Astrophysics - The morphological evolution of galaxies

Many galaxies have taken on their familiar appearance relatively recently. in the distant Universe, galaxy morphology deviates significantly (and syst ematically) from that of nearby galaxies at redshifts (z) as low as 0.3. Th is corresponds to a time similar to3.5 x 10(9) years in the past, which is only similar to 25% of the present age of the Universe. Beyond z = 0.5 (5 x 10(9) years in the past), spiral arms are less well developed and more cha otic, and barred spiral galaxies may become rarer. At z = 1, around 30% of the galaxy population is sufficiently peculiar that classification on Hubbl e's traditional "tuning fork" system is meaningless. On the other hand, som e characteristics of galaxies have not changed much over time. The space de nsity of luminous disk galaxies has not changed significantly since z = 1, indicating that although the general appearance of these galaxies has conti nuously changed over time, their overall numbers have been conserved.