USING LOW POWER RADIO GALAXIES AS BEACONS FOR CLUSTERS TO “FILL THE GAP”

AT 1<z<2

Marco ChiabergeSpace Telescope Science Institute

A. Capetti INAF- OATOG. Tremblay RITP. Tozzi INAF-OATSP. Rosati ESOD. Macchetto STScIW.B. Sparks STScI 3C31 - ACS/HRC

MORPHOLOGICAL CLASSIFICATION OF RADIO GALAXIES

FR I FR II

LOW POWER HIGH POWER

Fanaroff & Riley 1974

L178 ~< 2 x 1026 W Hz -1 L178 >~ 2 x 1026 W Hz -1

Jet decelerates tov<<c at ~1kpc

Jet is relativisticon scales >100kpc

Zirbel &Baum 1995

The radio-loud AGN unification model

LOW POWER HIGH POWER

FR I

FR II

BL Lac

FSRQ

NLRG LEG? HEG

BLRG & SSRQ

QSO

Urry & Padovani 1995L178 ~< 2 x 1026 W Hz -1 L178 >~ 2 x 1026 W Hz -1

THE UNIFICATION SCHEME IS NOT JUST A MERE GEOMETRIC EXERCISE

It is a fundamental tool to investigate crucialaspects related to the physical properties of

the innermost regions of active nuclei andgalaxies in general

• Accretion/ejection

• The origin of radio loudness

• The relationship between the AGN and the environment (Induced/suppressed star formation, feedback…)

Radio galaxies are particularly important since theyare associated with the most massive elliptical galaxies

3C 338 - HST/ACS F814W 700s exp

THE NUCLEI OF FRI RADIO GALAXIESHST is able to show faint nuclei superimposed to bright host galaxies

Chiab, Capetti & Celotti 1999, Capetti et al. 2002, Verdoes-Kleijn et al. 2001, Whysong and Antonucci 2004; Balmaverde et al. 2006; Baldi , Chiab et al . in press

NON-THERMAL SYNCHROTRON EMISSION FROM THE BASE OF THE JET

THE RADIO-OPTICAL CORE CORRELATIONOF 3CR FR I NUCLEI

Optical emission from the base ofthe jet is observed in 80% of FRIs

FRIs are unobscured

Ldisk < 10-5 Ledd

No BLR (Nicastro 2000, Laor 2000)

Similar correlations are found in near IR and X-rays

The radio-loud AGN unification model

FR I

BL Lac

X-ray properties of FRIs

Nuclei: LX ~ 1041 erg s-1 NH < 1022 cm-2

The nuclear emission is jet-dominated (e.g. Balmaverde, Capetti & Grandi 2006, Evans et al. 2006)

Extended emission: synchrotron, from jets(e.g. Harris & Krawczynski 2006)LX < 1042 erg s-1 X-ray properties of FRIIs (and QSOs)

Nuclei: more powerful and absorbed

Extended emission (jets): IC (SSC or IC from CMB photons) (e.g. Celotti, Ghisellini and Chiab 2001)

LX ~ 1044-45 erg s-1

ASSOCIATED WITH GIANT ELLIPTICAL GALAXIES

HOSTING THE MOST MASSIVE BLACK HOLES (e.g. Donzelli , Chiab et al. 2007, Zirbel & Baum 1997)

ENVIRONMENT: CLUSTERS (e.g Hill &Lilly 91,Zirbel 1997)

MOST FRI ARE HOSTED BY cD GALAXIES

FRIIs are typically not in clusters

FRIs at low redshifts

“STARVED” QUASARSe.g. Chiab et al. 1999

WHY ARE WE LOOKING FOR FRIs AT 1 < z <2 ?

Cosmological Evolution of FRIs is basically unknown

Hints for strong evolution up to z~0.7 (Sadler et al. 2007)

FRI-QSOs are absent in the low-z universe: what is the fractionof FRI-QSO at high z? (e.g Blundell et al. 2002, Heywood et al. 2007)

The role of FRIs in the framework of the AGN unification scheme

FRIs as probes for studying the formation and co-evolution of the most massive galaxies and most massive BH

FRI as tracers of high-z clusters to bridge the gap 1 < z < 2When does the red sequence form?

Differently from FRIIs, in FRIs the AGN does not dominate the emission in crucial bands (IR, X-rays)

z=0.8

z = 1.2

Red sequence selected clustersIn the SpARCS survey

Demarco et al 2010

At what redshift does the red sequence form?

At what z do giant elliptical galaxiesform?

THE RED SEQUENCE IN HIGH-Z CLUSTERS

GIANT Ly a EMITTERS AROUND POWERFUL HIGH-Z RADIO GALAXIES

4C 41.17 z = 3.8

Miley & De Breuck 2008

WHY ARE WE LOOKING FOR FRIs AT 1 < z <2 ?

