My work mainly focuses on the physics of the atomic phase of the interstellar medium. We therefore conduct HI emission and absorption studies to explore the processes leading up to the formation of molecular clouds, the sites of star formation.
My research interests are atomic/molecular cloud formation, filaments, high-mass star formation, and magnetic fields.

HI filaments

Here we present one particular filament of atomic hydrogen (HI) that stands out because of its mere size. "Maggie", named after el Río Magdalena, the largest river in Colombia, is a largely atomic elongated gas cloud that has a mass of more than half a million solar masses.
While in recent years astronomers have studied many molecular filaments and clouds, the sites of star formation, Maggie shows only little detection of molecular gas. Given its length of ≈1200 pc (~3900 light years), Maggie is the largest coherent object in the Milky Way that we know of. Maggie's formation history and whether it is an anomaly or an object of regular occurrence is still not understood.

By clicking on the image on the right you can get an interactive 3D (position-position-velocity) view on Maggie! The colored volume render shows the distribution of the atomic hydrogen gas. The red curve marks the modelled spine of the filament.
Check out the paper here and the accompanying press release here!


The HI/OH Recombination line survey of the inner Milky Way (THOR; Beuther et al. 2016, Wang et al. 2020a) is a large survey of the inner Galactic plane. The program includes observations of the HI 21cm line, four OH lines, 19 radio recombination lines, and the continuum emission between 1 and 2 GHz. The THOR observations cover the inner portion of the Milky Way's midplane at Galactic longitudes between 17 and 67 degrees and Galactic latitudes between -1.25 and +1.25 degrees.
My work mainly relies on the atomic hydrogen (HI) data. The HI data have an angular resolution of 40″ (i.e. we can resolve angles that are just 2% of the Moon's diameter in the sky!). To see what the THOR-HI observations look like, check out this beautiful rendition by one of our collaborators. After zooming into the coverage of the THOR survey, the video shows the atomic hydrogen emission as the view moves along the Galactic longitude axis. At the same time, it moves back and forth through the entire spectral range of the data.

HI self-absorption (HISA)

HI spectrum
Fig. 2 - HI, HISA, and 13CO spectrum. Taken from Syed et al. (2020).

HI self-absorption, also referred to as "HISA", occurs when a cold gas cloud of atomic hydrogen (HI) is located in front of a warmer HI cloud along our line of sight. We therefore observe the cold cloud in absorption against the warmer emission background. By measuring HISA, we can disentangle individual cold HI clouds from the otherwise ubiquitous HI gas that creates "messy" spectra, mostly due to the Galactic rotation. Figure 1 shows an example spectrum of the HI emission toward the inner Galactic plane at a Galactic longitude of ℓ≈20°.

Using first and second order polynomial fits to the baselines of the absorption features (red dashed), we can isolate HISA spectra (red). We use molecular line tracers, such as 13CO (blue), to identify molecular clouds. By correlating molecular line emission with HISA, we can identify cold atomic gas within those star-forming regions.
We conducted an analysis built upon previous case studies that identified HI self-absorption using polynomial baseline fitting. For an unbiased baseline extraction, we developed the automated extraction routine astroSABER (as in Self-Absorption Baseline ExtractoR) that uses a supervised machine learning technique to find optimal baselines for self-absorption. In doing so, we can systematically obtain HISA independent of molecular line emission. This may help us understand how molecular clouds form out of the atomic gas phase of the interstellar medium.
Check out the case study here and the paper introducing the new method here!

Temperature and kinematics of massive star-forming clumps

NH<sub>3</sub> spectrum
Fig. 4 - NH3 spectrum

Here I present the research conducted within the scope of my Bachelor thesis. We have investigated the kinematics and temperature of two high-mass gas clumps using ammonia observations. Ammonia (NH3) is a suitable molecule to trace very cold (T ~ 20 K) and dense (n >104 cm-3) gas. By observing different metastable lines of the NH3 hyperfine structure, which are well detectable with radio telescopes (wavelength λ≈1.3 cm), we can determine the underlying kinematics and temperature of the clumps.


Publications on ADS
1st author publications
Cold atomic gas identified by HI self-absorption. Cold atomic clouds toward giant molecular filaments
[publisher, arXiv]
2023, Astronomy & Astrophysics, 679, A130
J. Syed, H. Beuther, P. F. Goldsmith, Th. Henning, M. Heyer, R. S. Klessen, J. M. Stil, J. D. Soler, L. D. Anderson, J. S. Urquhart, M. R. Rugel, K. G. Johnston, and A. Brunthaler

The "Maggie" filament: Physical properties of a giant atomic cloud [publisher, arXiv]
2022, Astronomy & Astrophysics, 657, A1
J. Syed, J. D. Soler, H. Beuther, Y. Wang, S. Suri, J. D. Henshaw, M. Riener, S. Bialy, S. Rezaei Kh., J. M. Stil, P. F. Goldsmith, M. R. Rugel, S. C. O. Glover, R. S. Klessen, J. Kerp, J. S. Urquhart, J. Ott, N. Roy, N. Schneider, R. J. Smith, S. N. Longmore, and H. Linz

