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Understanding Star Formation in Dwarf Galaxies: Step One
Janice C. Lee (STScI)Lowell Observatory Dwarf Galaxy WorkshopJune 19, 2012
twanight.org?id=3001717LMC, SMC, MW
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Understanding Star Formation in Dwarf Galaxies: Step One
Janice C. Lee (STScI)Lowell Observatory Dwarf Galaxy WorkshopJune 19, 2012
twanight.org?id=3001717LMC, SMC, MW
“The Outer Edges of Dwarf Irregular Galaxies” 2002
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Understanding Star Formation in Dwarf Galaxies: Step One?From a theoreticalperspective… perhaps begin from first principles…
review talks by MacLow, Krumholz, Bournaud
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Understanding Star Formation in Dwarf Galaxies: Step One?From an observationalperspective…
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Understanding Star Formation in Dwarf Galaxies: Step One?From an observationalperspective…
Review talks byLeroy (dust)Bolatto (molecular gas)
N4449 Haro11
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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
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IZw18IIZw40 IZw18IIZw40Samples 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
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progression toward statistically complete samples of dwarfs….
LVL/11HUGSKennicutt+08Dale+09Lee+11
ANGSTDalcanton+09Weisz+11
ALFALFAGiovanelli+05Huang+12
AVOCADO (N~7000!)Sanchez-Janssen+12
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LVL/11HUGSKennicutt+08Dale+09Lee+11
ANGSTDalcanton+09Weisz+11
ALFALFAGiovanelli+05Huang+12
AVOCADOSanchez-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
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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
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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?
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Weisz+08
time t(now)t(now)-1 Gyr
Methods of measuring SFRs
Resolved stellar populations and CMD fitting:e.g., Gallart+96; Tolstoy & Saha 96; Dolphin+97review talk by Weisz
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UV H PAHs MIR
FIR[OII]
a galaxy SED…
Methods of measuring SFRs
Why the need for so many different diagnostics?
dusttimescalesredshift
considerations
UV continuum[OII]3727H-alpha 6563A (H recombination lines)PAHTotal IR (monochromatic LIR)[CII] 158um (fine structure cooling lines)Radio Continuum
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Theme 1: progression from representative samples to statistically complete samples of SF dwarfs
Theme 2: progression toward broad UV-IR multi-wavelength coverage
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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+)
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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 oflocal vs. global properties in determining SF.
M83
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UV H PAHs MIR
FIR[OII]
a galaxy SED…
UV continuum[OII]3727H-alpha 6563A (H recombination lines)PAHTotal IR (monochromatic LIR)[CII] 158um (fine structure cooling lines)Radio Continuum
Theme 2: progression toward broad UV-IR multi-wavelength coverage
enables comparison between diagnostics.
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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 relativelyTransparent
-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.
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-4 -2 0
-6
-
4
-2
0
J.C. Lee+09b
Theme 2: progression toward broad UV-IR multi-wavelength coverage
enables comparison between diagnostics.
Example 2: H-alpha & UV emission
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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
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Slidecourtesy of U. Klein (Bonn)
Theme 2: progression toward broad UV-IR multi-wavelength coverage
enables comparison between diagnostics.
Example 3: radio continuum, IR
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Little known about radio continuum properties of typical dIrrs….
Slidecourtesy of U. Klein (Bonn)
Theme 2: progression toward broad UV-IR multi-wavelength coverage
enables comparison between diagnostics.
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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
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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
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From population synthesis with ~105 M SSPs…
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…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 massimpact observed and physical properties of dwarfs?
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…enables interpretation of observed properties of low mass, low SFR systems.
How does stochastic formation of high massimpact observed and physical properties of dwarfs?
J.C. Lee+09b
Fumagalli+11
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Lee&Gil de Paz+11
An example: star formation efficiencies
How does stochastic formation of high massimpact observed and physical properties of dwarfs?
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Lee&Gil de Paz+11
How does stochastic formation of high massimpact observed and physical properties of dwarfs?
An example: star formation efficiencies
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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
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IZw18IIZw40 IZw18IIZw40Samples 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 < 2.3WFC3 IR grism surveys:WISPS (Atek+10)3D-HST (van Dokkum+11)
z=0.8 & z=2.2 IR NB surveysHayes+10; Sobral+12; Lee+12
Theme 4: Using old tricks to find dwarf galaxies athigher redshift.
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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
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From…
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M81
M82
N3077
HoIX
Croxall+2009 I-bandYun+1994 HI
… to galaxy ecology…
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POSS/DSS
…even for seemingly isolated dwarf galaxies.
N4449
“The Dr. Jeckyll/Mr. HydeOf Irregular Galaxies”Hunter et al. 1998
Martinez-Delgado+2012see also Rich+2012N4449
D125
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POSS/DSS
Martinez-Delgado+2012see also Rich+2012
…even for seemingly isolated dwarf galaxies.
N4449
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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
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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?