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The Role of Galaxy Mergers Among High Redshift ULIRGs

Hubble Fellows Symposium 2012 March 7. The Role of Galaxy Mergers Among High Redshift ULIRGs. Jeyhan S. Kartaltepe Hubble Fellow - NOAO . Hubble Fellows Symposium 2012 March 7. The Role of Galaxy Mergers Among High Redshift ULIRGs. z ~2. z~2. z < 0.3. Jeyhan S. Kartaltepe

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The Role of Galaxy Mergers Among High Redshift ULIRGs

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  1. Hubble Fellows Symposium 2012 March 7 The Role of Galaxy Mergers Among High Redshift ULIRGs Jeyhan S. Kartaltepe Hubble Fellow - NOAO

  2. Hubble Fellows Symposium 2012 March 7 The Role of Galaxy Mergers Among High Redshift ULIRGs z~2 z~2 z < 0.3 Jeyhan S. Kartaltepe Hubble Fellow - NOAO

  3. What are LIRGs/ULIRGs? • LIR(8-1000 mm) > 1011 LLIRGs • LIR > 1012 L ULIRGs, LIR > 1013 LHyLIRGs!! • Rare locally … PAH Complex Dust Stellar Continuum Arp 220 Kennicutt et al. 2003

  4. High Redshift (U)LIRGs • LIRGs dominate IR energy density (and cosmic star formation rate) at z > 0.7 • Le Floc’h et al. 2005 • ULIRGs as important or dominate by z~2 • Caputi et al. 2007; Magnelli et al. 2009, 2011; Bethermin et al. 2011; Murphy et al. 2011 • Important role at the peak of galaxy assembly Comoving Infrared Energy Density Low Lum LIRGs ULIRGs Le Floc’h et al. 2005

  5. Motivation • What drives star formation and AGN activity and how does this change as a function of redshift? • What is the role of galaxy mergers? • Are mergers necessary for the extreme luminosities of (U)LIRGs? • What was the role of ‘cold flow’ gas accretion in the early universe? • How does galaxy morphology correlate with luminosity and therefore star formation rate?

  6. Properties of Local (U)LIRGs • ULIRGs: IRAS 1 Jy Sample, med(z) = 0.145 (Veilleux, Kim, & Sanders 2002) • > 99% are major mergers of gas rich spirals • LIRGs: RBGS, med(z) =0.0082 (Sanders et al 2003, Ishida 2004) • log(LIR) > 11.5 • strongly interacting major mergers (65%) • doubles (18%) • minor interactions (18%) • log(LIR) < 11.5 • strongly interacting major mergers (36%) • doubles (23%), • minor interactions (15%) • high luminosity end of normal starforming disks (26%) Fraction of mergers increases systematically with LIR!

  7. Properties of Local (U)LIRGs • Fraction of (U)LIRGs with an AGN increases with LIR • Veilleux et al. 1995, 1999; Tran et al. 2001; Yuan et al. 2010 • < 20% for LIR < 1011 L • > 50% for LIR > 1012.3 L • Large fraction of composites • Mix of SF, AGN, shocks • Difficult to disentangle Yuan et al. 2010

  8. The Merger Scenario • Mergers among ULIRGs are ubiquitous • High AGN fraction among ULIRGs • Leads to the merger scenario (Sanders et al. 1988) • Evolutionary connection: Gas-rich mergers LIRG  ULIRG  QSO • Eventually form “red and dead” elliptical Hopkins et al. 2008

  9. The Role of Cold Flows • Theoretical simulations suggest that the high SFRs of (U)LIRGs can be sustained at high redshift (z~2) by ‘cold flows’ (e.g., Dekel et al. 2009, Davé et al. 2009) • Accretion of cold gas along filaments • Minor mergers • Observationally supported by apparent lack of mergers among high redshift (U)LIRGs(e.g.,Genzelet al. 2006; Forster-Schreiber et al. 2009) • Mix of results at high redshift so far • High redshift mergers are hard to see • Cold flows have yet to be observed!

