MPIA Hauscolloquium
12 5 2006
The Cluster Environments of
High Redshift Radio Galaxies
Jaron Kurk
MPIA Hauscolloquium
12 5 2006
Other Leiden PhDs involved:
Laura Pentericci
Carlos De Breuck
Michiel Reuland
Leiden students and postdocs:
Andrew Zirm
Huib Intema
Prof George Miley
Others:
Chris Carilli,
Wil van Breugel,
Adam Stanford
Steve Croft
G. De Lucia
T. Heckman
H. Ford
P. McCarthy
Dr Huub Röttgering
JK
PhD May 2003
Leiden HzRG
Cluster Program
Bram Venemans
PhD April 2005
Roderik Overzier
PhD May 2006
Thesis defense: May 30
Outline of Talk
• Introduction
– Clusters
– HzRGs
– HzRG-Cluster Program
• Some examples
– 1138 at z = 2.2
– 1338 at z = 4.1
• Program Results
– Line emitters
– Distant clusters
Importance of Distant Clusters
Distant clusters are of interest because
•
their presence constrains cosmological parameters (e.g. Eke et al. 1996)
•
their galaxies provide unique reservoir to investigate galaxy evolution
– clusters at z ~ 0.5 contain more blue galaxies (Butcher & Oemler 1984)
– scatter in colour-magnitude relation constrains formation mode
– central brightest cluster galaxies do not fit on LF
But difficult to find because of
•
•
contamination by foreground galaxies
cosmological surface brightness dimming of extended X-ray emission
Most distant clusters found to date
•
•
at z = 1.11 by X-rays (Stanford et al. 2002)
at z = 1.26 by X-rays and NIR imaging (Rosati et al. 1999, Stanford et al. 1997)
Properties of HzRGs
Indirect evidence that HzRGs are located in (forming) clusters
•
Radio galaxies observed in clusters or over-densities of galaxies
– Half of powerful RGs at z ~ 0.5 inhabit rich clusters (Hill & Lilly 1991, Yates et al.
1989), strong correlation with redshift as at z < 0.15 RGs avoid clusters (Prestage &
Peacock 1989)
– Nearby example of Cygnus A (Owen et al. 1997)
– Over-density of K band galaxies in 3CR fields (Best 2000, 2003)
and other z ~ 1 RG and QSO fields (Hall et al. 2001, Barr et al. 2004)
– Over-density of EROs and sub-mm galaxies near 4C41.17 (Ivison et al. 2000)
•
Radio galaxies observed in dense ambient gas
– High (> 1000 rad m-1) radio RMs (Carilli et al. 1997, Pentericci et al. 2000)
•
Hosts of HzRGs resemble brightest cluster galaxies
•
HzRGs are amongst the most massive galaxies up to z ~ 5 (De Breuck et al.
2002)
Properties of HzRGs
HzRGs are amongst the
most massive galaxies up
to z ~ 5
K-z diagram
Powerful AGN 
massive black hole 
massive galaxy
(Magorrian relation)
De Breuck et al. (2002)
Example HzRG: 1138-262 at z = 2.2
ACS/HST 20 orbits g+i
100 kpc
• Elements of both
hierarchical and
monolithic formation
• Morphological types that
dominate the faint
population in the UDF
(chains, tadpoles and
clump-clusters)
• Star formation in two
modes: LBG-like (50%)
and diffuse (50%)
Pentericci et al. (2002), Kurk (2003),
Miley et al. (in prep.)
Example HzRGs: emission line halos
1338 at z = 4.1
VLT line emission
ACS continuum
Zirm et al. (2005)
1138 at z = 2.2
VLT line emission
Radio 8 GHz continuum
Kurk (2003)
The Leiden HzRG Cluster Program
• Use HzRGs as beacons of forming clusters
– HzRGs have properties of forming BCGs
– Seem to live in dense environments at z ~ 1
– Most massive galaxies at any z and therefore found in most massive
DM halos
• Use Ly emitting galaxies as tracers of galaxy overdensities
– Strongest (intrinsic) emission line
– LAEs occupy faintest accesible part of LF
– Spectroscopic confirmation relatively easy
• VLT Large Program
– Eight radio galaxy fields at 2.2 < z < 5.2
– Twenty nights with FORS/VLT (and twenty hours LRIS/Keck)
– Narrow band imaging of 33 Mpc2 fields and MOS spectroscopy
Line emitting galaxies at high redshift
• Primordial galaxies should emit 3-6% of their bol. lum. in Ly, resulting
in EW0 = 100-200 Å (Charlot & Fall 1993)
• Ly is resonant, so large extinction can occur: only 25% of LBGs have
EW0 > 20 Å (Shapley et al. 2003)
• LAE surveys fashionable
– Hu et al. (1998), Rhoads et al. (2000),
Stiavelli et al. (2001), Ouchi et al. (2002),
Hu et al. (2004), Tapken et al. (2006),
Steidel et al. (2000)
– Little evolution of UV continuum with z
– Controversy about red colours and high
equivalent widths
– Clustering observed in large fields
• LAEs are currently redshift record holders
Intermezzo I - LAE at z = 6.5
• FORS2/VLT slitless spectroscopy combined with a medium band filter
• One LAE emitter found at z = 6.518 with flux of 210-17 erg s-1 cm-2
• Comparison of LFs at z = 5.7 and z = 6.5 shows little evolution and
therefore reionization earlier than z = 6.5 (Malhotra & Rhoads 2004)
Kurk et al. (2004)
The NB Imaging Technique
Kurk (2003)
Individual HzRG Fields
• PKS 1138-262 at z = 2.16
–
–
–
–
–
–
Pilot VLT project (first VLT visitor observations, in 1999)
Lowest redshift of sample
Indications of dense environment
Suitable redshift for H narrow band imaging
Chandra X-ray , NICMOS, MOIRCS observations
Main subject of my thesis  my favourite object!
