How can I recognize H alpha line?

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In summary, identifying a single line in a redshifted galaxy spectrum is not definitive, but having multiple lines can determine the redshift with high accuracy. This is because all lines are shifted by the same factor, making the pattern of lines unmistakable. You can refer to a specific figure on the Wikipedia page for a visual illustration of this concept.
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19matthew89
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Hi everyone!
If I measure a galaxy spectrum in order to compute galaxy redshift, and I know that Balmer's H alpha line is evident in the spectrum, how can I recognize it? In other words, how can I be sure that the peaked line I clearly see on the spectrum is really H alpha line and not another line that I don't know?
I cannot obiously use the wavelength because it'll be shifted...can I use line intensity instead? But the intensity could be attenuated...and so...could I use H alpha shape to recognize it?
I'd be grateful towards you if you could help me.

Thank you
 
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You really can't be sure you have identified a single line in a redshifted spectrum. But if you have several lines, then you can determine the redshift with high confidence. This is because all of the lines are redshifted by the same factor, so the pattern of the lines is unambiguous. Look at the second figure down on the left (with the caption that begins "Absorption lines in the...") on this page:

http://en.wikipedia.org/wiki/Redshift
 

1. What is the H alpha line and why is it important to recognize it?

The H alpha line is a spectral line in the visible range of the electromagnetic spectrum, specifically at a wavelength of 656.28 nanometers. It is important to recognize because it is a signature of hydrogen gas and can provide valuable information about the structure and dynamics of various astronomical objects, such as stars and galaxies.

2. How can I identify the H alpha line in a spectrum?

To identify the H alpha line, you can look for a peak or dip in the spectrum at a wavelength of 656.28 nanometers. This is the characteristic wavelength of the H alpha line. Additionally, the line may appear broader than other lines in the spectrum due to the Doppler effect caused by the motion of the gas emitting the line.

3. What equipment do I need to detect the H alpha line?

You will need a spectrometer or a spectrograph, which are instruments used to split light into its component wavelengths. These can be found in many telescopes and observatories, or you can purchase a spectrometer for personal use. You will also need a light source, such as a star or nebula, that emits the H alpha line.

4. Can I see the H alpha line with my naked eye?

No, the H alpha line is not visible to the naked eye. It is in the red portion of the visible spectrum, which is just beyond the range of colors that the human eye can see. It can only be detected and studied using specialized equipment, such as a spectrometer.

5. What can the presence or absence of the H alpha line tell us about an astronomical object?

The presence of the H alpha line can indicate the presence of hydrogen gas, which is the most abundant element in the universe. The line's width and shape can also provide information about the temperature, velocity, and density of the gas. The absence of the H alpha line can indicate the absence of hydrogen gas, or it may be indicative of other factors such as dust blocking the line's emission.

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