ABSTRACT Few intergalactic, plausibly primordial clouds of neutral atomic hydrogen (H i) have been found in the local Universe, suggesting that such structures have either dispersed, become

ionized or produced a stellar population on gigayear timescales. The Leo ring1,2, a massive (_M_H i ≈ 1.8 × 109, denoting the solar mass), 200-kpc-wide structure orbiting the galaxies M105

and NGC 3384 with a 4-Gyr period, is a candidate primordial cloud. Despite repeated atttempts3,4, it has previously been seen only from H i emission, suggesting the absence of a stellar

population. Here we report the detection of ultraviolet light from gaseous substructures of the Leo ring, which we attribute to recent massive star formation. The ultraviolet colour of the

speculate that the complexes are dwarf galaxies observed during their formation, but distinguished by their lack of a dark matter component5. In this regard, they resemble tidal dwarf

galaxies, although without the enrichment preceding tidal stripping. If structures like the Leo ring were common in the early Universe, they may have produced a large, yet undetected,

population of faint, metal-poor, halo-lacking dwarf galaxies. Access through your institution Buy or subscribe This is a preview of subscription content, access via your institution ACCESS

OPTIONS Access through your institution Subscribe to this journal Receive 51 print issues and online access $199.00 per year only $3.90 per issue Learn more Buy this article * Purchase on

SpringerLink * Instant access to full article PDF Buy now Prices may be subject to local taxes which are calculated during checkout ADDITIONAL ACCESS OPTIONS: * Log in * Learn about

institutional subscriptions * Read our FAQs * Contact customer support SIMILAR CONTENT BEING VIEWED BY OTHERS OBSERVATIONS OF A MAGELLANIC CORONA Article Open access 28 September 2022 AN

EXTENDED HALO AROUND AN ANCIENT DWARF GALAXY Article 01 February 2021 A SUPER-EDDINGTON-ACCRETING BLACK HOLE ~1.5 GYR AFTER THE BIG BANG OBSERVED WITH JWST Article Open access 04 November

2024 REFERENCES * Schneider, S. E., Helou, G., Salpeter, E. E. & Terzian, Y. Discovery of a large intergalactic HI cloud in the M96 group. _Astrophys. J._ 273, L1–L15 (1983) Article  ADS

  CAS  Google Scholar  * Schneider, S. E. et al. Multifrequency survey of the intergalactic cloud in the M96 group. _Astron. J._ 97, 666–673 (1989) Article  ADS  CAS  Google Scholar  *

Pierce, M. J. & Tully, R. B. The extragalactic HI cloud in Leo. _Astron. J._ 90, 450–453 (1985) Article  ADS  CAS  Google Scholar  * Kibblewhite, E. J., Cawson, M. G. M., Disney, M. J.

& Phillips, S. An optical search for the intergalactic HI cloud in Leo. _Mon. Not. R. Astron. Soc._ 213, 111–115 (1985) Article  ADS  CAS  Google Scholar  * Schneider, S. E., Salpeter,

E. E. & Terzian, Y. High-resolution observations of the intergalactic HI cloud in the M96 group. _Astron. J._ 91, 13–22 (1986) Article  ADS  CAS  Google Scholar  * Sil’chenko, O. K.,

Moiseev, A. V., Afanasiev, V. L., Chavushyan, V. H. & Valdes, J. R. The Leo I cloud: Secular nuclear evolution of NGC 3379, NGC 3384, and NGC3368? _Astrophys. J._ 591, 185–203 (2003)

Article  ADS  Google Scholar  * Rood, H. J. & Williams, B. A. The intergalactic HI cloud in Leo – a simple modelling of the Spitzer-Baade collision event. _Astrophys. J._ 288, 535–550

(1985) Article  ADS  CAS  Google Scholar  * Spitzer, L. & Baade, W. Stellar populations and collisions of galaxies. _Astrophys. J._ 113, 413–418 (1951) Article  ADS  Google Scholar  *

Bekki, K., Koribalski, B. S., Ryder, S. D. & Couch, W. J. Massive HI clouds with no optical counterparts as high-density regions of intragroup HI rings and arcs. _Mon. Not. R. Astron.

Soc._ 357, L21–L25 (2005) Article  ADS  Google Scholar  * Schneider, S. E. Neutral hydrogen in the M96 group – the galaxies and the intergalactic ring. _Astrophys. J._ 343, 94–106 (1989)

Article  ADS  CAS  Google Scholar  * Reynolds, R. J., Magee, K., Roesler, F. L., Scherb, F. & Harlander, J. H-alpha scans of the intergalactic HI cloud in Leo. _Astrophys. J._ 309,

L9–L12 (1986) Article  ADS  CAS  Google Scholar  * Donahue, M., Aldering, G. & Stocke, J. T. Low surface brightness H-alpha observations of local intergalactic hydrogen clouds.

