Browsing by Author "Broadhurst, TJ"

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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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    Evolution of the color-magnitude relation in high-redshift clusters
    (2006) Mei, S; Blakeslee, JP; Stanford, SA; Holden, BP; Rosati, P; Strazzullo, V; Homeier, N; Postman, M; Franx, M; Rettura, A; Ford, H; Illingworth, GD; Ettori, S; Bouwens, RJ; Demarco, R; Martel, AR; Clampin, M; Hartig, GF; Eisenhardt, P; Ardila, DR; Bartko, F; Benítez, N; Bradley, LD; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Cross, NJG; Feldman, PD; Golimowski, DA; Goto, T; Gronwall, C; Infante, L; Kimble, RA; Krist, JE; Lesser, MP; Menanteau, F; Meurer, GR; Miley, GK; Motta, V; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    The color-magnitude relation has been determined for the RDCS J0910+5422 cluster of galaxies at redshift z = 1.106. Cluster members were selected from the Hubble Space Telescope Advanced Camera for Surveys (HST ACS) images, combined with ground-based near-IR imaging and optical spectroscopy. The observed early-type color-magnitude relation (CMR) in i(775) - z(850) versus z(850) shows an intrinsic scatter in color of 0.060 +/- 0.009 mag, within 10 from the cluster X-ray emission center. Both the elliptical and the S0 galaxies show small scatter about the CMR of 0.042 +/- 0.010 and 0.044 +/- 0.020 mag, respectively. From the scatter about the CMR, a mean luminosity weighted age t > 3: 3 Gyr (z(f) approximate to 3) is derived for the elliptical galaxies, assuming a simple stellar population modeling (single-burst solar metallicity). Strikingly, the S0 galaxies in RDCS J0910+5422 are systematically bluer in i(775) - z(850), by 0.07 +/- 0.02 mag, than the ellipticals. The ellipticity distribution as a function of color indicates that the face-on S0s in this particular cluster have likely been classified as elliptical. Thus, if anything, the offset in color between the elliptical and S0 populations may be even more significant. The color offset between S0 and E galaxies corresponds to an age difference of approximate to 1 Gyr for a single-burst solar-metallicity model. A solar-metallicity model with an exponential decay in star formation will reproduce the offset for an age of 3.5 Gyr; i.e., the S0s have evolved gradually from star-forming progenitors. The early-type population in this cluster appears to be still forming. The blue early-type disk galaxies in RDCS J0910+5422 likely represent the direct progenitors of the more evolved S0s that follow the same red sequence as elliptical galaxies in other clusters. Thirteen red galaxy pairs are observed, and the galaxies associated in pairs constitute similar to 40% of the CMR galaxies in this cluster.
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    The luminosity function of early-type field galaxies at z≈0.75
    (2004) Cross, NJG; Bouwens, RJ; Benítez, N; Blakeslee, JP; Menanteau, F; Ford, HC; Goto, T; Holden, B; Martel, AR; Zirm, A; Overzier, R; Gronwall, C; Homeier, N; Clampin, M; Hartig, GF; Illingworth, GD; Ardila, DR; Bartko, F; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Feldman, PD; Franx, M; Golimowski, DA; Infante, L; Kimble, RA; Krist, JE; Lesser, MP; Meurer, GR; Miley, GK; Postman, M; Rosati, P; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    We measure the luminosity function of morphologically selected E/S0 galaxies from z = 0.5 to 1.0 using deep high-resolution Advanced Camera for Surveys (ACS) imaging data. Our analysis covers an area of 48 arcmin(2) ( 8 times the area of the Hubble Deep Field North) and extends 2 mag deeper (I similar to 24 mag) than was possible in the Deep Groth Strip Survey (DGSS). Our fields were observed as part of the ACS Guaranteed Time Observations. At 0.5 < z < 0.75, we find M-B* - 5 log h(0.7) = - 21.1 +/- 0.3 and alpha = - 0.53 +/- 0.2, and at 0.75 < z < 1.0, we find M-B*-5 log h(0.7) = - 21.4 +/- 0.2, consistent with 0.3 mag of luminosity evolution ( across our two redshift intervals). These luminosity functions are similar in both shape and number density to the luminosity function using morphological selection ( e. g., DGSS), but are much steeper than the luminosity functions of samples selected using morphological proxies such as the color or spectral energy distribution (e.g., CFRS, CADIS, or COMBO-17). The difference is due to the "blue,'' (U - V)(0) < 1.7, E/S0 galaxies, which make up to ∼ 30% of the sample at all magnitudes and an increasing proportion of faint galaxies. We thereby demonstrate the need for both morphological and structural information to constrain the evolution of galaxies. We find that the blue E/S0 galaxies have the same average sizes and Sersic parameters as the "red,'' (U - V)(0) > 1.7, E/S0 galaxies at brighter luminosities (M-B < -20.1), but are increasingly different at fainter magnitudes, where blue galaxies are both smaller and have lower Sersic parameters. We find differences in both the size-magnitude relation and the photometric plane offset for red and blue E/S0s, although neither red nor blue galaxies give a good fit to the size-magnitude relation. Fits of the colors to stellar population models suggest that most E/S0 galaxies have short star formation timescales (τ < 1 Gyr), and that galaxies have formed at an increasing rate from z similar to 8 until z similar to 2, after which there has been a gradual decline.