Kellie de Vos
Gather.town id
GC06
Poster Title
Clusters’ far-reaching influence on narrow-angle tail radio galaxies
Institution
University of Nottingham
Abstract (short summary)
The hydrodynamical interactions between galaxies and their surrounding gas in clusters is a major driver of galaxy evolution, and nowhere is this interaction more dramatically demonstrated than for narrow-angle tail radio sources (NATs); active galaxies whose radio jets are bent back to an acute angle by their motion through the intracluster medium of galaxy clusters. As such, they offer us an interesting diagnostic of these systems’ orbital motion to study their interaction with the gas. We have therefore used the Low-Frequency Array (LOFAR) Two-metre Sky Survey first data release to compile the largest ever sample of 255 NATs matched to clusters, based on both photometric and spectroscopic redshifts. The spectroscopic subset confirms that line-of-sight contamination remains modest out to 7R_500, so we use a sample that excludes BCGs but extends out to these radii, and find a large excess of galaxies with their tails pointing away from the cluster centre. The spectroscopic subsample indicates that this excess persists to at least 15R_500. At small radii, we also find a small excess of jets bent toward the cluster centre. The large-radii results are very surprising, as the effects are found far beyond the cluster virial radius where we might expect such hydrodynamical phenomena to occur. They indicate that infalling filaments are dense enough to start to experience hydrodynamic deceleration, and perhaps preferentially trigger AGN activity. We seem to be seeing AGN as they fall radially in down such filaments, and emerge after passing pericentre, making NATs a potential indicator not just for the location of clusters, but also for the filaments that connect them.
Plain text (extended) Summary
What is a NAT?
NAT stands for narrow-angle tail, and is in reference to radio galaxies that have had their jets bent behind them such that the angle between their lobes is acute This is usually due to ram pressure exerted by the surrounding gas.
We use a sample of 208 NATs identified by Mingo et al. (2019) from the LOFAR Two-Metre Sky Survey (LoTSS) DR1, and a cluster catalogue compiled by Wen et al. (2015) from the Sloan Digital Sky Survey (SDSS) DR8 & DR12 to match NATs to clusters. This is the largest study of NATs in clusters to date.
LOFAR is the best tool for finding NATs, as the low frequency at which it detects radio sources allows the telescope to trace synchrotron emission from the electrons at the furthest tips of the source’s lobes, thus imaging the NAT’s larger tail structure.
So how do you calculate a NAT’s orbit?
The offset of the radio lobes behind the NAT’s host galaxy compared to the position of the cluster centre tell us which direction the galaxy is travelling on the plane of the sky, as shown in the diagram in the centre.
This results in NATs with tails pointing away from the cluster centre (inbound) having an orbital angle of 0°, and NATs with tails pointing towards the cluster centre (outbound) having an orbital angle of 180°.
Results: radially infalling NATs in filaments
Producing a histogram from these orbital angles shows that NATs are primarily on radially infalling orbits, significant to the 99.99% confidence level. The histogram below contains non-BCG NATs out to 7𝑅_500, which is an unexpectedly high radius at which to see NATs travelling towards the cluster centre.
The polar plot shows the orbital angle vs. 𝑅_500 of NATs that are spectroscopically confirmed to be associated with the velocity dispersion of their matched cluster. NATs on radially inbound orbits still make up a large portion of this reduced sample, and can be seen to as far out as 10𝑅_500!
Since this is far past the cluster outskirts, and NATs have to be in a dense enough environment for their lobes to be bent behind them as they travel, we deduce that they must be falling through filaments towards the cluster centre. We aim to confirm this in future work.
NAT stands for narrow-angle tail, and is in reference to radio galaxies that have had their jets bent behind them such that the angle between their lobes is acute This is usually due to ram pressure exerted by the surrounding gas.
We use a sample of 208 NATs identified by Mingo et al. (2019) from the LOFAR Two-Metre Sky Survey (LoTSS) DR1, and a cluster catalogue compiled by Wen et al. (2015) from the Sloan Digital Sky Survey (SDSS) DR8 & DR12 to match NATs to clusters. This is the largest study of NATs in clusters to date.
LOFAR is the best tool for finding NATs, as the low frequency at which it detects radio sources allows the telescope to trace synchrotron emission from the electrons at the furthest tips of the source’s lobes, thus imaging the NAT’s larger tail structure.
So how do you calculate a NAT’s orbit?
The offset of the radio lobes behind the NAT’s host galaxy compared to the position of the cluster centre tell us which direction the galaxy is travelling on the plane of the sky, as shown in the diagram in the centre.
This results in NATs with tails pointing away from the cluster centre (inbound) having an orbital angle of 0°, and NATs with tails pointing towards the cluster centre (outbound) having an orbital angle of 180°.
Results: radially infalling NATs in filaments
Producing a histogram from these orbital angles shows that NATs are primarily on radially infalling orbits, significant to the 99.99% confidence level. The histogram below contains non-BCG NATs out to 7𝑅_500, which is an unexpectedly high radius at which to see NATs travelling towards the cluster centre.
The polar plot shows the orbital angle vs. 𝑅_500 of NATs that are spectroscopically confirmed to be associated with the velocity dispersion of their matched cluster. NATs on radially inbound orbits still make up a large portion of this reduced sample, and can be seen to as far out as 10𝑅_500!
Since this is far past the cluster outskirts, and NATs have to be in a dense enough environment for their lobes to be bent behind them as they travel, we deduce that they must be falling through filaments towards the cluster centre. We aim to confirm this in future work.
URL
ppykd1@nottingham.ac.uk
Poster file