<p>The NVSS survey has been carried out at 1.4 GHz. From what I could gather,
the bandwidth of the NVSS survey includes HI 21 cm (~1.420 GHz) emission line.</p>
<p>Suppose I have a region of the sky in which I see NVSS emission also. Then how
do I know whether the NVSS emission is due to the atomic hydrogen emission (i.e.
HI at 21 cm) or due to free-free emission due to HII regions (which is also
prominent at ~1 GHz) ?
Or, to put it in a slightly differently, if we want to examine only continuum
radio emission, can we use NVSS ? Because won't it be contaminated by emission
of atomic hydrogen spectral line at 21 cm/1.420 GHz ?</p>

CC BY-SA 4.0
2024-06-10T14:59:14.163Z
https://astronomy.stackexchange.com/questions/49770/why-was-the-nvssnrao-vls-sky-survey-conducted-at-1-4-ghz-continuum?rq=1 may help
Jon Custer
CC BY-SA 4.0
2024-06-11T06:47:47.353Z
I have seen the post. The post, as well as the NVSS paper, does not resolve my query on how to discriminate whether an NVSS detection somewhere is due to 21 cm spectral line or, say, free-free continuum ?
kkr01
<radio-astronomy>
Are continuum observations in NVSS contaminated by HI spectral line?
kkr01
# Are continuum observations in NVSS contaminated by HI spectral line?

(Asked by: username_0 on 2024-06-10)

The NVSS survey has been carried out at 1.4 GHz. From what I could gather,
the bandwidth of the NVSS survey includes HI 21 cm (~1.420 GHz) emission line.

Suppose I have a region of the sky in which I see NVSS emission also. Then how
do I know whether the NVSS emission is due to the atomic hydrogen emission (i.e.
HI at 21 cm) or due to free-free emission due to HII regions (which is also
prominent at ~1 GHz) ?
Or, to put it in a slightly differently, if we want to examine only continuum
radio emission, can we use NVSS ? Because won't it be contaminated by emission
of atomic hydrogen spectral line at 21 cm/1.420 GHz ?

**Tags:** radio-astronomy
> **Comments:**
> **username_1**: https://astronomy.stackexchange.com/questions/49770/why-was-the-nvssnrao-vls-sky-survey-conducted-at-1-4-ghz-continuum?rq=1 may help  
> **username_0**: I have seen the post. The post, as well as the NVSS paper, does not resolve my query on how to discriminate whether an NVSS detection somewhere is due to 21 cm spectral line or, say, free-free continuum ?  

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