1. Direct-Detection Spectroscopy at the CSO with Z-Spec and ZEUS
Probing galaxies near and far with
two new bolometers-based grating spectrometers
Matt Bradford with input from Gordon Stacey
August 4, 2008

2. Dominant gas coolants are in the far-IR / submm Redshifted to the submm / mm
SED courtesy A. Blain CO C0 N+ C+ O0
O++
z=0
z=1.2
z=2.6
z=4.4

3. The World’s Only Submillimeter Grating Spectrometers
ZEUS
The Redshift (z) and Early Universe Spectrometer
Stacey et al. (Cornell) w/ GSFC, NIST
Short submm windows: 350mm, 450mm
Slit-fed echelle grating, 4th and 5th order
Resolving power ~1200 (300 km/s)
20 GHz (~2-4%) instantaneous bandwidth
1x32 bolometer array, but TES upgrade underway
Z-Spec
Glenn (U. Colorado); Bradford, Bock, Zmuidzinas, (Caltech), Aguirre (CU-> Penn), Matsuhara (ISAS)
1 mm window: GHz
Single beam w/ new waveguide grating architecture
Resolving power ~300 (1000 km/s)
115 GHz instantaneous bandwidth
160 individually-mounted Ge-sensed bolometers
Both with sensitivity very close to fundamental limits at the CSO

4. Primary Scientific Objectives
Embedded energy sources and conditions of star forming gas in local-universe infrared-bright galaxies (LIRGS and ULIRGS).
Interstellar medium conditions and spatial extent of star formation extent in the era of peak star-formation history (z=0.5 to 2) and prior.
Evolutionary history of energy release via unbiased redshift surveys.
ZEUS
J=6->5 and 7->6 in both 12CO and 13CO and [CI] J=2->1 constrain the mass and energy budget of the warm molecular gas.
Z-Spec
Complete 1-mm spectrum includes multiple high-critical-density species: CN, CS, HCN, HNC, HCO+. A rapid census of the dense molecular gas.
ZEUS
C+ at z= and C+ to dust continuum ratio measures the UV field intensity, constrains the extent of the starburst.
Access [OI], [NII], [OIII] at the highest redshifts.
Z-Spec
Full band provides at least 2 CO transitions to measure redshift as well as temperature, density, and mass of the molecular gas.
Unexplored rest-frame short-submm.
C+, other fine-structure transitions accessible beyond z=6.

5. ZEUS on the CSO Mounted on the left Nasmyth focus
Can be co-mounted with both Z-Spec and Bolocam
First light in 2006
Steve Hailey-Dunsheath PH.D. (Cornell 2008)
Thanks to NSF and NASA support:
NSF ATI: 01-04, 04-07, 07-10
NSF MRI for ZEUS-2
NASA GSRP

6. ZEUS Observations of LIRGs & ULIRGs
Pre-ZEUS: 1 ULIRG in CO 6-5 (Mrk 231, Papadopoulos et al. 07)
ZEUS has observed ~19 LIRGs and ULIRGs to date
Most in CO (6-5)
Some also in CO (7-6) & [CI] (2-1) or CO (8-7)
Fractional mid-J CO luminosity decreases in the most powerful sources (as with C+).
-> More concentrated systems than the less-luminous starbursts.
Arp 220 CO(6-5)
NGC 6240 CO(6-5)
IRAS 18293
CO(6-5)
TMB(K)
VLSR(km/s) VLSR(km/s)
IRAS CO(6-5)
NGC 6240 [CI] (2-1) & CO (7-6)
NGC 6240 CO(8-7)
Nikola et al. in prep.

7. ZEUS High-Redshift Example: [CII] from MIPS J142824.0 +352619
Identified as red object in MIPS Bootes field (Borys et al. 2006)
Integrated far-IR SED indicates Lfar-IR ~ 3.21013 L
Likely a mildly lensed super-starburst galaxy
ZEUS/CSO detection in April hours of good (but not great) weather (225 GHz ~ 0.05 to 0.06)
I[CII] ~ 6 K-km/sec
Fline ~ 9.0  W m-2
L[CII] ~ 2.5  1010 L
CII / far-IR ratio much greater than in local ULIRGs. Conclude that starburst is 2-3 kpc in extent – “galaxy wide starburst”
Hailey-Dunsheath et al. 2008

