Molecular gas and dust in the Magellanic Clouds C. Bot on behalf of Mónica Rubio Dusty, 29 oct 2004

Collaborators Monica Rubio, Santiago, Chile Francois Boulanger, IAS, France Alessandra Contursi, MPE, Germany Fredrik Rantakyro,UCH &ESO, Chile Marc Sauvage, CEA, France Caroline Bot, Strasbourg, France

Motivation - Dust emission at sub-mm/mm wavelengths is used as tracer of interstellar matter over a wide range of environments. -Dust emission is precious for tracing matter in the densest and most shielded regions in star forming molecular clouds. -Complements the HI and CO observations to provide a complete view of the interstellar matter in molecular clouds - In low metallicity interstellar clouds, due to reduce shielding, CO traces the densest part of molecular clouds but nor their diffuse envelope which makes most of the mass in galactic molecular clouds.Thus, in low metallicity star forming clouds a large fraction of the mass may consist of molecular gas with no CO (Lequeux et al 1994)

Motivation - In the SMC, this expectation is empirically supported by the reduced ratio between CO luminosity and virial mass compared to the Milky Way value (Rubio et al. 1993).

Motivation THUS, - Observations of the dust emission can be a unique mean in tracing this so-far hidden matter. - Study of the dust and grain properties.

SEST observations SEST 15 m Beam size for CO 45" (10 pc) (115 GHz) 23" (5 pc) (230 GHz) SIMBA 1.2 mm Continuum Array 37 pix

SMC

SMC Regions SMC SW Bar N66 CO1-0: ESO SEST CO Key Programme ( )

SMC B1-1 molecular cloud Simple laboratory to study dust properties from FIR/mm emission Quiescent molecular cloud serendipitously discovered in CO (Rubio et al. 1993)

Mgas = 2.7x10 5 MoMvir = 1.2x10 4 Mo Rubio et al. 2004, A&A, 425, L1 Unexpected result: the gas mass is a factor of 20 times the mass derived from the CO observations Dust emissivity/H 1/10 Galactic (metallicity difference) Tdust=15K

-Dust emissivity higher in solar neighbourhood molecular clouds ~3 * diffuse ISM (Stepnik et al 200, Cambresy et al, 2001, del Burgo et al M etallicity : Fe deficiency smaller than that of C and O could be higher in HII regions (Hill et al. 97) but not too much - Dust temperature: warmer dust ? if T > the gas mass increase only linearly with T >15K. And no heating sources

(Lequeux et al 1994) CO emission arise from high column density clumps SIMBA observations are detecting emission from an extended enveloppe of HI/H 2 gas with a lower density than that of the CO emitting gas SMC Low metallicity Low Dust content

The other southern SMC molecular clouds Free-free contribution: estimation thanks to ATCA continuum radio sources catalog M(1.2mm)/Mvirial

LMC

LMC Regions 30 Doradus N159 Doradus Complex Nanten cloud N11 SEST KEY Programme CO(1-0) N4

LMC results 30 Dor : the 1.2mm emission can be totally explained as thermal free-free emission. N4, continumm emission is due to a combination of free- free emission and dust emission, ==>SED : millimeter excess N159 S: an LMC cold molecular cloud, Mdust=Mvirial

Conclusions -f=M(1.2mm)/Mvirial in the range 1 to 20 -the f factor could be measuring the evolution stage of the clouds: -- gravitationnal concentration f  -- photodissociation of CO after star formation  -- f minimum at the onset of star formation? -future observations: Apex, mm dust observations, Herschel CI