Cambridge, June 13-16, 2005 A Study of Massive Proto- and Pre-stellar Candidates with the SEST Antenna Maite Beltrán Universitat de Barcelona J. Brand – IRA, Bologna R. Cesaroni – Arcetri, Firenze F. Fontani – Arcetri, Firenze L. Testi – Arcetri, Firenze S. Pezzuto, S. Molinari – IFSI, Roma

Cambridge, June 13-16, 2005 Introduction Massive stars (> 8 M O ) play a crucial role in the appeareance and evolution of galaxies: heavy elements + energetic winds, SN, … Massive star formation understanding behind that of lower mass counterparts Study of clouds associated with UC HII embedded luminous IRAS with no radio continuum emission Palla et al. (1991) selected plausible candidate of massive protostars with  > -30 O: Criteria Selection :1. IRAS colours according to criteria of Richards et al (1987) to identify Compact Molecular Clouds 2. not associated with HII regions (no cm emission) Sub-samples: Low and High: according to the IRAS colour criteria of Wood & Churchwell (1989) for identifying UC HII regions

Cambridge, June 13-16, 2005 [25-12] > 0.57 [60-12] > 1.30 IRAS colour-colour diagram

Cambridge, June 13-16, 2005 Introduction H 2 O masers (Palla et al. 1991); different continuum and molecular line tracers, from cm no NIR wavelengths (Molinari et al. 1996, 1998, 2000, 2003; Brand et al. 2001; Zhang et al. 2001) Main findings: 1. High and Low have L > 10 3 L O 2. Low sources lower association with H 2 O masers 3. High higher association with UC HII regions 4. Low have T dust ~ 30 K (Molinari et al. 2000) much lower than that of “hot cores” (> 100 K) Low massive protostar candidates are younger than High

Cambridge, June 13-16, 2005 Southern Survey Extend the study to the southern hemisphere, we selected sources with  < -30 O from the IRAS-PSC following the Palla et al. (1991) criteria: 115 Low observed in C 17 O and/or CS by Fontani et al. (2005) Low + 93 High previously observed in CS by Bronfman et al. (1996) Additional Low with  > - 30 O observed in NH 3 by Molinari et al. (1996) 235 sources with Luminosities > 10 3 L O OBSERVATIONS:1.2 mm continuum observations with 37-channel bolometer array SIMBA at the 15-m SEST antenna maps 900” x 400” + 3 mosaics HPBW ~ 24” ~ 3 x 10 4 L O ~ 1x 10 5 L O

Cambridge, June 13-16, 2005 Morphology of the sources Clumps identified with Clumpfind 2D (Williams et al. 1994). Massive dust clumps detected in all but 7 regions, usually more than one clump per region: > 650 clumps in 235 regions No milimeter source or faint emission mostly towards Low sources with no C 17 O or CS detected Dust emission presents a variety of complex morphologies: - sometimes a single millimeter source - sometimes with massive clumps clustered towards the IRAS position - sometimes with multiple clumps linked forming chains or filaments

Cambridge, June 13-16, 2005 Morphology of the sources: Low 1.2 mm + 8  m

Cambridge, June 13-16, 2005 Morphology of the sources: High 1.2 mm + 8  m

Cambridge, June 13-16, 2005 IRAS and IRAS mm + 8  m 1.2 mm + 21  m

Cambridge, June 13-16, 2005 Low versus High LowHigh 163 M O 561 M O 0.23 pc0.33 pc 1.4 x 10 6 cm x 10 5 cm x 10 4 L O 1.3 x 10 5 L O 98 L O /M O 101 L O /M O M calculated for T dust = 30 K 4-5 times lower than L/M of UC HII regions with same M High and Low could be in a pre-UC HII phase

Cambridge, June 13-16, 2005 MSX versus non MSX We have searched for prestellar or precluster cores in the surroundings of the candidate massive protostars, as one may expect that these cores are located close to massive luminous cores hiding already formed high-mass YSOs. Such cores are expected to have similar density and size than those with embedded protostars but lower L and T. The bulk of its L is expected to be emitted at mm and sub-mm wavelengths with faint mid- and far-IR emission. To search for such cores we have cross-correlated our sample with mid-IR MSX PSC + compared the mm continuum maps with MSX images. 130 massive mm clumps not associated with mid-IR emission, which are potential prestellar/precluster cores 94 Low (25% of Low clumps) 36 High (15% of High clumps)

Cambridge, June 13-16, 2005 MSX versus non MSX 1.2 mm + 8  m 1.2 mm + 21  m 1.2 mm + 8  m

Cambridge, June 13-16, 2005 MSX versus non MSX nonMSX ~ 101 M O MSX ~ 370 M O T lower?? Other surveys suggest T < 20 K; e.g. Garay et al. (2004) have found T < 17 K for clumps not associated with MSX for T = 30 K

Cambridge, June 13-16, 2005 The Mass Spectrum of the clumps Completeness limit Normalized cumulative mass distribution d < 2 kpc 10 < M < 130 M O d < 6 kpc M > 92 M O dN/dM ~ M -   = 2.35  = 1.70 Salpeter (1955) Molecular clouds from gas obs.

Cambridge, June 13-16, 2005 The Mass Spectrum of the clumps Williams et al. (2004) Reid & Wilson (astro-ph/053190) Sample of 68 high-mass protostellar candidates NGC 2.8 kpc 15 M O 97 M O 25 M O 120 M O ~3000 M O 100 M O 10 M O 800 M O SCUBA observations  =1.14  =2.32  =2.0  =0.9

Cambridge, June 13-16, 2005 The Mass Spectrum of the clumps Mass Range(Mo)(Mo) Dust emission Tothill et al. (2002) 1.7 Beuther & Schilke (2004) 2.5 Williams et al. (2004) This Work Reid & Wilson (2005) Gas emission Kramer et al. (1998) Power-law at the high-mass end (M > 100 M o ) consistent with stellar IMF (e.g. Salpeter 1955) -> IMF of high-mass (proto)clusters is determined at the very early stages of evolution? Power-law for M <100 M o flatter: is this break real? or an artifact, due to incompleteness, or to low spatial resolution of the single-dish observations? Need of higher angular resolution and sensitivity observations Beuther & Schilke (2004) IRAS ~ 2 kpc PdBI

Cambridge, June 13-16, 2005 Summary We have carried out a 1.2mm dust continuum emission of 235 massive protostar candidates with L > 10 3 L O, mostly with  < -30 O. Massive dust clumps have been detected in all but 7 out of 235 regions, usually more than one clump per region: > 650 clumps in 235 regions. The dust emission presents a variety of complex morphologies: single sources, clusters of clumps, chains or filaments of clumps. Low and High samples have similar physical properties, and a similar mean value of the L/M ratio, much lower than that of known UC HII regions. This suggests that the sources in our survey could be in a younger pre-UC HII phase. There are 130 massive mm clumps in the surroundings of candidate massive protostars not associated with mid-IR MSX emission that are potential prestellar/precluster cores. Their properties are similar to those of embedded YSOs, although their mean mass is smaller. The mass spectrum of clumps with M > 92 M O resembles the Salpeter stellar IMF, while for 10 M O < M < 130 M O is better fit with a power-law with  = 1.7.