We report on the energetics of molecular outflows in 14 local Ultraluminous Infrared Galaxies (ULIRGs) that show unambiguous outflow signatures (P-Cygni profiles or high-velocity absorption wings) in the far-infrared lines of OH measured with the Herschel/PACS spectrometer. All sample galaxies are gas-rich mergers at various stages of the merging process. Detection of both ground-state (at 119 and 79 µm) and one or more radiatively-excited (at 65 and 84 µm) lines allows us to model the nuclear gas ( 300 pc) as well as the more extended components using spherically symmetric radiative transfer models. Reliable models and the corresponding energetics are found in 12 of the 14 sources. The highest molecular outflow velocities are found in buried sources, in which slower but massive expansion of the nuclear gas is also observed. With the exception of a few outliers, the outflows have momentum fluxes of (2 − 5) × L IR /c and mechanical luminosities of (0.1 − 0.3)% of L IR . The moderate momentum boosts in these sources ( 3) suggest that the outflows are mostly momentum-driven by the combined effects of AGN and nuclear starbursts, as a result of radiation pressure, winds, and supernovae remnants. In some sources (∼ 20%), however, powerful (10 10.5−11 L ⊙ ) AGN feedback and (partially) energy-conserving phases are required, with momentum boosts in the range 3 − 20. These outflows appear to be stochastic, strong-AGN feedback events that occur throughout the merging process. In a few sources, the outflow activity in the innermost regions has subsided in the last ∼ 1 Myr. While OH traces the molecular outflows at sub-kpc scales, comparison of the masses traced by OH with those previously inferred from tracers of more extended outflowing gas suggests that most mass is loaded (with loading factors ofṀ /SFR = 1 − 10) from the central galactic cores (a few × 100 pc), qualitatively consistent with an ongoing inside-out quenching of star formation. Outflow depletion timescales are < 10 8 yr, shorter than the gas consumption timescales by factors of 1.1 − 15, and are anti-correlated with the AGN luminosity.

We report rest-frame submillimeter H 2 O emission line observations of 11 ultra-or hyper-luminous infrared galaxies (ULIRGs or HyLIRGs) at z ∼ 2-4 selected among the brightest lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we have detected 14 new H 2 O emission lines. These include five 3 21 -3 12 ortho-H 2 O lines (E up /k = 305 K) and nine J = 2 para-H 2 O lines, either 2 02 -1 11 (E up /k = 101 K) or 2 11 -2 02 (E up /k = 137 K). The apparent luminosities of the H 2 O emission lines are µL H 2 O ∼ 6-21 × 10 8 L (3 < µ < 15, where µ is the lens magnification factor), with velocity-integrated line fluxes ranging from 4-15 Jy km s −1 . We have also observed CO emission lines using EMIR on the IRAM 30m telescope in seven sources (most of those have not yet had their CO emission lines observed). The velocity widths for CO and H 2 O lines are found to be similar, generally within 1 σ errors in the same source. With almost comparable integrated flux densities to those of the high-J CO line (ratios range from 0.4 to 1.1), H 2 O is found to be among the strongest molecular emitters in high-redshift Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H 2 O (L H 2 O ) and infrared (L IR ) that L H 2 O ∼L IR 1.1-1.2 , with our new detections. This correlation could be explained by a dominant role of far-infrared pumping in the H 2 O excitation. Modelling reveals that the far-infrared radiation fields have warm dust temperature T warm ∼ 45-75 K, H 2 O column density per unit velocity interval N H 2 O /∆V 0.3 × 10 15 cm −2 km −1 s and 100 µm continuum opacity τ 100 > 1 (optically thick), indicating that H 2 O is likely to trace highly obscured warm dense gas. However, further observations of J ≥ 4 H 2 O lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. We have also detected H 2 O + emission in three sources. A tight correlation between L H 2 O and L H 2 O + has been found in galaxies from low to high redshift. The velocity-integrated flux density ratio between H 2 O + and H 2 O suggests that cosmic rays generated by strong star formation are possibly driving the H 2 O + formation.

In this paper, we propose a Q stability parameter that is more realistic than those commonly used, and is easy to evaluate [see Eq. (19)]. Using our Q N parameter, you can take into account several stellar and/or gaseous components as well as the stabilizing effect of disc thickness, you can predict which component dominates the local stability level, and you can do all that simply and accurately. To illustrate the strength of Q N , we analyse the stability of a large sample of spirals from The H i Nearby Galaxy Survey (THINGS), treating stars, H i and H 2 as three distinct components. Our analysis shows that H 2 plays a significant role in disc (in)stability even at distances as large as half the optical radius. This is an important aspect of the problem, which was missed by previous (two-component) analyses of THINGS spirals. We also show that H i plays a negligible role up to the edge of the optical disc; and that the stability level of THINGS spirals is, on average, remarkably flat and well above unity.

