USING LOW POWER RADIO GALAXIES AS BEACONS FOR CLUSTERS AT 1<z<2 Marco Chiaberge INAF-IRA Space Telescope Science Institute A. Capetti INAF- OATO G. Tremblay RIT P. Tozzi INAF-OATS P. Rosati ESO D. Macchetto STScI W.B. Sparks STScI Abell 370 HST/ACS SM4 ERO (K. Noll, Chiab and the HST SM4 ERO Team)

MORPHOLOGICAL CLASSIFICATION OF RADIO GALAXIES FR IFR II LOW POWERHIGH POWER Fanaroff & Riley 1974 L 178 ~< 2 x W Hz -1 L 178 >~ 2 x W Hz -1 Jet decelerates to v<<c at ~1kpc Jet is relativistic on scales >100kpc

3C HST/ACS F814W 700s exp THE NUCLEI OF FRI RADIO GALAXIES HST 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 CORRELATION OF FR I NUCLEI Optical emission from the base of the jet is observed in 80% of FRIs No “thick” dusty tori in FRI: FRIs are unobscured L disk < L edd 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 emission in 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 limited samples In the 3C catalog, FR Is are present only at z < 0.2 A few FR Is (~10) are included in the 6C and 7C samples up to z~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 FRI CANDIDATES RADIO (VLA) AND OPTICAL (HST) IMAGES Schinnerer et al. 07 Koekemoer et al. 07 Chiab et al 2009

For each RG we count how many objects have 1.6 < z phot < 2.3 with 90” radius from the RG COSMOS FRI objects COSMOS FRI objects COSMOS FRI 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 4  90” ~ 0.8Mpc at z =1.8 3 cluster candidates at z~1.8 Chiab et al 2010

COSMOS FRI 03 z phot = 1.96 RED = Spitzer 3.6  m GREEN = r band BLUE = B band Mostly blue objects? A significant number of RED galaxies have no z phot estimate

PHOTO-z DISTRIBUTIONS RED FRI fields BLACK control fields COSMOS FRI 03 COSMOS FRI 05 COSMOS FRI 226 BINS:  z = 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 01 z phot = 0.92 Chandra kev VLA 1.4GHz R = 3.6  m G = r band B = B band

FRI at z phot = 0.35 VLA 1.4GHzChandra kev XMM kev LOW-z FRI in the COSMOS field

What about FRIIs? We have identified 3 FRIIs in our sample between 1< z phot < 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 way to 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

Selection Process

FRII z phot = 1.17