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Globular Cluster Systems and Host Galaxies in the ACS Virgo Cluster Survey

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Title: Globular Cluster Systems and Host Galaxies in the ACS Virgo Cluster Survey


1
Globular Cluster Systems and Host Galaxiesin the
ACS Virgo Cluster Survey
Eric Peng NRC / Herzberg Institute of
Astrophysics (HIA) / DAO and the ACSVCS Team
2
The ACS Virgo Cluster Survey Project Team
Patrick Côté (NRC-HIA) David Merritt
(Rochester Inst. of Tech.) John Blakeslee
(Washington State Univ.) Milos Milosavljevic
(CalTech) Laura Ferrarese (NRC-HIA)
Eric Peng (NRC-HIA) Andrés Jordán (ESO)
John Tonry (Univ. of Hawaii, Manoa) Simona
Mei (Johns Hopkins University) Michael West
(Gemini South)
Dalia Chakrabarty (Rutgers) Elena Dalla
Bontá (Padova/HIA) Monica Hasegan
(Rutgers) Dean McLaughlin (Leicester) Steffen
Mieske (ESO) Marianne Takamiya (UH, Hilo)
3
Star Cluster Dim Sum
  • Cuisine
  • Star Clusters in Early-Type Galaxies
  • Restaurant The ACS Virgo Cluster Survey
  • On the Menu
  • Globular Cluster Color Distributions
  • GC Specific Frequencies
  • Diffuse Star Clusters
  • Metallicity-Color Relations

4
GC Color Distributions and Host Galaxies

Motivation Studying galaxy evolution
  • Individual galaxies (Milky Way) in great detail
  • Many galaxies of different properties with
    coarser observations

Star cluster studies represent a middle ground
Blakeslee et al 2005
Peng et al (2006a), ApJ, 639, 95
5
GC Color Distributions and Host Galaxies
  • Correlations with host galaxy luminosity
  • Mean metallicity of GCSs (van den Bergh 1975,
    Brodie Huchra 1991, Gebhardt Kissler-Patig
    1999)
  • Mean color of red GCs (Forbes et al 1997 Kundu
    Whitmore 2001)
  • Mean color of blue GCs (Larsen et al 2001
    Burgarella et al 2001 Strader et al 2004)
  • Blue GCs in dEs (Lotz et al 2004)


Larsen et al (2001)
Goal Study color distributions across early-type
galaxy properties using a single, large,
homogeneous data set.
6
Globular Cluster Color Distributions
For old (gt 10 Gyr) populations, color is a proxy
for Fe/H Bimodality Seen in most luminous
galaxies
7
Globular Cluster Color Distributions
For old (gt 10 Gyr) populations, color is a proxy
for Fe/H Bimodality Seen in most luminous
galaxies
8
Globular Cluster Color Distributions
For old (gt 10 Gyr) populations, color is a proxy
for Fe/H Bimodality Seen in most luminous
galaxies Control Fields essential for fainter
galaxies Prominence of red GCs a diminishes for
fainter galaxies.
9
Globular Cluster Color Distributions
For old (gt 10 Gyr) populations, color is a proxy
for Fe/H Bimodality Seen in most luminous
galaxies Control Fields essential for fainter
galaxies Prominence of red GCs a diminishes for
fainter galaxies.
10
Globular Cluster Color Distributions
For old (gt 10 Gyr) populations, color is a proxy
for Fe/H Bimodality Seen in most luminous
galaxies Control Fields essential for fainter
galaxies Prominence of red GCs a diminishes for
fainter galaxies.
11
Globular Cluster Colors vs MB
12
Globular Cluster Colors vs MB
Two-gaussian fits to individual GC systems GC
equivalent to the color-magnitude relation for
early-type galaxies
13
Globular Cluster Color Distributions
14
Correlations with Galaxy Magnitude and Color
  • Colors of both GC subpopulations correlate with
    galaxy magnitude and color
  • Red GCs have steeper slope

15
Color-Metallicity Relation
  • Absolutely crucial for interpretation
  • Previous work used linear V-I relation,
    heterogeneous data
  • MW, M49, M87 GCs
  • Relation is nonlinear
  • More later...

16
Stellar Mass vs Fe/H
  • Slopes for two populations similar in
    metallicity, ZM0.23, ZM0.17 (within 1 sigma)
  • Similar to slope of M-Z relation for SDSS
    galaxies (coincidence?)
  • Nearly constant 1 dex offset
  • Universal chemical enrichment between two
    epochs?
  • Formation of GCs similar across wide range of
    galaxies and metallicities

17
Truth in Advertising
Caution! Slope for metal-poor peak particularly
sensitive to slope of Fe/H-(g-z) relation
assumed.
18
Metallicity Dispersions
Red GCs have broader distribution in color, but
narrower distribution in Fe/H
Need to fit metal-rich GC formation into 0.3 dex.
Can we do this in episodic formation models?
What is the metallicity dispersion of first epoch
of Pop II star formation?
Caveat Results dependent on color-metallicity
relation, but no models produce a metal-rich GC
distribution wider than for metal-poor GCs.
19
Diffuse Star Clusters in Early-Type Galaxies
The Star Cluster Zoo Globular Open Populous Youn
g Massive Faint Fuzzies
NGC 4833


Pleiades
Peng et al. (2006b), ApJ, 639, 838
20
Diffuse Star Clusters in Early-Type Galaxies
  • Globular Cluster selection
  • Use Custom control fields
  • Knowledge of GC locus in size-magnitude diagram

(NGC 4472)
(NGC 4382)
Some galaxies have excess of low surface
brightness objects!
21
Diffuse Star Clusters
Typical Globular Clusters
22
Extended Star Clusters in Stellar Disks
  • Faint Fuzzies in S0 galaxies NGC 1023, 3384.
    Not in NGC 3115 (S0) or NGC 3379 (E).
  • Red, Fe/H-0.6, old (gt7 Gyr)
  • (Larsen Brodie 2000 Larsen et al 2001 Brodie
    Larsen 2002)

Extended, old star clusters in spiral galaxies
M81, M83, N6946, M101, M51 (Chandar, Whitmore
Lee 2005) Also in N5195 (Hwang Lee 2006)
23
Twelve galaxies with low surface brightness
excess gt 3-sigma
Lenticulars
M49 halo
LSB dE
3-sigma
24
The Colors of Diffuse Star Clusters


25
Spatial Distributions of Diffuse Star Cluster
Candidates

Blue (g-z) lt 1.0
Red (g-z) gt 1.0

Red star cluster Candidates follow stellar disk
26
Ages/Metallicities of Diffuse Star Clusters


27
Comparison with Milky Way Star Clusters
Globular
Old Open
28
Comparison with Extragalactic Star Clusters
UCDs
M81,M83, N6946 M101,M51
M31
Faint Fuzzies
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