Transcript Stellar populations in the intergalactic space (invited talk)

Magda Arnaboldi
INAF, Observatory of Turin
Intracluster Planetary Nebulae as
Dynamical Probes of the Diffuse
Light in Galaxy Clusters
• Observations of Diffuse Light
• Intracluster Light in Cosmological Simulations
• ICPNe in the Virgo Cluster: projected phase-space
distribution
• Future prospects
M. Arnaboldi
Magda
Arnaboldi,
 ICPNe
PNe as
asAstronomical
probes of diffuse
Tools
light in clusters
nd, 2005
July
July 22nd
Observations of
ICL in clusters
 1951. Zwicky claimed the discovery of
diffuse light in the regions between galaxies
belonging to the Coma cluster.
 1971-1977. Follow-up photographic surveys
for diffuse light in Coma and rich clusters.
 1989-1995. CCD photometry of diffuse light.
First accurate measurements in Coma
(Berstein et al. 1995).
Problems
 typical surface brightness of the ICL is less than 1% of sky brightness;
 it is difficult to disentangle between diffuse light associated with the
halo of the cD galaxy at the cluster centre and the diffuse light
component
Since 1995, large CCD and mosaic cameras have allowed
measurements of ICL in Abell clusters.
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Measurements of * in nearby clusters
Presence of diffuse light is traced by existence of tails, arcs and/or plumes
with typical B = 27.8 mag •
”, very narrow (~ 2 kpc ) and extended (~ 100
kpc) in Coma and Centaurus.
(Gregg & West 1998, Threntam & Mobasher 1998, Calcáneo-Roldán et al. 2000)
Diffuse light measured by deep CCD photometry out to large radii in clusters.
(Abel 1651: Gonzalez et al. 2000; Abell 1413 & MKW7: Feldmeier et al. 2002,
2004a; HGC 90: White et al. 2003; Gonzalez et al. 2004).
Diffuse light measured in z∼0.25 clusters from stacking of SDSS imaging
data.
SB measurements of the ICL ranges from 27.5 mag •
” at 100 kpc to 32
mag •
” at 700 kpc in the observed R band (Zibetti et al. 2005).
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Direct detections of IC stars
An alternative method for probing intracluster light is through the direct
detection and measurements of the stars themselves
•Intergalactic Supernovae (Gal-Yam et al. 2003) & Novae (Neil et al. 2004).
•Intergalactic Globular Clusters (West et al. 1995, Jordàn et al. 2003)
•UltraCompact Dwarfs (Drinkwater et al. 2003)
IC stars and gas in Virgo cluster
• Intracluster red giant stars (IRGB) (Ferguson, Tanvir & von Hippel, 1998;
Durrell et al. 2002). Excess
to the HDF.
of red number counts in Virgo IC fields with respect
• Compact isolated HII region (Gerhard, Arnaboldi, Freeman, Okamura 2002).
It will dissolve by internal process in 108 yr. Stars and metals will then be
added to the diffuse stellar population nearby.
• IC HI cloud (Oosterloo & Van Gorkom 2005)
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Importance of ICL in galaxy clusters
The ICL in cluster is relevant for the baryonic fraction condensed in stars, star
formation efficiency, and the metal enrichment of ICM via IC stars, especially
in the cluster centre. It contains a fossil record of galaxy evolution and
interactions in the cluster.
We expect different distribution functions
f(x,v) for the ICL depending on the formation
mechanism.
Merritt (1984): The ICL is removed from galaxies early during
the cluster collapse and its distribution is predicted to follow
Moore
(1996): the
is produced
duringand
galaxy harassment
closely
thatetofal.
galaxies.
ICLICL
smoothly
distributed
and tidalold
stirring during late infall. ICL still distributed in tails
dynamically
or plumes, dynamically young.
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Cosmological Simulations of Cluster Formation
from Springel et al. (2001)
High-resolution resimulation of a part of a Universe that collapes into a
galaxy cluster. Dark matter subhalos grow, fall into the cluster, may
survive or merge into larger halos.
 same processes may act on stars in galaxies, producing also ICL
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Velocity distributions and projected phase space
diagrams for the IC stars
Transvr.
Velocities
Radial
Velocities
R,V
z
x,Vz
y,Vz
The two-dimensional phase space diagrams in one cluster show filaments, clusters
of particles, and empty regions, all of which indicate a young dynamical age!
