Galaxies visible only in infrared?

[Superdavo]

I've had the same thought, I don't think it's possible in radio wavelengths, as you'd have to go back to before the CMB, when there weren't any galaxies. Furthermore, I think redshift increases exponentially the further back you go. I think that means that infrared is too far for galaxies, but i'm sure stars go back that far.

[JulianO]

Well you go back far enough - its all microwaves

(CMB)

[nytecam]

I think the crucial word is "visibility". An object is "visible" if you have a detector able to detect it, otherwise it is "invisible". Distant galaxies emit most of their radiation at infra-red, but will also emit faintly at shorter wavelengths (e.g. normal "visible light"). Whether they are visible at those wavelengths would depend on whether the telescope was powerful enough to detect that faint radiation. The Hubble Ultra Deep Field Team detected a galaxy that was visible using a 1600nm infra-red filter, but was not detectable through a 1400nm filter. In other words it was invisible to that telescope at 1400nm (and at "visible light" wavelengths). A bigger telescope might have been able to see it at 1400nm, and a sufficiently huge one (with long enough exposure) might see it at "visible light" wavelengths. http://www.spacetele.../news/heic1219/

Yes - I took the OP to mean 'visible' to the human eye [assuming a scope big enough] - not an IR camera as you describe for Hubble.

ps: once did a spectrographic redshift of quasar APM 08279+5255 at 12BLY where the Lyman Alpha etc @ ~120nm is shifted into visible - recent field shot below!

[nightvision]

Nice graphical representation!

[Tiki]

...

My question is about galaxies which are redshifted enough so we can't see them with the naked eyes, even when there is no dust obscuring them

Galaxies as a whole are relatively well behaved black bodies and have pretty much continuous spectra. Our eyes have evolved to be sensitive to the most numerous photons which we know as sunlight/starlight. Therefore when we visually observe a redshifted galaxy we are detecing photons which are not the most numerous. Galaxies will appear progessively dimmer at higher and higher redshifts.

It makes sense to search for distant emitters of starlight in the longer wavelengths as this is where the peak intensity is likely to be. More signal I suppose.