Hubble Looks Back In Time To See Shape Of Galaxies 11 Billion Years Ago

What we’re gonna’ do here is go back. Way back into time. Back to when the only thing that existed was… galaxies? When astronomers employed the power of Hubble’s CANDELS survey to observe different galaxy types from the distant past, they expected to see a variety of spiral, elliptical, lenticular and peculiar structures, but what they didn’t expect was that things were a whole lot more “peculiar” a long time ago!

Known as the Hubble Sequence, astronomers use this classified system for listing galaxy sizes, shapes and colors. It also arranges galaxies according to their morphology and star-forming activity. Up to the present, the Hubble Sequence covered about 80% of the Universe’s history, but the latest information shows that the sequence was valid as much as 11 billion years ago! Out of what we currently know, there are two dominant galaxy types – spiral and elliptical – with the lenticular structure as a median. Of course, this is constrained to the regions of space which we can readily observe, but how true did the sequence hold back when the Universe theoretically began?

“This is a key question: when and over what timescale did the Hubble Sequence form?” says BoMee Lee of the University of Massachusetts, USA, lead author of a new paper exploring the sequence. “To do this you need to peer at distant galaxies and compare them to their closer relatives, to see if they too can be described in the same way.”

Using the Hubble Space Telescope, astronomers took on the sequence challenge to peer back 11 billion years in time to study galaxy structure. Up until now, researchers could confirm the sequence was valid as long ago as 8 billion years, but these new studies pushed CANDELS, the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, to the outer limits. It is simply the largest project ever, and soaked up 902 assigned orbits of observing time. Using the WFC3 and ACS cameras, the team examined structures that existed less than one billion years after the Big Bang. While earlier studies had aimed for lower-mass galaxies in this era, no study had really taken on serious observation of mature structures – ones similar to our own galaxy. Now the new CANDELS observations show us that all galaxies, regardless of size, fit into a totally different classification!

“This is the only comprehensive study to date of the visual appearance of the large, massive galaxies that existed so far back in time,” says co-author Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany. “The galaxies look remarkably mature, which is not predicted by galaxy formation models to be the case that early on in the history of the Universe.”

Just what did this study see that’s so different? Just the power of two. Galaxies were either complex, with blue star forming regions and irregular structures, or they were like our nearby neighbors: massive red galaxies that exhibit no new star-formation. In the early Universe, galaxies like the Milky Way were uncommon. With so little to study, it was nearly impossible to get a large enough sample to sufficiently catalog their characteristics. Early research could only peer back in visible light, a format which emphasized star formation and revealed the red-shifted ultraviolet emission of the galaxies. This information was inconclusive because galaxy structure appeared disrupted and unlike the formations we see near to us. Through the use of infra-red, astronomers could observe the now red-shifted massive galaxies in their visible rest frame. Thanks to CANDELS lighting the way, astronomers were able to thoroughly sample a significantly larger amount of mature galaxies in detail.

“The huge CANDELS dataset was a great resource for us to use in order to consistently study ancient galaxies in the early Universe,” concludes Lee. “And the resolution and sensitivity of Hubble’s WFC3 is second to none in the infrared wavelengths needed to carry out this study. The Hubble Sequence underpins a lot of what we know about how galaxies form and evolve — finding it to be in place this far back is a significant discovery.”

Original Story Source: ” Hubble Explores the Origins of Modern Galaxies” – Hubble News Release.

Pinning The Tails On Galaxy Clusters

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When it comes to understanding how galaxies behave both inside and outside of galaxy clusters, it would seem that we still have quite a lot to learn. Tom Scott from the Instituto de Astrofisica de Andalucia in Granada, Spain, and a group of international astronomers have been busy with the Expanded Very Large Array (EVLA) of the National Radio Astronomy Observatory (NRAO) in the USA, checking out an assortment of galaxies associated with galaxy cluster Abell 1367. What they have found is unexpectedly long one-sided gaseous tails in two sets of galaxies… the longest of their type ever observed.

Located in the constellation of Leo and about 300 million light years away, galaxies CGCG 097-026 and FGC1287 are displaying gaseous tail structures that may rearrange thinking on how stripping of materials behaves. Current thinking has hot gases trapped within the galaxy cluster’s gravitational field – with incoming galaxies being depleted of their cold hydrogen gases when captured by the gravitational influence. Through this impact, galaxies added to the cluster generally tend to lose their star-forming abilities and begin to quickly age. Astronomers assume this is why less aggressive galaxy structures tend to be found in lower density environments. However, thanks to Scott’s research, astronomers might be able to assume that galaxies can be robbed of their gases before entering a clustered environment.

“When we looked at the data, we were amazed to see these tail structures” says Tom Scott. “The projected lengths of the gaseous tails are 9 to 10 times that of the size of the parent galaxies, i.e., 520,000 and 815,000 light years respectively. In both cases the amount of cold hydrogen gas in the tails is approximately the same as that remaining in the galaxy’s disk. In other words, these galaxies have already left behind half of their fuel for star formation before entering the sphere of influence of the cluster.”

As stated, the commonly accepted theory for gaseous tail structures is interaction with the hot, gaseous medium located within the cluster’s influence – a process known as ram-pressure stripping. But this case is different. Galaxies CGCG 097-026 and FGC1287 aren’t being perturbed by the nearby cluster just yet… But they are still displaying long tails of material.

“We considered the various physical processes proposed by theorists in the past to describe gas removal from galaxies, but no one seems to be able to explain our observations” says Luca Cortese, researcher at ESO-Garching, Germany, and co-author of this work. “Whereas in the case of CGCG97-026, the gravitational interaction between the various members of the group could explain what we see, FGC1287 is completely different from any case we have seen before.”

Right now, ram-pressure stripping isn’t the answer – and gravitational interactions don’t seem to fit the picture, either. It’s leaving scientists at a loss to explain these long tails and lack of stellar disturbance.

“Although the mechanism responsible for this extraordinary gas tail remains to be determined, our discovery highlights how much there still is to learn about environmental effects in galaxy groups” says team member Elias Brinks, a scientist at the University of Hertfordshire. “This discovery might open a new chapter in our understanding of environmental effects on galaxy evolution.”

Original Story Source: Royal Astronomical Society News Release. For Further Reading: Two long tails in the outskirts of Abell 1367.