USING LOW POWER RADIOGALAXIES AS BEACONS FOR

CLUSTERS AT 1<z<2

Marco ChiabergeINAF-IRA

Space Telescope Science Institute

A. Capetti INAF- OATOG. Tremblay RITP. Tozzi INAF-OATSP. Rosati ESOD. Macchetto STScIW.B. Sparks STScI

Abell 370 HST/ACS SM4 ERO (K. Noll, Chiab and the HST SM4 ERO Team)

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

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, Balmaverde et al. 2006, Baldi et al . in prep

NON-THERMAL SYNCHROTRON EMISSION FROM THE BASE OF THE JET

THE RADIO-OPTICAL CORE CORRELATIONOF FR I NUCLEI

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

No “thick” dusty tori in FRI:FRIs are unobscured

Ldisk < 10-5 Ledd

No BLR (Nicastro 2000, Laor 2000)

Similar correlations are found in near IR and X-rays

ASSOCIATED WITH GIANT ELLIPTICAL GALAXIES

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

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

MOST FRI ARE HOSTED BY cD GALAXIES

FRIs at low redshifts

“STARVED” QUASARS

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)

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 < 2

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

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 USED

MULTIWAVELENGTH SELECTION

COSMOS (Scoville et al 2007….) is perfectly suitable

2sq deg survey of an equatorial area of the sky

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

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 have1.6 < zphot < 2.3 with 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 ~1.7 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 < z < 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

FRI atzphot = 0.35

VLA 1.4GHzChandra 0.5-2 kev

XMM 0.5-2 kev

LOW-z FRI in the COSMOS field

What about FRIIs?

We have identified 3 FRIIs in our sample between 1< zphot < 2

None of them show signs of over-densities

CONCLUSIONS

We 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 around our FRIs at z~1.8

FRIs are better than FRIIs as “beacons” for clusters