1. Great Barriers in HMSF 2010: Gerhardt R. Meurer International Centre for Radio Astronomy Research University of Western Australia

2. Great Barriers in HMSF 2010: Outline High Mass Star formation tracers SINGG & SUNGG Surveys Why study extragalactic HMSF? Results The Star Formation Law The Initial Mass Function Modes of star formation Take home points 2

3. Great Barriers in HMSF 2010: H  vs. FUV 3  H  traces O stars M * > ~20 M sun t < ~7 Myr  Vacuum UV traces O and B stars M * > ~3 M sun B stars dominate Dominates emitted spectrum of star forming regions t < ~ 300 Myr Starburst99 CSFR models (Leitherer et al 1999, ApJS, 123, 3) M u = 100 M sun UV H  M u = 30 M sun UV H 

4. Great Barriers in HMSF 2010: Dust reprocessing IRX-  : dust absorption correlates with UV colour Requires that much of dust is in a foreground screen or shell near SF Allows crude dust correction Different relationships for starburst and normal galaxies Meurer et al. (1999, ApJ, 521, 64) Wong et al. (2010 in prep…) Gil de Paz et al. (2007, ApJS, 173, 185) 4

5. Great Barriers in HMSF 2010: Other HMSF tracers Mid-IR Radio continuum 24 8 3.6 24  m + H  trace O stars 8  m (PAH) not as good HMSF tracer Calzetti et al. (2007, ApJ, 666, 870) Strong linear Radio – FIR correlation neither trace HMSF well at low L FIR + FUV should trace HMSF well Bell (2003, ApJ, 586, 794) 5

6. Great Barriers in HMSF 2010: 6 HIPASS, SINGG, and SUNGG HI Parkes All Sky Survey (HIPASS) HI 21cm Parkes 64m 4315 sources Survey of Ionization in Neutral Gas Galaxies (SINGG) H  & R band CTIO 1.5m 468 sources selected 331 observed Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) FUV & NUV Galex 0.5m 139 selected ~200 observed

7. Great Barriers in HMSF 2010: Some results All HI galaxies are forming stars Multiple emission line galaxies common Diverse morphologies 7 Meurer et al. 2006, ApJS, 165, 307 Hanish et al. 2006, ApJ, 649, 150

8. Great Barriers in HMSF 2010: Why study extragalactic HMSF? Obvious reasons: Avoid galactic plane Known distance Sample large ranges of Gas densities Abundance Radiation intensity (extremes esp. important) HMSF useful for Highlighting dynamics Finding companions …the most luminous galaxies..the most distant galaxies Tracing cosmic evolution Probe Physics of HMSF! 8

9. Great Barriers in HMSF 2010: Highlighting dynamics with HMSF NIR: stellar mass distribution H  : better defined usually UV: often washed out, but outer disks light up 9

10. Great Barriers in HMSF 2010: Finding companion galaxies HIPASS J2149-60 HIPASS J1059-09 10

11. Great Barriers in HMSF 2010: The most luminous galaxies Ultra-Luminous Infrared Galaxies (ULIRGs) L bol > 10 12 L sun Highly dust extincted Usually disturbed or interacting Hyper-Luminous Infrared Galaxies L bol > 10 13 L sun Mostly known at z > 1 Often contain AGN Disturbed morphology Arp220 HST/ACS HST/NICMOS Farrah et al. (2002, 329, 605) 11

12. Great Barriers in HMSF 2010: The most distant galaxies Lyman Break Galaxies z > ~1 Need a rest frame UV spectrum dominated by HMSF z ~ 8 is state of the art Can also select in Rest frame FIR Radio Dickinson (1998, astro-ph/9802064) Bouwens et al. (2010, ApJL, 709, L133) 12

13. Great Barriers in HMSF 2010: Tracing cosmic evolution HMSF as shorthand for galaxy evolution Over 10x decline since z~1.5 (~7 Gyr ago) Fuel running out? Less accretion? SFRD from H  and UV differ Hopkins & Beacom (2006, ApJ, 651, 142) 13

