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Probing the properties of Luminous IR Galaxies with Spitzer/IRS

This study explores the characteristics of Ultra Luminous IR Galaxies (ULIRGs) utilizing Spitzer/IRS data. The research delves into the power sources, spectral evolution, and mid-IR shapes of these galaxies. With detailed extragalactic spectroscopic observations and diverse ULIRG programs, the study aims to advance the understanding of these enigmatic galaxies.

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Probing the properties of Luminous IR Galaxies with Spitzer/IRS

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  1. Probing the properties of Luminous IR Galaxies with Spitzer/IRS V. Charmandaris (Univ. of Crete & Cornell Univ.) IRS ULIRG team:J. Houck(PI), L. Armus, H. Spoon, B.T. Soifer(CoI), S. Higdon, J. Bernard-Salas, J. Marshall, V. Desai, T. Herter(CoI), P. Appleton, H. Teplitz, B. Brandl (Cornell, Spitzer Science Center, Caltech, Leiden, Crete)

  2. ULIRG Basics Properties • LIR 1012 L ; Lbol ~ LIR ; Lopt < 0.1 LIR • 90 – 95% are interacting, or in merging systems • 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.) ? • How does evolution in mid-IR spectral shapes affect the interpretation of IR number counts?

  3. Basic IRS Extragalactic Science Spectroscopic observations of previously known sources (IRAS, ISO, 2MASS, etc.) and those discovered by Spitzer itself • the physical conditions (ISM, power sources) within dusty galaxies. • theredshifts of optically obscured, distant galaxies. The IRS delivers superior sensitivity and wavelength coverage compared to the ISO spectrographs.  ULIRG program  NDWS/Bootes survey PHT-S (R~90; 2.5-11.6m) limit > 0.2Jy CAM-CVF (R~40; 2.5-17.3m) limit > 0.1Jy SWS (R~1500; 2.4-45m)* limit > 1Jy IRS low-res (R~80; 5.2-38m) 1-2 mJy (5, 500 seconds) IRS high-res (R~600; 10-37m) 3-5x10-18 W m-2 * Only 5 galaxies were observed with SWS over the full range

  4. The ULIRG program - details Of the 110 sources • Flux limited: 32 have S25 0.3 Jy and log LFIR  11.85 L. We are observing all 32 in low and high-res modes. • High redshift: 27 have z  0.3. 12/27 are being observed in low and high-res. • High luminosity: 11 sources have log LFIR 12.5 L. 10/11 are being observed in low and high-res.. • Mix of Far-IR colors: 68 are “cold” (S25/S60 < 0.2) and 21 are “warm”. This is a higher fraction of warm sources than in a flux-limited survey (typically ≤ 10%). • GO Programs: Veilleux et al., Lutz et al., Imanishi et al., Verma et al. Sturtm et al. • Additional IRS spectroscopy of ~30 “Template” galaxies “usual suspects”

  5. The IRS ULIRG Program

  6. 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)

  7. Dale et al., 2001 Chary & Elbaz, 2001 Templates Used (to date) • Sources of PAH templates used to date: • Theoretical/Lab PAH band models. • Few bright ISO galaxies (e.g. Arp220) • Average ISO Key Project “normal” galaxy spectrum.

  8. Papovich et al., 2004 Lagache et al., 2004 Fitting the Number Counts

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

  10. IRS Spectra of BGS Sources Armus et al. 2005 ISO PHT-S spectra of BGS Sources

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

  12. Armus et al. 2006

  13. MIR Diagnostic Diagram

  14. PAH EQW vs. LIR

  15. Averaged ULIRG SEDs Charmandaris et al. 2006

  16. The Most Luminous ULIRGs (so far) Charmandaris et al. 2006

  17. IRS/NDWFS optically faint sources 31 optically faint sources with f24 > 0.75 mJy selected for IRS follow-up (17 have R > 26 mag - no optical ID) • 17 have redshifts measured with IRS (silicate and/or PAH) 16 with 1.7 < z < 2.8 (+/- 0.1-0.3 in z) • 13 best fit with AGN-like templates (00183, Mrk 231) 4 best fit with SB-like templates (Arp 220, N7714) • 16 have high q = log (f24 / f20cm) > 0.8 (SB or radio quiet AGN) • All have very large implied LIR: 1x1013 < LIR < 5x1013 L • MIR, optical selections bias initial IRS redshift survey in favor of dusty, warm, AGN-like ULIRGs with 1.6 < z < 3. z < 1.6  strong silicate reduces MIPS 24 z > 3  silicate drop moves out of LL

  18. 7.7,8.6 PAH 7.7,8.6 PAH 9.7 silicate absorption 9.7 silicate absorption IRS/NDWFS optically faint sources Houck, et al. (2005)

  19. IR diagnostics of an AGN • Most work on identifying AGN in the IR started from IRAS using the differences in IRAS colors -warm/coldsources(i.e. de Grijp 1985) • Difficulty:Broadband colors only. • The availability of sensitive mid-IR spectrographs on board ISO enabled us to make considerable progress: • 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)

  20. 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

  21. NGC 7714 [Brandl et al. 2004] UGC 5101 [Armus et al. 2004] NGC 4151 [Weedman et al. 2005] 6.2 PAH Variation in IRS low resolution spectra

  22. M 17 [ISO-SWS/1000.] 3C 273 [Hao et al. 2005] NGC 7023 [Werner et al. 2004] Selection of the three extreme spectra

  23. Starburst/HII-like 75% 75% PAH/PDR-like 75% AGN-like Modified “Laurent” Diagram The mid-IR [AGN/SB/PDR] parameter space

  24. Starburst/HII-like PAH/PDR-like AGN-like Populating the [AGN/SB/PDR] diagram

  25. IRS ULIRG Summary • Composite (AGN+SB) spectra are common (Mrk 273, 05189, Mrk 1014, UGC 5101, etc.). There are a wide range of MIR spectra shapes among ULIRGs due to PAH emission, silicate and H2O / hydrocarbon absorptions, and hot dust. • Fitting number counts with 1-2 “templates” can be misleading. • Only 3/10 BGS sources have detectable [NeV]. Some (Arp 220, 14348 and 12112) are consistent with pure SB’s ([NeV]/[NeII] < 0.02-0.05). Arp 220 (low [NeV], low 6.2 PAH EQW, low 6.2 PAH/LIR) may have both a heavily obscured SB and a buried AGN (Spoon, et al. 2004; Iwasawa, et al. 2004). • The combination of fine structure line ratios, PAH strengths, and continuum fitting (hot dust) will provide an accurate assessment of the AGN/SB fraction. Comparison to HX data is critical. • High-luminosity ULIRGs tend to have smaller 6.2 PAH emission by 5-10x, and less silicate absorption, but there are obvious exceptions (e.g. 14537 and 00183). The high-luminosity ULIRGs are much more AGN-like in the MIR.

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