Browsing by Author "Barrientos, LF"

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    Gemini-South plus FLAMINGOS demonstration science
    (2003) Stern, D; Hall, PB; Barrientos, LF; Bunker, AJ; Elston, R; Ledlow, MJ; Raines, SN; Willis, J
    We report an infrared 1-1.8 mum (J+H-band), low-resolution (R=450) spectrogram of the highest redshift radio-loud quasar currently known, SDSS J083643.85+005453.3, obtained during the spectroscopic commissioning run of the FLAMINGOS multiobject, near-IR spectrograph at the 8 m Gemini-South Observatory. These data show broad emission from both C IV lambda1549 and C III] lambda1909, with strengths comparable to lower redshift quasar composite spectra. The implication is that there is substantial enrichment of the quasar environment, even at times less than a billion years after the big bang. The redshift derived from these features is z=5.774+/-0.0003, more accurate and slightly lower than the z=5.82 reported in the discovery paper based on the partially absorbed Lyalpha emission line. The infrared continuum is significantly redder than lower redshift quasar composites. Fitting the spectrum from 1.0 to 1.7 mum with a power law f(v) proportional to nu(-alpha), the derived power-law index is alpha=1.55 compared to the average continuum spectral index =0.44 derived from the first Sloan Digital Sky Survey composite quasar. Assuming an SMC-like extinction curve, we infer a color excess of E(B-V)=0.09+/-0.01. Only approximate to6% of quasars in the optically selected Sloan Digital Sky Survey show comparable levels of dust reddening.
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    RCS 043938-2904.9
    (2004) Barrientos, LF; Gladders, MD; Yee, HKC; Infante, L; Ellingson, E; Hall, PB; Hertling, G
    We present deep imaging and optical spectroscopy of the newly discovered Red-Sequence Cluster Survey cluster RCS 043938 - 2904.9. This cluster, drawn from an extensive preliminary list, was selected for detailed study on the basis of its apparent optical richness. Spectroscopy of 11 members places the cluster at z = 0.951 +/- 0.006 and confirms the photometric redshift estimate from the (R-z) color-magnitude diagram. Analysis of the infrared imaging data demonstrates that the cluster is extremely rich, with excess counts in the K-s band exceeding the expected background counts by 9 sigma. The properties of the galaxies in RCS 043938 - 2904.9 are consistent with those seen in other clusters at similar redshifts. Specifically, the red-sequence color, slope, and scatter and the size-magnitude relation of these galaxies are all consistent with that seen in the few other known high-redshift clusters and indeed are consistent with appropriately evolved properties of local cluster galaxies. The apparent consistency of these systems implies that the rich high-redshift RCS clusters are directly comparable to the few other systems known at, most of which have been selected on the basis of X-ray emission.
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    The optical afterglow of the gamma-ray burst GRB 012111
    (2002) Holland, ST; Soszynski, I; Gladders, MD; Barrientos, LF; Berlind, P; Bersier, D; Garnavich, PM; Jha, S; Stanek, KZ
    We present early-time optical photometry and spectroscopy of the optical afterglow of the gamma-ray burst GRB 011211. The spectrum of the optical afterglow contains several narrow metal lines that are consistent with the burst's occurring at a redshift of 2.14 +/- 0.001. The optical afterglow decays as a power law with a slope of alpha = 0.83 +/- 0.04 for the first approximate to2 days after the burst, at which time there is evidence of a break. The slope after the break is greater than or equal to 1.4. There is evidence of rapid variations in the R-band light approximately 0.5 days after the burst. These variations suggest that there are density fluctuations near the gamma-ray burst on spatial scales of approximately 40-125 AU. The magnitude of the break in the light curve, the spectral slope, and the rate of decay in the optical suggest that the burst expanded into an ambient medium that is homogeneous on large scales. We estimate that the local particle density is between approximately 0.1 and 10 cm(-3) and that the total gamma-ray energy in the burst was (1.2-1.9) x 10(50) ergs. This energy is smaller than, but consistent with, the "standard" value of (5 +/- 2) x 10(50) ergs. Comparing the observed color of the optical afterglow with predictions of the standard beaming model suggests that the rest-frame V-band extinction in the host galaxy is less than or similar to0.03 mag.