Rebuilding local discs with gas-rich major mergers Mathieu PUECH - PowerPoint PPT Presentation

Rebuilding local discs with gas-rich major mergers Mathieu PUECH Coll.: F. Hammer, H. Flores, M. Rodrigues, Y. Yang, J. Wang, L. Athanassoula, P. Hopkins et al. Malta Conf. Oct. 2017

Local Hubble Sequence 72% of M stellar = 2x10 10-11 M o galaxies are spirals SDSS images 2 Delgado-Serrano et al. 2010

Hubble Sequence at z~0.6 31% of M stellar > 1.5x10 10 M o galaxies are spirals HST/ACS images 3 Same depth, resolution and rest-frame wavelengths than SDSS Delgado-Serrano et al. 2010

Morphology vs. Kinematics IMAGES survey z~0.6, Neichel+08 95% of complex kinematics have Pec morpho. # Complex 86% of perturbed rotation have Pec morpho. # Perturbed 80% of rotating galaxies have Sp # Rotating morpho. 50% of intermediate-mass galaxies at z~0.6 have perturbed morphologies OR kinematics Hammer+09

How to identify all mergers? Rotation-dominated Adapted from Turner+17; Puech et al., in prep. Rotating disc IMAGES z~0.6 Re-analysis of KMOS3D data 1. VF with single gradient z~0.9 2. V/ s > 1 Rodrigues+17 3. s peak = rotation center 4. PA kin = PA morph 5. rotation center = center of mass See also Kassin+12, Simons+17

How to identify all mergers? Rotation-dominated Adapted from Turner+17; Puech et al., in prep. Rotating disc IMAGES z~0.6 Re-analysis of KMOS3D data 1. VF with single gradient z~0.9 2. V/ s > 1 Rodrigues+17 3. s peak = rotation center 4. PA kin = PA morph 5. rotation center = center of mass Interacting discs can look like rotating discs

How to identify all mergers? Rotation-dominated Adapted from Turner+17; Puech et al., in prep. 1. VF with single gradient 2. V/ s > 1 3. s peak = rotation center 4. PA kin = PA morph 5. rotation center = center of mass See Rodrigues+17 See also Robertson&Bullock08; See M. Rodrigues’ poster Gonçalves+10; Hung+15,16

Major merger models 2/3 of perturbed galaxies have secured major merger models Hammer+09

Merger rate: observations vs. theory Rodrigues+17b, pairs Puech+12, IMAGES Puech+12, IMAGES Rodrigues+17, KMOS Curves: L CDM predictions from Hopkins+10 Excellent agreement on the gas-rich major merger rate

Expected Impact of gas fraction Rodrigues+12 Hopkins+10 z=2, Erb+06 z=2, Erb+06 S E G A z=1.5, Daddi+10 M I z=0.6, IMAGES z=2, Tacconi+10 z=1, Tacconi+10 Hopkins et al 2010 z=0 ; Schiminovich08 z=0 ; GASS survey Reformation of a significant disk after gas-rich major mergers Barnes02; Springel & Hernquist05; Robertson+08; Hopkins+09-12 ; Governato+09; Aumer+13,14; Athanassoula+16

“Mergers do not contribute significantly to the star formation history” Puech+12, 14

“Mergers do not contribute significantly to the star formation history” Puech+12, 14 23% ≈ Morphologically-selected mergers Consistent with Robaina+09: 15-21% (see also Jogee+09)

“Mergers do not contribute significantly to the star formation history” Puech+12, 14 11% SFR enhancement Consistent with Robaina+09: 8±3% (see also Jogee+09)

“Mergers do not contribute significantly to the star formation history” Puech+12, 14 23% Total SFR fraction associated to major mergers: 53-88%

Scatter of the SFR-mass relation Puech+14 Cox+08 0.3 dex Duty cycle: 0.4-2.5 Gyr SFR Peak amplitude and (1-2 s ) duration too small/short? Duty cycle is statistical: need to consider the average SFR peak duration in an representative sample!

Scatter of the SFR-mass relation Puech+14 Cox+08 0.3 dex Duty cycle: 0.4-2.5 Gyr Average: much larger (1-2 s ) SFR peak duration Duty cycle is statistical: need to consider the average SFR peak duration in an representative sample!

Scatter of the SFR-mass relation Average peak in the IMAGES representative sample Puech+14 0.3 dex Duty cycle: 0.4-2.5 Gyr (1-2 s ) 1.8 Gyr No tension between major mergers and the SFR-mass relation

LIRGs and major mergers IMAGES sample: 58% of LIRGS are in the fusion phase Elbaz+11 Compact LIRGs 18 From Melbourne+06, see also Zheng+04 ~ 42% expected to have spiral morphologies

Most present-day spirals have no or pseudo-bulges (Kormendy+10) Gas-rich major mergers can (often) produce pseudo-bulges Sauvaget+17 See also Kelseman&Nusser12

Conclusions ● 50 % of z~0.6 intermediate-mass galaxies show strong kinematic and morphological perturbations; interacting galaxies can look like rotation-dominated or even rotating discs! ● The 2/3 of them are well reproduced by major merger models and match merger rate expectations from L CDM: ~ 50 % of local galaxies have undergone a major merger since z~1.5 ● These mergers are gas-rich => disk dominated remnants => ~ 50% local spiral galaxies should have rebuilt a disc since z~1.5 ● Fraction of SFR associated to major mergers at z~0.6: hugely definition-dependent! <10% if just considering the SFR enhancement; > 50% if accounting for all merger phases ● There is no tension between the role of major mergers and the scatter of the SFR- mass relation, the fraction of LIRGs with Sp morphologies, or the fraction of local pseudo-bulged galaxies