 350 857 0.86 0.47 1936 2244 1084 1257 620 484 1.14 0.64 716 629 723 634 740 405 0.43 0.75 639 1488 690 1607 865 347 0.28 1223 4413 1205 4348 1400 214 0.30 1.00 1517 5093 1299 4361 Total Time 6312 5084 450 667 0.63 3082 1725 1100 273 0.07 23136 19809 2000 150 0.96 1579 1352 3300 91 8.55 177 152 Number of hours/year (round the clock) available for observing at a given l (PWV) for Sairecabur (~5500 m) vs. the Chajnantor plateau (~5000 m). “# CL fields” is the number of fields that can be observed to the confusion limit over a year. The “Total Time” is the sum of available hours and represents all time (day or night) with PWV < 1.1 mm. The last four rows are possible alternate uses of time.
CCAT SSC Charter Establish top-level science requirements Determine and document major science themes Flow down science requirements to facility requirements Telescope, instrumentation, site selection criteria, operations, etc. Outputs Science document Write-ups on major science themes using uniform format (science goals, motivation/background, techniques, CCAT requirements, uniqueness and synergies Requirements document Specifies requirements for aperture, image quality, pointing, tracking, scanning, chopping, etc.
CCAT SSC Membership Co-Chairs Leads on Science Themes Terry Herter (Cornell) and Jonas Zmuidzinas (CIT) Leads on Science Themes Distant Galaxies – Andrew Blain (CIT) Sunyaev-Zeldovich Effect – Sunil Gowala (CIT) Cold Cloud Cores Survey – Paul Goldsmith (Cornell) + Neal Evans (UT) Kuiper Belt Objects – Jean-Luc Margot (Cornell) Circumstellar Disks – Darren Dowell (JPL/CIT) Local galaxies – Shardha Jogee (UT) Ex-officio members Riccardo Giovanelli (Cornell), Simon Radford (CIT), and Gordon Stacey (Cornell) Others attend calls as necessary
The Process Convene weekly science telecons 19 have been held thus far Science discussions at monthly status reviews Face-to-face meetings, etc Establish common sensitivity and confusion limits Source confusion is the limiting factor in the continuum sensitivity of CCAT Pick-out science that drives facility requirements Mainly wide-field cameras but spectrographs for pointing Write-ups by science leads Review by subgroups members and entire committee Write-up reports Science report Facility requirements report
Status/Progress Established Wiki (collaborative) web site for documents Repository for Tech Memos, Science Write-up drafts, etc Sensitivity and confusion limits well defined Can easily compute sensitivity and confusion limits vs. D, PWV, and rms surface accuracy for different wavelengths Need to complete heterodyne sensitivity calculations (but this is not a facility driver) – Tech memo write-up awaiting this but info on Wiki site Science reports Write-ups “done” on Distant Galaxies, Sunyaev-Zeldovich Effect, Cold Cloud Cores Survey, and Kuiper Belt Objects First draft on Local Galaxies completed Observatory/Telescope requirements Fairly well stabilized – going from .ppt to .doc file (80% done) Some relevant tech memos Optical performance requirements Survey Speed (CCAT vs. ALMA)
Sub-mm Number Counts & Confusion Limits Sub-mm galaxy counts vs. flux density (number of sources with flux greater than S vs. S) for different wavelengths (after Blain et al.). Crossing lines show 30 (lower) and 10 (upper) beams/source confusion limits for D = 25 m.
CCAT Sensitivity 5s, 1-hour CCAT and ALMA sensitivities. CCAT sensitivities computed for precipitable water vapor appropriate to that band. Confusion limits shown are 30 beams/source except for 10 beams/src case shown for CCAT.
CCAT Science: 1 Galaxy science: SZE science Find huge numbers of distant galaxies (z~1-5) at rate >103 hr-1 Use colors to sift the sample to find examples with extreme redshifts/luminosities to better confront galaxy formation models Resolve the emission from a large sample of low-redshift galaxies to reveal the final, authoritative galaxy luminosity function to z~0.2 Covering the whole sub-mm/mm band, it will provide the best possible photometric redshifts, based on redshifted far-IR SEDs SZE science Thousands of clusters to be detected by wide-area surveys (APEX-SZ, ACT, SPT) with 1’ resolution CCAT can do mapping and radial profiles at ~0.4’ resolution Characterize SZ-mass mapping, effects of cluster astrophysics
Detecting Distant Galaxies Sensitivity to star formation rate vs. redshift for an Arp 220-like galaxy. All flux limits are set by the confusion limit except for CCAT(200) which is 5s in 104 sec. The conversion used is 2 Msun/yr = 1010 Lsun & LArp220 = 1.3x1012 Lsun.
