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Infrared properties of Interacting Galaxies: from Spirals to (U)LIRGs

Infrared properties of Interacting Galaxies: from Spirals to (U)LIRGs. Vassilis Charmandaris Univ. of Crete, Greece. IAG team: P. Appleton, C. Struck, B. Smith Paper: Smith et al. 2007, AJ, 133, 791 (U)LIRG team: L. Armus & V. Desai (Caltech), T. Diaz-Santos (Crete), H. Spoon (Cornell)

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Infrared properties of Interacting Galaxies: from Spirals to (U)LIRGs

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  1. Infrared properties of Interacting Galaxies: from Spirals to (U)LIRGs Vassilis Charmandaris Univ. of Crete, Greece IAG team: P. Appleton, C. Struck, B. Smith Paper: Smith et al. 2007, AJ, 133, 791 (U)LIRG team:L. Armus & V. Desai (Caltech), T. Diaz-Santos (Crete), H. Spoon (Cornell) Papers: Armus et al. 2007, ApJ 656, 148 ; Desai et al. 2007, ApJ 669, 810 ; Diaz-Santos et al. 2010 ApJ in press (@arXiv:1009.0038)

  2. Outline of the talk • Why perform extragalactic studies at infrared wavelengths • Why study Interacting galaxies and major results we have learned? • Where is most of the energy produced in Interacting galaxies • Discuss some IR diagnostics for the presence of an active nucleus • Global mid-IR properties (U)LIRGs based on Spitzer/IRS samples.

  3. Photospheric light reprocessed by dust Microwave Background Photospheric light from stars History of Star-Formation in the Universe Blain et al. 2002 • Optical surveys indicate that the mean SFR in the Universe was much greater at z > 1 (e.g. Madau et al. 1996) • COBE revealed a cosmic far-IR background with energy > the integrated UV/optical light  dust extinction is important in the early Universe! • IR/sub-mm surveys indicate even greater rates of star formation than seen in optical.  To accurately determine the “SFR” requires bothopticalandfar-IR/sub-mmsurveys.

  4. Extragalactic IR from 1971 until today Number of extragalactic sources detected at ~10μm : 1971  13 (Neugebauer et al. ARA&A ) 1978  ~100 (Rieke & Lebofsky ARA&A) 1988  IRAS PSC ~250,000 entries (~75,000 CGQ) 1995: ISO is launched first mid-IR spectroscopy 2003: Spitzer is launched. New era of IR begins 2009: Herschel is launched! Far-IR possibilities

  5. IRS MIPS IRAC 10/00 Spitzer Instruments – BALL Oct. 2000 Price ~$30 million

  6. Spitzer Cape Canaveral Launch Aug. 25, 2003

  7. The Advantages of Space... The Advantages of Space: 100% Transmission and a One-Million Fold Decrease in Sky Brightness. The outer Space is cold!

  8. Why study Interacting Galaxies • Most galaxies are not isolated (Baade 1920) • Interactions determine the morphology and evolution of galaxies. • Our own Galaxy is interacting with the LMC and SMC • The galaxy merging rate increases with redshift ~(1+z)m, m>2 (Carlberg et al. 1990, Lavery et al ’96, ‘04) => Cosmological implications (a must in order to attract attention and funding!) • Massive starbursts are found in regions with high dust content • they are often hidden in the optical -> IRAS (Soifer et al. 1984, Houck et al. 1984, Bushouse 87) • most of the energy is emitted in the infrared wavelengths • Nearly all Luminous IR galaxies (LIGs) are mergers (ie. Sanders 1988) • The optical/near-IR morphology is misleading (Bushouse & Werner 1990, Mirabel et al. 1998)

