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Hi-GAL: Mapping the Inner Galactic Plane with Herschel

Hi-GAL is an infrared survey using Herschel to map the inner Galactic Plane, studying star formation, dust structures, and the nature of thresholds in the interstellar medium. The survey covers a wide range of galactocentric radii, metallicity, and environmental conditions.

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Hi-GAL: Mapping the Inner Galactic Plane with Herschel

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  1. Hi-GAL composite 47° > l > 36° Hi-GAL The Herschel infrared Galactic Plane Survey S. Molinari – INAF/IFSI, Rome Hi-GAL team IFSI - Arcetri - Univ. Rome 1/2 - Univ. Lecce (Italy), CESR - OAMP - IAS - Saclay (France), RAL - Herts - Liverpool - Cardiff - UCL (UK), IPAC/SSC/JPL - Univ. Colorado - CfA (USA), Toronto - Calgary - U. Laval (Canada), MPIfR - (Germany) et al. 20”

  2. Hi-GalA Herschel Key-Project for the Far-IR mapping of the inner Galactic Plane • -60°<l<60° - |b| <1°, i.e. the GLIMPSE and MIPSGAL areas • 5 bands 70-500m imaging using PACS and SPIRE in Parallel Mode with crossed-rasters • Area already surveyed in continuum and spectroscopy over few wavelength decades Galaxy-wide Census, Luminosity, Mass and SED of dust structures at all scales from massive YSOs to Spiral Arms

  3. Hi-GALThe Herschel infrared Galactic Plane Survey • The High-Mass Star Formation Timeline • Measure the star formation rate and history Galaxy-wide • Cold dust in the Galactic Plane and the Formation of Molecular Clouds • Understanding star formation laws and the nature of thresholds as a function of ISM properties across a full range of galactocentric radii metallicity and environmental conditions • Determining the relative importance of global vs local, spontaneous vs triggering, agents that give rise to star formation. • Build bottom-up recipes and prescriptions useful for Xgal science -70°< l < 70° |b|<1° - 70/160/250/350/500mm – 343 hours Toward a Predictive Global Model of Galactic Star Formation 20”

  4. Hi-GAL 70/160/350 Composite – Molinari+ 10 1” Bally+ 10 W43 PACS 160 Beuther et al. 2007 G29.96-0.02 Motte, Schilke & Lis 2003 The black circle is the ALMA Band 9 primary beam !! Herschel is crucial for ALMA

  5. Nature of the compact sources A Mass-Size power-law with exponent 1.33 is found to discriminate structures on the basis of their ability to form massive stars (Kauffmann et al. 2010) The majority of sources are dense clumps which should be able to form M* > 10 M stars.

  6. Nature of the compact sources Jeans conditions for gravitational instability Mean Clumps Temperature The majority of the detected cores are gravitationally supercritical M=MJ

  7. Krumholz & McKee (2008) Nature of the compact sources L/M due to accretion onto low-mass protostars, at given SFR and IMF Molinari+ 2008 ZAMS L/M where accretion radiation is sufficient to halt fragmentation of low-mass cores S≈1 g cm-2 ACCRETION A significant fraction of the clumps should be already forming high-mass protostars (M≥10M)

  8. However… The actual core surface density is significantly below what the Krumholz & McKee 08 theory predicts (Elia+ 10) Other agents supporting against fragmentation, other than accretion radiation from low-mass protostars, must be at work. Magnetic field is a possibility (Commerçon+ 10, although in a slightly different context)

  9. The Filamentary Nature of Star Formation Molinari+ 10 l = 59° - SPIRE 250

  10. Filament and compact objects • Compact sources are mostly found associated to filamentary structure • There is no apparent correlation between mass of compact sources and the column density of the hosting filament • There is a strong suggestion for a threshold effect around AV≈1 Hollenbach et al. 1991

  11. Filament fragmentation Preliminary filament section measurements in the l=59° region give values between 0.5 and 1pc. Heitsch et al. 2008 Local filaments density Local filaments temperature Conclusion: filaments form from diffuse ISM and grow in column density until at AV≈1 heating and cooling go out of balance. Gravitational instability comes in and high-density fragments start to appear.

  12. Is B important in filament fragmentation ? Filaments M/F=1 Crutcher et al. 2010 Fiege & Pudritz 2000 Filaments hosting compact sources span a N(H2) range which is compatible with structures losing magnetic support and starting to collapse

  13. Census of Filaments (Schisano+, in prep.) Automated Filament Detection • Complete catalogue of filaments • Statistics of filaments length and cross-size • Multi-scale analysis to obtain hierarchical information

  14. Properties of filaments and their relationship to cores/clumps(Schisano+, in prep.) • Cross-matching to compact source catalogues to: • subtract flux of compact sources from the integral under the RoIs • Obtain statistics of filament/clump associations • Subtract background from nearby regions • Fit greybodies to measure Masses and Temperatures • Cross-match to molecular line databases to (e.g. GRS) to obtain velocity dispersion: virial masses, confirm physical nature, …

  15. and Lights The Earliest Stages of High-Mass SF : Shadows… D=3kpc Peretto+ 10 PACS 70 PACS 160 SPIRE 250 D=12 kpc • ALMA will allow comprehensive studies of SF regions over the entire Galaxy, “unlocking” access to the same level of detail we currently have for nearest regions • Hi-GAL will constitute the essential input database for statistically significant studies of the earliest stages of massive SF and the lifetime of pre-stellar phase • ALMA will enable us to • resolve the Jeans length Galaxy-wide • address the early fragmentation of clumps and filaments across a variety of Galactocentric distances, metallicities and environmental conditions (morphology, chemistry and dynamics)

  16. Triggered Star Formation(5’x5’ field) – Zavagno+ 10

  17. Hi-GAL coming along… SPIRE 250mm 300° 298° 296° 294° 292° 290°

  18. The future is bright ALMA avoidance (d<+40°) • The outer Galaxy is unique to complete a large and otherwise uncharted parameters space: • Get SFR, SFE, SFH vs R. Different SF thresholds ? Different S-K law ? • Is the path from clouds to protostars the same ? Different timescales ? Different agents ? • Build the bottom-up recipe of an entire Galaxy The HOTAC granted 278 hours in OT1 to cover another 120° longitude range centered on the anti-center. The greater Hi-GAL now covers 520 sq. deg. Most of it will be accessible by ALMA !!

  19. The future is bright ALMA avoidance (d<+40°) Hi-GAL is a goldmine for the Community to peruse !! For your science….to plan ALMA science….to maximize ALMA science Data are already public as they come out of the standard pipeline The Hi-GAL Consortium will start incremental releases of high-quality products (images and catalogues) 6 months after the data taking of 1st survey The SDP tiles enhanced products will be released shortly

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