VLT/VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies: 2D kinematic properties

Abstract

We present and discuss the 2D kinematic properties of the ionized gas (Hα) in a sample of 38 local (ultra) luminous infrared galaxies [(U)LIRGs] (31 LIRGs and 7 ULIRGs, 51 individual galaxies) observed with VIMOS at the Very Large Telescope using optical integral field spectroscopy (IFS). This sample covers well the less studied LIRG luminosity range and includes the morphological types corresponding to the different phases along the merging process (i.e., isolated disks, interacting systems, and mergers). The majority of the galaxies have two main kinematically distinct components. One component (i.e., narrow or systemic) extends over the whole line-emitting region and is characterized by small to intermediate velocity dispersions (i.e., σ from 30 to 160 km s −1 ). The second component (broad) has in general a larger velocity dispersion (up to 320 km s −1 ); it is mainly found in the inner regions and is generally blueshifted with respect to the systemic component. The largest extensions and extreme kinematic properties of the broad component are observed in interacting and merging systems, and they are likely associated with nuclear outflows. The systemic component traces the overall velocity field showing a large variety of kinematic 2D structures, from very regular velocity patterns typical of pure rotating disks (29%) to kinematically perturbed disks (47%) and highly disrupted and complex velocity fields (24%). Thus, most of the objects (76%) are dominated by rotation. We find that rotation is more relevant in LIRGs than in ULIRGs. There is a clear correlation between the different phases of the merging process and the mean kinematic properties inferred from the velocity maps. In particular, isolated disks, interacting galaxies, and merging systems define a sequence of increasing mean velocity dispersion, and decreasing velocity field amplitude, characterized by average dynamical ratios (v * shear /σ mean ) of 4.7, 3.0 and 1.8, respectively. We also find that the ratio between the nuclear (σ c ) and the mean velocity dispersions (σ mean ) vs. σ mean is an excellent discriminating plane between disks and interacting/merging systems: disks show a mean ratio a factor of 2 larger than those characterizing the other two classes. The LIRGs classified as isolated disks have similar velocity amplitudes but larger mean velocity dispersions (44 vs. 24 km s −1 ) than local spirals, implying a larger turbulence and thicker disks. Interacting systems and mergers have values closer to those of low velocity dispersion ellipticals/lenticular galaxies (E/SOs). The subclass of (U)LIRGs classified as mergers have kinematic properties similar to those shown by the Lyman break analogs (LBAs), although the dynamical mass of LBAs is five times lower on average. Therefore, despite the difference in mass and dust content, the kinematics of these two local populations appears to have significant noncircular motions. These motions may be induced by the tidal forces, producing dynamically hot systems. The dynamical masses range from ∼ ...

Neutral gas outflows in nearby [U]LIRGs via optical NaD feature

“…Before integration, the spectra were corrected from the general stellar velocity pattern. For this step, we used the narrow component of the ionized gas velocity field, which describes the systemic behavior (Bellocchi et al 2013 Fig. 1.…”

“…The mean redshift of the LIRGs and ULIRGs subsamples are 0.024 and 0.069, respectively (see Table 1). The sample is not complete either in luminosity or in distance (Rodríguez-Zaurín et al 2011;Bellocchi et al 2013), however, it is representative of the [U]LIRGs population. Indeed, this sample covers a variety of morphological types along the merging process (i.e., rotating disks, interacting systems, and mergers) and encompasses objects with different nuclear ionization types (i.e., HII, Seyfert and LINER).…”

“…Column (5): morphology class defined as follows: 0 identifies isolated rotating disks, 1 interacting systems, and 2 mergers. We refer to Rodríguez-Zaurín et al (2011) and Bellocchi et al (2013) for further details about this classification. Column (6): S.C. stands for (nuclear) spectroscopic classification of the ionization type.…”

“…significant blueshifted velocities ( > ∼ 60 km s −1 ) with respect to the systemic, which cannot be explained by rotation. For this identification, we consider the velocity field of the narrow component of Hα as reference, for which Bellocchi et al (2013) have shown follows systemic behavior (Appendix A); 2. EW(NaD) > 1.3 Å, to guarantee that the NaD feature is dominated by ISM absorption; and 3. a relatively broad kinematic component (σ > 90 km s −1 ).…”

“…Column (2): observed extent of the neutral winds corrected for the inclination using the inclination values of Bellocchi et al (2013). Column (3): area covered by the GW.…”