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0answers
12 views

Virial coefficient when computing dynamical mass enclosed by a rotating galactic disk of gas

Suppose I have a large thin disk of rotating gas in a galaxy -- the disk has a maximum inclination-corrected $V_{max}$ and a maximum radial extent of $R_{max}$ corresponding to that $V_{max}$ ...
11
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2answers
142 views

Conventional matter to dark matter ratio, outside of galaxies (Bounty!)

I'm pleased to offer a bounty to attract more attention to the fantastic Astronomy site. Consider say this outstanding diagram from another question, To begin with galaxies have a typical ...
8
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2answers
119 views

Boötes Void numbers, 2016

As a general science (hence Wikipedia!) reader, the latest information I have is that 60 galaxies "have been found and counted" inside the Boötes void, this of 1997. (1) What is the latest count of ...
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1answer
42 views

Question regarding the Milky Way when calculating galactic space velocities for galaxies

I have been calculating galaxy space velocities (where proper motions are known) in order to measure their orbits of the Milky Way using the method proposed in the appendix of http://www.aanda.org/...
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0answers
26 views

How do people derive ionized gas mass from optical emission lines in a galaxy spectrum?

Suppose you had an optical spectrum of a galaxy, and you unambiguously detected emission lines from cooling ionized gas -- both forbidden lines like [O II] 3727AA and [O III] 4959,5007AA, as well as ...
3
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1answer
58 views

Estimating galactic dust extinction for medium band filters

I have a set of medium-band filters and I would like to compute $A_{\lambda}/E(B-V)$ for each filter which are not reported in the literatures. The magnitudes of the objects in the photometry ...
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2answers
122 views

Are there any galaxies which fell out of sight horizon due to cosmic expansion?

If farthest galaxies run away from us with acceleration making them exceed speed of light, we should expect them to disappear from sky among time with increasing quantity. Did we observe this? Can we ...
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1answer
47 views

Create Position-Velocity diagram from a velocity field

Can someone explain to me how I can generate a Position-Velocity (PV) diagram from a galaxy's radial velocity field? I understand that usually PV diagrams are generated across the major axis of the ...
4
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1answer
56 views

How to determine the ellipticity of galaxies in SDSS

What is the best approach to determine the ellipticity of galaxies in the SDSS DR12. I have read this page. Are those really good methods? Do flux-weighted second moments (as given in the stokes ...
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0answers
46 views

What percentage of galaxies rotate with trailing arms?

I am looking for the percentage of galaxies that rotate with trailing arms. I know that only a small percentage of galaxies rotate with leading arms and would like to know whether there are any ...
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1answer
20 views

Could a “burping” supermassive black hole be responsible for a spiral galaxy's look?

I read an article which suggests black holes could influence the production of stars in the galaxy as the black hole can burst out powerful X-rays to "snowplow" the surrounding dust and gas. Although ...
0
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1answer
30 views

Number of galaxies per redshift

Does exist something like a distribution of number of galaxies per redshift interval? I'm studying galaxy formation and evolution, and I'm curious to know how many todays' galaxies (with redshift <...
11
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2answers
109 views

Why do we believe that the super massive black holes at the centers of two merging galaxies would themselves merge?

When listening to podcasts or watching youtube videos of astronomers discussing galaxy mergers, I often hear talk about how the super massive black holes at their centers will themselves merge during ...
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4answers
137 views

Oldest in the universe

When the big bang happened and all that exist today came into existence from singularity, how do you determine which part of the universe is the oldest? Its natural to think that looking back at the ...
2
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0answers
47 views

Are there equal number of planets, stars, galaxies etc in observable universe spinning in both directions?

Just because we observed that our milky way galaxy is spinning in a certain direction therefore we assume it is applicable to all other galaxies, I am curious to find out if hypothetically most of the ...
3
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1answer
114 views

What is meant by matter distribution?

Frustratingly, I find this could be a very simplistic question and may leave me feeling a little stupid for asking it. But I have to ask this. My lecturer keeps refering to "matter distributions" for ...
4
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1answer
109 views

Luminosity Schechter function for galaxies

Just a question I am having trouble understanding. I have the Schechter luminosity function for galaxies, given as: $$\Phi(L)dL=\Phi_{0}\left({\frac{L}{L_{\star}}}\right)^{\alpha}e^{-\frac{L}{L_{\...
3
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0answers
24 views

Halpha 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 ...
2
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1answer
66 views

Difference in redshift between 2 interacting galaxies

I have a galaxy 'A', say at redshift 1. Let's suppose this galaxy has no peculiar velocity. What would be the redshift of another galaxy 'B', that has a radial velocity of 500 km/s, relative to A? ...