1. Starburst Galaxies Starburst Galaxies Tom Muxlow 8 th EVN Symposium, Torun Sept 27 2006 Jodrell Bank Observatory Jodrell Bank Observatory University of Manchester UK University of Manchester UK A brief introduction to star-forming galaxies, both nearby and at high redshift – with regard to what high resolution radio observationshave revealed A brief introduction to star-forming galaxies, both nearby and at high redshift – with regard to what high resolution radio observations have revealed,

2. What is a starburst galaxy? High star-formation rate ~ 10 – 100 M๏/year – much higher than normal gas-rich galaxies (eg Milky Way star-formation rate ~ 1 – 5 M๏/year) High star-formation rate ~ 10 – 100 M๏/year – much higher than normal gas-rich galaxies (eg Milky Way star-formation rate ~ 1 – 5 M๏/year) Total gas content can be estimated from integrated line profiles Total gas content can be estimated from integrated line profiles Integrated HI profile  HI Mass Integrated HI profile  HI Mass From gas available to fuel the star-formation event  lifetimes From gas available to fuel the star-formation event  lifetimes ~few x 10 9 years for Milky Way – can be maintained for the lifetime of the galaxy ~few x 10 9 years for Milky Way – can be maintained for the lifetime of the galaxy ~10 8 years for starburst galaxy - short compared with the galaxy lifetime ~10 8 years for starburst galaxy - short compared with the galaxy lifetime  Implies a ‘burst’ of star-formation  Implies a ‘burst’ of star-formation

3. What is a starburst galaxy? Typically they are disturbed galaxies, many involved in mergers Typically they are disturbed galaxies, many involved in mergers Star-formation sites are marked out by the rare highly- luminous high-mass stars Star-formation sites are marked out by the rare highly- luminous high-mass stars SED often dominated by strong (F)IR emission SED often dominated by strong (F)IR emission NGC 1808 NGC 4038 /4039

4. Starburst galaxies Size of starburst region typically ~ kpc Size of starburst region typically ~ kpc Radio synchrotron emission from plasma (SNR) Radio synchrotron emission from plasma (SNR) Strong FIR emission from UV-heated dust (O stars) Strong FIR emission from UV-heated dust (O stars) L FIR >10 10 L o (ULIRGS>10 12 L o ) L FIR >10 10 L o (ULIRGS>10 12 L o ) RadioFIR Thermal free-free emission from HII regions Thermal free-free emission from HII regions

5. Estimating star-formation rate (SFR) SFR indicators are many and varied Extensively studied - eg Cram et al 1998 ApJ 507 155 Extensively studied - eg Cram et al 1998 ApJ 507 155 FIR, Radio Continuum, UV, SN etc…. FIR, Radio Continuum, UV, SN etc…. SFR estimated from FIR and radio are found to be highly correlated over many orders of magnitude SFR estimated from FIR and radio are found to be highly correlated over many orders of magnitude x5.5 to convert to SFR over complete stellar mass range (>0.1 M๏) [Salpeter IMF] Both FIR and radio emission determined by the properties of high-mass stars SFR can also be estimated from the numbers of O stars required to ionize the medium and produce thermal free- free continuum emission and forbidden lines (eg [NeII]) SFR can also be estimated from the numbers of O stars required to ionize the medium and produce thermal free- free continuum emission and forbidden lines (eg [NeII]) Measuring UV flux directly suffers from extinction problems Measuring UV flux directly suffers from extinction problems No dust extinction problems for thermal free-free emission, but difficult to separate from non-thermal component No dust extinction problems for thermal free-free emission, but difficult to separate from non-thermal component  SN rate can be used to derive the SFR for stars more massive than 8M๏

6. Arp 220 and M82 Arp 220 and M82 Nearby starburst galaxies Arp 220 HST ACS M82 Spitzer

7. Arp220 Merging ULIRG 77Mpc Merging ULIRG 77Mpc HI emission VLA C+D array HI emission VLA C+D array Low angular resolution Low angular resolution (Hibberd et al NRAO) (Hibberd et al NRAO) Dominated by HI absorption Dominated by HI absorption

