Supernova Remnants in the Central Starburst Region of

Supernova Remnants in the Central Starburst Region of M 82 EVN Symposium 2006 27/09/06 D. Fenech Jodrell Bank Observatory

Introduction • • M 82 is one of the closest starburst galaxies. First radio observations 1972 (Kronberg & Wilkinson 1975). Ref. Tom’s Talk! ~50 known sources in the central kpc, supernova remnants and HII regions. • Talk will focus on a few compact sources – VLBI observations. • Also discuss VLBI+MERLIN observations! 27/09/06 D. Fenech Jodrell Bank Observatory

VLBI • VLBI observations have concentrated on four most compact sources – 41. 95+57. 5, 43. 31+59. 2, 44. 01+59. 6 and 45. 17+61. 2. (Pedlar et al. 1999, Mc. Donald et al. 2001, Beswick et al. 2006. ) • These sources remain relatively unresolved in MERLIN observations. • Expansion studies of 41. 95+57. 5 and 43. 31+59. 2 using EVN observations from 1986 and 1997, as well as global VLBI observations from 1998 and 2001. • Fifth epoch observed 3 rd March 2005! (global VLBI) 27/09/06 D. Fenech Jodrell Bank Observatory

41. 95+57. 5 • • Most compact source in M 82. Peak flux decreasing by ~8. 5% per year! Bi-polar structure not typical of supernova remnant. Expanding at ~1500 km/s 27/09/06 Previous epoch Images taken from Beswick et al. MNRAS 369, 1221, 2006 D. Fenech Jodrell Bank Observatory

43. 31+59. 2 • Youngest remnant in M 82, first observed in 1972. (Kronberg & Wilkinson 1975) • Almost complete shell structure. • EVN and VLBI observations have followed it’s expansion since 1986. • Expansion velocity ~10, 500 km/s 27/09/06 Previous epoch Images taken from Beswick et al. MNRAS 369, 1221, 2006 D. Fenech Jodrell Bank Observatory

43. 31+59. 2 • Fit various deceleration parameters to data. • Size evolution: D=k. Tδ (Huang et al. 1994) • D size, T is the age, δ is the deceleration parameter. • Birth date unknown but can constrain from first detection in 1972. 27/09/06 Sedov D. Fenech Jodrell Bank Observatory

More VLBI • 44. 01+59. 6 – partial shell structure • 45. 17+61. 2 • 2005 images. • Will study expansion in a similar fashion to 43. 31+58. 3. 45. 17+61. 2 44. 01+59. 6 27/09/06 D. Fenech Jodrell Bank Observatory

Combination • Simultaneous observations of M 82 at 1. 6 GHz using MERLIN seven element array on 3 rd March 2005. • Successfully combined the two datasets to produce images with angular resolutions from ~5 -100 mas • Images comparable to MERLIN deep integration observations at 5 GHz with angular resolution 35 mas. • Study size and structure of ~30 remnants at 1. 6 GHz 27/09/06 D. Fenech Jodrell Bank Observatory

MERLIN Deep Integration 5 GHz Observations • MERLIN observations in 2002 1 -28 April. • 8 day deep integration. • ~ 175 hours on source. • Rms ~ 17μJy beam-1 • 2002 intended to be comparable to 1992 observations as well as a first epoch to future e-MERLIN observations. • 1992 Observations 2 -3 July • Rms ~ 46 μJy beam-1 27/09/06 D. Fenech Jodrell Bank Observatory

Combination 27/09/06 D. Fenech Jodrell Bank Observatory

A Personal Favourite 1. 6 GHz 5 GHz 27/09/06 • 40. 68+55. 1 – largest detected remnant in M 82. • 129 mas at 5 GHz corresponds to ~1. 9 pc. • Expansion of ~ 5000 km/s D. Fenech Jodrell Bank Observatory

Conclusions • Confirmed expansion of 43. 31+58. 3 at 1. 6 GHz. • Continued observations of 41. 95+57. 5. • Observe size and structure of a large number of sources at 1. 6 GHz. • Detailed comparison of sources at 5 and 1. 6 GHz 27/09/06 D. Fenech Jodrell Bank Observatory