current and future sz surveys sunil golwala california institute of technology july 7, 2001

Current and Future SZ Surveys

Sunil GolwalaCalifornia Institute of Technology

July 7, 2001

Current and Future SZ Surveys Sunil Golwala/2001/07/072

Overview

•The Sunyaev-Zeldovich effect in galaxy clusters•Science with blind SZE surveys•Interferometers and bolometer arrays•Calculating expected sensitivities •Laundry list of current and future instruments: specifications and sensitivities

•Summary for the near future

•Thanks to all the instrument teams for specs and numbers!


The Sunyaev-Zeldovich Effect in Galaxy Clusters

•Thermal SZE is the Compton up-scattering of CMB photons by electrons in hot, intracluster plasma

last scatteringsurfacez ~ 1100

CMB photonsT = (1 + z) 2.725K

galaxy cluster with hot ICM

z ~ 0 - 3

scatteredphotons(hotter)

observerz = 0

∆TCMB/TCMB depends only on cluster y ~ line-of-sight integral of neTe. Both ∆TCMB and TCMB are redshifted similarly ratio unchanged as photons propagate and independent of cluster distance

thermal SZE causes nonthermal change inspectrum. CMB looks colder to left of peak, hotter to right

Sunyaev & Zeldovich (1980)


Current SZE Data

•Beautiful images of the SZE inclusters at a large range ofredshifts from Carlstrom groupusing 1 cm (30 GHz) receiversat BIMA and OVRO

•But sensitivity of this and other instruments too poor for blind surveys C

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SZE only, ~15 - 40 µK/beam rms

CL0016+16, SZE + X-ray (ROSAT PSPC)


The Sunyaev-Zeldovich Effect in Galaxy Clusters

•Proportional to line integralof electron pressure:

•Fractional effect is independent of cluster redshift

•Thermal SZE causes unique spectral distortion of CMB

“hole in the sky” to left of peak

•Simplifies in Rayleigh-Jeans limit

But same spectrum as CMB in this limit


Secondary CMB Anisotropy

•The thermal SZE is the dominant contributor to CMB secondary anisotropy (beyond the damping tail) = thermal SZE from LSS at low z

•Probes baryon pressure distribution, early energy injection•Spectrally separable from primary anisotropy•Other effects (kinematic/Ostriker-Vishniac, patchy reionization) at much lower level, same spectrum as primary

Predictions for secondary anisotropy:

Springel et al, Ap. J.,549: 681 (2000)

Seljak et al, PRD, 63: 063001 (2001)

Limits (95%CL):

ATCA: Subrahmanyan et al, MNRAS, 315: 808 (2000).

BIMA: Dawson et al, Ap. J., 553: L1 (2001)

Ryle: Jones et al, Proc. PPEU (1997).

Springel

Seljak

BIM

A

Ryle

ATC

A


Unbiased Cluster Detection via the SZE

•Central decrement is bad observable because of dependence on core characteristics

•Integrated SZE over cluster face more robust and provides largely z-independent mass limit (Barbosa et al (1996), Holder et al (2000), etc.)

M200 is virial mass (inside R200), equal to volume integral of ne/fICM

Ten is electron-density weighted electron temperature Under “fair sample” assumption, fICM given by BBN value dA

2 factor arises from integration weak z-dependence arises from fortuitous cancellation:

•dA2 factor tends to reduce flux as z increases (1/r2 law)

•But for a given mass, a cluster at high redshift has smaller R200 and hence higher Ten:M200 ~ (R200

)3, increases with z, so R200 must decrease to get same M200, and T ~ M200/R200


Unbiased Cluster Detection via the SZE

•Holder, Mohr, et al (2000) modeled the mass limit of an interferometric SZE survey (synth. beam ~ 3’) using simulations

•Bears out expectation of weak dependence of mass limit on z:SZE provides an essentially z-independent selection function; it allows detection of all clusters above a given mass limit

•v. different selection function from optical/x-ray surveys

•For any survey, careful modelling will be required to determine this precisely, understand uncertainties

