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Resolving the H i in damped Lyman α systems that power star formation

Abstract

Reservoirs of dense atomic gas (primarily hydrogen) contain approximately 90 per cent of the neutral gas at a redshift of 3, and contribute to between 2 and 3 per cent of the total baryons in the Universe1,2,3,4. These ‘damped Lyman α systems’—so called because they absorb Lyman α photons within and from background sources—have been studied for decades, but only through absorption lines present in the spectra of background quasars and γ-ray bursts5,6,7,8,9,10. Such pencil beams do not constrain the physical extent of the systems. Here we report integral-field spectroscopy of a bright, gravitationally lensed galaxy at a redshift of 2.7 with two foreground damped Lyman α systems. These systems are greater than 238 kiloparsecs squared in extent, with column densities of neutral hydrogen varying by more than an order of magnitude on scales of less than 3 kiloparsecs. The mean column densities are between 1020.46 and 1020.84 centimetres squared and the total masses are greater than 5.5 × 108–1.4 × 109 times the mass of the Sun, showing that they contain the necessary fuel for the next generation of star formation, consistent with relatively massive, low-luminosity primeval galaxies at redshifts greater than 2.

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Fig. 1: Spatial variation of neutral hydrogen column density.
Fig. 2: Maps of H i and metal absorption strengths in the absorber source-plane.
Fig. 3: Lyman α emission maps of the DLA host galaxies.
Fig. 4: Lyman α emission from the background DLAs in their source planes.

Data availability

Data that support the findings of this study are publicly available at the Keck Observatory Archive, https://www2.keck.hawaii.edu/koa/public/koa.php, under project codes N083 and K338 and the Barbara A. Mikulski Archive for Space Telescope under project code GO-13003. Fully reduced data are available from the corresponding author upon request.

Code availability

All codes used in this work are publicly available. The H i column density measurements were performed using the linetools package (https://doi.org/10.5281/zenodo.168270). Reduction and analysis of the KCWI data cubes were done using the kcwitools package (https://doi.org/10.5281/zenodo.6079396). The lensing raytracing and absorption line measurements are done using the rbcodes package (https://doi.org/10.5281/zenodo.6079264). HST image analysis and lens modelling were performed with AstroDizzle31 software and Lenstool34, respectively.

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Acknowledgements

This work was supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration (NASA) through the agency’s scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research was conducted, in part, by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. We wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This research made use of Montage. It is funded by the National Science Foundation under grant number ACI-1440620, and was previously funded by the NASA’s Earth Science Technology Office, Computation Technologies Project, under cooperative agreement number NCC5-626 between NASA and the California Institute of Technology.

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Authors and Affiliations

Authors

Contributions

R.B. and J.M.O. developed the idea for the project, wrote the NASA/Keck telescope proposal and designed and performed the observations. R.B. developed the analysis tools, performed the analysis, devised original ways to interpret the results and authored majority of the text. J.M.O. reduced the KCWI data. A.S. performed the metal absorption line measurements. K.S. performed the lens model and provided Extended Data Fig. 1. J.R.R. provided the ancillary data from MagE and metal absorber information from MagE spectra. J.C., J.M.O. and R.B. provided steps to correct astrometric offsets and J.C. confirmed the redshift of the second DLA, and contributed to the interpretations. M.M., L.R., G.D., D.C.M., A.M.M., P.M. and J.D.N. developed the KCWI data reduction pipeline and built and delivered the instrument when initial commissioning data provided the data needed to verify the target as an object of interest. All authors, including J.M.O., J.R.R. and J.C., contributed to the overall interpretation of the results and various aspects of the analysis and writing.

Corresponding author

Correspondence to Rongmon Bordoloi.

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Nature thanks Zachary Hafen and Marcel Neeleman for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Source plane reconstruction of SGAS J152745.1+065219.

a, WFC3/HST images of SGAS J152745.1+065219 in the WFC3-IR F160W, WFC3-UVIS F606W and WFC3-UVIS F475W filters32. North is up and east is to the left. The gravitational lensing critical curve is shown in red, representing areas in the image plane with extreme magnification. Three boxes mark the locations of the three partially lensed images. The lensing potential is caused by the z = 0.43 elliptical galaxy at the centre of this field, boosted by a cluster of galaxies at z = 0.39, located within 1 arcminute in projection northeast of this galaxy. b, The reconstructed source plane image of the galaxy. The source-plane caustic is marked in yellow, representing regions with extreme magnification, and defining the multiplicity of the strongly lensed source. The region interior to the cusp is lensed into three images, whereas areas outside the cusp are magnified, but not multiply imaged.

Extended Data Fig. 2 Pairwise H i column density variation versus physical separation.

Variation in H i column density between six individual pointings to the background arc as a function of physical separation between them. Error bars correspond to the ±1σ uncertainty in column density ratios. The z ≈ 2.5 DLA (blue squares) shows an order-of-magnitude variation in column density in 2–3 kpc separations. This suggests significant small-scale variation inside the DLA, at 2–3 kpc physical scales. By contrast, the z ≈ 2.05 DLA (red circles) shows very little variation in column densities across different sightlines. The red circles are offset in the x direction by 1 kpc for clarity of presentation.

Extended Data Fig. 3 Variation in metal absorption line strengths of the two DLA systems.

ae, Metal absorption line strength variations of different ions across the arc for the z ≈ 2.5 DLA (blue squares) and the z ≈ 2.05 DLA (red circles), respectively. The physical separations are in the source-plane of the absorbers and centred on the centre of the background arc. The filled symbols are detections, and the open symbols are 2σ limits of non-detections. Error bars correspond to the ±1σ uncertainty measurement of absorption strengths. In all cases, the z ≈ 2.5 DLA exhibits much weaker metal absorption lines as compared to the z ≈ 2.05 DLA.

Extended Data Fig. 4 Spatial variation of neutral hydrogen column density of the z ≈ 2.05 DLA.

a, The extracted 1D Lyman α absorption profiles are shown for apertures A–C. The best-fit Voigt profiles with ±1σ error bounds are shown as solid green and dashed orange lines, respectively. The DLA column densities are marked in each panel and are in units of atoms cm−2. In each absorption profile, the DLA absorption trough reaches zero flux, indicating that the aperture is fully covering the DLA gas cloud. The emission spike in the middle of the absorption trough corresponds to Lyman α emission leaking out of the corresponding DLA host galaxy. b, As in a, but for apertures D–F.

Extended Data Table 1 Absorption line measurements for the z = 2.54290 DLA
Extended Data Table 2 Absorption line measurements for the z = 2.05601 DLA

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Bordoloi, R., O’Meara, J.M., Sharon, K. et al. Resolving the H i in damped Lyman α systems that power star formation. Nature 606, 59–63 (2022). https://doi.org/10.1038/s41586-022-04616-1

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