Study helps prove galaxy evolution theory

Study helps prove galaxy evolution theory
The Atacama Large Millimeter/submillimeter Array (ALMA), as captured in phenomenal panorama from 5,000 meters at Chilean Altiplano -- the highlands of the Andes Mountains. The Milky Way was passing through its zenith at that very moment, and Zodiacal light is also visible in the lower part of the image, with Venus shining through as well. Credit: Yuri Beletsky, Carnegie Observatories

Everyone has a backstory, even our own Milky Way galaxy. And much like social media, the picture is not always as pretty as it appears on the current surface, says Texas A&M University astronomer Casey Papovich.

Papovich notes that large disk like our own Milky Way were not always the well-ordered, pinwheel-like, spiral structures we see in the universe today. On the contrary, he and other international experts who specialize in galaxy formation and evolution believe that about 8-to-10 billion years ago, progenitors of the Milky Way and similar disk/spiral galaxies were smaller and less organized, yet highly active in their youth.

In previous NASA and National Science Foundation-funded research, Papovich and his collaborators showed that these younger versions of such galaxies were churning out new stars faster than at any other point in their lifespans, suggesting that they must be amazingly rich in star-forming material. And now, they have compelling evidence—the galactic equivalent of a smoking gun.

Using the National Radio Astronomy Observatory's Atacama Large Millimeter/submillimeter Array (ALMA)—a huge, highly sophisticated radio telescope array situated at 16,500 feet altitude in the high desert of Chile—a Papovich-led team of astronomers studied four very young versions of galaxies like the Milky Way that are 9 billion light-years distant, meaning the team could see them as they looked approximately 9 billion years ago. They discovered that each galaxy was incredibly rich in carbon monoxide—a well-known tracer of molecular gas, which is the fuel for star formation.

The team's findings are reported in a paper posted to arXiv and set to be published in the inaugural issue of Nature Astronomy in January.

"We used ALMA to detect adolescent versions of the Milky Way and found that such galaxies do indeed have much higher amounts of molecular gas, which would fuel rapid star formation," said Papovich, lead author on the paper and a member of the George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy. "I liken these galaxies to an adolescent human who consumes prodigious amounts of food to fuel their own growth during their teenage years."

In addition to Papovich, the research team also includes fellow Texas A&M astronomers Ryan Quadri and Kim-Vy Tran, as well as astronomers from Leiden Observatory in Holland, Swinburne University and Macquarie University in Australia, the National Optical Astronomy Observatory (NOAO), the University of Texas at Austin, Lyon Observatory in France and the Max Plank Institute for Astronomy in Germany.

Study helps prove galaxy evolution theory
Composite image of the molecular gas (indicated in red), superimposed on Hubble Space Telescope images of the four young Milky Way-like galaxies studied by Texas A&M astronomer Casey Papovich and his collaborators using ALMA. These Hubble images are much sharper than the images of the gas from ALMA. Therefore, while the gas appears as a halo here, Papovich says it is more likely to be co-spatial with the starlight in the galaxies. Credit: National Radio Astronomy Observatory

Though the relative abundance of star-forming gas is extreme in these galaxies, Papovich says they are not yet fully formed and rather small compared to the Milky Way as we see it today. The new ALMA data indicate that the vast majority of the mass in these galaxies is in cold rather than in stars—a situation that Papovich says is reversed at present in our Milky Way, where the mass in stars outweighs that in gas by a factor of 10 to 1. These observations, he notes, are helping build a complete picture of how matter in Milky-Way-size galaxies evolved and how our own galaxy formed.

"Most stars today exist in galaxies like the Milky Way, so by studying how galaxies like our own formed, we've come to understand the most typical locations of stars in the universe," said Papovich, a member since 2008 of the Texas A&M Department of Physics and Astronomy, where he is a co-holder of the Marsha L. '69 and Ralph F. Schilling '68 Chair in Experimental Physics. "Our current research shows that Milky Way-mass galaxies appear to accumulate most of their gas during their first few billion years of history. At that stage, they have most of the fuel they need to produce the stars they currently encompass in the present."

The presence of extensive gas reservoirs backs up the team's previous observations that provided the first tangible pictures showcasing the unprecedented life story of Milky Way galaxy evolution. Among other details, their prior study revealed a stellar birth rate 30 times higher than it is in the Milky Way today—roughly one per year, compared to about 30 each year 9.5 billion years ago.

"Thanks to ALMA and other innovative instruments that allow us to peer 9 billion years into the past to analyze galaxies that are likely similar to the progenitor of our own Milky Way galaxy, we can actually prove what our observations show," Papovich said.

Papovich and his team recently have been awarded more highly competitive time with ALMA to study the temperature and density of the star-forming gas, allowing them to measure and map its transitions and phases and ideally the related impacts within the galaxies.

