J. M. Guie

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Publications (3)0 Total impact

  • Source
    Article: E/S0 Galaxies on the Blue Color-Stellar Mass Sequence at z=0: Fading Mergers or Future Spirals?
    S. J. Kannappan, J. M. Guie, A. J. Baker
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    ABSTRACT: We identify a population of morphologically defined E/S0 galaxies lying on the blue sequence at the present epoch. Using three samples, we analyze blue-sequence E/S0s with stellar masses >10^8 Msun, arguing that individual objects may be evolving either up toward the red sequence or down into the blue sequence. Blue-sequence E/S0 galaxies become more common with decreasing stellar mass, comprising <2% of E/S0s near the "shutdown mass" M_s ~ 1-2 x 10^11 Msun, increasing to >5% near the "bimodality mass" M_b ~ 3 x 10^10 Msun, and sharply rising to >20-30% below the "threshold mass" M_t ~ 4-6 x 10^9 Msun. The strong emergence of blue-sequence E/S0s below M_t coincides with a previously reported global increase in mean atomic gas fractions below M_t for galaxies of all types on both sequences, suggesting that the availability of cold gas may be basic to blue-sequence E/S0s' existence. Environmental analysis reveals that many sub-M_b blue-sequence E/S0s reside in low to intermediate density environments. In mass-radius and mass-sigma scaling relations, blue-sequence E/S0s are more similar to red-sequence E/S0s than to late-type galaxies, but they represent a transitional class. While some of them, especially in the high-mass range from M_b to M_s, resemble major-merger remnants that will likely fade onto the red sequence, most blue-sequence E/S0s below M_b show signs of disk and/or pseudobulge building, which may be enhanced by companion interactions. We argue that sub-M_b blue-sequence E/S0s occupy a "sweet spot" in stellar mass and concentration, with both abundant gas and optimally efficient star formation, which may enable the formation of large spiral disks. [abridged] Comment: AJ, submitted, revised, 21 pages with 15 figures (one in two parts, one color); full resolution version available at http://www.physics.unc.edu/~sheila/kgb.pdf
    03/2009;
  • Source
    Article: Extending the Search for Counterrotating Gas and Stars in Galaxies: A Study of Late-Type Dwarfs
    J. M. Guie, S. J. Kannappan, Z. Balog, P. Berlind
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    ABSTRACT: In a previous study on gas-stellar counterrotation for a large sample of E/S0 and spiral galaxies (Kannappan & Fabricant 2001), two dwarf irregular galaxies were included, of which one was tentatively identified as a counterrotator. Here we extend the search for counterrotation to include 10 more irregular/spiral dwarf galaxies. We find that all systems with well defined gas and stellar rotation show kinematics consistent with co-rotation. However, we see evidence of decoupled gas and stellar kinematics in >~ 50% of the sample, possibly reflecting minor interactions too small to create large-scale gas-stellar counterrotation.
    08/2005;
  • Article: Extending the Search for Counterrotating Gas and Stars in Galaxies
    J. M. Guie, S. J. Kannappan
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    ABSTRACT: In a previous study of the frequency of gas-stellar counterrotation for a sample of E/S0 and spiral galaxies from the Nearby Field Galaxy Survey, counterrotation was found to occur primarily in low-luminosity early-type systems. However, no conclusions on counterrotation frequency could be reached for later type low-luminosity galaxies, due to inadequate sampling of their stellar kinematics. We present new stellar kinematic data for 10 late-type dwarf galaxies from the Nearby Field Galaxy Survey, obtained with the FAST spectrograph on the 60 inch telescope on Mount Hopkins. Our sample consists of galaxies with absolute B magnitudes between -16.5 and -19.1, and B-band effective surface brightnesses between 20.8 and 23.6. Of these, seven are classified as type Sdm-Im and three are classified as type Pec. We attempt to measure both gas and stellar rotation curves using emission and absorption lines in the 4000-6000 Angstrom range. All galaxies with well defined gas and stellar rotation show kinematics consistent with co-rotation. However, we see preliminary evidence of decoupled gas and stellar kinematics in some systems. We relate our results to plausible scenarios for the origin of kinematically decoupled gas, including late-stage gas accretion and galaxy mergers. In addition, we examine new, deeper stellar kinematic data for the four E/S0 galaxies in the Nearby Field Galaxy Survey with previously identified gas-stellar counterrotation, in order to search for stellar-stellar counterrotation. We present preliminary results from this analysis. JMG acknowledges support under NSF grant AST-0444634. SJK acknowledges support as an NSF Astronomy & Astrophysics Postdoctoral Fellow under grant AST-0401547.
    04/2005; 37:444.

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