Dr Sarah Ragan
Senior Lecturer
Astronomy Group
Cardiff Hub for Astrophysics Research and Technology
School of Physics and Astronomy
- Available for postgraduate supervision
Overview
I've been a member of staff in the School of Physics and Astronomy since 2016, and I am currently a Senior Lecturer. Since earning my PhD in 2009 at the University of Michigan, Ann Arbor, I have held reserach positions at Max Planck Institute for Astronomy in Heidelberg, the University of Leeds and Cardiff University. I took on an academic position in 2018.
My research is on the early phases of star formation, and I use a combination of observational and modeling techniques to understand what conditions in molecular clouds are necessary for star formation, which of those conditions promote the formation of high mass stars in particular, and what causes the formation of the molecular clouds in the first place. Our research has shown that these topics are all interlinked, and connected to the broader environment in the Galaxy as well!
Publication
2024
- King, S. M. et al. 2024. CHIMPS2: 13CO J = 3→2 emission in the central molecular zone. Monthly Notices of the Royal Astronomical Society 533(1), pp. 131–142. (10.1093/mnras/stae1854)
- Priestley, F. D., Clark, P. C., Glover, S. C. O., Ragan, S. E., Feher, O., Prole, L. R. and Klessen, R. S. 2024. NEATH III: A molecular line survey of a simulated star-forming cloud. Monthly Notices of the Royal Astronomical Society 531(4), pp. 4408–4421. (10.1093/mnras/stae1442)
- Fehér, O., Ragan, S. E., Priestley, F. D., Clark, P. C. and Moore, T. J. T. 2024. N2H+(1–0) as a tracer of dense gas in and between spiral arms. Monthly Notices of the Royal Astronomical Society 530(2), pp. 1311–1327. (10.1093/mnras/stae918)
- Rigby, A. J. et al. 2024. The dynamic centres of infrared-dark clouds and the formation of cores. Monthly Notices of the Royal Astronomical Society 528(2), pp. 1172–1197. (10.1093/mnras/stae030)
2023
- Priestley, F. D., Clark, P. C., Glover, S. C. O., Ragan, S. E., Feher, O., Prole, L. R. and Klessen, R. S. 2023. NEATH – II. N2H+ as a tracer of imminent star formation in quiescent high-density gas. Monthly Notices of the Royal Astronomical Society 526(4), pp. 4952–4960. (10.1093/mnras/stad3089)
- Priestley, F. D., Clark, P. C., Glover, S. C. O., Ragan, S. E., Feher, O., Prole, L. R. and Klessen, R. S. 2023. Non-equilibrium abundances treated holistically (NEATH): the molecular composition of star-forming clouds. Monthly Notices of the Royal Astronomical Society 524(4), pp. 5971–5983. (10.1093/mnras/stad2278)
- Ahmadi, A. et al. 2023. Kinematics and stability of high-mass protostellar disk candidates at sub-arcsecond resolution. Astronomy & Astrophysics 677, article number: A171. (10.1051/0004-6361/202245580)
2022
- Wells, M. R. A. et al. 2022. ATLASGAL - star forming efficiencies and the Galactic star formation rate. Monthly Notices of the Royal Astronomical Society 516(3), pp. 4245–4255. (10.1093/mnras/stac2420)
- Neralwar, K. R. et al. 2022. The SEDIGISM survey: Molecular cloud morphology II. Integrated source properties. Astronomy & Astrophysics 664(2022), article number: A84. (10.1051/0004-6361/202142513)
- Neralwar, K. R. et al. 2022. The SEDIGISM survey: Molecular cloud morphology. Astronomy & Astrophysics 663, article number: A56. (10.1051/0004-6361/202142428)
- Urquhart, J. S. et al. 2022. ATLASGAL - evolutionary trends in high-mass star formation. Monthly Notices of the Royal Astronomical Society 510(3), pp. 3389–3407. (10.1093/mnras/stab3511)
- Colombo, D. et al. 2022. The SEDIGISM survey: the influence of spiral arms on the molecular gas distribution of the inner Milky Way. Astronomy & Astrophysics 658, pp. 1-38., article number: A54. (10.1051/0004-6361/202141287)
2021
- Anderson, M. et al. 2021. An ALMA study of hub-filament systems - I. On the clump mass concentration within the most massive cores. Monthly Notices of the Royal Astronomical Society 508(2), pp. 2964–2978. (10.1093/mnras/stab2674)
- Smith, M. W. L. et al. 2021. The HASHTAG project: The first submillimeter images of the Andromeda Galaxy from the ground.. Astrophysical Journal Supplement Series 257, article number: 52. (10.3847/1538-4365/ac23d0)
- Elia, D. et al. 2021. The Hi-GAL compact source catalogue - II. The 360° catalogue of clump physical properties. Monthly Notices of the Royal Astronomical Society 504(2), pp. 2742–2766. (10.1093/mnras/stab1038)
- Eden, D. J. et al. 2021. Characteristic scale of star formation. I. Clump formation efficiency on local scales. Monthly Notices of the Royal Astronomical Society 500(1), pp. 191-210. (10.1093/mnras/staa3188)
- Duarte Cabral, A. et al. 2021. The SEDIGISM survey: molecular clouds in the inner galaxy. Monthly Notices of the Royal Astronomical Society 500(3), pp. 3027-3049. (10.1093/mnras/staa2480)
- Urquhart, J. S. et al. 2021. SEDIGISM-ATLASGAL: dense gas fraction and star formation efficiency across the galactic disk. Monthly Notices of the Royal Astronomical Society 500(3), article number: staa2512. (10.1093/mnras/staa2512)
