Final Report Summary - MINE BOSS (Mining for Metals in a Massive Spectroscopic Survey of the Intergalactic Medium)
During the course of this fellowship, the fellow has made great advances in attaining his two proposed objectives. One was to develop an improved understanding of the emergence of dark energy by measuring the expansion of the universe during the 1st half of its history (an epoch where the universe was still decelerating in its expansion ahead of the dark energy driven acceleration phase). This was to be achieved by measuring the size of characteristic structures on the largest scales (baryon acoustic oscillations, BAO) using gas on the largest scales (the intergalactic medium, IGM). This gas was probed by observing hydrogen absorption in the spectrum of bright background quasars. The other was to explore the properties of gas around galaxies (the circumgalactic medium) in order to improve our understanding of how they form and evolve from their explosions and accretion.
During the final months of 2012 he consolidated the data set required for both these goals (Paris et al., Noterdaeme et al., Lee et al.) and began data analysis. This data set is a massive spectroscopic survey of the intergalactic medium. It is the largest survey ever conducted by more than an order of magnitude.
During 2013, three key large scale structure analyses were published based on this data. Two were parallel studies intended to break new ground (Busca et al., Slosar et al). Here we made the 1st measurement of the expansion rate of the universe during the 1st half of its history. This was the 1st direct detection of a universe continuing to decelerate in its expansion by using BAOs. While only based on a third of the final data set expected from the BOSS survey they allowed us to demonstrate the potential power of this technique, and were consistent the consensus in the cosmology community (that dark energy is a consequence of space itself and the more space between objects the greater the acceleration between them). The third paper that year (Palanque-Delabrouille et al.) probes somewhat smaller scales with the intention of providing improved measurements primarily to constrain the properties of neutrinos.
In 2014, the data set grew and we refined the analysis in Delubac et al. This was combined with our analysis correlating gas structures with the locations of the quasars themselves (Font-Ribera et al). These results together give us our most precise measurement of expansion in the universe during the 1st half of its history (high redshift) and seem to be in tension with results from the 2nd half (low redshift) and properties of the cosmic microwave background (produced shortly after the Big Bang). This tension is currently not accounted for.
These cosmology studies required analyses of the contaminating impact of elements embedded in gas around galaxies and so there has been significant overlap with the other research objective. This 2nd objective was explored in 2014 through a major paper studying the circumgalactic medium (Pieri et al). This paper involved using hydrodynamic simulations, phenomenological models and supporting data to confirm our sensitivity to circumgalactic regions in 10s of thousands of Gigaparsecs of quasar path length. Composite spectra of these galaxy environments were then produced to study such regions with high precision. We have demonstrated that this method allows the measurement of several previously undetected elements, ionization species and transitions, all of which allow is to break degeneracies between different intergalactic effects. Despite the size of this sample, we were able to determine the properties of gas on just 30 parsec scales. A catalogue of absorption lines and the composite spectra were provided for the astrophysics community, and we have begun to build collaborations to interpret these measurements.
This project has allowed the fellow the freedom to pursue new, unforeseen opportunities to address the project objectives. The fellow wrote a single author ‘idea paper’ bringing his two major research interests together to add novel value to studies of dark energy (Pieri 2014). He argued that an additional measurement of BAO may be made as part of eBOSS for free. Intermediate redshift quasars will be observed by eBOSS to fill the redshift gap between the high redshift IGM studies described above, and low redshift large scale structure traced by the locations of galaxies. The survey goal is to use only the locations of these quasars as they do not provide hydrogen absorption information. The fellow has shown that carbon absorption is still present (and indeed dominant) and a viable tracer of structure. Furthermore, a third measurement presents itself by cross-correlating carbon absorption and the quasar locations. This project was particularly inspired by valuable discussions with University of Portsmouth experts in tracing BAO with galaxy/quasar locations.
The fellow has also utilized this level of independence to invest time in planning surveys. The fellow wrote the proposal to include a massive spectroscopic survey of the IGM to a major (largely European) survey called WEAVE planned to take place on the William Herschel Telescope starting in 2017 for 5 years. This proposal was accepted, and the fellow is now the quasar absorption survey lead for WEAVE. In addition, he has also been selected as co-chair of the working group to pursue this science as part of the Dark Energy Spectroscopic Instrument (DESI). DESI will take place over a similar timespan to WEAVE and will be highly complementary. As a result, this fellowship has aided the fellow to take on responsibility for the only two next generation surveys planned to explore his two science objectives over the next 8 years.
