Stochas(c Stellar Feedback in Low-Mass Galaxies Chris Power, - - PowerPoint PPT Presentation

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Stochas(c Stellar Feedback in Low-Mass Galaxies Chris Power, - - PowerPoint PPT Presentation

Sep 27, 2022 261 likes •435 views

Stochas(c Stellar Feedback in Low-Mass Galaxies Chris Power, ICRAR/UWA with Lilian Garra,-Smithson, Mark Wilkinson, Graham Wynn (U Leicester), Mar<n Bourne (KICC Cambridge) The Role of Gas in Galaxy Dynamics, Malta, October 2017 1 What do

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Stochas(c Stellar Feedback in Low-Mass Galaxies

Chris Power, ICRAR/UWA

with Lilian Garra,-Smithson, Mark Wilkinson, Graham Wynn (U Leicester), Mar<n Bourne (KICC Cambridge)

The Role of Gas in Galaxy Dynamics, Malta, October 2017

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What do we mean by stochas(c feedback?

  • Condi<ons for massive stars capable of producing poten<ally

disrup<ve feedback - UV photo-ioniza-on, strong winds, supernovae, X-ray binaries - not determinis(c.

  • Effects most likely to be pronounced in low-mass galaxies, reflec<ng;
  • Inefficient star forma<on & triggering by perturba(ons.
  • Low masses of star forming regions & random sampling of ini(al

mass func(on regulates numbers of massive stars.

  • Inefficient stellar feedback – sites of star forma<on biased

towards central regions, sensi(ve to local condi(ons (e.g. gas density, cooling, radia<on field, etc..)

  • Forma<on paths of binaries into energe<c (high) mass X-ray

binaries subject to complex evolu(on

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What is the impact of stochas(c feedback?

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  • 1. Low masses of star forming regions & random sampling of ini(al

mass func(on regulates numbers of massive stars.

  • 2. Inefficient stellar feedback – sites of star forma<on biased towards

central regions, sensi(ve to local condi(ons (e.g. gas density, cooling, radia<on field, etc..)

  • 3. Forma<on paths of binaries into energe<c (high) mass X-ray binaries

subject to complex evolu(on How does this stochas(city impact the abundance and star forma(on histories in low-mass galaxies?

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M31

  • Occupancy of low-mass dark ma,er sub-

haloes with satellite galaxies apparently stochas(c (e.g. Boylan-Kolchin et al. 2011)

  • Power et al 2014 - result of stochas<c star

forma<on and feedback?

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Stochas(c Feedback in Low-Mass Halos I

Essen(al Idea

  • Binding energy of gas comparable

to a single supernova in halo with 108-109 M¤

  • Star forma<on proceeds in random
  • rder in molecular clouds.
  • Pre-MS <mescale varies as M-2.5 –

high mass stars form more rapidly than lower mass counterparts.

  • How does this influence stellar

popula<on that forms…?

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NGC1569 Credit: ESA/NASA

Power et al. 2014

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Stochas(c Feedback in Low-Mass Halos II

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Power et al. 2014 Model

  • Monte Carlo Merger Trees for

distribu<on of progenitors of present-day low-mass halos.

  • Mvir=107.7-1010 M¤ at z=0
  • When were they first massive

enough to support cooling, i.e. Tvir~103-104 K?

  • Es<mate binding energy of gas in

halo progenitor, and energy liberated by supernovae, assuming stochas-c high mass star forma-on.

Redshi> when cooling first supported. 0 10 20 30 40

1010 M¤ 107.7 M¤

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Stochas(c Feedback in Low-Mass Halos III

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Power et al. 2014

More massive subhalos at z=0 support cooling earlier – feedback can have greater effect, but more <me to re-accrete gas and form stars – effects of stochas(city more pronounced for lower mass subhalos.

Late forming, low-mass haloes at present day

Note spread in zcool Zcool Zcool P(Zcool) Log10 fbind=ESN/Ebind

0 10 20 30 40 0 10 20 30

Reioniza(on Complete

Note spread in fbind

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Locally Regulated Feedback Efficiency I

Assump(on: Stellar-driven oujlows (winds, supernovae) sufficiently energe<c to expel ambient gas from the galaxy. Caveat: How oujlow couples to ambient gas is as important as energy and momentum carried by the oujlow. Test: Use hydrodynamical simula<ons to explore coupling of stellar wind driven oujlow from a nuclear star cluster couples to gas.

