Selection criteria:

21 < R < 24 (-14 < MR < -11)

0.45 < (B – V) < 1.1 (3 arcsec apertures)

Highest priority to sources showing any sign of having profiles broaderthan stellar in ACS images

Unresolved in ground-based images (CFHT/CFH12K Adami et al. 2006)

Higher priority to sources with 0.15 < R – I < 0.6

Located in the core region with processed ACS images available beforeFeb. 11, 2007.

UCDs in the Coma ClusterKnown properties:

-13.5 < MV < -10.5

7 < Re < 100 pc

(V-I) = 0.8 - 1.2 Fornax – red, Virgo - blue

Kristin Chiboucas – Liverpool Coma Cluster Treasury Team Meeting – 16 April 2009

Targetted 47 candidates in 4 masks:

Measured secure redshifts for 29,

including 4 background objects 6 stars

Z = 0.021R = 23.4MR = -11.6

Z = 0.025R = 21.7MR = -13.3

Z = 0.023R = 22.1MR = -12.9

17.5˝

19 confirmed UCDs (4000 < cz < 10,000 km/s)6 questionable UCDs6 stars4 background galaxies12 failed (S/N too low)

47 targets18 / 27 (with R < 23.3) cluster members66% are members!

Properties of our confirmed UCDs

UCD Colors

Velocity distribution

<vr> = 7207 ± 144 km/s<vr> = 6299 ± 242

<vr> = 6968 ± 316 km/s<vr> = 6473 ± 207

<vr> = 6968 ± 172, σv = 1218<vr> = 6681 ± 183, σv = 797

7 UCDs near NGC 4874:

<vr> = 7313 ± 114 km/sσv = 300 km/s Maximum projected distance 3.7 arcmin (108 kpc)Consistent with being boundto NGC 4874.

Globular Cluster color distribution

F814W > 24.7

F814W < 24.7

GC (g – I)0 Peaks:Blue: 0.94Red: 1.19

UCD:Blue ave = 0.95Red ave = 1.17

Physical Sizes

(Sersic profile fitting)

(Kin

g p

rofil

e fit

ting)

Goal 2nd LRIS run (27-29 March): To fully characterize the properties and spatial distribution of the UCD population.

3 masks, ~40 - 45 objects per mask

Lousy weather: 1st 2 nights thick cirrus, 3rd night thin cirrus + poor seeingTargetted mask centered on IC 4051 first 2 nights, and central mask the 3rd night

New candidate selectionbased on confirmed UCDs

What we’ve learned so far:

• Large population of UCDs in the rich, dynamically evolved Coma cluster • UCDs appear to reside preferentially in core region or associated with giant galaxies in the core and have a lower population velocity dispersion than other galaxy types.• Properties are consistent with what has been found in other clusters.• Properties and spatial distribution consistent with UCDs as bright extension of GC sequence• However, that would not explain the high M/L ratios found for UCDs in other clusters. We also see some similarities with cEs.

Still to do: • Line index stellar population ages, metallicities• Comparison with properties of nuclei of dE,Ns

Ultra Compact Dwarfs in the Coma ClusterUltra Compact Dwarfs in the Coma Cluster

Kristin ChiboucasKristin Chiboucas Brent TullyBrent Tully Ron MarzkeRon Marzke Steve PhillippsSteve Phillipps James PriceJames Price Eric PengEric Peng ……