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Galactic evolution both “nature” and “nurture”

Dec. 6, 2006
Courtesy European Southern Observatory
and World Science staff

A team of as­tro­no­mers has found that galax­ies “e­volve” as a re­sult of in­flu­ences from their sur­round­ings.

The sci­en­tists said their work showed that the dis­tri­bu­tion of galax­ies has con­sid­er­a­bly changed over time, de­pend­ing on the galax­ies’ sur­round­ings. The sur­pris­ing find­ing chal­lenges ex­ist­ing the­o­ries on ga­lac­tic for­ma­tion and ev­o­lu­tion, they added.

In bi­ol­o­gy, re­search­ers have de­bat­ed for cen­turies wheth­er hu­man de­vel­op­ment is pri­mar­i­ly a re­sult of “na­ture” or “nur­ture”—that is, genes or ex­pe­ri­ence.

As­tro­no­mers face si­m­i­lar co­nun­drums, said Oliv­i­er Le Fevre of the As­tro­phys­ics Lab­o­ra­to­ry in Mar­seille, France, who co­or­di­nat­ed the new re­search. Are galax­ies to­day simp­ly the prod­ucts of pri­mor­di­al con­di­tions in which they formed, or did ex­pe­ri­ences change their ev­o­lu­tion? 

His team conducted a three-year sur­vey using an in­stru­ment on the Very Large Tel­e­scope ar­ray at the Eu­ro­pe­an South­ern Ob­serv­a­to­ry’s Paranal Ob­serv­a­to­ry.

The as­tro­no­mers stud­ied more than 6,500 galax­ies at wide­ly var­y­ing dis­tances to see how their prop­er­ties vary in dif­fer­ent en­vi­ron­ments and for var­y­ing gal­axy lu­mi­nosi­ties. The fur­thest galax­ies were seen as they were when the uni­verse was a third its pre­s­ent age, more than 9 bil­lion years ago. This is be­cause that time frame is how long their light takes to reach us. 

This cen­sus found what the re­search­ers called a sur­pris­ing trend in the “colour-density re­la­tion,” a de­scrip­tion of the re­la­tion­ship be­tween the prop­er­ties of a gal­axy and its en­vi­ron­ment. This re­la­tion­ship was mark­ed­ly dif­fer­ent 7 bil­lion years ago, the re­search­ers said. 

The as­tro­no­mers concluded that the galax­ies’ lu­mi­nos­i­ty, their in­i­tial “ge­net­ic” prop­er­ties, and their en­vi­ron­ments pro­found­ly af­fect their ev­o­lu­tion.

“There’s no sim­ple an­swer to the ‘na­ture ver­sus nur­ture’ prob­lem,” said Le Fevre. The re­sults “sug­gest that galax­ies as we see them to­day are the prod­uct of their in­her­ent ge­net­ic infor­ma­tion, evolved over time, as well as com­plex in­ter­ac­tions with their en­vi­ron­ments, such as merg­ers.” 

Sci­en­tists have known for decades that galax­ies in an­cient times, which we see far off, look dif­fer­ent to those of to­day, which we see near­by. 

To­day, galax­ies can be rough­ly clas­si­fied as “red,” where few or no new stars are be­ing born, or “blue,” where star for­ma­tion is on­go­ing. There is a strong link be­tween a gal­ax­y’s colour and its en­vi­ron­ment. The so­cia­ble types found in dense clus­ters of galax­ies are like­li­er to be red than more iso­lat­ed ones.

The as­tro­no­mers aimed to study how this cor­re­la­tion has evolved us­ing a de­vice called the Vis­i­ble Multi-Object Spec­tro­graph on the tel­e­scope, in north­ern Chil­e.

The find­ing of marked var­i­a­tion in the colour-density re­la­tion­ship, de­pend­ing on wheth­er a gal­axy is found in a clus­ter or alone, and on its lu­mi­nos­i­ty, has many po­ten­tial im­pli­ca­tions, the re­search­ers said. The find­ings sug­gest, for ex­am­ple, that a clus­ter en­vi­ron­ment quenches a gal­ax­y’s abil­i­ty to form stars quick­ly com­pared with those in iso­la­tion. And bright galax­ies run out of star-forming ma­te­ri­al ear­li­er than faint­er ones.

“We were able to use the larg­est sam­ple of galax­ies cur­rent­ly availa­ble for this type of stu­dy, and be­cause of the in­stru­ment’s abil­i­ty to study many ob­jects at a time we ob­tained many more mea­sure­ments than pre­vi­ously pos­si­ble,” said An­ge­la Iovino of the Br­era As­tro­nom­i­cal Ob­serv­a­to­ry in It­a­ly, an­oth­er mem­ber of the team.

The findings were pub­lished in the Oct­o­ber IV is­sue of the re­search jour­nal Ast­ro­no­my and Ast­ro­phys­ics.

* * *

A team astronomers has found that galaxies “evolve” as a result of influences from their surroundings. The scientists said their work showed that the distribution of galaxies has considerably changed over time, depending on the galaxies’ surroundings. The surprising finding challenges existing theories on galactic formation and evolution, they added. In biology, researchers have debated for centuries whether our own development is primarily a result of “nature” or “nurture”—that is, genes or experience. Astronomers face similar conundrums, said Olivier Le Fevre of the Astrophysics Laboratory in Marseille, France, who coordinated the new research: are the galaxies we see today simply the product of the primordial conditions in which they formed, or did experiences change their evolution? In a large, three-year long survey carried out with an instrument on the Very Large Telescope array at the European Space Agency’s Paranal Observatory in northern Chile. The astronomers studied more than 6,500 galaxies at widely varying distances to see how their properties vary in different environments and for varying galaxy luminosities. The furthest galaxies were seen as they were when the universe was a third its present age, more than 9 billion years ago, because that’s how long their light takes to reach us. This census found what the researchers called a surprising trend in the “colour-density relation,” a description of the relationship between the properties of a galaxy and its environment. This relationship was was markedly different 7 billion years ago, the researchers said. The astronomers thus found that the galaxies’ luminosity, their initial “genetic” properties, and their environments profoundly affect their evolution. “There’s no simple answer to the ‘nature versus nurture’ problem,” said Le Fevre. The results “suggest that galaxies as we see them today are the product of their inherent genetic information, evolved over time, as well as complex interactions with their environments, such as mergers.” Scientists have known for decades that galaxies in ancient times, which we see far off, look different to those of today, which we see nearby. Today, galaxies can be roughly classified as “red,” where few or no new stars are being born, or “blue,” where star formation is still ongoing. There is a strong link between a galaxy’s colour and its environment. The sociable types found in dense clusters of galaxies are likelier to be red than more isolated ones. The astronomers were aiming to study how this peculiar correlation has evolved, using an instrument on the telescope called the Visible Multi-Object Spectrograph. The finding of marked variation in the colour-density relationship, depending on whether a galaxy is found in a cluster or alone, and on its luminosity, has many potential implications, the researchers said. The findings suggest, for example, that a cluster environment quenches a galaxy’s ability to form stars quickly compared with those in isolation. And bright galaxies run out of star-forming material earlier than fainter ones. “We were able to use the largest sample of galaxies currently available for this type of study, and because of the instrument’s ability to study many objects at a time we obtained many more measurements than previously possible,” said Angela Iovino of the Brera Astronomical Observatory in Italy, another member of the team.