Molecular g gas a as a a d dynamical IMF v variation probe o - - PowerPoint PPT Presentation

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Molecular g gas a as a a d dynamical IMF v variation probe o - - PowerPoint PPT Presentation

May 27, 2023 647 likes •1.04k views

Molecular g gas a as a a d dynamical p probe o of Molecular g gas a as a a d dynamical IMF v variation probe o of I IMF v variation Timo mothy A y A. Da . Davis Ernest Rutherford Fellow & Lecturer, Cardiff University With

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Molecular g gas a as a a d dynamical p probe o

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IMF v variation

Molecular g gas a as a a d dynamical probe o

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IMF v variation

Timo mothy A y A. Da . Davis Ernest Rutherford Fellow & Lecturer, Cardiff University

With R. McDermid, and with thanks to the ATLAS3D and WISDOM teams

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Stars in the Milky Way seem to form following a universal initial mass function.

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Stars in the Milky Way seem to form following a universal initial mass function. For every high mass star formed…

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Stars in the Milky Way seem to form following a universal initial mass function. For every high mass star formed… a fixed number of low mass stars also form

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Stars in the Milky Way seem to form following a universal initial mass function. For every high mass star formed… a fixed number of low mass stars also form

In the Milky Way: Kroupa/Chabrier IMF

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We typically assume this is true in

  • ther galaxies too. This

assumption underpins almost everything we know about galaxy formation…

  • Luminosity à Mass
  • Flux à SFR
  • Supernova rates
  • Metal enrichment
  • Dust formation and gas return to

the ISM

Hα UV FIR Radio Cont.

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e.g. Cappellari et al., 2012

Stellar Kinematics

  • 1. Measure the mass of a galaxy with

stellar kinemaQcs / lensing

  • 2. Measure the light emiRed using

imaging.

  • 3. Compare M/L with that expected

given the stellar populaQon present Lensing Stellar populations

Stellar Kinematics / Lensing

The IMF is clearly crucial. How is it measured extragalactically?

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Molecular g gas a as a a d dynamical p probe o

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à Mass of star à à dN/N à Why the M/L? Milky Way IMF: Reference M/L

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Molecular g gas a as a a d dynamical p probe o

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à Mass of star à à dN/N à Most mass here Milky Way IMF: Reference M/L Why the M/L?

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Molecular g gas a as a a d dynamical p probe o

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à Mass of star à à dN/N à Most mass here Most light here Milky Way IMF: Reference M/L Why the M/L?

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Molecular g gas a as a a d dynamical p probe o

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à Mass of star à à dN/N à Most mass here Most light here Top heavy IMF: More light for a very similar mass Milky Way IMF: Reference M/L Why the M/L?

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à Mass of star à à dN/N à Most mass here Most light here Top heavy IMF: More light for a very similar mass Milky Way IMF: Reference M/L Bottom heavy IMF: More mass and less light For any age, metallicity and IMF stellar models predict the M/L Why the M/L?

M/Lpop(Age, Z, [α/Fe], IMF)

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e.g. Conroy and van Dokkum et al., 2011

Stellar Kinematics

  • 1. Use gravity sensiQve features within

spectra of galaxies.

  • 2. More dwarf stars à stronger abs. in

those bands

  • 3. Infer the IMF required to give those

line strengths, given the age/Z of populaQon Lensing Stellar populations

Stellar populations

The IMF is clearly crucial. How is it measured extragalactically?

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So is this assumption of a universal IMF a good one?

  • Seems to work reasonably well

for spiral galaxies

(Bell+deJong01, Kassin+06, Bershady+11, Brewer+12) Lenses from Brewer+12

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So is this assumption of a universal IMF a good one?

  • Seems to work reasonably well

for spiral galaxies

  • What about early-type galaxies

(ETGs)?

(Bell+deJong01, Kassin+06, Bershady+11, Brewer+12) Lenses from Brewer+12

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IMF appears to vary with:

Martin-Navarro et al., 2015

  • Metallicity
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IMF appears to vary with:

Cappellari et al., 2013

  • Metallicity
  • Velocity dispersion
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IMF appears to vary with:

Conroy & van Dokkum 2012

  • Metallicity
  • Velocity dispersion
  • Alpha element

abundances…

  • etc
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IMF appears to vary with:

  • Metallicity
  • Velocity dispersion
  • Alpha element

abundances…

  • etc

BUT:

  • Lack of consistency

between methods!

  • Stellar kinematics
  • Stellar pops
  • Lensing

Smith 2014

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IMF appears to vary with:

  • Metallicity
  • Velocity dispersion
  • Alpha element

abundances…

  • etc

BUT:

  • Lack of consistency

between methods!

  • Stellar kinematics
  • Stellar pops
  • Lensing

Smith 2014

Can molecular gas kinematics help?

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Our technique:

  • 1. Take an ETG with molecular gas

Davis & McDermid 2017

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Our technique:

  • 1. Take an ETG with molecular gas
  • 2. Observe with an IFU

à get age, metallicity etc à Predict M/L for an assumed IMF

M/Lpop(Age, Z, [α/Fe], IMF)

Davis & McDermid 2017

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Our technique:

  • 1. Take an ETG with molecular gas
  • 2. Observe with an IFU

à get age, metallicity etc à Predict M/L for an assumed IMF

  • 3. Take image of galaxy, measure light

as a funcQon of radius

M/Lpop(Age, Z, [α/Fe], IMF)

Davis & McDermid 2017

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Our technique:

  • 1. Take an ETG with molecular gas
  • 2. Observe with an IFU

à get age, metallicity etc à Predict M/L for an assumed IMF

  • 3. Take image of galaxy, measure light

as a funcQon of radius

  • 4. Model CO kinemaQcs to give mass

as a funcQon of radius

  • 5. Compare M/L_dyn to M/L_pop

à IMF! ALSO: have radial information!

M/Lpop(Age, Z, [α/Fe], IMF)

Davis & McDermid 2017

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Davis & McDermid 2017

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Davis & McDermid 2017

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Salpeter type IMFs strongly ruled out Davis & McDermid 2017

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Davis & McDermid 2017

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Salpeter type IMFs needed… Davis & McDermid 2017

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Davis & McDermid 2017

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Intermediate needed? Davis & McDermid 2017

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Good agreement with prior measurements Davis & McDermid 2017

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Do we reproduce find local/global drivers found by others? NO

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Do we reproduce find local/global drivers found by others? NO

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  • Molecular gas provides a nice alterna6ve dynamical tracer of

the mass in galaxies

  • IMF varia6on seems to be required
  • Stellar kinema6c mismatch parameters reproduced…
  • But at least in these 7 objects no clear driving correla6on seen
  • Metallicity rela6on not reproduced
  • Sigma correla6on may hold globally, but not locally?

Next step: more massive systems (ALMA), spirals

Davis & McDermid 2017 (arXiv:1609.03559)

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So what is the cause of IMF variation? Vcirc? nope Davis & McDermid 2017

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So what is the cause of IMF variation? Alpha elements? Seems not Davis & McDermid 2017