Periodic Reporting for period 3 - FirstGalaxies (Finding the most distant galaxies with NIRSpec guaranteed time on the James Webb Space Telescope)
Período documentado: 2023-05-01 hasta 2024-10-31
Over the past 20 years, my team have pushed the frontier for the most distant known objects to higher redshifts, exploring galaxies when the Universe was young using the Hubble Space Telescope and large ground-based telescopes. As well as discovering galaxies within the first billion years (90percent of the way back in time to the Big Bang), our knowledge of the composition of the Universe has also grown - dark matter and dark energy dictate the expansion history and initial collapse of structures which ultimately form galaxies. We now know that the gas between the galaxies, initially plasma, became mostly neutral about 300,000 years after the Big Bang, but again became plasma about a billion years later. The first few generations of stars to form, with a contribution from high redshift quasars, might be responsible for this reionization, but we have yet to find the galaxies accounting for the bulk of the ionizing photons and key questions remain: what is the contribution from the faintest dwarf galaxies in the luminosity function at high redshift? what fraction of ionizing photons emitted by stars reach the intergalactic gas? is the first generation of stars forming from primordial hydrogen and helium more efficient in producing ionizing photons?
Thanks to the recent launch of the James Webb Space Telescope (JWST) at the end of 2021, we are able to start addressing these questions. JWST has unprecedented sensitivity, and works at longer wavelengths than the Hubble Space Telescope, which is crucial to explore the most distant (and highly redshifted) galaxies. I have been member of the ESA Instrument Science Team since 2005 for the near-infrared spectrograph (NIRSpec) on JWST, and much of our 900 hours of guaranteed time will be spectroscopy of high redshift galaxies. I have assembled a team under this ERC grant to measure accurate redshifts of candidate very distant galaxies, measure their stellar populations (ages and star formation rates), assess the escape fractions of ionizing photons and determine the metal enrichment. The first reporting period of this ERC grant (May 2020-October 2021) has seen the successful launch and commissioning of JWST, and in the past few months the first science data has been taken. My team analysed the Early Release Observations of some very distant galaxies (magnified by the gravitational lensing of a foreground massive cluster of galaxies), measuring the conditions of the interstellar medium at these early epochs and finding it to be significantly hotter than in galaxies at more recent times. In the past few days we have obtained spectroscopy as part of our JADES collaboration between the NIRSpec and NIRCam instrument science teams, targetting the Hubble Ultra Deep Field (the most sensitive image of the sky taken before JWST). We have spectroscopically confirmed several tens of galaxies within a billion years of the Big Bang (at redshifts beyond 6), including four selected from NIRCam images with JWST which are at record-breaking redshifts beyond 10 (within 350 million years of the Big Bang).
Thanks to the recent launch of the James Webb Space Telescope (JWST) at the end of 2021, we are able to start addressing these questions. JWST has unprecedented sensitivity, and works at longer wavelengths than the Hubble Space Telescope, which is crucial to explore the most distant (and highly redshifted) galaxies. I have been member of the ESA Instrument Science Team since 2005 for the near-infrared spectrograph (NIRSpec) on JWST, and much of our 900 hours of guaranteed time will be spectroscopy of high redshift galaxies. I have assembled a team under this ERC grant to measure accurate redshifts of candidate very distant galaxies, measure their stellar populations (ages and star formation rates), assess the escape fractions of ionizing photons and determine the metal enrichment. The first reporting period of this ERC grant (May 2020-October 2021) has seen the successful launch and commissioning of JWST, and in the past few months the first science data has been taken. My team analysed the Early Release Observations of some very distant galaxies (magnified by the gravitational lensing of a foreground massive cluster of galaxies), measuring the conditions of the interstellar medium at these early epochs and finding it to be significantly hotter than in galaxies at more recent times. In the past few days we have obtained spectroscopy as part of our JADES collaboration between the NIRSpec and NIRCam instrument science teams, targetting the Hubble Ultra Deep Field (the most sensitive image of the sky taken before JWST). We have spectroscopically confirmed several tens of galaxies within a billion years of the Big Bang (at redshifts beyond 6), including four selected from NIRCam images with JWST which are at record-breaking redshifts beyond 10 (within 350 million years of the Big Bang).
