Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

TL;DR

This study investigates the star-formation history of the Galactic bulge using planetary nebulae, revealing a mostly constant star-formation rate over the past 3 to 10 billion years and highlighting the need to adjust post-AGB evolutionary models.

Contribution

It introduces a modified post-AGB evolutionary model with accelerated tracks and a steeper initial-final mass relation to better match observed white dwarf masses and bulge age distribution.

Findings

Star-formation rate in the bulge is roughly constant between 3 and 10 Gyr ago.

Post-AGB tracks need to be accelerated by a factor of three for consistency.

Planetary nebulae mainly originate from younger, metal-rich bulge populations.

Abstract

We study the star-formation history of the Galactic bulge, as derived from the age distribution of the central stars of planetary nebulae that belong to this stellar population. The high resolution imaging and spectroscopic observations of 31 compact planetary nebulae are used to derive their central star masses. The Bloecker tracks with the cluster IFMR result in ages, which are unexpectedly young. We find that the Bloecker post-AGB tracks need to be accelerated by a factor of three to fit the local white dwarf masses. This acceleration extends the age distribution. We adjust the IFMR as a free parameter to map the central star ages on the full age range of bulge stellar populations. This fit requires a steeper IFMR than the cluster relation. We find a star-formation rate in the Galactic bulge, which is approximately constant between 3 and 10 Gyr ago. The result indicates that planetary nebulae are mainly associated with the younger and more metal-rich bulge populations. The constant rate of star-formation between 3 and 10 Gyr agrees with suggestions that the metal-rich component of the bulge is formed during an extended process, such as a bar interaction.