- Schuller, F. et al. 2021. The SEDIGISM survey: first data release and overview of the Galactic structure*. Monthly Notices of the Royal Astronomical Society 500(3), article number: staa2369. (10.1093/mnras/staa2369)
2020
- Eden, D. J. et al. 2020. CHIMPS2: survey description and 12CO emission in the Galactic centre. Monthly Notices of the Royal Astronomical Society 498(4), pp. 5936-5951. (10.1093/mnras/staa2734)
- Henshaw, J. D. et al. 2020. Ubiquitous velocity fluctuations throughout the molecular interstellar medium. Nature Astronomy 4, pp. 1064-1071. (10.1038/s41550-020-1126-z)
- Syed, J. et al. 2020. Atomic and molecular gas properties during cloud formation. Astronomy and Astrophysics 642, article number: A68. (10.1051/0004-6361/202038449)
- Wang, Y. et al. 2020. Dense gas in a giant molecular filament. Astronomy and Astrophysics 641, article number: A53. (10.1051/0004-6361/202037928)
- Beuther, H. et al. 2020. Dynamical cloud formation traced by atomic and molecular gas. Astronomy and Astrophysics 638, article number: A44. (10.1051/0004-6361/202037950)
- Mottram, J. C. et al. 2020. From clump to disc scales in W3 IRS4. Astronomy and Astrophysics 636, article number: A118. (10.1051/0004-6361/201834152)
- Wang, Y. et al. 2020. Cloud formation in the atomic and molecular phase: HI self absorption (HISA) towards a giant molecular filament. Astronomy and Astrophysics 634, article number: A139. (10.1051/0004-6361/201935866)
- Li, Z. et al. 2020. The HASHTAG project I. A survey of CO(3–2) emission from the star forming disc of M31. Monthly Notices of the Royal Astronomical Society 492(1), pp. 195-290. (10.1093/mnras/stz3409)
- Pettitt, A. R., Ragan, S. E. and Smith, M. C. 2020. Young stars as tracers of a barred-spiral Milky Way. Monthly Notices of the Royal Astronomical Society 4914(2), pp. 2162-2179. (10.1093/mnras/stz3155)
2019
- Rigby, A. J. et al. 2019. CHIMPS: physical properties of molecular clumps across the inner Galaxy. Astronomy and Astrophysics 632, article number: A58. (10.1051/0004-6361/201935236)
- Clark, P. C., Glover, S. C. O., Ragan, S. E. and Cabral, A. 2019. Tracing the formation of molecular clouds via [CII], [CI] and CO emission. Monthly Notices of the Royal Astronomical Society 486(4), pp. 4622-4637. (10.1093/mnras/stz1119)
- Henshaw, J. D. et al. 2019. ‘The Brick’ is not a brick: A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016. Monthly Notices of the Royal Astronomical Society 485(2), pp. 2457-2485. (10.1093/mnras/stz471)
- Soler, J. D. et al. 2019. Histogram of oriented gradients: a technique for the study of molecular cloud formation. Astronomy and Astrophysics 622, article number: A166. (10.1051/0004-6361/201834300)
- Rugel, M. R. et al. 2019. Feedback in W49A diagnosed with radio recombination lines and models. Astronomy and Astrophysics 622, article number: A48. (10.1051/0004-6361/201834068)
2018
- Rugel, M. et al. 2018. OH absorption in the first quadrant of the Milky Way as seen by THOR. Astronomy and Astrophysics 618, article number: A159. (10.1051/0004-6361/201731872)
- Ahmadi, A. et al. 2018. Core fragmentation and Toomre stability analysis of W3(H20): A case study of the IRAM NOEMA large program CORE. Astronomy and Astrophysics 618(46), article number: A46. (10.1051/0004-6361/201732548)
- Beuther, H. et al. 2018. Fragmentation and disk formation during high-mass star formation: the IRAM NOEMA (Northern Extended Millimeter Array) large program CORE. Astronomy and Astrophysics 617, article number: A100. (10.1051/0004-6361/201833021)
- Ragan, S. E., Moore, T. J. T., Eden, D. J., Hoare, M. G., Urquhart, J. S., Elia, D. and Molinari, S. 2018. The role of spiral arms in Milky Way star formation. Monthly Notices of the Royal Astronomical Society 479(2), pp. 2361-2373. (10.1093/mnras/sty1672)
- Barnes, A. T. et al. 2018. Similar complex kinematics within two massive, filamentary infrared dark clouds?. Monthly Notices of the Royal Astronomical Society 475(4), pp. 5268-5289. (10.1093/mnras/sty173)
2017
- Marsh, K. et al. 2017. Multi-temperature mapping of dust structures throughout the Galactic Plane using the PPMAP tool with Herschel Hi-GAL data. Monthly Notices of the Royal Astronomical Society 471(3), pp. 2730-2742. (10.1093/mnras/stx1723)
- Elia, D. et al. 2017. The Hi-GAL compact source catalogue. I. The physical properties of the clumps in the inner Galaxy (−71.0 ◦ < ` < 67.0◦). Monthly Notices of the Royal Astronomical Society 471(1), pp. 100-143. (10.1093/mnras/stx1357)
2016
- Ragan, S. E., Moore, T. J. T., Eden, D. J., Hoare, M. G., Elia, D. and Molinari, S. 2016. The prevalence of star formation as a function of Galactocentric radius. Monthly Notices of the Royal Astronomical Society 462(3), pp. 3123-3129. (10.1093/mnras/stw1870)
- Beuther, H. et al. 2016. The HI/OH/Recombination line survey of the inner Milky Way (THOR). Survey overview and data release 1. Astronomy and Astrophysics -Berlin then Les Ulis- 595, article number: A32. (10.1051/0004-6361/201629143)
- Marsh, K., Ragan, S., Whitworth, A. P. and Clark, P. 2016. Evidence that widespread star formation may be underway in G0.253+016, 'The Brick'. Monthly Notices of the Royal Astronomical Society 461(1), pp. L16-L20. (10.1093/mnrasl/slw080)
