Iraj Vaezzadeh
Career Stage
Student (postgraduate)
Poster Abstract
Galaxy clusters grow through colliding and merging with other clusters and groups of galaxies. Minor mergers are relatively common and create sloshing cold fronts in the ICM of the host cluster, which are seen as sharp discontinuities in X-ray surface brightness which persist for extended times. We present preliminary results from a suite of triple cluster mergers exploring whether subsequent minor mergers can disrupt sloshing cold fronts and whether this more complex merger history can be determined from sloshing patterns.
Plain text summary
Slide 1 (Introduction):
Galaxy clusters are the largest objects in the Universe that have settled into a stable configuration. They contain anywhere from 50 galaxies to thousands, weighing, in total, around 10^14-10^15 Solar masses. They grow by accreting smaller groups of galaxies and by merging with one another due to their mutual gravity. Cluster mergers drive shocks through the Intra-cluster medium (ICM), the hot plasma that pervades the whole cluster, compressing and heating it, leading to interesting observable effects. Mergers are categorized in two ways: major (clusters of roughly equal mass) or minor (the primary cluster is roughly four to ten times more massive than the secondary).
Four examples of sloshing fronts (seen as bright edges) are shown with false-colour X-ray images, of the Abell clusters 2142, 2029, 496 & 85, with optical counterparts.
Cold fronts (CFs) and shocks appear in X-ray surface brightness as sharp edges. Unlike shocks, CFs are colder on the denser side of the discontinuity and ICM pressure is continuous across the front. Sloshing CFs wrap around the cluster core; they arise when an off-axis minor merger perturbs the core of the primary cluster, imparting angular momentum and causing the primary cluster’s ICM to ‘slosh’ about the gravitational potential, producing arc-like edges close to the core (≲100kpc). Sloshing fronts persist for extended times (>1Gyr) and are expected to be common in massive clusters because minor mergers are common.
Slide 2 (Simulations):
We have performed simulations exploring the resilience of sloshing fronts to subsequent mergers and how sloshing fronts can be used to trace merger histories.
We use the FLASH hydrodynamics+N-body code to model the ICM gas as a beta profile with dark matter particles overlaid in a Hernquist profile. The main cluster has a mass of 5.0×10^14MSun and the accreted clusters each have a mass of 5.0×10^13MSun. The main cluster starts at rest, with the secondary and tertiary clusters travelling on merger trajectories in accordance with the findings of Vitvitska et al. (2002). The two simulations chosen for preliminary analysis here share a common trajectory for the first infalling cluster, but differ in the trajectory of the second infaller. The state of the simulations at initialisation is shown in figure 2 (Simulation A starts with both clusters to the east of the primary with an off-axis trajectory, simulation B starts with the tertiary cluster to the west of the primary with an off-axis trajectory). The sloshing fronts established in both simulations by the first merger are seen in figure 3 (a temperature map of the simulation).
Slide 3 (Results):
Presented here are snapshots of key stages of the triple merger scenarios introduced previously. The images are slices of the temperature in the merger plane. The colour-scale ranges from 1.16×10^7-1.16×10^8K.
Sloshing fronts are seen at 4.7Gyr in the first panel of each figure (4 and 5) prior to the tertiary cluster’s first impact.
Sloshing fronts become disturbed throughout the first infall of the tertiary cluster (~4.9-6.8Gyr) before reappearing when the tertiary cluster is at its furthest from the primary.
At the end of the simulations (8.95Gyr) both systems exhibit clear CFs.
Slide 4 (Summary):
Future Work:
Determine whether CFs further from the core can be used to distinguish single from multi-mergers.
Consider whether merger viewing angle has an effect on whether sloshing fronts can be used to disentangle the merger history – does viewing angle allow an infalling cluster to ‘hide’ in some cases?
Explore whether certain observables (e.g. temperature) provide a key insight into merger history via sloshing
Contact: I.M.Vaezzadeh-2018@hull.ac.uk
Galaxy clusters are the largest objects in the Universe that have settled into a stable configuration. They contain anywhere from 50 galaxies to thousands, weighing, in total, around 10^14-10^15 Solar masses. They grow by accreting smaller groups of galaxies and by merging with one another due to their mutual gravity. Cluster mergers drive shocks through the Intra-cluster medium (ICM), the hot plasma that pervades the whole cluster, compressing and heating it, leading to interesting observable effects. Mergers are categorized in two ways: major (clusters of roughly equal mass) or minor (the primary cluster is roughly four to ten times more massive than the secondary).
Four examples of sloshing fronts (seen as bright edges) are shown with false-colour X-ray images, of the Abell clusters 2142, 2029, 496 & 85, with optical counterparts.
Cold fronts (CFs) and shocks appear in X-ray surface brightness as sharp edges. Unlike shocks, CFs are colder on the denser side of the discontinuity and ICM pressure is continuous across the front. Sloshing CFs wrap around the cluster core; they arise when an off-axis minor merger perturbs the core of the primary cluster, imparting angular momentum and causing the primary cluster’s ICM to ‘slosh’ about the gravitational potential, producing arc-like edges close to the core (≲100kpc). Sloshing fronts persist for extended times (>1Gyr) and are expected to be common in massive clusters because minor mergers are common.
Slide 2 (Simulations):
We have performed simulations exploring the resilience of sloshing fronts to subsequent mergers and how sloshing fronts can be used to trace merger histories.
We use the FLASH hydrodynamics+N-body code to model the ICM gas as a beta profile with dark matter particles overlaid in a Hernquist profile. The main cluster has a mass of 5.0×10^14MSun and the accreted clusters each have a mass of 5.0×10^13MSun. The main cluster starts at rest, with the secondary and tertiary clusters travelling on merger trajectories in accordance with the findings of Vitvitska et al. (2002). The two simulations chosen for preliminary analysis here share a common trajectory for the first infalling cluster, but differ in the trajectory of the second infaller. The state of the simulations at initialisation is shown in figure 2 (Simulation A starts with both clusters to the east of the primary with an off-axis trajectory, simulation B starts with the tertiary cluster to the west of the primary with an off-axis trajectory). The sloshing fronts established in both simulations by the first merger are seen in figure 3 (a temperature map of the simulation).
Slide 3 (Results):
Presented here are snapshots of key stages of the triple merger scenarios introduced previously. The images are slices of the temperature in the merger plane. The colour-scale ranges from 1.16×10^7-1.16×10^8K.
Sloshing fronts are seen at 4.7Gyr in the first panel of each figure (4 and 5) prior to the tertiary cluster’s first impact.
Sloshing fronts become disturbed throughout the first infall of the tertiary cluster (~4.9-6.8Gyr) before reappearing when the tertiary cluster is at its furthest from the primary.
At the end of the simulations (8.95Gyr) both systems exhibit clear CFs.
Slide 4 (Summary):
Future Work:
Determine whether CFs further from the core can be used to distinguish single from multi-mergers.
Consider whether merger viewing angle has an effect on whether sloshing fronts can be used to disentangle the merger history – does viewing angle allow an infalling cluster to ‘hide’ in some cases?
Explore whether certain observables (e.g. temperature) provide a key insight into merger history via sloshing
Contact: I.M.Vaezzadeh-2018@hull.ac.uk
Poster file
Poster Title
How does a second minor merger affect the sloshing cold fronts in a galaxy cluster?
Url
I.M.Vaezzadeh-2018@hull.ac.uk