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Questions tagged [galaxy]

Questions regarding systems of large numbers of stars held together by gravity.

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0answers
17 views

How to calculate S/N in galaxy absorption spectra?

I want to calculate the S/N of an galaxy absorption spectrum. I therefore chose a part of the spectrum which contains very little to none absorption features and should be only made up of noise and ...
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20 views

How to find x-values of fourier-transformed correlation functions in velocity space?

I am trying to extract the kinematic parameters (rotation velocity, velocity dispersion, ...) of an elliptical galaxy by extracting the kinematical broadening function using the FCQ-Algortihm first ...
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1answer
152 views

How many stars are in the Milky Way galaxy?

So, I've always heard that the Milky Way hosts between 100 billion to 400 billion stars. My problem is very simple: I'm unable to find any research papers on that topic or giving those estimates. I'm ...
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If all objects move, where do we go?

Yes I know that the sun and planets in the solar system travel fast with an average speed of 448,000 mph. Are we going to the center of the galaxy? If so, does that mean our galaxy is getting smaller ...
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Milky Way vs Milky Way Galaxy

I saw this question on Quizlet which said: What is the difference between the Milky Way and the Milky Way Galaxy? And the answer was: The Milky Way is a fairly narrow band of faint diffuse light ...
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How to remove redshift from galaxy spectra in Python?

Hello I extracted a spectrum from the central region of the 2D spectrum of the major axis from NGC 4697 (I just took a central row in the 2D data set, see this question for more information: How to ...
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1answer
22 views

How to calculate an infrared SED from the specific intensities?

I have values of total infrared fluxes (SED) in literature expressed in Jy (Jansky) for galaxies. I want to assure that my infrared radial profiles of the same galaxies in MJy/sr (and other in Jy/...
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1answer
54 views

Universe is a cluster of orbiting Galaxies?

Like planets orbiting stars, solar systems and other celestial objects orbiting a blackhole in the center of a galaxy, are the Galaxies and Galaxy clusters orbiting the centre of a universe (for ...
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1answer
41 views

E(B-V) , the color excess between B and V bands, for galaxy at redshift 0

Following Mo et al. 2010 (page 479), the quantity $E(B-V)$, called the color excess between B and V bands, is equal to: $$E(B-V) = A_B - A_V = (B - V) - (B - V)_0 = (m_B - m_V) - (M_B- M_V)$$ where $...
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Are there python packages to calculate mean line of sight velocity, linewidth and other distributions from galaxy simulation snapshots?

Does anyone know of any packages/functions in packages that can give mean line of sight velocities (losv) from a simulation snapshot (from the spatial and velocity coordinates or directly from the ...
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1answer
100 views

How to calculate mean line of sight velocity of stars after rotation of galaxy?

I am trying to calculate the mean line of sight velocity from a simulation snapshot of a galaxy after the galaxy is inclined by a certain angle, theta. I am coding it in python. What I have done so ...
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2answers
230 views

Why do other galaxies have such a low surface brightness?

Why do we need to take exposure photos of other galaxies, considering their stars should have roughly the same luminosity per square degree as the ones in the milky way? I'm not saying it should be ...
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How would it possible to Andromeda collide with Milky way? [duplicate]

If galaxies are moving away from each other how is it possible to Andromeda collide with Milky Way?
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1answer
392 views

Using masers to measure rotational velocity of a galaxy

When measuring the rotation velocity of a galaxy, most of the times we can only directly measure radial velocity, by looking at the redshift. I read in a lecture slide that some times it is possible ...
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2answers
40 views

How can I find more information on a certain galaxy when NED isn't helping?

The paper High Frequency Peakers: Young radio sources or flaring blazars? by S.Tinti et.al. lists some nice radio-wavelength SEDs, like these for instance: When looking for more photometric info on a ...
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starting from SSP spectra to evaluate galaxy spectrum and observed mag

I know that the galaxy spectrum, namely the flux per unit wavelength versus the wavelength, is the sum of the Simple Stellar Population (SSP) spectra at a fixed redshift (e.g. similar to eq. 1 in ...
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1answer
608 views

Are there black holes and neutron stars in satellite dwarf galaxies orbiting around Milky Way?

