1. The morphology and angular momentum of simulated galaxy populations
Shy Genel
Hubble Fellow
Columbia University

2. Introduction
An observed relation between the most basic morphological classification and a fundamental physical quantity: the specific angular momentum (j=J/M)
Romanowsky & Fall 2012

3. Introduction The theoretical challenge for cosmological simulations:
Reproduce two separated relations
And their scatter
Understand what puts a galaxy on one or the other
Navarro et al. 1995
Fall & Romanowsky 2013

4. Teklu et al. 2015 - Magneticum
The current status of simulations
Genel et al Illustris
Teklu et al Magneticum
Zavala et al EAGLE
The stellar specific angular momentum correlates with galaxy mass with a slope close to (2/3)
Shape, concentration & SFR separate relations
Overall relation is shallower, (at least in part) due to mass-dependent mix between late- and early-types

5. The current status of simulations
Genel et
al. 2015
Placing Mhalo instead of M* on the x-axis allows comparison with simple theory:
Late-types are consistent with having % of the mean specific angular momentum of dark matter halos
Early-types retain ≈15-50%

6. The current status of simulations
Genel et
al. 2015
What is the actual role of cosmological tidal torques?
Do some galaxies retain the original value and some lose most?
What role does the merger history play?
How is feedback related?

7. Correlation with halo spin
The scaling with redshift approximately matches the scaling for DM halos: (1+z)-1/2,
i.e. angular momentum retention is approximately redshift-independent
Illustris

8. Correlation with halo spin
Rodriguez-Gomez et al. in prep (Illustris)
Teklu et al (Magneticum)
z=0
In both Magneticum and Illustris, DM halo spin distribution (in the DM-only run!) separates by the galaxy ‘normalized specific angular momentum’
In Magneticum:
The separation is smaller than of the stellar spin difference
The separation is large at high redshift, weaker at z=0

9. Rotation support vs. ang. mom.
Kinetic energy in coherent rotation:
(Sales et al. 2012)
Similarly, fractional rotation:
(Emsellem et al. 2007)
(‘Normalized specific’) Angular momentum and rotation support are only well correlated for M*<1011Msun:
Rodriguez-Gomez et al. in prep

10. Correlation with halo spin
(‘Normalized specific’) Angular momentum and halo spin are correlated at all masses
Rotation support is only correlated with halo spin for M*<1011Msun
Rodriguez-Gomez et al. in prep

11. The role of formation history
Large variety of mass and j evolution histories
Several classes defined based on zoom- in simulations, but not enough population statistics
Mergers may increase or reduce the specific angular momentum
Naab et al. 2014

12. The role of formation history
Illustris reproducing ETGs:
slow/fast rotators
Rotation support anti-correlates with stellar mass
ATLAS3D
Illustris
Penoyre, Moster
& Sijacki in prep.
Naab et al. 2014

13. The role of formation history
Slow rotators only emerge at z<~1
The z=1 progenitors of z=0 slow/fast rotators are almost indistinguishable
Penoyre, Moster
& Sijacki in prep.

14. The role of formation history
Slow rotators gain much more stellar mass through major mergers than fast rotators – in particular at high M*
Penoyre, Moster
& Sijacki in prep.

15. The role of formation history
Fast rotators lose significant rotation support during a major merger, within ≈100Myr
Recovery, over ≈1-2Gyr, is dependent upon gas fraction after the merger
Penoyre, Moster
& Sijacki in prep.

16. The role of formation history
Low gas fraction:
Late mergers:
Major mergers:
All correlate with and can be ‘summarized’ together using the ‘ex- situ’ fraction, which also strongly correlates with M*
Rodriguez-Gomez et al. in prep

17. Formation history and halo spin
Rotational support correlates with both halo spin and ex-situ fraction
But at low M* the ex-situ fraction is small and not no significant
And at high M* the rotational support and halo spin (as well as j) are no longer correlated
and the formation history dominates
Rodriguez-Gomez et al. in prep

18. Feedback Enhancement/addition of feedback always makes galaxies larger
Genel et al. 2015
Enhancement/addition of feedback always makes galaxies larger
But while galactic winds boost the angular momentum, radio- mode AGN feedback reduces it
angular momentum
size

19. Feedback Enhancement/addition of feedback always makes galaxies larger
But while galactic winds boost the angular momentum, radio- mode AGN feedback reduces it
AGN feedback
(Dubois et al. 2013)
Galactic wind feedback
(Übler et al. 2014)

20. Galactic winds and CGM
Promotion of later accretion that has higher angular momentum
(Übler et al. 2014)
Preferential ejection of low-j galaxy gas
(Governato et al. 2009)
Re-accretion of previously-ejected gas after it gained angular momentum
(Brook et al. 2012)

21. Galactic winds and CGM
DeFellipis, Genel & Bryan in prep.
A Lagrangian analysis of baryonic flows using Monte Carlo tracer particles (Genel et al. 2013) allows comparing the angular momentum of unique mass elements at different times
Baryons retain their angular momentum, on average, while in the galactic/halo fountain
Mh≈1011Msun
Mh≈1012Msun
Mh≈1013Msun

22. Galactic winds and CGM z=0 z=1 No feedback Illustris
DeFellipis, Genel & Bryan in prep.
With feedback, the distribution of stellar angular momenta is shifted and skewed to higher values, already at z>1
At z=1, there exists a new population of (recycled) gas with angular momentum intermediate between central galaxy and satellites
z=0
z=1
No feedback
Illustris

23. Formation history and AGN feedback
AGN feedback makes mergers dry, increasing the ex-situ fraction
AGN feedback reduces galactic angular momentum
But the ex-situ fraction does not correlate directly with angular momentum
Possible conclusion: AGN feedback does not reduce angular momentum through mergers
Genel et al. 2015
Rodriguez-Gomez et al. in prep

24. Formation history and AGN feedback
An alternative, to be explored:
AGN feedback prevents late-accreting (recycled?) high-j gas, reducing angular momentum
At the same time:
AGN feedback makes galaxies, and mergers, dry, forcing sizes up
The result: dispersion-dominated galaxies
spec. ang. mom.
Genel et al. 2015
size

25. Formation history and AGN feedback
Feedback increases ex-situ fractions as well as reduces rotation support at a given ex-situ fraction
Rodriguez-Gomez et al. in prep
Full Illustris model
No feedback simulation

26. Stellar dynamics
DeFellipis, Genel & Bryan in prep.
Stars generally conserve their angular momentum after they are formed, until z=0
Stars formed ex-situ tend to have higher angular momentum than in-situ stars
Mh≈1011Msun
Mh≈1012Msun
Mh≈1013Msun

27. Conclusions Feedback:
Galactic winds generate a reservoir of high-j circumgalactic gas
AGN feedback prevents accretion from this reservoir, effectively reducing j
Mergers:
Dry mergers send j to large radii, making galaxies dispersion-dominated
Wet mergers reduce rotation support only temporarily
Halo spin:
Stellar j strongly correlated with halo spin (at all masses)
Rotation support becomes more sensitive to merger history at high mass