Holder et al, Ap. J., 544:629 (2000)

limiting mass vs. z for an interferometric survey fordifferent cosmologies


Science with Blind SZE Surveys

•Galaxy clusters largest virialized objects so large that formation not severely affected by “messy”

astrophysics – star formation, gas dynamics mass, temperature, radius understood within simple spherical

tophat collapse model

good probe of cosmological quantities: power spectrum amplitude (8) total matter density (m) volume element (tot) growth function (m, ) with higher statistics, equation of state p = w, dependence of w

on z (see talks by Holder, Kamionkowski)

•Non-Gaussianity: clusters are high-significance excursions, sensitive to non-Gaussian tails



•Constraining cosmological parameters Best done with redshift distribution Separation at high redshift between OCDM and CDM due to

different growth functions, volume element (more high-z volume in open universe)

Normalization of redshift distribution v. sensitive to 8 (= power spectrum normalization)

Reichardt, Benson, and Kamionkowski, in preparation



•Looking for non-Gaussianity assume a cosmology non-Gaussianity changes z-

distribution: if tail is longer, get more clusters at high z

Reichardt, Benson, andKamionkowski, in preparation


•Where is it possible to do high-l measurements (from the ground)?

•Rayleigh-Jeans tail (10s of GHz) atmosphere not a big problem HEMT receivers provide good

sensitivity have to contend with radio pt srces,

but subtraction demonstrated(DASI, CBI, BIMA, ATCA)

•near the peak (100-300 GHz) least point source contamination have to contend with sky noise bolometric instruments provide

best sensitivities in this band

•shorter wavelengths sky noise horrendous IR point sources difficult

(impossible?) to observe and subtract

SZE Instrument Parameter Space

poin

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urc

es

(radio

, IR

)

dust

free-free and synchrotron


Techniques

Interferometers•pros:

many systematics and noises do not correlate (rcvr gains, sky emission)

phase switching and the celestial fringe rate can be used to reject offsets, 1/f noise, non-celestial signals (if not comounted)

individual dish pointing requirements not as stringent as for single dish (if not comounted)

HEMT rcvrs, no sub-K cryogenics

•cons: not natural choice for brightness sensitivity – must make array look like single dish to achieve

operating frequency, BW limited by rcvr technology, correlator cost

Bolometers•pros:

sensitivity, bandwidth simplicity of readout chain scalability (big FOV arrays)

•cons: sub-K cryogenics standard single-dish problems: spillover, sky noise, etc.

requires chopping or az scan to push signal out of 1/f noise


•Noise sources: specified as noise-equivalent power (NEP), power incident on detector that can be detected at 1 in 1 sec, units of W√sec

detector noise: Johnson noise of thermistor, phonon noise, amplifier noise, etc.

BLIP noise: shot noise on DC optical load; present even if sky is perfectly quiet

sky noise: variations in sky loading

•These yield noise-equivalent flux density (NEFD):flux density (Jy) that can be detected at 1 in 1 sec; units of Jy√sec

•Beam size gives noise-equivalent surface brightness (NESB): units of (Jy/arcmin2)√sec

•Can then calculate noise-equivalent temperature (NETCMB), units of (µKCMB/beam)√sec

•and finally, noise-equivalent y parameter (NEy), units of (1/beam)√sec

Instantaneous Bolometer Sensitivity


•Single-antenna noise sources: summed to give Tsys

Trcvr (receiver noise): ~ bolometer detector noise, like a NEP Tsky (optical loading): due to DC optical load, but, unlike bolometers,

this NEP scales with Tsky, not as √Tsky √Psky because coherent receiver sky noise: nonexistent unless imaging the atmosphere

•Tsys and number of baselines n yield NEFD

•As for bolometers, calculate NET [(µK/beam)√sec] from NEFD must assume well-filled aperture (uv) plane so it is valid to use simple

Ωbeam

should include correction for central hole in uv plane, ignore for this In RJ limit, simplifies greatly:

And using antenna theorem

•finally, NEy, units of (1/beam)√sec

Instantaneous Interferometer Sensitivity


Mapping Speed

•Straightforward to calculate a mapping speed for a bolometer array

•Also pretty trivial for an interferometer

and in RJ limit

counterintuitive? Increased FOV hurts unless beam size also increased: fixed sensitivity spread over larger sky area

•Comparing mapping speeds: must be careful about beam size. Affects NET and FOV, though in different ways for bolometers and interferometers.

