CARMA(Combined Array for Research in Millimeter Astronomy)

Capabilities and Future Prospects

Dick Plambeck

SF/ISM Seminar, 9/5/2006

outline

• background

• capabilities

• what is CARMA good for?

• science example: does the clump mass spectrum in molecular clouds determine the IMF?

+ UChicago SZA 8 3.5-m antennas

Berkeley-Illinois-Maryland array

10 6.1-m diameter antennas

Caltech array 6 10.4-m antennas

CEDAR FLAT

Aug 2005Apr 2004

Cedar Flat

21 Jul 2004 – lifting off the first reflector

panel adjustmentsurface error determined from holography

before adjustment: 127 μm rms

→ 75% loss at 225 GHz

after adjustment: 28 μm rms

→ 7% loss at 225 GHz

all antennas assembled10 Aug 2005

95 GHz continuum map of SS43325 Aug 200625 Aug 2006

rms noise 0.6 mJy/beam

basicsincoming signals accepted:

3mm 80-116 GHz 1mm 220-270 GHz

downconverted (1-5 GHz), amplified signal sent to lab on optical fiber

mostly noise from sky and receiver; source contributes < 10-3

cross-correlation spectrum

correlator

tuning example

• LO1 tunable 85 -115 GHz, or 220 -270 GHz (1)

• receive 4 GHz wide bands above (USB) and below (LSB) LO1 (2)

• 8 independent spectrometers process (USB+LSB) (3)

• USB and LSB signals separated in each spectrometer

12CO 115.27 GHz13CO 110.20 GHz

LO1 112.73 GHz

(1) no 1mm band on OVRO yet; (2) currently 1.5 GHz for BIMA 3mm receivers; (3) currently only 2.5

sky freq

BIMA, OVRO

correlator sections

correlator (spectrometer) modes(for first 3 bands)

correlator modes(for remaining 5 bands)

5 arrays (A,B,C,D,E)57 pads for 15 telescopes

Cedar FlatE-array

(most compact)

synth beam 4.5" at 230 GHz

Highway 168

D-arraysynth beam

1.8"

C-arraysynth beam

0.8"

B-arraysynth beam

0.32"

A-array synth beam

0.13"

a reminder: interferometer acts as a spatial filter

E-array

• BIMA antennas within collision range

• SZA provides even shorter spacings

• combine with single dish measurements from 10.4-m antennas

colliding antennas

what can we do now that we couldn’t do before?

• better site should allow routine observing at 1.3 mm

• much improved sensitivity (3 x collecting area of BIMA, 5 x instantaneous bandwidth)

• high dynamic range imaging owing to more baselines, hence better sampling of u,v plane

225 GHz zenith opacity

% tau mm H2O

SSB Tsys

25 <.12 <1.8 <290

50 <.16 <2.4 <350

75 <.28 <4.3 <520

Tsys computed for 1.5 airmasses, Trcvr(DSB) = 45 K

sensitivity examples

• 5σ detection of dust continuum from .04 Mo clump at 300 pc (5 mJy at 230 GHz)

• 5σ detection of 1-0 CO emission from 2500 Mo cloud in M33 (2.5 K in 3’’ beam, ΔV = 2 km/sec)

tau BW mins

BIMA 0.32 0.8 GHz 3400

CARMA 0.16 1.5 GHz 100

CARMA 0.16 4.0 GHz 40

tau BW mins

BIMA 0.32 0.7 MHz 470

CARMA 0.27 0.7 MHz 60

Comparison with other arrays

CARMA

+ SZASMA IRAM ALMA

elevation 2200 m 4200 2500 5000

antennas 23 8 6 50+

baselines 253 28 15 1225+

diameter 10, 6, 3.5 6 15 12, 7

area 850 m2 226 1060 5600+

max baseline

1900 m 500 m 400 m 14 km

Comparison of u,v coverage6 hr track on source at decl +10º

OVRO E, 15 baselines CARMA D, 105 baselines

Synthesized beams5% contours

problems with poor u,v sampling

• missing Fourier components (u,v spacings) → an infinite number of maps are consistent with the data!

• how can we publish papers? sources with a few compact components are no problem

• CLEAN, max entropy methods are ways of interpolating/extrapolating based on our bias about the sources (e.g., sources consist of a few compact components).

CLEANed map, point source at centerTsys = 0; no atmospheric phase noise

CLEANed map, point source at centerTsys = 0; atmospheric phase noise 150 um

at 100 m; 1% contours

extended source 12 x 6 arcsec FWHM, total flux 1 Jy

integrated flux = 0.77integrated flux = 0.006

scientific examplewhat determines the IMF?

• physics of infall from disk to star

– ‘stars determine their own mass’

• fragmentation of interstellar clouds

– some (approximately fixed) percentage of a clump mass will find its way onto the star

• observational test: measure the mass spectrum of prestellar clumps

– want ~ a few x 103 AU resolution, ~ 5-10’’ in nearby clouds

– an example: Testi and Sargent 1998, OVRO mosaic of 5’x5’ region in Serpens

Serpens mosaic Testi & Sargent 1998

99 GHz continuum

5“ resolution, about 1500 AU

noise level 0.9 mJy/beam

1σ contours beginning at +/- 3σ

anything > 4.5 σ (4 mJy/beam) considered real

strongest sources are ~100 mJy

cumulative mass spectrum of 26 clumps not associated with IR sources

dotted line is best fitting power law, dN/dM ~ M-2.1

dashed line is Salpeter IMF, dN/dM ~ M-2.35

dash-dot line is power law characteristic of larger cores, dN/dM ~ M-1.7 (Williams, Blitz, McKee 1998)

→ mass spectrum of protostellar dust condensations closely resembles local IMF

strongest sources are ~100 mJy

anything > 4 mJy/beam is considered real

→ need dynamic range of 25:1

synthesized beams are particularly ugly near declination 0

configurations, beam pattern for Serpens mosaic

comparison with BIMA mosaic

Lowest contour 2.7 mJy/beam, peak ~105 mJy, beam 5"

Lowest contour 8 mJy/beam, peak 256 mJy, beam ?

simulate: OVRO C,D,E

2 sources (300 mJy and 12 mJy), no atmospheric phase fluctuations

same model, but include atmospheric phase fluctuations of 150 um on 100-m baseline

extended source in the field

CARMA D array

CARMA D

CARMA D array + SZA(23 antennas, 253 baselines)

CARMA DZ

summary

• accurate measurements of clump mass spectrum in complicated regions require not only high sensitivity, but also high dynamic range, image fidelity

• many antennas, ability to get close spacings are critical

• mosaicing many fields necessary to survey sufficiently large regions

• CARMA is an important step in this direction