The fellow continues to pursue these science objectives and leadership roles from within the EU at Aix-Marseille Université and the Laboratoire d’Astrophyique de Marseille.
During the final months of 2012 he consolidated the data set required for both these goals (Paris et al., Noterdaeme et al., Lee et al.) and began data analysis. This data set is a massive spectroscopic survey of the intergalactic medium. It is the largest survey ever conducted by more than an order of magnitude.
During 2013, three key large scale structure analyses were published based on this data. Two were parallel studies intended to break new ground (Busca et al., Slosar et al). Here we made the 1st measurement of the expansion rate of the universe during the 1st half of its history. This was the 1st direct detection of a universe continuing to decelerate in its expansion by using BAOs. While only based on a third of the final data set expected from the BOSS survey they allowed us to demonstrate the potential power of this technique, and were consistent the consensus in the cosmology community (that dark energy is a consequence of space itself and the more space between objects the greater the acceleration between them). The third paper that year (Palanque-Delabrouille et al.) probes somewhat smaller scales with the intention of providing improved measurements primarily to constrain the properties of neutrinos.
In 2014, the data set grew and we refined the analysis in Delubac et al. This was combined with our analysis correlating gas structures with the locations of the quasars themselves (Font-Ribera et al). These results together give us our most precise measurement of expansion in the universe during the 1st half of its history (high redshift) and seem to be in tension with results from the 2nd half (low redshift) and properties of the cosmic microwave background (produced shortly after the Big Bang). This tension is currently not accounted for.
These cosmology studies required analyses of the contaminating impact of elements embedded in gas around galaxies and so there has been significant overlap with the other research objective. This 2nd objective was explored in 2014 through a major paper studying the circumgalactic medium (Pieri et al). This paper involved using hydrodynamic simulations, phenomenological models and supporting data to confirm our sensitivity to circumgalactic regions in 10s of thousands of Gigaparsecs of quasar path length. Composite spectra of these galaxy environments were then produced to study such regions with high precision. We have demonstrated that this method allows the measurement of several previously undetected elements, ionization species and transitions, all of which allow is to break degeneracies between different intergalactic effects. Despite the size of this sample, we were able to determine the properties of gas on just 30 parsec scales. A catalogue of absorption lines and the composite spectra were provided for the astrophysics community, and we have begun to build collaborations to interpret these measurements.
This project has allowed the fellow the freedom to pursue new, unforeseen opportunities to address the project objectives. The fellow wrote a single author ‘idea paper’ bringing his two major research interests together to add novel value to studies of dark energy (Pieri 2014). He argued that an additional measurement of BAO may be made as part of eBOSS for free. Intermediate redshift quasars will be observed by eBOSS to fill the redshift gap between the high redshift IGM studies described above, and low redshift large scale structure traced by the locations of galaxies. The survey goal is to use only the locations of these quasars as they do not provide hydrogen absorption information. The fellow has shown that carbon absorption is still present (and indeed dominant) and a viable tracer of structure. Furthermore, a third measurement presents itself by cross-correlating carbon absorption and the quasar locations. This project was particularly inspired by valuable discussions with University of Portsmouth experts in tracing BAO with galaxy/quasar locations.
The fellow has also utilized this level of independence to invest time in planning surveys. The fellow wrote the proposal to include a massive spectroscopic survey of the IGM to a major (largely European) survey called WEAVE planned to take place on the William Herschel Telescope starting in 2017 for 5 years. This proposal was accepted, and the fellow is now the quasar absorption survey lead for WEAVE. In addition, he has also been selected as co-chair of the working group to pursue this science as part of the Dark Energy Spectroscopic Instrument (DESI). DESI will take place over a similar timespan to WEAVE and will be highly complementary. As a result, this fellowship has aided the fellow to take on responsibility for the only two next generation surveys planned to explore his two science objectives over the next 8 years.
The fellow continues to pursue these science objectives and leadership roles from within the EU at Aix-Marseille Université and the Laboratoire d’Astrophyique de Marseille.