Astronomers using data from the extended Planetary Nebula Spectrograph (ePN.S) early-type galaxy survey find that galaxies that are efficient in forming stars, like discs, are also efficient in retaining angular momentum. In early-type galaxies (ETGs), it is not so: there is a strong dependence as a function of total stellar mass, with the most massive galaxies being least efficient in forming stars and in retaining the angular momentum.

An international collaboration, including astronomers from Australia, Germany, the Netherlands and the UK, using the Planetary Nebulae Spectrograph (PN.S) mounted on the William Herschel Telescope (WHT) has found that stars and gas dominate gravity in the inner parts of the disc galaxy NGC 6946, while dark matter dominates in its outer parts.

Astronomers using Suprime-Cam on the Subaru Telescope and the Planetary Nebula Spectrograph (PN.S) on the William Herschel Telescope (WHT) have been able to unveil the presence of an old and metal-poor halo in the outskirts of a giant elliptical galaxy in a loose group. This is the first study to clearly establish the link between a metal poor population of stars and the excess of planetary nebulae (PNe) in the outer regions of an elliptical galaxy.

Cosmological simulations predict that early-type galaxies (ETGs) are the results of extended mass accretion histories characterised by different numbers of mergers and merger mass ratios, their timing, and gas fractions. Depending on the sequence and nature of the mergers following the first phase of in-situ star formation, these accretion histories may lead to ETGs that have low or high mass halos, and that rotate fast or slow.

Using data obtained with the Planetary Nebula Spectrograph (PN.S) on the William Herschel Telescope (WHT), astronomers pursued an original investigation to constrain the mass of the satellite progenitors of the stars in the halos and determine a proxy for their dynamical age by measuring the motions along the lines of sight of hundreds of stars that are in a particular stage of their evolution: the Planetary Nebulae (PNe). Instead of a uniform stellar population floating in the gravitational potential of the galaxy, astronomers identified three populations, one associated with the smooth halo of M49, a sub-component of bright planetary nebulae associate with the recent accretion of a dwarf galaxy (VCC 1249), and a population of stars associated with the intra-group light.

The missing mass problem is a long-standing issue in astrophysics, being present in galaxies, cluster of galaxies and even at the cosmological scale. Astronomers from Taiwan have used archival data from PN.S and SAURON to study the internal dynamics of seven nearby elliptical galaxies, and report finding a dearth of dark matter. They conclude that the dynamics of these galaxies are well explained by MOdified Newtonian Dynamics (MOND).