What are those dark red galaxies called?

[Manok101]

In the Hubble deep field there are galaxies that are a deep deep red, not the orange elliptical galaxies, or are they normal galaxies done in a different light?

[lukebl]

No idea of the name, but I've always assumed they were 'ordinary' galaxies with such a big red shift that they appeared deep red.

[nytecam]

No idea of the name, but I've always assumed they were 'ordinary' galaxies with such a big red shift that they appeared deep red.

Not sure it works like that and "big red shift = deep red" may be a popular misconception going back over 100yrs. Quasar APM08279+5255 in Lynx [that I've recorded], is at ~12BLY but appears 'white' even though the light is redshift eg 1000A Lyman alpha light is shifted to red ~6500A. I suspect these Hubble images are colour coded

[acey]

I think they're highly red-shifted galaxies but not shown in true colour. Quote from Wikipedia:

The data processing yielded four monochrome images (at 300 nm, 450 nm, 606 nm and 814 nm), one at each wavelength.^[8] One image was designated as red (814 nm), the second as green (606 nm) and the third as blue (450 nm), and the three images were combined to give a colour image.^[9] Because the wavelengths at which the images were taken do not correspond to the wavelengths of red, green and blue light, the colours in the final image only give an approximate representation of the actual colours of the galaxies in the image; the choice of filters for the HDF (and the majority of Hubble images) was primarily designed to maximize the scientific utility of the observations rather than to create colours corresponding to what the human eye would actually perceive.^[8]

[dph1nm]

Well I am sure there is some added colour saturation for popular display in the Hubble images, but in general high redshift elliptical galaxies are indeed red. There is a steep drop in their light output blueward of about 4000A. As this gets redshifted to higher and higher wavelengths the overall light output becomes redder and redder. There is actually another drop in the spectra of all objects blueward of ~1000A, where the Universe becomes opaque. At very high redshifts (>6) this causes objects to vanish entirely from optical images, and you can only see them in infra-red light.

NigelM