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SINGS: Panchromatic Data and Star Formation in Nearby Galaxies

SINGS: Panchromatic Data and Star Formation in Nearby Galaxies. Daniela Calzetti (UMass, Amherst). Gas Accretion and Star Formation in Galaxies, Garching bei Munchen, Germany, Sept 10-14, 2007. SINGS (Spitzer Infrared Nearby Galaxies Survey).

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SINGS: Panchromatic Data and Star Formation in Nearby Galaxies

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  1. SINGS: Panchromatic Data and Star Formation in Nearby Galaxies Daniela Calzetti (UMass, Amherst) Gas Accretion and Star Formation in Galaxies, Garching bei Munchen, Germany, Sept 10-14, 2007

  2. SINGS (Spitzer Infrared Nearby Galaxies Survey) • Cambridge University of Massachusetts • Rob Kennicutt (PI) Daniela Calzetti (Deputy PI) • STScI • Claus Leitherer, Michael Regan, (Martin Meyer) • Caltech/IPAC/SSC • Lee Armus, Brent Buckalew, George Helou, Tom Jarrett, Kartik Sheth, Eric Murphy (Yale) • Arizona • Chad Engelbracht, (Karl Gordon), Moire Prescott, George Rieke, Marcia Rieke, JD Smith • Arizona State • Sangeeta Malhotra • Bucknell • Michele Thornley • Hawaii • Lisa Kewley • MPIA • Fabian Walter, Helene Roussel • NASA Ames • David Hollenbach • Princeton • Bruce Draine • Wyoming • Danny Dale • Imperial College • George Bendo

  3. Introduction: Theory vs. Obs. ACS-GOODS Giavalisco et al. • Star formation links the invisible (driven by gravity and the subject of theoretical modeling) and the visible (directly measurable) `Universe’ • SF shapes its surroundings by: • depleting galaxies of gas • controlling the metal enrichment of the ISM and IGM • regulating the radiative and mechanical feedback into the ISM and IGM • shaping the stellar population mix in galaxies. • Need to: • Characterize the laws of SF • Derive unbiased SFR measurements.

  4. SFR Measurements Dale et al. 2007 `calorimetric’ IR  (m) 1 10 100 1000 24 m 70 m 160 m 8 m [OII] P H UV Dust-processed light Direct stellar light • Derived virtually at all wavelengths, from the X-ray to the radio. • Measure massive stars emission - requires IMF assumptions.

  5. The `ground truth’ - 1 • FIR, UV+FIR? (GALEX, Spitzer) • FIR is calorimetric measure (not a problem at low-z; IRAS, ISO, Spitzer, Herschel,…); • for extended sources (whole galaxies), contribution of evolved (non-star-forming) populations to both UV and FIR. • Optical lines (mainly H recombination lines)? • Dust extinction (blue lines) • Upper end IMF • Underlying stellar abs. (Balmer) • `Difficult to observe’ (IR lines) M51: UV, H, 24 m

  6. The `ground truth’ - 2 Scale ~ 100-600 pc NGC925 • Use P (1.876 m) as `ground truth’, i.e., an `unbiased’ measure of instantaneous SFR (Boeker et al. 1999; Quillen & Yukita 2001) for investigating SINGS galaxies: • Relatively insensitive to dust (AV=5 mag implies P < 2x) • Sensitive to timescale ~ 10 Myr • But … limited to central regions of galaxies M51 33 normal galaxies (220 regions) 34 starbursts

  7. UV, Dust, and Age (Meurer et al. 1999, Goldader et al. 2002, C. et al. 1994,1995,1996,1997,2000) Starbursts 26 A dusty stellar population may have similar UV characteristics of an old population SFR > 0.3 – 1 Mo/yr/kpc2 SFR(UVcorr, ), SFR(UV+FIR) OK for starbursts at all redshifts (e.g., LBGs at z~3)

  8. SFR-Extinction (Wang & Heckman, 1996; Heckman et al. 1998; Calzetti 2001 Hopkins et al. 2001, Sullivan et al. 2001, C. et al. 2007) AV = 3.1 E(B-V) = 14.4 Z SFR0.64 Starbursts SF regions in normal galaxies

  9. UV, Dust, and SF Activity SFR << 0.3 – 1 Mo/yr/kpc2 (Buat et al. 2002, 2005, Bell 2002, Gordon et al. 2004, Xu et al. 2004, Seibert et al. 2005, C. et al. 2005) Major boost from GALEX • Deviations due to time-averaged SFH? (Xu et al. 2004) • Johnson et al. (2007) find little correlation with Dn(4000) < 1.7 • Due to recent SFH? (<100-200 Myr, C. et al. 2005) • displacement between UV and line or IR emission in M51. Blue= starbursts Red= normal SF 26

  10. FIR to SFR? Dale et al. 2007 `calorimetric’ IR  (m) 1 10 100 1000 24 m 70 m 160 m 8 m FIR - sensitive to heating from old, as well as young, stellar populations 8 m - mostly single photon heating (PAH emission) 24 m - both thermal and single photon heating 70 m and 160 m - mostly thermal, also from old stars