We report on the Herschel/PACS observations of OH in Mrk 231, with detections in nine doublets observed within the PACS range, and present radiative-transfer models for the outflowing OH. Clear signatures of outflowing gas are found in up to six OH doublets with different excitation requirements. At least two outflowing components are identified, one with OH radiatively excited, and the other with low excitation, presumably spatially extended and roughly spherical. Particularly prominent, the blue wing of the absorption detected in the in-ladder 2 Π 3/2 J = 9/2−7/2 OH doublet at 65 μm, with E lower = 290 K, indicates that the excited outflowing gas is generated in a compact and warm (circum)nuclear region. Because the excited, outflowing OH gas in Mrk 231 is associated with the warm, far-infrared continuum source, it is most likely more compact (diameter of ∼200−300 pc) than that probed by CO and HCN. Nevertheless, its mass-outflow rate per unit of solid angle as inferred from OH is similar to that previously derived from CO, > ∼ 70 × (2.5 × 10 −6 /X OH ) M yr −1 sr −1 , where X OH is the OH abundance relative to H nuclei. In spherical symmetry, this would correspond to > ∼ 850 × (2.5 × 10 −6 /X OH ) M yr −1 , though significant collimation is inferred from the line profiles. The momentum flux of the excited component attains ∼15 L AGN /c, with an OH column density of (1.5−3) × 10 17 cm −2 and a mechanical luminosity of ∼10 11 L . In addition, the detection of very excited, radiatively pumped OH peaking at central velocities indicates the presence of a nuclear reservoir of gas rich in OH, plausibly the 130 pc scale circumnuclear torus previously detected in OH megamaser emission, that may be feeding the outflow. An exceptional 18 OH enhancement, with OH/ 18 OH < ∼ 30 at both central and blueshifted velocities, is most likely the result of interstellar-medium processing by recent starburst and supernova activity within the circumnuclear torus or thick disk.

Context. The luminous infrared galaxy Zw 049.057 contains a compact obscured nucleus where a considerable amount of the galaxy's luminosity is generated. This nucleus contains a dusty environment that is rich in molecular gas. One approach to probing this kind of environment and to revealing what is hidden behind the dust is to study the rotational lines of molecules that couple well with the infrared radiation emitted by the dust. Aims. We probe the physical conditions in the core of Zw 049.057 and establish the nature of its nuclear power source (starburst or active galactic nucleus). . We modeled the unresolved core of the galaxy using a spherically symmetric radiative transfer code. To account for the different excitation requirements of the various molecular transitions, we use multiple components and different physical conditions. Results. We present the full high-resolution SPIRE FTS spectrum of Zw 049.057, along with relevant spectral scans in the PACS range. We find that a minimum of two different components (nuclear and extended) are required in order to account for the rich molecular line spectrum of Zw 049.057. The nuclear component has a radius of 10−30 pc, a very high infrared surface brightness (∼10 14 L kpc −2 ), warm dust (T d > 100 K), and a very large H 2 column density (N H 2 = 10 24 −10 25 cm −2 ). The modeling also indicates high nuclear H 2 O (∼5 × 10 −6 ) and OH (∼4 × 10 −6 ) abundances relative to H 2 as well as a low 16 O/ 18 O-ratio of 50−100. We also find a prominent infall signature in the [O I] line. We tentatively detect a 500 km s −1 outflow in the H 2 O 3 13 → 2 02 line. Conclusions. The high surface brightness of the core indicates the presence of either a buried active galactic nucleus or a very dense nuclear starburst. The estimated column density towards the core of Zw 049.057 indicates that it is Compton-thick, making a buried X-ray source difficult to detect even in hard X-rays. We discuss the elevated H 2 O abundance in the nucleus in the context of warm grain and gas-phase chemistry. The H 2 O abundance is comparable to that of other compact (ultra-)luminous infrared galaxies such as NGC 4418 and Arp 220 -and also to hot cores in the Milky Way. The enhancement of 18 O is a possible indicator that the nucleus of Zw 049.057 is in a similar evolutionary stage as the nuclei of Arp 220 -and more advanced than NGC 4418. We discuss the origin of the extreme nuclear gas concentration and note that the infalling gas detected in [O I] implies that the gas reservoir in the central region of Zw 049.057 is being replenished. If confirmed, the H 2 O outflow suggests that the nucleus is in a stage of rapid evolution.