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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
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Radio multiobject spectrographC. 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
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
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? • MAMBO/30m • 117 pixels • 250 GHz • 10.6” • 0.9 mJy rms • ~ 20 sources in typical 20’x20’ field COSMOS/MAMBO 250GHz survey Bertoldi, Carilli, Schinnerer, Voss, Smolcic +
Difficulty: Optical Ids and Redshifts 250GHz1.4GHz 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’
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