Dynamical modelling of the Milky Way Paul McMillan y r o t a v - - PowerPoint PPT Presentation

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Dec 05, 2023 400 likes •688 views

Dynamical modelling of the Milky Way Paul McMillan y r o t a v r e s b O , h d c n i r u L n h E c V S A h R p l e a h n R t o i , , t y s a r e r n e d o n b n i a B a l S l s o

SLIDE 1

Dynamical modelling of the Milky Way

Paul McMillan

L u n d O b s e r v a t

y w . J a m e s B i n n e y , R a l p h S c h ö n r i c h , J a s

S a n d e r s , t h e R A V E C

l a b

a t i

, t h e G a i a C

l a b

a t i

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The Problem

It’s so slow…

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M e a s u r e m e n t s

Can’t measure the acceleration Can measure positions and velocities

For billions of stars…

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Great data needs a great model

Need a model to find gravitational field from the

bservations

Stars move, but the distribution (density profile, velocity distribution) stays the same

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Model orbits

McMillan & Binney 2008 Binney 2012 Binney & McMillan 2016 Bovy 2015

Action- angle coordinates

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What can action-angle modelling do for you?

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Gravitational f ield (Dark matter)

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F i n d t h e d a r k m a t t e r d e n s i t y

Many different techniques. Some mostly Galactic plane (e.g., McMillan 2011, 2017) Some mostly perpendicular (e.g., Garbari et al. 2012) (see Read 2014 for a review)

github.com/PaulMcMillan-Astro/GalPot

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F i n d t h e d a r k m a t t e r d e n s i t y

Global approach (Piffl et al 2014)

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C h e m

y n a m i c s

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Understanding chemical evolution

Wojno et al 2016 (see also Lee et al 2011) Old – Type-II SN enrichment Younger – Type Ia SN enrichment

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Explained by a dynamical model and inside-out formation

(Schönrich & McMillan 2017)

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M e t a l l i c i t y g r a d i e n t s

Metal rich gas Metal rich young stars Metal poor gas Metal poor young stars

(Galaxy picture, McMillan priv comm)

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Natural explanation for (younger) lower-α stars

From R<R0 From R>R0

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How does it get reversed for high α? Inside-out formation

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t ≈ 0 t = 2 Gyr R [ Fe/H ]

Inside out formation

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But also: asymmetric drift (high vel. disp. = velocity lag)

[ Fe/H ]

vφ at R0

If low [Fe/H] has higher vel.

disp. (e.g.

because it’s

lder)

If two populations have the same mean radius (i.e. there is no radial metallicity gradient) and velocity dispersion

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Velocity Substructure

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V e l

i t y s u b s t r u c t u r e

Dehnen (1999) (see also Kushniruk et al 2017) Modelled by: Sellwood 2010, McMillan 2011, 2013, Monari et al 2016

Real data Smooth model

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C

c l u s i

s

Action-angle coordinates are a toolset for understanding galaxy dynamics We can find the gravitational potential, understand chemical evolution, and the effect of the spirals/bar Data are coming! Thank you!

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B l a n k s l i d e

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Bensby, Feltzing, Oey 2014

The α-Fe plane

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The α-Fe plane

Wojno et al 2016

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H e l m i ’ s s t r e a m

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W e n e e d a g

m

e l

Gaia data is an incredible

pportunity to understand

a galaxy

(actually several…)

Need a model to find gravitational field from the

bservations

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Found in many surveys. From the field of streams… (Belokurov et al 2006) to DES (Shipp et al 2018)

Streams do not follow

rbits

(see poster)

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W e n e e d a g

m

e l

Gaia data is an incredible

pportunity to understand

a galaxy

(actually several…)

Need a model to find gravitational field from the

bservations