A core area of research for astronomers at ASTRON is the study of the formation and evolution of nearby galaxies. WSRT-APERTIF and other international telescopes operating at different wavelengths are used.
Dynamics and Star Formation in Nearby Disk Galaxies
Neutral hydrogen is the raw material that stars are made of. A recent surge in high resolution observations of neutral hydrogen in nearby galaxies has allowed astronomers to study their dynamics in detail and map the distribution of their dark matter.
Stars form out of neutral hydrogen (HI) clouds which cool and turn into denser molecular hydrogen gas before collapsing into stars. When stars die, they spew energy back into the interstellar medium. We can study this process from end-to-end by combining high resolution HI observations that can discern individual star-formation sites in a galaxy with data at other wavelengths. Such studies will increase our understanding of the links between star formation and galaxy dynamics, and prepare us to effectively use and interpret observations of high-redshift HI from SKA precursors and the SKA itself.
Simulations of galaxy evolution predict that accretion of gas from the intergalactic medium drives the star formation in galaxies. However, observationally we do not see enough accretion to sustain the current star formation rates in galaxies.
Astronomers at ASTRON use the SKA precursor MeerKAT in South Africa to conduct the MHONGOOSE Large Survey. The project aims to obtain ultra-deep HI images of 34 nearby galaxies with the goal to detect signs of gas accretion.
Dwarf galaxies are the smallest and most ubiquitous type of galaxy in the Universe, and they offer unique insights into galaxy formation and evolution. Dwarf galaxies can be relatively un-evolved, pristine systems that offer a local window into conditions in the early Universe. They are also important tests for our simulations of galaxy formation, as many simulations that can reproduce more massive galaxies struggle to get the properties of dwarf galaxies correct.
At ASTRON, much of the emphasis is on using neutral hydrogen (HI) studies to understand dwarf galaxies. HI is an excellent tool for studying dwarf galaxies as most isolated dwarf galaxies have the majority of their normal (not dark matter) mass in the form of HI. The upcoming surveys with the new phased-array feed, Apertif for the Westerbork Synthesis Radio Telescope (WSRT) will be excellent for finding and studying dwarf galaxies in HI. The HuDaGa project will search for the lowest mass, "darkest" galaxies and compare to predictions from simulations. Another project will use the HI data along with radio continuum (a tracer of star formation), to connect the gas directly to star formation. Since the galaxies are selected based on HI, they include dwarf galaxies with extremely low surface brightness optical counterparts that would otherwise be overlooked.
Erwin de Blok