Catalogue of Mg2 line strength index
We are collecting the Mg2 measurements of galaxies published in the
This catalogue is described in a paper by
V. Golev and Ph. Prugniel
1998, AAS 132, 255.
The published catalogue gathered 3541 measurements for 1491 objects
(galaxies or globular clusters) from 55 datasets.
Compiled raw data for 1060 galaxies were zero-point corrected and transformed
to a homogeneous system.
This catalogue is being updated. In 2014, the compilation counted 9593 measurements for 3267 objects from 88 datasets.
The homogenization procedure, as described in the original publication, aims to provide a single value for each measured galaxy. It proceeds in three steps:
- Correct each measurement for aperture effect (i.e. statistically takes into account the internal gradient of the stellar population).
- Correct for systematics between different datasets.
- Compute a weighted average of the corrected measurements.
The dataset parameters table provides the metadata of each dataset (e.g. the slit or aperture size), and homogenization constants computed to shift each dataset into a standard system.
The fields are:
- Data system (group of datasets homogeneous with each others). Used to determine the systematics.
- Aperture correction code, indicating whether an aperture correction was applied to the original measurements. The coding is:
|0||no aperture correction was applied|
|1||aperture corrected as in Davies et al. (1987ApJS...64..581D). The reference is the distance of the Coma cluster|
|2||aperture corrected as in Jorgensen et al. (1995MNRAS.276.1341J). The reference is the distance of the Coma cluster|
- Slit width, in arcsec. Used to compute the aperture correction.
- Extraction aperture height, in arcsec. Used to compute the aperture correciton.
- Estimated external error. rms of the difference between the corrected measurements and the mean value for each object.
- Computed zero-point: corrected value= raw value + zp
- Error rescaling factor : rescaled_error = raw_error * e_sc
- Number of measurements in dataset
- Number of galaxies in common with the standard system
- Homogenization flag: When 1, the corresponding dataset is corrected (zero-point) and rescaled to the homogeneous system - otherwise 0. In the last case the fields of the zero-point correction, its r.m.s. error, and rescaled error, as well as the number of comparison galaxies, contain also 0.