Browsing by Author "Coe, D"

Now showing 1 - 3 of 3
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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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    The nature of blue cores in spheroids
    (2005) Menanteau, F; Martel, AR; Tozzi, P; Frye, B; Ford, HC; Infante, L; Benítez, N; Galaz, G; Coe, D; Illingworth, GD; Hartig, GF; Clampin, M
    We investigate the physical nature of blue cores in early-type galaxies through the first multiwavelength analysis of a serendipitously discovered field blue-nucleated spheroid in the background of the deep Hubble Space Telescope ACS/WFC griz multicolor observations of the cluster A1689. The resolved g - r, r - i, and i - z color maps reveal a prominent blue core identifying this galaxy as a "typical'' case study, exhibiting variations of 0.5 - 1.0 mag in color between the center and the outer regions, opposite to the expectations of reddened metallicity- induced gradients in passively evolved elliptical galaxies. From a Magellan-Clay telescope spectrum we secure the galaxy redshift at z = 0.624. We find a strong X-ray source coincident with the spheroid galaxy. Spectral features and a high X-ray luminosity indicate the presence of an active galactic nucleus (AGN) in the galaxy. However, a comparison of the X-ray luminosity to a sample derived from the Chandra Deep Field - South displays L-X to be comparable to type 1/QSO galaxies while the optical flux is consistent with a normal star-forming galaxy. We conclude that the galaxy's nonthermal component dominates at high-energy wavelengths, while we associate the spheroid blue light with the stellar spectrum of normal star-forming galaxies. We argue for a probable association between the presence of blue cores in spheroids and AGN activity.
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    Ultracompact dwarf galaxies in Abell 1689
    (2004) Mieske, S; Infante, L; Benítez, N; Coe, D; Blakeslee, JP; Zekser, K; Ford, HC; Broadhurst, TJ; Illingworth, GD; Hartig, GF; Clampin, M; Ardila, DR; Bartko, F; Bouwens, RJ; Brown, RA; Burrows, CJ; Cheng, ES; Cross, NJG; Feldman, PD; Franx, M; Golimowski, DA; Goto, T; Gronwall, C; Holden, B; Homeier, N; Kimble, RA; Krist, JE; Lesser, MP; Martel, AR; Menanteau, F; Meurer, GR; Miley, GK; Postman, M; Rosati, P; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    The properties of ultracompact dwarf (UCD) galaxy candidates in Abell 1689 (z = 0.183) are investigated, based on deep high-resolution images from the Hubble Space Telescope Advanced Camera for Surveys. A UCD candidate has to be unresolved, have i < 28 mag (M-V < -11.5 mag), and satisfy color limits derived from Bayesian photometric redshifts. We find 160 UCD candidates with 22 mag < i < 28 mag. We estimate that about 100 of these are cluster members, based on their spatial distribution and photometric redshifts. For i greater than or similar to 26.8 mag, the radial and luminosity distribution of the UCD candidates can be explained well by Abell 1689's globular cluster ( GC) system. For i less than or similar to 26.8 mag, there is an overpopulation of 15 +/- 5 UCD candidates with respect to the GC luminosity function. For i less than or similar to 26 mag, the radial distribution of UCD candidates is more consistent with the dwarf galaxy population than with the GC system of Abell 1689. The UCD candidates follow a color-magnitude trend with a slope similar to that of Abell 1689's genuine dwarf galaxy population, but shifted fainter by about 2-3 mag. Two of the three brightest UCD candidates (M-V similar or equal to -17 mag) are slightly resolved. At the distance of Abell 1689, these two objects would have King profile core radii of similar or equal to35 pc and r(eff) similar or equal to 300 pc, implying luminosities and sizes 2-3 times those of M32's bulge. Additional photometric redshifts obtained with late-type stellar and elliptical galaxy templates support the assignment of these two resolved sources to Abell 1689 but also allow for up to four foreground stars among the six brightest UCD candidates. Our findings imply that in Abell 1689 there are greater than or equal to10 UCDs with M-V < -12.7 mag, probably created by stripping "normal" dwarf or spiral galaxies. Compared with the UCDs in the Fornax Cluster - the location of their original discovery - they are brighter, larger, and have colors closer to normal dwarf galaxies. This suggests that they may be in an intermediate stage of the stripping process. Checking the photometric redshifts of the brightest UCD candidates with spectroscopy would be the next step to definitely confirm the existence of UCDs in Abell 1689.