Program PI: Joseph M. Mazzarella (Caltech, IPAC) Collaborators:

1. Part I: Our Spitzer Imaging Program of a Complete Sample of 200 LIRGs and ULIRGs in the Local Universe Program PI: Joseph M. Mazzarella (Caltech, IPAC) Collaborators: Justin H. Howell (Caltech, IPAC); Steven Lord (Caltech, IPAC); Jason A. Surace (Caltech, SSC); David T. Frayer (Caltech, SSC); Aaron S. Evans (Stony Brook); Catherine M. Ishida (Subaru); Joseph B. Jensen (Gemini); David B. Sanders (UH/IfA); Greg Bothun (U. Oregon); Bernhard Schulz (Caltech, IPAC); Sylvain Veilleux (U. Maryland); Dong-Chan Kim (U. Maryland); Kevin Xu (Caltech, IPAC); Phil Appleton (Caltech, SSC); Lee Armus (Caltech, SSC); Barry F. Madore (OCIW & IPAC)

2. Motivation: Importance of LIRGs • ULIRGs ! • Dominate the energenics and the physical evolution of the early Universe • Represent hypothesized evolutionary connections with QSOs, powerful radio galaxies, and elliptical galaxy formation: via tidal dissipation and violent relaxation • Present unsettled controversy over whether their bolometric luminosities are dominated by dust-obscured AGNs or vigorous star formation rates (SFRs) • Prior history of ULIRGs and their subsequent evolution are poorly understood. • We hypothesize that ULIRGs evolve from a subset of the much larger population of LIRGs. • Some LIRGs are in a pre-ULIRG phase of increasing SFRs and/or AGN fueling • Some LIRGs are in a post-ULIRG phase of diminishing SFRs or AGN fueling • Some LIRGs may lack conditions required to elevate Lbol >1012 Lduring a merger, thus never becoming ULIRGs • Can we disentangle these different cases, statistically and possibly in individual systems?

3. The Importance of LIRGs • LIRGs make up the infrared galaxy luminosity function over the range of Lir where tidal interactions and mergers begin to dominate over isolated, massive gas-rich galaxies. • It is important to sample ir completely through the region where it crosses the rapidly declining high luminosity tail of optical (Schechter function). This is where the emergence of infrared-enhanced galaxy mergers begin to dominate the light output in the local Universe. • The high-luminosity tail of the IR-galaxy LF evolves strongly with redshift, increasing by ~100 between z=0 and z ~ 2.5 (Sanders 2003).

4. Motivation: Importance of LIRGs • Cosmic star formation density is dominated by an increasing fraction of LIRGS and ULIRGs with increasing redshift • LIRGs far more important than ULIRGs in terms of the total star formation density • Studying the low-z LIRGs and ULIRGs with Spitzer gives us a chance to understand the properties of their much more numerous high-redshift analogs, which at z ≳ 0.6 appear to dominate the total luminosity output of all galaxies. Le Floc’h et al. (2005)

5. Primary Science Questions & Goals • How do star formation rates and the spatial distribution of dust emitting regions vary with the stage of the interaction/merger, the mass ratio of the galaxies, the geometry of the encounter, and the properties of each galaxy known from optical, near-infrared, H I, CO, and radio continuum observations? • Which LIRGs most likely represent progenitors of ULIRGs and QSOs, and what characteristics of the galaxies and their merger geometries likely lead to dust heating dominated by AGNs rather than starbursts? • What are the relative amounts of cold (10 - 30 K), cool (30-50 K) and warm (Td > 50 K) dust components in LIRGs and ULIRGs, and can this be used to age-date merger events? Are there regions with very hot dust (600 - 1000 K) in some of these objects? • This survey will also provide an important archive of data for interpreting the global infrared properties of high redshift IR/sub-mm galaxies that can be well resolved only in local analogs.

6. The RBGS LIRG+ULIRG Sample • The parent population is the IRAS Revised Bright Galaxy Sample (RBGS), a complete flux-limited survey of all 638 extragalactic objects with total 60μm flux density greater than 5.24 Jy, covering the entire sky surveyed by IRAS at Galactic latitudes |b| > 5o (Sanders, Mazzarella, Kim, Surace & Soifer 2003, AJ, 126, 1607). • A complete sample of the brightest extragalactic FIR sources in the sky • Far-infrared counterpart to the RSA (optically selected) or 3C (radio selected) • Offers the best sources for detailed, close-up study of IR emission processes, and for multiwavelength investigations with spatial resolution.

