1. Radio multiobject spectrograph C
Radio multiobject spectrograph C. Carilli, NRAO, GBT new instrumentation workshop, Sept 06
Multiobject Spectrographs: Revolution in Optical astronomy redshift surveys – 10,000’s redshifts SDSS,VIMOS, 2DF, DEIMOS…
10’s – 100’s galaxies per night
Slit positions pre-set based on optical/submm/radio/Xray imaging

2. MAMBO 250GHz bolometer camera/IRAM30 MMIC heterodyne array/FCARO
Radio: typical cm/mm focal plane arrays: ‘Integral field units’ = continuous coverage of center of focal plane
MAMBO 250GHz bolometer camera/IRAM30
Needed for extragalactic radio astronomy: true multiobject spectrograph with adjustable ‘slit’ positions
MMIC heterodyne array/FCARO

3. COSMOS/MAMBO 250GHz survey
Need for radio multiobject spectrograph I
Submm galaxies: formation of large spheroids in dusty starbursts at z=1 to 3 (SFR ~ 100’s to 1000 Mo/year?
COSMOS/MAMBO 250GHz survey
MAMBO/30m
117 pixels
250 GHz
10.6”
0.9 mJy rms
~ 20 sources in typical 20’x20’ field
Bertoldi, Carilli, Schinnerer, Voss, Smolcic +

4. Difficulty: Optical Ids and Redshifts
250GHz 1.4GHz Opt
Selection with 1.4 GHz imaging gets 50% to 75% at 10’s uJy sensitivity, with low z bias.
Missing most interesting sources = most distant?

5. PdBI dedicated study (10’s hours/source) of radio selected submm galaxies with optical redshifts (Greve et al. 2005)
Massive gas reservoirs (~1e10 Mo) = requisite fuel for star formation
z=2.4
 Need multiobject spectrograph for unbiased search for CO, other molecules in complete submm galaxy sample.

6. Need for radio multiobject spectrograph II
Ly a emitters into cosmic reionization: probing ‘first light’
~ 100 LAEs at z=5.8+/-0.1 in COSMOS Field (2square deg)
SFR (Lya) ~ 10 Mo/year
Represents ‘normal’ galaxy population during EoR?

7. Radio/MAMBO analysis: No bright, dust obscured starbursts
Radio stacking analysis:
<S1.4> < 3 uJy/beam
<SFR> < 120 Mo/year
 Need multiobject spectrograph to perform ‘stacking analysis’ to gain factor > 5 in effective sensitivity for <CO> properties, and to find rare, dusty starbursts

8. Need for radio multiobject spectrograph III
Dense as tracers – HCN, HCO+, …
Trace r > 1e3 cm^-3 => gas directly related to star forming clouds
Typically few to 10x fainter than CO => only seen in most pathologic and/or highly lensed sources
VLA obs of HCN in Cloverleaf uJy!
 need multiobject spectrograph to perform stacking analysis on sample of submm galaxies to get mean dense gas properties

9. Need for radio multiobject spectrograph IV
Nearby galaxies: Giant HII regions, GMCs, superstar clusters
M101 Chen et al
K/Ka band lines: water, ammonia, methanol, C3H2, SO…
 Need MOS to get spectra of many regions simultaneously
10’

10. Feed ring Radius=30 cm or 45cm
Use of Focal plane at GBT
(Norrod & Srikanth)
Feed ring Radius=30 cm or 45cm
Offset = 50cm =>
Throw = 9arcmin
Efficiency = 60%

11. Specifications FoV = 10’ to 30’ (10’s submm gal, LAEs, egal SFRs…)
Number of receivers = 16 to 25 (space limitations?)
Reconfiguration (at most) once per day
Tracking = +/- few hours (=> rotate)
Spectrometer & IF (K/Ka/Q band)
LBGs and LAEs: Dz_spec ~ 100 km/s => ~20 MHz/source
Submm gals: Dz_phot ~ 0.2 => ~2 GHz/source
Potentially trade-off of ‘slits’ for bandwidth?
Sky removal: use full array?
Integral field spectroscopy: close-pack configuration?

12. Implementation Individually adjustable receivers and feeds.
Challenge: Cryogenics?
Dense-packed receivers + adjustable feeds + flexible waveguide.
Challenge: Noise performance?
Dense-packed receivers and feeds + mirrors.
Challenge: Optics and tracking?
Very large array?
Overkill