SAM GEEN (ITA/ZAH HEIDELBERG)

Transcription

1 SAM GEEN (ITA/ZAH HEIDELBERG) WITH PATRICK HENNEBELLE JUAN SOLER AND RALF KLESSEN Credit: Lost Valley Observatory

2 Star formation is self regulating HII HII regions, regions, supernovae supernovae Molecular Molecular Cloud Cloud Stars Stars form form in in dense dense gas gas in in molecular molecular clouds clouds Massive Massive stars stars drive drive outflows outflows via via radiation, radiation, winds, winds, jets jets Dense Dense gas gas is is expelled, expelled, star star formation formation ends ends

3 How Many Stars Stars Stars form form from from dense dense gas gas with with some some given given efficiency efficiency factor factor Lada+ Lada+ (2010), (2010), Heiderman+ Heiderman+ (2010) (2010) and and others others argue argue for for a a fixed fixed efficiency efficiency in )) threshold in gas gas above above a a column/surface column/surface density density (Σ (Σgas threshold in in local local clouds clouds gas Other Other suggestions suggestions that that in in reality, reality, star star formation formation is is related related to to volume volume density density (Krumholz+ (Krumholz+ 2012, 2012, Clark Clark & & Glover Glover 2014), 2014), and... and......volume...volume density density ρ ρ has has no no single single mapping mapping to to column column density density Σ Σ (depends (depends on on the the depth depth of of the the gas, gas, too) too) Complicating Complicating the the picture picture are are environmental environmental effects, effects, turbulence, turbulence, magnetic magnetic fields fields and and energetic energetic stellar stellar processes processes (lots (lots of of previous previous work, work, see see Hennebelle Hennebelle & & Falgarone Falgarone 2012, 2012, Dale Dale (reviews), (reviews), Mac Mac Low Low & & Klessen Klessen 2004, 2004, Elmegreen Elmegreen & & Scalo Scalo 2004, 2004, McKee McKee & & Ostriker Ostriker 2007, 2007, Hennebelle Hennebelle & & Chabrier Chabrier 2008,11,13, Wang+ 2010, Padoan & Nordlund 201 1, Federrath & Klessen 2012, Dobbs+ 2013, Krumholz ,11,13, Wang+ 2010, Padoan & Nordlund 2011, Federrath & Klessen 2012, Dobbs+ 2013, Krumholz Dale+ Dale+ 2014, 2014, Padoan+ Padoan+ 2014, 2014, and and far far more, more, ifif II forgot forgot a a reference reference come come shout shout at at me me in in the the break) break) Can Can we we reproduce reproduce these these observed observed relations relations with with simulations? simulations?

4 Simulations Use AMR code RAMSES-RT + MHD (Teyssier 2002, Fromang et al 2006, Rosdahl et al 2013, 2015) Take an isothermal gas sphere of 1044 Msun four sizes, labelled L (diffuse), M, S and XS (densest) Include Kolmogorov turbulence, self-gravity, B-field (20 μg peak in cloud M at t=0) Put it in a box, refine in the central volume and on Jeans unstable cells (effective resolution ) Max resolution 0.03 pc in L and M, in S and in XS Relax the cloud with reduced gravity for 1 freefall time, then allow sink particles to form Sink particles emit photons treat cluster as a population and distribute photons across sinks Trace ionising photons with M1 method photons are a fluid on the AMR grid See Geen, Hennebelle, Tremblin & Rosdahl, 2015 or 2016 for previous setups

5 Processing the SImulations Stars Stars form form in in the the cloud. cloud. They They produce produce UV UV radiation, radiation, which which heats heats the the gas. gas. This This drives drives outflows, outflows, which which stop stop accretion accretion and and end end star star formation formation locally. locally. Star Star formation formation happens happens in in other other places places in in the the cloud cloud Eventually, Eventually, all all dense dense gas gas is is depleted. depleted. We We want want a a simple simple first-order first-order estimate estimate of of observed observed properties properties of of our our clouds clouds We We make make gas gas column column density density maps maps of of the the simulations simulations and and identify identify pixels pixels above above a a density density threshold threshold We We identify identify the the fraction fraction of of sink sink particle particle mass mass in in Young Young Stellar Stellar Objects Objects (YSOs, (YSOs, formed formed in in the the last last ~3 ~3 Myr) Myr) inside inside the the cloud cloud (in (in comparison comparison to to Lada+ Lada+ 2010) 2010) L cloud Red: Young stars White: Old stars

6 Our clouds vs Reality We We convolve convolve our our maps maps with with the the PSF PSF of of various various instruments instruments (Via Juan Soler, see Planck Paper XXXV) (Via Juan Soler, see Planck Paper XXXV) LL cloud cloud is is most most similar similar to to nearby nearby clouds clouds PSF reduces upper end of density PSF reduces upper end of density curve curve Column density Sink particles Volume density