Some of this ERC team (including the PI, Andrew Bunker) were heavily involved in the commissioning the NIRSpec near-infrared spectrograph, following the successful launch of the James Webb Space Telescope in December 2021. This included the first use of a multi-object spectrograph in space.
The main research achievements so far related to this grant have been successfully obtaining spectra of candidate distant galaxies to unambiguously confirm that some do indeed lie at very high redshift, and using these spectra to constrain the physical conditions in these galaxies (in particular the temperature and ionization of the interstellar medium).
The main research achievements so far related to this grant have been successfully obtaining spectra of candidate distant galaxies to unambiguously confirm that some do indeed lie at very high redshift, and using these spectra to constrain the physical conditions in these galaxies (in particular the temperature and ionization of the interstellar medium).
The availability of multi-object spectroscopy on the James Webb Space Telescope is a breakthrough well beyond the observational state-of-the-art prior to 2022.
Hubble Space Telescope only observes up to the H-band (1.7 microns) in the near-infrared, and ground-based observatories lacks significant sensitivity beyond 2 microns.
NIRSpec on JWST works at wavelengths between 0.8-5microns and hence can for the first time observe the rest-frame optical spectra of galaxies within the epoch of reionization (beyond redshift 6).
In terms of sensitivity, JWST is 10-100 times more sensitive than previous missions such as the Spitzer Space Telescope operating at these wavelengths, and has significantly larger collecting area and lower background noise than Hubble, as well as for the first time the ability to do multi-object spectroscopy with a configurable slit mask in space (affording a multiplex gain of more than 100 over single-object spectroscopy done with Hubble). Hence the gain in observational capability is many orders of magnitude, which was expected from the design specification of JWST. The high-risk technology of individually-commandable microshutters used in NIRSpec to achieve its multi-object spectroscopic capability has been demonstrated to work, and we have obtained several successful observations of more than a hundred targets simultaneously, which is a breakthrough in observational astronomy.
We are now able to routinely measure the spectroscopic redshift for the faintest galaxies seen with the Hubble Space Telescope, and see for the first time rest-frame optical line emission at the highest redshifts to robustly determine physical quantities such as star formation rate and metallicity.
An unexpected advance in this field has been the detection of strong auroral line emission in distant galaxies, which indicates that the temperature of the interstellar medium is significantly hotter than at lower redshift.
Hubble Space Telescope only observes up to the H-band (1.7 microns) in the near-infrared, and ground-based observatories lacks significant sensitivity beyond 2 microns.
NIRSpec on JWST works at wavelengths between 0.8-5microns and hence can for the first time observe the rest-frame optical spectra of galaxies within the epoch of reionization (beyond redshift 6).
In terms of sensitivity, JWST is 10-100 times more sensitive than previous missions such as the Spitzer Space Telescope operating at these wavelengths, and has significantly larger collecting area and lower background noise than Hubble, as well as for the first time the ability to do multi-object spectroscopy with a configurable slit mask in space (affording a multiplex gain of more than 100 over single-object spectroscopy done with Hubble). Hence the gain in observational capability is many orders of magnitude, which was expected from the design specification of JWST. The high-risk technology of individually-commandable microshutters used in NIRSpec to achieve its multi-object spectroscopic capability has been demonstrated to work, and we have obtained several successful observations of more than a hundred targets simultaneously, which is a breakthrough in observational astronomy.
We are now able to routinely measure the spectroscopic redshift for the faintest galaxies seen with the Hubble Space Telescope, and see for the first time rest-frame optical line emission at the highest redshifts to robustly determine physical quantities such as star formation rate and metallicity.
An unexpected advance in this field has been the detection of strong auroral line emission in distant galaxies, which indicates that the temperature of the interstellar medium is significantly hotter than at lower redshift.