View Full Version : Hubble Sees Ancient Galactic Building Blocks

2007-Sep-06, 07:20 PM
Let's go back, way back, to an earlier time when the Universe was a fraction of its current age. Tiny galaxies, just a fraction of the mass of the Milky Way came together, piece by piece, building up larger and larger galaxies. ...

Read the full blog entry (http://www.universetoday.com/2007/09/06/hubble-sees-ancient-galactic-building-blocks/)

2007-Sep-06, 10:54 PM
Well, we have seen many, many papers and articles like this in the past:

In the distant Universe, galaxy morphology started to deviate significantly (and systematically) from that of nearby galaxies at redshifts, z, as low as z = 0.3. This corresponds to a time ~3.5 Gyr in the past, which is only ~25% of the present age of the Universe. Beyond z = 0.5 (5 Gyr in the past) spiral arms are less well-developed and more chaotic, and barred spiral galaxies may become rarer. By z = 1, around 30% of the galaxy population is sufficiently peculiar that classification on Hubble’s traditional “tuning
fork” system is meaningless.

Images from the Hubble Deep Field (HDF) North and South show a large percentage of dusty, high redshift galaxies whose appearance falls outside traditional classification systems. The nature of these objects is not yet fully understood.


Evidence for Evolving Spheroidals in the Hubble Deep Fields
North and South

We investigate the dispersion in the internal colours of faint spheroidals in the Hubble Deep Fields North and South. In high redshift rapid-collapse scenarios, the dispersion in internal colours should be small at moderate redshift apart from a small metallicity-induced reddening in the enriched cores. However, recentlyassembled spheroidals are likely to show non-homologous internal colours, at least until younger stellar populations become fully mixed...
Although the samples are currently small, we find evidence for an increase in SFR between z = 0 to z = 1.We discuss the implications of this rise in the context of that observed in the similar rise in the abundance of galaxies with irregular morphology. Regardless of whether there is a connection our results provide strong evidence for the continued formation of field spheroidals over
0< z <1.


Hubble Space Telescope Imaging of the CFRS and LDSS Redshift Surveys – IV. Influence of mergers in the evolution of faint field galaxies from z ~ 1

We have performed visual and machine-based merger identifications, as well as counts of bright pairs of galaxies with magnitude differences m <= 1.5 mag. We find that the pair fraction increases with redshift, with up to ~ 20% of the galaxies being in physical pairs at z = 0.75− 1. We derive a merger fraction varying with redshift as / (1 + z)3.2±0.6, after correction for line-of-sight contamination, in excellent agreement with the merger fraction derived from the visual classification of mergers for which m = 3.4 ± 0.6. After correcting for seeing effects on the ground-based selection of survey galaxies, we conclude that the pair fraction evolves as / (1 + z)2.7±0.6.

The elliptical sample is too small for precise evolutionary constraints. However, we find a substantial increase in the proportion of galaxies with irregular morphology at large redshift from 9% ± 3% for 0.3 ≤ z ≤ 0.5 to 32% ± 12% for 0.7 ≤ z ≤ 0.9.
We should know by now that searching latests-and-greatest deep field surveys for the most distant redshifted objects will not provide us with a representative sample of that fraction of space and time. The Hubble Ultra Deep Field Surveys showed that most, if not all, of the galaxy evolution morphologies based upon the Hubble Deep Field Surveys were artifacts of the selection process, and to a lesser degree, weak analytical tools and wishful thinking.