8. HI absorption studies at high angular resolution probe the merger dynamics HI absorption studies at high angular resolution probe the merger dynamics Two counter-rotating disks – original galaxy cores that have survived the initial encounter Two counter-rotating disks – original galaxy cores that have survived the initial encounter Now in final stages of merger Now in final stages of merger MERLIN - Mundell, Ferruit & Pedlar (2001) OH mega-masers within eastern disk show a velocity gradient of 320 km s -1 kpc -1 OH mega-masers within eastern disk show a velocity gradient of 320 km s -1 kpc -1 Radius ~80pc  Enclosed mass ~1.2x10 7 M ๏ Radius ~80pc  Enclosed mass ~1.2x10 7 M ๏ No 10 8 M ๏ BH… but Chandra finds hard X-rays in western disk No 10 8 M ๏ BH… but Chandra finds hard X-rays in western disk Clements et al 2002 Rovilos, Diamond et al (2003) Masers are excellent tracers of star-formation See Sessions 7 & 8 this afternoon – and Megan Argo’s poster on OH masers in M82

9. Arp220 Global VLBI Lonsdale, Lonsdale, Diamond, Conway, Smith, Rovilos, Parra, Thrall… et al Both east and west components show radio Sn and SNR. No obvious AGN seen – but in west component some unusual structures & velocity gradients detected…… Both east and west components show radio Sn and SNR. No obvious AGN seen – but in west component some unusual structures & velocity gradients detected…… MERLIN Latest images - New detections + variability Latest images - New detections + variability Sn + SNR + AGN ? - See Rodrigo Parra’s presentation

10. Starbursts can have embedded AGN Often the AGN is obscured and may only contribute a small proportion of the total flux density Often the AGN is obscured and may only contribute a small proportion of the total flux density eg ULIRG Mkn273 – twin merging nuclei Knapen et al 1997 eg ULIRG Mkn273 – twin merging nuclei Knapen et al 1997 Flat spectrum radio component detected Flat spectrum radio component detected HST Contours: MERLIN 5GHz Greyscale: CFHT K-Band

11. Mkn273 Dynamical signature of super-massive object Dynamical signature of super-massive object MERLIN HI absorption (Cole et al 1999) MERLIN HI absorption (Cole et al 1999) Rotating disk Rotating disk M<500pc ~1.4x10 10 M o M<500pc ~1.4x10 10 M o VLBA (Carilli & Taylor 2000) VLBA (Carilli & Taylor 2000) M<220pc ~2x10 9 M o M<220pc ~2x10 9 M o EVN (Bondi et al 2005) EVN (Bondi et al 2005) Compact AGN candidate Compact AGN candidate Could be a compact RSn Could be a compact RSn Hard X-rays  AGN Hard X-rays  AGN

12. M82 One of the nearest (3.2 Mpc) & best studied starburst galaxies One of the nearest (3.2 Mpc) & best studied starburst galaxies Starburst located in central ~1 kpc Starburst located in central ~1 kpc Starburst driven wind (H  ) - Subaru image, X-rays - (Chandra) Starburst driven wind (H  ) - Subaru image, X-rays - (Chandra)

13. Triggering the starburst - tidal interaction over the past ~200 x 10 6 years Interaction with M81/NGC3077 – M82 in high-speed motion with respect to the M81/NGC3077 group Interaction with M81/NGC3077 – M82 in high-speed motion with respect to the M81/NGC3077 group HI observations Yun et al (1994) HI observations Yun et al (1994) M82 M81 NGC3077 -34 km/s +14 km/s +203 km/s

14. Previous Starburst Activity ? - evidence from optical clusters Several ‘super’ starclusters identified ~ 1kpc NE of the centre of M82 Several ‘super’ starclusters identified ~ 1kpc NE of the centre of M82 Correspond to 10 9 year old fossil starburst. Ages derived from evolutionary spectral synthesis models Correspond to 10 9 year old fossil starburst. Ages derived from evolutionary spectral synthesis models Last close encounter with M81 (de Grijs et al 2001) Last close encounter with M81 (de Grijs et al 2001) N E

15. Current starburst: - has existed for at least 50 x 10 6 years - heavily obscured optically ~ 20-30 M v Tidal interaction has channeled large amounts of gas into the central region of M82 inducing a burst of star- formation Current supernova rate ~ 0.1 yr -1 Current star-formation rate (for M > 5 M๏) ~ 2 M๏ yr -1