Mapping speed comparing other facilities CCAT is an ultrafast mapper Assumptions 10000 pixel detector, Nyquist sampled at all bands 0.2, 0.35, 0.45, 0.67, 0.85,1.1mm (in order from violet-red) Observationally verified counts (good to factor 2) Confusion and all sky limits 1.2/0.85/0.35mm imaging speeds are compatible To reach confusion at 0.35mm go several times deeper at 0.85mm Detection rates are ~150SCUBA-2; ~300ALMA About 100-6000 per hour Lifetime detection of order 107-8 galaxies: ~1% of ALL galaxies! `1/3 sky survey’: ~1000 deg-2 for 3 deg2hr-1 gives 5000 hr
CCAT Science: 2 Star Formation Studies Kuiper Belt Object Science Survey continuum emission from dust and spectral line emission from molecules Study fragmentation and collapse of cloud cores to form protostars (including disks) and star clusters. Sub-solar mass cores (< 0.1 Msun) detectable in continuum Kuiper Belt Object Science Measure the sizes and albedos of hundreds of KBOs, providing the observational constraints needed to further our understanding of planet formation and evolution. CCAT can detect several hundred KBOs in 1000 hrs. Potential for discovery of large, distant minor planets in piggy- back mode. Observe periodic variations in thermal emission indicative of KBO spin states.
KBO sub-mm advantage Predicted 350 um flux for KBOs with 10% albedo (mR=22, solid and mR=23, dotted) or 4% albedo (mR=23, solid and mR=24, dotted). Horizontal lines show 5-sigma detection in 1 and 2 hours, respectively. For 4 (10) % albedo, mR = 23, rKBO = 140 (90) km at 45 AU. Multiply the KBO size by factors of 5 and 10 for heliocentric distances of 100 and 140 AU, respectively.
CCAT Science: Debris Disks Debris disks, a.k.a. “Vega phenomenon”, a.k.a. “extra-zodiacal dust”: solid particles surrounding main sequence stars, especially youngish ones (10-100 Myr), after the gas has been expelled or absorbed into giant planets product of collisional grinding of planetesimals in Kuiper belts probably episodic in nature tracer of orbital dynamics (analogous to Saturn’s rings) CCAT niches high-quality images of statistical sample of nearby disk systems surveys for undiscovered cold disks (T < 40 K) around nearby stars important data points on spectral energy distribution characteristics of particles evolutionary clues? much better measurement of mass than is possible with scattered light images unbiased surveys for disks in stellar clusters b Pictoris: debris disk discovery image Smith & Terrile (1984) Saturn’s rings: result of the interaction of moons and dust
Selected (Key) Facility Drivers Aperture Sensitivity improves as D2 (hence time to a given S/N D-4) Confusion limit D-a (a 2 and 1.2 at 350 and 850 mm respectively) Field-of-view (5’ x 5’ initially, up to 20’ across eventually) The major role of CCAT will be its unchallenged speed for moderate-resolution wide-field surveys CCAT strongly complements ALMA (which will do follow-up) Chopping/Scanning Bolometer arrays require modulating the signal through chopping and/or scanning the telescope For chopping, this must be done at the secondary (~ 1’ at ~ 1Hz) Scanning requires moderately large accelerations for reasonable efficiency (~ 1 deg/sec2) Pointing For spectrographs require placing to a fraction of slit width And guiding to maintain spectrophotometric accuracy => 0.57”/0.71” [R] and 0.33/0.41” [G] arcsec pointing/guiding (1D rms)
Next Steps Complete remaining science write-ups Integration of science write-ups into report Finish facility requirements document Find gaps/holes Is 200 mm operation well justified? Heterodyne science (and spectroscopy in general) Look further into science trades for site (PWV), aperture, surface quality, etc. React to “push-back” from technical challenges