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The Zwicky Transient Facility sees “first light”: a new era in the study of the dynamic sky

The Zwicky Transient Facility sees “first light”: a new era in the study of the dynamic sky

The Zwicky Transient Facility is now ready to start operations. A new robotic camera with the ability to capture hundreds of thousands of galaxies in a single shot has taken its first image of the sky. The recently installed camera is part of a new automated sky-survey project based at the Palomar Observatory in California and a revolutionising tool for the study of rapidly varying cosmic phenomena

On November 14, scientists with the California Institute of Technology, the Oskar Klein Centre and eight additional partner institutions, announced that the Zwicky Transient Facility (ZTF) is now ready to start operations. Every night, ZTF will scan a large portion of the Northern sky, discovering objects that erupt or vary in brightness, including exploding stars, also known as supernovae; stars being munched on by black holes; and new kinds of transient phenomena changing at very short time scales, to which current instruments are largely insensitive.

The regular 3-year operations of ZTF start in February 2018. The Oskar Klein Centre at Stockholm University leads the science on supernova cosmology and on stripped envelope supernovae.

- "This simply means 10-15 times more supernovae", says Jesper Sollerman, professor at the Department of Astronomy at Stockholm University and Board member of the ZTF. I am very relieved that things are now finally in place."

- "ZTF will allow us to do unique observations of rare and very precious phenomena, like gravitationally lensed supernovae and collisions of neutron stars", adds Ariel Goobar, professor at the Department of Physics. He is leading the cosmology investigations within ZTF and his GREAT-centre has recently purchased an i-band filter for the ZTF camera to explore the skies at longer wavelengths, approaching the near—Infrared regime, needed to enable this science.

The Horsehead nebula can be seen in this portion of the "first-light" image from ZTF. The head of the horse (middle) faces up toward another well-known nebula known as the Flame. Violet to green wavelengths detected by ZTF are represented as cyan, while yellow to deep red wavelengths are shown as red. Computers searching these images for transient, or variable, events are trained to automatically recognize and ignore non-astronomical sources, such as the vertical "blooming" lines seen here. Image credit: Caltech Optical Observatories

The Zwicky Transient Facility is the powerful sequel to the intermediate Palomar Transient Factory, where OKC scientists made important discoveries. The name Zwicky refers to the first astrophysicist at Caltech, Fritz Zwicky, who discovered 120 supernovae over his lifetime. ZTF's new state-of-the-art survey camera, recently installed at the 1.2–metre Samuel Oschin Telescope, can see 47 square degrees of sky at a time, or the equivalent sky area of 247 full moons. That's seven times more sky than its predecessor could see in a single image. What's more, ZTF's upgraded electronics and telescope-drive systems enable the camera to take 2.5 times as many exposures each night. ZTF will scan the entire sky over three nights and the visible plane of the galaxy twice every night.

OKC postdocs Ragnhild Lunnan (astronomy) and Uli Feindt (physics) are coordinating two science working groups within ZTF: the study of the physics behind supernovae and the use of Type Ia supernovae to measure distances in the universe.

“The study of the expansion of the universe and the main cosmic constituents, dark energy and dark matter, will be greatly aided by the very rich dataset that ZTF will provide”, says Uli Feindt.

“ZTF will allow us to make new breakthroughs in the understanding of what powers the most luminous stellar explosions, known as superluminous supernovae”, adds Ragnhild Lunnan.

This animation made by Rahul Biswas at OKC shows the motion of the ZTF field of view in different filters across the sky over a period of two consecutive nights in the month of March. The pointings are based on a realitic scheduler simulation output from Eric Bellm (UW). The title indicates the night (since the first night of the science survey) and the local time of observation. The bright spots are Type Ia supernoave, bright enough to be above detection threshold fro ZTF. They are sampled from a simulation catalog made by Ulrich Feindt at OKC. The size (area) of the points being related to the apparent brightness at the time of observation, while the color indicates the redshift of the points. The scaling is such that one can see points which are at the ZTF five sigma depth of 20.5 in any of the three bands. The white dotted lines show the approximate region of the Milky Way which is the observing target of rich galactic science, but obscures the extra-galactic sky of cosmological supernovae.     A description of code is in the repository https://github.com/oskarkleincentre/cadence_demo_for_ztf/  and the version used for the above animation is https://github.com/oskarkleincentre/cadence_demo_for_ztf/tree/v0.2.0

While about half of ZTF is funded by the NSF in the US, the rest comes from its partners, including the, Caltech, the Oskar Klein Centre at Stockholm University, Weizmann Institute for Science the University of Maryland, University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, the Los Alamos and Lawrence Berkeley National Laboratories.

ZTF's new first-light image is a taste of what's to come. It showcases the large-scale of the images and highlights the turbulent star-forming nebula known as Orion.

The participation of OKC in the ZTF is funded by VR and in particular by a project grant from KAW.

Contacs:

Ariel Goobar, ariel@fysik.su.se
Jesper Sollerman, jesper@astro.su.se

Oskar Benjamin Klein

was born in Stockholm the 15th of September 1894. He is the greatest Swedish theoretical physicist of the 20th century, and also an International authority on quantum mechanics in his time but even more recognised after his death for his pioneering work in several fields. Oskar Klein studied very fundamental theoretical questions.

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The Zwicky Transient Facility sees “first light”: a new era in the study of the dynamic sky

Oskar Benjamin Klein

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