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Interaction Driven Galaxy Evolution: The Fate of the Cold Gas

Interaction Driven Galaxy Evolution: The Fate of the Cold Gas. John E. Hibbard NRAO-CV. “The Evolution of Galaxies through the Neutral Hydrogen Window”, Arecibo Observatory, Feb 1-3 2008. Outline of Talk. Interactions happen locally Two burning questions:

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Interaction Driven Galaxy Evolution: The Fate of the Cold Gas

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  1. Interaction Driven Galaxy Evolution: The Fate of the Cold Gas John E. Hibbard NRAO-CV “The Evolution of Galaxies through the Neutral Hydrogen Window”, Arecibo Observatory, Feb 1-3 2008

  2. Outline of Talk • Interactions happen locally • Two burning questions: • If gas rich galaxies merge to form spheroidals, what happens to the cold gas? • Are interactions any more important at higher redshift? Gas holds the answers!

  3. Peculiar Galaxies: dynamically unrelaxed (non-equilibrium) forms Toomre Sequence of On-going Mergers (Toomre 1977) from Arp Atlas of Peculiar Galaxies (Arp 1966)

  4. Morphologies (& Kinematics!) can be explained by galaxy-galaxy interactions Seminal Paper (1369 citations): Toomre & Toomre 1972

  5. Tidal forces drive large scale inflows and outflows Mihos 2001, ApJ, 550, 94

  6. Simulated merger morphologies: J. Barnes, personal communication (see also Barnes & Hernquist 1992 ARAA)

  7. 5%-10% of population in local universe • In UGC, ~600 out of 9000 galaxies (~7%) with morphological descriptions including: disrupted, distorted, disturbed, interacting, eruptive, peculiar, bridge, loop, plume, tail, jet, streamer, connected (note, some are multiple systems, but not all need be interacting) • Total fraction that went through a peculiar phase = %peculiar * T/tpeculiar

  8. Fraction of galaxies with peculiar morphology increases strongly with LIR (~SFR) % Peculiar (Sanders & Mirabel 1996, ARAA): Log LIR=10-11: ~10% Log LIR=11-12: ~90% Log LIR>12: ~100% ACS Survey of IR Luminous Galaxies: A. Evans 2007

  9. Q1: When Gas-rich galaxies merge, what happens to the gas? • Interaction-driven inflows drive disk-wide star formation • leads to large central concentrations of cold gas

  10. Models (w/o feedback) predict these dense gaseous concentrations will leave sharp spikes in luminosity profiles of remnants

  11. NGC2623 NGC3256 NGC3921 NGC7252 HST NICMOS of late-stage Toomre Sequence Rossa et al. 2007, AJ, 134, 2124 But light profiles of likely merger remnants show no discrete feature identifying central burst population

  12. EA2 EA3 EA4 EA5 Light profiles of likely merger remnants show no discrete feature identifying central burst population HST F702W of four E+A Wang et al. 2004, ApJ, 607, 258

  13. Light profiles of likely merger remnants: luminosity enhancements are modest Ground-based K-band of Fine structure ellipticals Rothberg & Joseph, 2004 AJ, 128, 2098

  14. Classic merger remnants NGC3921 and NGC7252 have post-burst spectra • Therefore had a sudden drop in SFR in past. • NGC7252: Peak SFR was 300-500 Mo/year (ULIG) • But….cold gas still rains in!! Fritz-v.Alvensleben & Gerhard 1994 A&A, 285, 775

  15. NGC 3921: smooth light profile, but dynamically unrelaxed molecular gas Greys: HST F550W image (left); image-model (right): Schweizer 1996 Contours: OVRO CO(1-0): Yun & Hibbard 1999

  16. NGC7252: HI streaming in from tidal tails • Tails must extend back into remnant, but HI ends abruptly • Tails must extend back into remnant, but HI ends abruptly • Gas is currently falling back into remnant at 1-2 Mo/yr • Tails must extend back into remnant, but HI ends abruptly • Gas is currently falling back into remnant at 1-2 Mo/yr • Yet body remains devoid of HI

