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Understanding Galaxy Evolution: A Comparison of ISOCAM 15µm and Spitzer 24µm Source Counts

This paper examines the evolution of galaxies using infrared (IR) surveys, specifically comparing the ISOCAM 15µm and Spitzer 24µm source counts. It highlights the importance of dust extinction in galaxy formation, and how the luminosity from galaxies forming stars reveals crucial insights into cosmic evolution. It explores findings from ISO and Spitzer surveys, discussing the population of ultra-luminous infrared galaxies (ULIGs) and their prevalence in the past compared to today. The future role of Herschel and ALMA in enhancing our understanding of galaxy formation is also outlined.

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Understanding Galaxy Evolution: A Comparison of ISOCAM 15µm and Spitzer 24µm Source Counts

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  1. Understand Galaxy Evolution with IR Surveys: Comparison between ISOCAM 15-mm and Spitzer 24-mm Source Counts as a Tool Carlotta Gruppioni – INAF OAB La Thuile 08/03/05

  2. Summary • General Perspective • Past: ISOCAM Surveys • Present: from ISOCAM to Spitzer : What can we learn from the comparison between 15- and 24-mm? • Future: from ISOCAM and Spitzer to Herschel and ALMA

  3. General Perspective • Locally stars form in giant molecular clouds, where optical and UV light is strongly absorbed byDUST • Thanks to IRAS we know that galaxies forming stars at > 20 M/yr radiate the bulk of their luminosity above 5 mm: LIGS: 11  log(LIR/L)  12 ULIGS: 12  log(LIR/L) 13

  4. In the Past, when galaxies were more gaseous and formed the bulk of their present-day stars, it would be logical to expect to detect a large population of LIGs/ULIGs. • ISO observations showed that Galaxy Formation could not be understood without accounting for dust extinction as a major ingredient

  5. ISO SURVEYS • Mid-IR: ISOCAM (at 15 mm a LIG is visible up to z~1.3) - Several Surveys were performed in Garanteed Time (IGTES: 0.1 < S < 0.5 mJy; Elbaz et al. 1999) and Open Time (ELAIS: 0.5 < S < 150 mJy; Oliver et al. 2000; Rowan-Robinson et al. 2004)

  6.  Source counts exhibit a strong excess of sources below S15~2 mJy. Galaxies above this flux density do fall within the “no-evolution region”(ELAIS counts: Gruppioni et al. ’02) The predicted Extragalactic Background Light at 15 mm is: EBLmodels(15 mm) ~ 3.3 nW m-2 sr-1  ISOCAM resolves ~73 % of EBL

  7. Nature of ISOCAM galaxies Most are star-forming galaxies, often in small groups and showing irregular/merging morphologies. • from Shallow Surveys (i.e. ELAIS; • La Franca, Gruppioni et al. ’04) : • <L15> ~ 1010 L , <z> ~ 0.2 • from Deep Surveys (i.e. IGTES; Elbaz et al. ’99,’01) : <L15> ~ 1011 L , <z>  0.8 •  LIG is an important phase in galaxy life: a galaxy might experience several bursts of intense SF < z > = 0.8 HDFN < z > = 0.2 ELAIS-S1

  8. Cosmic Evolution Several authors have produced backwards evolution models to reproduce source counts and redshift distributions of ISOCAM galaxies (and IR galaxies): i.e. Devriendt & Guiderdoni ’00; Dole et al. ’00; Chary & Elbaz ’01; Pearson ’01, ’05; Franceschini et al. ’01, ’03; Malkan & Stecker ’01; Xu et al. ’01, ’03;King & Rowan-Robinson ’03; Lagache, Dole & Puget ’03;Pozzi, Gruppioni, Oliver et al. ‘04

  9. Cosmic Evolution All use a combination of luminosity and density evolution as a function of z of the IR luminosity function at 15 or 60 mm The major output of these models was to showthat LIGs/ULIGs were much more commonin the pastthan they aretoday (i.e.Chary & Elbaz ’01:comoving IR luminositydue to LIGs ~ 70 times larger at z~1 than today) Pozzi et al. ‘04 Lagache et al.’04 Pearson et al. ’01 Franceschini ’01 Franceschini upd.