8. Z-Spec: A New Ultracompact Waveguide Grating
curved grating in parallel plate waveguide
K.A. McGreer, 1996, IEEE Phot. Tech. 8
H.A. Rowland, 1883, Phil. Mag 16
Propagation confined in parallel-plate waveguide
2-D Geometry
Stray light eliminated
Curved grating diffracts and focuses
Efficient use of space
No additional optical elements
Custom “stigmatic” grating design possible at long wavelengths

9. Z-Spec Layout Focal ARC FRIDGE ADR 3He RADIATION SHIELD INPUT FEEDHORN
GRATING ARC
Individually mounted
SiN bolometers
Focal ARC
CSO, Mauna Kea
FRIDGE
ADR
3He RADIATION SHIELD

10. Z-Spec graduate students @ 13,400 ft Lieko Earle (Colorado),
Z-Spec Support
NSF career (Glenn) + CSO
NASA SARA
JPL DRDF, Caltech Pres. Fund + Millikan
U. Colorado + Research Corp
Z-Spec graduate 13,400 ft
Lieko Earle (Colorado),
Bret Naylor (Caltech)

11. Lieko Earle, U. Colorado Ph.D. ‘08
Z-Spec 1 mm survey of NGC 253
Lieko Earle, U. Colorado Ph.D. ‘08
3.5 hours telescope time
>15 ID’d transitions > 3s
+2-4 unID’d as of yet.

12. Z-Spec Spectra from the CSO

13. Z-Spec Spectra from the CSO

14. Molecular Gas in Local-Universe Galaxies, ex. M82
B. Naylor et al., ApJ in prep.
Compile all transitions, use RADEX to model excitation & transfer in the lines
-> Generate Bayesian likelihoods NE
HCO+ SW
Cen
Also include: CS
HNC
SO2 Combine in a
single model:
-> evidence of cold, dense gas component
-> the material actually forming the stars?

15. 7.9 hours total time

16. Weiss et al. continuum estimates

17. Z-Spec
Barvainis et al., 1997
Weiss et al., 2003

18. APM at z=3.91
Flux Density [Jy]
Rest
322 mm
200 mm

19. APM 08279+5255 at z=3.91 A reminder: Arp 220 in the far-IR
ISO LWS, Gonzalez-Alfonso et al. 04
Flux Density [Jy]
Rest
322 mm
200 mm

20. APM at z=3.91
Flux Density [Jy]
Rest
322 mm
200 mm

21. Plans for the next cycle ZEUS & Z-Spec instrument teams funded
ZEUS upgrade to ZEUS-2
Funded by NSF MRI
Incorporating (3) NIST 2-d TES bolometer arrays which share the focal plane and can operate simultaneously:
10 x 24 at 200 mm
9 x 40 at mm
5 x 12 at 650 mm
Up to 5 lines simultaneously (in extended sources)
Some imaging capability (9-10 beams)
Closed cycle refrigerators
Z-Spec Survey Program
Funded by NSF AAG
(Aguirre et al. U. Penn)
Dense gas in Local-Universe dense molecular gas surveys.
50 galaxies, 8 hours per
Mid-J CO + spectral discovery in high-z objects with and without prior redshifts.
20 galaxies, 24 hours per
Excellent use of low-frequency time at CSO.
Baseline 300 hours per year, could be more.
Helium recycler under study to reduce cryogen costs.

22. Backup material

23. Direct-Detection Spectroscopy A survey capability which complements the high spatial and spectral resolution of interferometers (CARMA / ALMA)
Submillimeter is the region of overlap between coherent (heterodyne) and incoherent (direct-detection) techniques for astrophysics.
Coherent approaches have yielded much of the spectroscopic work to date.
High spectral resolution required for Galactic cores.
Large bandwidths not essential for Galactic sources or nearby galaxies.
SIS mixers near quantum limit, (also near background limit at 1 mm).
Until recently, direct detectors neither sufficiently sensitive, nor sufficiently arrayed to be compelling.
Direct-detection spectrometers (gratings and Fabry-Perots) for long wavelengths are large and expensive.
Direct-detection submillimeter spectrometers are now compelling
Submillimeter spectroscopy coming of age as an extragalactic probe.
Spectral resolution greater than few x 1000 not required.
Direct detectors are now readily background-limited, and are undergoing a revolution in format (driven by cameras).
Large fractional bandwidth presents a new discovery space for measuring redshifts and multiple lines.
Multi-object capability a natural progression with a direct-detection system.

