Star formation and agn regulation in early type galaxies
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Star formation and AGN regulation in early-type galaxies. Sugata Kaviraj Hertfordshire Heidelberg 14 July 2014 With: Stas Shabala, Richard Ellis, Adam Deller, Enno Middelberg, Kevin Schawinski, Sukyoung Yi. Key points. Massive early-type galaxies have widespread star formation (not ‘dead’)

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Star formation and agn regulation in early type galaxies

Star formation and AGN regulation in early-type galaxies

Sugata Kaviraj

Hertfordshire

Heidelberg

14 July 2014

With: Stas Shabala, Richard Ellis, Adam Deller, Enno Middelberg, Kevin Schawinski, Sukyoung Yi


Key points
Key points

  • Massive early-type galaxies have widespread star formation (not ‘dead’)

  • Star formation largely driven by minor mergers, adds 20-30% of galaxy stellar mass after z~1

  • Not strongly regulated by AGN feedback


Uv colours galex and sdss evidence for widespread star formation
UV colours: GALEX and SDSSEvidence 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
Rest frame UV colours at 0.5<z<1: CDF-S

Persistent star formation in ETGs since z~1

Low z

SK +08, MNRAS, 388, 67


What drives the star formation
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
What drives the star formation?Are blue ETGs morphologically disturbed?

Relaxed ETGs

SK +11, MNRAS, 411, 2148


What drives the star formation are blue etgs morphologically disturbed1
What drives the star formation?Are blue ETGs morphologically disturbed?

Relaxed ETGs

Disturbed ETGs (~35% of the ETG population)

Disturbed ETGs (30% of the ETG population)

SK +11, MNRAS, 411, 2148


Minor merger driven star formation at z 1
Minor-merger-driven star formation at z<1

  • 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

[Rest-frame NUV-g]

SK+ 11, MNRAS, 411, 2148


Summary of star formation in etgs 0 z 1
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
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 106 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
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 107 yr)

  • AGN are not prompt (c.f. Schawinski +10 using SWIFT-BAT)

SK in prep.


Do agn regulate minor merger driven sf1
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 107 yr)

  • AGN are not prompt (c.f. Schawinski +10 using SWIFT-BAT)

SK in prep.


Do agn regulate minor merger driven sf2
Do AGN regulate minor-merger-driven SF?

  • 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.


Summary
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)