SFB2023_overview

Massive stars, due to their short lifetime and high energy output, drive the evolution of galaxies across cosmic time. Hence, they substantially contribute to shaping the present-day Universe. The Collaborative Research Centre (CRC) will unravel the “habitats of massive stars across cosmic time”. “Habitats” are the gaseous environments within which massive stars are born and which they interact with via their feedback. Over the anticipated 12-year lifetime of this new CRC initiative, we aim to connect the physical processes that govern the habitats of massive stars across the full range of environments hosting massive stars – from sub-parsec to mega-parsec scales and from the Milky Way to the high-redshift Universe, where massive stars leave their cosmological fingerprint by driving cosmic reionisation.

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Key Profile Area “Dynamics of the Universe”

The Dynamics of the Universe is a Key Profile Area (KPA) of the University of Cologne since 2025. Please check back soon for more information and our new website

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Science Highlight

  • C5: Does the [CII]-molecular gas relation evolve over time? (Prachi Khatri)

    C5: Does the [CII]-molecular gas relation evolve over time? (Prachi Khatri)
    • C5: Does the [CII]-molecular gas relation evolve over time? (Prachi Khatri)

      In recent years, the fine-structure line of C+ at 158 microns – the [CII] line – has gained significant attention as a molecular gas tracer, particularly at z ≳ 4.  Being one of the brightest emission lines in galaxies, it offers a unique window into the molecular ISM of distant galaxies, where conventional tracers like CO become observationally expensive. 

      We have tested the reliability of this line as a tracer of the molecular gas mass (Mmol) using a statistical sample of galaxies at different cosmic epochs from high-resolution cosmological simulations – the Marigold simulations. Our analysis reveals that the [CII]- Mmol correlation is relatively weak at z ≳ 5, but becomes progressively stronger over time. We also identify a clear secondary dependence on the star formation rate (SFR), accounting for which, significantly improves Mₘₒₗ predictions by a factor of 2.3 at all redshifts. 

      We have further examined the time evolution of the [CII] luminosity function and the cosmic [CII] luminosity density (ρ[CII]) and found that faint (L[CII] < 107 L⊙) galaxies contribute nearly half of the cosmic ρ[CII] at z ≳ 7. Since these faint galaxies fall below the sensitivity limits of current instruments, detecting them would require alternative observational strategies.

      The paper describing our findings has been published in A&A. 
      DOI:  10.1051/0004-6361/202453048

      Figure caption: a) Figure showing the redshift-evolution of the [CII]-Mmol relation in galaxies from the Marigoldsimulations. The purple bins show the distribution of simulated galaxies and the red line gives the ordinary least squares linear fit to these galaxies. The blue, lime, and orange lines show previous empirical and numerical estimates for specific redshifts. We note that the [CII]-Mmol correlation tightens and strengthens over time, as indicated by the decreasing scatter (σ) and increasing Spearman’s rank correlation coefficient (ρ) towards lower redshifts.

      b) Figure showing the redshift-evolution of the simulated [CII] luminosity function (LF) and a comparison with observational estimates (in black). The coloured lines represent the best-fit double power-law to the simulated LF and the shaded area represents the central 68% credibility range obtained using MCMC chains. 

1st funding period: 10/2023 – 06/2027

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