The Astrophysical Journal, 630:68–81, 2005 September 1 # 2005. The American Astronomical Society. All rights reserved. Printed in U.S.A. FEEDBACK AND BRIGHTEST CLUSTER GALAXY FORMATION: ACS OBSERVATIONS OF THE RADIO GALAXY TN J1338À1942 AT z =4.11 Andrew W. Zirm,2 R. A. Overzier,2 G. K. Miley,2 J. P. Blakeslee,3 M. Clampin,4 C. De Breuck,5 R. Demarco,3 H. C. Ford,3 G. F. Hartig,6 N. Homeier,3 G. D. Illingworth,7 A. R. Martel,3 H. J. A. Ro¨ttgering,2 B. Venemans,2 D. R. Ardila,3 F. Bartko,8 N. Benı´tez,9 R. J. Bouwens,6 L. D. Bradley,3 T. J. Broadhurst,10 R. A. Brown,6 C. J. Burrows,6 E. S. Cheng,11 N. J. G. Cross,12 P. D. Feldman,3 M. Franx,2 D. A. Golimowski,3 T. Goto,3 C. Gronwall,13 B. Holden,6 L. Infante,14 R. A. Kimble,4 J. E. Krist,15 M. P. Lesser,16 S. Mei,3 F. Menanteau,3 G. R. Meurer,3 V. Motta,14 M. Postman,3 P. Rosati,5 M. Sirianni,3 W. B. Sparks,3 H. D. Tran,17 Z. I. Tsvetanov,3 R. L. White,3 and W. Zheng3 Receivedv 2005 February 15; accepted 2005 May 11 ABSTRACT We present deep optical imaging of the z ¼ 4:1 radio galaxy TN J1338À1942, obtained using the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope, as well as ground-based near-infrared imaging data from the European Southern Observatory (ESO) Very Large Telescope (VLT). The radio galaxy is known to reside within a large galaxy overdensity (both in physical extent and density contrast). There is good evidence that this ‘‘protocluster’’ region is the progenitor of a present-day rich galaxy cluster. TN J1338 is the dominant galaxy in the protocluster in terms of size and luminosity (in both the optical and near-infrared) and therefore seems destined to evolve into the brightest cluster galaxy. The high spatial resolution ACS images reveal several kiloparsec-scale features within and around the radio galaxy. The continuum light is aligned with the radio axis and is resolved into 9 two clumps in the i775 and z850 bands. These components have luminosities 10 L and sizes of a few kpc. The estimated nebular continuum, scattered light, synchrotron- and inverse Compton–scattering contributions to the aligned continuum light are only a few percent of the observed total, indicating that the observed flux is likely À1 dominated by forming stars. The estimated star formation rate for the whole radio galaxy is 200 M yr .Asimple model in which the jet has triggered star formation in these continuum knots is consistent with the available data. A striking, but small, linear feature is evident in the z850 aligned light and may be indicative of a large-scale shock associated with the advance of the radio jet. The rest of the aligned light also seems morphologically consistent with star formation induced by shocks associated with the radio source, as seen in other high-z radio galaxies (e.g., 4C 41.17). An unusual feature is seen in Ly emission. Awedge-shaped extension emanates from the radio galaxy perpendicularly to the radio axis. This ‘‘wedge’’ naturally connects to the surrounding asymmetric, large-scale (100 kpc) Ly halo. We posit that the wedge is a starburst-driven superwind associated with the first major epoch of formation of the brightest cluster galaxy. The shock and wedge are examples of feedback processes due to both active galactic nucleus and star formation in the earliest stages of massive galaxy formation. Subject headinggs: galaxies: active — galaxies: halos — galaxies: high-redshift — galaxies: individual (TN J1338À1942) 1. INTRODUCTION gions of the universe. The study of young overdensities at high redshift (‘‘protoclusters’’) then also traces the history of the fu- The most massive galaxies in the local universe reside in the ture brightest cluster galaxies. centers of rich clusters. Within the context of hierarchical models Many observing programs, spanning wavelengths from radio of biased galaxy formation, the mass of a galaxy and its clus- to X-ray, have been devoted to identifying galaxy overdensities tering properties are naturally connected via the initial density fluctuations (e.g., Kaiser 1984). Therefore, not only locally, but over a large range of redshifts (e.g., Postman et al. 1996, 2002; Scharf et al. 1997; Stanford et al. 1997, 2002; Rosati et al. 1998, throughout cosmic time, massive galaxies mark the densest re- 9 Instituto de Astrofı´sica de Andalucı´a (CSIC), Camino Bajo de Hue´tor 24, 1 Based on observations made with the NASA/ESA Hubble Space Tele- Granada E-18008, Spain. scope, which is operated by the Association of Universities for Research in 10 Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel. Astronomy, Inc., under NASA contract NAS 5-26555. These observations are 11 Conceptual Analytics, LLC, 8209 Woburn Abbey Road, Glenn Dale, associated with program 9291. MD 20769. 