  11. SFR[MidIR()] • ISO provided ground for investigating monochromatic IR emission as SFR tracers, esp. UIB=AFE=(?)PAH (e.g., Madden 2000, Roussel et al. 2001, Boselli et al. 2004, Forster-Schreiber et al. 2004, Peeters et al. 2004, …).  F() 8 m 24 m • Spitzer has opened a `more sensitive’ window to the distant Universe: • A number of studieshas looked at the viability of monochromatic IR emission (mainly 8 and 24 m) as SFR indicator (Wu et al, 2005, Chary et al., Alonso-Herrero et al. 2006, etc.) • Appeal of PAH emission (restframe 7.7 m emission for z~2) for investigating star formation in high-z galaxy populations (e.g., First Look, GOODS, MIPS GTO, etc.; Daddi et al. 2005) • Monochromatic 24 m (restframe) emission also potentially useful for measuring high-z SFRs (see Dickinsons’ Spitzer Cy3 Legacy)

  12. SFR(24) Slope is `super-linear’ (1.23) Slight dependence on metallicity (Walter et al. 2007) Spread is significant (0.4 dex FWHM) SFR(Mo yr-1) = 1.27 x 10-38 [L24(erg s-1)]0.885 Can we understand (and interpret) the slopes, and the spread, of the data? Red: High Metallicity SF regions Green: Medium Metallicity SF regions Blue: Low Metallicity SF regions Black filled symbols: Low Met Starbursts and LIRGs C. et al.2007

  13. Models L(IR) = 0 FS() [1- 10(-0.4 A()) ] d SFR - Extinction attenuation law/geometry=> A() FS() ~ FS(mass/age,SFR,Z) Calzetti et al. 1994, Meurer et al. 1999; Calzetti 2001; implicit foreground. Starburst99; Leitherer et al. 1999 H, P (intr.) H, P (obs) L(IR) Draine & Li 2006; assume mass fraction of low-mass PAH depends on metallicity L(8), L(24)

  14. SFR(24) in Models 4 Myr burst (or 100 Myr constant) SF, solar metallicity L(IR) ~ L(P) for E(B-V) > 1 mag How do we get a super-linear slope? Myr: 10 8 6 4 2 1/10 Z Draine & Li 2006 • Larger-than-unity slope (in log-log scale) is effect of increasing `dust temperature’ • Non-linear behavior at decreasing luminosities is due to increasing ISM transparency • Spread due to range of HII regions ages (~2-8 Myr) • Some dependence on metallicity (Walter et al. 2007)

  15. 24 m Morphology vs IR/UV S/nuc L(IR)/L(UV) Spirals D/Irr Dale et al. 2007 F(70)/F(160)

  16. SFR(8) Slope is `sub-linear’ Strong dependence on metallicity Dependence on region measured Same spread as SFR(24) for high metallicity data. C. et al.2007 Red: High Metallicity SF regions Green: Medium Metallicity SF regions Blue: Low Metallicity SF regions Black symbols: Low Met Starbursts and LIRGs

  17. SFR(8) in Models 4 Myr burst (or 100 Myr constant) SF, solar metallicity Myr: 10 8 6 4 2 1/10 Z Draine & Li 2006 • Lower-than-unity slope and region-size dependence unaccounted for by models; measured L(8) may be `contaminated’ by diffuse emission heated by underlying (non-star-forming) populations; or may be destroyed/fragmented by high intensity radiation. • L(8 m) is strongly dependent on metallicity; lower metallicity may lower number of low-mass PAH

  18. F(8 m) vs. metallicity Draine et al. 2007

  19. A new `ground truth’ How can we compensate for increasing medium’s transparency at low IR emission end? L(H) = unobscured SF L(24m) = dust-obscured SF a L(H)+b L(24 m) Kennicutt et al. 2007 C. et al. 2007 best fit slope ~ 1 SFR (Mo yr-1) = 5.3 x 10-42 [L H, obs + 0.031 L24m (erg s-1)] Not necessarily `practical’ for high-z studies

  20. Dust Masses and Xco Draine et al. 2007

  21. The Large Millimeter Telescope/Grande Telescopio Millimetrico • A Mexico/USA collaboration • Single-dish 50 m antenna; 2.5 m secondary • 8’ non-aberrated FOV; 6” resolution at 1 mm • ~1-4 mm science: cold dust emission, CO, HCN, etc. • Sensitivity is such that dwarf galaxies and interarm regions in spirals will be observable (or tight upper limits will be placed): • Will remove major limitations in current studies of the laws of star formation • Will be instrumental in understanding dependencies of the H2/CO ratio (X-factor) Expected first light ~ mid/end 2008

  22. Conclusions • SFR(UV, ) and SFR(UV+FIR) measure intrinsic SFRs in starbursts (SFR > 0.3 – 1 Mo/yr/kpc2); • In normal SF galaxies, the UV probes timescales up to ~ 100 Myr. Affected by both dust extinction and dust-age degeneracy. Conversion to SFR not immediate without `second parameter’ dependence. • SFR(FIR) probes star-forming as well as non-star-forming stellar populations, thus also potentially problematic (at the ~2-3x factor level) in normal SF galaxies. It is a `calorimetric’ measure (potentially limiting at high z). • SFR(8) and SFR(24) are more closely associated with H than with UV (C. et al. 2005). • In the absence of AGNs, L(24) and L(24)+aL(Hprovide more robust SFR indicators than L(8) (possibly also better than UV in normal SF galaxies) • Use of the 8 m emission requires extreme caution: very sensitive to both metallicity (30x) and presence of diffuse emission (PAH heated by the general stellar population; ~2x) • Although derived for HII regions/starbursts, preliminary studies indicate that calibrations should be applicable to general SF galaxy population (within 20%)

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