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Can a 7-m single-dish radio telescope detect a nearby galaxy cluster with z ‑ 0.02?

Our department has access to a 7-meter dish primarily used for education. For a ambitious student project, we're considering pointing it at a nearby cluster like Virgo (z~0.004). The HI signal from individual galaxies is weak, but could the combined flux from many cluster members be detectable with very long integration, or is the collecting area fundamentally too small for this science goal?

 

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By Meghna R Answered 2 years ago

This is pushing the instrument to its absolute limit, but it's an excellent pedagogical exercise in sensitivity calculations. The fundamental issue is beam dilution and flux density. A 7-m dish has a very wide beam at 21 cm, potentially encompassing several cluster galaxies, but its small collecting area means the received flux is minuscule. For a cluster's integrated HI, the signal is extremely extended and faint. With extremely long integrations (hundreds of hours) under perfect conditions, you might detect a hint of a spectral line from the very brightest aggregates, but extracting a usable profile for science would be exceptionally challenging. I would recommend a more feasible target, like a single, massive, gas-rich spiral galaxy within the cluster.

 

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