Element Abundances in a Gas-rich Galaxy at z = 5: Clues to the Early Chemical Enrichment of Galaxies

Element abundances in high-redshift quasar absorbers offer excellent probes of the chemical enrichment of distant galaxies, and can constrain models for population III and early population II stars. Recent observations indicate that the sub-damped Lyman-alpha (sub-DLA) absorbers are more metal-rich than DLA absorbers at redshifts 0$<$$z$$<$3. It has also been suggested that the DLA metallicity drops suddenly at $z$$>$4.7. However, only 3 DLAs at $z$$>$4.5 and none at $z$$>$3.5 have "dust-free" metallicity measurements of undepleted elements. We report the first quasar sub-DLA metallicity measurement at $z$$>$3.5, from detections of undepleted elements in high-resolution data for a sub-DLA at $z$=5.0. We obtain fairly robust abundances of C, O, Si, and Fe, using lines outside the Lyman-alpha forest. This absorber is metal-poor, with O/H]=-2.00$\pm$0.12, which is $\gtrsim$4$\sigma$ below the level expected from extrapolation of the trend for $z$$<$3.5 sub-DLAs. The C/O ratio is 1.8$^{+0.4}_{-0.3}$ times lower than in the Sun. More strikingly, Si/O is 3.2$^{+0.6}_{-0.5}$ times lower than in the Sun, while Si/Fe is nearly (1.2$^{+0.4}_{-0.3}$ times) solar. This absorber does not display a clear alpha/Fe enhancement. Dust depletion may have removed more Si from the gas phase than is common in the Milky Way interstellar medium, which may be expected if high-redshift supernovae form more silicate-rich dust. C/O and Si/O vary substantially between different velocity components, indicating spatial variations in dust depletion and/or early stellar nucleosynethesis (e.g., population III star initial mass function). The higher velocity gas may trace an outflow enriched by early stars.Comment: 42 pages including 9 figures, accepted for publication in Ap

Índices de calidad de habitat y macroinvertebrados en siete Cuencas del Parque Nacional Yanachaga Chemillén y su Zona de Amortiguamiento:

We present the characterization of the aquatic environment, riparian ecosystem and macroinvertebrate communities in 7 basins of the west slope of the Yanachaga Chemillén National Park (PNYCh). The CERA protocol, including the Andean Biotic Index (ABI), the Fluvial Habitat Index (IHF), the Andean Creek Index (Qbr-And) were estimated and the combination of these 3 indexes allowed to calculate the Ecological Status Index of Andean Rivers (ECOSTRIAND) at each sampling point. Additionally the FBI and BMWP-Col indexes were calculated. Sampling was carried out in the 7 basins, between 1800 and 2500 meters of altitude, including the upper basins inside the PNYCh, in the middle and lower basins, both in the buffer zone of the park. We found 179 taxa, 66 families and 14 orders in all basins evaluated. Within the PNYCh, the values of IHF and Qbr-And were optimal, but to go down basins, the indexes generally were decreasing in quality. The IBA was very good in all basins and all sampling points. However, when the 3 indexes were combining, the ECOSTRIAND index decreased, changed from very good to good and regular in some basins. The final results show that the ecological status index decreased as it moves away from PNYCh, this is associated with a greater riparian forests disturbance. Finally, we discussed the legal protection of this type of forest in several countries of America and specifically in Peru.Se presenta la caracterización del ambiente acuático, el ecosistema ribereño y las comunidades de macroinvertebrados en siete cuencas del flanco oeste del Parque Nacional Yanachaga Chemillén (PNYCh). Se aplicó el protocolo CERA que incluye el Índice Biótico Andino (IBA), el Índice de Hábitat Fluvial (IHF), el Índice de quebrada Andina (Qbr-And) y la combinación de los tres índices para determinar el Índice de Estado Ecológico de Ríos Andinos (ECOSTRIAND) en cada punto de muestreo. Asimismo, se estimaron los índices FBI y BMWP-Col para comparar la calidad de agua. Los muestreos se realizaron en las siete cuencas, entre los 1800 y los 2500 m de altitud, en la parte alta dentro del PNYCh, y en las cuencas media y baja, ambas en la zona de amortiguamiento del PNYCh. En las cuencas evaluadas se colectaron 179 taxa, 66 familias y 14 órdenes. Dentro del PNYCh los valores de IHF y Qbr-And fueron óptimos y en general fueron disminuyendo en calidad al alejarse del PNYCh. El IBA fue muy bueno en todas las cuencas y en todos los puntos de muestreo. Sin embargo, al combinar los 3 índices se observó una disminución del estado ecológico (ECOSTRIAND) de Muy bueno a Bueno y Regular. Los resultados finales muestran que el índice de estado ecológico disminuye al alejarse del PNYCh y esto coincide con un mayor disturbio de los bosques ribereños. Por último, se discute la protección legal de este tipo de ecosistemas ribereños en varios países de América y específicamente en Perú