Accretion Histories of BCGs: Angular Momentum and Stellar Populations

Review talk at the Massive Galaxies conference, Sydney 2015

Transcript

1. Paola Oliva-Altamirano In collaboration with Sarah Brough, Warrick Couch, Kim-Vy Tran, Jimmy, Chris Lidman and Richard McDermid The Accretion Histories of Brightest Cluster Galaxies: Angular Momentum and Stellar Populations
2. Brightest Cluster Galaxy (BCGs) Oliva-Altamirano 2 C4 2055 Refers to the central dominant galaxy in a cluster
3. Oliva-Altamirano 3 Lacey & Cole (1993) BCG Evolution
4. Mergers are important in BCG evolution Oliva-Altamirano 4 Some connect the evolution of BCGs with many dry minor mergers (Bernardi +2009). Others found major mergers to be as important as minor (e.g. De Lucia & Blaizot 2007, Lui +2009). De Lucia & Blaizot (2007) Mass accreted by merger Mass growth by in-situ star formation as in yesterday talks!
5. Mergers are important in BCG evolution Oliva-Altamirano 5 Lin +2013 Current picture (as in Chris Lidman’s talk): At 0.8 < z < 1.5: BCGs stellar mass grows by major mergers. Burke & Collins 2013, Lidman +2013. At z < 0.3: BCGs stellar mass grows by minor mergers. Edwards & Patton 2012, Oliva-Altamirano +2014. Semi-analytical model Guo +2011 Observations of Lin +2013 Lin +2013
6. The accretion histories of BCGs can be traced by … Oliva-Altamirano 6 Stellar Populations Stellar Kinematics
7. Oliva-Altamirano 7 Etc.. Integral Field Unit (IFU) Spectroscopy
8. Oliva-Altamirano 8 Kinematics as an inside of Mergers: Hydrodynamical models Gas rich major mergers are predicted to create disks and show rotation (Bournaud +2005) Dissipationless major mergers: Are predicted to create dispersion supported galaxies. (Boylan-Kolchin +2006, Naab & Burkert 2003) Bois +2011 0.0 ε 1.0 0.8 λR 0.0 0.0 ε 1.0 0.8 λR 0.0 No KDC Yes KDC
9. Oliva-Altamirano 9 Naab +2014 2.0 1.0 0.0 v σ z FR with gas rich minor mergers SR with gas rich major mergers SR with gas poor minor mergers Major merger
10. BCGs are predicted to be Slow Rotators Oliva-Altamirano 10 This can not be proven by SAURON and ATLAS3D or CALIFA because their samples cover a small volume. SAURON/ ATLAS3D only include one BCG, M87
11. Individual studies of BCGs suggest no trend in the stellar kinematics of these galaxies… Oliva-Altamirano 11 BCGs in the COMA cluster (Houghton +2013)
12. Oliva-Altamirano 12 Individual studies of BCGs suggest no trend in the stellar kinematics of these galaxies… M87 is massive slow rotator with KDC and outer minor axis rotation (Emsellem +2014)
13. Dedicated IFU observations of BCGs Brough +2011, Jimmy +2013, Oliva-Altamirano +submitted Oliva-Altamirano 13 10 BCGs, 7 of them with close massive companions. 4 companions were resolved. Selected from SDSS C4 catalogue (von der Linden +2007). Observed with VIMOS on the VLT.
14. Jimmy +2013 found slow AND fast rotators within the 10 BCGs… Oliva-Altamirano 14 Brough +2011, Jimmy +2013
15. Around 30% of the BCGs are FR Oliva-Altamirano 15 Observations Jimmy +2013 AMR simulations of Martizzi +2013 0.8 λR 0.0 0.0 ε 1.0
16. Oliva-Altamirano 16 0L[HG0HUJHU+LVWRU\ )DVW5RWDWRU 6ORZ5RWDWRU 0HUJLQJ 1RW0HUJLQJ
17. Oliva-Altamirano 17 The rotation of the BCGs could depend on the host cluster formation as well as the merger activity of the galaxy Fogarty +2014 studies the angular momentum distribution in different clusters, correlating the galaxy rotation with the cluster density. See Fogarty’s talk, later today!
18. Conclusions 18 The slow and fast rotation in BCGs, as well as in early-type galaxies is a temporary state that could depends on galaxy recent mergers and or other physical processes connected to their host cluster environment.
19. The accretion histories of BCGs can be traced by … Oliva-Altamirano 19 Stellar Kinematics Stellar Populations
20. Oliva-Altamirano 20 R Met Accretion histories from stellar population gradients Steep gradients could be due to a core collapsed formation or major mergers Involving high fractions of gas. Metallicity gradient > -0.4. Met R Flat to shallow gradients are the result of major dissipationless mergers. Metallicity gradient < -0.3. Kobayashi +2004, Hopkins +2009, Hirschmann +2014.
21. Previous stellar population gradients Oliva-Altamirano 21 Loubser +2012, ΔZ/H = -0.28+/-0.06 Brough +2007, ΔZ/H = -0.31+/-0.05 Long-slit spectroscopy Loubser +2012
22. BCGs stellar population gradient of from IFU spectroscopy (Observations from Jimmy +2013) Oliva-Altamirano 22 Gradient = -0.3 The BCG stellar populations gradients are similar to those of early-type galaxies (Oliva-Altamirano +submitted) BCGs, ΔFe/H = -0.11+/-0.1 E-T, ΔZ/H = -0.19+/-0.1
23. Previous central stellar population measurements Oliva-Altamirano 23 1.9 Log σ 2.5 1.1 Log Age 0.5 1.9 Log σ 2.5 0.02 [Fe/H] -0.14 Fitzpatrick +2012, Stacked SDSS galaxies BCGs show: Slightly younger ages, Slightly higher metallicities
24. Previous central stellar population measurements Oliva-Altamirano 24 Log Age [Z/H] Loubser +2009, Long-slit spectroscopy BCGs have: Wide range of ages, Slightly higher metallicities young old
25. Central stellar populations of BCGs from IFU spectroscopy (Observations from Jimmy +2013) Oliva-Altamirano 25 The BCGs central stellar populations are similar to those of early-type galaxies (Oliva-Altamirano +submitted) BCGs, age = 8.9+/-3.1 E-T, age = 12.0 +/-3.8
26. BCGs have diverse evolutionary paths Oliva-Altamirano 26 Wen +2014 Continuous star-formation Passive evolution
27. Oliva-Altamirano 27 Tonini +2012, see talk on Wednesday
28. Conclusions 28 BCGs show diverse evolutionary paths, some show passive evolution across cosmic time (no SF since z=2), and some other show younger ages at their central regions, suggesting that the last SF burst took place at z~1. Their shallow stellar population gradients suggest disipationless major mergers.
29. Open questions •  Does the Angular momentum of BCGs correlate with the Angular momentum of its host clusters? •  How do the stellar kinematics and stellar population profiles of BCGs change out of one effective radii? •  What is the star formation history of these galaxies? When do they quench? Oliva-Altamirano 29 Hopefully some of them will be soon solved by the SAMI and MASSIVE survey!