ALBERT

Description: We investigate the evolution of the mass–metallicity ( M – Z ) relation with a large sample of 53 444 star-forming galaxies (SFGs) at 0.04 〈  z  〈 0.12, selected from the catalogue of Max-Planck-Institute for Astrophysics–John Hopkins University (MPA–JHU) emission-line measurements for the Sloan Digital Sky Survey Data Release 7. Regarding the sample of SFGs, we correct the observational bias and raise the aperture covering fractions to check the reliability of the metallicity evolution. (i) We show that the redshift evolution of the log (Hα) and log([O  iii ]) luminosities is displayed in our sample. (ii) We find the metallicity evolution of ~0.15 dex at log ( M * /M ) ~ 9.3 in SFGs at 0.04 〈  z  〈 0.12. (iii) After applying the luminosity thresholds of log ( L Hα ) 〉 41.0 and $\log (L_{\rm [O\,\scriptscriptstyle {III}]}) 〉 39.7$ , we find that the metallicity evolution is shown well, and that the evolution of the star formation rate (SFR) is still shown well under the latter luminosity threshold, but the evolution is not observed under the former. (iv) The evolution of the M – Z relation seems to disappear at about log ( M * /M ) 〉 10.0 after applying the luminosity threshold of log ( L Hα ) 〉 41.0 or $\log (L_{\rm [O\,\scriptscriptstyle {III}]}) 〉 39.7$ . (v) We find α = 0.09 and α = 0.07 in the equation, μ = log M * – αlog (SFR), for log ( L Hα ) 〉 41.0 and $\log (L_{\rm [O\,\scriptscriptstyle {III}]}) 〉 39.7$ samples, respectively, and these imply that the evolution of the M – Z relation might have a weaker dependence on the SFR in our sample.

Description: Utilizing the observational data of 55 318 star-forming galaxies (SFGs) selected from the catalogue of MPA-JHU emission-line measurements for the Sloan Digital Sky Survey DR8, we investigate the galaxy downsizing effect of their O and N enrichments, and the nitrogen production mechanism in them. We show the redshift evolution of O and N abundances and specific star formation rates for different galaxy mass ranges, demonstrating the galaxy downsizing effect caused by less massive progenitors of less massive galaxies. The O and N abundances do not remain constant for different galaxy mass ranges, and the enrichment (and hence star formation) decreases with increasing galaxy stellar mass. We find evidence of the O enrichment for galaxies with stellar masses M *  〉 10 11.0 (in units of M ), i.e. (log (O/H)) ~ 0.10 and (log (N/H)) ~ 0.28 from redshift 0.023 to 0.30. Based on the evolutionary schematic model of N/O ratios in Coziol et al., who proposed the scheme that the production of nitrogen is the consequence of a sequence of bursts in SFGs, we conclude that the nitrogen production is dominated by the intermediate-mass stars, which dominate the secondary synthesis in SFGs. However, for galaxies with M *  〉 10 10.35 we find evidence of enhanced N/O abundance ratios, which are significantly above the secondary synthesis line. This suggests that outflows of massive stars, which deplete oxygen efficiently, are more important in massive galaxies. Finally, we find an excellent linear relation between M * and log(N/O), indicating that the N/O abundance ratio is a good indicator of the stellar mass in a SFG and may be used as a standard candle for studying cosmology, if confirmed with further studies.

Description: We present the second release of value-added catalogues of the LAMOST Spectroscopic Survey of the Galactic Anticentre (LSS-GAC DR2). The catalogues present values of radial velocity Vr, atmospheric parameters – effective temperature Teff, surface gravity log g, metallicity [Fe/H], α-element to iron (metal) abundance ratio [α/Fe] ([α/M]), elemental abundances [C/H] and [N/H] and absolute magnitudes MV and $$M_{K_{ m s}}$$ deduced from 1.8 million spectra of 1.4 million unique stars targeted by the LSS-GAC since 2011 September until 2014 June. The catalogues also give values of interstellar reddening, distance and orbital parameters determined with a variety of techniques, as well as proper motions and multiband photometry from the far-UV to the mid-IR collected from the literature and various surveys. Accuracies of radial velocities reach 5 km s−1 for the late-type stars, and those of distance estimates range between 10 and 30 per cent, depending on the spectral signal-to-noise ratios. Precisions of [Fe/H], [C/H] and [N/H] estimates reach 0.1 dex, and those of [α/Fe] and [α/M] reach 0.05 dex. The large number of stars, the contiguous sky coverage, the simple yet non-trivial target selection function and the robust estimates of stellar radial velocities and atmospheric parameters, distances and elemental abundances make the catalogues a valuable data set to study the structure and evolution of the Galaxy, especially the solar-neighbourhood and the outer disc.