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Unveiling the ?-Discrepancy in Infrared-Luminous Mergers. I. Dust and Dynamics
Mergers in the local universe present a unique opportunity for studyingthe transformations of galaxies in detail. Presented here are recentresults, based on multi-wavelength, high-resolution imaging and mediumresolution spectroscopy, which demonstrate how star formation and thepresence of red supergiants and/or asymptotic giant branch stars haveled to a serious underestimation of the dynamical masses ofinfrared-bright galaxies. The dominance of a nuclear disk of young starsin the near-infrared bands, where dust obscuration does not block theirsignatures, can severely bias the global properties measured in agalaxy, including mass. This explains why past studies of gas-richluminous infrared galaxies (LIRGs) and ultraluminous infrared galaxies,which have measured dynamical masses using the 1.62 or 2.29 ?m COband heads, have found that these galaxies are forming m < m*ellipticals. On the other hand, precisely because of dust obscuration,I-band photometry and velocity dispersions obtained with the calcium IItriplet at 0.85 ?m reflect the global properties of the mergers andsuggest that all types of merger remnants, including infrared-brightones, will form m > m* ellipticals. Moreover, merger remnants,including LIRGs, are placed on the I-band fundamental plane for thefirst time and appear to be virtually indistinguishable from ellipticalgalaxies.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
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| A Survey of Merger Remnants. II. The Emerging Kinematic and Photometric Correlations
This paper is the second in a series exploring the properties of 51optically selected, single-nuclei merger remnants. Spectroscopic datahave been obtained for a subsample of 38 mergers and combined withpreviously obtained infrared photometry to test whether mergers exhibitthe same correlations as elliptical galaxies among parameters such asstellar luminosity and distribution, central stellar velocity dispersion(σ0), and metallicity. Paramount to the study is totest whether mergers lie on the fundamental plane. Measurements ofσ0 have been made using the Ca triplet absorption lineat 8500 Å for all 38 mergers in the subsample. Additionalmeasurements of σ0 were made for two of the mergers inthe subsample using the CO absorption line at 2.29 μm. The resultsindicate that mergers show a strong correlation among the parameters ofthe fundamental plane but fail to show a strong correlation betweenσ0 and metallicity (Mg2). In contrast toearlier studies, the σ0 values of the mergers areconsistent with objects that lie somewhere between intermediate-mass andluminous giant elliptical galaxies. However, the discrepancies withearlier studies appear to correlate with whether the Ca triplet or COabsorption lines are used to derive σ0, with the latteralmost always producing smaller values. Finally, the photometric andkinematic data are used to demonstrate for the first time that thecentral phase-space densities of mergers are equivalent to those inelliptical galaxies. This resolves a long-standing criticism of themerger hypothesis.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
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