1. Compact Extragalactic Star Formation: Peering Through the Dust at Centimeter Wavelengths Jim Ulvestad NRAO 7 Sept. 2004

2. Collaborators Susan Neff Stacy Teng Thanks to Kelsey Johnson for supplying several viewgraphs! Outline –Context –Starburst radio emission –Super Star Clusters –Supernovae Arp 299 (NGC 3690) case study

3. Some Global Questions What are the properties of the youngest massive star clusters? How do they evolve to become globular clusters today? What is the luminosity function of SSCs, and the mass function of their star formation? Is optical/IR modeling of star formation in SSCs consistent with radio observations? How do supernovae evolve in dense environments?

4. Formation of Stars & Star Clusters The first few stages are not visible optically and in near-IR Even SSCs may be hidden in dust From Kelsey Johnson

5. What Can Radio Emission Reveal about Extragalactic Starbursts? Optical radiation from youngest star- formation regions is hidden by dust Radio emission due to –Complexes of dense H II regions energized by Super Star Clusters Estimate ionizing flux  massive star population –Individual supernova remnants or young SNe Estimate supernova rate & evolution –Overlapping supernova remnants

6. Nearby Starbursts M82 (Kronberg et al. 1985; Muxlow et al. 1994) NGC 253 (Ulvestad & Antonucci 1997) 25 pc 8 mJy thermal source

7. Results from M82, NGC 253 Little or no source variability Steep spectrum sources resolve into SNRs Flat-spectrum sources typically H II complexes energized by hot stars N(UV)/s = 10 51 (D/2.5 Mpc) 2 (S 5 GHz /1 mJy) –10 49 photons/s = 1 O7 star –Strongest NGC 253 thermal source is ~8 mJy 750 O7-equivalent stars in a few parsecs

8. NGC 5253 (~4 Mpc) Linear Resolution ~ 2-4 pc N Lyc  7  10 52 s -1  Super star clusters 7mm VLA, 25 pc (2 arcsec) square (Turner & Beck 2004) From KJ

9. SBS 0335-052 (Johnson et al., in prep) 53 Mpc, ultra-low metallicity (Z  1/40 Z  ) Massive proto-cluster detected in mid-IR: A v > 15 - 30 AND similar embedded stellar mass Hunt, Vanzi, & Thuan (2001) Plante & Sauvage (2002) VLA 1.3cm contours, HST I-band colorSpectral Index: 1.3cm & 3.6cm Linear Resolution ~ 75pc N Lyc  12,000  10 49 s -1  Super star cluster(s) Yikes! See also: radio observations of Hunt, Dyer, Thuan, & Ulvestad (2004) From KJ

10. Nearest Merger—The “Antennae” WFPC2, with CO overlay (Whitmore et al. 1999; Wilson et al. 2000) VLA 5 GHz image (Neff & Ulvestad 2000) –Needs EVLA sensitivity and resolution 5 mJy  30,000 O7-equivalent stars

11. SSC and Related Radio Sources

12. N Lyc ~ 700 - 2500  10 49 s -1 (700 - 2500 O7* stars) Stellar Masses  10 5-6 M  HII masses < 5% stellar masses Radii of HII regions < 4 pc Electron densities >10 4 - 10 6 cm -3 Pressures > 10 8 k B What do we think we know about the embedded HII regions? Example: He2-10 Johnson & Kobulnicky 2003 (1.3cm on 3.6cm) From KJ

13. Global Lessons from Radio SSCs Most recent star formation regions are bright in mid-IR and radio –Radio SSC diameters are a few parsecs –Tens to thousands of O7-equivalent stars Recombination linewidths and sizes indicate some SSCs are bound, depending on stellar mass function (e.g., Turner et al. 2003) –Otherwise, overpressure would cause the SSCs expansion in ~10 6 yr or less

14. Arp 299 History At least one previous interaction –~700 million years ago –HI and stellar tidal tails, ~ 150 kpc in extent Near beginning of current interaction –Two disks still clearly identifiable –Nuclear separation ~3.5 kpc –Disks interacting and distorted Burst of star formation 6-8 million years ago (at the beginning of current pass) –Should be seeing supernovae J. Hibbard HST WFPC2 (Alonso- Herrero et al. 2000) Tidal tails in Arp 299 Stars: blue; HI: contours 30 kpc

15. Arp 299 Radio Emission No radio emission at optical SN positions Four Strong Radio Peaks –A and B: galaxy nuclei –C and C’: overlap region Alonso-Herrero et al. IR/opt. (2000) –Assume starbursts Gaussian in time, 5 Myr wide, peak 5 Myr after start –A: 7 Myr post-peak, 0.6 SN/yr 700 million solar masses in young stars 140 solar masses/yr in star formation –B1: 5 Myr post-peak, 0.1 SN/yr –C & C’: 4 Myr post-peak, 0.05 SN/yr Red: VLA 6cm Blue: HST 250nm Green: HST 814nm Arp 299

16. Arp 299 Inside Source A A “nest” of four young SNe, within 100 pc and A young supernova, only 2 pc from one of the other sources  Tracing super- star clusters? April 2002 Feb. 2003 13cm 3.6cm 3 pc Neff, Ulvestad, & Teng 2004

