Can spiral galaxies form in major mergers?

Transcription

1 Can spiral galaxies form in major mergers? E. Athanassoula LAM/CNRS/AMU/DAGAL/S4G Collaborators : S. Rodionov, N. Peschken, A. Bosma, J.C. Lambert

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3 Disc shape Gas rich Structures ~circular orbits Speroidal shape Gas poor Hardly any structures Kinematics : elongated orbits

4 Toomre & Toomre Barnes etc

5 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

6 Hopkins et al. 2009

7 «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

8 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

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11 Face-on and edge-on views if discs initially in the orbital plane, or at 60 degrees from it

12 Both galaxies at 0 degrees One at 90 degrees

13 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)

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15 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

16 Migration and formation of breaks See also Roskar et al (with simple collapse)

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21 Compare bars with those of idealised simulations (pre-existing discs)

22 Observations : S4G, Diaz-Garcia et al 2015 Our 3 fiducial simulations : Black filled circle

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24 z < zc z >zc Thick disc : mainly (but not only) from old stars formed before merging

25 Circularity = Jz/Jz,circ

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27 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.

28 B/T (bulge to total baryonic mass ratio) From kinematics 0.12 (mdf728), 0.11 (mdf732) and 0.18 (mdf730) From decompositions (mdf728), (mdf732) and (mdf730)

29 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..

30 Anything but... THE END