- Lippok, N. et al. 2016. Earliest phases of star formation (EPoS). Dust temperature distributions in isolated starless cores. Astronomy and Astrophysics -Berlin then Les Ulis- 592, article number: A61. (10.1051/0004-6361/201525792)
- Feng, S., Beuther, H., Zhang, Q., Henning, T., Linz, H., Ragan, S. and Smith, R. 2016. Are infrared dark clouds really quiescent?. Astronomy and Astrophysics -Berlin then Les Ulis- 592, article number: A21. (10.1051/0004-6361/201526864)
- Abreu-Vicente, J., Ragan, S., Kainulainen, J., Henning, T., Beuther, H. and Johnston, K. 2016. Giant molecular filaments in the Milky Way II. the fourth Galactic quadrant. Astronomy and Astrophysics 590, article number: A131. (10.1051/0004-6361/201527674)
- Bertram, E., Glover, S., Clark, P., Ragan, S. and Klessen, R. 2016. Synthetic observations of molecular clouds in a galactic centre environment - I. Studying maps of column density and integrated intensity. Monthly Notices of the Royal Astronomical Society 455(4), pp. 3763-3778. (10.1093/mnras/stv2619)
2015
- Beuther, H., Ragan, S. E., Johnston, K., Henning, T., Hacar, A. and Kainulainen, J. T. 2015. Filament fragmentation in high-mass star formation. Astronomy and Astrophysics 584, article number: A67. (10.1051/0004-6361/201527108)
- Walsh, A. et al. 2015. A survey for hydroxyl in the THOR pilot region around W43. Monthly Notices of the Royal Astronomical Society 455(4), pp. 3494-3510. (10.1093/mnras/stv2446)
- Beuther, H. et al. 2015. Hierarchical fragmentation and collapse signatures in a high-mass starless region. Astronomy and Astrophysics 581, article number: A119. (10.1051/0004-6361/201526759)
- Bihr, S. et al. 2015. THOR: The H i, OH, Recombination line survey of the Milky Way. The pilot study: H i observations of the giant molecular cloud W43. Astronomy and Astrophysics 580, article number: A112. (10.1051/0004-6361/201425370)
- Bihr, S. et al. 2015. Kinematic and thermal structure at the onset of high-mass star formation. Astronomy and Astrophysics 579, article number: A51. (10.1051/0004-6361/201321269)
- Ragan, S. E., Henning, T., Beuther, H., Linz, H. and Zahorecz, S. 2015. Fragmentation and kinematics of dense molecular cores in the filamentary infrared-dark cloud G011.11–0.12. Astronomy and Astrophysics 573, article number: A119. (10.1051/0004-6361/201424948)
- Tobin, J. et al. 2015. Characterizing the youngest Herschel-detected protostars. I. envelope structure revealed by CARMA dust continuum observations. Astrophysical Journal 798(2), article number: 128. (10.1088/0004-637X/798/2/128)
2014
- Beuther, H. et al. 2014. Carbon in different phases ([CII], [CI], and CO) in infrared dark clouds: cloud formation signatures and carbon gas fractions. Astronomy and Astrophysics 571, article number: A53. (10.1051/0004-6361/201424757)
- Ragan, S. E., Henning, T., Tackenberg, J., Beuther, H., Johnston, K. G., Kainulainen, J. and Linz, H. 2014. Giant molecular filaments in the Milky Way. Astronomy and Astrophysics 568, article number: A73. (10.1051/0004-6361/201423401)
- Johnston, K., Beuther, H., Linz, H., Schmiedeke, A., Ragan, S. and Henning, T. 2014. The dynamics and star-forming potential of the massive Galactic centre cloud G0.253+0.016. Astronomy and Astrophysics 568, article number: A56. (10.1051/0004-6361/201423943)
- Tackenberg, J. et al. 2014. Kinematic structure of massive star-forming regions. I. accretion along filaments. Astronomy and Astrophysics 565, article number: A101. (10.1051/0004-6361/201321555)
- Wang, K. et al. 2014. Hierarchical fragmentation and differential star formation in the Galactic `Snake': infrared dark cloud G11.11-0.12. Monthly Notices of the Royal Astronomical Society 439(4), pp. 3275-3293. (10.1093/mnras/stu127)
2013
- Ragan, S., Henning, T. and Beuther, H. 2013. APEX/SABOCA observations of small-scale structure of infrared-dark clouds I. early evolutionary stages of star-forming cores. Astronomy and Astrophysics 559(Novemb), article number: A79. (10.1051/0004-6361/201321869)
- Kainulainen, J., Ragan, S., Henning, T. and Stutz, A. 2013. High-fidelity view of the structure and fragmentation of the high-mass, filamentary IRDC G11.11-0.12. Astronomy and Astrophysics 557(Septem), article number: A120. (10.1051/0004-6361/201321760)
- Beuther, H. et al. 2013. Fragmentation and dynamical collapse of the starless high-mass star-forming region IRDC 18310-4. Astronomy and Astrophysics 553(May), pp. 115., article number: A115. (10.1051/0004-6361/201220475)
- Clark, P., Glover, S. C. O., Ragan, S., Shetty, R. and Klessen, R. S. 2013. On the temperature structure of the galactic center cloud G0.253+0.016. Astrophysical Journal Letters 768(2), article number: L34. (10.1088/2041-8205/768/2/L34)
- Pitann, J. et al. 2013. G048.66-0.29: physical state of an isolated site of massive star formation. Astrophysical Journal 766(2), article number: 68. (10.1088/0004-637X/766/2/68)
- Launhardt, R. et al. 2013. The Earliest Phases of Star Formation (EPoS): a Herschel key project: the thermal structure of low-mass molecular cloud cores. Astronomy and Astrophysics 551(March), article number: A98. (10.1051/0004-6361/201220477)
2012