• TN J1338-1942 at z = 4.10
– One of the brightest (in Ly line and radio continuum)
– Most overdense field (in terms of LAEs)
– Drop-out imaging with ACS and Suprime-Cam
1138 Imaging
Imaging: 0.5 hr B band, 4 hr narrow band
- Fifty LAEs with EW0 > 20 A and F > 210-19 erg s-1 cm-2 A-1
Spectroscopy: 6, 5.5, 4 hr for each FORS1 mask
- Fifteen confirmed (out of 27)
Kurk et al. (2000)
1138 Spectroscopy results
Spectroscopic confirmation of 15 LAEs
- Single line rules out [OII], [OIII], Hβ
- One QSO: FWHM ~ 5800 km s-1, CIV emission
Pentericci et al. (2000)
1138 Spectroscopy results
Spectroscopic confirmation of 15 LAEs
- LAE redshifts centered on radio galaxy
- Probability redshifts drawn from random distr. < 0.4%
- Redshifts seem to be distributed in two groups
Monte Carlo Simulation
Kurk et al. (2004)
σv = 385, 205 km s-1
σv = 900 km s-1
2
3
Actual redshift distribution
1138 H imaging
• Two 2.5’2.5’ ISAAC fields
– HAEs have 5 higher density within 0.66’ radius compared
with outside 1.0’ radius
– No blank field HAE surveys deep enough to compare with
Kurk et al. (2004)
-
1138 H spectroscopy
Two nights of ISAAC spectroscopy confirmed redshifts nine HAEs, including one QSO, v = 360 km s-1
Kurk et al. (2004)
-
Intermezzo II - Wide field H survey
•
•
•
•
•
Finally NIR detectors with large FoV available
WFCAM survey at z = 2.2 of 1.5 deg2 (on-going, P.I. Smail)
VISTA survey at z = 0.8 of 1.6 deg2 (proposed, P.I. Fynbo)
LF of H emitting galaxies, good estimate of (global) SFR at z > 2
Comparison with HzRG fields (also other emission lines)
1138 X-ray sources
• Chandra imaging (40 ksec) reveals
– apart from RG 17 serendipitous sources in FORS field
– about 50% more soft sources with flux > 10-15 erg s-1 cm-2 than
in CDF (1.5 significance)
– coincidence with 3 LAEs, 1 HAE, 1 ERO
– optical/X-ray ratios indicate AGN
– four X-ray sources and RG roughly aligned
Pentericci et al. (2002), Croft et al. (2005)
-
1138 SCUBA companions
Field of 1138 is
second densest in
sample of seven
HzRG fields
(Stevens et al. 2003)
with three
companions, two of
them aligned E-W
1138 NICMOS CMD
Factor nine
overdensity in
red sequence
galaxies (1.3 < JH < 2.1) in six
NICMOS fields
near 1138
Zirm et al.
(in preparation)
RG Lya Ha
UDF/HDFN
1138 Subaru CMD
Red sequence galaxies (J-K > 2.3) in 4’7’ MOIRCS field (Kodama et al., in prep.)
Subaru NIR MOS and VLT optical MOS proposed
Red sequence
Lya Ha
(Vega)
1338 ACS imaging
ACS/HST FoV 3.4’3.4’
gri imaging to detect g-dropouts at z ~ 4
Compare with cloned GOODS B-dropouts
Factor 2.5 more g-dropouts than expected,
representing a 3 excess (i < 26)
More than 50% within 1 Mpc radius
Even stronger at i < 27
Alternative of a cluster of z ~ 0.5 Balmer
break objects improbable
RG
-
LAE
-
LAE
-
LAE
-
Miley et al. (2004)
-
g (4 orbits)
-
r (4 orbits)
i (5 orbits)
1338 Subaru imaging
Suprime-Cam FoV 25’24’
BRI imaging to detect LBGs at 3.5
< z < 4.5 (6% cont.)
