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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Expansion-Collapse cycle in cosmological structures?

Concerning cosmological structures (like galaxies, clusters of galaxies, gas bodies, superclusters...etc) if the elements that make them are close enough they will be attracted towards each other by ...
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2 votes
0 answers
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Formation scenarios for elliptical galaxies?

I am trying to get an overview of the latest research on different formation scenarios for elliptical galaxies and filter out old scenarios in the literature that are today proved to be not sufficient/...
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4 votes
1 answer
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What is the distance of the closeset galaxy outside our local group and what is its name?

The Milky Way is 2.5 million light years from Andromeda and the size of the Local Group has a diameter of approxmiately 10 million light years across. What is the distance from this Local Group to the ...
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3 votes
1 answer
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3d distance between the Galaxies inside the galaxy cluster

I am currently working on the dynamics of the galaxy cluster, so i am trying to get the distance between the galaxies inside the galaxy cluster from its centre. As a input i have RA , DEC and Z (...
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6 votes
0 answers
86 views

How many galaxies are currently merging?

On the homepage of the galaxies research group at CfA SAO, it states, "Astronomers discovered that as many as 25% of galaxies are currently merging with others." They do not provide a ...
3 votes
0 answers
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Deviations of conservation laws in the context of cosmological evolution?

If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an accelerating expanding spacetime (like it happens in our Universe), are ...
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2 votes
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Database of distant stars

I'm writing a report on using machine learning techniques in astrophysics. I'd like to perform 3 tasks: Generating a Hertzsprung-Russel diagram and clustering the results into the main types of stars ...
1 vote
0 answers
53 views

Angle to the line of sight

I don't understand this angle used in galaxy clustering. There is the line of sight and this angle to the line of sight which is not clear to me. Here is a transcript of a description from 1705.05442: ...
1 vote
0 answers
50 views

Power law distribution for galaxy populations

I've learned that observed galaxy populations exhibit single power-law clusterings within several tens of megaparsecs in comoving scale. I'm trying to sample some astronomical data from this project: ...
49 votes
1 answer
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Is there a better explanation of this picture showing the very distant star "Earendel"?

"Close-up of the tiny region where Earendel happened to fall right on top of the narrow line where the magnification increases by (tens of) thousands of times. A cluster of many stars is seen ...
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3 votes
1 answer
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Is there a consistent missing mass ratio for Galaxy Clusters?

The Coma Cluster is what famously lead Fritz Zwicky to the conclusion that Dark Matter exists. As the velocities of the galaxies within the cluster were too fast for them to remain within orbit of ...
1 vote
0 answers
33 views

Pairs of galaxies that look like the Whirlpool-galaxy with companion?

I need examples of pairs of galaxies that look like the Whirlpool-galaxy with its companion NGC-5195. That is spirals with a companion galaxy attached to one arm, see picture below. I already know ...
5 votes
2 answers
1k views

Why does the Bullet Cluster have many names?

On Wikipedia, there are two names to call the Bullet Cluster, '1E 0657-56' and '1E 0657-558'. Furthermore, even on the NASA Hubble Space Telescope site, they call it '1E 0657-556'. Why is the bullet ...
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4 votes
0 answers
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How are shockwaves used to study magnetic fields of merging galaxy clusters?

Recently i read an article about how a shockwave 60 times larger than milky way galaxy is generated.When these shockwaves interacts with magnetic field, radio waves are emitted. I wanted to know how ...
4 votes
1 answer
77 views

Why does the first measurements of the thermal Sunyaev-Zel’dovich effect from ALMA show a temperature decrease and not an increase at the cluster?

Seeing the phrase a fully functional Stewart Platform I Wikipediad it and that article shows the AMiBA a CMB interferometer mounted on a hexapod (shown below). Wikipedia's Sunyaev–Zeldovich effect; ...
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1 vote
0 answers
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Are there galaxy clusters or dark matter halos in the void?

The void usually refers to the region of the Universe where the overdensity $\delta(x)$ is less than zero. What I'm curious about is whether there are virialized objects, like galaxy clusters or dark ...
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9 votes
1 answer
578 views

Local neighbourhood and Superclusters

Recently, I watched a YouTube video on Limits of Humanity, by famous Youtube channel Kurzgesagt. It talked about the local neighbourhood, and it is the only group of galaxies which are gravitationally ...
6 votes
3 answers
234 views

How do astronomers know that distant galaxies aren't actually nearby star clusters?

