A multi-tracer view on the assembly of galaxy halos and intra-group light in nearby groups and clusters

Dr. Johanna Hartke, Turku University, Turku, Finland

11 Ottobre 2023
11:30, Aula Piazzi

Abstract: How are the extended and low-surface brightness halos of early-type galaxies built up, and which role does their environment play in their evolution? While resolved stellar populations from deep HST imaging are excellent tracers of nearby galaxy halos in pencil-beam fields, it is challenging to use them as tracers of extended haloes in galaxies or of the diffuse intracluster and intragroup light (IGL) at large spatial scales. Instead, at these distances, Planetary Nebulae (PNe) are a viable alternative. In my talk, I will focus on two non-isolated early-type galaxies: M49 in the Virgo Subcluster B and M105 in the Leo I Group. In the case of M49, the brightest galaxy in the Virgo Cluster, we can measure a rising galaxy velocity dispersion from the velocities of individual stars (PNe). This rise is a tell-tale sign of halo-to-IGL transition. Based on the IGL kinematics and information from deep wide-field photometry, we infer that the progenitors of the IGL stars had to be low-mass satellite galaxies with old and metal-poor stellar populations. The results on the early-type galaxy M105 in the Leo I group represent a benchmark for the quantitative analysis of halo and intra-group light. Since the Leo I group lies at just 10 Mpc distance, it is ideal for comparing results from resolved stellar populations with the homogeneous constraints over a much larger field of view from the PN populations and deep wide-field photometry. In M105, we have — for the first time — established a direct link between the emergence of a metal-poor halo as traced by resolved red-giant branch stars and the presence of a PN population with a high specific frequency. This result confirms our earlier inferences, e.g. for M49 in the Virgo Subcluster B, that metal-poor halos and intra-group light are predominantly traced by PN populations with high specific frequencies.