16. M82 VLA HI absorption (Wills et al 2000) Velocity field shows strong rotation Velocity field shows strong rotation Detailed fit along major axis suggests an inner bar which is thought to be fuelling the central starburst Detailed fit along major axis suggests an inner bar which is thought to be fuelling the central starburst Also seen in molecular lines (eg CO) Also seen in molecular lines (eg CO)

17. M82 Supernova remnants O & B stars are tracers recent star-formation O & B stars are tracers recent star-formation Typically these become supernovae after ~ 10 7 years Typically these become supernovae after ~ 10 7 years  SNR trace out star-formation sites ~10 7 years old  SNR trace out star-formation sites ~10 7 years old 50-60 compact sources discovered in M82 50-60 compact sources discovered in M82 All resolved with MERLIN+VLBI All resolved with MERLIN+VLBI Most are SNR Most are SNR Although ~16 are compact HII regions Although ~16 are compact HII regions

18. MERLIN (MFS) +VLA 1995 M82 SNR – How old are they? MERLIN resolves all the SNR visible in M82 – derive size distribution Cumulative number-size diagram infers that SNR expansion slows with time: Cumulative number-size diagram infers that SNR expansion slows with time: D ~ t 0.6 D ~ t 0.6 Assuming an initial expansion rate ~ 5000km/s  ages ~1000 yr with a SNR appearing every ~ 20-40 yr Expansion velocities of ~5-10,000km/s are detected by MERLIN and VLBI

19. VLBI Imaging of SNR - in M82 and other nearby starburst galaxies Measure expansion velocities and deceleration Measure expansion velocities and deceleration Probe the nature of the environment – thought to be extremely clumpy Probe the nature of the environment – thought to be extremely clumpy Investigate how the ejecta interact with the environment and eventually move into the Sedov phase of expansion Investigate how the ejecta interact with the environment and eventually move into the Sedov phase of expansion Do SN in environmental voids produce no observable remnant? In M82, SFR  SN rate of 1 every ~12 years (cf SNR rate of 1 every ~30 years) Do SN in environmental voids produce no observable remnant? In M82, SFR  SN rate of 1 every ~12 years (cf SNR rate of 1 every ~30 years) M82 SNR43.31+592 0.5 pc M81 SN1993J: Marcaide et al Bietenholz, Bartel, Rupen et al SN43.31+592: Beswick et al 2006 See review talk by Rob Beswick on SNR-Session 9 See talk by Danielle Fenech on M82 SNR

20. 41.95+575 has decreased in flux density by 8.5% per year since monitoring began in the 1970s. 100 years at 8.5%/yr  x 3500 !!! In 2000 41.95+575 had a flux density of 24mJy – at birth 100 years ago it would have been ~100 Jy !!!! What sort of violent event is this ??- GRB afterglow ?? VLBI Imaging of SNR - 41.95+575 An unusual object in M82 !! Structurally-evolving double-lobed structure unlike ring/partial rings seen for all other M82 SNR Expansion velocity(<1800km/s)  age ~ 100 years

21. Deep galaxy studies indicate that early galaxies merge to form larger systems in a ‘bottom-up’ scenario of galaxy assemblyDeep galaxy studies indicate that early galaxies merge to form larger systems in a ‘bottom-up’ scenario of galaxy assembly This implies that galaxy- galaxy interactions were common at early epochsThis implies that galaxy- galaxy interactions were common at early epochs Such interactions are likely to trigger major star-formation activity.Such interactions are likely to trigger major star-formation activity. Star-formation at High Redshift HDF (N) Multi-wavelength studies of a number of fields including deep radio observations involving VLA, ATCA, MERLIN, EVN… have shown that at flux densities <1mJy (1.4GHz) there is new population of faint radio sources that are associated with distant star-forming galaxies Richards, Fomalont, Kellermann, Windhorst, Norris, Garrett, Muxlow…….

