1. The cluster environment of high redshift FRI radio galaxies
Gianluca Castignani
(SISSA)
Collaborators:
Marco Chiaberge (STScI, INAF-IRA Bologna, JHU), Annalisa Celotti (SISSA), Colin Norman (JHU, STScI), Ranieri Baldi (SISSA)

2. Radio morphologies, Fanaroff & Riley (1974)
FRIs
FRIIs
Zirbel (1996)
FRI: Jet decelerates to v << c at ~1kpc
FRII: Relativistic jet on scales ~100 kpc up to ~1Mpc
FRI / FRII divide: L178 MHz<2 x 1026 W Hz-1
Zirbel, 1996
FRI: Jet decelerates to v << c at ~1kpc
FRII: Relativistic jet on scales ~100 kpc up to ~1Mpc
FRI / FRII divide: L178 MHz<2 x 1026 W Hz-1

3. FRIs
Locally:
“starved quasar”: faint optical nuclear emission (Chiaberge et al. 1999, Leiptzki et al. 2009, Baldi et al. 2010)
Host galaxy: mainly giant elliptical (cD) with the most massive BHs (Donzelli et al. 2007, Zirbel & Baum 1997)
~70% of them in rich clusters, at variance with FRIIs (Hill & Lilly 1991; Zirbel 1997; Wing & Blanton 2011)
At high redshift:
Two FRIs at z~1 (Snellen & Best 2001)
~30 FRI candidates at z~1-2 (Chiaberge+09)

4. FRIs at z~1-2. Why? Clusters AGN Beacons for HIGH REDSHIFT CLUSTERS
Link between z>~2 protoclusters and clusters
Formation and evolution of the red sequence
AGN
Cosmological evolution unknown
Hints for strong evolution up to z~0.7 (Sadler et al., 2007)
Formation and evolution of the most massive galaxies and Bhs
Feedback: BH accretion - environment

5. The sample Redshifts Redshifts
FRIs candidates at z~1-2, Chiaberge et al., 2009 (C09)
COSMOS (2sq degrees)
Mainly based on radio (FIRST) and optical selection, NOT on redshifts
Redshifts
Accurate redshifts (Baldi et al. 2013) are required to redefined the sample in radio power
Few spectroscopic-z: zCOSMOS bright (Lilly et al. 2007) Magellan (Trump et al. 2007)
Photo-z: SED modeling stellar population(s) and dust component(s)
FRIs candidates sample z~1-2, Chiaberge et al., 2009 (C09)
COSMOS field (2sq degree)
Mainly based on radio (FIRST) and optical selection, NOT on redshifts
Redshifts
Accurate redshifts (Baldi et al., 2013) are required to redefine the sample in radio power
Few spectroscopic-z: zCOSMOS, Lilly et al., 2007; Magellan, Trump et al., 2007
Photo-z: SED modeling stellar population(s) and dust component(s)

6. Clusters around LLRGs? Cluster candidates around Low Luminous Radio Galaxies? (FRIs)
The C09 sample redefined in radio power
21 LLRGs
11 High Luminous Radio Galaxies (HLRGs)

7. Two cluster candidates
Figure: Field of COSMOS-FRI 01, cluster from visual inspection
RGB images. Red: Spitzer 3.6μm. Green: optical i-band. Blue: optical V-band
Figure: Field of COSMOS-FRI 026, cluster?

8. Cluster search techniques
SZ effect, only a few at z>1 (e.g. Planck coll. XXIX 2013; Hasselfield et al. 2013, Reichardt et al. 2013)
X-ray (Rosati et al., 2002): B~(1+z)-4
Photo-z and number counts (Eisenhardt et al. 2008; Knobel 2009, 2012; George et al. 2011)
Color selection (e.g. Gladders & Yee 2005; Papovich et al, 2008). Red-sequence is just forming between z~1-2 (Hilton et al. 2010; Fassbender et al. 2011; Santos et al. 2011)
Search around radio galaxies (Miley & De Breuck 2008, Galametz et al. 2012, Wylezalek et al ) only FRIIs adopted

