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

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

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

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

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

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

IZw18 IIZw40 IZw18 IIZw40 Samples are well- characterized & statistically complete (e.g. Markarian 1967; SBS: Markarian et al. 1986; KISS: Salzer et al. 2000) 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

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

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

Enables study of star formation statistics: - starburst duty cycles - prevalence of different SF states - maturation from dependence on taxonomy to quantitative characterization and analysis BCDs? HII galaxies? Sargent-Searle objects? starbursts? What is a “blue compact dwarf?” What is a [dwarf] “starburst?” Bergvall 12 BCDs? HII galaxies? Sargent-Searle objects? 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) Lee+09a

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?

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

UV HH PAHs MIR FIR[OII] a galaxy SED… Methods of measuring SFRs 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 L IR ) [CII] 158um (fine structure cooling lines) Radio Continuum

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

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

Methods of measuring SFRs: exploring SF at low density with GALEX 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. M83

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

a galaxy SED… Example 1: IR, dust reprocessed emission Kennicutt+09 Theme 2: progression toward broad UV-IR multi-wavelength coverage enables comparison between diagnostics. -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.

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

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

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

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

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

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

From population synthesis with ~10 5 M  SSPs…

…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 “MASSive CLuster Evolution and ANalysis Package” (Popescu & Hanson 09;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?

…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? J.C. Lee+09b Fumagalli+11

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

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

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

IZw18 IIZw40 IZw18 IIZw40 Samples are well- characterized & statistically complete (e.g. Markarian 1967; SBS: Markarian et al. 1986; KISS: Salzer et al. 2000) “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 Theme 4: Using old tricks to find dwarf galaxies at higher redshift.

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

From…

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

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

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

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

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?