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Nearby mergers: ellipticals in formation?

Nearby mergers: ellipticals in formation?. Thorsten Naab University Observatory, Munich. October 4th, 2006 From the Local Universe to the Red Sequence Space Telescope Science Institute, Baltimore . Making ellipticals by mergers.

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Nearby mergers: ellipticals in formation?

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  1. Nearby mergers: ellipticals in formation? Thorsten Naab University Observatory, Munich October 4th, 2006 From the Local Universe to the Red Sequence Space Telescope Science Institute, Baltimore

  2. Making ellipticals by mergers “Merger hypothesis” : ellipticals form by major mergers of … but what merged when? Do present day disk mergers evolve into elliptical galaxies?

  3. Making elliptcals by mergers of disk galaxies

  4. Collisionless mergers of disks Encounter survey, statistical properties of 96 remnants Naab & Burkert 2003, ApJ, 893

  5. Collisionless mergers of disks • Formation of tidal tails and bridges, similar to local interacting • galaxies : formation of ellipticals?! (Toomre & Toomre 1972,1977) • Equal-mass remnants are spherical, slowly rotating, show shells, loops etc. similar to elliptical galaxies (Barnes 1988,1992; Hernquist 1992,1993) • Phase-space constraints and kinematics rule out pure exponential disks as progenitors for ellipticals - bulges • and/or dissipation needed (Hernquist 1993, Jesseit et al. 2005, Naab & Trujillo 2006, Cox et al. 2006) • Mass ratio determines the kinematics, orbital content and shape of the remnants (Bekki 1998, Barnes 1998; Naab, Burkert & Hernquist 1999; Bendo & Barnes 2000, Naab & Burkert 2003; Gonzalez-Garcia, Cesar & Balcells 2005; Jesseit, Naab & Burkert 2005) • Shape of the LOSVD in general not in agreement with observed rotating ellipticals (Bendo & Barnes 2000; Naab & Burkert 2001; Naab, Jesseit & Burkert 2006; Jesseit, Naab & Burkert 2006, astro-ph)

  6. Surface density profiles of collisionless mergers no gas Distribution peaks at nser ≤ 4 for all mass ratios! with gas, stars analyzed Sersic-function: =0*exp(-r 1/n), Naab & Trujillo 2006, MNRAS

  7. Collisionless mergers of disks • Unequal-mass mergers • rotate faster • are more elongated • are less supported • by random motions • are more dominated by • tube orbits Naab & Burkert 2003

  8. Orbital content of merger remnants: The stellar backbone Minor-axis tubes Box shape of tubes only in triaxial potentials!!! Box orbits Outer major-axis tubes Inner major-axis tubes Boxlets Jesseit, Naab & Burkert 2005, MNRAS, 1185

  9. Orbital content of merger remnants: The stellar backbone • 1:1 mergers are dominated by • box orbits scattered from • the progenitor disks and bulges • 3:1 mergers are dominated by • tube orbits from the more • massive progenitor disks All collisionless merger remnants are dominated by box orbits at their centers (Barnes 1998; Bendo & Barnes 2000) and orbital content correlates with shape and kinematics (Jesseit, Naab & Burkert 2005)

  10. Mergers with gas… 3:1 disk merger, 10% gas Naab et al., 2006

  11. Mergers of disks: Gasdynamics • Galaxy merger drive large gas fractions to the centres of the • merger remnants (Negroponte & White 1983; Hernquist 1989, 1991; • Barnes & Hernquist 1991, 1996) • Central gas concentration makes the potential more axisymmetric • and favours the population of tube orbits (Barnes & Hernquist 1996; • Barnes 1998, Naab, Jesseit & Burkert 2006) • The stellar body of the remnants becomes more axisymmetric • Global stellar kinematics is only weakly affected, isophotal shape • and shape of the LOSVD changes (Naab et al. 2006) • Structure of the progenitors influences gas flow: Central bulges • suppress inflow after first encounter (Mihos & Hernquist 1994,1996) • Left over gas settles in large-scale disks (Mihos & Hernquist 1996; • Naab & Burkert 2001; Barnes 2002; Naab et al. 2006; Jesseit et al. 2006)

  12. Merger dynamics • Disks are heated after first encounter and during the final merger • Apparent mass ratios • 12reff,1/22 reff,2 • trace real mass ratios and agree with observed separated nearby ULIRGS which are in the range 1:1 - 3:1 (Dasyra et al. 2006) • Galaxies might follow theMBH- relation after first encounter Naab et al. 2006; Dasyra at al. 2006 a,b

  13. see Bendo & Barnes 2000 Influence of gas on the stellar component • Fraction of box orbits • is reduced • Remnants are more axisymmetric • Global kinematic • properties only weakly • affected • Isophotal shape strongly • affected • Shape (asymmetry) • of the LOSVD changes Naab et al. 2006; Data Rothberg & Joseph 2006; Dasyra et al. 2006

  14. a4 < 0 boxy a4 > 0 disky Line-of-sight velocity distribution LOSVD analysis using Gauss-Hermite polynomials – vlos, slos, h3, h4 Bender, Saglia & Gerhard 1994

  15. Influence of gas on the LOSVD: statistics All “dry” remnants: star particles analysed

  16. Influence of gas on the LOSVD: statistics All “wet” remnants: only star particles analysed

  17. Influence of gas on the LOSVD: statistics All “wet” remnants: star and gas particles analysed

  18. 2D kinematical analysis of merger remnants Encounter survey, statistical properties of 96 remnants 2D analysis and comparison to observations helps to figure out formation mechanisms (see Bendo & Barnes 2002) Jesseit, Naab & Burkert 2006, submitted

  19. A model for disk galaxy evolution • Analytical model for the formation of galactic disks • Milky Way (vc, sol, rdisk) • During initial merger phase follow most common halo • bulge formation • vhalo= const., 0 = const., • rdisk rhalo  1/H(z), cooling gas forms exponential disk rbulge  0.25 rdisk • Infallrate known: • star formation, • chemical evolution, • photometric evolution • Radial distribution of gas and stars is known at any time • Full evolution of a galaxy, the Galaxy Naab & Ostriker, MNRAS, 2006

  20. Bulge formation Disk formation Assembly of an early-type disk galaxy

  21. Assembly of an early type disk galaxy • Outer young “disk” with a scale • length of 3kpc • Inner old “bulge” with a scale • length of 600 pc • B/T ≈ 0.2

  22. The ideal disk merger • Take stellar populations of two equal • mass disks • Convert gas inside 2 rd into stars at • given metallicity • Stop infall and further star formation • to make the galaxies “red & dead” • Check present day properties for • different merger redshifts Naab & Ostriker 2006, in prep.

  23. Conclusions • Kinematic and photometric properties of nearby ongoing mergers • and merger remnants are in agreement with disk merger simulations • with mass ratios in the range 1:1 - 3:1 • Good agreement of both with intermediate mass giant elliptical galaxies (see also Cox et al. 2006) • Disk merger remnants, as well as ULIRGS, can follow the Fundamental Plane and the MBH-relation (Robertson et al. 2005; Springel et al. 2005) • Mergers trigger strong central and extended starbursts and AGN activity (Barnes 2002, di Matteo et al 2006) • So far most dynamical, kinematical and photometric constraints indicate that gaseous 1:1 to 3:1 disk mergers can have evolved • into intermediate mass M* elliptical galaxies and if merging now • be ellipticals within the next 4-6 Gyrs • Present day formation rate is low, was higher in the past but then the disks were smaller and less massive • Ellipticals more massive than M*ellipticals are not and have not formed by binary disk mergers!

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