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From Bourne & Power 2016

Feedback from mul-ple sources superposes, seeds dense clumps in the ouAlow, frac-on of mass expelled lower than one might naively expect.

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Locally Regulated Feedback Efficiency II

Problem: MulEple sources less efficient at clearing out gas from nuclear regions – seeds dense clumps robust to feedback – available to grow stars, grow central black hole?

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Radial Inflow

From Bourne & Power 2016

Mul(ple Sources Single Source

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Locally Regulated Feedback Efficiency III

Problem: Cooling efficiency will influence rapidity with which gas clumpiness is seeded – and therefore efficiency with which gas is expelled from the poten<al.

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Radial Inflow

From Bourne & Power 2016

Efficient cooling Inefficient cooling

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High Mass X-Ray Binaries (XRBs)

  • Binary frac<on for massive stars close to unity; some uncertain frac<on

survives to form high mass X-ray binaries (e.g. Sana et al. 2012).

  • Compact object accretes from main sequence companion via wind

capture or Roche Lobe Overflow.

  • Accre<on liberates energe<c radia<on with luminosity

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XRBs poten(ally important stochasEc source of feedback?

Sana et al. 2012

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HMXB Photo-Ionizing Feedback I

  • Explore ionizing output – UV

and X-ray - from a coeval stellar popula<on as a func<on of

  • IMF (e.g. Kroupa, Chabrier)
  • HMXB survival frac<on
  • HMXB spectra (hard to sop)
  • Can extend photo-ionizing

life(me of star cluster up to >80 Myrs….

  • … but photo-ionizing feedback

is non-local in nature.

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From Power et al. 2009

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HMXB Photo-Ionizing Feedback II

Ionizing power depends on hardness of spectrum (Power et al. 2009) – power-law spectra usually assumed, but more realis<c empirical spectra have quite different shape (Power et al. 2013). Energy available for ioniza(on indicates importance…!

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From Power et al. 2013 From Power et al. 2009

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HMXB Kine(c Feedback I

  • Cygnus X-1 - stellar mass black

hole fed by wind accre<on.

  • Gallo et al. 2005 - amount of

energy in form of kine<c feedback (i.e. jet) as high as photo-ionizing feedback (i.e. X-ray luminosity).

  • Expect outbursts to occur over

an extended period of <me.

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Jet inflates a lobe that is

  • ver-pressured rela<ve to

its surroundings, driving a thermalising shock Gallo et al. 2005

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HMXB Kine(c Feedback II

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From Garrah-Smithson, Wynn, & Power, In Prep Hydrodynamic simula<ons to explore impact of kine(c feedback from HMXBs in addi<on to supernovae, in isolated star-forming clouds Gradual injec-on of energy acts to open up chimneys, releases thermal pressure, alters star forma-on rate. Lilian Garrah-Smithson Final year PhD student

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HMXB Kine(c Feedback III

  • Inherently stochas<c
  • Single ULX outburst

powerful enough to unbind gas in a dwarf galaxy

  • Loca(on, loca(on,

loca(on….

  • Can sweep galaxy free of

gas…

  • … or triggers star forma<on.

Power & Bourne, In Prep

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Summary

  • Sound physical reasons to expect that effects of stochas(c feedback

should be especially important in low-mass galaxies.

  • Not captured in current galaxy forma<on models – a physics and numerical

resolu<on problem. Necessary to reconcile theory and observa<on?

  • How energy couples to ambient gas can drama<cally impact

efficiency of gas explusion and influence subsequent star forma<on – very sensi<ve to local condi<ons

  • Photo-ioniza<on? Gas frac<on? Instabili<es?
  • High mass X-ray binaries – whose forma<on is effec<vely stochas(c -

can release significant amounts of energy, providing non-local feedback and powerful kine<c oujlows.

  • Drive turbulence in gas rich galaxies at high redship? Suppress collapse of gas
  • nto low-mass halos?

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