- Nielbock, M. et al. 2012. The Earliest Phases of Star formation (EPoS) observed with Herschel: the dust temperature and density distributions of B68. Astronomy and Astrophysics 547(Novemb), article number: A11. (10.1051/0004-6361/201219139)
- Ragan, S. et al. 2012. The Earliest Phases of Star Formation (EPoS): a Herschel key program: the precursors to high-mass stars and clusters. Astronomy and Astrophysics 547(Novemb), article number: A49. (10.1051/0004-6361/201219232)
- Ragan, S., Heitsch, F., Bergin, E. and Wilner, D. 2012. Very large array observations of ammonia in infrared-dark clouds. II. internal kinematics. Astrophysical Journal 746(2), article number: 174. (10.1088/0004-637X/746/2/174)
- Beuther, H. et al. 2012. The onset of high-mass star formation in the direct vicinity of the Galactic mini-starburst W43. Astronomy and Astrophysics 538(Februa), article number: A11. (10.1051/0004-6361/201117850)
2011
- Ragan, S., Bergin, E. and Wilner, D. 2011. Very large array observations of ammonia in infrared-dark clouds. I. column density and temperature structure. Astrophysical Journal 736(2), article number: 163. (10.1088/0004-637X/736/2/163)
2010
- Henning, T. et al. 2010. The seeds of star formation in the filamentary infrared-dark cloud G011.11-0.12. Astronomy and Astrophysics 518, article number: A95. (10.1051/0004-6361/201014635)
2009
- Gibson, D., Plume, R., Bergin, E., Ragan, S. and Evans, N. 2009. Molecular line observations of infrared dark clouds. II. physical conditions. Astrophysical Journal 705(1), pp. 123-134. (10.1088/0004-637X/705/1/123)
- Ragan, S., Bergin, E. A. and Gutermuth, R. A. 2009. Detection of structure in infrared-dark clouds with Spitzer: characterizing star formation in the molecular ring. Astrophysical Journal 698(1), pp. 324-349. (10.1088/0004-637X/698/1/324)
2006
- Ragan, S., Bergin, E., Plume, R., Gibson, D., Wilner, D., O'Brien, S. and Hails, E. 2006. Molecular line observations of infrared dark clouds: seeking the precursors to intermediate and massive star formation. Astrophysical Journal Supplement 166(2), pp. 567-584. (10.1086/506594)
Articles
- King, S. M. et al. 2024. CHIMPS2: 13CO J = 3→2 emission in the central molecular zone. Monthly Notices of the Royal Astronomical Society 533(1), pp. 131–142. (10.1093/mnras/stae1854)
- Priestley, F. D., Clark, P. C., Glover, S. C. O., Ragan, S. E., Feher, O., Prole, L. R. and Klessen, R. S. 2024. NEATH III: A molecular line survey of a simulated star-forming cloud. Monthly Notices of the Royal Astronomical Society 531(4), pp. 4408–4421. (10.1093/mnras/stae1442)
- Fehér, O., Ragan, S. E., Priestley, F. D., Clark, P. C. and Moore, T. J. T. 2024. N2H+(1–0) as a tracer of dense gas in and between spiral arms. Monthly Notices of the Royal Astronomical Society 530(2), pp. 1311–1327. (10.1093/mnras/stae918)
- Rigby, A. J. et al. 2024. The dynamic centres of infrared-dark clouds and the formation of cores. Monthly Notices of the Royal Astronomical Society 528(2), pp. 1172–1197. (10.1093/mnras/stae030)
- Priestley, F. D., Clark, P. C., Glover, S. C. O., Ragan, S. E., Feher, O., Prole, L. R. and Klessen, R. S. 2023. NEATH – II. N2H+ as a tracer of imminent star formation in quiescent high-density gas. Monthly Notices of the Royal Astronomical Society 526(4), pp. 4952–4960. (10.1093/mnras/stad3089)
- Priestley, F. D., Clark, P. C., Glover, S. C. O., Ragan, S. E., Feher, O., Prole, L. R. and Klessen, R. S. 2023. Non-equilibrium abundances treated holistically (NEATH): the molecular composition of star-forming clouds. Monthly Notices of the Royal Astronomical Society 524(4), pp. 5971–5983. (10.1093/mnras/stad2278)
- Ahmadi, A. et al. 2023. Kinematics and stability of high-mass protostellar disk candidates at sub-arcsecond resolution. Astronomy & Astrophysics 677, article number: A171. (10.1051/0004-6361/202245580)
- Wells, M. R. A. et al. 2022. ATLASGAL - star forming efficiencies and the Galactic star formation rate. Monthly Notices of the Royal Astronomical Society 516(3), pp. 4245–4255. (10.1093/mnras/stac2420)
- Neralwar, K. R. et al. 2022. The SEDIGISM survey: Molecular cloud morphology II. Integrated source properties. Astronomy & Astrophysics 664(2022), article number: A84. (10.1051/0004-6361/202142513)
- Neralwar, K. R. et al. 2022. The SEDIGISM survey: Molecular cloud morphology. Astronomy & Astrophysics 663, article number: A56. (10.1051/0004-6361/202142428)
- Urquhart, J. S. et al. 2022. ATLASGAL - evolutionary trends in high-mass star formation. Monthly Notices of the Royal Astronomical Society 510(3), pp. 3389–3407. (10.1093/mnras/stab3511)
- Colombo, D. et al. 2022. The SEDIGISM survey: the influence of spiral arms on the molecular gas distribution of the inner Milky Way. Astronomy & Astrophysics 658, pp. 1-38., article number: A54. (10.1051/0004-6361/202141287)
- Anderson, M. et al. 2021. An ALMA study of hub-filament systems - I. On the clump mass concentration within the most massive cores. Monthly Notices of the Royal Astronomical Society 508(2), pp. 2964–2978. (10.1093/mnras/stab2674)
- Smith, M. W. L. et al. 2021. The HASHTAG project: The first submillimeter images of the Andromeda Galaxy from the ground.. Astrophysical Journal Supplement Series 257, article number: 52. (10.3847/1538-4365/ac23d0)