  10. High Redshift (U)LIRGs • Are mergers necessary to produce these extreme luminosities? • Studies at high redshift have been limited so far • Small samples • Uncertain luminosities • Lack of rest-frame optical imaging • Most previous studies have been based on Spitzer 24 mm selection • Pre-Herschel, longer wavelength data has only been available for small numbers of objects (e.g., Spitzer 70/160 mm, Submillimeter)

  11. Previous High Redshift (z~2) Studies • 24 mm / color selected samples • e.g., Dasyra et al. 2008; Melbourne et al. 2009; Bussmann et al. 2009, 2011; Zamojski et al. 2010 • Wide range of results • Submillimeter Galaxies (SMGs) • Morphology (e.g., Conselice et al. 2003; Swinbank et al. 2010) • Kinematics (e.g., Tacconi et al. 2008) • Tend to find high fractions of mergers • IFU Kinematics of massive star forming galaxies (SMGs/BzKs, etc.) • e.g., Genzel et al. 2008; Forster-Schreiber et al. 2009 • Mixed results – 1/3 mergers, 1/3 rotation dominated, 1/3 dispersion dominated

  12. GOODS-Herschel • Herschel coverage of both GOODS fields (PI: D. Elbaz) • Deepest Herschel data taken! • Full GOODS-N field: 1.6 mJy (@ 100 mm) • Central part of GOODS-S: 0.6 mJy (@ 100 mm) • Small area coverage but very deep • Well suited for identifying high redshift (z > 1) sources • 100-500 mm coverage is closer to the peak of emission • Better for constraining LIR and Tdust GOODS-N GOODS-S

  13. Identifying Merging Galaxies • Easy in the local universe! Nearby Examples: The Mice & NGC 520

  14. Identifying Merging Galaxies • Easy in the local universe! • At high redshift surface brightness dimming becomes a problem… Hibbard & Vacca 1997

  15. Identifying Merging Galaxies • And band shifting becomes important! Rest-frame UV versus Rest-frame optical ACS I band WFC3 H band

  16. CANDELS • Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (PIs: S. Faber & H. Ferguson) • Multi-cycle HST Treasury Program • WFC3 NIR imaging of portions of 5 deep fields • GOODS-N, GOODS-S, UDS, COSMOS, EGS UDS Mosaic

  17. GOODS-Herschel & CANDELS • A match made in heaven! • Rest-frame optical imaging for z~2 galaxies • Ideal for probing structure of z~2 ULIRGs

  18. GOODS-Herschel ULIRG Sample • Focus on all ULIRGs with z = 1.5 - 3.0 in GOODS-S • 52 ULIRGs with CANDELS imaging • First complete, FIR selected sample of ULIRGs at z~2! • Additional 70 LIRGs over this z range • <log(LIR)> ~ 12.26 • <z> ~ 2.2

  19. Comparison Sample • Selected 260 comparison galaxies (5 for each ULIRG) • Not Herschel detected  less luminous z~2 population • Matched to redshift and H magnitude • Randomized and classified ULIRGs + comparison • Visual classification scheme • Classified by me + 3-5 other classifiers • Analyzed agreement • Eventually compare to quantitative merger selections

  20. Visual Classification Scheme Main Morphological Class Interaction Class

  21. Results Merger+Int+Irr Kartaltepe et al. 2012

  22. Comparison with z ~ 1 • COSMOS 70 mm • 277 sources 0.8 < z < 1.2 • Relatively shallow, but large area coverage • log(LIR) = 11.3 - 12.9 • GOODS-Herschel • North+South • 100/160 mm • Smaller area, significantly deeper • 293 sources w/ 0.8 < z < 1.2 • Log(LIR) = 10.6 – 12.4 • Classified using ACS imaging and same scheme

  23. ”Main Sequence” and Starburst Galaxies • Correlation between star formation rate (SFR) and stellar mass • True locally (e.g., Brinchmann et al. 2004) and at high redshift (e.g., Noeske et al. 2007; Daddi et al. 2007) • Evolves with redshift (increase in gas fraction?) • Galaxies elevated above this relation  Starbursts Noeske et al. 2007

  24. ”Main Sequence” and Starburst Galaxies Rodighiero et al. 2011 Elbaz et al. 2011 What is the role of mergers among starbursts and “main sequence” galaxies at z~2?