It is thought that the number of satellite dwarf galaxies orbiting around Milky Way is counted in hundreds. Are there black holes and neutron stars in satellite dwarf galaxies orbiting around Milky ...
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Is the Condor Galaxy (NGC 6872) the result of a non-collision galaxy interaction?

All the interacting galaxies that I can find are of collisions, I'm trying to find an example of a fly-by galaxy interaction. Is the Condor Galaxy an example of one? Wikipedia's NGC 6872; Possible ...
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1answer
36 views

The Sun's motion around the galaxy [duplicate]

As the Sun orbits the Milky Way, I understand that it also moves up and down through the plane of the Galaxy. How long does this movement take and can we tell where we are in the current cycle.
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24 views

Are the distribution of globular cluster systems in giant elliptical galaxies spherical?

I have been trying to find literature sources on the posted question in the title. The only source I found is from a 1991 review by William Harris which is provided here. In the review, the author ...
2
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1answer
92 views

What is the distance between solar system and a distant galaxy

When we say a galaxy is 300 million light-years away, is that its distance now or 300 million years ago?
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1answer
1k views

Is oxygen an alpha element?

Type II (core-collapse) supernovae occur shortly after star formation and enrich a galaxy with $\alpha$ elements such as O, C, NE, Mg, Ca and Si. On the other hand, Type Ia supernovae occur on a more ...
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1answer
90 views

How to extract galaxy spectra for different radii in Python for spectra taken by long slit spectrograph?

I am trying to extract the kinematics from the elliptical galaxy NGC 4697 using the Fourier Correlation Quotient (FCQ) algorithm described by Bender (http://adsabs.harvard.edu/full/1990A%26A...229.....
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1answer
47 views

Can the pebbles growth model be applied to the rotations of planetary systems? [duplicate]

I've just read the University of Amsterdam 2019 News item Pebbles determine the direction in which planets rotate (which links to R.G.Visser et al (2020) Spinning up planetary bodies by pebble ...
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4answers
128 views
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1answer
132 views

Can violet astronomical objects exist?

According to black-body radiation, violet stars are not possible. Even if there are 1 million Kelvin, they are blue, not violet. But are violet galaxies, nebulae, clusters etc. possible? Google found ...
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1answer
933 views

How big is the energy content of the magnetic field of the Milky Way?

Galaxies have associated magnetic fields. So does the Sun and so does the Earth. In the case of the Earth and Sun it seems clear that the energy content of the magnetic fields is much less than their ...
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30 views

Questions re galaxies clusters and galaxies mergers within them

An introduction (containing the info I gathered from several Wikipedia articles). A galaxy cluster, or cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of ...
7
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1answer
99 views

Why is the Milky Way's SMBH inactive?

Our galaxy is not an active galactic nucleus (AGN). With so many stars and so much gas orbiting it, as explained here Central kiloparsec of Seyfert and inactive host galaxies: a comparison of two-...
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1answer
93 views

Why was it so difficult to figure out the form of the Milky Way?

The exact form of the Milky Way was figured out the in early fifties of the 20-th century. Why did it take so long to see? Is it because we are in the "middle" of it? In general, it's easier ...
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0answers
30 views

Young galaxies VS. old galaxies spectra differences

What are the main (UV/optical) spectral differences between a young star-forming galaxy and an old galaxy with no ongoing star formation?
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24 views

Looking for analytical expression of Cosmic Variance - Poisson distribution?

I have an expression of Matter Angular power spectrum which can be computed numerically by a simple rectangular integration method (see below). I make appear in this expression the spectroscopic ...
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3answers
4k views

How are constellations intact if the stars are rotating around galactic nuclei?

