September 8, 2010

Observations Could Explain Galaxy Evolution

Researchers have observed the signs of distant dwarf galaxies being swallowed up by spiral galaxies, and their findings "could shed further light on the evolution of galaxies," according to BBC News.

A team of researchers, led by David Martinez-Delgado of Germany's Max Planck Institute for Astronomy (MPIA), noted that the dwarf galaxies that are being absorbed tend to form vine-like structures and long strands of stars known as stellar streams that are produced due to tidal forces.

While the phenomenon has been seen in nearby "Local Group" galaxies for years, this marks the first time that it has been spotted in spiral galaxies farther away--some as far as 50 million light years from Earth, according to BBC reports on Tuesday.

"As part of a pilot survey for such interaction signatures, we have carried out ultra deep, wide field imaging of 8 isolated spiral galaxies in the Local Volume, with data taken at small (D =0.1-0.5m) robotic telescopes that provide exquisite surface brightness sensitivity (ÃŽ¼lim(V ) ∼ 28.5 mag/arcsec2)," Martinez-Delgado and his colleagues wrote in The Astronomical Journal.

"This initial observational effort has led to the discovery of six previously undetected extensive (to ∼ 30kpc) stellar structures in the halos surrounding these galaxies, likely debris from tidally disrupted satellites," they added. "In addition, we confirm and clarify several enormous stellar over-densities previously reported in the literature, but never before interpreted as tidal streams."

The research was conducted using lower-powered, remotely controlled telescopes belonging to amateur astronomers in the U.S. and Australia, according to the BBC. Furthermore, the British news agency notes that the telescopes were fitted with apertures ranging from 10cm to 50cm and were also equipped with commercially-available charged-coupled device (CCD) cameras.

"Even this pilot sample of galaxies exhibits strikingly diverse morphological characteristics of these extended stellar features: great circle-like features that resemble the Sagittarius stream surrounding the Milky Way, remote shells and giant clouds of presumed tidal debris far beyond the main stellar body, as well as jet-like features emerging from galactic disks," the researchers wrote. "Together with presumed remains of already disrupted companions, our observations also capture surviving satellites caught in the act of tidal disruption."

"The common existence of these tidal features around 'normal' disk galaxies and the morphological match to the simulations constitutes new evidence that these theoretical models also apply to a large number of other Milky Way-mass disk galaxies in the Local Volume," they concluded.

Joining Martinez-Delgado on the research team were R. Jay Gabany of the Black Bird Observatory, Ken Crawford of the Rancho del Sol Observatory, Stefano Zibetti and Hans-Walter Rix of the MPIA, Steven R. Majewski and David A. McDavid of the University of Virginia, Taylor S. Chonis from the University of Texas, as well as researchers from Spain's Instituto de Astrofısica de Canarias, the Massachusetts Institute of Technology (MIT), Germany's Argelander Institut fur Astronomie, the Observatories of the Carnegie Institution of Washington, and the University of Cambridge.


Image Caption: Stellar streams around the galaxy M 63: remnants of a satellite galaxy that M 63 has swallowed. The central part is an ordinary positive image; in the outer regions, the negative of the image is shown. In this way, the faint structures that are the target of this survey are more readily discerned. This galaxy's distance from Earth is around 30 million light-years. The new survey has, for the first time, shown the presence of such tell-tale traces of spiral galaxies swallowing smaller satellites for galaxies more distant than our own "Local Group" of galaxies. Image Credit: R. Jay GaBany (http://www.cosmotography.com/images/small_ngc5055.html) in collaboration with David Martinez-Delgado.


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