7 Total SFE of a cloud Total stellar mass per initial cloud mass We We define define this this as as the the fraction fraction of of the the initial initial cloud cloud mass mass that that is is accreted accreted onto onto sink sink particles particles Stars Stars form form in in localised localised bursts bursts in in the the cloud cloud UV UV photoionisation photoionisation heats, heats, pushes pushes out out dense dense gas, gas, ends ends local local accretion accretion Eventually, Eventually, all all star star formation formation in in the the cloud cloud ends ends SFE SFE (with (with radiation radiation included) included) is is a a sum sum over over independent independent local local star star formation formation events events ~~ Myr Myr long long SFR per sink particle

8 ''ObservEd'' SFE Observed SFE = YSO mass / dense gas mass Lada We We measure measure recently recently accreted accreted mass mass (YSOs) (YSOs) // mass mass in in pixels pixels above above a a column column density density limit limit (equivalent (equivalent to to Lada+ Lada+ 2010) 2010) Without Without UV UV photoionisation, photoionisation, only only weak weak dependence dependence between between SFE SFE and and cloud cloud initial initial conditions conditions With With UV UV photoionisation, photoionisation, SFE SFE drops drops dramatically dramatically in in the the most most diffuse diffuse clouds clouds (see (see Geen+ Geen+ 2015, ,16 for for discussion discussion of of stalling stalling of of ionisation ionisation fronts) fronts) Caution Caution about about denser denser clouds: clouds: these these start start with with high high gas gas densities densities need need a a mechanism mechanism to to collect collect gas gas at at this this mass mass with with no no star star formation formation Dense gas mass (Ak > 0.8)

9 Some Thoughts Stars form in dense gas in molecular clouds. They regulate their environment through energetic processes such as UV photoionisation Stars form in short local (0.1-1 Myr) bursts Different Different star star formation formation efficiency efficiency (SFE) (SFE) measures measures in in simulations simulations vs vs observations observations No No clear clear 1:1 1:1 mapping mapping between between the the two two Comparisons Comparisons should should be be made made carefully! carefully! Our simulations lie on observed trends, but only for local-like clouds Are denser clouds rarer? Are our initial conditions too artificial / don't exist in reality? Need more work on role of environment in setting the SFE Other things to be wary about: Missing physics (winds, jets, other forms of radiation, external forces,???) Resolution issues? Sensitivity in sink formation / stellar energy output recipe More analytic/quantitative work needed on role of regulation of SFE by stars

10 ANY QUESTIONS? If If you you enjoyed enjoyed this this talk, talk, why why not not try try one one of of our our other other papers? papers? GEEN, GEEN, HENNEBELLE, HENNEBELLE, TREMBLIN, TREMBLIN, ROSDAHL ROSDAHL (2015) (2015) GEEN, GEEN, HENNEBELLE, HENNEBELLE, TREMBLIN, TREMBLIN, ROSDAHL ROSDAHL (2016) (2016)

11 Extra slides HIDDEN SECRETS

12 What Else? Winds Winds are are important important Difficult Difficult to to simulate simulate (high (high T, T, small small dt) dt) See, See, e.g., e.g., Rogers Rogers & & Pittard Pittard (2013), (2013), several several people people here here Geen et al 2016 Supernovae Supernovae happen happen too too late? late? (4 (4 Myr+) Myr+) 5 Difficult Difficult to to destroy destroy a a massive massive (10 ( Msun) Msun) cloud cloud See See Walch Walch & & Naab Naab 2015, 2015, Geen+ Geen+ 2016, 2016, Haid+ Haid+ 2016, 2016, Padoan+ Padoan (and (and more) more)

13 What else? Radiation Radiation pressure pressure might might be be important? important? (Lots (Lots of of debate debate still) still) Early Early images images this this simulation simulation had had a a bug, bug, but but itit looks looks like like a a duck duck so so \_( \_( ツ ツ )_/ )_/ Cyan: ionised Red: neutral We We can can do do better better comparisons comparisons with with observations observations see see talk talk by by Eric Eric Pellegrini Pellegrini tomorrow tomorrow (Image (Image from from prototype prototype 3D 3D visualisation) visualisation)

14 What do we see? Sample Sample YSO YSO mass mass // gas gas mass mass every every Myr Myr Gould Gould Belt-like Belt-like simulations simulations lie lie on on observed observed trend trend Lada Sink particles

15 Comparing SFEs Sink particles Gigantic Gigantic mess, mess, no no good good 1:1 1:1 mapping mapping (factor (factor of of variation) variation)

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17 NO MORE SLIDES WE ARE DONE