A peek into the merging galaxy cluster Abell 3888

February 17, 2016 by Tomasz Nowakowski, Phys.org report

10 arcmin x 10 arcmin field showing luminosity (top) and temperature (bottom) maps of Abell 3888 before (left) and after (right) point source removal. The color scale in the luminosity map is set so that white corresponds to the maximum cluster flux. The point source is 100 times brighter than this level. The scale in the temperature map ranges from 2 to 10 keV. Credit: Andersson, K. et al., 2009.
(Phys.org)—Studying substructures of galaxy clusters can reveal important information about the morphology and evolution processes of these gravity-bound groups of galaxies. Optical spectroscopy is very helpful in this matter, capable of unraveling the history of large-scale structure formation in the universe. That's why a team of astronomers from New Zealand conducted a series of spectroscopic observations to peek into the galaxy cluster Abell 3888, unveiling that this cluster is dynamically young and might be an indicator of an ongoing or past merger event. A paper detailing the findings was published online on Feb. 11 on the arXiv pre-print server.

The team, led by Associate Professor Melanie Johnston-Hollitt of the Victoria University of Wellington in New Zealand, has used the AAOmega spectrograph installed on the 3.9-meter Anglo-Australian Telescope (AAT) situated at the Siding Spring Observatory in Australia. Thanks to the spectrograph's 400 fibres covering a two-degree field when projected on sky, it is an excellent instrument for examining the optical substructure in nearby southern clusters.

The researchers carried out their observations in May 2013. They were initially targeting nearly 800 up to 30' radius from the centre of the cluster. In result, the team detected 254 new redshifts in this region and in combination with previous findings, they determined that Abell 3888, as the main structure, has 71 member galaxies. Importantly, the astronomers were able to identify substructures in the field that were very helpful in unraveling the merging nature of this galaxy cluster.

"The combination of pieces of evidence from the optical analysis, the elongated optical galaxy distribution, and our substructure test which showed that Abell 3888 is bimodal strongly suggests that this cluster has had dynamical interactions and is highly likely to be a young cluster in an active merging state," the paper reads.

Galaxies and galaxy groups come together and merge to form larger units such as . Cluster merging is believed to be a key parameter in formation and evolution of galaxy clusters. The process is very common and has a significant impact on cluster characteristics such as velocity dispersion, temperature and mass. It often generates clumps of galaxies within the cluster volume. This change in galaxy volumetric density is known as "substructure."

"Substructures may be formed through the infall of individual galaxies or into a relaxed cluster or during the merging of two or more entire galaxy clusters," the researchers wrote in the paper.

Currently, the most robust method to detect merging is the combination of the optical and X-ray substructure analyses of clusters. Therefore, Shakouri and her colleagues underline that results from of Abell 3888 are consistent with previous findings from the X-ray studies focused on unveiling morphology of galaxy clusters.

In addition, the team also detected six galaxy over-densities in the field. Three of them were classified as new galaxy clusters.

The researchers concluded that further spectroscopic analysis of Abell 3888 would be useful to further probe its dynamics. They also stressed the need for single slit spectroscopy or more usefully observations with an integral field unit are required to increase the spectroscopic coverage in the cluster core.

"This would allow a more detailed probe of the cluster core and better statistics on the merging populations," the scientists noted.

Explore further: In galaxy clustering, mass may not be the only thing that matters

More information: An Optical Analysis of the Merging Cluster Abell 3888, arXiv:1602.03756 [astro-ph.CO] arxiv.org/abs/1602.03756

In this paper we present new AAOmega spectroscopy of 254 galaxies within a 30' radius around Abell 3888. We combine these data with the existing redshifts measured in a one degree radius around the cluster and performed a substructure analysis. We confirm 71 member galaxies within the core of A3888 and determine a new average redshift and velocity dispersion for the cluster of 0.1535 +- 0.0009 and 1181 +- 197 km/s, respectively. The cluster is elongated along an East-West axis and we find the core is bimodal along this axis with two sub-groups of 26 and 41 members detected. Our results suggest that A3888 is a merging system putting to rest the previous conjecture about the morphological status of the cluster derived from X-ray observations. In addition to the results on A3888 we also present six newly detected galaxy over-densities in the field, three of which we classify as new galaxy clusters.

