Peter-Christian Zinn | AGN feedback works both ways | The Modern Radio Universe | 22 APR 2013 AGN feedback works both ways Positive AGN feedback through jet-induced star formation? Peter-Christian Zinn 1,2 with Enno Middelberg 1, Ray P. Norris 2, and Ralf-Jürgen Dettmar 1 1 Astronomical Institute of Ruhr-University, Bochum, Germany 2 CSIRO Astronomy & Space Science, Sydney, Australia RUHR-UNIVERSITÄT BOCHUM

Peter-Christian Zinn | AGN feedback works both ways | The Modern Radio Universe | 22 APR /8 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)

Peter-Christian Zinn | AGN feedback works both ways | The Modern Radio Universe | 22 APR /8 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 Page et al. (Nature, 2012) Several issues: - Number of objects - Determination of L X - AGN selection - no pure X-ray selection - radio AGN need to be accounted for → Use mid-IR criteria!

Peter-Christian Zinn | AGN feedback works both ways | The Modern Radio Universe | 22 APR /8 Analysis of the AGN sample MIR-selected AGN X-ray only Cross-matching of X-ray (Chandra 4 Ms) and radio (deep VLA image by N. Miller) data Stacking of Herschel/SPIRE 250 µm images from HerMES survey (Oliver et al. 2012) 94 sources 47 sources 111 sources 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 X-ray + radio radio only Stern et al. (ApJ, 2005)

Peter-Christian Zinn | AGN feedback works both ways | The Modern Radio Universe | 22 APR /8 SFR vs. L X Zinn et al. (subm.) SFR of X-ray + radio sample 5 times higher than for the X-ray only sample with the same (!) L X Radio-detected samples show large difference between SFR FIR and SFR radio − 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

Peter-Christian Zinn | AGN feedback works both ways | The Modern Radio Universe | 22 APR /8 Jet power among our samples Zinn et al. (subm.) 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 SFR FIR − L AGN = L total – L SF − P jet = f(L AGN ) − Jet power 8 – 10 times higher in radio-detected samples → Jets play an important role for star formation!

Peter-Christian Zinn | AGN feedback works both ways | The Modern Radio Universe | 22 APR /8 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) Van Breugel et al. (2004) Only one scenario: - need not be this strict - mild forms involving AGN winds also possible Van Breugel et al. (2004)

Peter-Christian Zinn | AGN feedback works both ways | The Modern Radio Universe | 22 APR /8 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. Summary & Outlook