Astronomers spot stars in the most distant galaxies for the first time

Astronomers spot stars in the most distant galaxies for the first time

Since its launch on December 25, 2021 (quite a Christmas present!), the James Webb Space Telescope (JWST) took the sharpest and most detailed images of the Universe, surpassing even its predecessor, the venerable The Hubble Space Telescope! But what’s particularly exciting are the kinds of sightings we can expect, where the JWST will use its advanced capabilities to solve some of the most pressing cosmological mysteries. For example, there is the problem presented by supermassive high redshift (SMBH) black holes or bright quasars that existed during the first billion years of the Universe.

To date, astronomers have not been able to determine how SMBHs could have formed so soon after the Big Bang. Part of the problem was that, until recently, stars in host galaxies with redshift values ​​of Z>2 (within 10.324 billion light-years) have been elusive. But thanks to the JWST, an international team of astronomers recently observed stars for the first time in quasars at Z>6 (less than 12.716 billion light-years away). Their observations could finally allow astronomers to assess the early quasar processes that governed the formation and evolution of early SMBHs.

The team was made up of astronomers from several institutes, universities and observatories in Japan, China, Europe, the UK, the US, Brazil, Taiwan and Israel. Notable institutions include the Kavli Institutes, Max-Planck Institutes, Institut d’Astrophysique de Paris (IAP), and observatories like the National Astronomical Observatory of Japan (NAOJ), WM Keck Observatory, Steward Observatory , Leiden Observatory. , and others. Their study, “First detections of starlight from quasar host galaxies at z > 6”, is being reviewed for publication in the journal Nature.

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NIRCam images of the field around J2255+0251 (upper panel) and J2236+0032 (lower panel). Credit: Ding, X. et al. (2022).

Prior to the JWST, observations of high redshift galaxies were limited by data quality and could not provide the necessary high-quality point spread function (PSF). This describes the ability of an optical system to obtain high-resolution, focused images of a distant point source of light. To shed some light on the new observations, Universe Today spoke with project leader and lead author Xuheng Ding (Kavli PMU) and co-authors Masafusa Onoue (Kavli PMU/Max Planck Institute for Astronomy) and John D. Silverman (Kavli PMU/University of Tokyo). As they recounted via email:

“Basically, to reveal the host galaxy of a quasar, decomposition of the quasar + host image must be performed. The quasar is a point source which is unresolved and can be described by a scaled PSF. Usually this PSF information comes from the isolated stars in the field of view.

“In addition, the JWST has higher resolution data and can observe the redder wavelength compared to the HST to enable this study at the highest redshift sample. Another advantage of this program is that we proposed to observe the quasar of lower luminosity, which facilitates the subtraction of quasar images.

The quasars they selected for their research were J2255+0251 and J2236+0032, two quasars of relatively low luminosity at redshifts of 6.34 and 6.40. This corresponds to a distance of approximately 13.43657 and 13.5637 billion light-years (when the light we see left these objects), or 24.876 and 25.11 billion light-years today. These quasars were first identified in a survey known as the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). This survey used the Subaru Telescope’s HSC instrument to observe 162 faint quasars that existed a billion years after the Big Bang.

These quasars are now undergoing follow-up observations by the JWST program to study high-redshift galaxies and observe the stars in their disks for the first time. For their study, the team looked at data obtained by the JWST near-infrared camera (NIRCam), then modeled and subtracted glare from the quasars themselves. They then compared their observations with studies of simulated high-redshift quasar hosts. The team noted some interesting features about these quasars and their SMBHs that set them apart from other early galaxies.

Images of four SMBHs captured by the Chandra X-ray Observatory. Credit: X-ray: NASA/CXC Illustration: CXC/M. Weiss

“The results show that the host galaxies of these two quasars are massive and compact,” said Ding and his colleagues. “The central positions are offset from the quasars, possibly due to uneven dust attenuation or may indicate that these SMBHs are not yet at the center of gravitational potential.”

This is similar to recent observations of Z > 6 quasar host galaxies that relied on the Atacama Large Millimeter-submillimeter Array (ALMA). These observations also noted shifts in the early quasars between the central SMBHs and the surrounding gas, dust, and interstellar stars. The team also notes that these shifts may be due to asymmetries generated by tidal forces, possibly due to interactions between galaxies or clumped accretion of cold gas. The team will test these hypotheses in further papers based on JWST’s near-infrared spectrograph (NIRSpec) data from 12 early quasars. As Ding and his colleagues put it:

“The significance of this first paper highlights the tremendous power of JWST and evidence that quasar host detection at z>6 is possible. Eventually, our program will establish the first z~6 quasar measurements of mass stellar host and the SMBH mass relationship, which will be used to understand their co-evolution of the galaxy and its central SMBH.This work will also be useful in understanding the origin of the SMBH in the early Universe.

Further reading: arXiv

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