What is the Local Group, and which galaxies does it include?

The Local Group is a collection of over 55 galaxies bound together by gravity, spanning a region roughly ten million light-years across. This galaxy group is part of the larger Virgo Supercluster and contains major well-known galaxies such as the Milky Way, Andromeda (M31), and the Triangulum Galaxy (M33), along with numerous dwarf galaxies.

Which dwarf galaxies did you study, and how was the study conducted?

We focused on a sample of dwarf galaxies visible in the northern sky. This sample included 43 dwarf spheroidal galaxies (dSph), six dwarf irregular galaxies (dIrr), six transitional dwarf galaxies (dTrans), and four isolated globular clusters. Among these were satellites of both the Andromeda and Milky Way galaxies, as well as isolated dwarf galaxies. This study was part of a long-term optical survey aimed at identifying long-period variable stars (LPVs) within Local Group dwarf galaxies.

Observations were made using the Wide Field Camera (WFC) attached to the 2.5-meter Isaac Newton Telescope (INT) at the Roque de los Muchachos Observatory in La Palma. The camera consists of four CCDs with a resolution of 2048×4096 pixels each and a pixel scale of 0.33 arcseconds. Data were collected in the optical V and i bands over three years, from June 2015 to February 2018. The resulting catalogs provide information on the positions of LPVs, their average magnitudes in the V and i filters with uncertainties, the amplitudes of their brightness variations, and photometric measurements for each star.

What are the next steps for this project?

The next phase, focusing on the IC10 galaxy, will use the long-period variable stars to reconstruct its star formation history. We also plan to calculate the mass-loss rates and dust production from evolved stars to better understand how this galaxy contributes to returning mass and dust to the interstellar medium.

Research team:

 Mahtab Gholami, Atefeh Javadi, Hamidreza Mahani, Jacco Th. van Loon, Habib Khosroshahi, Elham Saremi, Iain McDonald, Samaneh Eftekhari, Yi Ren and Hamed Altafi

CMD of i–band versus color (V–i) for sources in IC 10