1. CCAT Science and Facility Requirements
Terry Herter
+ CCAT Science Steering Committee
13-Jul-2005

2. 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

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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

9. 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

10. 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)

11. 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.

12. 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.

13. 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

14. 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.

15. 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
~150SCUBA-2; ~300ALMA
About per hour
Lifetime detection of order galaxies: ~1% of ALL galaxies!
`1/3 sky survey’: ~1000 deg-2 for 3 deg2hr-1 gives 5000 hr

16. 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.

17. 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.

18. 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 ( 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

19. 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)

20. 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