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Understood! What I was asking is: Is the target's normally-visible light redshifted into the same bands that JWST is measuring, higher? or lower frequency? Th

Understood! What I was asking is: Is the target's normally-visible light redshifted into the same bands that JWST is measuring, higher? or lower frequency? That doesn't have anything to do with why JWST uses IR.

sbierwagen 4y ago
Redshift refers to how the wavelength of a photon can change if the observer is moving relative to it, (Doppler shift, redshift if you're moving away from the photon, blueshift if you're moving towards it) or cosmological redshift. (The fabric of the universe expanding, reducing photon energy) NGC3372 is a cloud of (relatively) hot gas and dust. It's emitting broad spectrum blackbody radiation: it's emitting on all wavelengths. You can look at the same cloud at different wavelengths and see different things, telling you what parts of the cloud are at what temperature, or relative chemical composition, or what parts are ionized: http://legacy.spitzer.caltech.edu/uploaded_files/graphics/fullscreen_graphics/0009/1118/ssc2004-15b_Sm.jpg http://legacy.spitzer.caltech.edu/uploaded_files/graphics/fu... Nothing here is redshifted, Spitzer is just capturing different light entirely. In the side by side of JWST and Hubble https://pbs.twimg.com/media/FXecm6vXwAMPhoc?format=jpg&name=large https://pbs.twimg.com/media/FXecm6vXwAMPhoc?format=jpg&name=... https://pbs.twimg.com/media/FXecnp2XkAE4Rs5?format=jpg&name=large https://pbs.twimg.com/media/FXecnp2XkAE4Rs5?format=jpg&name=... you see broadly the same thing, but Hubble is almost all visible-light while JWST goes deeper into infrared and sees cloud structure that Hubble doesn't.
heisenzombie 4y ago
Ok, disclaimer: I am not an astronomer and this might all be rubbish. I suspect I'm neglecting relativistic effects that might be important, for example. The NIRCAM instrument on JWST has a wavelength range of about 600 - 5000nm [1]. The human eye is sensitive to around 380nm - 700nm. To shift blue light (380nm) down to the upper frequency range of NIRCAM (600nm) requires a redshift of: z = Δλ / λ0 = 0.58 This is related to the velocity of the object by: z = v / c and the velocity is related to distance (approximately) by the Hubble constant (H0 ~ 71 km/s / Mpc): d = v/ H0 So we can rearrange and solve for distance to get: d = z c / H0 = 8 billion light years. The southern ring nebula is more like 2000 light years from us, so not even vaguely far enough that NIRCAM would see "originally-visible" light. The deep field image might actually be far enough... the faintest galaxies there might be something like 12 billion light years away [2]. [1] https://www.stsci.edu/jwst/instrumentation https://www.stsci.edu/jwst/instrumentation [2] https://www.nasa.gov/content/discoveries-hubbles-deep-fields https://www.nasa.gov/content/discoveries-hubbles-deep-fields

sbierwagen 4y ago

Redshift refers to how the wavelength of a photon can change if the observer is moving relative to it, (Doppler shift, redshift if you're moving away from the photon, blueshift if you're moving towards it) or cosmological redshift. (The fabric of the universe expanding, reducing photon energy) NGC3372 is a cloud of (relatively) hot gas and dust. It's emitting broad spectrum blackbody radiation: it's emitting on all wavelengths. You can look at the same cloud at different wavelengths and see different things, telling you what parts of the cloud are at what temperature, or relative chemical composition, or what parts are ionized: http://legacy.spitzer.caltech.edu/uploaded_files/graphics/fullscreen_graphics/0009/1118/ssc2004-15b_Sm.jpg http://legacy.spitzer.caltech.edu/uploaded_files/graphics/fu... Nothing here is redshifted, Spitzer is just capturing different light entirely. In the side by side of JWST and Hubble https://pbs.twimg.com/media/FXecm6vXwAMPhoc?format=jpg&name=large https://pbs.twimg.com/media/FXecm6vXwAMPhoc?format=jpg&name=... https://pbs.twimg.com/media/FXecnp2XkAE4Rs5?format=jpg&name=large https://pbs.twimg.com/media/FXecnp2XkAE4Rs5?format=jpg&name=... you see broadly the same thing, but Hubble is almost all visible-light while JWST goes deeper into infrared and sees cloud structure that Hubble doesn't.

heisenzombie 4y ago

Ok, disclaimer: I am not an astronomer and this might all be rubbish. I suspect I'm neglecting relativistic effects that might be important, for example. The NIRCAM instrument on JWST has a wavelength range of about 600 - 5000nm [1]. The human eye is sensitive to around 380nm - 700nm. To shift blue light (380nm) down to the upper frequency range of NIRCAM (600nm) requires a redshift of: z = Δλ / λ0 = 0.58 This is related to the velocity of the object by: z = v / c and the velocity is related to distance (approximately) by the Hubble constant (H0 ~ 71 km/s / Mpc): d = v/ H0 So we can rearrange and solve for distance to get: d = z c / H0 = 8 billion light years. The southern ring nebula is more like 2000 light years from us, so not even vaguely far enough that NIRCAM would see "originally-visible" light. The deep field image might actually be far enough... the faintest galaxies there might be something like 12 billion light years away [2]. [1] https://www.stsci.edu/jwst/instrumentation https://www.stsci.edu/jwst/instrumentation [2] https://www.nasa.gov/content/discoveries-hubbles-deep-fields https://www.nasa.gov/content/discoveries-hubbles-deep-fields