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Questions tagged [galaxy-cluster]

Questions regarding gravitationally bound systems of hundreds to thousands of galaxies as well as interactions between such systems.

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2
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0answers
95 views

What is the meaning of ellipticity of a galaxy being more than 1?

I was recently doing a project on calculating ellipticities of galaxies using SDSS data. I downloaded the stokes parameter values (q and u) from data $e = 1 - \frac{b}{a} = 1 - \frac{1 - \sqrt{Q^2 + ...
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1answer
104 views

Why is this Einstein ring pink?

I'm having a hard time understanding this image in the CNN News item This glowing ring of light is from a distant galaxy. The caption (from this version of the article) says: This image shows ...
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1answer
28 views

How to get ellipticities of galaxies from SDSS using casjobs?

How to get ellipticities of a list of random galaxies. I saw few programs written in SQL and they were only giving stokes parameters and isophotes values for ONE galaxy(for which we input the ObjID). ...
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1answer
50 views

Virial Shock Heating

In the review paper on protoclusters, Roderik Overzier (pg 25) mentions the concept of virial shock heating which seems to be a process involved with galaxy cluster formation. I'm not fully certain ...
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1answer
162 views

How to determine the mass of a galaxy?

I am having a slight disagreement with my professor. We can measure the mass of a distant star cluster from: A.Its color B.Its radius C.Its metallicity D.Smearing of lines in ...
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43 views

Deducing distance of closest neighbor galaxy from expression of correlation and mean galaxy density

The original post was on physics exchange but I prefer to move it here : I am trying to estimate the distance of closest galaxy neighbor knowing the expression of number of neighbors $\text{d}N$ into ...
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1answer
43 views

number density of Dark Matter Halos Versus number density of Galaxies

Can we count only one dark matter halo for each Galaxy ? Indeed, I am trying to estimate the total density of galaxies in given volume and I have often seen on physics exchange and other forums the ...
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138 views

Total number density of galaxies and problematic expression in practise

This post comes from physics exchange forum, I have transfered it here, maybe I will be luckier since I have not received answers on the other forum. Here is the issue : I am asked to give the ...
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59 views

Questions on dark matter observations in galaxy clusters

For cluster of galaxies we can observe velocity distributions and so we can deduce mass from multiwavelength observations. I suppose total mass of the cluster could be deduced by observing velocities ...
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31 views

Interpretation of Angular Correlation results

Long story short, what I am doing is to split the spherical space around my device into equal size pixels (49,152 pixels) with HealPix algorithm. If the power that my device can receive at each pixel ...
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0answers
48 views

Coma cluster of galaxies

According to wikipedia (https://en.wikipedia.org/wiki/Coma_Cluster), Coma cluster contains over 1000 galaxies. Is there any upto date catalogue of these galaxies with the following given parameters <...
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64 views

Energy conservation in Barnes-Hut algorithm [closed]

I wrote a code that follows the Barnes-Hut algorithm for gravitational dynamics. Everything looks pretty good, except that when I plot the total energy $$E_{tot}\equiv E_k+E_u=const$$ I get this ...
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1answer
87 views

What distance is considered 'close' for the 9th nearest neighbor of a galaxy?

I am currently working on determining the nth nearest neighbors of a large survey of galaxies. I am not an astronomer by trade, so I am unsure of interpreting some of my results. I have discovered for ...
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464 views

Which galaxy is closest to the center of the KBC void?

I was reading up on Bootes void and came across this list of the largest voids in the visible universe, and apparently the one we're in, the KBC void, is not only the biggest, but damned-near ...
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2answers
206 views

Do other supercluster like Laniakea also get pulled by the Great Attractor?

I'm not sure, whether there is any other observable super cluster like our local one, Laniakea, and if they do exists, do they also get pulled by the Great Attractor? I am a little confused about ...
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53 views

Efficiently calculating power spectra from galaxy catalogs

I am dealing with a problem which requires calculating either the correlation function or the power spectrum. At times, the 2-point-correlator seems the better route, at others, the PS. Right now I am ...
5
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1answer
318 views

Generating random galaxy catalogs for correlation functions

The galaxy correlation function, when computed directly from a galaxy catalog, relies on computing a randomly generated counterpart catalog. When dealing with a simulated galaxy mock-catalog, where ...
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1answer
119 views

Are there small voids of 10 - 20 megaparsecs also within, and not only between superclusters?

