Image copyright ©2006- 2010 Spitzer Legacy Program, GALEX Nearby Galaxy Survey & R. Jay GaBany

Unveiling the Nature of M94’s (NGC4736) Outer Region:
a Panchromatic Perspective

An investigation by:
  • Ignacio Trujillo, Inma Martinez-Valpuesta and David Martínez-Delgado   ( IAC),
  • Jorge Peñarrubia   (Institute of Astronomy, Univ. of Cambridge),
  • R. Jay GaBany   (Blackbird Observatory),
  • Michael Pohlen   (Cardiff)

  • We have conducted a deep, multiwavelength analysis to study the outer region of the nearby galaxy, M94 (NGC4736). We found that non-optical data supports the idea that the outskirts of this galaxy were not formed by a closed stellar ring, as traditionally claimed in the literature, but by an extensive structure of spiral arms.

    In this sense, M94 (NGC4736) is a good example of a Type III galaxy with a bright outer disk. Significantly, we found that the outer disk of this galaxy is active. It contains approximately 23% of the galaxy's total stellar mass and contributes about 10% of the galaxy's new stars. In fact, the star formation rate of the outer disk is approximately two times greater than the inner disk because it is more efficient per unit of stellar mass.

    There are several possible external events that could have led to the origin of M94's outer disk including the accretion of a satellite galaxy or the gravitational interaction with a nearby star system. However, our research found problems with each of these scenarios. So, we looked for an internal explanation and that approach produced the most plausible result. Therefore, we strongly suspect that the inner disk of M94 (NGC4736) is an oval distortion which led to the creation of this galaxy's peripheral disk. Our models also demonstrate that the oval distortion can
    • dynamically create a spiral arm structure which subsequently triggers the (relatively) high star formation rate our data reported and
    • form an inner ring similar to what is observed in this galaxy. More...

    • Click here for the optical image
    • Click here to view multi-spectral comparison imagery.
    • View a N-body simulation movie here.
    • Click here for a larger image.
    • Click here to download complete PDF documentation.

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