science with carma: the combined array for research in millimeter-wave astronomy alberto bolatto...
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Science with CARMA:Science with CARMA:The Combined Array for Research
in Millimeter-Wave Astronomy
Alberto Alberto BolattoBolatto
Radio Astronomy LabRadio Astronomy LabUC BerkeleyUC Berkeley
Adam Leroy*Adam Leroy*Josh Simon*Josh Simon*Erik Rosolowsky*Erik Rosolowsky*Leo BlitzLeo BlitzFabian WalterFabian Walter
NGC 2976CO on H
What is CARMA?
• CARMA is the merger of the OVRO, BIMA, and SZA arrays
• It is a partnership between Caltech, UC Berkeley, Illinois, Maryland, and Chicago
U.C. BerkeleyLeo Blitz Don Backer Alberto Bolatto Calvin Cheng Danning Chou Greg Engargiola Ed Fields Matt FlemingRick Forster Carl HeilesDavid McMahonAlessandro Navarrini Imke de PaterColby Kraybill Dick Plambeck Doug Thornton Lynn Urry Harold Weaver Jack Welch Mel Wright
CaltechAnneila Sargent Andrew Beard Geoff Blake Paul Daniel Jim Fredsti Curt Giovanine Dave Hawkins Rick Hobbs Mark Hodges Stan Hudson Russ Keeney Derrick Key James Lamb Ron Lawrence Steve Miller Nick Scoville Steve Scott Brad Wiitala David Woody
U. IllinoisDick Crutcher You-Hua ChuRobert GruendlLeslie LooneyKee-Tae KimJason KirkDave MehringerDavid MeierJoe MohrJun-ichi NakashimaRay PlanteLew SnyderEdmund Sutton
U. MarylandStuart Vogel Mike A'Hearn Andy Harris Mukul Kundu Lee Mundy Glen Petitpas Marc Pound Eve Ostriker Kevin Rauch Jim Stone Peter Teuben Stephen WhiteMark Wolfire
U. ChicagoJohn CarlstromJohn CartwrightKim CobleFrank DiDonnaRyan HennessyEllen LaRueErik LeitchMichael LohClem PrykeBen RedallChris ReerMarkus RunyanDan Siegal
Project Manager: Douglas Bock (Tony Beasley)
What is CARMA?
• OVRO, BIMA, and the SZA are relocating to Cedar Flat (Inyo Mountains, altitude 2.2 km)
VR simulation in D-array configuration
200 m
Central Array Area just cleared, late August
The role of CARMA
• Training grounds for next generations of ALMA users
• First rate science: millimeter-wave interferometry facility on road to ALMA, together with IRAM’s PdBI
• Simpler, flexible platform for new developments:– E.g., array receivers for wide-field
interferometry and large scale surveys
Specifications• 23 dishes:
– 6 OVRO 10 m dishes– 9 BIMA 6 m dishes– 8 SZA 3.5 m dishes
• 800 m2 collecting area• Superb image fidelity:
– 253 baselines– Heterogeneous array
• 5 configurations: – 4 m to 2.2 km long baselines– 10” to 0.1” angular resolution
• 4 mm median WV burden, 225~0.25 • Atmosphere ×2 more stable than Hat Creek and OVRO:
– frequent operation at 1mm and in extended arrays
The Instrument
• RF & IF system:– Laser link system: 8 GHz × 2 polarizations– fiber support for array receivers– 1mm Rx: OVRO 4 GHz– BIMA upgrading to 4 GHz– 3mm Rx: planned upgrade to MMICs– Currently developing dual polarization Rx
• First light correlator:– Based on COBRA FPGA technology– 8 × 500 MHz windows (3 LR, 5 HR)
• Next generation correlator:– Full Stokes parameters
• Tropospheric phase correction:– Correlation WVR under development
Construction is moving forward• OVRO stopped and upgrading• BIMA deconstructed and transported
• First telescope pads in place• Building foundations poured• Power and fiber trenching proceeding
Operations beginning August 2005
Why am I excited about this?
• The processes that control the conversion from atomic gas to molecular gas to stars on galactic scales are not well understood
• Molecular cloud properties of extragalactic GMCs are basically unknown
• Without this information, baryons cannot be reliably incorporated into large scale simulations
Two words: Extragalactic Vermin
HI H2
The link between atomic and molecular gas
• Why are GMCs only found on top of HI filaments?
• Why are GMCs only found inside a certain radius, even though there is little change in N(HI)?
• What is regulating the HI→H2→SF transition on galactic scales?
GMCs over color HI map in M33Engargiola et al. (2003)
The link between atomic and molecular gas
• Why are GMCs only found on top of HI filaments?
• Why are GMCs only found inside a certain radius, even though there is little change in N(HI)?
• What is regulating the HI→H2→SF transition on galactic scales?
Color GMCs over HI contours in IC10Leroy, Walter et al. (in prep.)
Clue # 1
• Azimuthally averaged H2 fraction is strongly correlated with local hydrostatic pressure, mostly set by stellar surface density
(Blitz & Rosolowsky 2004;
Wong & Blitz 2002)
N(H2)/N(HI) = 0.8(P/PO)0.9
(ΣHIΣ*0.5)0.9
N(H2)/N(HI) = 0.8(P/PO)0.9
(ΣHIΣ*0.5)0.9
IC10
Clue # 2
• Very tight correlation between molecular and stellar mass in a large sample of local galaxies(Leroy et al., submitted, poster)
Taken together, these findings suggest that the surface density of the stellar disk plays an important role in regulating the HI→H2
Taken together, these findings suggest that the surface density of the stellar disk plays an important role in regulating the HI→H2
Studying GMCs in other galaxies
• The challenges:– Low S/N we only see “the tips” of the GMCs– Marginal resolution beam deconvolution is
essential– Confusion & blending what is a cloud?
Cloud Radius
Spatial Mask
Line Profile
GMC properties across the Local Group
M/R2 = const
• Cloud properties appear remarkably constant regardless of environment
• M RV2
V R1/2
ΣH2 ~ constant
Pcl ~ ΣH22 ~ const
• If Jeans instability determines cloud fragmentation,
IMF ~ invariant
Bottom line
A strong observational program on nearby galaxies is crucial to understand the
fundamental processes at work in the near and far universe
A strong observational program on nearby galaxies is crucial to understand the
fundamental processes at work in the near and far universe
Taking over from BIMA: the
first 32 antennas of the ATA under construction at
Hat Creek