Early formation and recent starburst activity in the nuclear disk of the Milky Way

Abstract

The nuclear disk is a dense stellar structure at the centre of the Milky Way, with a radius of ~150 pc (ref. 1). It has been a place of intense star formation in the past several tens of millions of years1,2,3, but its overall formation history has remained unknown2. Here, we report that the bulk of its stars formed at least 8 Gyr ago. After a long period of quiescence, a starburst event followed about 1 Gyr ago that formed roughly 5% of its mass within ~100 Myr, in what may arguably have been one of the most energetic events in the history of the Milky Way. Star formation continued subsequently on a lower level, creating a few per cent of the stellar mass in the past ~500 Myr, with an increased rate up to ~30 Myr ago. Our findings contradict the previously accepted paradigm of quasi-continuous star formation at the Galactic Centre4. The long quiescent phase agrees with the overall quiescent history of the Milky Way2,5 and suggests that our Galaxy’s bar may not have existed until recently, or that gas transport through the bar was extremely inefficient during a long stretch of the Milky Way’s life. Consequently, the central black hole may have acquired most of its mass already in the early days of the Milky Way.

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Fig. 1: Observed region, CMD and KLF.
Fig. 2: SFH of the nuclear stellar disk as derived from the model fits to the KLF with BaSTI (green) and MIST (light green) isochrones.

Data availability

All the raw data used in this study are available at the ESO Science Archive Facility (http://archive.eso.org/eso/eso_archive_main.html) under programme IDs 195.B-0283 and 091.B-0418. The final version of the GALACTICNUCLEUS survey (images and point source catalogues) will be released to the public via the ESO Phase 3 platform within the next year. This Letter makes use of the GALACTICNUCLEUS data published in ref. 7. The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.

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Acknowledgements

This work has made use of BaSTI web tools. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 614922. This work is based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 195.B-0283 and 091.B-0418. We thank the staff of ESO for their great efforts and helpfulness. F.N.-L. acknowledges financial support from a MECD pre-doctoral contract, code FPU14/01700. We acknowledge financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). R.S., A.T.G.-C. and B.S. acknowledge financial support from the national grant PGC2018-095049-B-C21 (MCIU/AEI/FEDER, UE). F.N. acknowledges financial support through Spanish grants ESP2015-65597-C4-1-R and ESP2017-86582-C4-1-R (MINECO/FEDER) and from the Spanish State Research Agency (AEI) through the Unidad de Excelencia “María de Maeztu” -Centro de Astrobiología (CSIC-INTA) project no. MDM-2017-0737. N.N. acknowledges support by Sonderforschungsbereich SFB 881 ‘The Milky Way System’ (subproject B8) of the German Research Foundation (DFG).

Author information

F.N.-L. reduced the data and produced the catalogue, carried out the main part of the analysis and wrote the draft version of the manuscript. R.S. planned the research project, collaborated in the data analysis and interpretation, and organized the writing of the manuscript. A.T.G.-C. collaborated in the data reduction. S.C. computed the theoretical LFs. E.G.-C., B.S., H.D., N.N., M.H., F.N., S.N., A.F.-K. and J.H.V.G. participated actively in the scientific discussion and interpretation and contributed to the production of the final version of the manuscript.

Correspondence to Francisco Nogueras-Lara.

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Competing interests

The authors declare no competing interests.

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Peer review information Nature Astronomy thanks Beatriz Barbuy and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 J-band density map.

The dark patches are clouds of molecular gas and dust. They impede the view into the GC and were therefore excluded from this study (white dashed line contours). The central cross-shaped region corresponds to a low completeness region.

Extended Data Fig. 2 Extinction map AKs.

White patches and pixels indicate regions where the number of stars was not enough to compute an extinction value. Those regions mainly correspond to dark clouds and were previously excluded from our analysis.

Extended Data Fig. 3 CMD Ks versus H-Ks (Vega magnitude system) showing original data (red dots) and the result after applying the extinction correction (in black).

The black dashed line shows the cut in H-Ks to exclude the foreground population. The red and cyan lines correspond to BaSTI isochrones of an old and a young population ~10 Gyr and ~1 Gyr, respectively according to our results. The zoom shows the RC region. Only a random fraction of the total amount of stars is shown for clarity.

Extended Data Fig. 4 Completeness at Ks (Vega magnitude system).

The red dashed line shows the 80 % completeness limit. The error bars, in blue, show the 1-sigma uncertainties.

Extended Data Fig. 5 Recovery of simulated star formation histories.

Red dots: Assumed SFH. Green, blue and orange bars: Recovered star formation. The error bars indicate the 1-sigma uncertainty.

Supplementary information

Supplementary Information

Supplementary discussion and Figs. 1–8.

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Nogueras-Lara, F., Schödel, R., Gallego-Calvente, A.T. et al. Early formation and recent starburst activity in the nuclear disk of the Milky Way. Nat Astron (2019). https://doi.org/10.1038/s41550-019-0967-9

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