The loneliest globular - ejected from Virgo Cluster?

[madbadgalaxyman]

Caldwell et al. report in a recent issue of the Astrophysical Journal that a probable globular cluster has been found which is likely being ejected from the Virgo Cluster, at very high speed:
http://arxiv.org/pdf/1402.6319v2.pdf

The above is a link to the preprint of the paper, and the actual published paper is : 2014, ApJ, 787, 11

The Virgo Cluster of Galaxies has an average recession velocity of some 1000-1300 km/s. The actual estimated value of the redshift of this cluster of galaxies depends upon who you ask, as this cluster of galaxies is not exactly a structure in equilibrium, and it contains several subgroups of galaxies that are arrayed in a complex pattern of velocities and distances;
so it is hard to say exactly which galaxies the astronomer should use in order to compute a mean recession velocity for the Virgo Cluster. Obviously, the orbits of the member galaxies within the Cluster imply that their individual velocities can differ considerably from the mean line-of-sight velocity of the cluster.

In very great contrast to the velocity of the Virgo Cluster of Galaxies, the newly discovered probable globular cluster associated with the Virgo Cluster has a radial velocity of minus 1025 km/s ( in the line-of-sight).
(the spectral lines are blue-shifted!!!!)

Thus, this globular star cluster which is probably associated with the Virgo Cluster of Galaxies has a velocity, as measured in our sight line, that differs by at least 2100 km/s from the mean radial velocity of the Virgo Cluster of Galaxies itself.

Because the relative velocity of this globular cluster and the Virgo Cluster of Galaxies (at least 2100 km/s) comfortably exceeds the radial velocity difference between the Virgo Cluster average velocity and the velocity of any galaxy that is a member of the Virgo Cluster, it is hard to resist the interpretation that this globular star cluster has been ejected by the Virgo Cluster of Galaxies.

These authors conclude that it is probable that the total space velocity of this star cluster will be above the escape velocity of the Virgo Cluster of Galaxies (Virgo has a mass of 4-8 x 10E14 solar masses), implying that this most lonely star cluster is leaving the Virgo Cluster of Galaxies forever!

Cheers,
Robert Lang

P.S.
In related work, there has been increasing scientific interest in the population of inter-galaxy (intracluster) stars and globular clusters within clusters of galaxies, stars and star clusters that orbit in the gravitational potential of the cluster of galaxies rather than orbiting around any individual galaxy. To the astrophotographer, these objects manifest as the vanishingly faint intracluster light between the cluster galaxies, assuming she/he has imaged deep enough and has done super-accurate background subtraction.

The following was an influential paper, published in 2010 Science, that observed the distribution of intracluster/inter-galaxy globular clusters in the Virgo Cluster of Galaxies.
http://arxiv.org/abs/1003.2499
This is a very preliminary result, is it is very shallow data (SDSS), at an angular res. of about 1 arcsecond; hardly spectacular for objects at a distance of 54 million light years .

This work has been quite influential, and there are now ongoing searches for intergalactic stars and intergalactic star clusters within clusters of galaxies.

[xelasnave]

Good morning Robert. Always a delight to see you have made a new post and I thank you for them all. Is there any speculation views or hypothysis as to why we observe such behaviour.

[xelasnave]

To be clear any ideas what is causing the motion

[madbadgalaxyman]

Thanks Alex,
glad you are enjoying my post about the Virgo Cluster.

I have a lot (70, maybe) of papers downloaded about this cluster of galaxies, and the number of published papers keeps snowballing, so it is very very hard to keep up with what is going on, even for this single cluster of galaxies.

Virgo Cluster, at 54 million light years, is "baseline truth" for fairly rich clusters of galaxies, as 10 meter class telescopes can begin to resolve its galaxies, and it is rich in sub-clusters that can be eventually expected to merge, and it has a mixed population of galaxies with plenty of examples of each hubble type. Also, the contrast with the Fornax Cluster, which has only a small amount of sub-structure and which is totally dominated by non-star-forming and gas-poor S0 and Elliptical galaxies, is remarkable. Fornax is considerably less massive than Virgo, but at least it is our Galaxy cluster, as it is far south!