22. Deep HDF-N MERLIN + VLA data Covers ~10 arcmin 2 centred on the HDF-N (Lovell telescope beam) Covers ~10 arcmin 2 centred on the HDF-N (Lovell telescope beam) High angular resolution ~0.2-0.5 arcsec High angular resolution ~0.2-0.5 arcsec rms ~3.3 µ Jybm -1 - one of the most sensitive 1.4GHz images made rms ~3.3 µ Jybm -1 - one of the most sensitive 1.4GHz images made Precis of results: Precis of results: 92 radio sources with flux densities >40 µ Jy. 92 radio sources with flux densities >40 µ Jy. Angular sizes of 0.2 ”– 3 ” Angular sizes of 0.2 ”– 3 ” 85% are associated with galaxies brighter than 25th mag 85% are associated with galaxies brighter than 25th mag Remaining 15% are optically faint EROs at high redshift (some seen at sub-mm) Remaining 15% are optically faint EROs at high redshift (some seen at sub-mm) Below ~60  Jy sources are dominated by starburst systems Below ~60  Jy sources are dominated by starburst systems Some starbursts show evidence for embedded AGN – See latest VLBI results... Some starbursts show evidence for embedded AGN – See latest VLBI results... VLA: Richards et al 2000 VLBI: Garrett et al 2001 Seungyoup Chi - this meeting Seungyoup Chi - this meeting MERLIN+VLA: Muxlow et al 2005

23. Contours: Radio linear CI=10µJy/bm Image: Optical colour One of the brighter (~200µJy) starburst galaxies in the NDF-N

24. GOODS NORTH: New ACS & Spitzer data The historical HDF-N is coincident with the GOODS north field. The historical HDF-N is coincident with the GOODS north field.  deeper wider field HST ACS images + deep Spitzer images  deeper wider field HST ACS images + deep Spitzer images 8.5’ x 8.5’ MERLIN+VLA radio field centred on HDF-N intersects with 13030 galaxies brighter that 28.3 mag in ACS z-band field 8.5’ x 8.5’ MERLIN+VLA radio field centred on HDF-N intersects with 13030 galaxies brighter that 28.3 mag in ACS z-band field Using these new data we can now extend the analysis, to investigate statistically the very weak radio source population below 20µJy. Rob Beswick, Hanna Thrall, Tom Muxlow, Anita Richards, Simon Garrington…. Using these new data we can now extend the analysis, to investigate statistically the very weak radio source population below 20µJy. Rob Beswick, Hanna Thrall, Tom Muxlow, Anita Richards, Simon Garrington….

25. Radio emission from ACS galaxies Radio flux density within 0.75 arcsecond of all 13030 z-band optical galaxies in the 8.5’ field, binned by magnitude Radio flux density within 0.75 arcsecond of all 13030 z-band optical galaxies in the 8.5’ field, binned by magnitude (Note: excluding all brighter radio sources with S 1.4 >40µJy) Control incorporates a random 7 arcsecond shift Of the ~2700 galaxies brighter than Z=24mag, around 1400 will have radio flux densities of ~4 µ Jy or greater (~8σ for a deep e-MERLIN/EVLA image) 927 23 mag galaxies

26. Radio source sizes: very weak (sub-20µJy) radio sources Average radio source sizes in each magnitude bin can be derived from flux densities found in annuli over radii of 0.25-2 arcsec For detected systems (brighter than 25 mag ) average radio source radii are in the range 0.6 – 0.8 arcsec Next generation radio interferometers will need sub-arcsec angular resolution !!

27. Starburst Luminosities Only ~1000 of the ~13000 galaxies have published spectroscopic redshifts available (Keck) Measured redshifts binned by magnitude. We may now derive average luminosities for galaxies brighter than ~24 mag 40µJy 4µJy 0.4µJy ● Starburst Sub-mm Average luminosities for systems with spectroscopic redshifts For those weak sources which we can at present only study statistically... e-MERLIN, EVLA and e-VLBI should image >1000 starburst systems to ~4 µ Jy with perhaps 150-200 at high redshift in a single field. e-MERLIN, EVLA and e-VLBI should image >1000 starburst systems to ~4 µ Jy with perhaps 150-200 at high redshift in a single field. Many thousands of systems with radio flux densities <1 µ Jy will be studied statistically SKA and ALMA will ultimately extend this by an additional order of magnitude. With more redshifts, improved SED templates, and extinction-free SFR indicators  solve for cosmic star-formation history – Madau diagram 377 Spitzer 24µm in 8.5’ field >20µJy 303 (80%) detected in radio (>3σ)  213 with redshifts Beswick et al – work in progress…. At present …… Can show that the SFR density increases dramatically to z~1 and then flattens … At higher redshifts, the position of the turnover point remains uncertain !! The next few years will be very exciting …