Browsing by Author "Bolte, M"

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    The CIV mass density of the universe at redshift 5
    (2003) Pettini, M; Madau, P; Bolte, M; Prochaska, JX; Ellison, SL; Fan, XH
    In order to search for metals in the Lyalpha forest at redshifts z(abs) > 4, we have obtained spectra of high signal-to-noise ratio and moderately high resolution of three QSOs at z(em) > 5: 4 discovered by the Sloan Digital Sky Survey. These data allow us to probe to metal enrichment of the intergalactic medium at early times with higher sensitivity than previous studies. We find 16 C IV absorption systems with column densities log N (C IV) = 12.50-13.98 over a total redshift path DeltaX = 3.29. In the redshift interval z = 4.5-5.0, where our statistics are most reliable, we deduce a comoving mass density of C3+ ions Omega(CIV) = (4.3 +/- 2.5) x 10(-8) ( 90% confidence limits) for absorption systems with log N (C-IV) greater than or equal to 13.0 ( for an Einstein - de Sitter cosmology with h = 0.65). This value of Omega(CIV) is entirely consistent with those measured at z < 4; we confirm the earlier finding by Songaila that neither the column density distribution of C iv absorbers nor its integral show significant redshift evolution over a period of time that stretches from similar to 1.25 to similar to 4.5 Gyr after the big bang. This somewhat surprising conclusion may be an indication that the intergalactic medium was enriched in metals at z >> 5, perhaps by the sources responsible for its reionization. Alternatively, the C iv systems we see may be associated with outflow from massive star- forming galaxies at later times, while the truly intergalactic metals may reside in regions of the Ly alpha forest of lower density than those probed up to now.
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    The dwarf galaxy population of the Dorado Group down to Mv ≈-11
    (2001) Carrasco, ER; de Oliveira, CM; Infante, L; Bolte, M
    We present V and I CCD photometry of suspected low surface brightness dwarf galaxies detected in a survey covering similar to2.4 deg(2) around the central region of the Dorado group of galaxies. The low surface brightness galaxies were chosen based on their sizes and magnitudes at the limiting isophote of 26 V mu. The selected galaxies have magnitudes brighter than V approximate to 20 (M-V approximate to -11 for an assumed distance to the group of 17.2 Mpc), with central surface brightnesses mu (0) > 22.5 V mag arcsec(-2), scale lengths h > 2 ", and diameters greater than or equal to 14 " at the limiting isophote. Using these criteria, we identified 69 dwarf galaxy candidates. Four of them are large very low surface brightness galaxies that were detected on a smoothed image, after masking high surface brightness objects. Monte Carlo simulations performed to estimate completeness, photometric uncertainties and to evaluate our ability to detect extended low surface brightness galaxies show that the completeness fraction is, on average, >80% for dwarf galaxies with -17 < M-V < -10.5 and 22.5 < (0) <25.5 V mag arcsec(-2), for the range of sizes considered by us (D 14 "). The V-I colors of the dwarf candidates vary from -0.3 to 2.3 with a peak on V-I = 0.98, suggesting a range of different stellar populations in these galaxies. The projected surface density of the dwarf galaxies shows a concentration toward the group center similar in extent to that found around five X-ray groups and the elliptical galaxy NGC 1132 studied by Mulchaey & Zabludoff, suggesting that the dwarf galaxies in Dorado are probably physically associated with the overall potential well of the group.