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CHIME: the Canadian Hydrogen Intensity Mapping Experiment. title. Mark Halpern Kris Sigurdson Sigi Stiemer Tom Landecker Jeff Peterson. UBC. CITA. Dick Bond Ue-Li Pen Matt Dobbs David Hanna. people. DRAO. McGill. Carnegie Mellon.

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CHIME: the Canadian Hydrogen Intensity Mapping Experiment.


Mark Halpern

Kris Sigurdson

Sigi Stiemer

Tom Landecker

Jeff Peterson



Dick Bond

Ue-Li Pen

Matt Dobbs

David Hanna




Carnegie Mellon


We have proposed to build a new telescope, CHIME, to study Baryon Acoustic Oscillations at the DRAO. The telescope will consist of 5 NS cylindrical reflectors coupled to a large digital correlator and will perform hydrogen intensity mapping of redshifted 21cm radiation.



Plan of the talk:

1. What are Baryon Acoustic Oscillations?

2. What will CHIME look like?


Evolution of a density spike in co-moving coordinates.

Notice when neutrinos and then photons decouple from baryons.

Animation: SDSS Collaboration


Animation: SDSS Collaboration


Eisenstein et al. 2005 ApJ


Eisenstein et al. 2005 ApJ

107/h = 148

h= 0.72


Hinshaw et al. 2009

Komatsu et al.


BAO have, of course, been seen in the CMB.

They form the “shape” of each hot or cold spot.

Komatsu et al. 2010


The cosmological constant is only one possibility for the nature of dark energy.

In a L dominated universe pressure is negative:

P/r = -1 = w,

but in general w can be a function of time or redshift, w(z).

To measure how w(z) evolves we need to measure at least one of:

A. Angular sizes of a distribution of standard rulers;

B. Brightnesses of a distribution of standard candles; or

C. Weak lensing patterns.

CHIME will supply option A.


DETF Figure of Merit

rDE= rDE (today) exp {-3[1 +w (a)] d ln a} LCDM: w (a)= -1

w(a) = w0+wa(1 -a) w=w0 today & w=w0 +wain the far past

Marginalize over all other parameters and find uncertainties in w0 and wa

DETF FoM = 1./(area of ellipse) = 450 for the nominal CHIME

LCDM value

If built now, CHIME will deliver precision at a tiny cost and well ahead of any competitive experiment.


Figure of Merit for an HI measurement from z1 to z2.

Pushing BAO measurements to low redshift drives the ultimate sensitivity of a survey.

Given the cell phone wall at 800 MHz, corresponding to z1=0.8, there is not much advantage to push the lower freq. Limit beyond z2=2.5, or 400 MHz


The size and frequency resolution of CHIME are chosen to resolve Baryon Acoustic Oscillations in three dimensions.

Resolution at z of a 100m telescope

Freq. of redshifted 21cm radiation

Redshift dc-m further away.

Frequency shift corresp. to Dz


CHIME will consist of five 20m x 100m cylindrical reflectors with feeds, amplifiers and digitizers spaced along the 100m focal line.


We have built room temperature amplifiers for CHIME which are much quieter than we had assumed for our sensitivity estimates.

This is the work of Greg Davis, UBC.


A CHIME amplifier.


The measured RF Interference at the proposed CHIME site at the DRAO in Penticton looks promising.

Measurement resolution is 10 kHz. The cell phone band at 850 GHz defines CHIME’s top frequency. Test noise floor is 400K.

Measured December 2009


CHIME anticipated sensitivity at z=1.5, two years of data.

Error bars grow at the right due to finite angular resolution and at the left because CHIME only surveys 40% of the sky

Spectrum w. BAO

Spectrum w.o. BAO


CHIME will produce data a decade earlier than experiments of comparable sensitivity, and for 1-10% of the cost.

Expt. “shot noise” is proportional to survey volume.


‘Canadian’ results from experiments not yet proposed when the last LRP was written:

1. BLAST resolved the cosmic IR background into emission from 24 um identified galaxies.


‘Canadian’ results from experiments not yet proposed when the last LRP was written:

2. The South Pole Telescope discovered hundreds of new clusters in a blank-field Sunyaev Zeldovich survey.


‘Canadian’ results from experiments not yet proposed when the last LRP was written:

3. The Atacama Cosmology Telescope (ACT) measured the CMB anisotropy at small angular scales.


The Canadian Long Range Plan for Astronomy should include support for a plan for funding of important modest-sized experiments with rapid schedules as they arise.

The CFI and the CSA have played a sporadic role at this scale and schedule of project, with restrictions. The importance of support for short-notice opportunities to astrophysics in Canada must be made clear.

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