A new technique for studying some of the brightest objects in the universe has upended scientists’ understanding of the link between active monster black holes and suppressed star formation.
Quasars are the ultra-luminous nuclei of galaxies that contain supermassive black holes. The intense radiation from a quasar comes from massive amounts of hot gas forming an accretion disk around the mouth of the black hole.
Use of the Atacama Large Millimeter/submillimeter Array in Chile (ALMA)researchers targeted quasar 3C 273. 2.4 billion light-years from Earth3C 273 is the closest quasar to Milky Way and the first quasar ever identified. Yet the glare from the quasar’s light makes it difficult to observe the rest of its host galaxy, especially at the radio wavelengths used by ALMA.
Seeing bright and dim features in the same shot requires a property known as high dynamic imaging range. A typical digital camera has a dynamic imaging range of thousands, compared to just a few hundred for ALMA, which means it’s difficult for ALMA to distinguish faint detail from brighter features.
So the research team, led by Shinya Komugi of Kogakuin University in Japan, used a new technique they call “self-calibration.” The trick is to reduce quasar glare by using 3C 273 itself to correct for fluctuations in earth’s atmosphere which may affect ALMA’s detection of sub-millimeter radio waves.
This method increases the contrast. ALMA observed 3C 273 at frequencies of 93, 233, and 343 GHz, and the self-calibration technique enabled dynamic imaging ranges of 85,000, 39,000, and 2500, respectively – the highest dynamic ranges never reached by ALMA.
The technique revealed never-before-seen details about 3C 273’s host galaxy, including what scientists described as an “unknown structure” in a discovery statement (opens in a new tab). The Komugi team saw a faint band of radio emission across the host galaxy spanning tens of thousands of light years. This radio emission comes from tens to hundreds of billions of solar masses of hydrogen gas that has been ionized by the quasar’s ultraviolet and X-ray radiation.
Astronomers strongly suspect there is a connection between the radiation output of the active supermassive black holes and the suppression of star formation in their host galaxies. Radiation exiting the accretion disk acts as a negative feedback, heating the molecular hydrogen so that it can no longer form stars.
However, there seems to be plenty of cold molecular hydrogen left in the host of 3C 273. galaxy, and star formation is in progress. So either the link between quasar feedback and the cessation of star formation isn’t as concrete as scientists thought, or we can catch 3C 273 and its galaxy in a short amount of time before the feedback effects do become apparent.
The Komugi team is now observing other quasars in the same way to gain a broader understanding of these processes.
“By applying the same technique to other quasars, we hope to understand how a galaxy evolves through its interaction with the central nucleus,” Komugi said in a statement (opens in a new tab).
The research was published online in April in The Astrophysical Journal (opens in a new tab).
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