The Chemical Evolution of High‐zGalaxies from the Relative Abundances of N, Si, S, and Fe in Damped Lyα Systems

Abstract

Abundances of N, Si, S, and Fe for 45 damped Lyman alpha systems (DLAs) have been compiled and detailed one-zone chemical evolution models have been constructed for 30 of them. Assuming continuous star formation, we found that final abundances in each object can be modelled by adjusting only two parameters, i.e. its time-averaged star formation efficiency and evolutionary age, with ranges in our sample of 0.01-1.5 Gyr −1 and 0.18-2.0 Gyr, respectively. In addition, average star formation efficiency and evolutionary age appear to be anticorrelated for the sample, suggesting that the star formation efficiency in a typical DLA decreases with age. At the same time, N/Si in DLAs is directly linked to an object's age. There is an apparent bimodality in the distribution of N/Si values which could be the result of a statistical accident or an effect produced by a truncated or flattened IMF. We find that the mean and small dispersion of Si/Fe values is related to the generally young ages of DLAs, wherein not all Fe has yet been expelled by Type Ia supernovae. Finally, the large scatter and generally lower values of N/Si of DLAs with respect to blue compact galaxies, despite their partially overlapping metallicities, indicate that DLAs are generally younger than the latter.Subject headings: galaxies gap between the normal N objects and the LNDLAs would likely not occur. Instead, their preferred hypothesis was a reduction in the effective N yield effected by a highly flattened or truncated IMF possessing a deficit of LIMS. (Prochaska et al. assumed that LIMS were responsible for most of the N production in the Universe, an issue which is yet to be settled.)

Physical conditions in high-redshift GRB-DLA absorbers observed with VLT/UVES: implications for molecular hydrogen searches

“…In addition, we measured [N/S] = −0.98 ± 0.05 and [Ar/S] = −0.11 ± 0.06. The former ratio is indicative of a high nitrogen enrichment dominated by intermediate-mass stars (4−8 M ), before significant oxygen production by supernovae, and a past low star-formation efficiency (e.g., Henry & Prochaska 2007;Petitjean et al 2008). The latter ratio is a tracer of the radiation field in H 0 regions (Vladilo et al 2003).…”

The ESO UVES advanced data products quasar sample – III. Evidence of bimodality in the [N/α] distribution

“…However, the clustering around two values would remain unexplained and the delayed model is unlikely capable of producing a factor 3 increase in the dispersion of the [N/O] values. The DLA galaxies show low star-formation rates and the time required to make a substantial amount of O becomes comparable to the lag time of the IMS (∼250 Myrs) to deliver primary N in the ISM (Henry & Prochaska 2007). This should lead to an increase of O and N almost in lockstep producing a scatter that should be comparable or even smaller than that observed in the BCGs.…”

THE FIRST OBSERVATIONS OF LOW-REDSHIFT DAMPED Lyα SYSTEMS WITH THE COSMIC ORIGINS SPECTROGRAPH: CHEMICAL ABUNDANCES AND AFFILIATED GALAXIES

“…Primary production occurs from newly synthesized C via the CNO cycle and secondary production uses C and O from previous star formation in the CNO cycle (Marigo 2001). Measurements of high-redshift DLAs, where N i lines are redshifted into wavelengths where ground-based observing is possible, find N to be underabundant relative to α-elements (Centurión et al 1998;Henry & Prochaska 2007;Pettini et al 2008). The study of N relative to α-process elements is useful because it can give insights into the star formation history of a gas system, since [N/α] will increase as a system ages and intermediate mass stars have time to inject more N into the system.…”