detection of a large-scale structure of intracluster globular clusters in the virgo cluster

Detection of a Large-Scale Structure of

Intracluster Globular Clusters in the Virgo Cluster

처녀자리 은하단내 은하간 구상성단의

거대구조 발견(Lee, Park, & Hwang 2010, Science)

박홍수 (Park, Hong Soo)

대형망원경사업그룹

2010. 3. 24 한국천문연구원 콜로퀴움

Contents

1. Introduction1.1 Properties of GCs1.2 Intracluster Objects1.3 Previous Studies of IGCs1.4 Limits of Study of Virgo IGCs

2. Virgo Intracluster GCs2.1 Data2.2 Method2.3 Density Map2.4 Radial Profile 2.5 Discussion and Implication

3. Summary and Future Work

M13, MW GC

M49, Virgo gEGlobular Clusters in the Virgo cluster

?

Introduction

Properties of Globular Clusters

GCs in our Galaxy

The number of GCs= 150 (Harris 2003)

Spatial distribution

Introduction


Color distribution of Galactic GCs

Metal Poor Metal Rich

Introduction


Color distribution of GCs in gEs

M87 Larsen et al.(2001)

Blue GCs Red GCsMetal Poor Metal Rich

Introduction


Luminosity function - Turn over magnitude - Mv(TOM) =-7.4 mag, width~1.6

M87 by Peng et al. (2009)

M87

Galactic GCs

Introduction


Radial number density profile

NGC 1399 by Brodie & Strader (2006)

Blue GCs Red GCs

(Stellar light)

Introduction


Spatial distributionBlue GCs : circular shapeRed GCs : stellar light

NGC 4636 by Park et al. (2010)

Blue GCs Red GCs

Stellar light

Introduction

How about GCs in a galaxy cluster ?

Introduction

Intracluster Objects

Zwicky (1951), van den Bergh (1956) :There may exist stars and interstellar mediumbetween galaxies in clusters of galaxies.

Intracluster Objects : They are gravitationally controlled by the potential of the galaxy cluster itself.ex) diffuse optical stellar light, planetary nebulae, resolved red giant stars, diffuse hot X-ray emitting gas

Introduction


Stellar Light : Mihos et al. (2005) : Virgo Cluster center.0.6 m Burrell Schmidt Telescope.~1.5x1.5deg : M,V filter.several long tidal streamers,a myriad of smaller scale tidal tails and bridges between galaxies.

Introduction


Planetary Nebulae (PN)Feldmeier et al. (2004)Intracluster PN in the Virgo cluster.KPNO-4m.PN luminosity density.

Introduction


Red Giant StarsDurrell et al.(2002) HST/WFPC2 Total(F814W)=33,800secan excess of a population of intracluster red giant branch (RGB) stars

Introduction


X-ray gasBohringer et al. (1994)ROSAT 12x12 degShowing hot luminous gas extending over most of the optically visible cluster.Showing that a large part of the mass of the cluster is centered on the galaxy M87.

Introduction

How about Intracluster GCs in a galaxy cluster ?

Introduction

Previous Studies of Intracluster GCs

White III (1987), Muzzio (1987), West et al.(1995)

Globular clusters should be stripped off from galaxies in a galaxy cluster and that there should be a cluster-wide population of

intracluster globular clusters (IGCs) in galaxy clusters.

Introduction


Marin-Franch et al. (2003) Coma cluster2.5 m Isaac Newton Telescope (INT).Using surface brightness fluctuation techniqueintracluster GCs do not exist in Coma.

Jordan et al. (2003) Abell 1185HST/WFPC2The point source excess is likely due to the presence of GCs.

Introduction


Tamura et al. (2006)Wide-field imaging survey of GC populations around M87

with Suprime-Cam on the 8.2m Subaru Telescope.

2x0.5 deg field extending fromthe centre of M87out to a radius of 0.5 Mpc.∼

Introduction


Williams et al. (2007)HST/ACS (I=26,880sec, V=63,440sec)discovery of 4 candidate IGCsin the Virgo cluster

Introduction

Study of Intracluster GCs

It is not yet known whether this cluster-wide population of IGCsexists in any galaxy cluster or not

because of shallow photometric limits or small area coverage.

The Virgo cluster is the best target to search for a cluster-wide

population of IGCs, because it is the nearest massive galaxy cluster.

Introduction

Virgo Galaxy Cluster

Distance=16.5 Mpc(m-M)=31Field of view : 12x18 deg

The GCs in the Virgo clusterare showed point sources through ground based telescopes .

Binggeli et al.(1985)Virgo Cluster Catalog (VCC) N=2096

Introduction

Study of Intracluster GCs

Because of its largest angular extent and the faintness of its globular clusters it has been difficult to find and study IGCs over the entire Virgo cluster.

