We study the kinematic properties of the ionised gas outflows and ambient interstellar medium (ISM) in a large and representative sample of local luminous and ultra-luminous infrared galaxies (U/LIRGs) (58 systems, 75 galaxies) at galactic and sub-galactic (i.e., star-forming clumps) scales, thanks to integral field spectroscopy (IFS)-based high signal-to-noise integrated spectra. The velocity dispersion of the ionized ISM in U/LIRGs ( σ ∼ 70 km s −1 ) is larger than in lower luminosity local star-forming galaxies ( σ ∼ 25 km s −1 ). While for isolated disc LIRGs star formation appears to sustain turbulence, gravitational energy release associated with interactions and mergers plays an important role in driving σ in the U/LIRG range. We find that σ has a dependency on the star formation rate density (Σ SFR ), which is weaker than expected if it were driven by the energy released by the starburst. The relatively small role of star formation (SF) driving the σ in U/LIRGs is reinforced by the lack of an increase in σ associated with high luminosity SF clumps. We also find that the impact of an active galactic nucleus (AGN) in ULIRGs is strong, increasing on average σ by a factor 1.5. Low-z U/LIRGs cover a range of velocity dispersion (σ ∼ 30 to 100 km s −1 ) and star formation rate density (Σ SFR ∼ 0.1 to 20 M yr −1 kpc −2 ) similar to those of high-z SFGs. Moreover, the observed weak dependency of σ on Σ SFR for local U/LIRGs (σ ∝ Σ +0.06 SFR ) is in very good agreement with that measured in some high-z samples. The presence of ionized gas outflows in U/LIRGs seems universal based on the detection of a broad, usually blueshifted, Hα line. The observed dependency of the maximum velocity of the outflow (V max ) on the star formation rate (SFR) is of the type+0.24 . We find that AGNs in U/LIRGs are able to generate faster (∼×2) and more massive (∼× 1.4) ionized gas outflows than pure starbursts. The derived ionized mass loading factors (η) are in general below 1, with only a few AGNs above this limit. The escaping gas fraction is low with only less massive (log(M dyn /M ) < 10.4) U/LIRGs having outflowing terminal velocities higher than their escape velocities, and more massive galaxies retaining the gas, even if they host an AGN. The observed average outflow properties in U/LIRGs are similar to high-z galaxies of comparable SFR. However, while high-z galaxies seem to require Σ SFR > 1 M yrfor launching strong outflows, this threshold is not observed in low-z U/LIRGs even after correcting for the differential fraction of the gas content. In the bright SF clumps found in LIRGs, ionized gas outflows appear to be very common (detection rate over 80%). Their observed properties are less extreme than those associated with the entire galaxy. The clumps in LIRGs follow the general size-L-σ scaling relations found for low-and high-z clumps, though they are in general smaller, less luminous, and are characterized by lower σ than at high-z. For a given observed (no internal extinction correction applied) star formation...

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 ∼ ...

Recent observations have revealed massive galactic molecular outflows 1-3 that may have physical conditions (high gas densities 4-6 ) required to form stars. Indeed, several recent models predict that such massive galactic outflows may ignite star formation within the outflow itself 7-11 . This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies 12 , to the evolution in size and velocity dispersion of the spheroidal component of galaxies 11,13 , and would contribute to the population of highvelocity stars, which could even escape the galaxy 13 . Such star formation could provide in-situ chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict that it may contribute substantially to the global star formation rate observed in distant galaxies 9 . Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report new spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star formation rate in the outflow is larger than 15 M ¤ /yr. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics 14,15 .IRAS F23128-5919 is a merging system (Fig.1a), in which the southern nucleus hosts an obscured active nucleus (AGN), detected in the X-rays 16 . Past observations had already revealed a prominent outflow developing from the southern nucleus 14,15,[17][18][19] , driven by the nuclear starburst, or by the AGN, or both. We analyzed archival Very Large Telescope (VLT) spectroscopic observations, obtained with the MUSE instrument, of the optical nebular lines to better characterize the outflow. The nebular emission line profiles can be clearly separated into a narrow component, associated with the interstellar medium in the two galactic disks, and a very broad (Full Width Half Maximum, FWHM~600-1,000 km/s), predominantly blueshifted component tracing the outflow. The velocity field, velocity dispersion, surface brightness maps of the two components are shown in Fig. 1a. The narrow component (bottom row in Fig. 1a) is probably tracing the bulk of the dynamics of the two merging disks. The outflow traced by the broad blueshifted component (top row in Fig. 1a) of the nebular lines extends towards the East of the southern nucleus for about 7-9 kpc (8"-10"), beyond the optical galactic disk. A receding counter-outflow is also observed in the opposite direction, i.e. towards the West (although weaker, owing to extinction by the galactic disk).We have observed the central and eastern outflows with the X-shooter spectrograph at the VLT, which enabled the detection of spectral diagnostics over the en...

