Among galaxies, a voracious flea

DDO 68: Among Galaxies, a Flea, but a Voracious One
This visible-light image taken with the Large Binocular Telescope shows dwarf galaxy DDO 68, which lies in a comparatively "empty" region of space 39 million light-years from Earth, and one of its companion objects, DDO 68 C. The scale bar indicates a distance of 3.6 kiloparsecs, or just under 12,000 light-years. Credit: Francesca Annibali/INAF.

Even a dwarf galaxy with very low mass is capable of accreting smaller nearby galaxies, according to an international team of astronomers led by Francesca Annibali of INAF, the Italian National Institute for Astrophysics. This result has been achieved thanks to observations of the region surrounding the dwarf galaxy DDO 68, which has a total stellar mass of only 100 million solar masses, roughly one thousandth of the Milky Way.

Theoretical models predict hierarchical galaxy formation in which form by successive mergers of smaller systems at all scales. However, until now, direct observational evidence confirming these predictions was available only for massive galaxies and their smaller companions. 

In the new study, Annibali and collaborators took advantage of  the sensitivity and the large field of view of the Large Binocular Telescope, or LBT, located on Mt. Graham in southeastern Arizona (U.S.). The team discovered that DDO 68, a dwarf galaxy located in an isolated region of space defined as a "void," is actually surrounded by a number of smaller satellite galaxies, and is accreting them. 

"In a way, what we saw reminded us of a quote by Jonathan Swift," Annibali said. "'So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite 'em; and so proceed ad infinitum.' It turns out that even the smallest of galaxies feed on companions that are even smaller, and so our paper bears that quote in its title." 

DDO 68: Among Galaxies, a Flea, but a Voracious One
A close-up view of DDO 68. Credit: Francesca Annibali/INAF

DDO 68 is one of three known least-evolved galaxies among those that still form stars, with a chemical composition similar to predictions of the Big Bang. Scientists had already thought that its extremely irregular morphology—with a long tail hosting both stars and gas—could be due to tidal effects resulting from gravitational interactions with other bodies. Incidentally, a candidate companion— possibly another small galaxy or a gas cloud—was spotted at a relatively large distance two years ago by a team led by John Cannon of Macalaster College in Minnesota. 

"When we analyzed our Hubble Space Telescope images, we detected an anomalous protuberance off DDO 68's main body," said Francesca Annibali, a postdoctoral fellow/researcher at the INAF – Astronomical Observatory in Bologna, Italy. "We thought that only LBT with its two 8.4 meter primary mirrors could have the power and the field of view necessary to prove, or disprove, the presence of a stream and other accreting satellites."

LBT's wide, deep images revealed that DDO 68 has a small, incoming stream in addition to its well-known long tail, and is orbited by a few other star and gas companions that are most likely satellites whose ultimate fate is to be accreted. The stream and satellites probably have about 100,000 – similar to, or even lower than, those of the ultra-faint Milky Way satellites, the least luminous and smallest galaxies known, believed to be the closest local analogs of the first galaxies in the universe.

"Our colleagues, Luca Ciotti and Carlo Nipoti of the Physics and Astronomy Department at the Bologna University, have computed numerical dynamical models of DDO 68's system that reproduce very well the observed configuration of the 'flea with its smaller fleas,'" Annibali said. "This is the first evidence of a stellar stream around an isolated dwarf galaxy of only a hundred million solar masses, and the observational proof that hierarchical galaxy formation processes also work at the smallest scales." 

DDO 68: Among Galaxies, a Flea, but a Voracious One
This image taken in visible light (g band) reveals features of the dwarf galaxy telling of its encounter with other, nearby objects. Credit: Francesca Annibali/INAF

"In other words, not only massive bodies cannibalize smaller ones that happen to lie in their surroundings, but the same appetite and digestion capabilities can be found in the smaller ones," said Monica Tosi, INAF astronomer and member of Annibali's team.   

Dwarf galaxies with active star formation are important in helping scientists understand the formation and evolution of galaxies in general. Of those, galaxies that are extremely poor in metals, such as DDO 68, are even more interesting, because in spite of having formed stars for many billions of years, they haven't been able to retain the chemical elements produced by nuclear fusion inside stars. Most likely, they have lost their metals via ejection into the surrounding medium through galactic winds triggered by supernova explosions. 

"It is very interesting to discover that a system whose gravitational potential is too low to retain ejecta from supernovae is still capable of attracting and accreting smaller galaxies," Tosi said. "Specific dynamical and hydrodynamical studies are necessary to understand what main mechanisms are at play here." 

"The results achieved with DDO 68 show the high discovery power of wide-field instrumentation mounted on 8- to 10-meter class telescopes for future projects devoted to the search of substructures around isolated ," she said. "It also emphasizes the importance of combining deep observations with theoretical studies on the evolution and the dynamics of both stars and gas in the galaxies we study."


Explore further

Dark matter satellites trigger massive birth of stars

More information: Francesca Annibali et al. DDO 68: A Flea With Smaller Fleas That Prey On Him, The Astrophysical Journal (2016). DOI: 10.3847/2041-8205/826/2/L27
Journal information: Astrophysical Journal

Provided by Large Binocular Telescope
Citation: Among galaxies, a voracious flea (2016, August 10) retrieved 21 September 2019 from https://phys.org/news/2016-08-galaxies-voracious-flea.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
43 shares

Feedback to editors

User comments

Aug 10, 2016
Why is this news? Matter attracts; attract particles of gas, dust, less body ... to galaxies and clusters of galaxies ..
If planets and smaller bodies attract each other why would some matter (the dwarf galaxy DDO 68) been an exception for first-class novelty?
Article is good (data) and without any unnecessary suggestions.

