Browsing by Author "Overzier, RA"

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    A large population of 'Lyman-break' galaxies in a protocluster at redshift z ≈ 4.1
    (2004) Miley, GK; Overzier, RA; Tsvetanov, ZI; Bouwens, RJ; Benítez, N; Blakeslee, JP; Ford, HC; Illingworth, GD; Postman, M; Rosati, P; Clampin, M; Hartig, GF; Zirm, AW; Röttgering, HJA; Venemans, BP; Ardila, DR; Bartko, F; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Cross, NJG; De Breuck, C; Feldman, PD; Franx, M; Golimowski, DA; Gronwall, C; Infante, L; Martel, AR; Menanteau, F; Meurer, GR; Sirianni, M; Kimble, RA; Krist, JE; Sparks, WB; Tran, HD; White, RL; Zheng, W
    The most massive galaxies and the richest clusters are believed to have emerged from regions with the largest enhancements of mass density(1-4) relative to the surrounding space. Distant radio galaxies may pinpoint the locations of the ancestors of rich clusters, because they are massive systems associated with 'over-densities' of galaxies that are bright in the Lyman-alpha line of hydrogen(5-7). A powerful technique for detecting high-redshift galaxies is to search for the characteristic 'Lyman break' feature in the galaxy colour, at wavelengths just shortwards of Lyalpha, which is due to absorption of radiation from the galaxy by the intervening intergalactic medium. Here we report multicolour imaging of the most distant candidate(7-9) protocluster, TNJ1338-1942 at a redshift zapproximate to4.1. We find a large number of objects with the characteristic colours of galaxies at that redshift, and we show that this excess is concentrated around the targeted dominant radio galaxy. Our data therefore indicate that TNJ1338-1942 is indeed the most distant cluster progenitor of a rich local cluster, and that galaxy clusters began forming when the Universe was only ten per cent of its present age.
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    Clustering of star-forming galaxies near a radio galaxy at z=5.2
    (2006) Overzier, RA; Miley, GK; Bouwens, RJ; Cross, NJG; Zirm, AW; Benítez, N; Blakeslee, JP; Clampin, M; Demarco, R; Ford, HC; Hartig, GF; Illingworth, GD; Martel, AR; Röttgering, HJA; Venemans, B; Ardila, DR; Bartko, F; Bradley, LD; Broadhurst, TJ; Coe, D; Feldman, PD; Franx, M; Golimowski, DA; Goto, T; Gronwall, C; Holden, B; Homeier, N; Infante, L; Kimble, RA; Krist, JE; Mei, S; Menanteau, F; Meurer, GR; Motta, V; Postman, M; Rosati, P; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    We present HSTACS observations of the most distant radio galaxy known, TNJ0924-2201 at z = 5.2. This radio galaxy has six spectroscopically confirmed Ly alpha-emitting companion galaxies and appears to lie within an overdense region. The radio galaxy is marginally resolved in i(775) and z(850), showing continuum emission aligned with the radio axis, similar to what is observed for lower redshift radio galaxies. Both the half-light radius and the UV star formation rate are comparable to the typical values found for Lyman break galaxies at z similar to 4-5. The Ly alpha emitters are sub-L-* galaxies, with deduced star formation rates of 1-10 M-circle dot yr(-1). One of the Ly alpha emitters is only detected in Ly alpha. Based on the star formation rate of similar to 3 M-circle dot yr(-1) calculated from Ly alpha, the lack of continuum emission could be explained if the galaxy is younger than similar to 2 Myr and is producing its first stars. Observations in V(606)i(775)z(850) were used to identify additional Lyman break galaxies associated with this structure. In addition to the radio galaxy, there are 22 V-606 break (z similar to 5) galaxies with z(850) < 26.5 (5 sigma), two of which are also in the spectroscopic sample. We compare the surface density of similar to 2 arcmin(-2) to that of similarly selected V-606 dropouts extracted from GOODS and the UDF parallel fields. We find evidence for an overdensity to very high confidence (> 99%), based on a counts-in-cells analysis applied to the control field. The excess suggests that the V-606 break objects are associated with a forming cluster around the radio galaxy.
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    Feedback and brightest cluster galaxy formation
    (2005) Zirm, AW; Overzier, RA; Miley, GK; Blakeslee, JP; Clampin, M; De Breuck, C; Demarco, R; Ford, HC; Hartig, GF; Homeier, N; Illingworth, GD; Martel, AR; Röttgering, HJA; Venemans, B; Ardila, DR; Bartko, F; Benítez, NB; Bouwens, RJ; Bradley, LD; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Cross, NJG; Feldman, PD; Franx, M; Golimowski, DA; Goto, T; Gronwall, C; Holden, B; Infante, L; Kimble, RA; Krist, JE; Lesser, MP; Mei, S; Menanteau, F; Meurer, GR; Motta, V; Postman, M; Rosati, P; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    We present deep optical imaging of the z 4: 1 radio galaxy TN J1338 - 1942, 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 two clumps in the i(775) and z(850) bands. These components have luminosities similar to 10(9) L-circle dot 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 dominated by forming stars. The estimated star formation rate for the whole radio galaxy is similar to 200M(circle dot) yr(-1). A simple 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 alpha emission. A wedge- shaped extension emanates from the radio galaxy perpendicularly to the radio axis. This `` wedge'' naturally connects to the surrounding asymmetric, large- scale (similar to 100 kpc) Ly alpha 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.