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Understanding Star Formation in Dwarf Galaxies: Step One

Understanding Star Formation in Dwarf Galaxies: Step One. Janice C. Lee ( STScI ) Lowell Observatory Dwarf Galaxy Workshop June 19, 2012. twanight.org?id=3001717 LMC, SMC, MW. Understanding Star Formation in Dwarf Galaxies: Step One. “The Outer Edges of Dwarf Irregular Galaxies” 2002.

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Understanding Star Formation in Dwarf Galaxies: Step One

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  1. Understanding Star Formation in Dwarf Galaxies: Step One Janice C. Lee (STScI) Lowell Observatory Dwarf Galaxy Workshop June 19, 2012 twanight.org?id=3001717 LMC, SMC, MW

  2. Understanding Star Formation in Dwarf Galaxies: Step One “The Outer Edges of Dwarf Irregular Galaxies” 2002 Janice C. Lee (STScI) Lowell Observatory Dwarf Galaxy Workshop June 19, 2012 twanight.org?id=3001717 LMC, SMC, MW

  3. Understanding Star Formation in Dwarf Galaxies: Step One? From a theoretical perspective… perhaps begin from first principles… review talks by MacLow, Krumholz, Bournaud

  4. Understanding Star Formation in Dwarf Galaxies: Step One? From an observational perspective…

  5. Understanding Star Formation in Dwarf Galaxies: Step One? From an observational perspective… Review talks by Leroy (dust) Bolatto (molecular gas) N4449 Haro11

  6. Identification of samples are challenging for intrinsically faint, relatively low surface brightness galaxies. Theme 1: progression from representative samples to statistically complete samples of SF dwarfs

  7. Samples are well- characterized & statistically complete (e.g. Markarian 1967; SBS: Markarian et al. 1986; KISS: Salzer et al. 2000) IIZw40 IIZw40 IZw18 IZw18 Samples are representative (e.g. Hunter & Gallagher 1985; van Zee 2001; Hunter & Elmegreen 2004) Previous work established dwarfs as crucial foil for studies of spirals & more massive galaxies: less dusty, gas rich, but generally low gas densities, no spiral density waves (low shear), blue, metal-poor, ~5% ~95% Lee+09a

  8. LVL/11HUGS Kennicutt+08 Dale+09 Lee+11 progression toward statistically complete samples of dwarfs…. ALFALFA Giovanelli+05 Huang+12 ANGST Dalcanton+09 Weisz+11 AVOCADO (N~7000!) Sanchez-Janssen+12

  9. LVL/11HUGS Kennicutt+08 Dale+09 Lee+11 Enables study of star formation statistics: - starburst duty cycles - prevalence of different SF states - maturation from dependence on taxonomy to quantitative characterization and analysis ALFALFA Giovanelli+05 Huang+12 ANGST Dalcanton+09 Weisz+11 AVOCADO Sanchez-Janssen+12

  10. Enables study of star formation statistics: - starburst duty cycles - prevalence of different SF states - maturation from dependence on taxonomy to quantitative characterization and analysis Bergvall12 BCDs? HII galaxies? Sargent-Searleobjects? starbursts? What is a “blue compact dwarf?” (e.g., Gil de Paz+03) What is a [dwarf] “starburst?” (e.g., Lee+09a; Knapen+09; McQuinn+09; Bergvall 12) BCDs? HII galaxies? Sargent-Searleobjects? starbursts? What is a “blue compact dwarf?” What is a [dwarf] “starburst?” Lee+09a

  11. Identification of samples are challenging for intrinsically faint, relatively low surface brightness galaxies. Theme 1: progression from representative samples to statistically complete samples of SF dwarfs How is the SFR measured in these samples?

  12. Methods of measuring SFRs Resolved stellar populations and CMD fitting: e.g., Gallart+96; Tolstoy & Saha96; Dolphin+97 review talk by Weisz Weisz+08 t(now)-1 Gyr time t(now)

  13. UV PAHs MIR FIR [OII] H Methods of measuring SFRs a galaxy SED… Why the need for so many different diagnostics? dust timescales redshift considerations UV continuum [OII]3727 H-alpha 6563A (H recombination lines) PAH Total IR (monochromatic LIR) [CII] 158um (fine structure cooling lines) Radio Continuum

  14. Theme 1: progression from representative samples to statistically complete samples of SF dwarfs Theme 2: progression toward broad UV-IR multi-wavelength coverage

  15. Methods of measuring SFRs Theme 2: progression toward broad multi-wavelength UV-IR coverage Dale+09 Herschel GALEX new results from Herschel DGS Key Program (Madden+) Spitzer

  16. Methods of measuring SFRs: exploring SF at low density with GALEX Conditions in extended disks of spirals similar to that in dwarf irregulars (e.g., Bigiel+08) … clues on the importance of local vs. global properties in determining SF. GALEX M83

  17. UV PAHs MIR FIR [OII] H Theme 2: progression toward broad UV-IR multi-wavelength coverage enables comparison between diagnostics. a galaxy SED… UV continuum [OII]3727 H-alpha 6563A (H recombination lines) PAH Total IR (monochromatic LIR) [CII] 158um (fine structure cooling lines) Radio Continuum

