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 R. McDermid, and with thanks to the ATLAS 3D and WISDOM teams
Molecular g gas a as a a d dynamical p probe o of IMF v variation Stars in the Milky Way seem to form following a universal initial mass function.
Molecular g gas a as a a d dynamical p probe o of IMF v variation Stars in the Milky Way seem to form following a universal initial mass function. For every high mass star formed…
Molecular g gas a as a a d dynamical p probe o of IMF v variation 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
Molecular g gas a as a a d dynamical p probe o of IMF v variation 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
Molecular g gas a as a a d dynamical p probe o of IMF v variation We typically assume this is true in other galaxies too. This assumption underpins almost everything we know about galaxy formation… Hα UV • Luminosity à Mass • Flux à SFR • Supernova rates • Metal enrichment • Dust formation and gas return to the ISM FIR Radio Cont.
Molecular g gas a as a a d dynamical p probe o of IMF v variation The IMF is clearly crucial. How is it measured extragalactically? Stellar Kinematics Stellar Kinematics / Lensing 1. Measure the mass of a galaxy with stellar kinemaQcs / lensing Lensing 2. Measure the light emiRed using imaging. 3. Compare M/L with that expected given the stellar populaQon present Stellar populations e.g. Cappellari et al., 2012
Molecular g gas a as a a d dynamical p probe o of IMF v variation Why the M/L? Milky Way IMF: Reference M/L à dN/N à à Mass of star à
Molecular g gas a as a a d dynamical p probe o of IMF v variation Why the M/L? Milky Way IMF: Reference M/L à dN/N à Most mass here à Mass of star à
Molecular g gas a as a a d dynamical p probe o of IMF v variation Why the M/L? Milky Way IMF: Reference M/L à dN/N à Most mass here Most light here à Mass of star à
Molecular g gas a as a a d dynamical p probe o of IMF v variation Why the M/L? Milky Way IMF: Reference M/L à dN/N à Top heavy IMF: More light for a very Most mass here Most light here similar mass à Mass of star à
Molecular g gas a as a a d dynamical p probe o of IMF v variation Why the M/L? Milky Way IMF: Reference M/L à dN/N à Top heavy IMF: More light for a very Most mass here Most light here similar mass Bottom heavy IMF: More mass and less light For any age, metallicity and IMF stellar models predict the M/L à Mass of star à M/L pop (Age , Z , [ α / Fe] , IMF)
Molecular g gas a as a a d dynamical p probe o of IMF v variation The IMF is clearly crucial. How is it measured extragalactically? Stellar Kinematics Stellar populations e.g. Conroy and van Dokkum et al., 2011 1. Use gravity sensiQve features within Lensing spectra of galaxies. 2. More dwarf stars à stronger abs. in those bands Stellar populations 3. Infer the IMF required to give those line strengths, given the age/Z of populaQon
Molecular g gas a as a a d dynamical p probe o of IMF v variation 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
Molecular g gas a as a a d dynamical p probe o of IMF v variation 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) • What about early-type galaxies (ETGs)? Lenses from Brewer+12
Molecular g gas a as a a d dynamical p probe o of IMF v variation IMF appears to vary with: • Metallicity Martin-Navarro et al., 2015
Molecular g gas a as a a d dynamical p probe o of IMF v variation IMF appears to vary with: • Metallicity • Velocity dispersion Cappellari et al., 2013
Molecular g gas a as a a d dynamical p probe o of IMF v variation IMF appears to vary with: • Metallicity • Velocity dispersion • Alpha element abundances… • etc Conroy & van Dokkum 2012
Molecular g gas a as a a d dynamical p probe o of IMF v variation 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
Molecular g gas a as a a d dynamical p probe o of IMF v variation IMF appears to vary with: • Metallicity • Velocity dispersion • Alpha element abundances… Can molecular gas kinematics help? • etc BUT: • Lack of consistency between methods! - Stellar kinematics - Stellar pops - Lensing Smith 2014
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017 Our technique: 1. Take an ETG with molecular gas
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017 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/L pop (Age , Z , [ α / Fe] , IMF)
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017 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/L pop (Age , Z , [ α / Fe] , IMF)
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017 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/L pop (Age , Z , [ α / Fe] , IMF) 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!
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017
Molecular g gas a as a a d dynamical p probe o of IMF v variation Salpeter type IMFs strongly ruled out Davis & McDermid 2017
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017
Molecular g gas a as a a d dynamical p probe o of IMF v variation Salpeter type IMFs needed… Davis & McDermid 2017
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017
Molecular g gas a as a a d dynamical p probe o of IMF v variation Intermediate needed? Davis & McDermid 2017
Molecular g gas a as a a d dynamical p probe o of IMF v variation Good agreement with prior measurements Davis & McDermid 2017
Molecular g gas a as a a d dynamical p probe o of IMF v variation Do we reproduce find local/global drivers found by others? NO
Molecular g gas a as a a d dynamical p probe o of IMF v variation Do we reproduce find local/global drivers found by others? NO
Molecular g gas a as a a d dynamical p probe o of IMF v variation Davis & McDermid 2017 (arXiv:1609.03559) Conclusions: • 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
Molecular g gas a as a a d dynamical p probe o of IMF v variation So what is the cause of IMF variation? Davis & McDermid 2017 Vcirc? nope
Molecular g gas a as a a d dynamical p probe o of IMF v variation So what is the cause of IMF variation? Davis & McDermid 2017 Alpha elements? Seems not
Recommend
More recommend
