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Dark Halos of Fossil Groups and Clusters

Dark Halos of Fossil Groups and Clusters. Habib Khosroshahi. Observations and Simulations. Ali Dariush, Trevor Ponman Graham Smith University of Birmingham, UK Frazer Pearce et al University of Nottingham, UK Andrew Benson et al Caltech, US. Motivation.

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Dark Halos of Fossil Groups and Clusters

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  1. Dark Halos of Fossil Groups and Clusters Habib Khosroshahi Observations and Simulations Ali Dariush, Trevor Ponman Graham Smith University of Birmingham, UK Frazer Pearce et al University of Nottingham, UK Andrew Benson et al Caltech, US

  2. Motivation • How do galaxies form and evolve? • How is the galaxy evolution connected to the environment? • What aspect of the environment matters? ( SDSS results, Blanton, 2006) • Can DM help us characterise environment? • Is the shape of the DM distribution a true indicator of the evolutionary stage of galaxy systems? • How well the models and cosmological simulations reproduce the observations of galaxies, DM and baryons? Challenges posed by observations of groups and clusters A lensing or X-ray map

  3. L* galaxies absent BGG is a giant Elliptical “Relaxed” X-ray emission Rasmussen et al 2006 Osmond et al 2004 Fossil group Fossil Galaxy Groups L* galaxies MR - 21.5 BGG could be late-type Irregular X-ray emission XMM- IMACS Galaxy group Non-fossil group X-ray contours

  4. Search fossils Optical: m12 ≥2 (R-band) X-ray: LX ≥1042 ergs/sec • Large area X-ray survey • Optical photometry Optical Spectroscopy • WARPS fossils • Fossils in SDSS: RAS + SDSS • Fossils in XCS (in progress) • Fossils in LoCuSS  • Are fossils really old systems? • Are there any differences in their halo and galaxy properties? Observations vs. Simulations • Extragalactic astronomy can benefit from fossil studies: Halo formation, Baryon physics, Feedback, Galaxy formation

  5. X-ray properties from Chandra observations M - TX relation Fossils appear to be hotter than normal groups for a given mass of the system Finoguenov et al 2001 Fossils Non-fossils LX - Lopt relation Excess X-ray luminosity for a given optical luminosity of the groups Khosroshahi et al 2007

  6. Khosroshahi, Ponman & Jones 2007 J1416.4+2315, Khosroshahi et al. 2006 Mass concentration in fossils • Hydrostatic equilibrium • Spherical symmetry • NFW profile (c200=r200/rs) Fossils show higher concentration in their mass profiles compared to non-fossils systems with similar masses. This is an indication of early formation epoch.

  7. Fossil Clusters in LoCuSSLocal Cluster Substructure Survey A survey to probe the relationship between the structure (assembly history) of galaxy clusters and the evolution of the hot gas and galaxies. LoCuSS targets 100 low z (0.15-0.3) clusters from X-ray through optical/IR to radio (PI Smith). For fossil study we use Ks imaging and HST/ACS (cycle 16) or WFPC2 observations .

  8. Halo – Galaxy connection10 clusters with lensing and X-ray analysis Mass concentration (X-ray) Clusters with largest luminosity gap are found in more concentrated halos (Zhang et al 2007). Mass concentration (lensing) Clusters dominated by BCGs show least sub-structures (Smith et al 2005).

  9. Fossils in the Millennium SimulationsLargest cosmological simulation available Hot gas Dark halo • Formation of fossils • Halo shape and evolution • Halo isolation • Space density • Cooling / heating • Semi-analytic galaxies + GALAXIES + Springel et al 2005 Croton et al 2006 Pearce et al 2007

  10. Halo mass evolution in Fossils Fossils accumulate most of their mass at high redshifts, they are therefore old (Dariush et al 2007)

  11. Space density of fossilsA remarkable agreement non-fossil fossil

  12. Optical vs. X-ray fossils No significant change in the fraction of fossils with mass suggests that may be merger is equally efficient in low and high velocity dispersion systems!

  13. Semi-analytic galaxies Compare the semi-analytic galaxies of Bower et al (2006) and Croton et al (2006). Better agreement in the luminosity gap (m12) in massive halos.

  14. Merger and star formation history m1/m2~0.3 Star formation in central galaxy (BGG, BCG) as a result of equal and non-equal mass mergers. Most of the merger induced star formation in fossils is originated from equal mass mergers in the first 5 Gyr while unequal mass mergers are the main source of SF in non-fossils. m12  2 m12 ~ 1.0 m12 ~ 0.2 m1/m2>0.9

  15. K-band, J1416.4+2315 The giant elliptical dominating fossils show non-boxy isophotes. No recent dry merger? K-band, NGC 6482 Brightest Cluster Galaxy Majority of brightest cluster galaxies have “boxy” isophotes. Boxy isophotes are produced in gas poor, equal mass galaxy mergers. Disky isophotes are produced in gas rich unequal mass galaxy mergers. Naab & Burkert (2003)

  16. Brightest Cluster Galaxy A similar trend can be seen in LoCuSS sample. Clusters with largest luminosity gap are dominated by non-boxy isophote giant elliptical galaxies.

  17. Summary • Both the observations and simulations point at fossils’ early formation. • Fossils appear to be the extension of galaxy clusters to lower mass systems. • There is a strong connection between the DM halo shape and galaxy properties. • Fossil central galaxies show non-boxy isophotes which is an indication of gas rich merger. • The space density of fossils in the observations and simulations are consistent. • It is not clear if the galaxy merger is more efficient in low mass halos. • Equal mass galaxy mergers form more stars in fossil central galaxies than in non-fossils.

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