The quiet life of Messier 94
M94 is a spiral galaxy located 16 million light-years away in the constellation Canes Venatici. University of Michigan doctoral student Katya Gozman investigated the galaxy’s halo to examine the galaxy’s merger history. Credit: ESA/Hubble & NASA

A bulge is a collective name for a group of tightly packed stars in the center of a galaxy.

bulges at the center of most galaxies The bulges have different names depending on their properties Stars within classical bulges move a bit randomly, like elliptical galaxies, and seem to be older than their galaxy, while stars within pseudobulges move by rotation.

Astronomers use a stellar halo as afossil record to study bulges Astronomers can use stellar halos to see if a galaxy has merged with another.

Despite the largest pseudobulge in the local universe, no massive galaxies crashed into M94 in the past.

The stellar halo of the galaxy it merged with is believed to contain material from the merger. We can learn more about the stars and stellar populations in the stellar halo by investigating and learning. We're doing extragalactic archaeology in the M94 area.

There was no evidence of a huge merger in the history of the galaxy. A dwarf galaxy the size of the Small Magellanic Cloud crashed into M94.

Gozman looked at M94's stellar halo using observational data from the Hyper Suprime-CAM located in Hawaii. Astronomers can look at the stellar halo to see if there are remnants of past mergers. Calculating the mass of a halo is one way of learning about the remnants.

The stars in M94's stellar halo were cataloged by Gozman. She used a color magnitude diagram to plot stars according to their brightness and how much light they are emitting.

A red-giant branch star is a type of star. The red or blue star is correlated with what kind of metallic elements it contains.

The light in the universe was divided into two regions, one of which was blue and the other of which was red. The blue and red RGBs had different levels of metal richness.

In order to focus on the blue RGBs, Gozman divided the galaxy into circles. She was able to figure out the mass of the stellar halo by calculating the surface brightness of the stars. The halo's mass can be used to estimate the mass of the galaxy that merged into it.

The mass of the halo is used to estimate the mass of the last crashed into the galaxy. If a large galaxy crashed into M94 a long time ago, it might have changed the components of the galaxy and given rise to this large pseudobulge in the center.

There was no big merger. The biggest galaxy that crashed into M94 was small. She believes that the pseudobulge was formed through the evolution of the galaxy.

Only a small number of studies have mapped the size of the halos. The stars in M94's stellar halo were resolved by Gozman.

This is the first data we've ever had of the population of stars. One of the best ways to learn about the merger history of the galaxy is to resolve stars. This is another data point in a very small field.