4 Conclusion

  We have compiled a catalogue of published absorption-line Mg₂ index measurements of galaxies and extragalactic globular clusters consisting of four tables available in electronic form only. In total, the catalogue contains 3541 measurements for 1491 galaxies and globular clusters from 55 datasets. Compiled raw data are aperture-corrected and transformed to our standard system.

The distribution of "raw'' Mg₂ index values for the whole sample is shown in Fig. 2.

  

Figure 1: The fractional distribution of "raw" Mg2 index measurements included in the catalogue (3542 entries, bin size 0$.\!\!^{\rm m}$02). The secondary peak near Mg2 = 0.05 corresponds to the globular clusters

The comparison of homogenised Mg₂ indices with most of the datasets may be seen in Table 2.

For the sake of intercomparison we have divided the corrected Mg₂ data of Table 4 in three sub-samples according the Hubble distance:

- nearby objects ($\le\,30$ Mpc),

- intermediate objects ($\gt\,30\ \div\ \le\,75$ Mpc), and

- distant objects ($\gt\,75\ \div\ \le\,200$ Mpc).

The most distant object in the catalogue is at 441 Mpc. Excluding 11 most distant objects, the rest of the galaxies lies within 200 Mpc.

Some overall statistical properties of these sub-samples are shown in Table 5. The mean Mg₂ decreases from one sub-sample to the next, reflecting the growing incompletness of the sample. Only the most luminous galaxies, with large Mg₂ are observed at large distances. This indicates the importance of the Malmquist-like bias in relations such as Luminosity vs. Mg₂.

 

Table 5: The overall statistical properties of the mean normalised Mg₂ index

  As the catalogues described in PS96 and in Prugniel et al. (1998), this catalogue is connected to a hypertext interface to databases and catalogues, HYPERCAT, developped at the Observatoire de Lyon (http://www-obs.univ-lyon1.fr/hypercat/).

Acknowledgements

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We have extensively use of the Lyon-Meudon Extragalactic Database (LEDA) supplied by the LEDA team at the CRAL-Observatoire de Lyon (France). This work benefited from the SIMBAD database operated by the Centre des Données astronomiques de Strasbourg (CDS) in Strasbourg (France). We acknowledge the use of the ADS Abstract Service. We are grateful to the anonymous referee for useful comments. VG thanks the CRAL-Observatoire Astronomique de Lyon (France) for the invited-astronomer position and the Bulgarian National Science Fundation grant No. F-575/1995.