Can spiral galaxies form in major mergers ?
E. Athanassoula
LAM/CNRS/AMU/DAGAL/S4G
Collaborators :
S. Rodionov, N. Peschken, A. Bosma, J.C. Lambert
Disc shape
Gas rich
Structures
~circular orbits
Speroidal shape
Gas poor
Hardly any structures
Kinematics : elongated orbits
Toomre & Toomre
Barnes
etc
Theory :
S + S ==> E (Toomre + Toomre 1972, Toomre 77)
Observations:
IMAGES team : Hammer, Puech, Flores., Yang, Wang, Rodriguez, Delgado-Serrano, Foucault, etc
IMAGES survey :galaxies at intermediate redhifts (with zmedian~0.65)
Complementary kinematics and HST morphologies
S (with gas) + S (with gas) ===> galaxy with a disc component, or (at best) lenticular
Hammer et al. (2007, 2009a, 2009b, 2010, 2012, 2013, 2014),
Puech et al (2006, 2007a, 2007b, 2008, 2009, 2010a, 2010b, 2014),
Flores et al. (2006), Yang et al. (2008, 2009, 2014), Wang et al. (2012),
Delgado-Serrano et al. (2010), Rodrigues et al. (2012), Fouquet et al (2012, 2014),
Peirani (2009), Pawlowski et al. (2014)
Simulations (and criticism thereof):
Barnes 2002, Springel & Hernquist 2005, Cox et al. 2006, Robertson et al. 2006,
Governato et al. 2007, Bournaud & Elmegreen 2009, Covington et al. 2009,
Hopkins P. et al. 2009a, 2009b, 2010, 2011, Borlaff et al 2015, Querejeta et al 2015a,b etc
Hopkins et al. 2009
« Constrained », or «Dynamical», or «Detailed » simulations, with partly «idealised» initial
conditions
Technical improvements :
Higher resolution simulations
Ntotal 5.5M - 15M, linear resolution 25 pc. ~ 200 simulations
Simulations continued 6 – 8 Gyrs after mergiging
More realistic simulations:
A better modelling of the progenitors
Better gas physics (add AGN feedback)
A more complete comparison of simulation results with nearby galaxy properties
(morphological, kinematical, photometrical)
Collaborators:
S. Rodionov, N. Peschken, A. Bosma, J.-C. Lambert
Pour ce type de projet une meso-machine est une l'ordinateur ideal :
---Il y a une très grand nombre de tests a faire pour mettre en place les améliorations
nécessaires (meilleure description des protogalaxies, meilleur modèle de la
physique du gaz, etc)
---Il y a un espace de parametres libres important a explorer
Avant de passer au très grosses simulations sur des superordinateurs plus puissants
Face-on and edge-on views if discs initially in the orbital plane, or at 60 degrees from it
Both galaxies at 0 degrees
One at 90 degrees
THREE TYPES OF BREAKS OBSERVED
Freeman 70, Pohlen & Trujillo 06; Erwin, Pohlen, Beckman 08, Munoz-Mateos et al. 13, Laine et al. 14
(figure from Laine et al. 14)
Type II profiles : Comparison with observations for inner and outer disc scale lengths
Data from Munoz-Mateos
et al 2013 ==> open symbols
Simulations ==> filled symbols
Inner
outer
Migration and formation of breaks
See also Roskar et al. 2008 (with simple collapse)
Compare bars with those of idealised simulations (pre-existing discs)
Observations : S4G, Diaz-Garcia et al 2015
Our 3 fiducial simulations : Black filled circle
|z| < zc
|z|>zc
Thick disc : mainly (but not only) from
old stars formed before merging
Circularity = Jz/Jz,circ
A very schematic and (over-)simplified model of a major merger remnannt:
1) Stars born before the merging
1a) Some, generally those in the central regions, go through a violent relaxation phase
and form a classical bulge.
1b) The rest, perhaps those further out, form a thick disc
2) The gas which before merging was in the disc is pushed in the centre. Its fate will
depend strongly on the AGN feedback. It can form a discy (pseudo-) bulge.
3) The gas that is accreted after the merging makes a thin extended disc and its
structures (bar, spirals, rings etc). Stars of different ages have different B/P shapes
(boxy up to X). The youngest stars are in the spiral
============>
Discs do NOT survive mergers, they are created after the merging.
B/T (bulge to total baryonic mass ratio)
From kinematics
0.12 (mdf728), 0.11 (mdf732) and 0.18 (mdf730)
From decompositions
0.09 – 0.15 (mdf728), 0.10 – 0.18 (mdf732) and 0.09 – 0.11 (mdf730)
Major mergers can form spiral galaxies whose properties and parameters are in good
agreement with observations
But not all spirals are necessarily formed this way. (What fraction? This work can't say)
The major merger origin of spiral galaxy formation accounts for all the components
The classical bulge and most of the thick disc are from stars born before the merging
(old stars now). Indications for the formation of a discy pseudo bulge from the merging.
Can make disc-dominated galaxies (small B/T ratios, ~0.1; but zero may not be trivial)
Find reasonable radial and vertical density profiles. Find type II and III breaks in radial
profiles and argue they form largely by migration
Horizontal and vertical scale lengths and breaks have values in the right ball park
Cold gas concentrates in the thin disc and particularly in the spirals or ring. That is where
young stars form
Bars have realistic properties / Ansae / B/P bulges form as expected
Thick discs also have realistic properties, and older stars than thin ones
Rotation curves
Etc etc …..
Anything but ... THE END