Coronagraphic Quasar Imaging

I led the first extragalactic science demo for the only-operating coronagraph onboard the Hubble Space Telescope (HST) – the Space Telescope Imaging Spesctrograph (STIS). This program – GO 16715 – uses 8 orbits of coronagraphic observations to image the host galaxy that is previously overwhelmed by the point spread function of the original quasar, 3C 273. (Project duration: 2022 January – 2024 February). You can access the paper at this ADS link.

Instrument facts:

STIS offers a 1024*1024 pixel (≈50 arcsec * 50 arcsec) field view to image astrophysical objects mainly in visible light (~0.2 µm to ~1.2 µm, see here for the filter response).
There are four occulters that you can use, and the typical locations are listed here.

Observation strategy recommendation: I designed program GO 16715 to use WedgeA0.6 and BAR5. The two occulters not just provide the smallest innter working angle by STIS – 0.3 arcsec and 0.2 arcsec, repectively. They also can provide a nearly 360 degree view since they are perpendicular to each other. In addition, by using multiple telescope rolls, STIS coronagraph users can additionally get rid of the diffration spikes for imaging with full angular coverage.

If you would like to image your favorite quasars' host galaxies, feel free to check out the VISIT-STIS-Coron tool that I developed for observation planing. This link leads to a usage demo.

What does the host galaxy of the original quasar, 3C 273, look like with HST/STIS coronagraphy? See below. There are no diffraction spikes blocking the host galaxy!

Left: "Best image of bright quasar 3C 273" in 2013, in ESA Hubble website. Right: Best image of bright quasar 3C 273 in 2024 (Ren et al. 2024), and the data in FITS format is publicaly available at CDS.

Background: upon my arrival as a postdoc in Caltech in 2019 fall, I was assigned to the office of Marteen Schmidt – who identified 3C 273 as the first quasar in history – as my office. While I started developing the idea with John Debes the HST/STIS team leader then in 2019 summer, the proposal did not get approved until in 2021. Although I wanted to show the results to Prof. Schmidt earlier, I was at a period of cris for both my career and life, and he passed away in 2022 september so that plan didn't pan out. His pioneering discovery, and our sharing of office in space (but not time), stimulates me to keep moving forward towards new directions.