Thought experiment

Suppose I am looking through Hubble's eyes,
at visible wavelenths.

As I see farther and farther away, when the
redshift of the objects I see increases,
I am not seeing the visible light emission of
the object but its UV emission, shifted to
visible wavelengths by the redshift.

Since the UV photo of a galaxy looks quite weird,
the beautiful arms disappearing in bizarre
structures, the shape of the galaxies should be
quite different from normal spirals as we look
farther and farther away.

Has anyone looked at this?

References welcome.

Thanks in advance for your attention.

jacob

jacob navia wrote:
Suppose I am looking through Hubble's eyes,
at visible wavelenths.

As I see farther and farther away, when the
redshift of the objects I see increases,
I am not seeing the visible light emission of
the object but its UV emission, shifted to
visible wavelengths by the redshift.

Since the UV photo of a galaxy looks quite weird,
the beautiful arms disappearing in bizarre
structures, the shape of the galaxies should be
quite different from normal spirals as we look
farther and farther away.

Has anyone looked at this?

References welcome.

Many people. The jargon term for this effect has come to be
"morphological K-correction". A few sample discussions:

http://www.cv.nrao.edu/~jhibbard/MUV...MUVsurvey.html
http://www.physics.unc.edu/~cecil/a245/morphology.html
http://www.sciencemag.org/cgi/conten.../293/5533/1273
http://www.astr.ua.edu/keel/galaxies/classify.html

It's manageable for typical spirals (i.e. the proper Hubble type
as seen in the optical can statistically be inferred from the UV
data) but making sure this applies more widely is still a major
issue in understanding galaxy evolution. This is particuarly true
at the highest redshifts, where the surface-brightness dimming
in an expanding Universe means that what we see is progressively more
strongly biased to the galaxies and regions of highest UV surface
brightness.

Bill Keel

In article , "William C.
Keel" writes:

It's manageable for typical spirals (i.e. the proper Hubble type
as seen in the optical can statistically be inferred from the UV
data) but making sure this applies more widely is still a major
issue in understanding galaxy evolution. This is particuarly true
at the highest redshifts, where the surface-brightness dimming
in an expanding Universe means that what we see is progressively more
strongly biased to the galaxies and regions of highest UV surface
brightness.

Luminosity distance is greater than angular-size distance by a factor of
(1+z)**2. This means that the bolometric surface brightness is
proportional to (1+z)**(-4). In a finite band, however, it is
proportional to (1_z)**(-5) (since the band corresponds to a smaller
portion in the frame of the galaxy). This means that the
signal-to-noise ratio is proportional to (1+z)**(-10).

All this is nothing new, just textbook stuff, but I thought I would
point it out since most people don't realise just how strong an effect
surface-brightness dimming is. (Of course, the above discussion assumes
that the intrinsic surface brightness is constant; it might have been
different in the past, of course.)