  9. Bushouse 1987

  10. Vigroux et al 1996 NGC 4038/39: The Antennae HST/WFPC2 Whitmore & Schweizer, AJ,1995

  11. NGC4038/39 – Mid-IR spectroscopy Mirabel et al., A&A, 1998 L(IR)~5x1010 Lsun

  12. Dust and Star Formation • Dust grains act as catalyst for the formation of molecular gas • Dust grains are responsible for the heating of the gas • A far-UV photon hits a dust grain and ejects an electron • The ejected photoelectron heats the gas (very inefficiently ~0.1 - 1 %) • 50% of gas heating is due to grains of sizes < 15 Å • Subsequently the gas cools via far-IR emission lines ( [OI] 63 um , [CII] 158 um) • Emission from Polycyclic Aromatic Hydrocarbons (PAHs), dominate the mid-IR (5-20 um) flux in normal galaxies and quiescent star forming regions • One can use mid- / far-IR prescriptions to estimate star formation rates (Far-IR:Kennicutt 1998, Mid-IR/ISO: Rousell et al. 2002, Forster-Schreiber et al 2004, Mid-IR/Spitzer: Calzetti et al. 2005, Wu et al. 2005, Relano et al. 2006)

  13. τabs: time between two photon hits a: grain size Draine 2002 A day in the life of a dust grain

  14. PAH Normal Modes • 10-20% of the total IR luminosity of a galaxy • Tens - hundreds of C atoms • Bending, stretching modes  3.3,6.2,7.7,8.6,11.2,12.7 m • PAH ratios  ionized or neutral, sizes, radiation field, etc. Leger & Puget (1984) Sellgren (1984) Desert, et al. (1990) Draine & Li, (2001) Peeters, et al. (2004)

  15. Mid-IR Emission as star formation tracer (ISO) Forster-Schreiber et al., A&A, 2004

  16. LP = (6.2μm + 11.2μm) PAH Farrah et al. 2007 Mid-IR Emission as star formation tracer (Spitzer) Calzetti et al., ApJ, 2007

  17. Energy Balance in Galaxies Helou et al., ApJ, 2001

  18. Sanders & Mirabel, ARA&A, 1996 The SED of LIGs • In the Mid-IR: • we are less affected by absorption • than in optical Av = 70*A (15μm) • better spatial resolution than Far-IR • BUT… • Only a fraction of the bolometric luminosity is emitted in the mid-IR. • Can we still say something about the global energy production • using the mid-IR? • Yes! or maybe...

  19. SED Decomposition of a Galaxy Credit: F. Galliano

  20. Toomre’s Sequence

  21. Mid-IR Far-IR Correlation in Toomre’s Sequence ISO: 15μm / 7μm IRAS 25μm / IRAS 12μm IRAS 60μm / IRAS 100μm Charmandaris et al., 2001 Mid-IR imaging does reveal the intensity/age of a starburst

  22. Interacting Galaxies with Spitzer • A Sample of 35 binary interacting systems has been imaged with Spitzer (IRAC/MIPS : GO-1 Struck et al.) • Systems are nearby (<150Mpc), disturbed in the optical, with extended tidal features (>3arcmin), well separated, with 8.9<log[L(IR)]<11.2 • Their mid-IR properties were analyzed and compared to a control sample of normal galaxies (Spirals, Es, Irr) (Smith et al. 2007)

  23. Interacting Galaxies with Spitzer (2)

  24. Interacting Galaxies: mid-IR Luminosities Smith, et, al 2007

  25. Interacting Galaxies: mid-IR Luminosities 7% of Arp disks

  26. Interacting Galaxies: mid-IR Luminosities <10% of Arp disks

  27. Interacting Galaxies: mid-IR Luminosities <10% of Arp disks

  28. Star Formation Rate & mid-IR nuclear concentration Smith, et, al 2007 The SFR for isolated spirals (SINGS) and well separated interacting Arp systems is similar ~ few Msun/yr. However, in the Arp systems the mid-IR flux is 2-4 times more centrally concentrated.

