Leader: Mina Pak
Email: mina.pak@mq.edu.au
Collaborators: Matt Owers, Gabriella Quattropani, Oguzhan Cakir, and this project is open for everyone who wants to collaborate.
Topic: The future fate of ram-pressure affected cluster galaxies
Status: under review by Science Committee
Abstract:
In Owers et al. (2019), they used SAMI data to show that a substantial fraction of star-forming cluster galaxies are being quenched from the outside-in by ram pressure stripping during their first passage through the cluster core. Around 50% of those galaxies harbour ongoing star formation at their centres, with the H-delta strong (> 3Å) galaxies (HDSGs) located in their outer regions. In order to better constrain quenching timescales in clusters, we are investigating a rapid quenching of their star formation activity by analysing star formation history (SFH) from the coadded spectrum of non-star forming regions in HDSGs (Pak, Owers et al. in prep.). We also investigated SFH of two subsets: star-forming galaxies with truncated H-alpha and no H-delta strong features, and passive spirals with no emission lines but spiral arms in their morphology. These two subsets are expected as the galaxies that have been affected by ram pressure stripping, but passive spirals are completely stripped, the other is not. We reproduced the truncated SFH (within ~1 Gyr) successfully for HDSGs by using Bagpipes code (Carnall et al. 2018) and showed a good correlation between quenching timescale and EW(H-delta) absorptions. The majority of truncated star-forming galaxies quenched their star-forming activity quite recently similar to the HDSGs, whereas passive spirals quenched earlier epochs than the others. We also investigated their position in the projected phase space (PPS). This allowed us to determine that the time since the last episode of star formation is consistent with the time since core passage by comparing the PPS positions with simulations as done in Owers et al. (2019).
The key question still remains: whether the HDSGs are completely stripped at pericentre, or whether they are only partially stripped, or whether both occur. HECTOR-GS will extend the SAMI-GS by providing a larger sample up to 2 R_200 of the HECTOR clusters. It allows us to collect samples at all the important places in PPS within 1 R_200, but also the important 1-2 R_200 region where the backsplash population lies. This extended HECTOR sample will enable us to understand the relative populations of truncated star-forming galaxies, passive spirals and HDSGs and also their SFHs to tell us if they are indeed approximately at apocentre.
Needed data products: Measurements of absorption and emission lines for spectroscopic classification, morphology of galaxies, properties of clusters, concentration measurements of emission lines
Publication Date: 31/12/2025