MAGMA: The Magellanic Mopra Assessment Tony Wong University of Illinois at Urbana-Champaign Collaborators: Annie Hughes (Swinburne/ATNF), Erik Muller (Nagoya U.), Jorge Pineda (JPL), Juergen Ott (NRAO), Y. Fukui, A. Kawamura, Y. Mizuno (Nagoya U.), S. Maddison (Swinburne), J.-P. Bernard (CESR), Y. Chu, L. Looney (U. Illinois), C. Henkel (MPIfR), U. Klein (U. Bonn)

Motivation Magellanic Clouds Can obtain both a local (pc-scale) and global view of star formation and the ISM But, may not be in dynamical equilibrium Metallicity lower than Galaxy Existing complete ISM surveys CO (2.6’): NANTEN surveys (Fukui et al. 1999, 2008) HI (1’): ATCA + Parkes surveys (Stanimirovic et al. 1999, Kim et al. 2003) H  : MCELS (Smith et al.) mid-IR: S 3 MC (Bolatto et al.), SAGE (Meixner et al.)

CO vs. HI in LMC Nearest actively star-forming galaxy; can easily achieve ~10 pc resolution with radio telescopes NANTEN CO ATCA HI Fukui et al. 2001, 2008Kim et al. 2003

Why A New Survey? ~40 pc resolution of NANTEN CO survey leaves many molecular clouds unresolved. SEST Key Program focused on clouds with bright H  emission, and did not employ OTF.

MAGMA Components: LMC 1.Molecular Ridge near 30 Doradus (MX002: 2005) Properties of GMC’s as a function of radiation field 2.Survey of Clouds in the Inner LMC (M172: ) Properties of GMC’s across range of environments Large scale dynamics and the CO-HI relationship 3.Verifying Cloud Masses (M226; 2007) Compare virial and IR-based methods 4.A Complete Flux-Limited Sample (M300; ) Properties of the smallest bright CO clouds

MAGMA Targets

Molecular Ridge 120 5’ x 5’ fields 3  sensitivity ~ 200 M  per beam NANTEN CO Molecular Ridge

CO vs. HI in LMC Mopra CO HI Peak T b Eff. lwidthHI integral

CO - HI Offsets At 1’ resolution, evidence for offsets between CO and HI peaks. Posibly “warm atomic haloes” such as seen around Galactic GMCs (e.g. Andersson et al. 1991).

X Factor Assuming clouds are virialized, there is little variation in the CO-to-H 2 conversion factor as a function of ambient FUV field or distance from 30 Dor.

Cloud Mass Spectrum Mass spectrum power law index of -1.8 resembles that observed in Galactic studies. Hint of steeper slope in low-FUV environments.

By survey locationBy SF activity LMC: log  = (-0.7 ± 0.1) + (0.7 ± 0.1) log R (our data) MW: log  = log R (Solomon ea 1987) Real variation in amplitude of turbulence between galaxies? M31: log  = (-0.5 ± 0.3) + (0.7 ± 0.2) (Rosolowsky 2007) Ridge clouds not shown in this panel

By survey locationBy SF activity M vir  L n MW: n = 0.8 (Solomon ea 1987) LMC: n = 1.2 ± 0.1 (our data) For constant X-factor: n = 1 More intracloud medium in larger GMCs, e.g. (e.g. HI or H 2 without associated CO)? Ridge clouds not shown in this panel

By survey locationBy SF activity Similar surface density to MW clouds if X-factor is (slightly) larger in LMC. For X-factor = 3.2 x cm -2 (K km s -1 ) -1, ∑ = 170 ± 70 M  pc -2 As per previous slide, large clouds not as luminous: L  R n ; n < 2. Ridge clouds not shown in this panel

Verifying GMC masses in the LMC Other methods to measure GMC mass besides virial hypothesis: 1) FIR emission from dust mixed with the molecular gas 2) Extinction of background stars by molecular gas 3) mm continuum from cold dust mixed with molecular gas… A three-way comparison between: X CO mass estimates from MAGMA data FIR mass estimate from SAGE 60  m & 100  m data (method 1) Extinction mass estimate from 2MASS 6X & Sirius data (method 2) With Bill Reach (SSC), Jean-Philippe Bernard (CESR, Toulouse) & Kazuhito Dobashi (Tokyo Gakugei)

Tracing H 2 with FIR Dust Emission Method outline: 70 and 160μm MIPS maps used to estimate dust temperature Optical depth derived from ratio of modified blackbody model at 160μm and actual 160μm map Measure dust emissivity per H locally using HI map Remove optical depth component associated with atomic ISM Regions of excess optical depth  molecular/ionized gas NB: Need cold clouds for single dust temperature assumption (See Reach et al 1994 for full description of method)

Some example clouds Contours: MAGMA CO data Greyscale: IR excess map

Tracing H 2 with NIR Extinction Method outline: Unlike FIR emission method, atomic and molecular ISM should have the same NIR extinction properties NIR star catalogue (2MASS) used to make map of extinction in the LMC (assume Cardelli reddening law & R V =3.1) Measure extinction per H locally using HI map Remove component associated with atomic ISM Regions with excess A V  molecular/ionized gas (See Dobashi et al 2008 for full description of method & comparison with NANTEN CO data across LMC)

Example & preliminary results From Dobashi et al 2008 NB NANTEN data (not MAGMA) shown Contours: NANTEN CO data Greyscale: Excess A V map cloud near 30 Dor

CO vs. HI in LMC Integrated HI (contour) on Integrated CO

CO vs. HI in LMC Peak HI Temp (contour) on Integrated CO

CO vs. HI in LMC HI vel dispersion (contour) on Integrated CO

CO vs. HI in LMC Bright CO associated with bright HI, but not vice versa.

CO vs. Stars in LMC CO correlates weakly with both recent and past star formation.

Molecular to Atomic Gas Ratio

CO vs. HI in LMC Are molecular clouds formed by colliding of HI flows? No correlation of I CO with HI linewidth.

CO vs. HI in LMC However, CO may be tracing a relatively late stage in molecular cloud evolution (Bergin et al. 2004). For typical values of v and n, timescale for CO emission to appear is >10 7 yr after shock. [CI]/CO ratio may be a much more sensitive probe of the early postshock gas.

Results: CO-HI Correlation HI necessary but not sufficient for CO detection Likelihood of CO detection increases with HI integrated intensity and peak brightness. Correlation is weak because a lot of bright HI emission is not associated with CO emission. CO is not associated with enhanced HI linewidth No indication of GMC formation from colliding HI flows, although subject to interpretation. CO/HI ratio not correlated with stellar surface density Probably limits the role of hydrostatic pressure

MAGMA Components: SMC

SMC Results Size-linewidth relation for northern clouds (triangles with errorbars) offset from relation for SW clouds (diamonds and solid line).

Summary 1.MAGMA will map the brightest CO clouds in the LMC and SMC (as detected by NANTEN) at a resolution of ~45” (11 pc). 2.Maps are revealing molecular cloud properties across flux-limited samples in both galaxies. 3.They are also being used to address long-standing questions about the ability of CO to trace H 2 in low- metallicity environments. 4.The relationship between CO and HI, which we are investigating globally using the NANTEN data, can be studied on the scales of individual clouds.