UR: Galactic Leftovers within the M81 Group – Understanding Galaxy Evolution through the Stellar Halo

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Michael Messere

College of Michigan

Michael Messere is an undergraduate on the College of Michigan, the place he’s finding out Physics/Astronomy with a Area Engineering minor.  This analysis was supervised beneath Professor Eric Bell and Dr. Adam Smercina from the College of Michigan Division of Astronomy. Extra particulars may be discovered within the poster introduced on the 237th American Astronomical Society assembly.

Astronomers inside my analysis group on the College of Michigan are galactic detectives that always ask themselves What precisely did the galaxy eat? When two or extra galaxies are available in shut sufficient proximity to one another, the galaxies exert a gravitational tug on each other and are introduced nearer and nearer collectively.  This could usually result in the galaxies shredding one another aside and even fully consuming smaller ones.  Regardless of the destiny of the incoming galaxies, there’ll at all times be crumbs of proof left over within the aftermath.  These crumbs are the person stars scattered in regards to the outskirts of galaxies from previous gravitational interactions with different galaxies.  This diffuse area of stars round galaxies is called the stellar halo and displays how these galaxies have developed over time.

The M81 Group, for instance, is a properly acknowledged triplet of galaxies situated within the Northern sky within the constellation Ursa Main and is situated at an unbelievable distance of 12 million gentle years.  Which means that the sunshine that’s reaching our eyes after we view the M81 Group is from 12 million years in the past! The M81 Group is the closest ongoing triple-interacting galaxy system with a stellar halo plagued by fuel and stars from latest interactions between the three most important galaxies – M81, M82, and NGC-3077.  The triplet of galaxies interacted with each other round 300 million years (Myr) in the past and is a first-rate topic for understanding the stellar halo in-between important merger occasions.  As astronomers serious about determining how the M81 Group interacted prior to now, the star-filled stellar halo of the M81 Group was the right place for my analysis group to place our detective magnifying glass over, or for this analysis, our telescope.  

The Subaru telescope on Mauna Kea in Hawaii was used for 2 nights of remark of the M81 Group and after some knowledge discount, enabled us to have a look at the person brightnesses and colours of stars inside the stellar halo.  Stars which are at completely different ages, lots, and burning completely different components at their cores will seem in numerous areas when these brightnesses and colours are plotted.  This is called a color-magnitude diagram (CMD) in astronomy.  Isochrones (iso = identical, chronos = time) can then be plotted on prime of the CMD to indicate the theoretical location of stars with the identical age.  We had been particularly serious about a subpopulation of stars that burn helium of their core since they cowl an age vary spanning the previous 300 Myr.  This allowed us to make use of these stars to probe the query: How did the M81 Group work together and evolve throughout the previous ~300 Myr because the important tidal interplay between M81, M82, and NGC-3077? The choice bin of helium burning stars and isochrones is proven within the CMD on the left in Determine 1.   

One attention-grabbing discovering in these helium-burning stars was the remark of a tidal bridge  between M82 and NGC-3077 that hadn’t been beforehand found as proven beneath on the right-side of Determine 1.  The age of the celebrities that compose this tidal bridge is roughly 200-300 Myr and this age matches the beforehand estimated time of a merger between the three galaxies.  This tidal bridge additional means that M82 and NGC-3077 had been in actual fact beforehand interacting.  With a view to type a tidal bridge as in depth because the one between M82 and NGC-3077, it’s attainable that the 2 galaxies fell into M81 as a pair 300 Myr in the past and the ensuing gravitational interactions resulted on this prolonged stellar function.  That is how the small and huge Magellanic clouds are thought to have fallen into our personal Milky Approach galaxy, too!

Left: The color-magnitude diagram of the M81 Group from the Subaru telescope with the helium burning star selection bin in red. Isochrones in black show that the range of helium burning stars used spans the past 300 Myr. Right: The spatial distribution of the helium burning stars within the color-magnitude diagram. The tidal bridge extends between NGC-3077 and M82 and contains stars approximately the same age as when the three galaxies are expected to have undergone a major tidal interaction 300 Myr ago.

Determine 1. Left: The colour-magnitude diagram of the M81 Group from the Subaru telescope with the helium burning star choice bin in pink.  Isochrones in black present that the vary of helium burning stars used spans the previous 300 Myr. Proper: The spatial distribution of the helium burning stars inside the color-magnitude diagram.  The tidal bridge extends between NGC-3077 and M82 and comprises stars roughly the identical age as when the three galaxies are anticipated to have undergone a serious tidal interplay 300 Myr in the past.

Astrobite edited by: Jamie Sullivan


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UR: Galactic Leftovers within the M81 Group – Understanding Galaxy Evolution through the Stellar Halo


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