RRI Study Finds Intergalactic Gas May Distort Galaxy Halo Measurements

A recent scientific study conducted by researchers at the Raman Research Institute (RRI) has raised important questions about how astronomers measure the mass of gas surrounding galaxies. The findings suggest that commonly used observational techniques may significantly overestimate the amount of gas in galaxy halos due to interference from intergalactic matter, potentially reshaping long-held theories of galaxy formation and evolution.

The study was carried out by RRI, an autonomous institute under the Department of Science and Technology, and was published in The Astrophysical Journal. It indicates that a large share of highly ionised oxygen detected around galaxies may not actually originate from the circumgalactic medium (CGM), as previously believed, but instead from the surrounding intergalactic medium (IGM).

Understanding Galaxy Halos and Their Role

What are CGM and IGM?

Galaxies are surrounded by massive, diffuse halos that can extend 10–20 times beyond their visible boundaries. These halos contain most of a galaxy’s total mass and are composed largely of dark matter and gas.

• Circumgalactic Medium (CGM): The gaseous region closest to the galaxy, crucial for regulating gas inflows and outflows that fuel star formation.

• Intergalactic Medium (IGM): The more distant gas spread between galaxies, forming a vast cosmic web.

Understanding the mass and composition of the CGM is essential because it directly influences how galaxies grow, evolve, and form new stars.

How Astronomers Measure Galaxy Gas

Limits of current observation techniques

Astronomers estimate the CGM’s mass by observing highly ionised oxygen when light from distant bright sources passes through the halo of a foreground galaxy. However, the new study points out a key limitation: these observations record all ionised oxygen along the line of sight, without clearly distinguishing whether it belongs to the CGM or the IGM.

This overlap, researchers argue, introduces a systematic bias into current measurements.

Key Findings of the RRI Study

IGM contribution may be larger than assumed

Using advanced theoretical models, the research team found that a substantial fraction of the ionised oxygen attributed to the CGM may actually originate in the IGM.

“We are challenging the notion that all observed ionised oxygen belongs to the CGM,” said Dr Kartick Sarkar, astrophysicist at RRI and one of the authors of the study published in The Astrophysical Journal.

Galaxy mass-wise impact

• Massive galaxies (like the Milky Way):
  The CGM may contribute only about 50 per cent of the observed ionised oxygen.

• Lower-mass galaxies:
  The CGM’s contribution could fall to as low as 30 per cent, with the remaining signal coming from the IGM.

These findings could explain why observations of smaller galaxies have long failed to align with existing theoretical models.

Implications for Galaxy Formation Models

Why the findings matter

The study suggests that ignoring the IGM’s contribution can lead to a systematic overestimation of CGM mass, especially in low-mass galaxies. This miscalculation may have distorted scientists’ understanding of how galaxies acquire and lose gas over cosmic time.

By accounting for intergalactic gas contamination, the revised framework could help reconcile persistent inconsistencies between observational data and theoretical predictions.

Next Steps in the Research

Towards a more accurate framework

Scientists from RRI, in collaboration with researchers from the Hebrew University of Jerusalem, are now working to refine their models by incorporating additional physical parameters. The goal is to develop a more comprehensive and accurate method to quantify the relative contributions of the CGM and IGM in galaxy observations.

Conclusion

The RRI study marks an important step toward refining how astronomers interpret observations of galaxy halos. By highlighting the overlooked role of intergalactic gas, the research challenges existing assumptions and opens the door to more accurate models of galaxy evolution. As scientists work to incorporate these findings into future observations, the study could significantly improve our understanding of how galaxies grow, interact, and evolve across the universe.