The formation of high-mass stars: new insights from Herschel, IRAM, and ALMA imaging

The formation of high-mass stars: new insights from Herschel, IRAM, and ALMA imaging Frédérique Motte (IPAG Grenoble & AIM Paris-Saclay) Special credits to S. Bontemps, T. Csengeri, P. Didelon, A. Gusdorf, F. Herpin, P. Hennebelle, M. Hennemann, T. Hill, P. Lesaffre, F. Louvet, A. Maury, Q. Nguyen Luong, T. Nony, N. Peretto, N. Schneider, F. Schuller, P. Tremblin, A. Zavagno and the Herschel/HOBYS and IRAM/W43-HERO consortia. October 28th, 2016 F. Motte, AstroLille2016 1

The french community (permanent staff) working on the physics of star formation AIM Paris-Saclay/CEA: P. André, P. Didelon, P.-A. Duc, M. Gonzalez, P. Hennebelle, A. Men shchikov, A. Maury, V. Minier, M. Sauvage, P. Tremblin IAS Orsay: F. Boulanger, L. Verstraete, N. Ysard LERMA/ENS Paris: S. Cabrit, M. Gerin, A. Gusdorf, P. Lesaffre, L. Pagani OAS Strasbourg: L. Cambrézy UTINAM Besançon: J. Montillaud CRAL/ENS Lyon: I. Baraffe, G. Chabrier, B. Commerçon LAB Bordeaux: A. Baudry, S. Bontemps, J. Braine, A. Dutrey, S. Guilloteau, F. Herpin IPAG Grenoble: A. Bacmann, C. Dougados, B. Lefloch, S. Maret, F. Motte IRAM Grenoble: F. Gueth, J. Pety IRAP Toulouse: J.-P. Bernard, A. Hughes, I. Ristorcelli LAM Marseille: N. Grosso, D. Russeil, A. Zavagno October 28th, 2016 F. Motte, AstroLille2016 2

AIM Paris-Saclay/CEA: P. André, P. Didelon, P.-A. Duc, M. Gonzalez, P. Hennebelle, A. Men shchikov, A. Maury, V. Minier, M. Sauvage, P. Tremblin IAS Orsay: F. Boulanger, L. Verstraete, N. Ysard LAB Bordeaux: A. Baudry, S. Bontemps, J. Braine, A. Dutrey, S. Guilloteau, F. Herpin The french community (permanent staff) working on the physics of star formation High-mass star formation Observational constraints LERMA/ENS Paris: S. Cabrit, M. Gerin, A. Gusdorf, P. Lesaffre, L. Pagani OAS Strasbourg: L. Cambrézy UTINAM Besançon: J. Montillaud CRAL/ENS Lyon: I. Baraffe, G. Chabrier, B. Commerçon IPAG Grenoble: A. Bacmann, C. Dougados, B. Lefloch, S. Maret, F. Motte IRAM Grenoble: F. Gueth, J. Pety IRAP Toulouse: J.-P. Bernard, A. Hughes, I. Ristorcelli LAM Marseille: N. Grosso, D. Russeil, A. Zavagno October 28th, 2016 F. Motte, AstroLille2016 3

Outline 1. Open questions and targeted clouds in the framework of the Herschel/HOBYS and W43-HERO surveys 2. Quest of the earliest phases of high-mass star formation: Do high-mass pre-stellar cores exist? 3. Discovery and characterization of 1-10 pc clouds forming massive star clusters: ridges 4. First measure of the core mass function (CMF) in massive protoclusters and their IMF origin October 28th, 2016 F. Motte, AstroLille2016 4

Evolutionary sequence of low-mass star formation (1) Molecular cloud (started by Shu et al. 1987, see e.g. André et al. 2000, 2010) (2) Prestellar phase (~10 6 yr) Fragmentation and contraction Prestellar core 1-10 pc 3) Protostellar phase (~10 5 yr) Outflow Protostellar envelope Accretion and outflow 10 4 AU ~ 0.1 pc (4) Filament 0.03 pc Pre-main sequence phase (~10 6-10 7 yr) T Tauri star Proto-étoile Protostar 0.03 pc Protoplanetary disk

