A tidally distorted dwarf galaxy near NGC 4449


NGC 4449 is a nearby Magellanic irregular starburst galaxy1 with a B-band absolute magnitude of −18 and a prominent, massive, intermediate-age nucleus2 at a distance from Earth of 3.8 megaparsecs (ref. 3). It is wreathed in an extraordinary neutral hydrogen (H i) complex, which includes rings, shells and a counter-rotating core, spanning 90 kiloparsecs (kpc; refs 1, 4). NGC 4449 is relatively isolated5, although an interaction with its nearest known companion—the galaxy DDO 125, some 40 kpc to the south—has been proposed as being responsible for the complexity of its H i structure6. Here we report the presence of a dwarf galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band absolute magnitude of −13.4 and a half-light radius of 2.7 kpc, with a full extent of around 8 kpc. It is in a transient stage of tidal disruption, similar to that of the Sagittarius dwarf7 near the Milky Way. NGC 4449B exhibits a striking S-shaped morphology that has been predicted for disrupting galaxies7,8 but has hitherto been seen only in a dissolving globular cluster9. We also detect an additional arc or disk ripple embedded in a two-component stellar halo, including a component extending twice as far as previously known, to about 20 kpc from the galaxy’s centre.

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Figure 1: Image and halo-subtracted imagery of NGC 4449.
Figure 2: Surface photometry of NGC 4449 and NGC 4449B.


  1. 1

    Hunter, D. A., van Woerden, H. & Gallagher, J. S. Neutral hydrogen and star formation in the irregular galaxy NGC 4449. Astron. J. 118, 2184–2210 (1999)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Böker, T. et al. A young stellar cluster in the nucleus of NGC 4449. Astron. J. 121, 1473–1481 (2001)

    ADS  Article  Google Scholar 

  3. 3

    Annibali, R. et al. Starbursts in the local Universe: New Hubble Space Telescope Advanced Camera for Surveys observations of the irregular galaxy NGC 4449. Astron. J. 135, 1900–1916 (2008)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Hunter, D. et al. The nature of extended HI gas around NGC 449: the Dr. Jekyll/Mr. Hyde of irregular galaxies. Astrophys. J. 495, L47–L50 (1998)

    ADS  CAS  Article  Google Scholar 

  5. 5

    de Vaucouleurs, G. in Galaxies and the Universe (eds Sandage, A., Sandage, M. & Kristian, J. ) 557–597 (Univ. Chicago Press, 1975)

    Google Scholar 

  6. 6

    Theis, C. & Koble, S. Multi-method-modeling of interacting galaxies. I. A unique scenario for NGC 4449? Astron. Astrophys. 370, 365–383 (2001)

    ADS  Article  Google Scholar 

  7. 7

    Peñarrubia, J. et al. The signature of Galactic tides in Local Group dwarf spheroidals. Astrophys. J. 698, 222–232 (2009)

    ADS  Article  Google Scholar 

  8. 8

    Capuzzo Dolcetta, R., di Matteo, P. & Miocchi, P. Formation and evolution of clumpy tidal tails around globular clusters. Astron. J. 129, 1906–1921 (2005)

    ADS  Article  Google Scholar 

  9. 9

    Odenkirchen, M. et al. The extended tails of Palomar 5: a 10° arc of globular cluster tidal debris. Astron. J. 126, 2385–2407 (2003)

    ADS  Article  Google Scholar 

  10. 10

    Brosch, N. et al. The Centurion 18 telescope of the Wise Observatory. Astrophys. Space Sci. 314, 163–176 (2008)

    ADS  Article  Google Scholar 

  11. 11

    Schombert, J. & Wallin, J. F. Arp 227: a case for shells without mergers? Astron. J. 94, 300–305 (1987)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Wallin, J. F. & Struck-Marcell, C. A collisional model for the formation of ripples in early-type disk galaxies. Astron. J. 96, 1850–1860 (1988)

    ADS  Article  Google Scholar 

  13. 13

    Purcell, C. W. et al. The Sagittarius impact as an architect of spirality and outer rings in the Milky Way. Nature 477, 301–303 (2011)

    ADS  CAS  Article  Google Scholar 

  14. 14

    Martin, D. C. et al. The Galaxy Evolution Explorer: a space ultraviolet survey mission. Astrophys. J. 619, L1–L6 (2005)

    ADS  CAS  Article  Google Scholar 

  15. 15

    Neff, S. G. et al. Ultraviolet emission from stellar populations within tidal tails: catching the youngest galaxies in formation? Astrophys. J. 619, L91–L94 (2005)

    ADS  CAS  Article  Google Scholar 

  16. 16

    Dale, D. A. et al. The Spitzer Local Volume Legacy: survey description and infrared photometry. Astrophys. J. 703, 517–556 (2009)

    ADS  CAS  Article  Google Scholar 

  17. 17

    Wang, J. L. et al. Luminous infrared galaxies in the local Universe. Astrophys. J. 649, 722–729 (2006)

    ADS  CAS  Article  Google Scholar 

  18. 18

    Majewski, S. R. et al. Discovery of Andromeda XIV: a dwarf spheroidal dynamical rogue in the Local Group? Astrophys. J. 670, L9–L12 (2007)

    ADS  MathSciNet  CAS  Article  Google Scholar 

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R.M.R. acknowledges support from the National Science Foundation. The Saturn Lodge 0.7-m telescope was funded and implemented by R.M.R. and F.A.L. The authors acknowledge members of the Polaris Observatory Association, who maintain the observatory infrastructure and who assisted in the construction and implementation of the telescope and enclosure, and J. Riffle, who designed and built the Centurion 28-inch telescope. This research has made use of the NASA/IPAC Extragalactic Database (NED) and of the Sloan Digital Sky Survey.

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R.M.R. conceived the project, obtained the data and coordinated the activity. M.L.M.C. fitted the surface photometry of NGC 4449 and NGC 4449B. C.M.B., F.M.L. and D.B.R. analysed and reduced various aspects of the dataset, including the surface photometry. F.A.L. and R.M.R. implemented the Saturn Lodge 0.7-m telescope and detector system. A.K. provided insight on dwarf galaxies and discussion, and A.B. provided a discussion of theoretical implications.

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Correspondence to R. M. Rich.

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Rich, R., Collins, M., Black, C. et al. A tidally distorted dwarf galaxy near NGC 4449. Nature 482, 192–194 (2012). https://doi.org/10.1038/nature10837

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