24. Grant Numbers ZEUS Z-Spec
NSF Grant AST (Advanced Technology and Instrumentation )
NSF Grant AST (Advanced Technology and Instrumentation )
NSF Grant AST (Advanced Technology and Instrumentation )
NASA Grant NGT (NASA GSRP )
NSF Grant AST (Major Research Instrumentation )
Z-Spec
NSF CAREER grant (Glenn): AST
NASA SARA grants: NAG
JPL DRDF
Caltech President's Fund
Caltech Millikan Fellowship
Research Corporation Innovation Award: RI-0928
University of Colorado

25. Dual Stage 3He Refrigerator
4He cryostat
M5: Primary
Grating
Detector Array
Scatter Filter
LP Filter 1
LP Filter 2
BP Filter Wheel M1 M2 M3 M4 M6
4He Cold Finger
Entrance Beam
f/12
Quartz & LP Filter 1
Refrigerator
ZEUS: Optical Path
35 cm long R2 echelle grating blazed for 5th 359 m
There is a series of a scatter, quartz, 2 long  pass, and a bandpass filter in series to achieve dark performance (Cardiff U.)
Total optical efficiency: ~ 30%, or 15% including bolometer DQE

26. Hailey-Dunsheath et al. in prep.
ZEUS observations of NGC 253: First Extragalactic Detection of 13CO(6-5)
ZEUS/CSO 
Line is bright ~ 10% that of the 12CO(6-5) line indicating optically thick emission in the main line.
Also re-observed (and mapped) the CO(7-6) line to constrain LVG models
35 to 55% of the molecular ISM is warm and dense: T~ 120 K, n~104 cm-3
Heating this much gas is difficult:
likely due to that X-rays from the starburst or the decay of micro-turbulence within clouds must dominate the heating.
These processes are powered by the starburst -> the starburst is self-regulating.
Hailey-Dunsheath et al. in prep.
[CI] (2-1) line only 1000 km/s to the blue and always within ZEUS band.

27. [CII]/far-IR Constrains Starburst Extent
[CII]/far-IR continuum luminosity ratio vs. density for various G (from Kaufman 1999).
L[CIII] ~ 2.5  1010 L
Lfar-IR ~ 3.2  1013 L
30% of [CII] from ionized medium
R = 5.5  10-4
 G ~ 2000
far-IR = L/(4D2) = 14
DL~ 9.2 Gpc
 = IR/(G 2) = 3.5 x 10-3
 =   beam = 0.083(”)2
d ~ 0.32”  2.75 kpc
+3600
Starlight that contributes to  but not G
Galaxy-wide starburst supports the contention that hyper-luminous systems may be giant elliptical galaxies in formation (unlike local ULIRGs)

28. Z-Spec channel spectral response
Measured with long-path FTS
(~100 MHz resolution)
Range: GHz
Resolving power:
(Not over sampled)
(750 < v < 1200 km/s)
Complete coverage from channel to channel -> no gaps

29. Observed noise white with atmospheric 1/f
Z-Spec Sensitivity
Observed noise white with atmospheric 1/f
Relative to an imaging system, fundamental noise levels are lower, but some systematic aspects are easier.
Chopping -> response to a single frequency
Narrow spectrometer bandwidth helps
NEFsky ~ 
NEFGaussian noise ~ sqrt()
Scaling consistent with e.g. Bolocam observations

30. Clear scaling with , very close to photon background limit
Z-Spec Sensitivity
Clear scaling with , very close to photon background limit
Blue -> achieved at =0, 0.1, 0.2
Black -> simple model for Z-Spec at CSO
Det, amplifier, & internal load NEP: 6.4e-18 W/sqrt(Hz)
(not tracking detector parameters in detail)
measured instrument trans (~0.25)
Aperture efficiency per taper + Ruze (60-70%)
measured chop duty cycle (65%)
photon noise from sky + telescope the most important term
-> additional factor of 1.2
=0.2
500
=0.1
300
=0

31. Z-Spec labor force James Aguirre -> U. Penn Bret Naylor Lieko Earle
Jansky Fellow
Colorado, NRAO
Bret Naylor
Recent Caltech Ph.D.
Lieko Earle
Colorado Ph.D. student
(finishing Spring 08)

32. ULIRG Survey Preliminary Results
[ Line fluxes in Jy km/s, HCN / CO ratio corrected for to TMB ]
Line fluxes SNR
Not finding overluminous HNC / HCN 3-2 ratio as per Aalto, Cernicharo.
will follow-up further at CSO.

33. Nearby Seyfert NGC 1068