<p>I'm very new to astronomy, trying to find the recessional velocity of galaxies by finding how shifted the H1 line is. The galaxy I am using currently is NGC 7600, which is about 49 Mpc away and should be redshifted, causing the H1 line frequency to be about 1404 MHz. Assuming that the H1 line would appear as a spike on this spectrum (I could be wrong, if I am, please explain), I don't see any form of spike that could be the H1 spectral line, aside from where the H1 line would be if the galaxy wasn't redshifted at all. Here is a link to the observation if that would help: <a href="https://www.gb.nrao.edu/20m/idlinks/126042.htm" rel="nofollow noreferrer">https://www.gb.nrao.edu/20m/idlinks/126042.htm</a></p>
<p>Thanks for the help!</p>

CC BY-SA 4.0
2024-12-01T07:40:37.987Z
Indeed, there is no emission line at 1404 MHz. Unclear what your question is. If you expect to see one then you would need to explain all tbe details of your observation and the instrument being used  carefully.
ProfRob
CC BY-SA 4.0
2024-12-01T10:32:22.200Z
NGC 7600 is an S0 galaxy; these, like elliptical galaxies, frequently don't have much or any neutral hydrogren, and so produce little or no H I emission. So it could be that NGC 7600 just doesn't have H I emission. (I note that the NASA Extragalactic Database entry for this galaxy has a redshift, but it's from absorption-line spectroscopy of the stellar light.)
Peter Erwin
<amateur-observing><radio-astronomy><redshift><spectra><hydrogen>
How to use shift of H1 line to determine recessional velocity with 20m telescope?
Jaxon Milam
# How to use shift of H1 line to determine recessional velocity with 20m telescope?

(Asked by: username_0 on 2024-12-01)

I'm very new to astronomy, trying to find the recessional velocity of galaxies by finding how shifted the H1 line is. The galaxy I am using currently is NGC 7600, which is about 49 Mpc away and should be redshifted, causing the H1 line frequency to be about 1404 MHz. Assuming that the H1 line would appear as a spike on this spectrum (I could be wrong, if I am, please explain), I don't see any form of spike that could be the H1 spectral line, aside from where the H1 line would be if the galaxy wasn't redshifted at all. Here is a link to the observation if that would help: <https://www.gb.nrao.edu/20m/idlinks/126042.htm>

Thanks for the help!

**Tags:** amateur-observing, radio-astronomy, redshift, spectra, hydrogen

> **Comments:**
> **username_1**: Indeed, there is no emission line at 1404 MHz. Unclear what your question is. If you expect to see one then you would need to explain all tbe details of your observation and the instrument being used  carefully.  
> **username_2**: NGC 7600 is an S0 galaxy; these, like elliptical galaxies, frequently don't have much or any neutral hydrogren, and so produce little or no H I emission. So it could be that NGC 7600 just doesn't have H I emission. (I note that the NASA Extragalactic Database entry for this galaxy has a redshift, but it's from absorption-line spectroscopy of the stellar light.)  

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## 0 answers

