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Star formation in forming galactic disks under UV field by RHD simulation

Star formation in forming galactic disks under UV field by RHD simulation. Hajime Susa Department of Physics, Konan university, Kobe, Japan. Susa ApJ 684, 226, 2008. Ultraviolet radiation field （ >13.6eV ）. Physical processes heating ： T ～ 10 4 K ionization+dissociation. background

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Star formation in forming galactic disks under UV field by RHD simulation

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  1. Star formation in forming galactic disks under UV fieldby RHD simulation Hajime Susa Department of Physics, Konan university, Kobe, Japan Susa ApJ 684, 226, 2008

  2. Ultraviolet radiation field （>13.6eV） • Physical processes • heating：T ～104 K • ionization+dissociation • background • I21= 0.1 - 1 @ z= 2 – 5 • I21=0.01- 0.001@ z=0 Keep the gas in the proto-galaxies hot (～ 104 K). Feedback on star formation? • Around forming gals • I21～ 1-100 (star formation) • I21～100(AGN @10kpc)

  3. Formation of dwarf gals. M=1e8Msun Zc～5 zreion～7 M < 1e8 Msun →SFshutdown Susa & Umemura 2004ab

  4. Aim of this work • Assess the effects of UV on massive DM halos with Tvir > 104K. Star formation in these systems are regulated or not ? As a first step, we investigate the stability of gas disksin massive halos under UV field, utilizing radiation hydrodynamics simulations.

  5. RSPH code Susa 2006 (http://ads.nao.ac.jp/abs/2006PASJ...58..445S) • Parallel BH Tree • SPH • Domain decomposition : ORB • RT solver (Ray-Tracing) • Implicit solver for reactions and energy equation • H2 • On-the-Spot approximation (Case B recom.) • Multiple sources (～< 10） • Any Spectrum

  6. The model Same as Wada & Norman 2007 except rotation velocity radiation radiation Uniform disk with slight perturbations

  7. Resolution Mass resolution : Maximally resolved density: (MJ～Mres) Gravity Softening: (～minimal SPH softening) Bate & Burkert 1997

  8. montage:I21=0 Disks in all modes (A、B、C) are unstable → fragmentation & star formation

  9. Toomre Ｑ and the tmperature PDF(I21=0) A B C Stable Unstable

  10. montage:I21=1 A, B :stable → star formation is strongly suppressed. C: still unstable →　fragmentation & starformation

  11. Density PDFs No dense components

  12. Distribution along z-axis density temperature Significant self-shielding effect HI

  13. Temperature PDFs Ar, Br : unshielded → Hot component dominates → large Q → stable Ｃｒ: shielded　→ Cold componentdominates → small Q → unstable

  14. Threshold column density for self-shielding Photoheating rate = Cooling rate below 104 K Numerical results : NH,sh～1-4×1021cm-2

  15. Can UV photons suppress the SF in disks hosted by massive dark halos?

  16. Hierarchical GF Fresh Gas accretion Fresh Gas accretion On going……… • Dynamical effects of merging (shock induced SF etc.) • Inhomogeneous distribution of heavy elements • Radiation from forming stars in building blocks, AGN

  17. Analytical model of Cosmological disks (1/2) • Dark halos parameterized by （ｚc, M, λ） • Assume half of the baryons settle onto the galactic disk • Keplar rotation & hydrostatic equilibrium in z-direction • NH, disk > NH,sh ? • Q >1 ?

  18. Analytical model of Cosmological disks （2/2） Unshielded & stable Unshielded & stable

  19. oldnew Bimordalityof galaxies Resent SF for galaxies with Mstar < 1010Msun Stellar age Some process to delay the SF in less massive galaxies is required. (Kauffman, G. et al, MNRAS, 341, 54, 2003) Photoheating

  20. Summary • We perform radiation hydrodynamics simulations on the fragmentation of galactic disks under the ultraviolet radiation background. • We find that ultraviolet radiation field strongly suppress the star formation in the disks in case the photoheating is not shielded enough. • In our simulations, we find a threshold column density of the disk (～ 1021(I21/1)cm-2) above which the fragmentation is not suppressed. • Presence of such critical threshold would be one of the reason for the so-called down-sizing problem in nearby galaxies.

  21. Tours Symposium 2009 • Nov. 16-20 @ Tours, France • Nuclear Physics, High energy astroparticle physics, Astrophysics • Astrophysics: “First & Second generation stars” SOC Ferrara, Schneider, Umemura, Omukai, Tominaga, Susa

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