The mass of the Virgo Cluster has often been estimated, but it is still quite uncertain. All we have available as an observational diagnostic for its mass is the various velocities of its member galaxies in our line-of-sight (redshifts or blueshifts), but we cannot, as yet, observe the tiny (in angular terms) tangential motions of its galaxies, those motions at right angles to our sight-line;
So, the actual motion through space of an individual galaxy, and its orbit, is highly uncertain.

You can sort of crudely look at the range of observed radial (line-of-sight) galaxy velocities in the Virgo Cluster, and come up with a rough idea of how the various objects in this cluster are orbiting within it. And it is these galaxy motions, resulting from the gravitational field of the cluster and from the momentum of its member galaxies, that can tell us something about how a star or cluster could be moving so quickly that it can potentially be permanently ejected from the Virgo Cluster of galaxies.

(Other moving objects within Clusters of Galaxies, notably "freely orbiting" planetary nebulae and globular clusters that orbit in the gravitational field of the cluster itself, are now beginning to be used as tracers of the mass and gravity of clusters of galaxies )

Here is a graph, from the paper I referred to in the initial post, of the line-of-sight velocities of the member galaxies, versus the number of galaxies at each specific velocity. This sort of graph is known, somewhat cryptically, to professional astronomers as a "Line-of-Sight Velocity Distribution" or just LOSVD:

164969

This sort of plot gives at least an intuitive idea of how objects might be moving around in the gravitational field of the Virgo Cluster. The shaded purple histogram is the numbers of galaxies moving at various radial velocities (= speeds in the line of sight), and the graph marked GCs is the speeds of various globular clusters that belong to the Virgo Cluster rather than to any individual galaxy within the cluster.
(The graph marked "stars" is actually the velocity of the foreground stars in our own galaxy)

For instance, it is quite evident, even from cursory inspection of this graph, that the inter-galaxy globular clusters in the Virgo Cluster are moving in a different way from the galaxies!

The velocity of the probable ejected globular cluster is marked "HVGC-1", and the high velocity relative to the average velocity of the galaxies is glaringly evident in this plot.

[xelasnave]

Thank you Robert. Unfortunately I am in hospital for spinal surgery and only have my phone which does not seem to handle the graph so when I get out or if I get out I will look at it using my lap top. I dont know how long I will be here so I will be patient. Nevertheless very intetesting so far. I had no idea thete was so much research on Virgo the only papers I get notice of are those mentionef on the site cosmo quest also stuff I pick up on science faily. Thats why I look forward to your posts. Forgive the sprlling i cant see what i am typing on this phone but wjat can you do
Regards alex

[madbadgalaxyman]

Sorry to hear you are having some health trouble. I hope that they fix you up and get you 100 percent again. Get well, soon!

You wouldn't be the only amateur astronomer who is starved of news about extragalactic research, as the popular science and astronomy journals do a poor job of reporting on it. I am one of the few non-professional astronomers out there who actually tries to keep up with the research of professional astronomers, which is why I used to address the scant coverage of extragalactic research with an e-newsletter on galaxies research.

[xelasnave]

Thank you Robert I certainly am happy you do what you do and take the time to share. I would like to ask you a question which I asked in this forum some time ago in a thread so wish to avoid opening another thread to ask the question again when it is your view which I seek. I cant provide a link to the material covering this but you may know. Have you read of the notion that spiral galaxies line up like buttons on a string. The material presenting this had surveyed as I recall a reasonable sample in the order of 200 galaxies and it did not present as a presentation or ideas of a crakpot. My question was answered and I cant recall the member here who gave the answer but it was to the effect that such configuration was consistant with mainstream cosmolgy ie big bang. If this situation exists I thought you may know and I seek your comment on the validy and also if you may be prepared to speculate upon what is going on. It seemed to me that if the gse gallaxies lined up as described this must be telling us more than a simple confirmati of current cosmology expectations. I will understand if this is a matter outside your interest or concern but if you hold a view I would welcome anything you can say about what I see as a most curious matter.