1. Subaru Wide-Field Survey of M87 Globular Cluster Populations N.Arimoto (NAOJ) N.Tamura, R.Sharples (Durham) M.Onodera (Tokyo, NAOJ), K.Ohta(Kyoto) J.-C.Cuillandre (CFHT)

2. Origin of GCs in Elliptical Galaxies Many luminous elliptical galaxies have bimodal or multimodal colour distributions of globular clusters (GCs) (Gebhardt & Kissler-Patig 1999, Larsen et al. 2001, Brodie et al. 2005). A model of elliptical galaxy formation with a simple monolithic collapse and subsequent star formation cannot produce the bimodal colour distribution of GCs. Multiple Collapse (Forbes et al. 1997) ― all GCs formed coevally with the host galaxy in massive star formation within a short time scale at high redshift but with discrete starburst phases, some of the red GCs formed in gas clouds more polluted. Merger (Ashman & Zepf 1992) ー luminous ellipticals formed via gas-rich mergers which induce formation of additional red GCs, while blue ones originate in the progenitor galaxies. Accretion (Cote et al. 1998) ー blue GCs were captured from other less luminous galaxies through tidal stripping and/or accretion. => intergalactic globular clusters (i-GCs)

3. search for intergalactic GCs By surveying directly for i-GCs and characterizing this population, it is possible to test the validity of the accretion scenario. HST Subar u

4. 2  x 0.5  (640 kpc x 130 kpc) A large area needs to be surveyed to see whether there are additional i-GCs and to discriminate them from GCs associated with the galaxy.

5. Subaru Suprime-Cam Observation of M87 GCs Data for HDF-N and Lockman Hole are retrieved from SMOKA. 17 & 18 March 2004 Typical seeing sizes during the observations were 1.”5 in B and 1.”0 in V and I.

7. Selection of GCs The colour criterion to select GC candidates is indicated by green. Open squares show z=0, 0.5, 1.0, 1.5, and 2.0 on each evolutionary track.

8. median smoothing & subtraction before after

9. GC Colours Bimodal Distribution M87 NGC4552 The colour distribution of GCs in the inner most region shows bimodality both in M87 and NGC4552. This bimodality becomes less clear in the outer regions due to a decreasing contribution of the red GC population. Red GCs (V- I>1.1) Blue GCs (V- I<1.1) [Fe/H]= -0.13 & - 1.0

11. Colour Gradients [Fe/H]=4.3(V-I)-5.3, Vazdekis et al. (1996) SSP, Salpeter IMF, 12.6Gyr Colour gradients are probably due to a combination of decreasing fraction of red GCs and colour gradients in each subpopulation. Blue GCs have no gradient in the outer region of luminous elliptical galaxies ([Fe/H]=-2.3).

12. Whilst red GCs has a similar distribution to the host galaxy halo light, the blue GC distribution tends to be more extended. Radial profiles of GC surface densities M87 NGC4552 Halo light 1’ = 4.67 kpc 1’ = 4.47 kpc RGC BGC TOTAL

13. Distribution of S N Frequency BGCs RGC s M87 (S N =13.2) NGC4552 (S N =4.8) The increasing trend of local S N with distance is due to the fact that blue GCs tend to be more extended that the host galaxy halo light distribution. total (luminosity of host galaxy halo calculated with de Vaucoulerurs law)

14. Surface Density of BGCs M87NGC4552 Virgo mass profile (McLaughlin 1999) The blue GC population around M87 is not extended as the Virgo cluster mass density profile.

15. Intergalactic GCs (i-GCs)? There is an excess of GCs by ～ 0.2 arcmin -2 in the surface number density at r ～ 100arcmin (450kpc) from M87, suggesting the existence of independent GC populations; ie., intergalactic GCs of inhomogeneous distribution (cf i-PNe). specific frequency S N =2.9 M87NGC4552

16. GC Luminosity Functions (GCLFs) A Gaussian is fit to the LF at magnitudes with ≥ 50% completeness Vpeak = 23.61±0.08 mag (M87), 23.49±0.16 mag (NGC 4552) (Consistent with the results from HST studies; Kundu et al. 1999; Kundu & Whitmore 2001)

17. GCLFs of Blue & Red GCs Assuming that GCs are uniformly old, this offset can be explained by a metallicity difference between the two GC subpopulations; [Fe/H] = -0.3 (red) and -1.6 (blue) (Jordan et al. 2002). In M87, the turnover mag for the red GC subpopulation appears to be fainter by ~ 0.5 mag than that for the blue GC subpopulation.

18.  An unprecedented wide-field survey ( ～ 0.6 Mpc from the M87 centre) of GCs around M87 with Subaru/Suprime-Cam Secure selection of GC candidates with an extended source cut and a colour selection on the B-V vs. V-I diagram. Analyzed the Suprime-Cam data of the HDF-N and the Lockman Hole, which are compatible with the M87 data set in terms of filter set, seeing sizes and limiting mags and enable to select contaminating objects with the identical criteria to those for GC candidates in the M87 fields. (1) Most of the blue GCs must be associated with the host galaxy, not the cluster, even in central cluster galaxies like M87. (2) Blue GCs are linked with the dark matter halo of a massive E galaxy, whilst red GCs are associated with the stellar body. (3) Formation of Blue GCs was accompanied by the collapse of the dark matter halo, whilst red GCs and field stars coevally formed in subsequent starbursts.

19. The blue GC population may have formed in situ at the very early stage of elliptical galaxy formation. If this is the case, the high S N values of luminous ellipticals at the cluster centre could be explained with biased GC formation in denser environments. Alternatively, the distinct spatial distribution between red and blue GCs is predicted by the merger scenario, although galaxy mergers accompanied by starbursts and red GC formation would need to be complete at very high redshift.

20. Simulation of Galaxy Formation Abadi et al. (2003) ApJ 591, 499 DM star The BGC populations seem to be associated with the dark matter distribution, which suggest that BGCs were formed even before sub-galactic clumps had coagulated into the progenitor of a massive elliptical galaxy (z>4?).