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Radio multiobject spectrograph C. Carilli, NRAO, GBT new instrumentation workshop, Sept 06

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 spectrograph C. Carilli, NRAO, GBT new instrumentation workshop, Sept 06

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  1. 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

  2. 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. 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 +

  4. 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?

  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 200 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. 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

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