Using gravitational lensing to measure mass of a quasar’s galaxy with precision

A staff of researchers from EPFL have discovered a means to make use of the phenomenon of sturdy gravitational lensing to find out with precision—about 3 times extra exact than another approach—the mass of a galaxy containing a quasar, in addition to their evolution in cosmic time. Realizing the mass of quasar host galaxies offers perception into the evolution of galaxies within the early universe, for constructing situations of galaxy formation and black hole improvement. The outcomes are printed in Nature Astronomy.

“The unprecedented precision and accuracy achieved with gravitational lensing present a brand new avenue for acquiring sturdy mass estimates within the distant Universe, the place standard strategies lack precision and are inclined to biases,” says EPFL astrophysicist Frédéric Courbin, senior creator of the research.

“The lots of host galaxies have been measured previously, however because of gravitational lensing, that is the primary time that the measurement is so exact within the distant universe,” explains Martin Millon, lead creator of the research and presently at Stanford College on an SNF grant.

Combining gravitational lensing and quasars

A quasar is a luminous manifestation of a supermassive black hole that accretes surrounding matter, sitting on the middle of a number galaxy. It’s typically troublesome to measure how heavy a quasar’s host galaxy is as a result of quasars are very distant objects, and likewise as a result of they’re so shiny that they overshine something inside their neighborhood.

Gravitational lensing permits us to compute the mass of the lensing object. Due to Einstein’s concept of gravitation, we all know how huge objects within the foreground of the evening sky—the gravitational lens—can bend mild coming from background objects. The ensuing unusual rings of sunshine are literally distortions of the background object’s mild by the gravitational lens.

Courbin was biking to the Sauverny Observatory, greater than a decade in the past, when he realized that he may mix the 2—quasars and gravitational lensing—to measure the mass of a quasar’s host galaxy. For this, he needed to discover a quasar in a galaxy that additionally acts as a gravitational lens.

A handful of gravitational lensing quasars noticed to date

The Sloan Digital Sky Survey (SDSS) database was an awesome place to seek for gravitational lensing quasars candidates, however to make sure, Courbin needed to see the lensing rings. In 2010, he and colleagues commissioned time on the Hubble Area Telescope to look at 4 candidates of which three confirmed lensing. Of the three, one stood out resulting from its attribute gravitational lensing rings: SDSS J0919+2720.

The HST picture of SDSS J0919+2720 seen right here reveals two shiny objects within the foreground that every act as a gravitational lens, “most likely two galaxies within the technique of merging,” explains Courbin. The one on the left is a shiny quasar, inside a number galaxy too dim to be noticed. The brilliant object on the best is one other galaxy, the principle gravitational lens. A faint object on the far left is a companion galaxy. The attribute rings are deformed mild coming from a background galaxy.

Computational lens modeling to the rescue

By fastidiously analyzing the gravitationally lensed rings in SDSS J0919+2720, it’s attainable to find out the mass of the 2 shiny objects… in precept. Disentangling the lots of the varied objects would have been unattainable with out the current improvement of a wavelet-based lens modeling approach by co-author Aymeric Galan, presently on the Technical College of Münich (TUM), additionally on an SNF grant.

“One of many largest challenges in astrophysics is to know how a supermassive black hole kinds,” explains Galan. “Realizing its mass, the way it compares to its host galaxy and the way it evolves by cosmic instances, are what permits us to discard or validate sure formation theories.”

“Within the native universe, we observe that probably the most huge galaxies additionally host probably the most huge black holes at their middle. This might counsel that the expansion of galaxies is regulated by the quantity of vitality radiated by their central black hole and injected into the galaxy. Nonetheless, to check this concept, we nonetheless want to review these interactions not solely domestically but in addition within the distant universe,” explains Millon.

Gravitational lensing occasions are very uncommon, with one galaxy in a thousand unveiling the phenomenon. Since quasars are seen in about one each thousand galaxies a quasar appearing as a lens is one in 1,000,000. The scientists anticipate to detect tons of of those lensing quasars with the ESA-NASA mission Euclid, to be launched this summer time with a Falcon-9 SpaceX rocket.