•Point source mapping speed? Only appropriate for large-beam experiments, hard to compare bec. SZ flux strong function of frequency.


New SZE Survey Instruments

•Now: ACBAR, BOLOCAM•Soon (2003/2004): SZA, AMI, AMiBA•Not so soon (>2004?): ACT, SP Bolo Array Telescope, etc.•Numbers:

all numbers calculated with true CMB spectrum; i.e., not in RJ limit For thermal SZ, best to compare y/beam sensitivity, since this can

be compared at different frequencies. Could also use Y = area integral of y.NEY is like NEFD, except corrected for SZ spectrum.•Using y assumes a beam-filling source, using Y assumes an unresolved source.

•y favors large-beam experiments, Y favors small-beam experiments, both impressions are artificial

Mass limits are those provided by each experiment, or in the literature. They are not consistent with each other! Further comment later.


ACBAR Instrument Specs

•Arcminute Cosmology Bolometer Array Receiver•UCB, UCSB, Caltech/JPL, CMU•2m VIPER dish at South Pole•spider-web bolometers at 240 mK•4 horns each at 150, 220, 270, 350 GHz

•4.5’ beams at 150 GHz•BW ~ 25 GHz

•Ndet Ωbeam ~ 64 arcmin2

•chopping tertiary, 3 deg chop, raster scan in dec

•Unique multifrequency coverage: promises separation of thermal SZE and primary CMB

250mK filt & lens

Corrugated feeds

4K filters & lenses

Bolometers

Thermal gap

274 219 150 345 GHz


ACBAR Sensitivity

•Achieved (2001), dominated by 4x150 NET = 440 µKCMB√sec (per row) NEy = 150 x 10-6 √sec (per row) MT = 34 deg2 (10 µK/beam)-2 month-1

My = 2.8 deg2 (10-6/beam)-2 month-1

MY = 0.55 deg2 (10-5 arcmin2)-2 month-1

•Map 10 deg2 in ~ 200 hrs (live) to Trms ~ 10 µK/beam yrms ~ 4 x 10-6/beam Yrms ~ 8 x 10-5 arcmin2

•2002: 4x150 + 12x280 focal plane NEy = 95 x 10-6 √sec (per row) My = 7.2 (10-6/beam)-2 month-1

MY = 1.4 (10-5 arcmin2)-2 month-1

significant improvement in NEy from better-matched multifrequency coverage Possibly ~2X better sensitivity if optical loading problem fixed

•Mapping speeds benefit from large beams, though also gives high mass limit (few x 1014 Msun)


BOLOCAM Instrument Specs

•Caltech/JPL, Colorado, Cardiff•10.4m CSO on Mauna Kea•Spider-web bolometer array at 300 mK

•144 horns at 150, 220, 270 GHz (not simultaneous)

•1’ beams at 150 GHz•BW ~ 20 GHz

•Ndet Ωbeam ~ 160 arcmin2

•drift scan + raster in dec, possible az. scan, raster in ZA

•Large number of pixels at high resolution – unique for SZ

•Multifrequency coverage, but at poorer sensitivity in otherbands and delayed in time


BOLOCAM Sensitivity

•Expected, based on extrapolation fromSuZIE 1.5:

NET = 1300 µKCMB√sec NEy = 470 x 10-6 √sec MT = 6.8 deg2 (10 µK/beam)-2 month-1

My = 0.53 (10-6/beam)-2 month-1

MY = 42 (10-5 arcmin2)-2 month-1

•Map 1 deg2 in ~ 100 hrs (live) Trms ~ 10-15 µK/beam yrms ~ 4 x 10-6/beam Yrms ~ 0.4 x 10-5 arcmin2

•Expectations consistent with achievedsensitivity in engineering run at 220 GHz

•Mapping speed degraded by small beams; but small beams yield low mass limit (~ 2-3 x 1014 Msun)


SZ Array Instrument Specs

•SZ Array•Chicago (Carlstrom), MSFC (Joy), et al

•8 x 3.5m at 30 GHz•NRAO HEMT receivers, ~10K noise, ~21K system noise

•8 GHz digital correlator (in conjunction with OVRO)

