2.  Provocation  Introduction  Recent Initial Mass Function (IMF) work  The Star Formation Law (SFL) › Mostly a review  Pearls, feathers, and spurs in › Galex Nearby Galxy Atlas › SINGG - SUNGG 2

3.  The IMF is not constant  All stars do not form in star clusters  Dust is a hassle but not a huge problem  The SFL works 3

4.  Started research by dissecting one galaxy (NGC1705)  Moved on to a second (NGC2915)  Progressed to larger and larger samples  Now prefer working with easily measured quantities from large surveys › Total flux › Effective surface brightness › Color, equivalent widths 4

5.  G.R. Meurer ( JHU ) ★✿  H.C. Ferguson (STScI) ★ ✿  R. Webster (Melbourne) ★ ✿  J. Bland Hawthorn (Sydney) ✿  M. Dopita (ANU) ★  M. Doyle (Queensland) ★ ✿  M. Drinkwater (Queensland) ★ ✿  K.C. Freeman (ANU) ★  D. Hanish (Michigan) ★ ✿  J. Heiner (Groningen) ✿  T. Heckman (JHU) ★  R. Kennicutt (Cambridge) ★✿  V. Kilborn (Swinburne) ★✿  J.H. Kim (Seoul) ★✿  P. Knezek (WIYN) ★ ✿  B. Koribalski (ATNF) ★  M. Meyer (UWA) ★ ✿  M. Putman (Columbia) ★✿  E. Ryan-Weber (Cambridge/Swinburne) ★ ✿  M. Seibert (OCIW) ✿  C. Smith (CTIO) ★  L. Staveley-Smith (UWA) ★ ✿  J. Werk (Michigan/Columbia) ★  I. Wong (Yale) ✿  M. Zwaan (ESO) ★ ✿ 5

6. 6

7.  SINGG - the Survey of Ionization in Neutral Gas Galaxies › H  and R band survey  SUNGG - the Survey of Ultraviolet emission in Neutral Gas Galaxies › Far and near ultraviolet (FUV, NUV) survey  Parent sample of both is HIPASS the HI Parkes All Sky Survey  Not related to SINGS, THINGS, SONG, MUSYC, STING, … 7

8.  HI Parkes All Sky Survey › HI 21cm › Parkes 64m › 4315 sources  Survey of Ionization in Neutral Gas Galaxies › H  & R band › CTIO 1.5m › 468 sources selected › 331 observed  Survey of Ultraviolet emission in Neutral Gas Galaxies › FUV & NUV › Galex 0.5m › 139 selected › ~200 observed 8

9.  H  traces O stars M * > ~20 M sun Secondary emission IMF sensitive  Vacuum UV traces O and B stars Dominates emitted SED of SF pops very sensitive to dust Starburst99 CSFR models (Leitherer et al 1999) M u = 100 M sun UV H  M u = 30 M sun UV H  9

10.  Ranges by a factor of 10  Strongly correlates with optical surface brightness  Most galaxies below expectations for Salpeter (or Kroupa) IMF  Data corrected for dust obscuration  From FUV data: all galaxies should have multiple O stars Meurer et al. (2009, ApJ, 695, 765) 10

11.  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 11

12.  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 12

13. 13

14.  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 14

15.  Stochastic effects: Integrated Galactic IMF (Pflamm-Altenburg et al. 2009, MNRAS, 395, 394 ). › Variable IMF › May be a good mathematical description of what IMF becomes  Krumholz & McKee ( 2008, Nature, 451, 1082 ) give minimum column density required for massive stars to form, predict H  /UV variations  Competitive accretion scenario › High mass stars from lower mass cores › growth from accretion of ISM in cluster potential › And “stealing” from lower mass stars › Bonnell et al. (2003, MNRAS, 343, 413; 2004, MNRAS, 349, 735 ; Bonnell & Bate, 2006, MNRAS, 370, 488 ) 15

16.  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  Consistent with cluster fraction versus surface brightness ( Meurer et al. 1995, AJ, 110, 2665; Larsen 2004, A&A, 416, 537 ) 16

17.  Spirals have high  R,  H  › “Normal” overall IMF › Total SFR probably OK  H  traces high P star formation  Spiral density waves increase P  Outer regions can be H  weak (Thilker et al. 2005, 2007) 17

18.  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  g  Q =  /(  g G) disk stability   = epicyclic frequency   ~ 0.7  Kennicutt ( 1998, ApJ, 498, 541 ) › N ~ 1.4 › Integrated over galaxies › Also starburst nuclei 18

19.   SFR ~  H2 (N = 1.0)  Linear relation between molecular gas and SFR 2. R mol =  H2 /  HI ~  R  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 ) 19

20.  H  /HI  SFR/HI  H 2 /HI  R mol  P(!)  Expect 1:1 correlation with  R  X-axis  SFR  R  r xy 0.76-0.80  Slope0.710.89 +- 0.04   y 0.280.27   x 0.400.30 20

21.  Method › Look at 2 and 3 color images › Brief description to text file › grep keywords (e.g. spiral, bar, nuke, ring, pearl, feather, spur, etc…)  GALEX Nearby Galaxy Atlas  Gil de Paz et al. ( 2007, ApJS, 173, 185 ) › 1034 galaxies  575 with comments  Rest featureless, small, or edge-on  SINGG & SUNGG › Only galaxies with H  and UV 3 color images › 99 galaxies with comments (72 HIPASS targets) 21

22.  FeatureNGASINGG  Spiral: 30%40%  Bar:16%27%  Ring:25%10%  Nuke:28%33% Note – did not exclude dwarfs Example: NGC7424 H  R, RNUVFUV, H  RFUV Impressions:  H  : nice high contrast, but often like connecting the dots  UV: lower contrast, worse resolution, but more continuous 22

23.  Pearls:10%32%  Spurs:9%16% Examples: NGC628 NGC3344 NGC1042 Impression: spiral arms, pearls and spurs have higher contrast in H  than UV 23

24.  feathers1% 2%  dust6%11% Examples: M51 NGC253 Cen A Galex resolution insufficient SF correlated with dust: Dust lanes “filled in”, hard to see 24

25.  IMF varies › O stars require high P ISM  Like spiral arms (pearls), bars, rings, nuclei › B stars can form in lower P ISM  In situ formation in outer disk and inter-arm?  SFL can explain › (inner) Radial profiles › Global SF scaling relations › Including H  /HI  Some spiral substructure easy to spot with SF tracers, and fairly common › Pearls › Spurs 25