7. The RBGS LIRG+ULIRG Sample • Our sample is of the local Universe at ~ D<200 Mpc • Our sample studies the transition region leading to the ULIRGS

8. The RBGS LIRG+ULIRG Sample • The sample under investigation with Spitzer consists of all 203 LIRGs (181) and ULIRGs (22) in the RBGS. • The sample contains objects representing all phases of this evolutionary sequence: NGC 5426/5427 NGC4038/4039 NGC 7252 NGC 3610 M 87

9. The RBGS LIRG+ULIRG Sample • Ishida et al. (2005) BVI images for ~40% of objects under investigation with Spitzer • In order of  Lir • Single galaxies  separated pairs  close pairs  double nuclei  merger remnants

10. The RBGS LIRG+ULIRG Sample Sanders & Mirabel (1996, ARA&A, 34, 749)

11. The Spitzer Observing Program • We were awarded 91.6 hours of GO-1 Spitzer time to image all RBGS (U)LIRGs not covered in the ROC. 362 AORs for ~180 targets were submitted • IRAC: 179 AORs in G0-1 program + 24 GTO/Legacy (ROC) = 203 targets • 3.6, 4.5, 5.8, 8.0 μm bands • 1.2" pixels and 5'x5' field well matched to most objects • HDR mode to correct pixels saturated in nominal 5x30 sec integrations • MIPS:183 AORs in G0-1 program + 20 GTO/Legacy (ROC) = 203 targets • 24, 70 & 160 μm bands • Photometric mapping & Super Resolution mode • Multiple 3 sec integrations with 2 or more mapping cycles • General Strategy • Mapping, clustering, and dithering to optimize coverage of pairs/groups • Each field visualized using SPOT to optimize the observingstrategy • Suitable redundancy for coverage, S/N, transient removal, etc. • Short integrations to minimize saturation problems near nuclei

12. The Spitzer Observing Program NGC 838, 839, 833 NGC 5257, 5268 MIPS 24 μm 70 μm IRAC 3.6 + 5.8 μm 4.8 + 8.0 μm MIPS 160 μm

13. IRAC & MIPS Images: log(Lir/L)~11.0

14. IRAC & MIPS Images: log(Lir/L)~11.5

15. IRAC & MIPS Images: log(Lir/L)~11.7

16. IRAC & MIPS Images: log(Lir/L)~12.0

17. Aperture Photometry & Our Future Goals • Our beginning method is to correlate aperture photometry on physical scales (eg. 2, 5 Kpc) with other measures: • Interaction state • Galaxy properties – molecular/atomic gas • Our ultimate goal is a system-by-system understanding of the evolutionary status of of these “Extreme Starburst Galaxies” – which LIRGS will become or were ULIRGS and why?

18. Steps towards future Goals • Surface brightness profiles and analysis: relative contributions of nuclear, bulge, disk, overlap, and tidal feature components, and of course the fluxes of each galaxy in the interacting systems • Higher resolution images will be beam-matched to lower resolution images to construct dust color temperature (flux ratio) maps. • Results will include an image atlas, color maps, tables of derived quantities, model fitting and interpretation to address the key questions outlined above. • B, V, R, I and K' (e.g, Fig. 1), combined with radio continuum images, CO and H I data from the literature (via NED) will be used to determine how the dust properties correlate with stellar populations, synchrotron radiation from relativistic electrons and free-free emission from HII regions, and the molecular and atomic gas content of the ISM. • We will compare with the SINGS results (Kennicutt et al. 2003) as per the dust, gas, UV illumination properties of (U)LIRGs vs. normal, optically selected galaxy sample • Additional discoveries will be facilitated by fusing our measurements with other data in the NASA/IPAC Extragalactic Database (NED), with connectivity to the NASA/IPAC Infrared Science Archive (IRSA) for the standard data products.

19. NGC 1365 – Barred + AGN Part II: A Spitzer view of the Galaxy NGC 1365 • A nearby (D~19 Mpc) barred supergiant galaxy • Fornax Cluster member but ?not interacting? • Tight barred spiral structure • Interstellar gas symmetry in the plane of the galaxy • Active AGN: Clusters w/ VLA brightness 100 x Cas A & strong x-ray from nucleus • Nuclear ionization cones

20. NGC 1365 - Questions • Tidal Influence from Fornax cluster? • Why is bar/spriral so symmetric? • Why is system so spatially constrained? • Why are the arms broken to the 2nd ary arms? • AGN destruction of PAHS in inner regions?

21. H-alpha etc. obs – Veilleux at al. • See [OIII] • on either side of nucleus, • stands- out in ratio map a) B cont, b) H-alpha, c) [OIII] 5007, d) [OIII]/Ha

22. [NII]/Ha: • Ratio map shows AGN influence • This extends 5 Kpc from center a) R Cont, b) Ha, c) [NII] 6583, d) [NII]/Ha

23. Central Region: B, Ha, [OIII] • “bi-conical” AGN region appears almost rectangular • nucleus biforcated by dust lane a) B cont, b) Ha, c) [OIII], d) [OIII]/H-beta

24. NGC 1365: log(Lir/L)~11.0 BCD Data IRAC 3.6 m IRAC 4.5 m IRAC 5.8 m IRAC 8 m NOTE: These are before extensive corrections for pull-down and MUXbleed as done for the following representations and analysis... MIPS 160 m MIPS 24 m MIPS 70 m

26. 8.0 μm [R] 4.5 μm [G] 3.6 μm [B] Deep log(log) stretch->

27. NGC 1365 • Initial Impressions: • Bar show paucity in 8 micron flux • Little initial evidence for PAH destruction over ionization cones (so far) • Secondary loop structure in nucleus • Highly delineated arms in 8 micron band over-reaching the bar – especially in the Northeast