N. Napolitano et al. 2003, ApJ, 594, 172
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Cosmological Hydrodynamic Simulations with Star
Formation and Feedback
• Studies of ICL in cosmological simulations require a model of star
formation from cold gas, including cooling and feedback effects.
Recent studies are by Murante+2004, Willman+2004, SommerLarsen+2005. Here we use Gadget-2 with the two-phase model of
Springel & Hernquist (2003).
• Current hydrodynamic simulations have significantly lower particle
number than dark matter only simulations. Thus they cannot resolve
small galaxies in clusters, probably causing overestimate of predicted
ICL fraction. Recent high-resolution simulations obtain correct halfmass radii for galaxies above few 1010M. The large galaxies
contribute a substantial part of the ICL; this part can be studied.
• Galaxies must be identified by a substructure-finding algorithm; here
we use SKID (Stadel 2001).
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
ICL in a Cosmological Tree+SPH Simulation
Gadget-2 (V. Springel)
Star Formation
Cooling (Z=0)
2x4803 particles
Mass Resolution:
DM: 4.6 109 h-1 M
Gas: 6.9 108 h-1 M
Softening: 7.5 h-1
Box Size: 192 h-1 Mpc
CDM Concordance
model (8=0.8)
• We identified 117 clusters
with M>1014 h-1M
• Stars in clusters were
divided in two classes:
bound & unbound.
• we evaluated radial density
profiles of the two
components
G. Murante et al. 2004, ApJ, 607, L83
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Sersic fits
• “stacked” 2D star
profile used.
• Fit range: from center
to radius@1/3 central
surface density
• Sersic fit is critically
sensitive to the range
• =3.66 (total average),
4.37 (low-luminosity objects),
1.24 (high luminosity objects)
Clear evidence for
ICL at large radii!
Galaxies
ICL
Sersic fit
1/
 r than

ICL more centrally concentrated
log (light
r ) (see
logalso
Zibetti
33
   1
e  3.et
galaxy
al. 2005)
 re 

M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
ICL fractions, star ages
• More massive clusters show greater
ICL fractions
• Stars in field are older than stars in
galaxies (“slow” tidal effects?).
Murante et al. 2004; see also Sommer-Larsen et al. 2005
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
High resolution cosmological simulations
Gadget-2 (V. Springel)
Star Formation
Cooling (Z=0)
Feedback
1.5 106 particles in
Cluster
Mass Resolution:
DM: 1.0 108 h-1 M
Gas: 1.5 107 h-1 M
Softening: 2.1 h-1
Mass 1.6 1014 h-1 M
Virial R: 1.1 h-1 Mpc
CDM Concordance
model (8=0.8, h=0.7)
Borgani et al. (2005)
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Distribution of Dark Matter and Stars
z=3
z=1
z=0
Murante et al. 2005, in prep.
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Galaxies and Intracluster Stars
z=3
z=1
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
z=0
July 2nd, 2005
ICPNe in the Vigo cluster: projected phase-space distribution
• PNe trace light because the luminosity-specific stellar death rate should be
independent of the precise state of the underlying stellar population (Renzini &
Buzzoni 1986).
• The [OIII] line emission at 5007Å is the strongest emission from a PN; it allows the
identification & the measurement of its radial velocity
ON-[OIII]
OFF-(V+R)
ON-H
• We obtain PN number density
distribution and 2D radial velocity
fields in regions where the stellar
surface brightness is too faint with
respect to the night sky!
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Planetary Nebulae as tracers of cluster evolution
ICPNe as light tracers:
1.
2.
Narrow band imaging surveys with large field mosaic cameras
(WFI@ESOMPI 2.2m tel. + SuprimeCam@SUBARU)
Development+tests of selection criteria based on photometric catalogs from
Sextractor (Arnaboldi et al. 2003, ESO Messenger 112, 37) for the identification of
the ICPNe associated with the ICL (Arnaboldi et al. 1996, 2002, 2003; Okamura et al.
2002; Feldmeier et al. 1998, 2002, 2003, 2004; Aguerri et al. 2005, AJ, 129, 2585).
ICPNe as kinematical tracers:
1.
2.