Open questions on high-mass star formation What physical mechanism does form high-mass (> 8 M!, OB) stars? Unlike low-mass stars, they emit copious UV radiation. Radiation barrier needs to be overcome for protostellar accretion to proceed. 1. powerful accretion from a turbulent core? (e.g., McKee & Tan 2003) 2. non-spherical and sporadic accretion from colliding flows? (e.g., Smith et al.09) 3. coalescence of low-mass protostars? (e.g., Bonnell & Bate 2002) What is the link between high-mass protostars, their parental clouds, and OB star clusters? Multi-scale studies of the earliest phases of high-mass star formation, feedback effects, and resulting clusters. October 28th, 2016 F. Motte, AstroLille2016 6

Molecular cloud complexes, more typical of Galactic disk clouds than those in the Gould Belt W43 in Hi-GAL: 7 10 6 M! 150 pc (Nguyen Luong et al. 2011b; Motte et al. 2014) (Figure adapted from Churchwell 2009) Sagitarius arm Local arm HOBYS mol. complexes: 10 5-10 6 M! 50-100 pc (Bontemps; Schneider et al. 2011) Orion in Gould Belt: 10 5 M! 50 pc October 28th, 2016 F. Motte, AstroLille2016 7

# Two surveys of star formation and cloud characteristics in denser environments than Gould Belt clouds The 9 closest cloud complexes forming high-mass stars. " FWHM = 50-100 pc " at d SUN = 0.7-3 kpc " M cloud = 2 10 5 1 10 6 M!# " Forming up to 20 M! stars " Herschel 70-500 µm, IRAM, The nearest cloud complex at the tip of the Galactic bar. " FWHM = 130 pc " at d SUN = 5.5 kpc " M cloud = 8 10 6 M! " Forming up to 50-100 M! stars " HI, CO, IRAM, Herschel, ALMA, # October 28th, 2016 F. Motte, AstroLille2016 8

Tight link between clouds and high-mass protostars DR21 ridge 10 4 M! 13 CO(1-0) IRAM 30m Gas inflow CygOB2, 45-100 O stars 8 pc 1mm and CO(2-1) outflow IRAM PdBI 100 pc Schneider et al. 2010 20 M!# protostars 0.05 pc Cygnus X with Herschel 70μm, 160μm, 250μm October 28th, 2016 Hennemann et al. 2012 F. Motte, AstroLille2016 Bontemps et al. 2010; Duarte Cabral et al. 2014 9

Spectral energy distribution of high-mass progenitors Herschel/PACS and SPIRE cover their SED peaks (10-50 K). Flux [Jy] Herschel ALMA Submm facilities Spitzer Submm telescopes & arrays probe clouds and protostellar envelopes. Spitzer traces heated envelopes and HII regions. Fréquence [GHz] Thermal dust emission is mostly optically thin at λ > 100 µm Accurate measurements of the gas mass reservoir associated with star formation (Herschel N H2 maps, see Hill et al. 2009, 2011) Herschel/HOBYS traces ~0.1 pc massive dense cores (MDCs) (Sub)mm interferometers trace ~0.01 pc individual protostars October 28th, 2016 F. Motte, AstroLille2016 10

Outline 1. Open questions and targeted clouds in the framework of the Herschel/HOBYS and W43-HERO surveys 2. Quest of the earliest phases of high-mass star formation: Do high-mass pre-stellar cores exist? 3. Discovery and characterization of 1-10 pc clouds forming massive star clusters: ridges 4. First measure of the core mass function (CMF) in massive protoclusters and their IMF origin October 28th, 2016 F. Motte, AstroLille2016 11

