AGN feedback works both ways Positive AGN feedback through jet-induced star formation?

1. RUHR-UNIVERSITÄT BOCHUM AGN feedback works both ways Positive AGN feedback through jet-induced star formation? Peter-Christian Zinn1,2 with Enno Middelberg1, Ray P. Norris2, and Ralf-Jürgen Dettmar1 1 Astronomical Institute of Ruhr-University, Bochum, Germany 2 CSIRO Astronomy & Space Science, Sydney, Australia

2. Start: How do galaxies evolve? • “Standard model”: • Merger of two gas-rich spirals • Triggering of strong SF and, with a certain offset, an AGN • AGN truncates SF → galaxy becomes “red & dead” elliptical • Scenario is strongly supported by simulations • Too many massive galaxies produced without negative AGN feedback Croton et al. (2006) e.g. Hopkins et al. (2008)

3. What about observations??? • Main criticism: Negative feedback was proposed “ad hoc” to fix simulations • First (quantitative) observations by Page et al. (Nature, 2012) investigating star formation in X-ray selected AGN • Star formation seems to be truncated in the (X-ray) brightest AGN Several issues: - Number of objects - Determination of LX - AGN selection - no pure X-ray selection - radio AGN need to be accounted for Page et al. (Nature, 2012) → Use mid-IR criteria!

4. Analysis of the AGN sample MIR-selected AGN Stern et al. (ApJ, 2005) Cross-matching of X-ray (Chandra 4 Ms) and radio (deep VLA image by N. Miller) data X-ray only X-ray + radio radio only 94 sources 111 sources 47 sources Stacking of Herschel/SPIRE 250 µm images from HerMES survey (Oliver et al. 2012) Measure star formation rate from median FIR luminosity which is unbiased from the AGN Calculate star formation rate from median radio luminosity which includes AGN emission

5. SFR vs. LX • SFR of X-ray + radio sample 5 times higher than for the X-ray only sample with the same (!) LX • Radio-detected samples show large difference between SFRFIR and SFRradio • Effect cannot be explained just by radio selection! • Only explanation for excess radio emission: AGN jet contribution • Occurrence of jets is linked to total star formation rate Zinn et al. (subm.)

6. Jet power among our samples • Jet powers are calculated using the scaling relation to AGN radio luminosity by Cavagnolo et al. (ApJ, 2010) • AGN radio luminosity is obtained by subtracting the emission caused by star formation at a rate SFRFIR • LAGN = Ltotal – LSF • Pjet = f(LAGN) • Jet power 8 – 10 times higher in radio-detected samples → Jets play an important role for star formation! Zinn et al. (subm.)

7. Our (preferred) explanation • Jet-induced SF?! • Seen in several objects, primarily at high z • Idea: jet shocks gas reservoirs and thereby induces shocks and turbulence → accelerated clumping of gas Bicknell et al. (ApJ, 2000) Only one scenario: - need not be this strict - mild forms involving AGN winds also possible Van Breugel et al. (2004) Van Breugel et al. (2004)

8. Summary & Outlook • AGN feedback is probably the most important mechanism regulating the growth and evolution of galaxies. • To date, the precise astrophysics behind negative and positive feedback processes and their relative occurrence are not well known. • Computational simulations mainly focus entirely on negative feedback, although positive feedback plays an important role. • A possible mechanism for positive feedback is jet-induced star formation since the occurrence of radio jets from an AGN seems to be linked to star formation activity in the host galaxy. • Future radio surveys such as ASKAP/EMU (and companion surveys at other wavelength ranges) will detect unpreceden-tedly large AGN samples, allowing for detailed studies of feedback mechanisms in various environments and redshifts.