Follow up studies aiming at measuring spectra from multi-slit spectrograph
(FORS2 @ ESO VLT; Gerhard et al. 2002, ApJ, 580, L121, Arnaboldi et al. 2003, AJ, 125, 514)
First spectra from multi-fiber spectrograph for a statistical significant sample
of ICPN (FLAMES @ ESO VLT; Arnaboldi et al. 2004, ApJ, 614, L33; ESO PR 24/04)
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Current surveys
Mosaic
imageinin
[OIII]
obtained
Mosaic image
[OIII]
obtained
withat
the SuprimeCam
@Subaru
8.2m
the
WFI@ESO-MPI
2.2m
tel.tel.
Layout of the fields already acquired
within this project in the Virgo cluster
(Map of Virgo from Binggelli et al. 1987).
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Results from narrow band
surveys
The ICPNe number density distribution in the Virgo
cluster is highly inhomogeneous:
• inhomogeneous distribution in single fields,
• field-to-field number density fluctuations.
HST RGBs. From Aguerri, Gerhard, Arnaboldi &
No ICPN in LPC.
Agreement with
Kud+2000
The distribution of
ICPNe in the Subaru
field is highly
inhomogeneous
al. 2005, AJ, 129, 2585
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Results from narrow band
surveys (cont.)
Significant field-to-field variation of the ICL in the Virgo cluster
No clear number density trend with distance from cluster center in M87
Mean surface luminosity density of ICL in Virgo core : 2.7 106 L 
’
(note the large rms = 2.1 106 L 
’ due to field-to-field variations!)
Mean surface brightness of ICL in Virgo core : B=29 mag ”
Mean fraction of light in ICL: <10 % (Aguerri et al. 2005; see also Feldmeier et al. 2004)
Fraction of stars in the ICL increases with the density of the environment:
<2% in loose groups (Castro-Rodriguez+2003, Durrel et al. 2004),
<10% in Virgo-like (Arnaboldi et al. 2003, Feldmeier et al. 2004, Aguerri et al. 2005),
 20% in rich clusters including cD halos (Gonzalez et al. 2000, Feldmeier et al. 2002,
Zibetti et al. 2005).
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Results from spectroscopic follow-up….
April 2002 FORS2 @ VLT &
DOLORES @ TNG (in the
Subaru field only)
March 2003 FLAMES @ VLT
for FCJ, Core and Subaru
fields
Flames FOV.
FORS2 & Flames of ICPNe
spectra show the [OIII]
doublet!
M.Arnaboldi et al. 2004, ApJ, 614, L33
Ly
ICPN single spectra
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
PN in the M87 halo
vmean = 1280 km/s
=240 km/s
ICPNe: they are
brighter than the
PNLF cut off for
M87
M84
NGC
4388
M86
M87
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
-150 750
226
2097 1151
721
730
1025
3049
I34, I35, I36, I38 are
over-luminous [OIII]
emitters & are bound
to M84 – Pop. Effects.
Flames FOV
1191
671
797
2373
Observed ICPN radial
velocities in the Subaru
field
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Summary spectroscopic results!
• Giant galaxies in clusters are very extended - PNe still associated
with M87 out to ~70 kpc & very extended halo also around M84
• The velocity histograms show strong field-to field variations.
• Dynamical times at the location of these fields are from 2× 108 yr
(FCJ) to 8×108 yr (SUB). Phase mixing to erase field-to-field
variations would take few Gyr.
Implications on adopted criteria
• We understand the selection biases that may lead to wrong identification, i.e.
continuum objects erroneously classified as emission line, in on-off imaging
surveys on mosaic frames.
• The fraction of spectroscopically confirmed targets is now f >80 % (down to
the limiting magnitudes), while in Freeman et al. (2000) was 50%!
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
Conclusions
1.
2.
3.
Observations indicate that diffuse light is important in
understanding cluster evolution, star formation history and the
ICM enrichment.
Measuring the projected phase space constraints how and when
this light originated and ICPNe are the only abundant stellar
component of the ICL whose kinematics can be measured.
We can then explore the effect of low/dense environment on
galaxy evolution with MSIS technique! (see O. Gerhard’s talk, this
conference. )
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005
M. Arnaboldi  ICPNe as probes of diffuse light in clusters
July 2nd, 2005