The luminosity-specific Planetary Nebulae density in Local Group galaxies

The value of the $α$ ratio, the number of PNe per unit bolometric luminosity in a galaxy, is computed using stellar population synthesis models covering the whole range of Hubble types of galaxies.

Model predictions are compared with the PNe counts in the Local Group, which indicate a fairly constant value of $α$ - between 1 and 6 PNe per 10$^7$ solar luminosities - along the Hubble sequence.