I sincerely apologize if this question is stupid, however after all the articles I read so far, I could not confirm this assumption, which I think is actually a fact, but I'm not completely confident. ...
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2answers
1k views

Does the Milky Way belong to a Galaxy cluster

I know that the Milky Way is a member of the Local Group and the Virgo Supercluster / Laniakea Supercluster. However, I can't seem to find any information about the Galaxy cluster we belong to. Does ...
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144 views

Great attractor is doing the big crunch? [closed]

Laniakea and other super clusters are moving towards shapely super cluster . Even the Great Attractor is moving towards it. Isn't it all about the Big Crunch?
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1answer
115 views

To what extent do the spin of smaller celestial bodies reflect the spin of the larger system’s of which they are a part?

One can ask whether two objects are spinning in the same direction or not. For example, the Sun, Earth, Luna, most of our solar planets (except Venus and Uranus), and the planets’ satellites all spin ...
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1answer
61 views

false to stable vacuum transition [closed]

if the universe transitioned from a meta-stable vacuum to a stable vacuum we assume a universal death scenario. However since it cannot propagate faster than the speed of light, from any particular ...
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2answers
114 views

Is it possible for galaxy clusters to interact?

Galaxies commonly interact and collide with other galaxies. Is it possible that clusters of galaxies similarly interact and collide? Have people tried to study this phenomenon previously? I couldn't ...
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126 views

Will galactic filament indefinitely expand while its galaxy clusters indefinitely disperse?

Exciting discoveries of weak gravitational lensing suggest the existence of galactic filaments made of dark matter that are the size of galactic superclusters. My questions involves the future of the ...
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2answers
101 views

Does the Abell 1689 supercluster have angular momentum?

The Abell 1689 is a large group of galaxies, containing a lot of elliptical galaxies : https://en.wikipedia.org/wiki/Abell_1689 Usually, an elliptical galaxy don't have large angular momentum around ...
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1answer
149 views

How long will it be until the nearby groups of galaxies are receding at speeds faster than light?

And subsequently how long will it be until we can never see them again?
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81 views

What's the density of dark matter (clouds)?

How much mass per unit volume do known dark matter have, for instance in the Bullet Cluster? Does the density vary in space, for example, do individual dark matter structures have denser cores?
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1answer
144 views

Why does the concentration-mass relation of galaxy clusters have a negative slope?

As reported in some recent observational works works (ref. Merten et al. 2015) the concentration-mass relation of galaxy clusters has a negative slope. This means that at a fixed redshift, haloes with ...
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2answers
739 views

Fingers of God effect for galaxy clusters

Galaxies that reside in galaxy clusters are know to have peculiar velocities that cause the Fingers of God effect. But what about galaxy clusters themselves? Do they also have peculiar velocites ...
2
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1answer
98 views

Centre (projected) of a galaxy cluster

A galaxy cluster consists of somewhere around a few tens to several hundred galaxies. To measure the position of a galaxy cluster, i.e. it's RA and DEC, do astronomers always assume it to be its ...
3
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1answer
84 views

Difference in the baryon acoustic oscillation measurements

I understand from this Wikipedia page about baryon acoustic oscillations (BAOs). I can also see that BAO measurements were first detected using luminous red galaxy samples. Now, many papers use ...
2
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1answer
274 views

What is the role of the random catalogue in calculating the two-point correlation function?

To study clustering of galaxies and clusters, one makes use of the two-point correlation function. However, we can see that all the estimators of $\xi(r)$ use a random catalogue. What is the random ...
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3answers
236 views

How to find out if a galaxy is in a specific cluster

I am trying to find out how to find out if a certain galaxy is located inside a cluster. For the famous ones this is quite easy (sometimes even on wikipedia!), but I haven't been able to do it for ...
3
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1answer
101 views

Would gravitational waves be subject to external gravitational perturbations?

Given that the gravitational wave detected by LIGO was a very weak echo of a very distant event, could it have been "deviated" and distorted on its way here by a sufficiently massive black hole in ...
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1answer
115 views

Are 3D coordinate data from Sloan DSS-III available & easily accessible to non-pros?

