Molecular gas and dust in the Magellanic Clouds

C. Boton 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 mmContinuum Array 37 pix

SMC

SMC Regions

SMC SW Bar

N66

CO1-0: ESO SEST CO Key Programme (1988-1995)

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 = 2.7x105 Mo Mvir = 1.2x104 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. 2003

- Metallicity: 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/H2 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)/Mvirial5

24

22

11 24

22

1817

LMC

LMC Regions

30 Doradus

N159 Doradus ComplexNanten cloud

N11

SEST KEYProgrammeCO(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