2 Leiden Observatory, Postbus 9513, 2300 RA Leiden, Netherlands. 12 Royal Observatory, Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK. 3 Department of Physics and Astronomy, Johns Hopkins University, 3400 13 Department of Astronomy and Astrophysics, Pennsylvania State Uni- North Charles Street, Baltimore, MD 21218. versity, 525 Davey Laboratory, University Park, PA 16802. 4 NASA Goddard Space Flight Center, Code 681, Greenbelt, MD 20771. 14 Departmento de Astronomı´a y Astrofı´sica, Pontificia Universidad Cato´lica 5 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 de Chile, Casilla 306, Santiago 22, Chile. Garching, Germany. 15 Jet Propulsion Laboratory, MS 183-900, 4800 Oak Grove Drive, Pasadena, 6 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, CA 91109. MD 21218. 16 Steward Observatory, University of Arizona, Tucson, AZ 85721. 7 UCO/ Lick Observatory, University of California, Santa Cruz, CA 95064. 17 W. M. Keck Observatory, 65-1120 Mamalahoa Highway, Kamuela, 8 Bartko Science and Technology, 14520 Akron Street, Brighton, CO 80602. HI 96743. 68 ACS OBSERVATIONS OF TN J1338À1942 AT z =4.1 69 1999; Oke et al. 1998; Holden et al. 1999, 2000; Kurk et al. 2000; The giant (100 kpc) Ly -emitting halos surrounding distant Pentericci et al. 2000b; Donahue et al. 2001, 2002; Francis et al. radio galaxies may be an observable consequence of feedback 2001; Mullis et al. 2003; Miley et al. 2004). To date, the most from galaxy formation (e.g., van Ojik et al. 1997; Reuland et al. distant protoclusters have been found at z 5 (Shimasaku et al. 2003). The enormous line luminosities of these objects, often in 2003; Venemans et al. 2004). Do these very young overdensities excess of 1044 ergs sÀ1, imply that they are massive reservoirs of already contain a dominant, massive galaxy? gas (Kurk et al. 2000; Steidel et al. 2000). What is the origin of There are several observational clues to the mass of a high- this gas: outflow from the galaxy or infall of primordial material? redshift galaxy. One is the observed K-band magnitude, which There are several pieces of circumstantial evidence that these probes the rest-frame optical data out to z 4. Another is the halos are connected with the AGN. The halos are often aligned presence of a high-luminosity active nucleus (a supermassive with the FR II radio axis, and in some cases Ly emission is di- accreting black hole), which implies the existence of a large rectly associated with radio structures (Kurk et al. 2003). Perhaps spheroidal host galaxy at least locally (Magorrian et al. 1998; photoionization by the AGN or shocks due to the radio source Gebhardt et al. 2000; Ferrarese & Merritt 2000). High-redshift expansion are responsible for the extended line emission. Spec- radio galaxies (HzRGs) are bright at the K band and harbor troscopically, Ly absorption is seen in addition to the bright powerful nuclei (Jarvis et al. 2001a; De Breuck et al. 2002; halo emission (e.g., van Ojik et al. 1997; Wilman et al. 2004). Willott et al. 2003; Jarvis & McLure 2002). Therefore, the fields There is a good correlation between the amount of absorption surrounding HzRGs are important targets for studying the and the size of the radio source (Jarvis et al. 2001b). A possible earliest examples of massive galaxies and clusters. Using a scenario is that a neutral hydrogen shell initially surrounds the narrowband Ly imaging program, Miley and collaborators radio source but is subsequently ionized during the growth of discovered an overdensity of star-forming galaxies around all the radio source. There are also some halos known that do not four radio galaxies observed to sufficient depth out to z ¼ 5:2 contain a bright radio source (Steidel et al. 2000), suggesting (Venemans et al. 2004). The resulting set of protoclusters is the that perhaps the halo phenomenon is associated with the more subject of several ongoing studies. This discovery also implies general processes of galaxy formation rather than being specific that the radio galaxies are the seeds of the brightest cluster to active nuclei. galaxies. The radio galaxy TN J1338À1942 (z ¼ 4:1; De Breuck et al. The brightest cluster galaxies (BCGs) are the most massive 1999) resides in one of the youngest protoclusters known galaxies known in the local universe, with stellar masses in ex- (Venemans et al. 2002; Miley et al. 2004). This galaxy lies within 12 cess of 10 M (Jørgensen et al. 1996; Bernardi et al. 2003). The alargeLy halo that shows unusually asymmetric morphology luminosities and sizes of BCGs are not drawn from the same when compared to other similar radio sources (Venemans et al. distributions as those for the majority of the galaxy population 2002).