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High redshift radio galaxies and
protoclusters
Laura Pentericci (INAF - Osservatorio di Roma)
G.K. Miley (Leiden),H.J.A.Rottgering (Leiden),
J Kurk (MPIA) B.Venemans (IoA-Cambridge), R.
Overzier (Leiden), C. Carilli(NRAO), W.
VanBreugel (LLNL), C. DeBreuck (ESO), T.
Heckman (JHU), H. Ford(JHU), P.McCarthy (OCIW),
S.A. Stanford (LLNL)
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Current known clusters at zgt1

• Optical searches have found clusters up to z 1
  e.g.
  ESO-DCS (Rudnick et al. 04), Las Campanas DCS ,
  Red Sequence Cluster Survey (Gladders et al. 05)
  .........
• X-ray searches have found clusters up to z1.45
  (Stanford et al. 06, Mullis et al. 2005)
  
• A handfull of clusters at zgt1 are now known and
  well studied (Bremer et al. 06, Mei et al. 06,
  Stanford et al. 05, Rosati et al. 04, Hashimoto
  et al.02)
• How do we go beyond this?
• ? Future SZ surveys (not sensitive enough now!!
  Carlstrom et al. 02)
• ? Selection of red sequence galaxies with Spitzer
  data _at_ 1ltzlt2 (e.g. Stanford
  et al. 05)
• ? Serendipitous discoveries (e.g. z3.09
  structure Steidel et al. 00)
• ? Protoclusters in large area surveys (e.g.
  Subaru DF, Ouchi et al. 05)
• ? Targetted searches fields of QSOs (Zheng et
  al. 06) and radio galaxies

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What can high redshift (proto)clusters tell us?
Determine the epoch of cluster formation so far
little evolution in cluster properties was found
up to z1.4 (Mullis et al.05, Mei et al.06)
Place constraints on cosmological models ??M
and ?8 (e.g. Eke et al. 99) Clusters provide
large numbers of galaxies with more or less
coeval formation epoch their properties and
evolution can be studied Study the influence
of environment on galaxies properties (e.g.
Postman et al. 05, Poggianti et al. 06)
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Proto-clusters around high redshift radio galaxies

• Why search in the environment of powerful radio
  galaxies at zgt2 ?
• HzRGs are presumably the progenitors of
  brightest cluster galaxies
  
  based on the fact that
• they are amongst the most massive galaxies at
  their redshift (Villar-Martin et al. 06,
  Zirm et al. 03, DeBreuck et al. 02)
• HzRGs have extremely high star formations rates
  based on UV spectroscopy
  (Dey et al. 97), detection of large amounts of
  dust ( Reuland et al. 04,Stevens et al. 03)
  and extended CO emission (Papadopuolos et
  al. 05, Klamer et al. 05)
• HzRgs are embedded in giant cD sized ionized gas
  halos (Kurk et al. 05, Pentericci et al.
  02)
• 20 of HzRGs exhibit extreme Faraday rotations
  (Pentericci et al. 02, Carilli et al.
  99) indicative of dense magnetized ICM

