1 / 14

21 cm cosmology = The history of hydrogen gas

21 cm Cosmology The global signal: Earth-based constraints and implications for lunar observations Judd D. Bowman (Caltech) Alan E. E. Rogers (MIT/Haystack) July 22, 2009. 21 cm cosmology = The history of hydrogen gas. Big Bang!. Today.  [MHz]. 10. 50. 100. 500. 50 0 -50 -100.

berny
Download Presentation

21 cm cosmology = The history of hydrogen gas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 21 cm CosmologyThe global signal: Earth-based constraints and implications for lunar observationsJudd D. Bowman (Caltech)Alan E. E. Rogers (MIT/Haystack)July 22, 2009

  2. 21 cm cosmology = The history of hydrogen gas Big Bang! Today  [MHz] 10 50 100 500 50 0 -50 -100 Tb [mK] 21 cm global brightness temperature 100 10 z [redshift] Model: Pritchard & Loeb 2008 Image: Scientific American 2006

  3. All-sky radio spectrum (100-200 MHz) RFI All-sky spectrum • Total spectrum components: • Diffuse Galactic (200K to >1000K) • - Synchrotron (99%) • - Free-free (1%) • Sun (variable) • Extragalactic sources (~50K) • CMB (2.7K) • Galactic RRLs (< 1 K) • 21 cm (10 mK) Instrument bandpass 21 cm global signal

  4. Terrestrial Radio Frequency Interference (RFI) US FM/TV coverage Orbcom LEO satellite constellation

  5. Site Selection (< 1 mK) Antenna beam pattern: CasA (1400 Jy)  ~50 K

  6. Measurement requirements Need to measure/model non-21 cm sky components and instrument response to 1 part in 100,0000 • Not possible! Solution: • If: 1) Assume foregrounds introduce a nearly power-law spectrum. • 2) Characterize instrument response accurately for everything but the antenna/environment • Then: Can fit a simple model for sky, instrument, and 21 cm signal to data. • Trade-offs: Reduces overall information return—no chance of direct measurement of signal, only model constraints.

  7. EDGES: Experiment to Detect the Global Epoch of Reionization SignatureAn ultra-high dynamic range comparison-switched RF spectrometer Chart: AEER

  8. “The trailer” (CSIRO) – digitizer antenna LNA ADC antenna

  9. Measured spectrum Murchison Radio-Astronomy Observatory (MRO) Boolardy Station, Western Australia Jan 25 – Feb 14, 2009 10 days, ~10 sky hours

  10. Instrument performance: residuals Jan/Feb 2009 Bowman et al. 2008 Green = 100 kHz Black = 2 MHz 75 mK rms – systematic limited 19 mK rms – thermally limited

  11. Question: When was reionization, how long did it last? z = 13 z = 6 68% 99% 21 cm model T21

  12. Forecasted instrument performance z = 6 z = 13 z = 25 NOT reionization… absorption Current fastest plausible reionization integrate to expected systematic limit Integrate + improve bandpass

  13. From the moon? • Reduce RFI: Terrestrial RFI environment may ultimately prove to be the limiting factor • Improve calibration: Use moon as blackbody calibration source to calibrate the antenna • Orbital payload, spinning spacecraft • Minimize degeneracy between signal and nuisance model • No/reduced environmental complications • Dual-purpose with lunar RFI survey instrument • Achieving long integrations may be a problem? • Best times avoid Earth, Sun, and Galactic center = Sep-Dec, new moon phases, spacecraft on farside

  14. Summary • Current: • 19 mK rms in measured spectrum • 11th-order polynomial required to fit unknown sky and antenna params • 21 cm step constrained to <90 mK between 7<z<10 • 21 cm derivative <40 mK / MHz between 7<z<10 (w/ caveats) • Aug-Dec 2009: 3 months, unattended deployment in Australia • Goal: cross “reionization barrier” to get <30 mk constraint on 21 cm step • Lunar orbit instrument should be considered if performance of earth-based observations saturates • Advantages: minimal RFI, new calibration options?, dual-purpose * This scientific work uses data obtained from the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site.

More Related