From what I understood, the Milky Way (or stars in the Milky Way) doesn't rotate like a collection of points in a disc due to the presence of some invisible matter. In theory, the angular velocities ...
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1answer
53 views

Derive LOSVD from galaxy spectrum, using fourier method

I am trying to implement a programm, that derives the kinematics (specifically the kinematic parameters: mean rotation velocity, velocity, dispersion, hermite coefficients h3 and h4) from an ...
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3answers
2k views

What observations show that galaxies are made of matter instead of anti-matter?

Galaxies are thought to be composed of matter. But what if they are composed of anti-matter? Can it be shown that they are composed of normal matter? What kind of observation could distinguish between ...
5
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3answers
201 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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1answer
101 views

Nearby galaxy distances

Type Ia supernovae are extremely useful in measuring the distance of remote galaxies. It is known that type Ia supernovae always reach the same brilliance at their peak. Like Cepheid variables, they ...
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21 views

How to create synthetic galaxy spectrum by broadening stellar spectra with a gaussian

I am trying to create a synthetic galaxy spectrum, by convolving a gaussian-velocity-distribution f(v) with my stellar spectra S. I have already logarithmically rebinned the spectrum and removed the ...
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0answers
86 views

Poisson noise for a squared contrast of density - expression of variance equal to $1/n^2$

I manage to compute the Poisson noise of a density field like this : If I take $N$ the density of galaxies and compute the Shot noise with a Poisson distribution, I get : $\langle N^2\rangle - \...
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0answers
44 views

Why we can approximate the mass of spiral galaxy like this?

This is a question from Galaxies in the Universe: An Introduction(2nd edition),Linda S.Sparke&John S. Gallagher III. As shown in the picture My question is why we can neglect the bulge of spiral ...
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1answer
72 views

I made a graph trying to show the Sun's movement relative to the Galactic Plane. It doesn't seem to be correct

I made a Desmos Graph following the most voted answer of this question, but I'm not sure if it is correct, because it suggest that the formation of the Sun happened shortly after it would have crossed ...
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0answers
22 views

What new instruments "so sensitive that we can see (large circumgalactic winds) have only been on telescopes for a few years"?

The Rhodes College press release Prof. David Rupke and Team of Astrophysicists Make Major New Discovery About Galaxy Evolution links to Astronomy Community/Nature.com: The Making of Makani; The story ...
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26 views

What do stars in galaxies without supermassive black holes revolve around? [duplicate]

I still don't quite understand what the stars in galaxies without SBHs revolve around. I mean, the stars must orbit something. If the Sun suddenly disappeared, the planets wouldn't just continue in ...
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29 views

About the formation of ultra diffuse galaxies (UDGs), what are "failed L∗ galaxies"?

Recent studies show that ultra diffuse galaxies or UDGs were formed by tidally disturbed dwarf galaxies and failed L∗ galaxies. So I've been searching for the failed L∗ galaxies but can't find what it ...
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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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1answer
136 views

Is our Solar System moving independently through our galaxy?

I would like know if our Solar System is moving independently through our galaxy or is stuck on the Orion Arm which is revolving around our galaxy? Is our solar system an onboard passenger of the ...
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0answers
72 views

Logarithmic rebinning and continuum removal of stellar spectra

I am trying to learn how to derive the line of sight velocity distributions from galaxy spectrum to extract kinematical parameters like rotational velocity and velocity dispersion. Therefore I need to ...
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2answers
2k views

How distorted will our galaxy be if we are viewing it from several thousand light years away?

I saw this answer and read this sentence regarding the distortion of our galaxy when viewed above the galactic plane: Once you got to a point where the entire [sic] galaxy was within your vision, the ...
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5answers
220 views

If our galaxy is mostly empty space then why does it look so solid?

This question has probably been asked quite a few times, but I'm having trouble finding anything due to the fact that this question is very specific in nature. So I'm asking again. We know that outer ...

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