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VLT large program
Sample fields of 8 radio galaxies at 2ltz lt 5.2
Extremely deep observations through a Narrow
Band filter centred around the Ly? line of the
radio galaxy Deep observations in a nearby
continuum band (typically R or I band) Selection
of objects with significant emission in the
narrow band (rest-frame EW0FLy? /CLy ?
gt15 Å and significance ?gt3 ) down to a
magnitude limits mNB lt 25.5-26.3 (line flux
limit 0.5-3x10-17 erg s-1cm-2 ) Follow-up
multi object spectroscopy (FORS2 MXU) of the
brightest emitter candidates with resolution
2-300 km/s The VLT observations were paralleled
by HST/ACS observations of several radio galaxy
fields
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The richest structure, MRC 0316-257 at z3.13
redshift distribution
In this field there are 77 candidates and 31
confirmed Ly? emitters at z ?3.13, of which 1 is
another broad line QSO The velocity distribution
is gt3? away from random and clusters around the
radio source redshift (the peak of the
distribution is within 200 km/s of the RG
) ?640 ? 195 km/s The galaxy density
compared to the field density is n0316
/nFIELD3.3 ? 0.5
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The richest structure, MRC 0316-257 at z3.13
space distribution
The spatial distribution of the confirmed
emitters circles are blu-shifted and diamonds
are red-shifted (with reference to the RG
z) There seems to be no boundary to the structure
in the observed field (6.8' x 6.8') The density
does not change with distance from the RG The
total size is gt3 Mpc
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The richest structure, MRC 0316-257 at
z3.13 morphologies
The morphologies of some of the confirmed Ly ?
emitters imaged in the narrow band (VLT- left)
and in the continuum (ACS F814 filter right) Few
of them have a complex extended morphology
similar to the RG, suggestive of mergers, while
the rest is compact and/or unresolved Half
light radii0.5-1.5 kpc smaller than LBGs at same
z (2.8 kpc Ferguson et al.04)
Complex emitters Compact emitters
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TN J1338-1942 at z4.11
The tight velocity distribution of the
confirmed emitters around TNJ 1338 The
distribution is much narrower than the NB filter
selection function velocity dispersion is
?260?65 km/s (FWHM 625 km/s i.e. 1/4 than the
narrow band filter width 2860 km/s) Comparison
to the density of field Ly? emitters _at_ z 4
LALA (Rhoads et al. 00) n1338 /nLALA 5.2 ?
1.4 SDF (Ouchi et al. 03 ) n1338 /nSDF 4.5 ?
1.3
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The most distant structure around TNJ 0924-2201
_at_z5.2
The spectra of the 6 confirmed Ly ? emitters, 2
low redshift OIII emitters and the radio galaxy
The confirmed emitters all show an asymmetric
profile,with a sharp blue cut characteristic of
the Ly ? line The implied overdensity compared
to the field is a factor 1.5-6 (Venemans et al.
04)
The NB filter efficiency selection is indicated
with a dotted line
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Large program results

• We find similar overdensities of Ly ?
  emitters, in at least 6 of our 8 radio
  galaxies fields, up to the highest redshifts
  probed i.e. more than 75 efficiency

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Large program results
? these are confirmed as H? emitters
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Properties of the Ly? emitters
STAR FORMATION RATES typical SFRs are --0.4-10
M?yr-1 from line emission --0.4-20 M?yr-1 from
the UV continuum The average SFRuv /SFRline
is around 1 indicating the presence of little/no
dust On average SFRs are slighly lower than
LBGs at similar redshift
COLORS UV continuum slopes have an average
?-1.76 About 2/3 of the emitters have
slopes consistent to the prediction for
unobscured starburst galaxies (-2.6-2.1,
Leitherer et al. 99) On average these Ly
? emitters are bluer than the Ly? emitting
Lyman break galaxies which have ?-1.09 (Shapley
et al. 03)
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SIZES from HST/ACS images of some Ly? emitters
(available for 0316,1338, 1138 and 0902), typical
sizes are around lt 1.5 kpc On average Ly?
galaxies are fainter bluer and smaller than LBGs

NATURE OF Ly? EMITTERS Most of the Ly?
emitters have properties (SFRs, colors and sizes)
consistent with very young star-burst
galaxies where dust has not formed yet
A (small) fraction of the emitters harbours
AGNs In some of the fields (1138, 0316)
there are confirmed broad line AGNs, In 1138
there are 5 Ly??(narrow line) emitters associated
to relatively bright X-ray sources. Chandra
observations of the 1338 and 0316 fields also
show overdensities of X-ray sources
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Properties of structures
TOTAL MASS can be estimated from the mass
over-density as M ?
V (1?m ) V is the comoving volume,

? is the the current mean density
of the universe
? m is the matter over-density, related to
the galaxy over-density ?gal
1b ?m C (1 ?gal ) b is
the bias parameter (3-6 e.g. Shimasaku et al. 03)
C takes into account
redshift space distortions due to peculiar
velocities assuming the structure is just
breaking away from the Hubble expansion (Steidel
et al. 98)

The resulting masses are in the order 2-10 x1014
M? i.e. comparable to clusters of Abell
richness class 0 or higher
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Properties of the structures

• VELOCITY DISPERSIONS
• calculated using the biweight scale estimator
  (Beers et al. 90) which is appropriate for small
  samples. They range from 300 to 1000 km/s
• In two proto-clusters there are 2 subgroups of
  emitters with smaller dispersion (300 km/s )
• STRUCTURE SIZES
• Most structures seem unbound in the fields imaged
  (FORS field, gt 3x3
  Mpc2). Emitters are distributed homogeneously
  and their density does not change with distance
  from central RG
• In some cases (1338, 0943, 1138 ) the density of
  Ly?? emitters decreases with distance from RG and
  a boundary can be seen the estimated sizes are
  around 2 Mpc consistent with other structures
  (e.g. Shimasaku et al .03, Keel et al. 99)

