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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Is gravitational lensing "additive" in a line of sight?

As usually depicted, gravitational lensing implies, at least, three objects: a distant source, an observer, and a "massive enough" object in the middle, where enough is the mass needed to ...
nuwe's user avatar
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Where can I find the $\mu$ value in galaxy clusters for ideal gas law?

I am studying hydrostatic equilibrium in galaxy clusters and encountered the following expression: $P=(kT/\mu m_p)\rho$ The interpretation of this formula is obvious. It is just the ideal gas law ...
Youngsub Yoon's user avatar
2 votes
1 answer
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Ejected galaxies, dynamical friction and dark energy?

I have a question after reading this paper (https://arxiv.org/abs/1411.5860). There the authors analyse the ejection of galaxies from their local groups in the presence of dark energy. I had some ...
vengaq's user avatar
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Does dark energy increase eccentricity in orbits of galaxies?

I came across this thesis dissertation which indicates that if a pair of orbiting galaxies are sufficiently far apart (with a sufficiently large orbital radius) then their orbits would change from ...
vengaq's user avatar
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Why is the dark matter component of MOND important in central regions?

A lot of papers say that even the theory of MOND requires the existence of dark matter, particularly in the central regions. However this is a bit counterintuitive to me considering that rotation ...
Ambica Govind's user avatar
2 votes
1 answer
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Why does the velocity dispersion within a galaxy cluster decrease as a function of radius?

In the paper 10.1093/mnras/sty2379, there are plots showing the velocity dispersion as a function of radius. Focusing on the right-hand plot, non-merging normal clusters, intuitively why should the ...
ABC's user avatar
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What causes the filaments of the cosmic web to spin?

The cosmic web is made from galaxies and dark matter clustered together forming long thin filaments up to 80 Megaparsecs long. The filaments border voids where there is much less mass density and ...
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ultra diffuse galaxies and dark matter

There are ultra diffuse galaxies (UDGs) like, NGC 1052-DF2, NGC 1052-DF4, which seem to have very little dark matter. And on the other hand UDG dragongly 44 has lots of it. How many UDGs are known to ...
Angela's user avatar
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What percentage of galaxies are isolated galaxies and what percentage are members of a cluster?

Some galaxies, such as NGC821 are classified as "isolated galaxies", others form parts of distinct groups or clusters (relevant link) Although isolated galaxies may be accompanied by small ...
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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 ...
vengaq's user avatar
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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/...
trynerror's user avatar
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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 ...
Sedumjoy's user avatar
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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 (...
Atul's user avatar
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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 ...
Daddy Kropotkin's user avatar
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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 ...
vengaq's user avatar
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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 ...
John Miller's user avatar
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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: ...
P. Ferreira's user avatar
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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: ...
8-Bit Borges's user avatar
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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 ...
Roger Wood's user avatar
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3 votes
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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 ...
Suzie Q.'s user avatar
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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 ...
Sven _Andersson's user avatar
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2 answers
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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 ...
BAO's user avatar
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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 ...
25 Simran Tiwari's user avatar
4 votes
1 answer
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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; ...
uhoh's user avatar
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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 ...
Wang Yun's user avatar
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9 votes
1 answer
617 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 ...
Kshitij Kumar's user avatar
6 votes
3 answers
253 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, ...
Kurt Hikes's user avatar
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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 ...
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3 votes
0 answers
108 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/...
kauii8's user avatar
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1 answer
292 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 ...
kenc_'s user avatar
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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 ...
AstroStudent123's user avatar
4 votes
1 answer
181 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 ...
Atsina's user avatar
  • 143
4 votes
1 answer
127 views

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 ...
Miguel Cárcamo's user avatar
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 ...
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2 votes
0 answers
30 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 ...
lordparthurnaax's user avatar
1 vote
1 answer
320 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
80 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?
Madara's user avatar
  • 183
2 votes
1 answer
149 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 ...
wrb98's user avatar
  • 231
1 vote
0 answers
93 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^{-...
Nownuri's user avatar
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2 votes
0 answers
52 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 ...
RandySavage's user avatar
3 votes
1 answer
88 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 ...
RUNN's user avatar
  • 165
5 votes
1 answer
157 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 ...
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2 votes
1 answer
428 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 ...
Stargazer's user avatar
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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 ...
Yos's user avatar
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2 votes
0 answers
308 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 + ...
Krishna K's user avatar
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3 votes
1 answer
499 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 ...
uhoh's user avatar
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2 votes
1 answer
94 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). ...
Krishna K's user avatar
  • 121
0 votes
1 answer
624 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 ...
chou's user avatar
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5 votes
1 answer
1k 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 ...
Jim's user avatar
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1 vote
0 answers
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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 ...
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