_Astrophys. J._ 450, L45–L49 (1995) Article  ADS  CAS  Google Scholar  * Martin, D. C. et al. The Galaxy Evolution Explorer: a space ultraviolet survey mission. _Astrophys. J._ 619, L1–L6

(2005) Article  ADS  CAS  Google Scholar  * Bruzual, G. & Charlot, S. Stellar population synthesis at the resolution of 2003. _Mon. Not. R. Astron. Soc._ 344, 1000–1028 (2003) Article 

ADS  Google Scholar  * Gil de Paz, A. et al. Chemical and photometric evolution of extended ultraviolet disks: optical spectroscopy of M83 (NGC 5236) and NGC 4625. _Astrophys. J._ 661,

115–134 (2007) Article  ADS  CAS  Google Scholar  * Meurer, G. et al. Evidence for a non-uniform initial mass function in the local Universe. _Astrophys. J._ (in the press) * Thilker, D. A.

et al. A search for extended ultraviolet disk (XUV-disk) galaxies in the local universe. _Astrophys. J. Suppl. Ser._ 173, 538–571 (2007) Article  ADS  CAS  Google Scholar  * Boissier, S. et

al. Radial variation of attenuation and star formation in the largest late-type disks observed with GALEX. _Astrophys. J. Suppl. Ser._ 173, 524–537 (2007) Article  ADS  CAS  Google Scholar 

* Mihos, J. C., Harding, P., Feldmeier, J. & Morrison, H. Diffuse light in the Virgo Cluster. _Astrophys. J._ 631, L41–L44 (2005) Article  ADS  Google Scholar  * Aloisi, A. et al. I Zw

18 revisited with HST ACS and Cepheids: new distance and age. _Astrophys. J._ 667, L151–L154 (2007) Article  ADS  CAS  Google Scholar  * Ryan-Weber, E. V. et al. The local group dwarf Leo T:

HI on the brink of star formation. _Mon. Not. R. Astron. Soc._ 384, 535–540 (2008) Article  ADS  CAS  Google Scholar  * de Jong, J. T. A. et al. The structural properties and star formation

history of Leo T from deep LBT photometry. _Astrophys. J._ 680, 1112–1119 (2008) Article  ADS  Google Scholar  * Bournaud, F. & Duc, P.-A. From tidal dwarf galaxies to satellite

galaxies. _Astron. Astrophys._ 456, 481–492 (2006) Article  ADS  Google Scholar  * Schneider, S. Neutral hydrogen in the M96 group – evidence for a giant intergalactic ring. _Astrophys. J._

288, L33–L35 (1985) Article  ADS  CAS  Google Scholar  * Millis, R. L. et al. The Deep Ecliptic Survey: a search for Kuiper Belt Objects and Centaurs. I. Description of methods and initial

results. _Astron. J._ 123, 2083–2109 (2002) Article  ADS  Google Scholar  * Adelman-McCarthy, J. K. et al. The sixth data release of the Sloan Digital Sky Survey. _Astrophys. J. Suppl. Ser._

175, 297–313 (2008) Article  ADS  CAS  Google Scholar  * Schlegel, D. J., Finkbeiner, D. P. & Davis, M. Maps of dust infrared emission for use in estimation of reddening and cosmic

microwave background radiation foregrounds. _Astrophys. J._ 500, 525–553 (1998) Article  ADS  Google Scholar  * Cardelli, J. A., Clayton, G. C. & Mathis, J. S. The relationship between

infrared, optical, and ultraviolet extinction. _Astrophys. J._ 345, 245–256 (1989) Article  ADS  CAS  Google Scholar  * O’Donnell, J. E. _R_ ν-dependent optical and near-ultraviolet

extinction. _Astrophys. J._ 422, 158–163 (1994) Article  ADS  Google Scholar  Download references ACKNOWLEDGEMENTS GALEX is a NASA Small Explorer, launched in April 2003. We gratefully

acknowledge NASA’s support of the construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d’Etudes Spatiales, France, and the

Korean Ministry of Science and Technology. This research draws upon data provided by B. Millis as distributed by the National Optical Astronomy Observatory (NOAO) Science Archive. NOAO is

operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation. This research has made use of the NASA/IPAC

Extragalactic Database, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. This research made use of NASA’s Astrophysics Data

System. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Center for Astrophysical Sciences, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA , David A.

Thilker & Luciana Bianchi * Department of Astronomy, Columbia University, Pupin Physics Laboratories, Mail Code 5246, 550 West 120th Street, New York, New York 10027, USA, Jennifer

Donovan & David Schiminovich * Laboratoire d'Astrophysique de Marseille, BP 8, Traverse du Siphon, 13376 Marseille Cedex 12, France , Samuel Boissier * Departamento de Astrofísica,

Facultad de Ciencias Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain Armando Gil de Paz * Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street,

Pasadena, California 91101, USA , Barry F. Madore & Mark Seibert * California Institute of Technology, MC 405-47, 1200 East California Boulevard, Pasadena, California 91125, USA , D.

Christopher Martin Authors * David A. Thilker View author publications You can also search for this author inPubMed Google Scholar * Jennifer Donovan View author publications You can also

search for this author inPubMed Google Scholar * David Schiminovich View author publications You can also search for this author inPubMed Google Scholar * Luciana Bianchi View author

publications You can also search for this author inPubMed Google Scholar * Samuel Boissier View author publications You can also search for this author inPubMed Google Scholar * Armando Gil

de Paz View author publications You can also search for this author inPubMed Google Scholar * Barry F. Madore View author publications You can also search for this author inPubMed Google

Scholar * D. Christopher Martin View author publications You can also search for this author inPubMed Google Scholar * Mark Seibert View author publications You can also search for this

author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to David A. Thilker. POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE FOR FIG. 2 POWERPOINT SLIDE FOR FIG. 3

POWERPOINT SLIDE FOR FIG. 4 RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Thilker, D., Donovan, J., Schiminovich, D. _et al._ Massive star formation

within the Leo ‘primordial’ ring. _Nature_ 457, 990–993 (2009). https://doi.org/10.1038/nature07780 Download citation * Received: 03 November 2008 * Accepted: 13 January 2009 * Issue Date:

19 February 2009 * DOI: https://doi.org/10.1038/nature07780 SHARE THIS ARTICLE Anyone you share the following link with will be able to read this content: Get shareable link Sorry, a

shareable link is not currently available for this article. Copy to clipboard Provided by the Springer Nature SharedIt content-sharing initiative