  25. Are z~2 (U)LIRGs Starbursts? Main Sequence (MS) from Elbaz et al. 2011 MS x3 Kartaltepe et al. 2012

  26. Are z~2 (U)LIRGs Starbursts? Starbursts Starbursts Kartaltepe et al. 2012

  27. Are z~2 (U)LIRGs Starbursts? Disks: med(sSFR/sSFRMS) = 2.4 Starbursts Starbursts Kartaltepe et al. 2012

  28. Are z~2 (U)LIRGs Starbursts? Interactions & Mergers: med(sSFR/sSFRMS) = 3.8 Starbursts Starbursts Kartaltepe et al. 2012

  29. What are z~2 “Main Sequence” Galaxies? Starbursts “Main Sequence” Non-interacting disks: 57% Interactions & Mergers: 24% Kartaltepe et al. 2012

  30. Are z~2 Starbursts Mergers? Starbursts Starbursts Non-interacting disks: 42% Interactions & Mergers: 50% Kartaltepe et al. 2012

  31. Conclusions • Morphologies of z~2 ULIRGs span a wide range • ‘Disks’ make up a significant fraction (many irregular) • 40% non-interacting, 60% total • ~45% are mergers or interactions • Additional ~25% are irregular (minor mergers?) • Comparable to fractions at z~1, slightly lower • More likely to be interacting pairs than advanced mergers • z~2 ULIRGs are more like z~0 LIRGs

  32. Conclusions • Most (U)LIRGs on the main sequence are non-interacting disks (57%) • BUT significant (24%) number are mergers/interactions • Significant enhancement of SFR for a short time during the merger • Half of starbursts are clear mergers/interactions • Large fraction of “Irregular Disks” • Enhanced role of minor mergers?

  33. Future Directions(aka: Next Year’s Talk) • The results presented were small numbers! • Need rest of CANDELS fields + expanded Herschel coverage for firm conclusions/statistics • Herschel+CANDELS– PI: M. Dickinson (OT2) • Coming soon! • NIR spectroscopic follow-up • Starburst-AGN emission line diagnostics • What is the role/contribution of the AGN? • Large international Subaru FMOS program of COSMOS

  34. Starburst Montage

  35. Fiber Multi-Object Spectrograph (FMOS) • Low-res (R~600) • Hi-res (R~2200) • In low-res mode, can cover 0.9-1.8 mm at once • 400 fibers • 30’ diameter FOV • Ideal for COSMOS!

  36. AGN Fraction 100% of HyLIRGs >70% for ULIRGs AGN Fraction 5% at low LIR log (LIR) Kartaltepe et al. 2010a AGN Fraction increases systematically with LIR (as it does locally)!

  37. Spectroscopic AGN Selection • Spectroscopic selection (e.g., Baldwin et al. 1981, Veilleux & Osterbrock 1987, Kauffmann et al. 2003, Kewley et al. 2006, Yuan et al. 2010) • Classes: SF, AGN dominated and composites • DAGN measure separates relative contribution Kewley et al. 2006 Yuan et al. 2010

  38. Spectroscopic AGN Selection • At low redshift, we can classify 283 galaxies from COSMOS 70 mm sample using standard line diagnostics • 0 < z < 0.5 (where Ha still observable, 38% of sample at these redshifts) • log(LIR) = 8.8 – 12.1, <log(LIR)> = 10.7 AGN HII Comp.

  39. At higher redshifts…. • Beyond z>0.5, lose Ha and [NII] lines, but have [OIII] and Hb out to z~1 • Color as a proxy for [NII]/Ha? (e.g., Yan et al. 2010) • Appears to work well for normal galaxies locally… Yan et al. 2010

  40. Applied to 70 mm Sample • 500 galaxies with [OIII] and Hb • 0 < z < 1 (~40% of sample in this range) • log(LIR) = 8.5 – 12.5, <log(LIR)> = 11.1 • 30 ULIRGs, 256 LIRGs • 70 mm selected galaxies just aren’t red! AGN

  41. Mass-Excitation • Method of Juneau et al. 2011 uses mass instead

  42. Applied to 70 mm Sample • Same 500 galaxies with O[III] and Hb • Appears to work better for infrared selected galaxies • X-ray mostly in AGN region • Trend with LIR AGN

  43. What about higher redshifts? • Current and future surveys with NIR spectrographs • Until now, only small samples possible with longslitspectographs • Several multi-object spectrographs now online or will be soon • MOIRCS, FMOS, LUCIFER, FLAMINGOS2, MOSFIRE, etc. • Will become possible to use BPT type analysis at z = 1 - 3 for large samples • COSMOS FMOS survey will cover 1000’s of IR selected galaxies and AGN over the next few years

  44. Sample Spectra

  45. Preliminary FMOS Results ~60 (U)LIRGs at 1.0 < z < 1.6 with coverage of all four lines

  46. Preliminary FMOS Results Same sources on Mass-Excitation Diagram

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