Aug 10, 2016
"It is very interesting to discover that a system whose gravitational potential is too low to retain ejecta from supernovae is still capable of attracting and accreting smaller galaxies,"

Just another assumption by committed merger maniacs. The smaller companions in the surrounding void were more likely spawned originally from the dwarf parent. The parent is growing from within.

Sure, some daughters then interact with the parent. The key question is not even asked: What is the true origin of both the parent and the siblings? To ask this question invites ridicule. Just watch what happens to this comment.

RNP
Aug 10, 2016
@Tuxford
Your claims are clearly nonsense. There is no physical mechanism by which a galaxy can "spawn" a companion. Indeed this claim flies in the face of all known physics.

What is more, observations of the spectroscopy of these systems shows that the companions in such systems are gravitationally bound and/or infalling, and therefore can not be being ejected from the system.

I am sure that you can not give references for any of these silly claims, but I challenge you to nonetheless.


RNP
Aug 10, 2016
@wduckss
It is article is important because it shows that, while such galaxies have too low a mass to hold on to their supernova ejecta, it is nonetheless massive enough to be accreting small satellite galaxies. This has important implications for how the stellar populations of such systems form and evolve.

Aug 10, 2016
@wduckss
It is article is important because it shows that, while such galaxies have too low a mass to hold on to their supernova ejecta, it is nonetheless massive enough to be accreting small satellite galaxies. This has important implications for how the stellar populations of such systems form and evolve.

Ah, another merger maniac convinced he has it all figured out. Known mechanisms are your limit? You have no chance. Ignorance is your future.

Aug 10, 2016
Why is it difficult to understand and apply the "law of attraction of matter"?
Too much simple?
THow would you now fitted the expansion of the universe (Big Bang) instead of rotation (all matter (the body) are attracted and connects but still are expanding and moving away)?

Aug 10, 2016
Why is it difficult to understand and apply the "law of attraction of matter"?
Too much simple?
THow would you now fitted the expansion of the universe (Big Bang) instead of rotation (all matter (the body) are attracted and connects but still are expanding and moving away)?

What a waste of time. I would rather teach French to a Poodle. Be happy. You already know all there is to know.

Aug 11, 2016
We listen to grandma on the green market in its monologue: "What a waste of time. I would rather teach French to a Poodle. Be happy. You already know all there is to know."
Pure science, knowledge and evidence.

RNP
Aug 11, 2016
@Tuxford
..................Known mechanisms are your limit? You have no chance. Ignorance is your future.


So, you would rather base your ideas on unknown mechanisms? That is just silly!

Aug 11, 2016
What is the unknown?
Rotation? The law of attraction of matter? Blue Shift? Over 75% of small stars in the Milky Way (blue, red and white)? The bodies move 270,000 km / sec at a distance of 13.7 (8) billion ly or is this speed in the past? Clusters of galaxies rotate and do not diverge? The light we have only to bodies outside the matter does not? etc.
What is the unknown?

RNP
Aug 12, 2016
What is the unknown?
Rotation? The law of attraction of matter? Blue Shift? Over 75% of small stars in the Milky Way (blue, red and white)? The bodies move 270,000 km / sec at a distance of 13.7 (8) billion ly or is this speed in the past? Clusters of galaxies rotate and do not diverge? The light we have only to bodies outside the matter does not? etc.
What is the unknown?


I can not respond as I have no idea what you are talking about. Sorry.

Aug 16, 2016
This comment has been removed by a moderator.

Aug 17, 2016
This comment has been removed by a moderator.

RNP
Aug 17, 2016
@FCC
I am indeed relatively new to the site. I watched a bit before I signed up after deciding to have my two pennies worth. I do appreciate the heads up, but will continue to try and provide an antidote to some of the craziness here.

Aug 17, 2016
This comment has been removed by a moderator.

RNP
Aug 17, 2016
@BTP

I take your point. I suppose just trying to make sure that nobody else falls for their craziness will have to be the aim.

Aug 18, 2016
The bottom line is this: these people are so far removed from reality, there's no chance of reasoning with them.


.....you mean like challenging you to prove 80-95% of the Universe is missing when you have no evidence for believing such a premise? If you ask this Nuclear/Electrical Engineer about "people...... so far removed from reality" as you claim, then you should be willing to engage in a cogent discussion or put up evidence for your premises, but that isn't your approach, your approach is to lay out a PREMISE & challenge an opponent to put forth their evidence IT ISN'T TRUE, the reverse of the scientific method of investigation.

I know you detest a challenge, the spiteful rhetorical responses you so prolifically engage in is not the demeanor scientific objectivity is conducted, but that isn't your intended purpose for being in this chatroom, if it were, you'd be on the forefront of demanding profanity & name calling cease by 100%, but you are totally silent.


Aug 18, 2016
Benni, forget them. Don't take the bate.

They are intellectual egomaniacs. It is an incurable mental illness. Just look at what they name themselves. They have nothing but their egos to console their empty lives. Right up there with Trump!

RNP
Aug 19, 2016
@Bennib @Tuxford

...you should... put up evidence for your premises......


What you always fail to realize is that the evidence you require has already been given in the paper under discussion and the references in it. All YOU have to do is actually read (and understand) the paper and then present YOUR evidence for calling it nonsense. Of course, you never do.....

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more