The X-ray Evolution of Young Post-Merger Nicky Brassington The Centre for Astrophysics Research University of Hertfordshire Collaborators: G. Fabbiano, E. O’Sullivan, A. Zezas

Galaxy Evolution Mergers suggested to be an important process in the formation of some elliptical galaxies Observational Studies generally support picture of spiral galaxy interactions leading to coalescence Supported by numerical simulations, e.g. Hopkins et al. (2008) Hopkins et al. (2008) SFR AGN Are these remnants young elliptical galaxies? 17th June 2014 The X-ray Universe 2014

Properties of Merger-Remnants Still unclear if merger-remnants will evolve to appear similar to mature elliptical galaxies Archetype post-merger NGC 7252 Central profile relaxed But prominent tidal tails Gas-rich major-merger ~1 Gyr since nuclear Coalescence X-ray faint compared to mature ellipticals 17th June 2014 The X-ray Universe 2014

Evolutionary Sequence Probing evolution in X-ray Determine X-ray binary population (ULXs) Observe changes in hot diffuse emission Chandra survey of nine gas-rich major-mergers From 1st perigalactic to 3 Gyr post-merger Post-merger remnants appear X-ray faint compared to mature ellipticals NGC 2434 - typical elliptical galaxy Increase in LX/LK >1 Gyr after coalescence Driven by hot gas, regeneration of X-ray halo? Brassington et al. (2007) 17th June 2014 The X-ray Universe 2014

Determining the Driver of Regeneration Halo regeneration predicted through hydrodynamical simulations (stellar mass loss/supernovae feedback) Ciotti et al. (1991) Cox et al. (2006) Or infall of expelled material shocking to X-ray Gradual regeneration hinted at through ROSAT observations (O’Sullivan et al. 2001) Chandra sample only single step between 1 Gyr & 3 Gyr Observations in this time period required to determine when regeneration begins 17th June 2014 The X-ray Universe 2014

Sample of ‘Infant’ Ellipticals To determine timescale of halo regeneration observe sample of post-merger galaxies Distinguish between infalling gas and different hydrodynamical models All galaxies: Within 50 Mpc Age estimates between 1 Gyr - 5 Gyr Multi-wavelength indicate single major-merger Constrained to remove complexities of multiple mergers 17th June 2014 The X-ray Universe 2014

Evolution of Post-Mergers Disturbed elliptical galaxy NGC 3656 Tidal features in R-band HI observations detect 2 tidal tails (Balcells et al. 2001) Coalescence 1.5 Gyr (dynamics & colours) Mass LK= 8x1010 M 17th June 2014 The X-ray Universe 2014

Chandra Observations of ‘Infant Elliptical’: NGC 3656 53 ks observation D=46 Mpc 11 point sources within D25 ellipse Limit LX > 1x1038 erg s-1 17th June 2014 The X-ray Universe 2014

Properties of Diffuse Emission Spectral decomposition required: Relations of Boroson, Kim & Fabbiano (2012) Low luminosity LMXBs ------- CVs & ABs ------ Diffuse ------- LxDIFF =4.2x1039 LxUNRSVL =2.2x1039 LxCV+AB =0.7x1039 (0.3-8.0 keV) LxLMXB =8.8x1039 17th June 2014 The X-ray Universe 2014

Regeneration of X-ray Halo Compare NGC 3656 with previous sample At 1.5 Gyr LX/LK still very low %Ldiff also low Halo regeneration may have started Reject infall scenario 4 major-mergers >2 Gyr 17th June 2014 The X-ray Universe 2014

Luminous LMXBs Kim & Fabbiano 2010 Ratio of Lx>5x1038 sources compared to >1x1038 erg s -1 Suggestion that ‘young’ elliptical galaxies have different XLF compared to older ellipticals (see Lehmer talk next) Two ellipticals recent minor-merger (Kim & Fabbiano 2010) Suggests flattening of XLF, similar to HMXBs No break ~ 5x1038 erg s-1 NGC 3656 11 LMXBs 0.22 fraction luminous sources KF10 average also 0.22 (old ellipticals 0.12) 17th June 2014 The X-ray Universe 2014

Summary Moderate depth surveys provide information about the overall behaviour of diffuse gas At 1.5 Gyr possible evidence of halo regeneration Systems between 2-5 Gyr required to differentiate ‘Infant’ elliptical X-ray binary population exhibits shallower XLF than mature galaxies 17th June 2014 The X-ray Universe 2014