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HST observations of three GHRs in M101

HST observations of three GHRs in M101. Rosie Chen et al. arXiv:astro-ph/0410240 Reporter: Feng Li. Outline. Introduction Observations Methods Clusters in three GHRs Discussion. Introduction. GHRs: Giant HII Regions sites of star and cluster formation.

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HST observations of three GHRs in M101

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  1. HST observations of three GHRs in M101 Rosie Chen et al. arXiv:astro-ph/0410240 Reporter: Feng Li

  2. Outline Introduction Observations Methods Clusters in three GHRs Discussion

  3. Introduction • GHRs: • Giant HII Regions sites of star and cluster formation. • Research clusters’ properties and relationship to the ISM around.

  4. NGC 5461,5462,5471 in M101

  5. Outline Introduction Observations Methods Clusters in three GHRs Discussion

  6. Observations HST WFPC2 images

  7. WFPC2 Range :120 nm to 1100 nm WFC—wide field camera PC– planetary camera with narrower-focused optics

  8. HST WFPC2 images

  9. b-F547M , g-F675W, r-Hα filter F656N • Note: cluster candidates-- F547M, F675W HII regions-- Hα-F656N

  10. Compact sources with obvious peaks

  11. Outline Introduction Observations Methods Clusters in three GHRs Discussion

  12. Methods • Methodology: The observed magnitudes and colors of the clusters can be used to determine their ages and masses through comparisons with those predicted by population synthesis models. • Synthetic Photometry: • Starburst99 models (Leitherer et al. ,1999)and BC03 models(Bruzual & Charlot,2003); • IMF: Salpeter initial mass function (1-100M_sun);

  13. SSP: a simple stellar population; • Metallicity: The luminosity, colors, and evolution of a cluster depend on its metallicity; observed oxygen abundances of the GHRs: 0.6-0.9 for NGC 5461 and NGC 5462 1Z_sun model 0.25 for NGC 5471 0.2Z_sun model

  14. Comparisons:

  15. Assessing Ages of Clusters: by examining the interstellar environment of the clusters to assess the approximate ages of the clusters. • a dense, luminous H II region-------------------------- <5Myr • a supershell with a visible cavity---------------------- 5-10Myr • diffuse gas with low surface brightness-------------- >10Myr

  16. Assessing Masses of Clusters: • With a rough estimate of the cluster age, it is then possible to compare the location of a cluster in the CMD with the synthetic evolutionary tracks of clusters to determine the cluster mass. • For MF547M <-9, we estimate the masses of clusters.

  17. Assessing Sizes of Clusters: • effective radius Reff: the radius that encircles half of the cluster light; • Reff can be estimated with the routine ishape(Larsen,1999).

  18. Outline Introduction Observations Methods Clusters in three GHRs Discussion

  19. Clusters in three GHRs • Clusters in NGC 5461 one of the most luminous GHRs in galaxies within 10 Mpc • HII regions: GHR H1105, 3 times as luminous as 30 Dor; GHR H1098, one-third as luminous as 30 Dor; 10 fainter HII regions. • Clusters: MF547M <=-9, cluster 6,8,9,10,11,1 superposed on bright HII regions; M= 1-3*104M_sun

  20. Clusters in NGC 5462 • 3.2kpc x 1.2kpc • HII regions: 33 HII regions H1170,H1176, one-third as luminous as 30 Dor; • Clusters: 25 distributed cluster candidates MF547M <=-9, cluster 6,18,23 , clusters 6 and 23 are not associated with any HII regions, M= 1-2*104M_sun

  21. Clusters in NGC 5471 • Bright knots: A,B,C,D,E A, B, C, and E display bright HII regions centered on clusters, The A component is as luminous as 30 Dor, and the B, C, and E components are comparable to or fainter than NGC 604. • Clusters: 19 candidates MF547M <=-9, 8 clusters M= 0.5-2*104M_sun

  22. Outline Introduction Observations Methods Clusters in three GHRs Discussion

  23. Discussion • The Fraction of Massive Stars Formed in Clusters: • methods to determine this fraction: one is based on the contribution of cluster light to the total light. Second is decided through ionizing luminosity

  24. four regions for analysis:

  25. Result: In the four regions we analyzed, about 25%–50% of the massive stars are formed in R136-class clusters. Note: less massive or luminous clusters contains massive stars.

  26. Cluster Luminosity Function: universal cluster LFs, power law: for young compact cluster systems in merging or starburst galaxies; for nonstarburst spiral galaxies.

  27. Evolutionary Aspects of the Clusters • The cluster mass, age, and size distribution of a cluster system may be used to investigate the dynamic evolution of clusters. • Recent studies of rich clusters in the LMC have shown that the spread in core radius increases with cluster age.

  28. three-dimensional diagram of cluster mass, age, and core radius:

  29. Thank you!

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