Cosmological Evolution of FRIs is basically unknown

Hints for strong evolution up to z~0.7 (Sadler et al. 2007)

FRI-QSOs are absent in the low-z universe: what is the fractionof FRI-QSO at high z? (e.g Blundell et al. 2002, Heywood et al. 2007)

The role of FRIs in the framework of the AGN unification scheme

FRIs as probes for studying the formation and co-evolution of the most massive galaxies and most massive BH

FRI as tracers of high-z clusters to bridge the gap 1 < z < 2When does the red sequence form?

Differently from FRIIs, in FRIs the AGN does not dominate the emission in crucial bands (IR, X-rays)

Only less than 10 clusters are confirmed in the Xrays at z>1

X- ray observations of high-z clusters

X-ray luminosity functions, mass, temperature, metallicity of the intraclustermedium are compared with predictions from cosmological models

CHANDRARDCS1252.9-2927z=1.24

kT= 6 keVZ= 0.36 Zsun

M= 2x1014 Msun

Rosati et al. 2004

3C 432 z=1.785

Fabian et al. 2003, Erlund et al. 2006

Extended emission around powerful high-z radio galaxies

Studies of the hot gas environment are hampered by the AGN

ICCMB radiation ~g 1000

CMB scales with (1+z)4

A SEARCH FOR LOW LUMINOSITY RADIO GALAXIES IN THE DISTANT UNIVERSE

FR I radio galaxies are known in the nearby universe only,as a result of the tight flux-redshift dependence in flux limitedsamples

In the 3C catalog, FR Is are

present only at z < 0.2

A few FR Is (~10) are includedin the 6C and 7C samples up toz~0.8

The most distant FR I known is at z ~1

(Snellen & Best 2001)

McLure et al (2004)

FLUX LIMITED SAMPLES CANNOT BE USEDThe search method must use of multiwavelength information

COSMOS (Scoville et al 2007, Koekemoer et al. 2007) has all the data we need

2sq deg survey of an equatorial area of the sky

Data were taken from the radio (VLA 1.4 GHz) to the X-rays

Basic assumptions:

the radio properties of high-z FRIs are similar to those of low z FRIs(no hot spots)

The FRI/FRII break does not change with redshift

The optical properties of high-z FRIs are similar to those of high-z FRIIs(they are hosted in red galaxies)

Selection Process

36 HIGH-Z FRICANDIDATES

RADIO (VLA)ANDOPTICAL(HST) IMAGES

Schinnerer et al. 07Koekemoer et al. 07

Chiab et al 2009

For each RG we count how many objects are at1.6 < zphot < 2.3 within a 90” radius from the RG

COSMOS FRI 03 58 objectsCOSMOS FRI 05 51 objectsCOSMOS FRI 226 53 objects

In 12 randomly selected control fields (that do not include any of our RGs):32 ± 2 objects

This is an overdensity factor ~2 at 4s

90” ~ 0.8Mpc at z =1.8

3 cluster candidates at z~1.8

Chiab et al 2010

COSMOS FRI 03 zphot = 1.96

RED = Spitzer 3.6mm GREEN = r band BLUE = B band

Mostly blue objects?

A significant numberof RED galaxieshave no zphot estimate

PHOTO-z DISTRIBUTIONS

RED FRI fieldsBLACK control fields

COSMOS FRI 03 COSMOS FRI 05 COSMOS FRI 226

BINS: Dz = 0.2

The extremely red galaxies are missed (too faint in i band to be in the catalog)

Chiab et al 2010

WHAT ABOUT FRIs at z~1 (and lower)?

5/8 FRI at 0.9 < zphot < 1.1 show clear over-densities

COSMOS FRI 01zphot = 0.92

Chandra 0.5-2 kev

VLA 1.4GHz

R = 3.6mm G = r band B = B band

Chiab et al. in prep.

1 orbit HST/ACS F814WCOSMOSKoekemoer et al. 2007

FRI atzphot = 0.35

VLA 1.4GHz

LOW-z FRI in the COSMOS field

What about FRIIs?

~5 FRIIs in our sample between 1< zphot < 2

2 FRII at z~1

None of them show signs of over-densities

FRIIzphot= 1.17

CONCLUSIONSWe discovered FRIs in the “unexplored” redshift range 1 < z < 2

The discovery of low luminosity radio galaxies at 1 < z < 2 opens a new wayto find clusters of galaxies in that range of redshift

It allows the study of the cosmological evolution of FRIs

We have 3 cluster candidates dominated by “blue” galaxies at z~1.8

FRIs are better than FRIIs as “beacons” for clusters

FUTURE WORK:The properties of high-z FRI: emission lines? X-rays? Radio? Host galaxies?Clusters: looking for X-ray emission (stacking)Detailed study of the z~1 cluster candidatesApply the same selection procedure to e.g. CDFs

WE NEED OBSERVING TIME!!VLT spectra of candidate cluster galaxies using MOSHST high resolution imaging and high-precision photometry

FRIIs: These are objects ~100 x less powerful than the FRIIs in the 3C sample, and still ~10x fainter than the FRIIs in the 6C and 7C