Of course the newly announced SDSS-III data and maps from the Sloan Digital Sky Survey with 1.2 million objects, along with all previous data sets are openly available, and I'm sure there are many ...
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1answer
78 views

How do I modify redshifts to gain corrected line of sight velocities?

I'm currently trying to collect the data to run an N-body simulation for 11 of the galaxies in the Local Group where proper motions are known, however I don't understand how to get the required line ...
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1answer
131 views

Initially non-flat space-time makes dark matter obsolete$\dots$

After the Big Bang, dark matter clusters and build the seeds for visible matter, that then forms stars, planet, you, me, everybody... But do we really need dark matter to build cluster first. What if ...
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1answer
661 views

Is our supercluster part of a galaxy filament?

It was discovered recently that the Milky Way galaxy lies inside a supercluster named Laniakea Supercluster. On the other hand, wikipedia says that galaxy filaments are "the largest known structures ...
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3answers
241 views

Can “dark matter” be the additional mass from the speed of the Galactic Cluster?

Considering that the Earth orbits the Sun at 100 000 km/h and that the Sun orbits the Milky Way at almost 1 000 000 km/h, could it be possible that the galactic cluster orbits some super cluster at ...
4
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1answer
94 views

What accounts into calculating the Hubble constant?

From my understanding, the Hubble constant $H_0$ calculates from observed redshifts $z$ of distant galaxys against their proper distance $D$. The current value appears to be 67.80(77) $\frac{km}{s}Mpc^...
4
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1answer
162 views

Are high-speed galactic collisions survivable?

This is a hypothetical question, but it really is meant as a vivid way of asking about the affects of high-speed galactic collisions. The November 27 APOD showed the Cheshire Cat galaxy group, and the ...
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1answer
553 views

Radial Density Profile Equation [closed]

The Virgo Galaxy Cluster has a mass of $10^{14} M_{\odot}$ and its centre is $16Mpc$ from Earth. The large elliptical galaxy $M87$ lies at the centre of the Virgo cluster. $M87$ has a supermassive ...
4
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2answers
327 views

Temperature of the intracluster medium (ICM)

I've read once in an article that the temperature of the medium within galaxy clusters (the intracluster medium or ICM) is extremely high. What does that temperature really mean? Particle velocity? ...
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0answers
62 views

H-alpha velocity fields of spirals falling into a cluster

What kind of impact would you expect ram pressure stripping / tidal interactions / harassment / interactions with the cluster potential (etc!) to have on the h-alpha velocity fields of infalling ...
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1answer
121 views

Concerning fate of Milky Way Galaxy

Andromeda Galaxy is the largest galaxy in the galaxy cluster[1] called Local Group[2] and our Milky Way Galaxy as well as some satellite/dwarf galaxies are orbiting around each other within Local ...
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3answers
240 views

what is the current explanation for the formation of cosmic voids?

Why aren't galaxies distributed evenly in space, but instead form those sponge-like structures, with huge voids between filaments?
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1answer
2k views

How many galaxies are there in the Hercules–Corona Borealis Great Wall?

The Hercules–Corona Borealis Great Wall is "to date (February 16, 2015), it is the largest and the most massive structure known in the observable universe" (source). How many galaxies is the Hercules–...
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1answer
4k views

When will the Milky Way “arrive” at the Great Attractor, and what all happen then?

The Great Attractor is described as a location to towards which the Milky Way, along with all other galaxies in the Laniakea Supercluster are moving. How long will it take for the Milky Way to "arrive"...
7
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1answer
278 views

Is there a paper on galaxy mergers in clusters of galaxies?

I'm looking for something to cite about galaxy mergers in clusters of galaxies. I need numbers on the frequency of mergers in the outer parts of galaxy clusters vs. the cluster center. In the center ...
2
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1answer
213 views

Beta profile fit of Virgo cluster gas?

I'm looking for the parameters $r_c$, $\rho_0$ and $\beta$ in a $\beta$-profile fit of the Virgo cluster's ICM density. I just can't find a reference for it. Unlike for Coma (Abell 1656) where it's in ...