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2.2 / 5 (10) Feb 17, 2016
I don't get it. Nothing about dark matter causing all this "morphology", but maybe I missed it because it's in the actual paper I will never bother to read. Stumpid will let us know.
5 / 5 (12) Feb 17, 2016
but maybe I missed it because it's in the actual paper I will never bother to read.

Serious question: Why do you even read the article - much less bother to comment on it - if you're not interested in the science/paper?

It's right at the bottom, free for view from arxiv.

(For that matter: since you're obviously not interested in science - why are you even here?)
4.3 / 5 (12) Feb 17, 2016
antialias_physorg5 /5 (1) 37 minutes ago
but maybe I missed it because it's in the actual paper I will never bother to read.

Serious question: Why do you even read the article - much less bother to comment on it - if you're not interested in the science/paper?

That's what trolls do. The passion is in the provocation. That's why Zephyr's sock puppet is the first comment.
2 / 5 (8) Feb 17, 2016
Do not feed the following
pariahs: bschott
psychos: Benni ichisan rodkeh
trolls: plasmasrevenge cantdrive45 liquidspacetime gkam kaiserderden antigoracle Seeker2 swordsman viko_mx DavidW BartV bluehigh baudrunner Solon hyperfuzzy julianpenrod emaalouf theprocessionist wduckss Old_C_Code Bigbangcon katesisco jimbraumcos indio007 LifeBasedLogic Reg Mundy vidyunmaya Osiris1 obama_socks promile
This list is updated continuously.

The moron says.
3.7 / 5 (12) Feb 17, 2016
I'm sorry but the 4*+ posters are right. Just about everyone in phys1's list doesn't care to fight over the same language which is science. They selectively pick what they want to back up what ever fan boy theory they have been following for the past 20-30 years. Standard model isn't perfect but atleast it can stand up on facts and science without selectively choosing evidence as being real or "fabricated" You guys in phys1's post are just a joke. They aren't convincing anyone who visits the site and comments that they're point of view is better. They are no better than people like myself who just vote on stars because thats what we like to do. nothing more nothing less they like to stir trouble that doesnt exist... and they like to try to win that argument even if it means by not playing by the same rules. Chumps and cheaters who lost and wana make others lose. Just wish them luck guys they need it.
3.4 / 5 (5) Feb 17, 2016
bschott claims
The standard model is wrought with holes and contradictions
Top 3 please ?

bschott is your issue with the standard model anything to do with your arbitrary religious like 'belief' that '..matter cannot self compress..' and a strange view of gravity ?

Why bschott, do you only throw barbs, why can't you articulate your position definitively ?
Captain Stumpy
3.7 / 5 (3) Feb 18, 2016
The standard model is wrought with holes and contradictions, selective evidence is my favorite to point out, especially when it contradicts another part of the same model
i have a couple serious questions for you- no snark, hyperbole or intentional anything. just a straightforward questions that i think deserve a valid and well elaborated answer

you have stated the above many times but why haven't you provided evidence?

and more to the point... if you had said evidence why is it not published and validated in the manner of modern peer reviewed journals supporting your claims?


as i have stated before

IF you are promoting a perspective of "fact" that is demonstrating the contradiction of the current SM (and the "denial")
THEN you would be able to provide said evidence refuting said model and proving the denial
(not just interjection with personal conjecture)

i follow the evidence and so do most others here serious about science

so... where is it?
Captain Stumpy
3.7 / 5 (3) Feb 18, 2016
FYI - i intentionally downrated your comment because, IMHO, you again have offered what you personally believe (conjecture) while not supporting it with evidence

you state
The standard model is wrought with holes and contradictions...
and yet, when you do point out your "holes and contradictions" you simply conjecture

not once to date do i remember you linking a peer reviewed paper from a reputable journal that has been validated to support any claim you have made

there is a serious absence of links or references which to me indicates that you are not presenting evidence for your argument (IOW: false claim-see link below for details)


why then should anyone else present refuting evidence when there is nothing to refute but your personal speculation? it retains the same validity and authority as any other speculation, including viko or wade

something to consider
5 / 5 (5) Feb 18, 2016
This is my first recollection of the term, "single slit spectroscopy". Could you elaborate a little?

Integrated field units is also a new one to me. But wikipedia has an article on it

From what I gather this is a simple single slit spectrography (as done in school experiments), but multiplexed with an image slicer like this one
or an array of fibres where each end is fed into a single slit spectroscopy unit.

In each case you get spectroscopy info for the full 2D plane of observation rather than just a single slit.

Sorry. I'm not an astronomer :-/

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