  10. The Pozzi et al. (‘04) 15 m model (a) • Data • ELAIS:larger OT ISO survey, 12 deg2 • (PI: M. Rowan-Robinson) • ELAIS-S1 :field (4 sq.deg) completely analysed • Bologna + Roma • 15 m :406 sources (‘Lari method’, Lari et al. ‘01) • R-band :81% (330/406) of the 15 µm • sources optically identified R23 • Spectra:72% (293/406) of the 15 m • source spectroscopically classified • R=23 at ESO+2dF (La Franca et al ‘04)

  11. Relation L15/L_opt of versus L15 More luminous IR galaxy having larger L15/Lopt Starbursts Arp220 M82 M51 Spirals (Pozzi et al. 04)

  12. The Pozzi et al. (2004)15 m model (b) 2) Luminosity Function Method Quantitative estimators: Maximum likelihood (Marshall et al.’83) + 1/Vmax formalism (Schmidt ‘68) 4 Populations: Spiral (M51), Starburst (M82), AGN1 (Elvis et al. ‘94) & AGN2 (Circinus) Evolution:Starburst : density & luminosity Normal Spiral : no evolution Agn1 & AGN2 : luminosity NEW !!!! L_15/L_opt to divide starburst/spiral

  13. ISOCAM extragalactic counts at 15m Pop. kl kd zb ------------------------- Spiral 0 0 0 Starb 3.5 3.8 1 Agn1 2.6 0 2 Agn2 2-2.6 0 2 (NGC1068 or Circinus) Starbursts evolve in luminosity [as (1+z)3.5] and density [(1+z)3.8] up to z=1

  14. Luminosity Function z-distribution

  15. From ISOCAMto Spitzer... Spitzer Telescope is now providing new insight into the IR population contributing to the CIB In particular with the MIPS 24-mmband, which is starting to detect the high-z (z~1.5-3.0) analogs of the 15-mm galaxies

  16. FLS Extragalactic Source Counts at 24 mm:comparison with some existing models Galaxy evolution models: Franceschini et al. (2001) & Rodighiero et al. (2004): non-evolving normal pop, fast-evolving type-II AGNs & starbursts, evolving type-I AGNs Lagache, Dole & Puget (2003):non-evolving normal spirals and starbursts with L density evolving with redshift IRAS data points (transformed to 24 μm) (Hacking & Soifer 1991; Sanders et al. 2003) No-evolution model normalized to IRAS counts Marleau, Fadda, Storrie-Lombardi, et al. 2004

  17. Spitzer 24 m FLS compared to 15 mm source counts(Marleau et al. ‘04) Shaded region: 24 mm counts • Confirm existence of rapidly evolving population discovered by ISOCAM • Question: how to compare with previous ISOCAM 15m counts? • ONLY one ratio assumed to convert 15 mto 24 m(S24/S151.2) ? ELAIS range empty symbol: 15 mcounts Gruppioni et al.’02

  18. Ratio for different IR prototype populations Considering M82 (dominant population): ratio strongly dependent on z(because of PAHs) S24/S152-2.5 z 0 S24/S151.2 z 1 S24/S15> 5 2<z< 3 The ratio assumed by FLS team is fine for objects at z1 but NOT for ELAIS sources or higher z ones

  19. Model predictions S24/S15as a function of z, S24 S > 2-3 mJy dominated by objects with S24/S152-2.5 S  0.3 mJy dominated by objects with S24/S15 1.5 S < 0.2-0.3 mJy dominated by objects with S24/S15 > 2-3 -> NEW POPULATION !

  20. Contributionsfrom different z While galaxies with z<1.3 dominate up to S0.3 mJy, at lower fluxes the new high-z population starts contributing for a significant fraction: Anyway, 70 % background qt z < 1.5 Spitzer deep counts resolve75 % background

  21. A bit of criticism ... After some months… Swire team (Shupeet al. 2005, in preparation) First published 24 m data FLS team (Marleau et al. ‘04)

  22. Our Model fit to other Spitzer Bands

  23. From ISOCAMto the longer l’s of Spitzer and to HERSCHEL • For the longer l’s  Fundamental Ingredient: Galaxy SEDs (FIR BUMP) !!! • For starburst galaxies we need “colder” SEDs than the prototypical M82 to fit the observed 70 and 160 mmsource counts • Use the phenomenological evolution model to make predictions also in the Herschel bands (PACS:75, 110, 170 mm; SPIRE: 250, 350, 500 mm)

  24. Strength of our Model • The evolution parameters are determined with a Maximum Likelihood fit of the 15-mm LF, source counts and redshift distributions • Thestarburst/normal galaxy separation is based on a physical property of galaxies (L15/Lopt ratio) instead of being an arbitrary variable

  25. Weakness of our Model • Is based on 15-mm data only: Extend the ML fit to all the MIR/FIR observables (i.e. source counts and redshift distributions)  find the best-fitting multi-l solution • Use a single SED for each galaxy population: • Better using a SED library, with SEDs changing (i.e. becoming “colder”) as function ofLIRorz (mainly for starbursts)

  26. Separation between evolving and non-evolving population is sharp: • Better considering a smoother variation (i.e. different evolutions for different intervals of L15/Lopt)  MUCH WORK TBD SPITZER WILL HELP !!!

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