Intro to Dwarf Galaxies

Let’s look at this beautiful picture of a spiral galaxy. This is a Hubble image of the Messier 101 (M101), also called the Pinwheel Galaxy. The Pinwheel Galaxy is a classic spiral galaxy that is nearly twice the size of the Milky Way and is located in the constellation Ursa Major. It is estimated to contain at least one trillion stars. It looks breathtaking, doesn't it?

_{The Pinwheel Galaxy. Source: European Space Agency & NASA.}

However, these are not the kinds of galaxies our research group studies.

Below is NGC 5477, an irregular galaxy with no obvious structure but with visible signs of ongoing starbirth within the clouds of glowing hydrogen gas. NGC 5477 is actually a dwarf galaxy in the neighborhood of the Pinwheel Galaxy. This is what many dwarf galaxies look like, often appearing very diffuse and featureless.

_{An archetypal dwarf galaxy. Source: ESA/Hubble & NASA.}

So, what is a dwarf galaxy?

A galaxy is a dwarf galaxy if it has baryonic mass < 10⁹ solar masses. Dwarf galaxies are the least massive, most abundant, and most widely distributed type of galaxies. Hence, they are key to testing theories in galaxy and universe evolution. Given their low metallicity, high gas content and ongoing star formation, these objects are supposed to resemble the first galaxies that formed at the earliest epochs, and may represent a window on the distant, early Universe.

The number of intriguing questions related to the extreme nature of dwarf population keeps increasing, as we obtain a more detailed view of their properties and we find puzzling discrepancies with theoretical expectations. The next decade promises to be full of discoveries, with missions and surveys such as the James Webb Space Telescope, the Vera Rubin Observatory, the Extremely Large Telescope, and the Nancy Roman Space Telescope, featuring state-of-the-art wide-field optical and infrared imagers combined with high-resolution spectrographs.