Current and Future SZ Surveys

1
Current and Future SZ Surveys

• Sunil Golwala
• California Institute of Technology
• July 7, 2001

2
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!

3
The Sunyaev-Zeldovich Effect in Galaxy Clusters

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

CMB photons T (1 z) 2.725K
?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
galaxy cluster with hot ICM z 0 - 3
scattered photons (hotter)
observer z 0
last scatteringsurface z 1100
thermal SZE causes nonthermal change in spectrum.
CMB looks colder to left of peak, hotter to
right
Sunyaev Zeldovich (1980)
4
Current SZE Data
SZE only, 15 - 40 µK/beam rms

• 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

Carlstrom et al, Phys. Scr., T 148 (2000)
CL001616, SZE X-ray (ROSAT PSPC)
5
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

6
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 (95CL) ATCA Subrahmanyan
et al, MNRAS, 315 808 (2000). BIMA Dawson et
al, Ap. J., 553 L1 (2001) Ryle Jones et al,
Proc. PPEU (1997).
ATCA
Ryle
BIMA
Springel
Seljak
7
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
• ?Te?n is electron-density weighted electron
  temperature
• Under fair sample assumption, fICM given by BBN
  value
• dA2 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 ?Te?nM200 ?
  (R200)3, ? increases with z, so R200 must
  decrease to get same M200, and T M200/R200

8
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 zSZE 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

limiting mass vs. z for an interferometric
survey for different cosmologies
Holder et al, Ap. J., 544629 (2000)
9
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

10
Science with Blind SZE Surveys

• 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
11
Science with Blind SZE Surveys

• 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
12
SZE Instrument Parameter Space

• 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

13
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

14
Instantaneous Bolometer Sensitivity

• Noise sources specified as noise-equivalent
  power (NEP), power incident on detector that can
  be detected at 1? in 1 sec, units of Wvsec
• 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 Jyvsec
• Beam size gives noise-equivalent surface
  brightness (NESB) units of (Jy/arcmin2)vsec
• Can then calculate noise-equivalent temperature
  (NETCMB), units of (µKCMB/beam)vsec
• and finally, noise-equivalent y parameter (NEy),
  units of (1/beam)vsec

15
Instantaneous Interferometer 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 vTsky ? vPsky 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)vsec
  from NEFD
• must assume well-filled aperture (uv) plane so it
  is valid to use simple ?beamshould 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)vsec

16
Mapping Speed

• Straightforward to calculate a mapping speed for
  a bolometer array
• Also pretty trivial for an interferometerand
  in RJ limitcounterintuitive? 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.

17
New SZE Survey Instruments

• Now ACBAR, BOLOCAM
• Soon (2003/2004) SZA, AMI, AMiBA
• Not so soon (gt2004?) 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.

18
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 ?beam 64 arcmin2
• chopping tertiary, 3 deg chop, raster scan in
  dec
• Unique multifrequency coverage promises
  separation of thermal SZE and primary CMB

274 219 150 345 GHz
Corrugated feeds
4K filters lenses
Thermal gap
250mK filt lens
Bolometers
19
ACBAR Sensitivity

• Achieved (2001), dominated by 4x150
• NET 440 µKCMBvsec (per row)
• NEy 150 x 10-6 vsec (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 vsec (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)

20
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 ?beam 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

21
BOLOCAM Sensitivity

• Expected, based on extrapolation fromSuZIE 1.5
• NET 1300 µKCMBvsec
• NEy 470 x 10-6 vsec
• 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)

22
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

23
SZ Array Sensitivity

• Sensitivity and mapping speed for 8x3.5m array
  assuming 2.25 beam
• NET 730 (mKCMB/beam)vs
• NEy 140 (10-6/beam)vs
• 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 wont need continuous
  monitoring, intermittent monitoring sufficient

SZA OVRO
24
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

25
AMI Expected Sensitivity
clusters detectable in simulated
observationsnote how redsfhit range increases
as Y is lowered

• Sensitivity and mapping speed
• NET 470 (mKCMB/beam)vs
• NEy 90 (10-6/beam)vs
• 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)

26
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

27
AMiBA Expected Sensitivity

• Sensitivity and mapping speed
• NET 590 (µKCMB/beam)vs
• NET 140 (10-6/beam)vs
• MT 28 deg2 (10 µK/beam)-2 month-1
• My 5 deg2 (10-6/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

28
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 NETs300, 500, 700 µKCMBvsdetector/BLIP
  limitedTsky 20K assumedsky noise expected to
  be negligible at l gt 1000 in Chile

29
ACT Sensitivity

• Sensitivity and mapping speed
• NET 300 (µKCMB/beam)vs
• NEy 115 (10-6/beam)vs
• MT 2600 deg2 (10 µK/beam)-2 month-1
• My 180 deg2 (10-6/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

30
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?

31
South Pole Bolometer Array Telescope

• Sensitivity and mapping speed
• NET 250 (µKCMB/beam)vs
• NEy 90 (10-6/beam)vs
• MT 2000 deg2 (10 µK/beam)-2 month-1
• My 160 deg2 (10-6/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

32
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 ?src2 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

(?src/?beam)2
(?src/?beam)-2
x-axis is ? src for scaling lines, ? beam for
experiments
(?src/?beam)4
33
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
  dont get a new measurement technique for free!

34
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