Yale: Is the Milky Way an "Outlier" Galaxy?

[bystander]

Is the Milky Way an "Outlier" Galaxy? Studying Its "Siblings" for Clues
Yale University | 2017 Sep 20

[img3="A three-color optical image of a Milky Way sibling. (Credit: Sloan Digital Sky Survey)"]https://news.yale.edu/sites/default/fil ... -02-lg.jpg[/img3][hr][/hr]

The most-studied galaxy in the universe — the Milky Way — might not be as “typical” as previously thought, according to a new study.

The Milky Way, which is home to Earth and its solar system, is host to several dozen smaller galaxy satellites. These smaller galaxies orbit around the Milky Way and are useful in understanding the Milky Way itself.

Early results from the Satellites Around Galactic Analogs (SAGA) Survey indicate that the Milky Way’s satellites are much more tranquil than other systems of comparable luminosity and environment. Many satellites of those “sibling” galaxies are actively pumping out new stars, but the Milky Way’s satellites are mostly inert, the researchers found.

This is significant, according to the researchers, because many models for what we know about the universe rely on galaxies behaving in a fashion similar to the Milky Way. ...

The SAGA Survey: I. Satellite Galaxy Populations Around Eight Milky Way Analogs - Marla Geha et al

• Astrophysical Journal 847(1):4 (20 Sep 2017) DOI: 10.3847/1538-4357/aa8626
  arXiv.org > astro-ph > arXiv:1705.06743 > 18 May 2017 (v1), 16 Sep 2017 (v3)

[Ann]

Jim Shelton of Yale University wrote:

Early results from the Satellites Around Galactic Analogs (SAGA) Survey indicate that the Milky Way’s satellites are much more tranquil than other systems of comparable luminosity and environment. Many satellites of those “sibling” galaxies are actively pumping out new stars, but the Milky Way’s satellites are mostly inert, the researchers found.

I'm surprised. I thought the Milky Way was unusual because it has two satellites that are so active, namely the Magellanic Clouds.

The Andromeda Galaxy has no satellites that are active at all, with the possible exception of NGC 205, which is at best very very mildly active.

One galaxy that might be a Milky Way analog is NGC 891, which doesn't seem to have any bright satellites at all.

One of the relatively few galaxies I know of that definitely has a bright starforming satellite galaxy is M90, but M90 is not a good Milky Way analog.

Ann

[neufer]

The Andromeda Galaxy has no satellites that are active at all,
with the possible exception of NFC 205, which is at best very very mildly active.

---

<<Star formation [in the Triangulum galaxy] is taking place at a rate per unit area is higher than in the neighboring Andromeda Galaxy. (The rate of star formation is about 3.4 Gyr⁻¹ pc⁻² in the Triangulum galaxy, compared to 0.74 in Andromeda.) The total integrated rate of star formation in the Triangulum galaxy is about 0.45 ± 0.1 solar masses per year.>>

---

<<Messier 110, also known as NGC 205, is a dwarf elliptical galaxy that is a satellite of the Andromeda Galaxy. M110 contains some dust and hints of recent star formation, which is unusual for dwarf elliptical galaxies in general.>>

[Ann]

M33 is located fairly far from M31. It doesn't strike me as a typical satellite galaxy at all.

Ann

[neufer]

M33 is located fairly far from M31. It doesn't strike me as a typical satellite galaxy at all.

Click to play embedded YouTube video.

<<Andromeda Galaxy was formed roughly 10 billion years ago from the collision and subsequent merger of smaller protogalaxies. This violent collision formed most of the galaxy's (metal-rich) galactic halo and extended disk. During this epoch, star formation would have been very high, to the point of becoming a luminous infrared galaxy for roughly 100 million years.

Andromeda and the Triangulum Galaxy had a very close passage 2–4 billion years ago. This event produced high levels of star formation across the Andromeda Galaxy's disk – even some globular clusters – and disturbed M33's outer disk.>>