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Comparison to simulation
Velocity dispersion of structures as a
function of redshift
the dispersion decreases with increasing redshift
in general agreement with numerical simulation of
massive clusters (e.g. Eke et al 1998)

Evolutionary line of DM velocity dispersion
of a simulated massive cluster structure with
??1000 km/s at z0 ? 800 km/s at z0



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Number densities-(i)
Are radio galaxy proto-clusters biased? Steidel
et al. estimate that there is one velocity spike
in each 9'x18' field of their survey or a total
of 9x 105 redshift spikes in the whole sky
between z2.7 and z3.4 (t0.6 Gyr)
translating in a number density of

From
the Subaru Deep field structures at z4 .9 the
implied number density is From Subaru Deep
Field overdensities of z5.7 the implied number
density is
3x 10-6 Mpc -3
7x 10-6 Mpc -3
gt2x 10-6Mpc -3
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Number densities- (ii)
How many HzRGs are there at 2ltz5.2 ?
From Dunlop
Peakok (90) there are 4x 10-8 Mpc -3 radio
sources with luminosity exceeding 1033 erg s
-1Hz -1sr -1 at 2.7 GHz (Cygnus A-type radio
sources) Assuming HzRGs are only active for 107
yr (Blundell Rawlings 99) the number of
(previously) active RGs is the 2 Gyr interval
between z5.2 and z2 is 200 x ------gt 8x 10-6
Mpc -3 About 75 of HzRGs have associated
protocluster ----gt This is consistent with
every velocity spike in the LBG surveys being
associated with a massive galaxy that has been
or will become a powerful radio source
6x 10-6 Mpc -3
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Number densities- (iii)
What objects in the local universe have
this density?? Cluster of galaxies with
masses Mgt 2-4 x1014 M? have a density
similar to these objects (Girardi et al. 98,
Reiprich Bohringer 02)
Consistent with the masses estimated earlier
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What are these structures?
Estimated masses larger than gt2 x1014 M?
Velocity dispersions of up to 1000 km/s
increasing with decreasing redshift in agreement
with simulations Number density of structures is
similar to that of clusters of Abel class 0 or
more in the local universe We conclude that
the structures observed around HzRGs are most
probably the progenitors of present day massive
clusters of galaxies, i.e. Proto-clusters
observed in the epoch of formation
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The high redshift radio galaxies
Parallel to the study of protoclusters we
have also investigated the properties of the
central radio galaxies, in the continuum and gas
emission
HST /ACS 19 orbit image of the central region
of the 1138 cluster (g475 I814 filters)
Several of the satellite galaxies have linear
tadpole and chain structures, similar to faint
galaxies in the HUDF . Relative velocities (from
Ly? line) are up to few hundreds km/s
(similar to proto-cluster dispersion) The
density of the linear galaxies is several times
higher than in the rest of the field (Miley et
al, 06 in press)
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VLT images of the extended Ly??halos that
surround the radio galaxies the images show a
wealth of structures, including low surface
brightness emission, cone shaped structures,
filaments and evidence of absorption..

Below 1138 Ly??halo extended by gt 200 kpc.
Emission is also seen from the satellite galaxies.
Above Ly? image of 1338 at z4.1. The surface
brightness ranges from 0.07 to 1 10-17 ergs s-1
cm-2 arcsec-2. The low-brightness halo is
extended to the NW, pointing away from the
overdensity structure. This Ly? halo is the most
asymmetric radio galaxy halo known.
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Summary
Proto-clusters around HzRGs are found out to
the largest distances where we have searched.
They have velocity dispersions in the range
300-1000 km/s and associated masses gt1014 M?
Targeting radio galaxies fields is a very
efficient (although not unique ) way to find
these distant structures The cluster populations
identified consists of very young, star forming
galaxies (with indications of nuclear activity in
few cases) Observations at other wavelengths are
on going, to study the rest of the cluster
galaxies population e.g. the red-sequence
galaxies (if present ) The central radio
galaxies show spectacular clumpy continuum with
many star-forming satellite galaxies, apparently
merging with the forming dominant galaxy, and
embedded in giant cD sizes gaseous halos
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MRC1138-262 _at_z2.2 and MRC0052-241 _at_z2.9
These two fields show a bimodal velocity
distribution bimodal velocity distribution of the
Ly? emitters i.e. there seem to be two
subgroups of galaxies (in velocity space)
perhaps in a merging phase. Each group has
?2-400 km/s The emitters have no preferred
location in space. PKS 1138-262 z2.2
MRC 0052-241 z2.9