  17. Suggest some process removes cold gas - at least from more massive systems From HI Rouges Gallery (www.nrao.edu/astrores/HIrogue): Peculiar Early Types with HI outside Optical Body, arranged by decreasing HI content

  18. Lower-luminosity systems may retain cold material, reforming gas disks From HI Rouges Gallery (www.nrao.edu/astrores/HIrogue): Peculiar Early Types with HI inside Optical Body, arranged by increasingly regular HI kinematics

  19. Examples of low-z “quenching”? Springel, Di Matteo & Hernquist 2003 (also Li et al. 2006; Hopkins et al. 2005, 2006)

  20. Q2: Are interactions any more important at higher redshift? • Should be for hierarchical cosmologies • Recent work suggest this is not the case

  21. Sanders & Mirabel 1996 ARAA Recent claims: No evolution in merger fraction from z=0.2-1 Late Types Late Types Early types Early types Fraction of total population Major Mergers Classfication by Gini-M20 indices Extended Groth Strip: Lotz et al. 2008, ApJ, 672, 177 (See also Bell et al. 2005, Wolf et al. 2005, Bundy et al. 2005)

  22. Evolution of star formation density since z~1 driven by SF in normal Hubble Types Late Types Peculiars Early types Classfication by eye Classfication by A-C indices Contribution to SFR density HUDF parallel fields: Menanteau et al. 2006, AJ, 131, 208

  23. At z=1, SF dominated by “normal Hubble Types” Spirals Peculiar Compact Early-type undetected A class of galaxy not known locally (e.g. Ishida 2002 PhD Thesis): Normal Hubble type with SFR>50 Mo/year Spitzer 24um & HST of GOODS-N: Melbourne, Koo & Le Floc’h 2005, ApJ, 632, L65

  24. Are interactions important at z<1.5? • Emerging Paradigm: • SFR evolution driven by same SF processes as locally, in morphologically normal galaxies • Higher SFR because galaxies are more gas-rich at higher-z e.g.: Daddi et al. 2008: 2 “disk” galaxies at z=1.5. SFR=100-150 Mo/yr, but Mgas~1E11 Mo, so SF timescales more like “normal” disk galaxies (~10* lower SFE than ULIGs) PdB CO(2-1) of BzK galaxies: Daddi et al. 2008, ApJL, 673, L21

  25. But…Can we trust classifications at higher redshift? Wang et al. 2004, ApJ, 607, 258 Also - Hibbard & Vacca 1997

  26. Automated classifiers only sensitive to most extreme morphologies MR MR mM pM=pre-merger mM=minor merger pM pM mM M M M=major merger MR=merger remnant M Pre-Mergers (pM), minor Mergers (mM) & Merger Remnants (MR) occupy same morphological parameter space as normal Hubble Types. Only major mergers (M) stand out M pM MR pM mM mM MR Taylor, 2005 PhD Thesis ASU See also: Conselice 2006

  27. Normal Hubble Types? M81/M82/NGC3077 VLA 12-pointing mosaic Yun et al. 1994

  28. HI Tidal Debris WSRT HI: Swaters et al. 2002 VLA HI: Mundell 2000

  29. Non-peculiar morphological parameters does not mean morphologically Normal • True population of interacting/peculiar objects will be greater than derived optically • This will be even more true in the past, when galaxies were much more gas rich • Gas holds the clues • Locally: HI reveals dynamical nature • z=0-1: ALMA will image SFR, gas kinematics & morphology on sub-arcsec scales. Disks or multi-component?

  30. “Normal” Spiral at z=1.08, SFR=30 Mo/yr “Normal” Elliptical at z=0.7, SFR=30 Mo/yr ALMA CO(2-1) at z=1 (b=1.5km; 0.4”) SKA HI at z=1 (1.5”) HUDF-S 5”x5”

  31. What to do before SKA**? • Data volumes to be delivered by next-generation radio/mm instruments (EVLA, ALMA) are >>100x current capabilities • SKA will continue this trend • Number of Astronomers/grad students have not increased by similar factors • We have to give astronomers the tools to properly mine these immense datasets • (who is “we”?) **: the content of this page represents the personal viewpoint of the author, and in now way indicates opinions or policies of the NRAO

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