When reading about the recent release of data from the Dark Energy Survey, and the 'pictures' of well over 200 million distant galaxies, I got to wondering: How can they know that a small, faint, ...
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2 votes
0 answers
36 views

Cosmic variance - Fourier Transform - a few precisions

I have posted initially on physics exchange but none answer, so I try my chance here (I am going to delete the physics exchange one) : I cite an original report of a colleague : If we are interested ...
3 votes
0 answers
94 views

Getting XYZ coordinates of Luminous Red Galaxies catalogue

So I want to get the XYZ (rectangular/Cartesian) coordinates of the LRG (luminous red galaxies) catalog. The catalog is available for download from here: https://data.sdss.org/sas/dr16/eboss/lss/...
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3 votes
1 answer
193 views

Converting equatorial coordinates to Cartesian coordinates for extragalactic distances

I'm trying to search for galaxy clusters with the friends-of-friends (FoF) algorithm. I have the equatorial coordinates ($\alpha, \delta$) and redshifts ($0.5<z<2.5$) of galaxies that I wish to ...
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2 votes
0 answers
27 views

Anatomy of a galaxy cluster: understanding the relationship between dark matter halos and subhalos and galaxies within the clusters?

In my understanding, galaxy clusters contain dark matter halos, which in turn contain subhalos, and the subhalos are what surrounds individual galaxies. I know that is a simplified picture, but I am ...
4 votes
1 answer
148 views

Recent research regarding if the local group of galaxies will remain bound to the Virgo Cluster?

The question of if the local group of galaxies will remain bound to the Virgo Cluster has been asked before (Is the local group bound to the Virgo cluster?). I am wondering if there is any more recent ...
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4 votes
1 answer
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Why does a right-handed circular polarized wave get lagged when going through ionized plasma?

I have a question related to Faraday rotation. In Abigail Polin's Faraday rotation video I have seen that a linearly polarized wave can be decomposed in a left-handed circular wave and a right-handed ...
4 votes
0 answers
48 views

Cross-correlations between Lagrange and Fourier synthesis

In the context of forecast for large surveys, I have to make cross-correlations between 2D (with angular coordinates of Lagrange transformation for GC photometric and Weak Lensing) and 3D (Fourier ...
2 votes
0 answers
27 views

Observed instances of massive gas inflow and AGN restart due to cluster-cluster merger?

Works such as Acreman et al. (2003) have demonstrated via simulations the possibility of gas being stripped off a galaxy due to interaction with a galaxy cluster. Have there been confirmed instances ...
1 vote
1 answer
311 views

Are there any predictions of what galaxies exist in the Norma cluster/ Abell 3267?

I am working on a map for a science fiction story and using what information is available I have a good idea of locations of nearby galaxy groups and clusters and where the known supermassive black ...
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3 votes
1 answer
77 views

Deep-CEE I data

I was reading Deep-CEE I: Fishing for Galaxy Clusters with Deep Neural Nets and I couldn't find the dataset. Could someone provide me with the links related to this?
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2 votes
1 answer
112 views

Strip Brightness in a Spherical System

My question concerns the following problem, published in Galactic Dynamics by Binney and Tremaine and based on a work by Schwarzschild. Specifically, I am having difficulties in deriving the given ...
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1 vote
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51 views

Estimating the virial mass of a galaxy cluster from its $M_{500}$ measurement

In this paper, the authors seem to calculate the virial mass of the Fornax cluster by using its $M_{500}$ value. In the section 4.1, they say its mass was measured to be $M_{500}=6.4\times 10^{13} h^{-...
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2 votes
0 answers
50 views

What will be the eventual result of the Milky Ways future mergers?

I am wondering, after the Milky Way merges with Andromeda and other near by dwarf galaxies and globular clusters, will it then merge with galaxies in the Virgo cluster and even Laniakea? And if so ...
3 votes
1 answer
86 views

What's so interesting about Coma-type galaxy clusters?

When the dynamical mass of a proto-cluster of galaxies is ~(1-2)x1014 Msolar, the proto-cluster is expected to evolve into a coma-type cluster. In almost every paper I read about the confirmation of ...
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5 votes
1 answer
149 views

Interpretation and understanding of the relation for the photometric redshift in a given bin

In the context of photometric probe of surveys (like LSST), I need to understand the relation I have to use for photometric bins. Considering $p_{ph}(z_p|z)$ the probability to measure a photometric ...
2 votes
1 answer
319 views

how to calculate distance between galaxies in the distant past

for example, assume there is a high redshift galaxy called "A" with z=6, so how to calculate the distance between us and another galaxy B when the light left the galaxy A? For example, say B has a ...
0 votes
0 answers
37 views

Must all galaxies in a galaxy cluster have the same expansion rate?

If we observe a distant galaxies cluster where all galaxies travel with the same speed away from us, except for one galaxy whose speed is significantly lower than of the neighboring galaxies. Does ...
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2 votes
0 answers
262 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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3 votes
1 answer
410 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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2 votes
1 answer
83 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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0 votes
1 answer
488 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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5 votes
1 answer
892 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 its total spectrum My ...
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1 vote
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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 ...
1 vote
1 answer
80 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 ...
3 votes
0 answers
285 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 ...
1 vote
0 answers
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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 ...
1 vote
0 answers
37 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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1 vote
0 answers
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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 <...
3 votes
0 answers
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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 ...
5 votes
1 answer
105 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 ...
5 votes
0 answers
698 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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3 votes
2 answers
428 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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