"This will begin to tell us how these galaxies formed stars at such a rapid pace, compared to conditions at present," he said.

Papovich, Quadri and Tran are among roughly two dozen astronomers around the world who have spent years studying carefully selected distant galaxies similar in mass to the progenitor of our own Milky Way that were found in two deep-sky program surveys of the universe, the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and the FourStar Galaxy Evolution Survey (ZFOURGE). Beyond ALMA, the team's research has used observations from NASA's Hubble and Spitzer Space Telescopes and the European Space Agency's Herschel Space Observatory. The Hubble images from the CANDELS survey also provided structural information about galaxy sizes and how they evolved. Far-infrared light observations from Spitzer and Herschel helped the astronomers trace the star-formation rate.

The team's paper, Large Molecular Gas Reservoirs in Ancestors of Milky Way-Mass Galaxies 9 Billion Years Ago, can be viewed online along with related images and captions.


Explore further

Our Sun came late to the Milky Way's star-birth party

More information: C. Papovich et al. Large molecular gas reservoirs in ancestors of Milky Way-mass galaxies nine billion years ago, Nature Astronomy (2016). DOI: 10.1038/s41550-016-0003
Citation: Study helps prove galaxy evolution theory (2016, December 19) retrieved 20 June 2019 from https://phys.org/news/2016-12-galaxy-evolution-theory.html
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Dec 20, 2016
Pray tell, how and where carbon monoxide (CO) in these galaxies came from without stars being formed first? After all, it is only the stars that cook up the higher elements like carbon and oxygen! The primordial gas from the so-called Big Bang was supposed to contain only hydrogen and helium gas!

The high rate of star formation in the presence of substantial amount of CO, does not mean that these are the first generation of stars being formed from the primordial gases and hence represents the earlier stage of the development (young galaxies, back in time) of these galaxies than the Milky Way! God-of-the-Gaps logic of modern official cosmology, I would say!

RNP
Dec 20, 2016
@Bigbangcon
Pray tell, how and where carbon monoxide (CO) in these galaxies came from without stars being formed first? After all, it is only the stars that cook up the higher elements like carbon and oxygen! The primordial gas from the so-called Big Bang was supposed to contain only hydrogen and helium gas!

The high rate of star formation in the presence of substantial amount of CO, does not mean that these are the first generation of stars being formed....

The article above does not do a very good job of explaining the paper, but it does not say that we are seeing the first generation of stars. Indeed, you are right, of course, that the carbon and oxygen in the detected CO must have been produced in earlier generations of stars. In fact, all the authors do is to use the total emission and ratio of specific CO emission lines to estimate the total gas content and star formation rates in these young galaxies. They then compare them to older galaxies, such as the Milky Way.

Dec 20, 2016
@ RNP

"The article above does not do a very good job of explaining the paper, but it does not say that we are seeing the first generation of stars."

So, on what basis does it claim that these galaxies are young and earlier stage of development (in time) than the Milky Way galaxy? It claims, "Study helps prove galaxy evolution theory", a major premise, propaganda (the whole intention of this "study" started with?) for the Big Bang creation of the universe to get recognition and kudos from official cosmology!

But unfortunately this is an unscrupulous and basically faulty attempt at the justification of the Big Bang Theology! Cheers!



RNP
Dec 21, 2016
@ RNP
So, on what basis does it claim that these galaxies are young and earlier stage of development (in time) than the Milky Way galaxy? It claims, "Study helps prove galaxy evolution theory", a major premise, propaganda (the whole intention of this "study" started with?) for the Big Bang creation of the universe to get recognition and kudos from official cosmology!

But unfortunately this is an unscrupulous and basically faulty attempt at the justification of the Big Bang Theology!


Firstly, at z=1.25 we are seeing galaxies when the universe was only ~5 Gyr old. The galaxies MUST therefore be younger than the Milky Way (which is about 10 Gyr old).

The results confirm a prediction of current galaxy evolution theory that such young galaxies should have a higher ratio of gas to stars than MW-like galaxies that have been forming stars for longer.

Finally, this is a piece of well supported science, unlike the wild unsupported claims made in some posts here.

Dec 21, 2016

Firstly, at z=1.25 we are seeing galaxies when the universe was only ~5 Gyr old. The galaxies MUST therefore be younger than the Milky Way (which is about 10 Gyr old).

Pure speculation based on pure speculation, but that is astrophysics in a nutshell.

RNP
Dec 21, 2016
@cantdrive85

Firstly, at z=1.25 we are seeing galaxies when the universe was only ~5 Gyr old. The galaxies MUST therefore be younger than the Milky Way (which is about 10 Gyr old).

Pure speculation based on pure speculation, but that is astrophysics in a nutshell.


The only way you can avoid looking foolish after such an inane post is to give YOUR explanation of the observations and ideas that are described above. Remember to make sure that it is NOT based on speculation.

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