- Elia, D. et al. 2021. The Hi-GAL compact source catalogue - II. The 360° catalogue of clump physical properties. Monthly Notices of the Royal Astronomical Society 504(2), pp. 2742–2766. (10.1093/mnras/stab1038)
- Eden, D. J. et al. 2021. Characteristic scale of star formation. I. Clump formation efficiency on local scales. Monthly Notices of the Royal Astronomical Society 500(1), pp. 191-210. (10.1093/mnras/staa3188)
- Duarte Cabral, A. et al. 2021. The SEDIGISM survey: molecular clouds in the inner galaxy. Monthly Notices of the Royal Astronomical Society 500(3), pp. 3027-3049. (10.1093/mnras/staa2480)
- Urquhart, J. S. et al. 2021. SEDIGISM-ATLASGAL: dense gas fraction and star formation efficiency across the galactic disk. Monthly Notices of the Royal Astronomical Society 500(3), article number: staa2512. (10.1093/mnras/staa2512)
- Schuller, F. et al. 2021. The SEDIGISM survey: first data release and overview of the Galactic structure*. Monthly Notices of the Royal Astronomical Society 500(3), article number: staa2369. (10.1093/mnras/staa2369)
- Eden, D. J. et al. 2020. CHIMPS2: survey description and 12CO emission in the Galactic centre. Monthly Notices of the Royal Astronomical Society 498(4), pp. 5936-5951. (10.1093/mnras/staa2734)
- Henshaw, J. D. et al. 2020. Ubiquitous velocity fluctuations throughout the molecular interstellar medium. Nature Astronomy 4, pp. 1064-1071. (10.1038/s41550-020-1126-z)
- Syed, J. et al. 2020. Atomic and molecular gas properties during cloud formation. Astronomy and Astrophysics 642, article number: A68. (10.1051/0004-6361/202038449)
- Wang, Y. et al. 2020. Dense gas in a giant molecular filament. Astronomy and Astrophysics 641, article number: A53. (10.1051/0004-6361/202037928)
- Beuther, H. et al. 2020. Dynamical cloud formation traced by atomic and molecular gas. Astronomy and Astrophysics 638, article number: A44. (10.1051/0004-6361/202037950)
- Mottram, J. C. et al. 2020. From clump to disc scales in W3 IRS4. Astronomy and Astrophysics 636, article number: A118. (10.1051/0004-6361/201834152)
- Wang, Y. et al. 2020. Cloud formation in the atomic and molecular phase: HI self absorption (HISA) towards a giant molecular filament. Astronomy and Astrophysics 634, article number: A139. (10.1051/0004-6361/201935866)
- Li, Z. et al. 2020. The HASHTAG project I. A survey of CO(3–2) emission from the star forming disc of M31. Monthly Notices of the Royal Astronomical Society 492(1), pp. 195-290. (10.1093/mnras/stz3409)
- Pettitt, A. R., Ragan, S. E. and Smith, M. C. 2020. Young stars as tracers of a barred-spiral Milky Way. Monthly Notices of the Royal Astronomical Society 4914(2), pp. 2162-2179. (10.1093/mnras/stz3155)
- Rigby, A. J. et al. 2019. CHIMPS: physical properties of molecular clumps across the inner Galaxy. Astronomy and Astrophysics 632, article number: A58. (10.1051/0004-6361/201935236)
- Clark, P. C., Glover, S. C. O., Ragan, S. E. and Cabral, A. 2019. Tracing the formation of molecular clouds via [CII], [CI] and CO emission. Monthly Notices of the Royal Astronomical Society 486(4), pp. 4622-4637. (10.1093/mnras/stz1119)
- Henshaw, J. D. et al. 2019. ‘The Brick’ is not a brick: A comprehensive study of the structure and dynamics of the Central Molecular Zone cloud G0.253+0.016. Monthly Notices of the Royal Astronomical Society 485(2), pp. 2457-2485. (10.1093/mnras/stz471)
- Soler, J. D. et al. 2019. Histogram of oriented gradients: a technique for the study of molecular cloud formation. Astronomy and Astrophysics 622, article number: A166. (10.1051/0004-6361/201834300)
- Rugel, M. R. et al. 2019. Feedback in W49A diagnosed with radio recombination lines and models. Astronomy and Astrophysics 622, article number: A48. (10.1051/0004-6361/201834068)
- Rugel, M. et al. 2018. OH absorption in the first quadrant of the Milky Way as seen by THOR. Astronomy and Astrophysics 618, article number: A159. (10.1051/0004-6361/201731872)
- Ahmadi, A. et al. 2018. Core fragmentation and Toomre stability analysis of W3(H20): A case study of the IRAM NOEMA large program CORE. Astronomy and Astrophysics 618(46), article number: A46. (10.1051/0004-6361/201732548)
- Beuther, H. et al. 2018. Fragmentation and disk formation during high-mass star formation: the IRAM NOEMA (Northern Extended Millimeter Array) large program CORE. Astronomy and Astrophysics 617, article number: A100. (10.1051/0004-6361/201833021)
- Ragan, S. E., Moore, T. J. T., Eden, D. J., Hoare, M. G., Urquhart, J. S., Elia, D. and Molinari, S. 2018. The role of spiral arms in Milky Way star formation. Monthly Notices of the Royal Astronomical Society 479(2), pp. 2361-2373. (10.1093/mnras/sty1672)
- Barnes, A. T. et al. 2018. Similar complex kinematics within two massive, filamentary infrared dark clouds?. Monthly Notices of the Royal Astronomical Society 475(4), pp. 5268-5289. (10.1093/mnras/sty173)
- Marsh, K. et al. 2017. Multi-temperature mapping of dust structures throughout the Galactic Plane using the PPMAP tool with Herschel Hi-GAL data. Monthly Notices of the Royal Astronomical Society 471(3), pp. 2730-2742. (10.1093/mnras/stx1723)
