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

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

Understanding Star Formation in Dwarf Galaxies: Step One?From a theoreticalperspective… perhaps begin from first principles…

review talks by MacLow, Krumholz, Bournaud

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

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

Review talks byLeroy (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

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

progression toward statistically complete samples of dwarfs….

LVL/11HUGSKennicutt+08Dale+09Lee+11

ANGSTDalcanton+09Weisz+11

ALFALFAGiovanelli+05Huang+12

AVOCADO (N~7000!)Sanchez-Janssen+12

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

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 12BCDs?

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

time t(now)t(now)-1 Gyr

Methods of measuring SFRsResolved stellar populations and CMD fitting:e.g., Gallart+96; Tolstoy & Saha 96; Dolphin+97review talk by Weisz

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

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 oflocal vs. global properties in determining SF.

M83

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.

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.

-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

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

Slidecourtesy 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….

Slidecourtesy 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 ~105 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 massimpact observed and physical properties of dwarfs?

…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

Lee&Gil de Paz+11

An example: star formation efficiencies

How does stochastic formation of high massimpact observed and physical properties of dwarfs?

Lee&Gil de Paz+11

How does stochastic formation of high massimpact 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

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.

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-bandYun+1994 HI

… to galaxy ecology…

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

POSS/DSS

Martinez-Delgado+2012see 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?