  29. Moving to higher Luminosities: GOALS • The Sample is drawn from the Great Observatory Allsky LIRG Survey (GOALS; Armus et al. 2009) of 202 systems (181 of which are LIRGs) • All systems are observed with all four Spitzer/IRS modules (5-37μm) • Additional Spitzer data with IRAC/MIPS, as well as HST, GALEX, VLA, CO

  30. (U)LIRG Basics Properties • LIR 1012 L ; Lbol ~ LIR ; Lopt < 0.1 LIR ; LIRGs 1012 L LIR 1011 L ; • 90 – 95% are interacting, or in merging systems (50% in LIRGs) • very strong OIR emission lines (H+, [OI,] [OIII], [NII], [SII], [FeII], etc.) • NIR CO absorption bands from young stars • large, compact reservoirs of cold molecular gas ( > 109 - 1010 M ) in their nuclei (R  1 kpc). • drive “superwinds” of hot, enriched gas into the IGM • relatively rare in the local Universe - only ~3% of galaxies in IRAS BGS are ULIRGs, but much more important at high-z Questions • What are the dominant power sources (50-500 Myr -1 SB or AGN ?) • Do we see any mid-IR spectral “evolution” indicative of a change in SF properties with redshift or luminosity (e.g. PAH strength, H2 fraction, etc.) ? Samples • IRS/GTO: 110 ULIRGs out to z=0.9 • GOALS Legacy program: 202 systems (181 LIRGs)

  31. ULIRGs dominate the high luminositygalaxy population in the local Universe LIRGs and ULIRGs are responsible for ~3% of of the L(IR) at z~0 but for >75% at z>~1 (Elbaz et al. 2003) Sanders & Mirabel 1996

  32. ULIRGs (LIR>1012) are Interacting Systems Sanders et al. 1988 Surace & Sanders 2001

  33. The first 18 low-resolution IRS spectra of ULIRGs Diversity! is the name of the game…

  34. IRS Spectra of BGS Sources Charmandaris et al. 2005 ISO PHT-S spectra of BGS Sources

  35. Spoon et al. 2004, A&A, 414,873 Arp220

  36. Use the 2D images of all LIRGs and re-extract total 5-15μm spectrum using the SSC pipeline algorithms • Use a standard star (HR7341) as our unresolved point source (PSF) • Scale the spatial profile of the standard star along the slit at every wavelength and subtract it from the corresponding profile of each source. • Define as fraction of Extended Emission (EE): Total LIRG flux (λ) - PSF (λ) Fraction of EE (λ) = Total LIRG flux (λ) Extended Emission: The Method

  37. Types of MIR spatial profiles Diaz-Santos et al. 2010 • Three spatial profiles are identified: Constant: no variation as a function of λ (~50% of sample), PAH/line extended: 20-70% of PAH flux is extended (~17% of sample), Si “extended”: Si at 9.7μm appears extended (~24% of sample) -> suggests that integrated spectrum underestimates nuclear extinction.

  38. Extended Emission and L(IR) The median fraction of extended emission decreases when L(IR) increases. Similarly for the 13μm continuum emission

  39. Extended Emission and Interaction stage • Use Merger optical/near-IR classification from Petric et al. 2010 (submitted) • 0: non interacting -> 5: mergers • More advanced mergers are more luminous and also more compact in their mid-IR continuum (Similar to what has been shown in other wavelengths) Diaz-Santos et al. 2010

  40. Extended Emission and AGN • Use mid-IR AGN classification from Petric et al. 2010 (ApJ submitted) • Using “Laurent diagram” (Laurent et al. 2000) • AGN dominated sources also more compact in their mid-IR continuum (Note that we refer to mid-IR dominant AGN) Diaz-Santos et al. 2010

  41. Extended Emission and FIR Colors • Use IRAS colors as probe of the global ISM “temperature” • Sources which are more compact in their mid-IR continuum have warmer far-IR colors To be tested with Herschel (Key Project: Hercules ; PI P. van der Werf) Diaz-Santos et al. 2010