- Elia, D. et al. 2017. The Hi-GAL compact source catalogue. I. The physical properties of the clumps in the inner Galaxy (−71.0 ◦ < ` < 67.0◦). Monthly Notices of the Royal Astronomical Society 471(1), pp. 100-143. (10.1093/mnras/stx1357)
- Ragan, S. E., Moore, T. J. T., Eden, D. J., Hoare, M. G., Elia, D. and Molinari, S. 2016. The prevalence of star formation as a function of Galactocentric radius. Monthly Notices of the Royal Astronomical Society 462(3), pp. 3123-3129. (10.1093/mnras/stw1870)
- Beuther, H. et al. 2016. The HI/OH/Recombination line survey of the inner Milky Way (THOR). Survey overview and data release 1. Astronomy and Astrophysics -Berlin then Les Ulis- 595, article number: A32. (10.1051/0004-6361/201629143)
- Marsh, K., Ragan, S., Whitworth, A. P. and Clark, P. 2016. Evidence that widespread star formation may be underway in G0.253+016, 'The Brick'. Monthly Notices of the Royal Astronomical Society 461(1), pp. L16-L20. (10.1093/mnrasl/slw080)
- Lippok, N. et al. 2016. Earliest phases of star formation (EPoS). Dust temperature distributions in isolated starless cores. Astronomy and Astrophysics -Berlin then Les Ulis- 592, article number: A61. (10.1051/0004-6361/201525792)
- Feng, S., Beuther, H., Zhang, Q., Henning, T., Linz, H., Ragan, S. and Smith, R. 2016. Are infrared dark clouds really quiescent?. Astronomy and Astrophysics -Berlin then Les Ulis- 592, article number: A21. (10.1051/0004-6361/201526864)
- Abreu-Vicente, J., Ragan, S., Kainulainen, J., Henning, T., Beuther, H. and Johnston, K. 2016. Giant molecular filaments in the Milky Way II. the fourth Galactic quadrant. Astronomy and Astrophysics 590, article number: A131. (10.1051/0004-6361/201527674)
- Bertram, E., Glover, S., Clark, P., Ragan, S. and Klessen, R. 2016. Synthetic observations of molecular clouds in a galactic centre environment - I. Studying maps of column density and integrated intensity. Monthly Notices of the Royal Astronomical Society 455(4), pp. 3763-3778. (10.1093/mnras/stv2619)
- Beuther, H., Ragan, S. E., Johnston, K., Henning, T., Hacar, A. and Kainulainen, J. T. 2015. Filament fragmentation in high-mass star formation. Astronomy and Astrophysics 584, article number: A67. (10.1051/0004-6361/201527108)
- Walsh, A. et al. 2015. A survey for hydroxyl in the THOR pilot region around W43. Monthly Notices of the Royal Astronomical Society 455(4), pp. 3494-3510. (10.1093/mnras/stv2446)
- Beuther, H. et al. 2015. Hierarchical fragmentation and collapse signatures in a high-mass starless region. Astronomy and Astrophysics 581, article number: A119. (10.1051/0004-6361/201526759)
- Bihr, S. et al. 2015. THOR: The H i, OH, Recombination line survey of the Milky Way. The pilot study: H i observations of the giant molecular cloud W43. Astronomy and Astrophysics 580, article number: A112. (10.1051/0004-6361/201425370)
- Bihr, S. et al. 2015. Kinematic and thermal structure at the onset of high-mass star formation. Astronomy and Astrophysics 579, article number: A51. (10.1051/0004-6361/201321269)
- Ragan, S. E., Henning, T., Beuther, H., Linz, H. and Zahorecz, S. 2015. Fragmentation and kinematics of dense molecular cores in the filamentary infrared-dark cloud G011.11–0.12. Astronomy and Astrophysics 573, article number: A119. (10.1051/0004-6361/201424948)
- Tobin, J. et al. 2015. Characterizing the youngest Herschel-detected protostars. I. envelope structure revealed by CARMA dust continuum observations. Astrophysical Journal 798(2), article number: 128. (10.1088/0004-637X/798/2/128)
- Beuther, H. et al. 2014. Carbon in different phases ([CII], [CI], and CO) in infrared dark clouds: cloud formation signatures and carbon gas fractions. Astronomy and Astrophysics 571, article number: A53. (10.1051/0004-6361/201424757)
- Ragan, S. E., Henning, T., Tackenberg, J., Beuther, H., Johnston, K. G., Kainulainen, J. and Linz, H. 2014. Giant molecular filaments in the Milky Way. Astronomy and Astrophysics 568, article number: A73. (10.1051/0004-6361/201423401)
- Johnston, K., Beuther, H., Linz, H., Schmiedeke, A., Ragan, S. and Henning, T. 2014. The dynamics and star-forming potential of the massive Galactic centre cloud G0.253+0.016. Astronomy and Astrophysics 568, article number: A56. (10.1051/0004-6361/201423943)
- Tackenberg, J. et al. 2014. Kinematic structure of massive star-forming regions. I. accretion along filaments. Astronomy and Astrophysics 565, article number: A101. (10.1051/0004-6361/201321555)
- Wang, K. et al. 2014. Hierarchical fragmentation and differential star formation in the Galactic `Snake': infrared dark cloud G11.11-0.12. Monthly Notices of the Royal Astronomical Society 439(4), pp. 3275-3293. (10.1093/mnras/stu127)
- Ragan, S., Henning, T. and Beuther, H. 2013. APEX/SABOCA observations of small-scale structure of infrared-dark clouds I. early evolutionary stages of star-forming cores. Astronomy and Astrophysics 559(Novemb), article number: A79. (10.1051/0004-6361/201321869)
- Kainulainen, J., Ragan, S., Henning, T. and Stutz, A. 2013. High-fidelity view of the structure and fragmentation of the high-mass, filamentary IRDC G11.11-0.12. Astronomy and Astrophysics 557(Septem), article number: A120. (10.1051/0004-6361/201321760)