Scenario for the formation of high-mass stars (>8 M! ) (1) Molecular cloud complex (2) Prestellar phase? OB star cluster? 3) Protostellar phase (~10 5 years) Massive dense core (MDC) Gas inflows, protostellar accretion and ejection (4) (e.g. Beuther et al. 2002; Csengeri et al. 2011) HII regions (~10 5-10 6 years) Ionization, expansion 0.01-10 pc HII region UV 0.1 pc Outflow Inflows (e.g. Churchwell et al. 1999; Zavagno et al. 2007) 12

Water in high-mass stars with Herschel/WISH IR-bright protostars within HMPOs Many studies by the group of Beuther et al. suggest high accretion rates. Constraints on the evolution from IRquiet (young) and IR-bright (evolved) protostars: Protostellar accretion is stronger in the IR-quiet phase (Herpin et al. 2006) and high-enough to overcome radiation only in a few cases. Shocks (from outflows, ) enhance the water abundance (Chavarria et al. 2010; Herpin et al. 2012, 2016) 13

Searching for the earliest phases of high-mass stars Massive dense cores (MDCs): $ small-scale cloud fragments 0.01-0.1 pc with high mean density n H2 > 10 5 cm -3 $ With stellar activity protostellar MDC Without starless MDC IRAM 30m Motte, Bontemps, Schilke et al. 2007 IRAM 30m / MAMBO-2 1.2mm Constraints on the evolutionary sequence of high-mass star formation: Starless MDCs (100 M!, 0.1 pc) are fewer than protostellar MDCs (Motte et al. 2007; Russeil et al. 2010.) October 28th, 2016 F. Motte, AstroLille2016 14

Herschel/HOBYS images of high-mass star-forming regions October 28th, 2016 F. Motte, AstroLille2016 15

Census of starless MDCs with Herschel/HOBYS data Extraction & SED 4μm - 1mm 24 microns 4432 160 microns 4432 0.5 pc 70 microns 250 microns Mass (M! ) Concentration of MDC masses down to the scale of prestellar cores NGC6334 Massive protostars? Starless MDCs (0.2 pc, 100 M! ) 4432 Prestellar cores (0.02 pc, 1 M! ) (Tigé et al. 2016) Size (pc) Starless MDCs are less concentrated (less dense and substructured). They should rather host intermediate-mass prestellar cores (1-5 M!, 0.02 pc). October 28th, 2016 F. Motte, AstroLille2016 16

An ALMA view of the W43-MM1 mini-starburst protocluster 1mm, 0.4 resolution Scales probed: 2 500-40 000 AU (0.4-7 ) ALMA : 300 cores extracted Μass completeness ~ 0.6-3 M! Among massive cores, ongoing search for high-mass prestellar cores (Nony et al. in prep.). They are fewer high-mass prestellar core candidates than protostars. December 10th, 2015 F. Motte, SIM M2 17

Outline 1. Open questions and targeted clouds in the framework of the Herschel/HOBYS and W43-HERO surveys 2. Quest of the earliest phases of high-mass star formation: High-mass pre-stellar cores are short-lived and possibly even not existant. 3. Discovery and characterization of 1-10 pc clouds forming massive star clusters: ridges 4. First measure of the core mass function (CMF) in massive protoclusters and their IMF origin October 28th, 2016 F. Motte, AstroLille2016 18

Different cloud structures form low- & high-mass stars Disorganized network of filaments versus single dominating filamentary clouds N H2 map of Vela D Hill et al. 2011 N H2 map of the DR21 ridge Hennemann et al. 2012 low-mass protostars high-mass protostars October 28th, 2016 F. Motte, AstroLille2016 19

Ridges/Hubs are extreme clumps forming clusters of high-mass stars ~50% of the high-mass stars form in clusters within high-density elongated ridges, the other 50% form in spherical high-density hubs Ridge/Hub definition: 5-10 pc 3 /1 pc 3 above 10 4-10 5 cm -3 W43-MM1, MM2 ridges Spitzer IRDC hub We use the 100 A v level to identify them but it is not a physical threshold. 5 pc JHK See Hill+ 2011, Nguyen Luong+ 2011, Hennemann+ 2012, Didelon+ 2014, Nguyen Luong et al. 2013 SDC335; Peretto et al. 2013 October 28th, 2016 F. Motte, AstroLille2016 20