  42. UV/mid-IR comparison of two LIRGs Images: HST/STIS UV - Contours: ISO/CAM7um • To be explored better with GOALS: • Preliminary GALEX/MIPS results (Howell et al. 2010) indicate that: • Among GOALs interacting systems 32% have one galaxy dominate the UV emission and the other the 24μm emission • Based on number counts 15-30% of z~2 systems are unresolved as VV114 7μm/UV ~800:10:35 7μm/UV ~330:160:190 The spatial resolution of ground & Spitzer/MIPS24 surveys of LIRGs at z~2 will result in blending of the emission from the unresolved interacting components leading to a systematic underestimation of their dust content. UV data: Goldader et al. 2002 Charmandaris, et, al 2004

  43. Averaged ULIRG SEDs Desai et al. 2007

  44. PAH EQW vs. LIR Armus et al. 2007

  45. Local ULIRGs & high-z ULIRGs/sub-mm Desai et al. 2007

  46. Probing the dominant energy source of galaxies • Many methods developed to quantify the fraction of star formation or emission from an accretion disk (AGN) in galaxies. • (Mushotzsky @astro-ph/0405144) • The presence of an AGN can be detected most ambiguously via: • Hard X-rays (>10keV) • Multi frequency radio observations (thermal/synchrotron fraction) • Difficulties: • Very few hard X-ray photons • Problems of self absorption in the interpretation of radio • For practical reasons most work has been performed via: • Optical spectroscopy (i.e. Kim et al. 1998, Hao et al. 2005) • Near-IR spectroscopy (i.e. Veilleux et al. 1999) • Advantages of IR: • Most galaxies emit a larger fraction of their energy in the IR. • Less affected by extinction than optical/near-IR

  47. IR diagnostics of AGN • IRAS Era: • using the differences in IRAS colors -warm/coldsources(i.e. de Grijp 1985) • Difficulty:Broadband colors only. • ISO Era: • Detect High Ionization lines(Genzel et al 1998, Sturm et al. 2002) • [NeV] at 14.3μm / 23.2μm (Ep~97eV) • [OIV] at 25.9μm (Ep~55eV) • Difficulty:the lines are faint • Detect changes in continuum / broad features • Presence of 7.7μm PAH(Lutz et al. 1999) • Relative strength of 7.7μm PAH with respect to the 5.5μm and 15μm continuum(Laurent et al. 2000) • Difficulties: • - The 7.7PAH is affected by the 9.7μm silicate feature • - The mid-IR continuum was not well defined with • ISO PHOT-S (~11.8μm) & ISOCAM/CVF (~16μm)

  48. IR diagnostics of AGN (2) • Spitzer Era: On-going efforts • Large sample of galaxies, both in the local universe and at high-z • Detect ISO High Ionization lines(Armus et al 2007, Farrah et al. 2007, Veilleux et al. 2009) • [NeV] at 14.3μm / 23.2μm (Ep~97eV) • [OIV] at 25.9μm (Ep~55eV) • Extend to other Ionization lines(Dale et al. 2009 & Hao et al. 2009) • [SiII] at 34.8μm & [S III] at 33.8μm • [FeII] at 26.0μm • Detect changes in continuum / broad features • Presence of 6.2μm PAH(Desai et al. 2007) • Measurements of 9.7μm Si extinction(Spoon et al. 2007) • Combine with L,M, band slope • PAH at 3.3μm (Imanishi et al. 2006) • Slope at 2-4μm(Nardini et al. 2008)

  49. MIR Diagnostic Diagram

  50. AGN thermal emission in mid-IR continuum • Rising slope of thermal emission from the AGN torus from 2-5μm due to grains radiating in near-equilibrium • Excess over starlight at ~4-5μm f(5μm)~10Jy z~0.004 D~14Mpc FSC15307+3252 Alonso-Herrero et al. 2003 f(5μm)~7mJy z~0.9 D~5.8Gpc

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