874 LBGs with IAB < 26.5
125 LBGs with IAB < 25.0
Correl length r0 = 3.7 / 4.6 h-1 Mpc
Largest overdensity at pos of 1338
Size of ~ 2 Mpc includes 104
LBGs
7 coincide with confirmed LAEs
28-35 LBGs associated with RG
Overdensity 5-7
Spectroscopy needed to trace web
Intema et al. (submitted)
-
Conclusions on Ly Emitters
• In total ~ 300 LAEs of which ~ 150 confirmed
– spectroscopic confimation succes rate ~ 90%
– AGN fraction < 10%, based on line widths (95% < 1000 km s-1)
• lines asymmetric, sometimes with absorption (M(HI) up to 5104 M)
– LLy < 1043 erg s-1, fainter than L* in UV continuum
– No evidence for zero metallicity (max EW0 < 240 A)
Conclusions on Ly Emitters
– Continuum colours are blueer ( = -1.7) than for LBGs ( = -1.1)
– SFRs in the range 1 - 10 M yr-1 (LBGs typically > 10 M yr-1)
– Low dust content (blue UV and consistent Ly and UV SFR)
• extinction correction on Ly SFR << 2
– Ages < 100 Myr, in 16% < 10 Myr (from UV continuum)
– Half light radii (~ 1.0 kpc) smaller than for LBGs in GOODS (~
2.3 kpc, Ferguson et al. 2004)
Venemans et al.
(in prep)
Large Program Results
Name of RG
MRC 2048-272
MRC 1138-262
MRC 0052-241
MRC 0943-242
MRC 0316-257
TN J2009-3040
TN J1338-1942
TN J0924-2201
z
2.06
2.16
2.86
2.92
3.13
3.15
4.10
5.19
IMG SPC σv (km/s)
N/A
10
3
~900
37
15
~980
57
37
~715
65
28
77
31
~640
21
11
~515
54
37
~265
14
6
~305
Conclusions on Distant Clusters
• At least six out of eight fields show overdensity
– surface overdensity on the order of 3-5
• Confirmed emitters are clustered in redshift space
– width of vel. distr. 2-5 smaller than NB
• Estimated protocluster masses 2-91014 M
– assuming bias parameter b = 3-6 and certain volume V (Steidel et al. 1999)
M = <>V(1+m), 1 + bm = C(1+gal), C = 1 + f - f (1 + m)1/3
where <> is mean density of universe and C redshift space distortions
• Velocity dispersion decreases with redshift
• FoV too small to give reliable estimate of sizes
– but from second field near 1338 radius of ~ 2 Mpc seems correct
Venemans et al. (in prep.)
Conclusions on Distant Clusters
N-body modelling by G. De
Lucia shows that
– LAEs in protoclusters can be
identified with young (< 100
Myr) galaxies
• luminosity or colour is not
enough
– velocity distribution of
simulated clusters increases
with decreasing redshift
– HAEs near 1138 lie within
virialized core and may be
older (as suggested by their
brighter K-band continua)
Millenium simulation will
improve results
Venemans et al. (in prep.)
RG proto-clusters
Subgroups
Simulated clusters
Hubble Flow
Conclusions on Distant Clusters
Theory of linear spherical collapse
predicts critical density at which
structure will collapse, almost
indendent of cosmology L = 1.686
(Peacock 1999)
Compare evolution of linear matter
overdensity of protoclusters with
this critical density
1138
0316
gal  M  L
L(z) in CDM (Carroll et al. 1992)
1338 collapses at z ~ 0.5
1138, 0316, 0924 at z ~ 0
Overzier et al. (in prep.)
0924
1338
Intermezzo III - a QSO field at z = 6.3
• Overdensity of i-dropout galaxies in the field of QSO SDSS 1030+0524
at z = 6.28 (Pentericci et al., submitted)
• Follow-up spectroscopy (on-going, P.I. Walter)
EROs: extremely red
LAEs: purple
Empty slide
RG PKS 1138-262
BIK FORS/ISAAC
Abbreviations used
•
•
•
•
•
•
•
HzRGs: High Redshift Radio Galaxies
LAEs: Ly Emitters (Lyman- emitting galaxies)
HAEs: H Emitters
EROs: Extremely Red Objects
ERGs: Extremely Red Galaxies (red distant galaxies)
DRGs: Distant Red Galaxies (really red distant galaxies)
LBGs: Lyman Break Galaxies (blue distant galaxies)