Davide Elia INAF-IAPS, Roma

1. Progresses on our understanding the processes of star formation in the Milky Way from Herschel observations Part IIThe Herschel photometric surveys Davide Elia INAF-IAPS, Roma

2. Herschel and star formation The wavelength range covered by the cameras on board Herschel containsthe emission peak of the cold dust. It is suited for studying the dense cloudsand the early stages of star formation!

3. Nature of the compact sources In a pre-Herschel SED analysis of sample of 42 intermediate and high-mass star forming region from the sample of Molinari et al. (1996), a Class 0-I-II sequence analogous to the low-mass regime was suggested: Warm Cores to Hot Cores to HII-driving objects Molinari et al. 2008 • Warm Cores SED sources are under-luminous with respect to UCHII/HotCores of similar envelope mass • Concurring indications suggesting that the dominant source in the Warm Core objects is not yet on the ZAMS Hot Core ZAMS Warm Core ACCRETION

4. Nature of the compact sources Molinari+ 2008Elia+ 2010 ZAMS S≈1 g cm-2 ACCRETION Krumholz & McKee (2008) A significant fraction of the clumps should be already forming high-mass protostars (M≥10M) Problem: Sources in Hi-GAL are mostly clumps, while SED models are available for single YSOs (Robitaille et al. 2006)

5. Herschel photometric surveys of star forming regions Gould Belt 460 hrs André et al. 2010, A&A, 518, L102 HOBYS 125 hrs Motte et al. 2010, A&A, 518, L77 Hi-GAL 900 hrs Molinari et al. 2010, PASP, 122, 314

6. Photometric imaging of nearby (d < 0.5 kpc) molecular clouds • Formation of solar-type stars • Reasonably well established evolutionary sequence, but physics ofearly stages unclear • What determines the distribution of stellar masses = the IMF? • What generates prestellar cores & what governs their evolution to protostars? • Timescale of core/star formation? Quasi-static or dynamic process? ?

8. Aquila rift and Polaris flare André et al. 2010, A&A, 518, L102; Könives et al. 2010, A&A, 518, L106

9. BTW: How to calculate N(H2) and T maps? • Pixel-to-pixel grey-body fit • Regrid the Herschel maps onto the map at the largest wavelength available (usually λMAX = 500 μm). • Reconvolve them with the Herschel FWHM at λMAX • Perform the pixel-to-pixel fit (time consuming: parallel computing is recommended)

10. Aquila rift and Polaris flare André et al. 2010, A&A, 518, L102; Könives et al. 2010, A&A, 518, L106 Prestellar cores are only observed above the threshold AV = 7 because they form out of a filamentary background and only the supercritical, gravitationally unstable filaments are able to fragment into bound cores.

11. Two First Hydrostatic Cores in Perseus Pezzuto et al. 2012, A&A, 547, A54 • FHCDifficult to see it, because it is: • Short-lived (t = 102-103 yr) • Invisible in the MIR • Hard to resolve, even at near distances (size = several AU) Perseus, d  235 pc

12. Two First Hydrostatic Cores in Perseus Pezzuto et al. 2012, A&A, 547, A54 envelope: T = 9 K , M = 7.3 Mʘ envelope: T = 9.4 K , M = 8 Mʘ The two sources are situated a few 10^3 AU apart, corresponding to a few Jeans lengths. It is then possible that these two sources formed at almost the same time from the fragmentation of a larger structure.

13. Photometric imaging of all the high-mass star forming regions at d < 3 kpc These data can allow us to determine the importance of external triggers for high-mass star formation in the nearest massive molecular cloud complexes.

14. Filaments in the Rosette molecular cloud Schneider et al. 2012, A&A 540, L11 “Confidence map” highligthing the filament junctions O-stars from NGC 2244 Existing infrared clusters and the most massive dense cores (potential sites of future massive star formation) identified in the same data set are overlaid on the image. All sources lie in the proximity of junctions

15. O-stars from NGC 2244 PDFs of the Rosette molecular cloud Schneider et al. 2012, A&A 540, L11

16. The Vela–C cloud Giannini et al. 2012, A&A 539, A156 HOBYS 3 deg2 b = 0º BLAST 250 μm It is the cloud “C” of the Vela Molecular Ridge (Murphy & May, 1991) distance = 700 ± 200 pc (Liseau et al. 1992) Site of star formation on a wide range of masses (Massi et al. 2003; Baba et al. 2006)

17. Vela–C - Compact source extraction • Sources are searched separately on each map • CuTEx: sources detected as local maxima in the curvature map (2nd derivative) • An elliptical Gaussian is fitted on them, and geometric parameters estimated • A list of sources with S/N>5 is obtained at each λ

18. Vela–C - SED fitting Giannini et al. 2012, A&A 539, A156 The SEDs eligible for the grey-body fit have been selected applying few constraints: i) fluxes at least 3 adjacent bands between 160 and 500 μm; ii) without concavities; iii) no peak at 500μm; iv) spatially resolved at 160 μm; v) not presenting multiple associations at λ ≥ 160 μm; vi) not belonging to the RCW34 region 268 objects selected for fit

19. Vela–C - Pre-stellar sources Giannini et al. 2012, A&A 539, A156 To determine if a starless source is gravitationally bound (then pre-stellar), a comparison of its mass with the corresponding Bonnor-Ebert mass has been performed: 206 out of 218 starless sources shave been recognized as pre-stellar (~94%, probably affected by selection). In the mass vs size plot, all the unbound starless sources lie below the Bonnor-Ebert mass curve at T = 8 K.

20. Vela–C - An evolutionary framework Giannini et al. 2012, A&A 539, A156 Although not completely separated, the pre- and proto-stellar core samples show a global trend to populate different regions of the diagram. Class 0 For proto-stellar cores, Lbol is probably underestimated, resulting in an underestimate of their actual age.

21. Kramer et al. 1998 D< 0.08 pc Kroupa 2001 Chabrier 2005 This work Vela–C - The Source Mass Distribution Giannini et al. 2012, A&A 539, A156 Vela-C :γ=1.1±0.2 Aquila RiftKönives et al. (2010): γ=1.45±0.2 (M > 0.3 Mʘ) Orion A Polychroni et al. γ=1.5±0.5, Ikeda et al. γ=1.3±0.1 (M > 9.3 Mʘ) Orion B Johnstone et al. 2006 γ=1.5±0.42 Perseus+Serpens+OphiuchusEnoch et al. 2008: γ=1.3±0.2 (M > 0.8 Mʘ)