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# The nature of giant clumps in distant galaxies probed by the anatomy of the cosmic snake

## Abstract

Giant stellar clumps are ubiquitous in high-redshift galaxies1,2. They are thought to play an important role in the build-up of galactic bulges3 and as diagnostics of star formation feedback in galactic discs4. Hubble Space Telescope (HST) blank field imaging surveys have estimated that these clumps have masses of up to 109.5 M and linear sizes of 1 kpc5,6. Recently, gravitational lensing has also been used to get higher spatial resolution7,8,9. However, both recent lensed observations10,11 and models12,13 suggest that the clumps’ properties may be overestimated by the limited resolution of standard imaging techniques. A definitive proof of this observational bias is nevertheless still missing. Here we investigate directly the effect of resolution on clump properties by analysing multiple gravitationally lensed images of the same galaxy at different spatial resolutions, down to 30 pc. We show that the typical mass and size of giant clumps, generally observed at ~1 kpc resolution in high-redshift galaxies, are systematically overestimated. The high spatial resolution data, only enabled by strong gravitational lensing using currently available facilities, support smaller scales of clump formation by fragmentation of the galactic gas disk via gravitational instabilities.

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• ### The Molecular Cloud Lifecycle

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## Acknowledgements

The work of A.C., D.S., M.D.-Z., L.M. and V.T. is supported by the STARFORM Sinergia Project funded by the Swiss National Science Foundation. J.R. acknowledges support from the European Research Council starting grant 336736-CALENDS. P.G.P.-P. acknowledges support from Spanish Government MINECO grants AYA2015-70815-ERC and AYA2015-63650-P. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM), partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC). Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).

## Author information

Authors

### Contributions

Data analysis and interpretation: A.C., D.S., J.R., P.P.-G., M.D.-Z., L.M. and V.T. SED fitting: D.S. and A.C. Photometry: A.C. and P.P-G. Lens modelling: J.R. and A.C. Drafting text, figures and methods: the bulk of the text was written by A.C. All authors commented on the manuscript at all stages.

### Corresponding author

Correspondence to Antonio Cava.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

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## Electronic supplementary material

### Supplementary Information

Supplementary Figures 1–10 and Supplementary Tables 1–5

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Cava, A., Schaerer, D., Richard, J. et al. The nature of giant clumps in distant galaxies probed by the anatomy of the cosmic snake. Nat Astron 2, 76–82 (2018). https://doi.org/10.1038/s41550-017-0295-x

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• DOI: https://doi.org/10.1038/s41550-017-0295-x

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