- Beuther, H. et al. 2013. Fragmentation and dynamical collapse of the starless high-mass star-forming region IRDC 18310-4. Astronomy and Astrophysics 553(May), pp. 115., article number: A115. (10.1051/0004-6361/201220475)
- Clark, P., Glover, S. C. O., Ragan, S., Shetty, R. and Klessen, R. S. 2013. On the temperature structure of the galactic center cloud G0.253+0.016. Astrophysical Journal Letters 768(2), article number: L34. (10.1088/2041-8205/768/2/L34)
- Pitann, J. et al. 2013. G048.66-0.29: physical state of an isolated site of massive star formation. Astrophysical Journal 766(2), article number: 68. (10.1088/0004-637X/766/2/68)
- Launhardt, R. et al. 2013. The Earliest Phases of Star Formation (EPoS): a Herschel key project: the thermal structure of low-mass molecular cloud cores. Astronomy and Astrophysics 551(March), article number: A98. (10.1051/0004-6361/201220477)
- Nielbock, M. et al. 2012. The Earliest Phases of Star formation (EPoS) observed with Herschel: the dust temperature and density distributions of B68. Astronomy and Astrophysics 547(Novemb), article number: A11. (10.1051/0004-6361/201219139)
- Ragan, S. et al. 2012. The Earliest Phases of Star Formation (EPoS): a Herschel key program: the precursors to high-mass stars and clusters. Astronomy and Astrophysics 547(Novemb), article number: A49. (10.1051/0004-6361/201219232)
- Ragan, S., Heitsch, F., Bergin, E. and Wilner, D. 2012. Very large array observations of ammonia in infrared-dark clouds. II. internal kinematics. Astrophysical Journal 746(2), article number: 174. (10.1088/0004-637X/746/2/174)
- Beuther, H. et al. 2012. The onset of high-mass star formation in the direct vicinity of the Galactic mini-starburst W43. Astronomy and Astrophysics 538(Februa), article number: A11. (10.1051/0004-6361/201117850)
- Ragan, S., Bergin, E. and Wilner, D. 2011. Very large array observations of ammonia in infrared-dark clouds. I. column density and temperature structure. Astrophysical Journal 736(2), article number: 163. (10.1088/0004-637X/736/2/163)
- Henning, T. et al. 2010. The seeds of star formation in the filamentary infrared-dark cloud G011.11-0.12. Astronomy and Astrophysics 518, article number: A95. (10.1051/0004-6361/201014635)
- Gibson, D., Plume, R., Bergin, E., Ragan, S. and Evans, N. 2009. Molecular line observations of infrared dark clouds. II. physical conditions. Astrophysical Journal 705(1), pp. 123-134. (10.1088/0004-637X/705/1/123)
- Ragan, S., Bergin, E. A. and Gutermuth, R. A. 2009. Detection of structure in infrared-dark clouds with Spitzer: characterizing star formation in the molecular ring. Astrophysical Journal 698(1), pp. 324-349. (10.1088/0004-637X/698/1/324)
- Ragan, S., Bergin, E., Plume, R., Gibson, D., Wilner, D., O'Brien, S. and Hails, E. 2006. Molecular line observations of infrared dark clouds: seeking the precursors to intermediate and massive star formation. Astrophysical Journal Supplement 166(2), pp. 567-584. (10.1086/506594)
Research
My research: observing Galactic star formation
My main research interests lie in the conditions necessary for star formation. I am involved in several projects with many international collaborators. I highlight below the projects that I've been leading recently. Please contact me if you are interested or want to inquire about possible projects!
Galaxy-scale star formation
Galactic plane surveys enable us to study the nature of star formation throughout the Milky Way over kiloparsec scales. The Herschel Space Observatory has conducted a survey of the entire Milky Way plane in the far-infrared wavelength regime. These wavelengths cover the peak of the spectral energy distribution of thermal emission from cold dust grains. Compact sources at these wavelengths represent the regions in the Galaxy which have the cold, dense conditions necessary for star formation.
In Ragan et al. (2016), we present large-scale trends in the distribution of star-forming objects revealed by the Hi- GAL survey. As a simple metric probing the prevalence of star formation in Hi-GAL sources, we define the fraction of the total number of Hi-GAL sources with a 70 μm counterpart as the 'star-forming fraction' or SFF. The mean SFF in the inner galactic disc (3.1 kpc < RGC < 8.6 kpc) is 25 per cent. Despite an apparent pile-up of source numbers at radii associated with spiral arms, the SFF shows no significant deviations at these radii, indicating that the arms do not affect the star-forming productivity of dense clumps either via physical triggering processes or through the statistical effects of larger source samples associated with the arms. Within this range of Galactocentric radii, we find that the SFF declines with RGC at a rate of −0.026 ± 0.002 per kiloparsec, despite the dense gas mass fraction having been observed to be constant in the inner Galaxy. This suggests that the SFF may be weakly dependent on one or more large-scale physical properties of the Galaxy, such as metallicity, radiation field, pressure or shear, such that the dense sub-structures of molecular clouds acquire some internal properties inherited from their environment.
