Download Heart of darkness: The cluster Abell 545 and its “star pile”

Heart of darkness: The cluster Abell 545 and its “star pile”
Ricardo Salinas (ESO & Concepcion), Tom Richtler (Concepcion),
Michael West (ESO), Aaron Romanowsky (UCO/Lick), Ed Lloyd­Davies (Sussex), Ylva Schuberth (Aifa­Bonn)
The shape of dark matter profiles
Dark matter in cluster of galaxies seems unavoidable.
But its constitution remains a mystery.
The shape of dark matter profiles
Dark matter in cluster of galaxies seems unavoidable.
But its constitution remains a mystery.
N­body simulations predict:
α=1; cuspy profile
α<1; core profile
with α ~ 1 for cold dark matter (Navarro et al 1997, 2008)
The shape of dark matter profiles
Dark matter in cluster of galaxies seems unavoidable.
But its constitution remains a mystery.
N­body simulations predict:
α=1; cuspy profile
α<1; core profile
with α ~ 1 for cold dark matter (Navarro et al 1997, 2008)
Different observational approaches tend to agree:
X­rays (e.g. Vikhlinin et al 2006), gravitational lensing (e.g. Bradac et al. 2008), galaxy kinematics (e.g. Wojtak & Łokas 2007), S­Z effect (e.g. Mahdavi et al. 2007).
But...
The shape of dark matter profiles
The innermost mass profile is usually dominated by baryons.
The shape of dark matter profiles
The innermost mass profile is usually dominated by baryons.
NGC6166
When the contribution of the central galaxies is considered the value for α is lower than 1:
α=0 for A2199 (Kelson et al. 2002)
α=0.52 for MS2137­23 (Sand et al. 2004)
α=0.45 for A383 (Sand et al. 2008)
Kelson et al. 2002
The shape of dark matter profiles
The innermost mass profile is usually dominated by baryons.
NGC6166
When the contribution of the central galaxies is considered the value for α is lower than 1:
α=0 for A2199 (Kelson et al. 2002)
α=0.52 for MS2137­23 (Sand et al. 2004)
α=0.45 for A383 (Sand et al. 2008)
Kelson et al. 2002
Cold dark matter model wrong?
Dynamical effects: adiabatic contraction (Gnedin et al. 2004, but see Zappacosta et al. 2006) and dynamical friction (El­Zant et al. 2004)
How can we discriminate between both scenarios?
Heart of darkness: The “star pile”in A545
Abell 545: Richness class 4, z=0.156, M~1*10^15Mo
“similar to the envelope of a cD galaxy, but without a nucleus” (Struble 1988)
50 kpc
FORS1
Heart of darkness: The “star pile”in A545
A cD halo?
Jordan et al. 2004
star pile
Photometry from FORS1 images
ICL? μR (star pile)~23 mag; μR(ICL)~26­30 mag (Zibetti et al. 2008)
Heart of darkness: The “star pile”in A545
A prediction:
M=1.5*10^15Mo
Salinas et al. 2007
Velocity dispersion profile of the star pile is coming soon!
The cluster Abell 545
<V>=47457 km/s ; z=0.158
σ = 1300 km/s
206 confirmed members
FORS2+GMOS
The cluster Abell 545
CFHT/MEGACAM
Learning from the X­rays
XMM­Newton
Learning from the X­rays
Tx = 8.79 +/­ 0.33 keV
Lx = (23.29 +/­ 0.14) *10^44 erg/s (16.0')
Total Mass = 2.9 x 10^14 Mo (<400kpc)
Gas Mass = 1.37 x 10^13 Mo
(< 400kpc)
f_gas~4.7% (<400 kpc)
FORS1 +XMM­Newton
Summary + Outlook
The “star pile” in Abell 545 is an extended low surface brightness structure at the center of a massive cluster.
As an old and metal rich population, its origin is probably connected to stripping and/or disruption of dwarf (giant) galaxies passing through the clusters' center.
It is an unrivaled object to test dark matter theories in cluster scales.
From 200+ member velocities the cluster is considered dynamically relaxed. More members coming from recent Blanco/Hydra observations.
The (distant) future: HST proposal to investigate the star pile's morphology?
Weak lensing to compare mass distribution?