9. Poisson Probabiliy Method (PPM) Castignani et al., in prep
Existing methods seem to be less efficient at z>~1.5 (only 9 spectroscopically confirmed z>~1.5 clusters, see Tozzi et al. 2013)
Methods based on photo-z and number counts (Scoville+2013 and and ref. therein) affected by:
1) low number counts
2) increasing photo-z uncertainties
3) photo-z catastrophic failure at z~1.5 (redshift desert)

10. PPM, how does it work?

11. PPM, how does it work?
> 2sigma
> 3 sigma
> 4sigma

12. PPM plots
3.5σ detection (LLRG)

13. PPM plots
3.9σ detection (LLRG)

14. PPM plots
2.5σ detection (LLRG)

15. Papovich (2008) method
1.6 μm bump in the SED of red galaxies (opacity of the H− ion in atmospheres of cool stars, John 1988)
Galametz et al. (2012)

16. Papovich (2008) method
Red galaxies are selected ([3.6]-[4.5])AB> -0.1 mag (SPITZER-COSMOS)
The overdensity is evaluated as a number excess of red galaxies with respect of the COSMOS mean number density
Seven >2σ orverdensities are detected
All of them are also found with the PPM
The Papovich (2008) test does not find our z~1 clusters
...and some of our z≈2 candidates (e.g. 05, 226, also suggested in Chiaberge et al. 2010). Are they blue clusters?

17. Two z~1 X-ray rich groups
Simulated clusters
Two z~1 X-ray rich groups
(M500 ≈ 6e+13 Msun - Finoguenov et al. 2007)
moved at higher z
Cluster membership based on:
1) PPM projected and redshift information
2) sources with the lowest (K-I)AB are selected
Statistical Photo-z redshift uncertainties included
IAB<25 selection (according to Ilbert et al. 2009)

18. The groups are detected up to z=1.5
Simulated clusters
The groups are detected up to z=1.5

19. The groups are detected up to z=1.5
Simulated clusters
The groups are detected up to z=1.5

20. The groups are detected up to z=1.5
Simulated clusters
The groups are detected up to z=1.5

21. Spherically symmetric simulated groups
Simulated clusters
Spherically symmetric simulated groups
- Richness (Nc = 10, 50, 100, 200, 300)
- Redshift (zc = 1.0, 1.5, 2.0)
- Comoving size (Rc = 1.0, 1.5, 2.0Mpc)
Rich groups (Nc≥100) are always detected
Groups with Rc = 1Mpc and Nc = 10 are detected at zc≥1.5
Groups detected up to an offset of ~100 arcsec from the position of the cluster

22. Overdensity detections
Gaussian filter to remove noisy patterns from the plot
Overdensities selected at ∆z=0.28 (i.e. 2σ photo-z uncertainty at z~1.25 for i+AB~24 galaxies)
Peak finding algorithm to detect each overdensity in the field
The overdensities found within the FRI redshifts uncertainties are associated with the radio galaxy.
LLRGs: 14/21
HLRGs: 8/11
...in agreement with what found locally
69%

23. Gravitational arc in the field of COSMOS-FRI 01!!
Figure: HST ACS image of the field of COSMOS-FRI 01

24. Stacked weak lensing analysis
Clusters around LLRGs only
NFW+stars (George et al )
Signal compatible with rich groups: M200~1013.3Msun
WORK in progress...
Courtesy of Matthew George (University of California – Berkley)

25. FRIs plus PPM → z∼1-2 cluster search around FRIs
Conclusions
FRIs plus PPM → z∼1-2 cluster search around FRIs candidates
~70% cluster detection success
high redshift FRIs are in dense environment, as found locally
Future work...
Weak lensing signal from the stacking of our (LLRGs) cluster candidates (in progress...)
CM plots, red sequence??
PPM and wide field surveys, e.g. SDSS Stripe 82, LSST:
∼1000 or more FRIs expected
PPM needs beacons and good photo-z
FRIs plus PPM → z∼1-2 cluster search around FRIs
candidates
● ~70% cluster detection percentage
● high redshift FRIs are in dense environment, as found locally
Future work...
● Weak lensing signal from the stacking of our (LLRGs)
cluster candidates (in progress...)
● CM plots, red sequence??
● PPM can be applied to wide field surveys, e.g. SDSS
● stripe 82, Chandra Deep field(s) North/South :
● ∼1000 or more FRIs expected
● PPM needs targets (e.g. FRIs) and good photo-z