Most hyper-massive clumps should form by cloud global collapse Column density (cm -2 ) Gas flows along sub-filaments 13 CO(1-0) Global infall 0.2-1 km/s infall speeds Sub-filaments (2-14 x Taurus) N H2 > 10 23 cm -2, 15 000 M!, 5 pc 3, <n> ~ 10 4 cm -3 Hennemann et al. 2012 Schneider et al. 2010 See also Peretto+ 2013, 2014; Beuther+ 2012; Nakamura+ 2014 October 28th, 2016 F. Motte, AstroLille2016 21

In ridges & hubs, the gas reservoir is not a single core : gas is accreted onto ridges/hubs and in turn onto protostars Molecular cloud complex Schneider,, Hennebelle et al. 2010 Cloud ridge/ hub 1-10 pc OB star cluster Dynamical picture consistent with: - numerical simulations by Inoue & Fukui 2013; Gomez & Vazquez- Semadeni 2014; Smith et al. 2012 - local shears and shocks at protostellar scales (Csengeri et al. 2011a-b; Louvet et al. 2016) October 28th, 2016 F. Motte, AstroLille2016 22

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Outline 1. Open questions and targeted clouds in the framework of the Herschel/HOBYS and W43-HERO surveys 2. Quest of the earliest phases of high-mass star formation: 3. Discovery and characterization of 1-10 pc clouds forming massive star clusters: Ridges high-density collapsing clumps which feed protostars at their center. 4. First measure of the core mass function (CMF) in massive protoclusters and their IMF origin October 28th, 2016 F. Motte, AstroLille2016 24

The quest of the origin of the Initial Mass Function Submm continuum surveys and NIR extinction of nearby protoclusters suggest that the mass distribution of pre-stellar cores (CMF) mimics the form of the stellar IMF. Motte et al. 1998, 2001; Testi & Sargent 1998; Johnstone et al.2000; Stanke et al. 2006; Alves et al. 2007; Enoch et al. 2008; André et al. 2010; Könyves et al. 2010, 2015 The IMF is at least partly determined by fragmentaion at the pre-stellar stage. But studies limited to <5 M! stars in regions not typical of the main mode of star formation in galactic disks. October 28th, 2016 F. Motte, AstroLille2016 25

An ALMA view of the W43-MM1 mini-starburst protocluster 1mm, 2 500 AU resolution (Motte et al.; Nony et al.) Color: T dust model Contour: 1.3 mm Temperature contraints: at large scale with Herschel and very high density from hot core tracers. Extrapolation from our knowledge of outflows and gas heating. October 28th, 2016 F. Motte, AstroLille2016 26

An ALMA view of the IMF origin in the mini-starburst protocluster of the W43-MM1 ridge ~300 pre- and proto-stellar cores of 2000 AU size. The 3-100 M! part of the CMF is much flatter than the IMF. Could get even flatter with competitive accretion (Motte, Nony, Louvet et al. in prep.) + Lower-mass SF events Possible interpretations: - either this ministarburst IMF will be atypical - or OB star feedback will steepen the CMF, - or additional lower star formation events will build a steeper IMF, - or Completeness limit feedback October 28th, 2016 F. Motte, AstroLille2016 27

Preliminary conclusions Clouds forming high-mass stars and massive clusters: They are high-density, massive, and dynamical clouds, which we call ridges or hubs (2-10 pc 3 @ >10 4-10 5 cm -3 ). Star formation in mini-starburst ridges/hubs: Gravity braids filaments in a collapsing cloud attracting even more filaments. Stars and filaments simultaneously form and grow and may not go through a high-mass prestellar core phase. Star formation is intense in ridges and hubs. Origin of the initial mass function of stars (IMF) Core mass function of mini-starburst clusters may not mimics the IMF. How will accretion streams and feedback effect transform it into the IMF? October 28th, 2016 F. Motte, AstroLille2016 28