Are X-shaped radio galaxies really merger induced spin flips? Chris Reynolds Department of Astronomy & Cntr. for Theory and Computation University of Maryland, College Park 1st April

Outline Brief intro to “winged” and X-shaped radio galaxies Models for winged radio galaxies Signposts of recently merged SMBHs? Hydrodynamic interaction of radio plasma with surroundings? Preliminary results from our Chandra survey Collaborators Edmund Hodges-Kluck (UMd) Teddy Cheung (GSFC) 1st April

I : Winged and X-shaped radio galaxies Winged radio galaxies comprise ~10% of radio galaxy population (Leahy & Williams 1984) They possess… Active/normal pair of radio lobes PLUS additional pair of lobes/wings Additional lobes show no signs of active jet or hotspot In extreme cases, get well defined X-shape 3C403 (Kraft et al. 2005) 1st April

NGC326 (ZRG) (Murgia et al. 2001) 1st April

Other examples… 1st April

II : Formation models Two classes of model Jet maintains fixed direction… Jets energize active lobes Wings created by “blowout” of the backflow Wings caused by jet reorientation… Slow precession with special geometry wrt l-o-s Rapid realignment of jets leaving fossil lobes in old direction and new active lobes (trealign<106yr) Scheuer (1974) See papers by Dennett-Thorpe et al. (2002), Merritt & Ekers (2002); Komossa (2003) 1st April

Signposts of recently merged SMBHs? Suppose jet axis is determined by black hole spin axis Rapid jet realignment may be caused by spin-axis changes during a SMBH merger Spin re-alignment occurs during Merger (Merritt & Ekers 2002), or Via accretion torques as the binary hardens (Liu 2004) Could be a rare signpost of recently merged SMBHs Inconsistent with spin alignment idea of Bogdanovic et al. (2007) 1st April

Wings know about the alignment of the alignment galaxy… Capetti et al. (2002) Discovered that wings are preferentially aligned with minor-axis of the stellar light distribution Appears to support the back-flow model (backflow blows-out along minor axis of gas distribution) Supported by Saripelli & Subrahmanyan (2008)… Winged sources have jets aligned along major axis of stellar distribution Normal sources have jets preferentially aligned along minor axis of stellar distribution Capetti et al. (2002) Also…Saripelli & Subrahmanyan (2008) 3C403 (WFPC2) 1st April

Capetti et al. (2002) 1st April

III : The Chandra survey of winged radio galaxies Motivation/questions To understand the hot gaseous environment of radio galaxies (ISM, intragroup and intracluster medium)… this is the gas that acts as the working surface for the radio jets! Investigate whether hot ISM/IGM/ICM shares the ellipticity/alignment of the stellar light? Does the Capetti correlation extend to the X-ray band? Assess differences in density/pressure/temperature of hot ISM/IGM/ICM between winged & normal radio galaxies. Are winged sources in unusual environments? Our study… Chandra ACIS-S imaging of 14 winged radio galaxies Sources within z<0.11; drawn from FIRST survey (Cheung 2002) Obtained seven 10ks exposures + seven archival observations (8ks100ks) Control sample of z<0.1 3CRR radio galaxies (DRAGN) 13 normal radio galaxies with Chandra ACIS-S imaging 1st April

3C403 (Kraft et al. 2005) Chandra ACIS-S 1st April

NGC326 1st April

NGC326 is on edge of the distribution of intragroup medium ROSAT PSPC (Worrall et al. 1995) 1st April

SDSS Chandra 1st April

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Spectral analysis Imaging analysis Confirm that we are really seeing hot gas! Determine temperature Crude estimates of density and pressure Imaging analysis Remove compact sources (including AGN and jet) Find best fitting ellipse for photon distribution (QL-method) Allows ellipticity to be characterized even in very photon starved data 1st April

Hodges-Kluck, CSR et al. (in prep) 1st April

Uniform distribution  PX=0.13, Popt=0.37 Hodges-Kluck, CSR et al. (in prep) 1st April

Uniform distribution  PX=0.02, Popt=0.13 Hodges-Kluck, CSR et al. (in prep) 1st April

Uniform distribution  PX=0.004, Popt=0.05 Hodges-Kluck, CSR et al. (in prep) 1st April

Results, implications and caveats Presence or absence of wings is strong function of the orientation of the radio-jet relative to hot gas distribution Exactly as expected in a backflow-blowout model for XRGs… not clear why any such correlation would arise in the SMBH merger model Caveat/question: Are we actually seeing the cocoon-bounding shock and not the ambient medium? Clearly the case in 3C452 Correlation between optical and X-ray ellipses suggests that this is not a general problem Need significantly deeper imaging to study details of hydrodynamic interaction between radio jets and surrounding medium 1st April

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Backup slides 1st April

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