All Questions
Tagged with redshift observational-astronomy
25
questions
0
votes
1
answer
92
views
Does a cosmological redshift occur within our local group, of galaxies?
I know that it is not supposed to be expanding but space is space and it is expanding everywhere else outside it so why not inside it too, and gravity just holds everything back.
I suppose if it is, ...
- 171
5
votes
0
answers
513
views
How far away must galaxies be before current telescopes can no longer measure how quickly they are rotating around one another or internally?
What is the distance limit and does it depend on the size of the galaxy and on noise and interference from gas clouds and our own Milky Way?
user50623
1
vote
1
answer
50
views
Interpreting the color of galaxies in deep field images
The HST produced some deep field images in mostly visible light, which contain thousands of galaxies that range in color from white to red (e.g. see here). I understand that the interpretation of ...
- 121
1
vote
1
answer
105
views
redshift puzzle
I have the central line of the spectrum of an elliptical galaxy (NGC:4697) and a template K-star. I have calculated the redshift z by computing the crosscorrelation function between the galaxy and the ...
- 849
5
votes
1
answer
319
views
How far away from us was Earendel star when it emitted the light that is just now reaching us?
From what I've read, the look back time is about 12.9 billion light years, and the current distance to the Earendel star is approximately 28 billion light years...
How close to us was it when it ...
- 5,307
6
votes
1
answer
135
views
Classifying 3C273 as a quasi-stellar object
I am currently reading A Brief History of Time and Chapter 6 about black holes.
Now, here it says
He found it too large to be caused by a gravitational field: if it had
been a gravitational redshift, ...
- 191
4
votes
2
answers
177
views
How to interpret this spectrum of the "new DESI Quasar at z = 6.53"; what causes the big edge at about 9150 Angstroms?
I'm not exacty sure why but Scitech Daily's Seeing Dark Energy’s True Colors: DESI Creates Largest 3D Map of the Cosmos includes the graphic and caption below.
It indicates a quasar in a Hubble image ...
- 30.7k
5
votes
1
answer
408
views
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 ...
- 849
3
votes
1
answer
3k
views
Comoving Volume Calculation
Suppose I have data from an astronomical survey at redshifts in the range $z = [2,3]$. Suppose that, on average in this range, the data covers an area on the sky of $A=1$ $\mathrm{Mpc}^2$. How would I ...
- 205
1
vote
1
answer
233
views
HR diagram x-axis (color) and redshift?
I've read several articles and watched some videos on the HR diagram, but no-one seems to mention the effect of redshift on the color of a star. Is there some calibration step that needs to be applied ...
- 113
1
vote
1
answer
111
views
Shouldn't the estimate of the universe's age be higher, not lower, after the attractive strength of gravity is taken into account?
From 'Fundamentals: Ten Keys to Reality', by Frank Wilczek :
"Running the movie of cosmic history backward in our minds, we found the galaxies all coming together to meet at a definite time. ...
- 5,307
4
votes
0
answers
71
views
K-correction vs resizing photometric bands
Is there a difference between a K-correction (see Wiki https://en.wikipedia.org/wiki/K_correction) and simply "resizing" the bands, e.g. the 2-10 keV x-ray band, with the redshift? I've read ...
- 1,105
1
vote
1
answer
4k
views
How to find the distance between two galaxies from ra and dec and redshift [duplicate]
I have ra and dec and corresponding redshift of galaxies. I would like to calculate the distance between two galaxies.
I did like this to find the nearest neighbour galaxies.
Suppose I am trying to ...
- 11
3
votes
1
answer
106
views
Were radio spectroscopic observations ever used to first measure a distance successfully?
Usually, especially for an extragalactic object, its redshift is determined by optical spectroscopic redshift. But the angular resolution of early radio observations is poor and an optical counterpart ...
- 3,137
1
vote
1
answer
221
views
Intuitive explanation for why the Doppler effect (and red-shift) happens?
I was looking for an intuitive explanation as to why the Doppler effect happens. I haven't found any, but this is what I thought:
-Waves emitted travel at a constant speed
-The source emits a wave
-If ...
- 201