Free Astronomy Magazine November-December 2024

37 NOVEMBER-DECEMBER 2024 ASTRO PUBLISHING 2348–3054 has a known dis- tance, deter- mined by pre- vious observa- tions with the Atacama Large Millimeter/sub- m i l l i m e t e r Array (ALMA), and DECam’s three-square- degree field of view provided an expansive look at its cos- mic neighbor- hood. Serendipitously, DECam is also equipped with a narrowband filter perfectly matched for detecting its compan- ion galaxies. “This quasar study re- ally was the perfect storm,” says Lambert. “We had a quasar with a well-known distance, and DECam on the Blanco telescope offered the massive field of view and exact filter that we needed.” DECam’s specialized filter allowed the team to count the number of companion galaxies around the quasar by detecting a very specific type of light they emit, known as Lyman-alpha radiation. Lyman-al- pha radiation is a specific energy signature of hydrogen, produced when it is ionized and then recom- bined during the process of star for- mation. Lyman-alpha emitters are typically younger, smaller galaxies, and their Lyman-alpha emission can be used as a way to reliably measure their distances. Distance measurements for multiple Lyman-alpha emitters can then be used to construct a 3D map of a quasar’s neighborhood. After sys- tematically mapping the region of space around quasar VIK J2348- 3054, Lambert and his team found 38 companion galaxies in the wider environment around the quasar — out to a distance of 60 million light- years — which is consistent with what is expected for quasars resid- ing in dense regions. However, they were surprised to find that within 15 million light-years of the quasar, there were no companions at all. This finding illuminates the reality of past studies aimed at classifying early-Universe quasar environments and proposes a possible explanation for why they have turned out con- flicting results. No other survey of this kind has used a search area as large as the one provided by DE- Cam, so to smaller-area searches a quasar’s environment can appear deceptively empty. “DECam’s extremely wide view is necessary for studying quasar neighborhoods thoroughly. You re- ally have to open up to a larger area,” says Lambert. “This suggests a reasonable explanation as to why previous observations are in conflict with one another.” The team also suggests an explanation for the lack of companion galaxies in the imme- diate vicinity of the quasar. They postulate that the intensity of the radiation from the quasar may be large enough to affect, or poten- tially stop, the formation of stars in these galaxies, making them invisi- ble to our observations. “Some quasars are not quiet neigh- bors,” says Lambert. “Stars in gal- axies form from gas that is cold enough to collapse under its own gravity. Luminous quasars can po- tentially be so bright as to illuminate this gas in nearby galaxies and heat it up, preventing this collapse.” Lambert’s team is currently follow- ing up with additional observations to obtain spectra and confirm star formation suppression. They also plan to observe other quasars to build a more robust sample size. [NOIRLab/NSF/AURA/M. Garlick/J. da Silva (Spaceengine)/M. Zamani] O bservations using the Dark Energy Camera (DECam) con- firm astronomers’ expectation that early-Universe quasars formed in regions of space densely populated with companion galaxies. DECam’s exceptionally wide field of view and special filters played a crucial role in reaching this conclusion, and the observations reveal why previous studies seeking to charac- terize the density of early-Universe quasar neighborhoods have yielded conflicting results. [NOIRLab/NSF/AURA/M. Gar- lick/J. da Silva (Spaceengine)/M. Zamani/CTIO/T. Slovinský/ ESO/M. Kornmesser/N. Bartmann. Music: Stellardrone - In Time] !