•FOVFWHM~ 10.5’, BeamFWHM ~ 2.25’? (unable to get definite number for beam, so scale from AMI)

•1-year survey of 12 deg2, part of time in heterogeneous mode

•later upgrade to 90 GHz


SZ Array Sensitivity

•Sensitivity and mapping speed for 8x3.5m array assuming 2.25’ beam:

NET = 730 (mKCMB/beam)√s NEy = 140 (10-6/beam)√s MT = 17 deg2 (10 µK/beam)-2 month-1

My = 4.7 (10-6/beam)-2 month-1

MY = 15 (10-5 arcmin2)-2 month-1

•Map 12 deg2 in 1 yr at 75% eff.: Trms ~ 2.8 µK/beam yrms ~ 0.5 x 10-6/beam Yrms ~ 0.3 x 10-5 arcmin2

•HETEROGENEOUS BASELINES HAVE NOT BEEN INCLUDED HERE!They improve sensitivity to low masses (counteract beam dilution)

•Mass limit ~ 1014 Msun, found by Monte Carlo in visibility space

•pt. src. subtraction – won’t need continuous monitoring, intermittent monitoring sufficient

SZA + OVRO


AMI Instrument Specs

•Arcminute Microkelvin Imager•MRAO/Cavendish/Cambridge group

•10 x 3.7m at 15 GHz•NRAO HEMT receivers,~13K noise, ~25K system noise

•6 GHz analog correlator

•FOVFWHM ~ 21’, BeamFWHM ~ 4.5’

•concurrent point source monitoring by Ryle Telescope (8 x 13m), no heterogeneous correlation

•Expect to upgrade receivers to InP HEMTs, ~6K rcvr noise, ~18K system noise


AMI Expected Sensitivity

•Sensitivity and mapping speed: NET = 470 (mKCMB/beam)√s NEy = 90 (10-6/beam)√s MT = 160 deg2 (10 µK/beam)-2 month-1

My = 47 deg2 (10-6/beam)-2 month-1

MY = 9.2 (10-5 arcmin2)-2 month-1

•Map 36 deg2 in 6 months at 75% eff.: Trms ~ 2 µK/beam yrms ~ 4 x 10-6/beam Yrms ~ 1 x 10-5 arcmin2

•Map 2 deg2 in 6 months at 75% eff.: Trms ~ 0.5 µK/beam yrms ~ 0.1 x 10-6/beam Yrms ~ 0.2 x 10-5 arcmin2

•Mass limit ~ 1014 Msun in deep survey

•As with ACBAR, mapping speed greatly helped by large beam, but also yields high mass limit (or long integration time and small area coverage for low mass limit)

clusters detectable in simulated observations;note how redsfhit range increases as Y is lowered


AMiBA Instrument Specs

•Array for Microwave Background Anisotropy

•ASIAA + ATNF + CMU•19 x 1.2m at 90 GHz•MMIC HEMT receivers under development in Taiwan, ~45K noise expected, ~75K system noise

•20 GHz analog correlator

•FOVFWHM ~ 11’, BeamFWHM ~ 2.6’

•Also: 19 x 0.3m for CMB polarization


AMiBA Expected Sensitivity

•Sensitivity and mapping speed: NET = 590 (µKCMB/beam)√s NET = 140 (10-6/beam)√s MT = 28 deg2 (10 µK/beam)-2 month-1


MY = 8.9 (10-5 arcmin2)-2 month-1

•3 different surveys (eff. = 50%): deep: 3 deg2 in 6 months to Trms ~ 0.2 µK/beam, yrms ~ 0.4 x 10-6/beam,Yrms ~ 0.3 x 10-5 arcmin2

med.: 70 deg2 in 12 months to Trms ~ 0.6 µK/beam, yrms ~ 1.5 x 10-6/beam,Yrms ~ 1.1 x 10-5 arcmin2

wide: 175 deg2 in 6 months to Trms ~ 1.4 µK/beam, yrms ~ 3.4 x 10-6/beam,Yrms ~ 2.6 x 10-5 arcmin2