14. Great Barriers in HMSF 2010: The Star Formation Law Definition: the SFR (M sun /year) given the properties of the ISM Schmidt (1959, ApJ, 129, 243)  SFR ∝  g n ; n ~ 2 Kennicutt (1989, ApJ, 344, 685; 1998, ApJ, 498, 541; Martin & Kennicutt 2001, ApJ, 555, 301)  SFR ∝  g N ; N ~ 1.4 when  g >  c =  Q  Q =  /(  g G) disk stability  = epicyclic frequency 14

15. Great Barriers in HMSF 2010: Kennicutt (1998) global SFL 15 Global And galaxy centers  SFR ~ 0.4 dex

16. Great Barriers in HMSF 2010: THINGS SFL results   SFR ~  H2 (N = 1.0)  Linear relation between molecular gas and SFR 2. R mol =  H2 /  HI ~  *  molecular fraction set by hydrostatic pressure 3. Q(2 Fluids) ~ constant  ISM disks maintained at constant stability Leroy et al. (2008, AJ, 136, 2782 ), Bigiel et al. (2008, AJ, 136, 2846 ) 16

17. Great Barriers in HMSF 2010: Test with SINGG global fluxes H  /HI  SFR/HI  H 2 /HI  R mol  P(!) Expect 1:1 correlation with  R 17  X-axis  SFR  R  r xy 0.76-0.80  Slope0.710.89   y 0.280.27   x 0.400.30

18. Great Barriers in HMSF 2010: SFL Implications Tighter than the Kennicut SFL From optical observations can estimate HI content to better than a factor of 2 Good physical understanding of the results Star formation in the molecular phase of a pressure regulated disk near critical stability Stellar disk important for setting the equilibrium pressure 18

19. Great Barriers in HMSF 2010: Some SFL complications from M83… SF edges not always seen in UV (e.g. Thilker et al. 2005, ApJ, 619, L79) SFR(UV) traces HI at very low  g (Bigiel et al. 2010, ApJ, 720, L31) 19

20. Great Barriers in HMSF 2010: The Initial Mass Function Definition: the mass distribution of stars formed in a single event The argument for a constant IMF: Same Salpeter IMF slope seen where it can be measured well - populous star clusters (Kroupa 2001, MNRAS, 322, 231) All stars form in star clusters (Lada & Lada, 2003, ARA&A, 41, 57) (later they disperse…) 20 Log(N)  -1)

21. Great Barriers in HMSF 2010: The H  /FUV ratio & the IMF Ranges by a factor of 10 Strongly correlates with optical surface brightness Most galaxies below expectations for Salpeter (or Kroupa) IMF From FUV data: all galaxies should have multiple O stars (Meurer et al. 2009, ApJ, 695, 765) 21

22. Great Barriers in HMSF 2010: A. Low F H  /f FUV  HIPASS J0249-02  log (F H  /f FUV ) = 0.51  log(  SFR,H  ) = -3.28  log(  R /  R,sun ) = 6.87  UGCA44  IB(s)m:  log(M HI /M sun ) = 8.85  log(L R /L R,sun ) = 8.29 22

23. Great Barriers in HMSF 2010: B. High F H  /f FUV  HIPASS J0419-54  log(F H  /f FUV ) = 1.33  log(  SFR,H  ) = -1.21  log(  R /  R,sun ) = 8.70  NGC1566  SAB(rs)bc  log(M HI /M sun ) = 10.19  log(L R /L R,sun ) = 11.09 23

24. Great Barriers in HMSF 2010: Effect of Dust 24

25. Great Barriers in HMSF 2010: Effect of Star Formation History Models of effects of bursting and gasping SFH CSFR + Gaussian increase (burst) or decrease (gasp) in SFR Max/min SFR: 2,10, 100 FWHM = 10, 100, 1000 Myr 25

26. Great Barriers in HMSF 2010: Escaping ionizing radiation? Perhaps low H  /FUV points are due to escaping ionizing radiation Direct measurements of escape fraction have only been attempted in HSB starbursts However LSB galaxies are gas rich Would require naked O stars O stars not seen or rare in CMDs of nearby LSB dwarfs (e.g. Tolstoy 1996, ApJ, 462, 684; Young et al. 2007, ApJ, 659, 331) But are seen in CMDs of higher SB irregulars (e.g. Annibali et al. 2008, AJ, 135, 1900) 26

