Research Interests

I study the process of reionisation, the origin and early evolution of galaxies, and more generally the Epoch of Cosmic Dawn. I do this by messing around with other people's models and simulations, analysing real data, and comparing the two. More often than not, they disagree.

So far, I have used mostly quasar spectroscopy as a tool to study this epoch. Quasars are accreting black holes, generating ultra-bright emission which is visible in detail 90% of the way through the observable Universe (at least). I have done a lot of research on ULAS J1120+0641, which was the most distant quasar for a long time. Roughly speaking, there are three features which can be used:

The Lyman-alpha emission line, a powerful transition due to hydrogen, potentially contains information about how much neutral gas is located around a quasar. This helps probe the process of reionisation.

Intervening metal absorption lines are caused when quasar light passes through enriched gas on its way to Earth - such as a galaxy. The imprints of various chemical compositions are extremely precise. This help probe galaxy formation, and because metals are made in stars, it helps probe the properties of the very first stars too. Checking that the light absorption processes happen at exactly the same wavelengths as here on Earth also helps us to confirm that physics was the same back then. We can search for changes in fundamental constants over time.

The Lyman-alpha forest is similar to this: it provides a very detailed record of how neutral the intergalactic hydrogen gas is. This helps us probe reionisation not only around the quasar but in a large 1D area in front of it. Different models of reionisation make very different predictions about the topology of neutral gas - whether the neutral patches should be elongated or round, or whether they should contain galaxies or not, for instance. Spoilers: none of them work at the moment.

When I ran out of things to do with ULAS J1120+0641 (for a while) I built the largest collection of high-redshift quasar spectra to do the same things, and also new things. At the moment the catalog contains around 120 spectra of 92 quasars. I have worked with data from most optical spectrographs: X-Shooter, EFOSC, FOCAS, GMOS-S, ESI, HIRES, MMT RCS, MagE, LBT MODS, LJT G5, LRIS, LDSS-3, HET, and MIKE. I got my first observing experience from using ESI in Hawaii to take quasar spectra in May 2016.

For more details on how those techniques work and how they can be used, you can read my research statement. I really try to keep the league table of most distant quasars up to date. It would be nice if people always published their discoveries! Even moderate spectra can be useful if you have enough of them! Also, please cite my thesis if you want to re-use the above illustration. .

Public data

Internal link to public data from SB+18: Data


Meyer, Romain A., Bosman, Sarah E. I., Kakiichi, Koki, Ellis, Richard S., The role of galaxies and AGNs in reionizing the IGM - II. Metal-tracing the faint sources of reionization at 5< z< 6 , 2019, MNRAS, 483, 19

Bosman, Sarah E. I., Fan, Xiaohui, Jiang, Linhua, Reed, Sophie L., Matsuoka, Yoshiki, Becker, George D., Haehnelt, Martin G., New constraints on Lyman-a opacity with a sample of 62 quasars at z > 5.7 , 2018, MNRAS, 479, 1055

Koki Kakiichi, Richard S. Ellis, Nicolas Laporte, Adi Zitrin, Anna-Christina Eilers, Emma Ryan-Weber, Romain A. Meyer, Brant Robertson, Daniel P. Stark, Sarah E. I. Bosman, The Role of Galaxies and AGN in Reionising the IGM - I: Keck Spectroscopy of 5 < z < 7 Galaxies in the QSO Field J1148+5251 , MNRAS submitted

Bosman, S. E. I., Becker, G., McMahon R. G., Mortlock D., Venemans B. P., Hewett P. C., Simpson C., Haehnelt M. G., A deep search for metals near redshift 7: the line of sight towards ULAS J1120+0641 , 2017, MNRAS, 470, 1919B

Chardin J., Haehnelt M. G., Bosman S. E. I., Puchwein E., A tale of seven narrow spikes and a long trough: constraining the timing of the percolation of HII bubbles at the tail-end of reionization with ULAS J1120+0641, MNRAS, 473, 765

Bosman, S. E. I. & Becker, G., Re-examining the case for neutral gas near the redshift 7 quasar ULAS J1120+0641, 2015, MNRAS, 452, 1105

Banerji, M., Jouvel, S., Lin, H., McMahon, R. G., Lahav, O., Castander, F. J., Abdalla, F. B., Bertin, E., Bosman, S. E. + 69 co-authors, Combining Dark Energy Survey Science Verification data with near-infrared data from the ESO VISTA Hemisphere Survey , MNRAS, 446, 2523

Research Talks and Posters

The Olympian Symposium, Paralia Katerini, Greece, May 2015: Poster
Cosmology and First Light, IAP, France, December 2015: Poster
Cosmic dawn of galaxy formation, IAP, France, June 2016: Talk slides , video recording
Illuminating the Dark Ages, MPIA Heidelberg, Germany, June 2016: Talk slides
Signals from the Deep Past, UOM, Malta, July 2016: Talk
Peering towards Cosmic Dawn, IAU 333, Dubrovnik, October 2017: Talk
Extremely Large Telescope: UK Community Day, January 2018: Talk
The Epoch of Reionisation: UK community update, February 2018: Talk
Tokyo Spring Cosmic Lyman-Alpha Workshop - Sakura CLAW, March 2018
European Week of Astronomy 2018, EWASS 2018, Liverpool, April 2018
The interstellar medium of high redshift galaxies, MIAPP Worshop, Munich, April 2018

Massive black holes in evolving galaxies: from quasars to quiescence, Paris, 25-29th June 2018