Current and forthcoming constraints on radio line broadcasts in M31 (left) and three example Virgo cluster ellipticals (right), assuming that all broadcasts in each galaxy have the same EIRP ℓ. The G17 observations of M31 exclude the red shaded region, while example future observations with FAST and GBT are in blue and green, respectively. Solid shading applies to individualist constraints when δM = 0, and hatched shading is for the noise confusion limit at high δM (vertical for M49, diagonal for M31 and M87, horizontal for M59). — astro-ph.GA
The search for extraterrestrial intelligence includes efforts to constrain populations of artificial broadcasts in other galaxies.
Previous efforts use individualist methods, searching for single broadcasts with high signal-to-noise ratio. These would be detected as observables with extreme values. This approach is limited to very bright broadcasts and also is subject to confusion, where a large number of broadcasts blend together to form a noise continuum. The mean value of the total emission provides an additional collective bound: the luminosity of the transmitters is no higher than the galaxy’s observed luminosity.
Using the framework developed in Paper I, I evaluate how confusion affects individualist searches. I then compare individualist and collective approaches for radio broadcasts from the Milky Way, M31, and three Virgo Cluster elliptical galaxies. For current observations, confusion blurs narrowband radio broadcasts together in the Virgo ellipticals when there is one broadcast per gigahertz per 1000 stars.
The collective bound implies fewer than ∼106(ℓ⎯⎯⎯⎯/1013W)−1 L-band broadcasts per star gigahertz GHz in the Milky Way and is about 10 and 400 times stronger in M31 and M59, respectively. Applying the collective bound to the far-infrared–radio correlation yields constraints on radio broadcast populations in star-forming galaxies throughout the Universe. The collective bound allows us to rule out large regions of broadcast population parameter space even for distant galaxies. It also imposes constraints on gamma-ray, neutrino, and gravitational-wave broadcasts in the nearest galaxies.
Brian C. Lacki
Comments: Published in ApJ; 48 pages, 8 figures, 5 tables, 4 appendices
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2405.04651 [astro-ph.GA] (or arXiv:2405.04651v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2405.04651
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Journal reference: ApJ 966, 183 (2024)
Related DOI:
https://doi.org/10.3847/1538-4357/ad11f1
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Submission history
From: Brian Lacki
[v1] Tue, 7 May 2024 20:16:21 UTC (984 KB)
https://arxiv.org/abs/2405.04646
Astrobiology, SETI,