27. Great Barriers in HMSF 2010: SFH / leaking HII regions from CMDs 27 Phoenix dI (Young et al. 2007) NGC4449 (Annibali et al. 2008)

28. Great Barriers in HMSF 2010: Related results Buat et al. (1987, A&A, 185, 33) use UV + H  to suggest possibility of IMF variations in nearby galaxies. Outer disks H  edges not so apparent in UV (Thilker et al 2005, ApJ, 619, L79; Thilker et al. ApJS, 2007, 173, 578; Boissier et al. 2007, ApJS, 173, 524) Hoversten & Glazebrook (2008, ApJ, 675, 163) use EW(H  ) versus g-r (SDSS) to infer variable IMF. Lee et al. (Lee et al. 2009, ApJ, 706, 599) similar results for 11 HUGS 28

29. Great Barriers in HMSF 2010: Field versus cluster About 60% of H  is diffuse (Oey et al. 2007, AJ, 661, 801) >~80% of UV is diffuse (Meurer et al. 1995, AJ, 110, 2665; Larsen 2004, A&A, 416, 537) 29

30. Great Barriers in HMSF 2010: Field: deficient in O stars Spectrum dominated by B stars (Tremonti et al. 2001, ApJ, 555, 322) Low H  /FUV (Hoopes et al. 2001, ApJ 559, 878) 30

31. Great Barriers in HMSF 2010: Stars don’t form just in clusters Two modes of star formation (Meurer et al. 1995, AJ 110, 2665) Bound clusters - prominent Diffuse star formation - dominant (groups, associations, star clouds) Lada & Lada (2003) is misleading Based on expansive redefinition of “cluster” to include unbound objects (groups, associations) Recent results on Galactic YSOs: (Bresert et al. 2010, MNRAS, arXiv:1009.1150) Stars form over a wide of densities No clear field vs. cluster distinction 26% of YSOs in dense clusters 31

32. Great Barriers in HMSF 2010: Our scenario  Highest mass stars form in bound clusters (Bonnell et al. 2003, MNRAS, 343, 413; 2004, MNRAS, 349, 735; Bonnell & Bate, 2006, MNRAS, 370, 488)  Bound clusters form in dense mol ISM  Hydrostatic pressure determines molecular fraction (McKee & Ostriker 1977, ApJ, 218, 148; Wolfire et al. 2003, ApJ,, 587, 278; Blitz & Rosolowsky 2006, ApJ, 650, 933)  Pressure also determines how well bound star clusters are when formed (Elmegreen & Efremov 2007, ApJ, 280, 235; Elmegreen 2008, ApJ, 672, 1006)  Stars dominate disk plane potential and set hydrostatic pressure  Hence we have the surface brightness IMF correlation:  *  P  cluster/field  O/B  H  /FUV  Consistent with cluster fraction versus surface brightness (Meurer et al. 1995, AJ, 110, 2665; Larsen 2004, A&A, 416, 537) 32

33. Great Barriers in HMSF 2010: Take Home Messages HMSF useful for tracing galaxy evolution at all redshifts Results depend on tracer: H  (P , 24  m) traces the most massive (O) stars, formed in: Tightly bound clusters Starbursts Spiral density waves UV (FIR, radio) sensitive to lower mass (O + B) stars: formed in: Clusters or field Outer disks IMF varies within and between galaxies  * is a key parameter for setting SF intensity and effective IMF Probably by setting the hydrostatic P of the ISM 33

34. Great Barriers in HMSF 2010: 34

35. Great Barriers in HMSF 2010: HMSF Tracers: H  and FUV 35 Wavelength [Angstroms] FUV  Ultraviolet   Optical  HH Spectrum of starburst galaxy NGC1705 (Meurer et al. 1992, AJ, 103, 60)

36. Great Barriers in HMSF 2010: SINGG SFL results X-axispseudo  HI  R r xy 0.590.75 slope1.661.01  y 0.500.29  x 0.300.29 Older populations also important for star formation regulation (cf Dopita & Ryder 1994, ApJ, 430, 163 ) 36

37. Great Barriers in HMSF 2010: Correlations with t gas ~ 2.3M HI /SFR X-axis  SFR  R r xy -0.75-0.77 slope-0.77-0.87  y 0.260.28  x 0.330.32 37