A new research study from Raman Research Institute (RRI), an autonomous institute of the Department of Science and Technology (DST) has revealed that contributions from matter in the intergalactic medium may be affecting measurements of the diffuse envelope surrounding a galaxy. The study has far-reaching implications, given that the envelope holds power to make or break galaxies and measuring the mass is crucial for tracing how galaxies form.
A galaxy evokes images of dust and stars sparkling within beautiful spirals. But beyond the galaxy’s outskirts lurks a diffuse, ghostly halo spreading out as far as 10-20 times the size of the galaxy. Most of the galaxy’s mass lies beyond the stars in this halo, composed of the mysterious dark matter — the invisible glue keeping the universe together — and gas. The gaseous component of the halo is called the circumgalactic medium or CGM. The region outside the CGM, constitutes the intergalactic medium or IGM.
Mapping the distribution of gas in CGM is essential because CGM connects the galaxy to the cosmic web — the filamentary scaffolding pervading the universe. In doing so, CGM plays a critical role in galaxy evolution by controlling the inflow of gas into the galaxy and outflow from it. By measuring the amount of highly ionized oxygen — oxygen with five of its electrons stripped off — contained in CGM, astronomers estimate the mass of CGM.
Observational astronomers use light from incredibly bright cores of distant galaxies to map the CGM. When light from such a background object passes through the gas in the CGM of a foreground galaxy, certain elements absorb particular wavelengths.
But there lies an inherent problem in the observational technique. When astronomers perform an observation, the measured ionized oxygen is the total integrated value along the line of sight. As CGM and IGM both lie along the line of sight, there is no way to tell apart the contribution from CGM and IGM in the observed values. Current models take all of the ionized oxygen observed to be from the CGM.