Giant filaments in the Milky Way
Throughout the Milky Way, molecular clouds typically appear filamentary in morphology on what seems like all possible scales. Using the wealth of Galactic plane survey data, we have identified velocity-coherent filaments on up to 100-pc size scales. This discovery enables us to begin connecting the ubiquitous filamentary clouds to Galactic structure. In Ragan et al. (2014 ) we identify and characterise the first sample of giant molecular filaments (GMFs) in the Galaxy. Many GMFs are clearly aligned with spiral arms but some are squarely in inter-arm regions of the Galactic plane. We find the GMFs in the spiral arms have a higher fraction of their mass in the densest structures, so-called "clumps". GMFs are an important new laboratory in which we can gain a greater understanding of how molecular cloud and star formation depends on their Galactic environment.
Fine structure line cooling in Galactic dark clouds
Stars are born in the densest regions of MCs, but the process appears to be very inefficient, with MCs converting only a few percent of their gas budget into stars per dynamical time. The underlying physical processes that regulate the star formation rate (SFR) in the ISM are still unknown and hotly debated, with candidates ranging from turbulence and magnetic fields to stellar feedback. Further debate stems from the observational evidence that while the "dense" regions in MCs in the solar neighbourhood appear to explain the observed galactic star formation relations, the same approach fails to explain the SFR towards the central molecular zone (CMZ) of the Milky Way. The primary reason for this debate is that we still do not understand how MCs are assembled and destroyed — the two processes that ultimately set the timescale over which a cloud can form stars. The problem is that carbon monoxide (CO), the main tracer of MC structure and dynamics, is only sensitive to the cold interiors of MCs and not their envelopes, and models show that CO may form relatively late in the assembly process. Therefore, alternative tracers that can probe gas in the absence of CO — so-called "CO-dark" gas — are needed to make further progress in understanding MC formation and destruction.
Fine structure line (FSL) tracers such as ionised and atomic carbon ([CII] and [CI]) and atomic oxygen ([OI]) are the key probes of the earliest stages of cloud assembly. These lines are important for several reasons. First, they are able to trace the low-density transition from atomic to molecular gas that marks the boundary from the warm ISM to the cold reservoirs in which stars form. Second, they constitute the main coolants of ISM during this transition, thus providing a way to measure the energetics of the ISM. Finally, due to the different excitation properties of the lines, they allow us to distinguish between different temperature and density regimes in the ISM.
In Beuther, Ragan et al. (2014), we conduct a pilot study of a sample of quiescent molecular clouds in tracers of all carbon phases. Our study revealed that the tracers show a range of behaviours depending on their environment. In one cloud (see figure) the [CII] emission shows intriguing signs of dynamical cloud formation, with strong emission on either side of the dense gas probed with CO. This could be cloud formation "caught in the act"! Our follow-up SOFIA observations of a larger area will help us disentangle the picture further... Stay tuned!
Teaching
- Module organiser of PX1120 Mathematical Methods for Physicists I
- Module organiser of PX2155 Observational Techniques in Astronomy, the second-year undergraduate astronomy laboratory module.
Biography
I've been a member of staff in the School of Physics and Astronomy since 2016, and I am currently a Senior Lecturer. Since earning my PhD in 2009 at the University of Michigan, Ann Arbor, I have held reserach positions at Max Planck Institute for Astronomy in Heidelberg, the University of Leeds and Cardiff University. I took on an academic position in 2018.
My research is on the early phases of star formation, and I use a combination of observational and modeling techniques to understand what conditions in molecular clouds are necessary for star formation, which of those conditions promote the formation of high mass stars in particular, and what causes the formation of the molecular clouds in the first place. Our research has shown that these topics are all interlinked, and connected to the broader environment in the Galaxy as well!
Honours and awards
- 2016 Marie Skłodowska-Curie Research Fellowship (Cardiff University, 2 years funding)
- 2011 Deutsche Forschungsgemeinschaft Grant (Max Planck Institut für Astronomie, 3 years funding)
- 2009 Ralph Baldwin dissertation award (University of Michigan, prize)
- 2007 Spitzer Space Telescope archival research grant (1 year funding)
- 2006 Green Bank Telescope student support grant (1 year funding)
Academic positions
Academic positions
- 2021 - present: Senior Lecturer, Cardiff University, School of Physics and Astronomy, Cardiff, UK
- 2018 - 2021 : Lecturer, Cardiff University, School of Physics and Astronomy, Cardiff, UK
Research positions
- 2016 - 2018: Marie Skłodowska-Curie Fellow, Cardiff University, School of Physics and Astronomy, Cardiff, UK
- 2014 - 2016: Postdoctoral Research Assistant, University of Leeds, School of Physics and Astronomy, Leeds, UK
- 2011 - 2014: Deutsche Forschungsgemeinschaft (self-funded) Postdoctoral fellow, Max Planck Insitut für Astronomie, Heidelberg, Germany
- 2010 - 2011: Star and Planet formation postoctoral fellow, Max Planck Institut für Astornomie, Heidelberg, Germany
Education
- 2009: PhD (Astronomy & Astrophysics) University of Michigan, Ann Arbor, MI, USA
- 2003: BSc ( [1] Astronomy, [2] Physics and [3] Mathematics ) Drake University, Des Moines, IA, USA
Committees and reviewing
- Director of Undergraduate Studies, School of Physics and Astronomy, Cardiff University (2021-24)
- Member of the Equity, Diversity and Inclusion committee, School of Physics and Astronomy, Cardiff University (current)
- Grant reviewer, STFC
- Journal referee, ApJ, A&A, MNRAS
Contact Details
+44 29208 74289
Queen's Buildings - North Building, Room N/2.15A, 5 The Parade, Newport Road, Cardiff, CF24 3AA
Research themes
Specialisms
- Data science
- Astronomical sciences
- Astronomical instrumentation
- Galactic astronomy