  18. Theme 2: progression toward broad UV-IR multi-wavelength coverage enables comparison between diagnostics. a galaxy SED… Example 1: IR, dust reprocessed emission -dIrrs relatively Transparent -Use calibrations based on more massive galaxies with care for measuring SFRs in dwarfs. TIR cannot be used alone to measure SFR in most dwarfs. Kennicutt+09

  19. Theme 2: progression toward broad UV-IR multi-wavelength coverage enables comparison between diagnostics. Example 2: H-alpha & UV emission J.C. Lee+09b -6 -4 -2 0 -4 -2 0

  20. Theme 2: progression toward broad UV-IR multi-wavelength coverage enables comparison between diagnostics. Example 2: H-alpha & UV emission J.C. Lee+09b Use calibrations (e.g., with form SFR=cL) with caution for dwarfs esp. for SFRsless than ~0.001 Msun/yr (Lee+09b; Leroy+12)! FUV more robust than H-alpha? But why? back to this in a moment…

  21. Theme 2: progression toward broad UV-IR multi-wavelength coverage enables comparison between diagnostics. Example 3: radio continuum, IR Slide courtesy of U. Klein (Bonn)

  22. Theme 2: progression toward broad UV-IR multi-wavelength coverage enables comparison between diagnostics. Little known about radio continuum properties of typical dIrrs…. Slide courtesy of U. Klein (Bonn)

  23. e.g., UV emission; radio; FIR SFR > c L(70 um) SFR > c L(1.4 GHz) yet L(70 um)/L(1.4 GHz) still on radio-FIR correlation!?

  24. Theme 1: progression from representative samples to statistically complete samples of SF dwarfs Theme 2: progression toward broad UV-IR multi-wavelength coverage Theme 3: increased mass resolution in population synthesis models

  25. From population synthesis with ~105 MSSPs…

  26. …to population synthesis with individual stars… • SLUG “A New Way to Stochastically Light Up Galaxies” • (da Silva+12) • BPASS “Binary Population and Spectral Synthesis” • (Eldridge+08; Eldridge & Stanway 09) • MASSCLEAN “MASSiveCLuster Evolution and ANalysis Package” • (Popescu & Hanson09;10 – only for SSPs) …enables interpretation of observed properties of low mass, low SFR systems. How does stochastic formation of high mass impact observed and physical properties of dwarfs?

  27. Fumagalli+11 J.C. Lee+09b …enables interpretation of observed properties of low mass, low SFR systems. How does stochastic formation of high mass impact observed and physical properties of dwarfs?

  28. An example: star formation efficiencies Lee&Gil de Paz+11 How does stochastic formation of high mass impact observed and physical properties of dwarfs?

  29. An example: star formation efficiencies Lee&Gil de Paz+11 How does stochastic formation of high mass impact observed and physical properties of dwarfs?

  30. Theme 1: progression from representative samples to statistically complete samples of SF dwarfs Theme 2: progression toward broad UV-IR multi-wavelength coverage Theme 3: increased mass resolution in population synthesis models Theme 4: using old tricks to find dwarfs at high-z

  31. Samples are well- characterized & statistically complete (e.g. Markarian 1967; SBS: Markarian et al. 1986; KISS: Salzer et al. 2000) IIZw40 IIZw40 IZw18 IZw18 Theme 4: Using old tricks to find dwarf galaxies at higher redshift. “Ultra Strong Emission Line Galaxies” USELs at high-z ? 0.35 < z < 2.3 WFC3 IR grism surveys: WISPS (Atek+10) 3D-HST (van Dokkum+11) z=0.8 & z=2.2 IR NB surveys Hayes+10; Sobral+12; Lee+12

  32. Theme 1: progression from representative samples to statistically complete samples of SF dwarfs Theme 2: progression toward broad UV-IR multi-wavelength coverage Theme 3: increased mass resolution in population synthesis models Theme 4: using old tricks to find dwarfs at high-z Theme 5: realizing that “no man is an island” may apply to all galaxies including dwarfs

  33. From…

  34. … to galaxy ecology… M82 M81 HoIX N3077 Croxall+2009 I-band Yun+1994 HI

  35. …even for seemingly isolated dwarf galaxies. “The Dr. Jeckyll/Mr. Hyde Of Irregular Galaxies” Hunter et al. 1998 POSS/DSS Martinez-Delgado+2012 see also Rich+2012 N4449 D125 N4449

  36. …even for seemingly isolated dwarf galaxies. POSS/DSS Martinez-Delgado+2012 see also Rich+2012 N4449

  37. might this yield answers to: “What goes wrong in Blue Compact [or starbursting] Dwarf Galaxies?” Theme 2b: progression toward spatially resolved studies of SF, dust, gas, nebular properties, kinematics – rise of IFU spectroscopy

  38. Theme 1: progression from representative samples to statistically complete samples of SF dwarfs Theme 2: progression toward broad UV-IR multi-wavelength coverage Theme 3: increased mass resolution in population synthesis models Theme 4: using old tricks to find dwarfs at high-z Theme 5: realizing that “no man is an island” may apply to all galaxies including dwarfs Theme 2b: progression toward spatially resolved studies of SF, dust, gas, nebular properties, kinematics – rise of IFU spectroscopy Is the equilibrium SF state simply determined by galaxy mass and cosmic time (through correlation with density), and all non-equilibrium states caused by interaction with externalsystems/material?

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