How gas shapes Milky Way-sized galaxies in cosmological simulations : - - PowerPoint PPT Presentation

Rob Grand

(Heidelberg Institute for Theoretical studies, Astronomisches Recheninstitut, Heidelberg)

• in collaboration with
• Volker Springel (HITS, ZAH), Rüdiger Pakmor (HITS), Facundo Gomez (MPA), Federico Marinacci

(MIT), Christine Simpson (HITS), Sebastian Bustamante (HITS), Adrian Jenkins (Durham), Carlos Frenk (Durham), Simon White (MPA), Hans-Walter Rix (MPIA), Daisuke Kawata (UCL) et al.

How gas shapes Milky Way-sized galaxies in cosmological simulations: mergers, accretion and feedback

The Auriga Project (www.auriga.h-its.org)

Aim: To produce a set of Milky Way mass haloes that:

• is high-resolution and large in number
• follows a comprehensive galaxy formation model capable of producing

realistic galaxy populations … that produces disc-dominated, late-type, star-forming spirals…

The Auriga Project: Cosmological zoom MW mass halo simulations (Grand+ 2017)

• 40 sims @ standard res:
• star mass res ~10^4 Msun
• grav softening ~ 300pc (optimal)

AREPO - moving mesh MHD code (Springel 2010)

• Star formation
• Reioinisation (z=6)
• Metal line cooling
• Mass & metal enrich.

(Type Ia & AGB)

• SNII feedback
• Black hole growth
• Radio & quasar

AGN feedback

• Magnetic fields
• 6 sims @ hi-res (x8 mass, x2 spat)
• 5x1011 < Mvir(z=0) < 2x1012

movie @ http://auriga.h-its.org/movies.html

Scaling relations

A large sample of hi-res, rotationally supported star-forming MW analogues: Scaling relations

Simulations evolve parallel to the stellar mass-halo mass abundance matching relation SFR vs. Mstar relation well reproduced over time

A large sample of hi-res, rotationally supported star-forming MW analogues: Scaling relations

Simulations evolve parallel to the stellar mass-halo mass abundance matching relation SFR vs. Mstar relation well reproduced over time

A large sample of hi-res, rotationally supported star-forming MW analogues: Scaling relations

Simulations evolve parallel to the stellar mass-halo mass abundance matching relation SFR vs. Mstar relation well reproduced over time

HI gas maps at redshift zero: A variety of sizes but all flat, disc-like distributions with small holes

Marinacci+17

HI gas properties (Marinacci+17 (data available: http://auriga.h-its.org/data))

Mass distributions contrasted with Bluedisk (Wang+ 14), SPARC (Lelli+ 16) and

• ther nearby galaxies

Mstar [Msol] HI gas fraction surface density R/RHI mass-size relation DHI [kpc]

Empirical (Leroy+ 08)

Theoretical (based on Gnedin+Kravtsov 2011) (dust-gas ratio) (Interstellar rad field)

Gas disc evolution

General evolution of Star-forming gas

thick+compact

z=1 z=0.5 z=0

thin+extended

• Merger phase z≳1
• Smooth increase (decrease)

in Vrot (𝜏) after z=1.

• Similar to ‘disc settling’ 


seen in DEEP2/SIGMA surveys of SF galaxies


(Kassin+12, Simons+17)

(also important in build up of magnetic field strength)

What drives the gas disc evolution? Turbulent gas accretion?

Pakmor+ 17

• Gas inflows highly turbulent at early times, and decays from z~1-2
• Rotational energy begins to dominate thereafter, marking the 


phase of strong disc growth

• Present day gas-disc scale heights correlate with SFR

What drives the gas disc evolution? Stellar feedback driven fountain flows?

declining SFR from z~2 —> naturally ‘deflating’ disc?

• Scatter indicates other drivers, e.g., mergers…

fountain flows push gas outside mid plane

Marinacci+17

What determines the radial disc size? Spin The diversity in disc size (Rd ~1-10 kpc) correlates with spin

• 1. late-time, violent,

major mergers z=0 companion (outlier)

—> bears out expectations of halo collapse models (e.g., Peebles 69, Mo+ 98)

Strong AGN feedback

Drivers of disc growth: Spin The diversity in disc size (Rd ~1-10 kpc) correlates with spin

• 1. late-time, violent,

major mergers z=0 companion (outlier)

• 2. prograde,

quiescent mergers

—> bears out expectations of halo collapse models (e.g., Peebles 69, Mo+ 98)

Strong AGN feedback

• 2. The Biggest discs: high-spins from in spiralling mergers

accretion of stripped, high-Lz gas from gas-rich mergers builds biggest discs

Drivers of disc growth: Spin The diversity in disc size (Rd ~1-10 kpc) correlates with spin

• 1. late-time, violent,

major mergers z=0 companion (outlier)

• 2. prograde,

quiescent mergers

{

• 3. intermediate region
• mix of 1+2
• quiescent history…


—> inherently have these spins

—> bears out expectations of halo collapse models (e.g., Peebles 69, Mo+ 98)

Strong AGN feedback

Late time Gas-rich minor mergers as a gas supply (Grand+17b)

Gas supplied by gas-rich merger (disc growth resumes) Violent, early phase disc growth phase begins stalls resumes Gas inflow rate is low and SF consumes gas at disc edge Suggestive of cold-mode accretion at late times

Summary

Galaxies match a range of observations and scaling relations *on the scales we care about*

• stellar halo mass relation, SFH, rotation curves (Grand+17)
• HI gas distributions (Marinacci+ 17)

Wide range of disc sizes driven by:

• Quiescent mergers (biggest discs)
• Violent mergers (small discs)

Star-forming gas disc ‘settles’ into extended, disc dominated systems

• Turbulent accretion decays from z~1-2, then rotation dominated
• Fountain flows may also play a role

Gas-rich minor mergers can be source of late-time cold-mode 
 accretion