Atomic and molecular gas properties during cloud formation [publisher, arXiv]
2020, Astronomy & Astrophysics, 642, A68
J. Syed, Y. Wang, H. Beuther, J. D. Soler, M. R. Rugel, J. Ott, A. Brunthaler, J. Kerp, M. Heyer, R. S. Klessen, Th. Henning, S. C. O. Glover, P. F. Goldsmith, H. Linz, J. S. Urquhart, S. E. Ragan, K. G. Johnston, and F. Bigiel

Co-authored publications
EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates of Planets around Late-M Dwarfs within 15 pc [publisher, arXiv]
2023, The Astronomical Journal, 165, 149
J. Dietrich, D. Apai, M. Schlecker, K. K. Hardegree-Ullman, B. V. Rackham, N. Kurtovic, K. Molaverdikhani, P. Gabor, Th. Henning, W. P. Chen, L. Mancini, A. Bixel, A. Gibbs, R. P. Boyle, S. Brown-Sevilla, R. Burn, T. N. Delage, L. Flores-Rivera, R. Franceschi, G. Pichierri, S. Savvidou, J. Syed, I. Bruni, W.-H. Ip, C.-C. Ngeow, A.-L. Tsai, C.-L. Lin, W.-J. Hou, H.-Y. Hsiao, C.-S. Lin, H.-C. Lin, and R. Basant

Properties of atomic hydrogen gas in the Galactic plane from THOR 21-cm absorption spectra: a comparison with the high latitude gas [publisher, arXiv]
2022, Monthly Notices of the Royal Astronomical Society, 517, 5063
A. Basu, N. Roy, H. Beuther, J. Syed, J. Ott, J. D. Soler, J. M. Stil, M. R. Rugel

Polarized Emission From Four Supernova Remnants In The THOR Survey [publisher, arXiv]
2022, The Astrophysical Journal, 939, 92
R. Shanahan, J. M. Stil, L. Anderson, H. Beuther, P. F. Goldsmith, J. Ott, M. R. Rugel, J. D. Soler, J. Syed

On the accuracy of HI observations in molecular clouds -- More cold HI than thought? [publisher, arXiv]
2022, Monthly Notices of the Royal Astronomical Society, 512, 4765
D. Seifried, H. Beuther, S. Walch, J. Syed, J. D. Soler, P. Girichidis, and R. Wünsch

Clustered star formation at early evolutionary stages. Physical and chemical analysis of the young star-forming regions ISOSS J22478+6357 and ISOSS J23053+5953 [publisher, arXiv]
2022, Astronomy & Astrophysics, 657, A3
C. Gieser, H. Beuther, D. Semenov, S. Suri, J. D. Soler, H. Linz, J. Syed, Th. Henning, S. Feng, T. Möller, A. Palau, J. M. Winters, M. T. Beltrán, R. Kuiper, L. Moscadelli, P. Klaassen, J. S. Urquhart, T. Peters, S. N. Longmore, Á. Sánchez-Monge, R. Galván-Madrid, R. Pudritz, and K. G. Johnston

The filamentary structures in the CO emission toward the Milky Way disk [publisher, arXiv]
2021, Astronomy & Astrophysics, 651, L4
J. D. Soler, H. Beuther, J. Syed, Y. Wang, Th. Henning, S. C. O. Glover, R. S. Klessen, M. C. Sormani, M. Heyer, R. J. Smith, J. S. Urquhart, J. Yang, Y. Su, X. Zhou

Fragmentation and kinematics in high-mass star formation: CORE-extension targeting two very young high-mass star-forming regions [publisher, arXiv]
2021, Astronomy & Astrophysics, 649, A113
H. Beuther, C. Gieser, S. Suri, H. Linz, P. Klaassen, D. Semenov, J. M. Winters, Th. Henning, J. D. Soler, J. S. Urquhart, J. Syed, S. Feng, T. Moeller, M. T. Beltran, A. Sanchez-Monge, S. N. Longmore, T. Peters, J. Ballesteros-Paredes, P. Schilke, L. Moscadelli, A. Palau, R. Cesaroni, S. Lumsden, R. Pudritz, F. Wyrowski, R. Kuiper, and A. Ahmadi

The history of dynamics and stellar feedback revealed by the HI filamentary structure in the disk of the Milky Way [publisher, arXiv]
2020, Astronomy & Astrophysics, 642, A163
J. D. Soler, H. Beuther, J. Syed, Y. Wang, L. D. Anderson, S. C. O. Glover, P. Hennebelle, M. Heyer, Th. Henning, A. F. Izquierdo, R. S. Klessen, H. Linz, N. M. McClure-Griffiths, J. Ott, S. E. Ragan, M. Rugel, N. Schneider, R. J. Smith, M. C. Sormani, J. M. Stil, and J. S. Urquhart

Jonas Syed (he/him)

See my CV


Jonas Syed, Dr. rer. nat.

syed [at]

Königstuhl 17
69117 Heidelberg