•Mass limits: 2, 4.5, 6.5 x 1014 Msun

•pt. src. confusion much less at 90 GHz; will do survey to check src. counts, but expect confusion from low-flux clusters will be more important


ACT Instrument Specs

•Atacama Cosmology Telescope•Princeton/Penn (Page, Devlin, Staggs)•6m off-axis dish with ground screen, near ALMA site•3 x 32x32 arrays of TES-based pop-up bolometers with multiplexed SQUID readout

•150, 220, 265 GHz bands•1.7’, 1.1’, 0.9’ beam sizes•22’ x 22’ FOV•azimuth scan of entire telescope

•l-space coverage from l ~ 200 to 104

•Expected NETs:300, 500, 700 µKCMB√sdetector/BLIP limitedTsky = 20K assumedsky noise expected to be negligible at l > 1000 in Chile


ACT Sensitivity

•Sensitivity and mapping speed: NET = 300 (µKCMB/beam)√s NEy = 115 (10-6/beam)√s MT = 2600 deg2 (10 µK/beam)-2 month-1


MY = 1700 (10-5 arcmin2)-2 month-1

•Huge mapping speed because of good sensitivity and large FOV: 100 deg2 in 4 months at eff. = 25% to

Trms ~ 2 µK/beam yrms ~ 0.7 x 10-6/beam Yrms ~ 0.2 x 10-5 arcmin2

Will actually do significantly better because of multi-frequency coverage (not accounted for in above)

•Expected mass limit ~ 4 x 1014 Msun (seems overly conservative!)

•Multi-frequency coverage promises excellent separation of thermal SZE and CMB-like secondary effects

•**Proposed, not yet funded**


South Pole Bolometer Array Telescope

•Chicago (Carlstrom et al, Meyer), UCB (Holzapfel, Lee), UCSB (Ruhl), CfA (Stark), UIUC (Mohr)

•32x32 bolometer array,~90% at 150 GHz,~10% at 220 GHz

•1.3’ beam at 150 GHz•FOV: telescope: 1 degarray: ~ 17’ x 17’?


South Pole Bolometer Array Telescope

•Sensitivity and mapping speed: NET = 250 (µKCMB/beam)√s NEy = 90 (10-6/beam)√s MT = 2000 deg2 (10 µK/beam)-2 month-1


MY = 4700 (10-5 arcmin2)-2 month-1

•4000 deg2 in 2 months live to Trms ~ 10 µK/beam yrms ~ 3.5 x 10-6/beam Yrms ~ 0.7 x 10-5 arcmin2

multi-frequency coveragenot so good, so has little effect

•Expected mass limit ~ 3.5 x 1014 Msun

•Proposal into NSF-OPP


Summary and Scalings

•Plot of mapping speeds vs. beam FWHM for y and Y = area integral of y

•Overresolution: can correct for this by coadding adjacent pixels. Corrects y and Y mapping speeds by src

2 and src-2, respectively.

Note: ratio of mapping speeds for two experiments scaled to same src is independent of whether y or Y is used.

•Beam dilution: for y mapping speed, beam-filling source is assumed. If not, apparent y in beam is degraded by (beam/src)2, mapping speed by (src/beam)4

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(src/beam)4

(src/beam)2

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Random Parting Thoughts

•Calculation of mass limits seems still to be highly scientist-dependent

Would be nice to have agreed-upon estimation method Of course, some disagreement is inevetible and indicative of our ignorance

•Expecting µK/beam maps with v. small pixels over large areas What kind of instrumental junk is going to turn up? Do we really not expect to run into diffuse backgrounds? When does point-source subtraction begin to fail? When do mm-wave instruments become point-source confused?

•Interferometers vs. Bolometers Will interferometers ever be competitive near the null? What about interferometers with multi-pixel receivers to increase FOV?

•Large telescopes with bolometer arrays getting too large for small groups (manpower + $$). Heading out of the small experiment regime. You don’t get a new measurement technique for free!


Conclusion

•First blind cluster surveys using SZE underway or beginning soon

•New instrumentson the horizon with remarkable raw sensitivities and mapping speeds

•Exciting new science coming in the next few years New, independent measures of 8, m,

Prospect for new measure of equation of state

current and future sz surveys sunil golwala california institute of technology july 7, 2001

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