The Sloan Digital Sky Survey

Virgo IGCs

Data

SDSS(The Sloan Digital Sky Survey)Photometric(ugriz) and spectroscopic survey.2.5m telescope at Apache Point Observatory, New Mexico1.5 square degrees of sky at a timeThe newest data catalog : DR7Legacy DR7 Imaging Sky Coverage(one-quarter of the entire sky)

Point source catalog in SDSS/DR6

Deep enough to study the bright GCs in Virgo.Wide enough to cover the entire Virgo cluster.

Virgo IGCs

Data

Hint to detect GCs in the Virgo cluster.Color-Magnitude Diagram (CMD) of GCs in 10 gEs and 10 control fields.Selection criteria for GC candidates.

0.6 < (g-i)0 < 1.3 19.5 < i0 < 21.7

-2.0<[Fe/H]<0.4

using the GCs known the radial velocity.

Virgo IGCs

Surface number density map of the Virgo GCs12x18 deg

Virgo IGCs

Method

Contamination by background or foreground sources

foreground stars disk and halo of our GalaxyPoint sources Virgo overdensity

unresolved background galaxies

not available of conventional method (target field-control field) Color-Magnitude Diagram(CMD) Method

Virgo IGCs

Method

Virgo overdensity (tidal stream or low-surface brightness dwarf galaxy)Juric et al. (2008)

Virgo IGCs

Method

CMD to make density map Selecting CMD regions for the foreground stars

Virgo IGCs

Method

Net GC density map= raw GC map – Foreground Star map

FS map=bright star map + faint star map

Virgo IGCs

Density Map

GCs in the Virgo cluster

- Diffuse large scale distribution of GCs

- Several strong concentrations

- Large size substructure

- Tidal feature: elingated structure, bridgelike feature

Virgo IGCs

Density Map

GCs vs. X-ray- similar to large scale

x-ray emission. (ROSAT all-sky survey)- not similar to

the west of M87the north of M87.

Virgo IGCs

Density Map

GCs vs. early-type galaxies(E+S0+dE) and late-type galaxies (S+SB+Irr)

Virgo IGCs

Density Map

Spatial distribution of Blue GCs and Red GCs- BGCs are more extended

than that of RGCs. IGCs are probably

dominated by Blue GCs. (stripped from dEs)- Blue GCs 0.6 < (g−i)0 ≤ 0.95 Red GCs 0.95 < (g−i)0 < 1.3

Virgo IGCs

Radial profile

Radial density profile after masking all galaxies with R<5R25

Change in the slope at R=40 arcmin(similar to edge of the stellar halo of M87, Doherty et al 2009) GCs at R>40 arcmin may be mostly IGCs.

Virgo IGCs

Radial profile

Similar to the slope of dE profile.Consistent with the slope from numerical simulations (Bekki et al. 2006). The IGCs may follow the dark matter distribution of the Virgo cluster.

Virgo IGCs

Radial profile

The density of the blue GCs is about twice as large as that of the red GCs for 40 arcmin < R < 6 deg

The IGCs may be dominated by the blue GCs.

Virgo IGCs

Radial profile

Radial density profile of the GCs inside masked galaxiesSlope is flat following the host galaxy potential

Virgo IGCs

The Number of IGCs

Total number of IGCs

N(IGC, 40’<R<6deg) = 1,500N(IGC corrected ) > 12,000

N(GC in galaxies) = 3,200N(total Virgo GCs) > 36,000

M87 by Peng et al. (2009)

M87

Virgo IGCs

Origin of IGCs

There is a wide distribution of IGCs and they are mostly blue (metal poor). The major origin of these IGCs is low-mass dwarf galaxies.

Mixture scenario for the origin of GCs in gEs (Lee, Park, et al. 2010) :Metal-poor GCs were formed mostly in low-mass dwarf galaxies.Metal-rich GCs were formed later with stars in massive galaxies or in dissipational merging galaxies.Elliptical galaxies grow via dissipational or dissipationless

merging of galaxies and via accretion of many dwarf galaxies.

IGCs in Virgo might have been stripped off from low-mass dwarf galaxies

and are now being accreted locally to nearby massive galaxies, and globally to the center of Virgo.

Virgo IGCs

Implication

Critical role in understanding how galaxies and galaxy clusters form and evolve.

If we get the radial velocity of the IGC candidates, we can investigate the detailed distribution of dark matter in galaxy clusters, the dynamical evolution of galaxy clusters, and the origin of the intracluster matter, with the help of theoretical modeling.

If we get their ages and metallicity either from the spectroscopy or from the high resolution imaging, we can explore the origin of globular clusters, and the formation of the first stars in the universe.

Summary and Future Work

Summary ?

M13, MW GC

M49, Virgo gEVirgo cluster


Ongoing Work

Next Generation Virgo Cluster Survey (NGVS) using CFHT/Megacamugriz filter


Future Work

To confirm of real IGCsDeep imaging of GCs candidates : HST, GMTRadial velocity of GC spectroscopy : 4m telescopes

Chemical properties of IGCs : Age and MetallcityCMD from deep imagesSpectra from spectroscopic observation : 8-10m telescopes, GMT

detection of a large-scale structure of intracluster globular clusters in the virgo cluster

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