Stellar Clusters in NGC 1313: Evidence of Infant Mortality

We present evidence that the infant mortality of stellar clusters is likely to be a major and very efficient process for the dissolution of young clusters in the spiral galaxy NGC 1313. Performing stellar PSF photometry on archival HST/ACS images of the galaxy, we find that a large fraction of early B-type stars are seen outside of star clusters and well spread within the galactic disk, consistent with the scenario of infant mortality. We also calculate the UV flux produced by the stars in and out of the clusters and find that 75%-90% of the UV flux in NGC 1313 is produced by stars outside the clusters. These results suggest that the infant mortality of star clusters is probably the underlying cause of the diffuse UV emission in starburst galaxies. Infant mortality would also explain the numerous B-type stars observed in the background field of our Galaxy as well. We exclude the possibility that unresolved low-mass star clusters and scaled OB associations might be the main sources for the diffuse UV emission.

[1]  S. M. Fall,et al.  Connection between the Age Distributions of Star Clusters and Field Stars: A First Application to the Small Magellanic Cloud , 2006, astro-ph/0609360.

[2]  S. Roser,et al.  Population analysis of open clusters: radii and mass segregation , 2006, astro-ph/0606225.

[3]  N. Bastian,et al.  Evidence for the Strong Effect of Gas Removal on the Internal Dynamics of Young Stellar Clusters , 2006, astro-ph/0602465.

[4]  S. M. Fall,et al.  The Age Distribution of Massive Star Clusters in the Antennae Galaxies , 2005, astro-ph/0509293.

[5]  C. Leitherer,et al.  The Stellar Content of Nearby Star-forming Galaxies. III. Unravelling the Nature of the Diffuse Ultraviolet Light , 2005, astro-ph/0505024.

[6]  Linda J. Smith,et al.  The Formation and Evolution of Massive Young Star Clusters , 2004 .

[7]  R. Walterbos,et al.  Star Formation in H I-Selected Galaxies. I. Sample Characteristics , 2004, astro-ph/0406317.

[8]  J. M. Mas-Hesse,et al.  NGC 604, the Scaled OB Association (SOBA) Prototype. I. Spatial Distribution of the Different Gas Phases and Attenuation by Dust , 2004, astro-ph/0406130.

[9]  W. K. Huchtmeier,et al.  A Catalog of Neighboring Galaxies , 2004 .

[10]  C. Leitherer,et al.  The Stellar Content of Henize 2-10 from Space Telescope Imaging Spectrograph Ultraviolet Spectroscopy , 2003 .

[11]  C. Lada,et al.  Embedded Clusters in Molecular Clouds , 2003, astro-ph/0301540.

[12]  Brazil.,et al.  A Catalogue of infrared star clusters and stellar groups , 2002, astro-ph/0210302.

[13]  J. Newman,et al.  Deviations from the Local Hubble Flow. I. The Tip of the Red Giant Branch as a Distance Indicator , 2002, astro-ph/0204192.

[14]  R. Walterbos,et al.  Far-Ultraviolet and Hα Imaging of Nearby Spiral Galaxies: The OB Stellar Population in the Diffuse Ionized Gas , 2001, astro-ph/0107449.

[15]  N. Benı́tez,et al.  The Photometric Performance and Calibration of the Hubble Space Telescope Advanced Camera for Surveys , 2005, astro-ph/0507614.

[16]  L. Ho,et al.  Hubble Space Telescope Ultraviolet Images of Five Circumnuclear Star-Forming Rings , 1996, astro-ph/9604012.

[17]  L. Ho,et al.  Hubble Space Telescope Observations of Circumnuclear Star-Forming Rings in NGC 1097 and NGC 6951 , 1995 .

[18]  R. Tully.  Nearby Galaxies Catalog , 1988 .

[19]  K. Janes,et al.  Properties of the Open Cluster System , 1988 .

[20]  J. O. W. Ardle,et al.  PARSEC-SCALE CIRCULAR POLARIZATION OBSERVATIONS OF 40 BLA ZARS , 2001 .

[21]  T. Heckman,et al.  Accepted for publication in The Astronomical Journal , 1995 .

[22]  Robert L. Kurucz,et al.  Model Atmospheres for Population Synthesis , 1992 .