Sugata Kaviraj Hertfordshire Heidelberg 14 July 2014 With: Stas Shabala, Richard Ellis, Adam Deller, Enno Middelberg, Kevin Schawinski, Sukyoung Yi Star formation and AGN regulation in early-type galaxies

Key points Massive early-type galaxies have widespread star formation (not ‘dead’) Star formation largely driven by minor mergers, adds % of galaxy stellar mass after z~1 Not strongly regulated by AGN feedback

UV colours: GALEX and SDSS Evidence for widespread star formation Tight optical colour relation (as expected) But NUV colour shows a spread of 6 mags Strong UV sources present in nearby ETGs UV is driven by star formation (UV from old stars insufficient) SK +07, ApJS, 173, 619 Yi +05, ApJ, 619, L111

Rest frame UV colours at 0.5<z<1: CDF-S Low z SK +08, MNRAS, 388, 67 Persistent star formation in ETGs since z~1

What drives the star formation? Stellar mass loss at z~0 not enough to produce blue UV colours (SK +07) Gas and stellar kinematics decoupled, suggests external accretion (Sarzi+06, Young+11, Davis+11) Dust masses typically exceed maximum stellar mass loss (e.g. Merluzzi 98, Knapp+89, Rowlands+12, SK +12) 70%+ of ETGs morphologically disturbed (van Dokkum+05, Yi +12) Young, kinematically decoupled cores in ETGs – signs of recent mergers (e.g. McDermid 2006)

What drives the star formation? Are blue ETGs morphologically disturbed? Relaxed ETGs SK +11, MNRAS, 411, 2148

Disturbed ETGs (30% of the ETG population) What drives the star formation? Are blue ETGs morphologically disturbed? Relaxed ETGs Disturbed ETGs (~35% of the ETG population) SK +11, MNRAS, 411, 2148

Minor-merger-driven star formation at z<1 [Rest-frame NUV-g] Star formation is merger driven But major merger rate (e.g. Lin et al. 04, Conselice et al. 07) too low to satisfy fraction of disturbed ETGs At least 60% (and up to 90%) of events are minor mergers SK+ 11, MNRAS, 411, 2148

Summary of star formation in ETGs (0<z<1) Widespread star formation in ETGs since z~1, which adds 20-30% of the stellar mass after z~1 Star formation is driven by minor mergers (minor mergers likely drive 50%+ of the local SF budget (SK 14, MNRAS, 437, L41 and SK 14, MNRAS, 440, 2944) Do AGN regulate this formation?

GALEX + SDSS + radio VLBI (mJIVE-20 ) AGN identification can be difficult: –Nuclear activity can be obscured, emission-line (BPT) selection does not necessarily trace the jet –Radio is best (no obscuration) but FIRST/NVSS do not resolve galaxy cores, contributions from SF and AGN hard to disentangle VLBI can identify AGN unambiguously, high resolution requires temperatures of order 10 6 K for a detection, only reached in non-thermal sources mJIVE is using VLBA filler time, 20k+ FIRST sources observed, 4k+ VLBI detections Is there evidence for AGN quenching in VLBI-detected ETGs (mainly tracing ‘cold-mode’ AGN because SF is merger-driven)?

Do AGN regulate minor-merger-driven SF? VLBI-detected galaxies overwhelmingly on the red sequence Blue to red transit times (>1 Gyr) much longer than AGN lifetimes (a few 10 7 yr) AGN are not prompt (c.f. Schawinski +10 using SWIFT- BAT ) SK in prep.

Do AGN regulate minor-merger-driven SF? VLBI-detected galaxies overwhelmingly on the red sequence Blue to red transit times (>1 Gyr) much longer than AGN lifetimes (a few 10 7 yr) AGN are not prompt (c.f. Schawinski +10 using SWIFT- BAT ) SK in prep.

AGN (optical and radio) triggered after several dynamical timescales Gas reservoir significantly depleted before AGN really switches on Cold-mode AGN do not regulate star formation (unlike hot mode AGN) SK in prep. Do AGN regulate minor-merger-driven SF?

Summary There are no truly passive galaxies Widespread star formation in ETGs at late epochs, adds 30% of stellar mass after z~1 Driven by minor mergers (a process that plausibly drives half the SF budget at low redshift) Cold-mode AGN (those fuelled by mergers) do not appear to regulate star formation (although most hot-mode AGN probably do)