We present a multi-wavelength integral field spectroscopic (IFS) study of the low-z luminous infrared galaxy IRAS F11506-3851 (ESO 320-G030) on the basis of the moderate spectral resolution observations (R ∼ 3400−4000) taken with the VIMOS and SINFONI instruments at the ESO VLT. The morphology and the 2D kinematics of the gaseous (neutral and ionized) and stellar components have been mapped in the central regions (<3 kpc) using the NaDλλ5890, 5896 Å absorption doublet, the Hαλ6563 Å line, and the near-IR CO(2-0)λ2.293 µm and CO(3-1)λ2.322 µm bands. The kinematics of the ionized gas and the stars are dominated by rotation, with large observed velocity amplitudes (∆V(Hα) = 203 ± 4 km s −1 ; ∆V(CO) = 188 ± 11 km s −1 , respectively) and centrally peaked velocity dispersion maps (σ c (Hα) = 95 ± 4 km s −1 and σ c (CO) = 136 ± 20 km s −1 ). The stars lag behind the warm gas and represent a dynamically hotter system, as indicated by the observed V/σ ratios (4.5 and 2.4 for the gas and the stars, respectively). Thanks to these IFS data we have disentangled the contribution of the stars and the interstellar medium to the NaD feature, finding that it is dominated by absorption of neutral gas clouds in the interstellar medium (∼2/3 of total EW). The 2D kinematics of the neutral gas shows a complex structure dominated by two main components. On the one hand, the thick slowly rotating disk (∆V(NaD) = 81 ± 12 km s −1 ) lags significantly compared to the ionized gas and the stars, and it has an irregular and off-center velocity dispersion map (with values of up to ∼150 km s −1 at ∼1 kpc from the nucleus). On the other hand, a kpc-scale neutral gas outflow perpendicular to the disk, as is revealed by the large blueshifted velocities (in the range 30−154 km s −1 ) observed along the galaxy's semi-minor axis (within the inner 1.4 kpc). On the basis of a simple free wind scenario, we derive an outflowing mass rate (Ṁ w ) in neutral gas of about 48 M yr −1 . Although this implies a global mass loading factor (i.e., η =Ṁ w /SFR) of ∼1.4, the 2D distribution of the ongoing SF as traced by the Hα emission map suggests a much larger value of η associated with the inner regions (R < 200 pc), where the current observed star formation (SF) represents only ∼3 percent of the total. However, the relatively strong emission by supernovae in the central regions, as traced by the [FeII] emission, indicates recent strong episodes of SF. Therefore, our data show clear evidence of the presence of a strong outflow with large loading factors associated with the nuclear regions, where recent starburst activity took place about 7 Myr ago, although it currently shows relatively modest SF levels. All together these results strongly suggest that we are witnessing (nuclear) quenching due to SF feedback in IRAS F11506-3851. However, the relatively large mass of molecular gas detected in the nuclear region via the H 2 1−0S(1) line suggests that further episodes of SF may take place again.

Context. Ultra luminous and luminous infrared galaxies [(U)LIRGs] are important galaxy populations for studying galaxy evolution, and are likely to have been responsible for a significant fraction of the star formation that occurred prior to z ∼ 1. Local (U)LIRGs can be used to study criteria that are suitable for characterizing similar high redshift populations. We are particularly interested in identifying reliable kinematic-based methods capable of distinguishing disks and mergers, as their relative fraction is a key observational input to constrain different evolutionary scenarios. Aims. Our goal is to analyze in detail the kinematics of the ionized gas of a small sample of LIRGs and study criteria that permit us to characterize the evolutionary status of these systems. Methods. We obtained Very Large Telescope VIMOS optical integral field spectroscopy (IFS) data of four LIRGs selected at similar distances (∼70 Mpc) to avoid relative resolution effects. Two of these systems had been previously classified as regular isolated disks galaxies and the other two as post-coalescence mergers based on their morphology. The kinemetry method (developed by Krajnović and coworkers) is used to characterize the kinematic properties of these galaxies and discuss new criteria for distinguishing their status.Results. We present and discuss new kinematic maps (i.e., velocity field and velocity dispersion) for these four galaxies. These kinematic data suggest that nuclear outflows exist in all these galaxies, and are particularly intense for the post-coalescence merger systems. The v c /σ c parameter has values between those that are typical of local spiral galaxies (i.e., v c /σ c = 5−15) and those obtained for Lyman break analogs at z ∼ 0.2 (i.e., v c /σ c = 0.4−1.8). Our use of one-dimensional parameters, such as v c /σ c or v shear /Σ, does not allow us to distinguish between the two groups (i.e., disks, post-coalescence systems). However, when the full two-dimensional kinematic information of the IFS data is analyzed by means of kinemetry, their morphological and kinematic classifications are consistent, with disks having lower kinematic asymmetries than post-coalescence mergers. We propose and discuss a new kinematic criterion to differentiate between these two groups. In particular, we introduce a weighting that favors the outer parts of the kinematic maps when computing the total asymmetries. This step is taken because post-coalescence mergers display relatively small kinematic asymmetries in their inner parts as a consequence of the rapid relaxation of gas into a rotating disk, whereas the outer parts continue to be out of equilibrium (i.e., to have larger asymmetries). We find that, in addition to distinguishing post-coalescence mergers from rotating disks, this new criterion has the advantage of being less sensitive to angular resolution effects. According to previous kinemetry-based analyses designed to distinguish disks and mergers at high-z, the present post-coalescence systems would have been classified a...