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

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

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 +

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?

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.

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?

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

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 200 uJy!  need multiobject spectrograph to perform stacking analysis on sample of submm galaxies to get mean dense gas properties

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’

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%

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?

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