17. More VLBA + GBT imaging 2.3, 8.4 GHz in 2003Dec, 2004Jun Total of 15 SNe at 2 and 8 GHz

18. Inside Source B1, 2 nd Nucleus

19. Beginning of a Luminosity Function Arp 299-A SN rate is reputed to be about 6 times M82. –Accounting for incompleteness, looks okay within a factor of two

20. Arp 299 Summary IR/optical SN rate looks about right Youngest source still has not broken out, and is not detected at 2.3 GHz –No other strongly inverted sources, so any other very young supernovae are 10 times less powerful (or don’t exist) –No obvious variability in other sources First detection of young supernovae in the 2 nd galaxy nucleus No radio supernovae seen in other star formation regions

21. Extra Slides Following …

22. Super Star Clusters in Radio/mid-IR Can account for most of the host’s radio and mid-infrared emission Poor correspondence with optical peaks Beck, Turner, & Gorjian 2001 Left: mid-IR image Right: 2-cm radio contours overlaid (from Kobulnicky & Johnson 1999)

23. The Problem with the Antennae At 20 Mpc, 1 arcsec=100 pc. Need resolution better than 10 pc, but then brightness sensitivity is a problem. Need EVLA-1 and EVLA2 for sensitivity and resolution 6 cm  2cm

24. Inside Source A: Component Spectra Components appear to be young SNe / SNR in dense environments –A0 resembles young (~1yr) embedded SN Inverted spectrum turns over ~ 15 GHz No detection at 2.3 GHz SN ejecta has not yet broken through remnants of former stellar wind. –Other components appear to be young (> 10 yr) SNR Flat / slightly steepening spectra SN ejecta expanding beyond former stellar winds SN1986J Young SN Young SNR

25. The Most Distant Quasar VLA image of CO from the first known star formation –Redshifted to 46 GHz Optical Image Artist’s conception of disk of molecules and dust Walter et al. 2003

26. Observational strategy: If we want to understand cluster formation, it’s not a bad idea to observe them while they are forming. HST image of the Antennae Galaxies B.Whitmore/NASA Problem: Once clusters are visible to HST, they have already emerged from their birth material From Kelsey Johnson

27. Typical Radio Supernovae Majority are Type II –M > 8 M sun progenitor –Massive pre-explosion wind Light Curves –Type II have slow radio turn-on (20- 100d) / turn off (few years) –Turn-on first at shorter wavelengths Spectral evolution with time –Turn-on (flux rising) spectrum peaks at shorter wavelengths Long wavelengths self-absorbed, thermal emission dominant –Later, radio spectrum is steep Optically thin, non-thermal synchrotron emission dominates In a Dense Environment M 20-30 Msun Wind > 10 -4 M sun / yr Turn-on few years / turnoff > 20yrs Spectrum flattens but does not become non-thermal (steep)

28. Arp 299: Inside the Starburst Extremely dense gas and dust in both nuclei –Prograde – retrograde encounter –Gas driven into nuclei, not thrown out into tails High star formation rate (SFR) –Nuclei forming ~30 (East) and ~15 (West) M sun / year, in massive stars –SFR led Weedman and collaborators to coin the term “starburst” (1983). –Four known SNe since 1990E Very high extinction in nuclei –Optical observations cannot penetrate –Require radio observations to see into the galaxy centers Arp 299 H  (Ionized Hydrogen) Arp 299 CO (cold gas) Aalto Hibbard EW

29. Why Do We Care About Arp 299? The most distant quasars contain lots of cool gas YFormation of stars and massive black holes in galaxies go together Where do the stars form? How is the star formation related to the rest of the evolution of the galaxy? A “picture” of the process is worth a thousand words! 250 LY

30. Arp 299 Science Summary Detected: – Supernova “factory” in merging galaxy pair Imaged, with the only telescope that can: –See through the dust AND –Provide adequate resolution to separate individual supernovae Is A1 an AGN?? –Optically thin spectrum and relatively stable flux. –L X (A)=1.3 x 10 40 ergs/s (Zezas et al. 2003) –  L  (5 GHz, A1)=10 37 ergs/s HST WFPC2 1 HST/PC2 pixel 10 LY 2.3 GHz8.4 GHz

31. The Newest SN, Source A0 It is 1000 times the power of Cassiopeia A, the strongest supernova remnant in our Galaxy. 8 GHz flux density is decaying rapidly over the last year. Still not detected at 2.3 GHz –Behind or within a screen that does not envelop A1?

32. NGC 3256 Colors—optical DSS Contours—HI (Hibbard et al.) Red=ULXs (Lira et al. 2002) Radio (Neff, Ulvestad, & Campion 2003)

33. NGC 3256: The Nuclei 8.4 GHz and 15 GHz VLA images of two nuclei (with X-ray positions indicated) 1.5-10 keV contours (Chandra archive)

34. Radio/X-ray Ratio as a Diagnostic ObjectRadio/X-ray* X-ray transients< 2 x 10 -5 NGC 5408 ULX5 x 10 -6 Radio-quiet AGN~1 x 10 -5 O stars + HII3 Cas A2 x 10 -2 NGC 253 “nucleus”1 x 10 -2 N6240 N (S)1 (6) x 10 -3 LLAGNs~1 x 10 -3 N3256 N (S)2 (10) x 10 -3 *Radio/X-ray =  L  (5 GHz)/L(2-10 keV) [Terashima & Wilson 2003]

35. NGC 3256 Northern Nucleus Strong diffuse component to X-rays BUT, 300 km/s velocity gradient across 40 pc –10 8 solar masses enclosed