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.

Recent observational studies have shown that H 2 O emission at (rest) submillimeter wavelengths is ubiquitous in infrared galaxies, both in the local and in the early Universe, suggestive of far-infrared pumping of H 2 O by dust in warm regions. In this work, models are presented that show that (i) the highest-lying H 2 O lines (E upper > 400 K) are formed in very warm (T dust 90 K) regions and require high H 2 O columns (N H 2 O 3 × 10 17 cm −2 ), while lower lying lines can be efficiently excited with T dust ∼ 45−75 K and N H 2 O ∼ (0.5−2) × 10 17 cm −2 ; (ii) significant collisional excitation of the lowest lying (E upper < 200 K) levels, which enhances the overall L H 2 O -L IR ratios, is identified in sources where the ground-state para-H 2 O 1 11 −0 00 line is detected in emission; (iii) the H 2 O-toinfrared (8−1000 μm) luminosity ratio is expected to decrease with increasing T dust for all lines with E upper 300 K, as has recently been reported in a sample of LIRGs, but increases with T dust for the highest lying H 2 O lines (E upper > 400 K); (iv) we find theoretical upper limits for L H 2 O /L IR in warm environments, owing to H 2 O line saturation; (v) individual models are presented for two very different prototypical galaxies, the Seyfert 2 galaxy NGC 1068 and the nearest ultraluminous infrared galaxy Arp 220, showing that the excited submillimeter H 2 O emission is dominated by far-infrared pumping in both cases; (vi) the L H 2 O −L IR correlation previously reported in observational studies indicates depletion or exhaustion time scales, t dep = Σ gas /Σ SFR , of 12 Myr for star-forming sources where lines up to E upper = 300 K are detected, in agreement with the values previously found for (U)LIRGs from HCN millimeter emission. We conclude that the submillimeter H 2 O line emission other than the para-H 2 O 1 11 −0 00 transition is pumped primarily by far-infrared radiation, though some collisional pumping may contribute to the low-lying para-H 2 O 2 02 −1 11 line, and that collisional pumping of the para-1 11 and ortho-2 12 levels enhances the radiative pumping of the higher lying levels.

Aims. We probe the physical conditions in the core of Arp 299A and try to put constraints to the nature of its nuclear power source. − doublet at 119 µm is found redshifted by ∼175 km s −1 compared with other OH and H 2 O lines, suggesting a low excitation inflow. We find that at least two components are required in order to account for the excited molecular line spectrum. The inner component has a radius of 20 − 25 pc, a very high infrared surface brightness ( 3 × 10 13 L ⊙ kpc −2 ), warm dust (T d > 90 K), and a large H 2 column density (N H 2 > 10 24 cm −2 ). The modeling also indicates high nuclear H 2 O (1 − 5 × 10 −6 ) and OH (0.5 − 5 × 10 −5 ) abundances relative to H nuclei. The outer component is larger (50 − 100 pc) with slightly cooler dust (70 − 90 K) and molecular abundances that are about one order of magnitude lower. In addition to the two components that account for the excited OH and H 2 O lines, we require a much more extended inflowing component to account for the OH 2 Π 3/2 − 2 Π 3/2 5 2− doublet at 119 µm. Conclusions. The Compton-thick nature of the core makes it difficult to determine the nature of the buried power source, but the high surface brightness indicates that it is either an active galactic nucleus and/or a dense nuclear starburst. Our results are consistent with a composite source. The high OH/H 2 O ratio in the nucleus indicates that ion-neutral chemistry induced by X-rays or cosmic-rays is important. Finally we find a lower limit to the 16 O/ 18 O ratio of 400 in the nuclear region, possibly indicating that the nuclear starburst is in an early evolutionary stage, or that it is fed through a molecular inflow of, at most, solar metallicity.

High-resolution (0.​​″03–0.​​″09 (9–26 pc)) ALMA (100–350 GHz (λ3 to 0.8 mm)) and (0.​​″04 (11 pc)) VLA 45 GHz measurements have been used to image continuum and spectral line emission from the inner (100 pc) region of the nearby infrared luminous galaxy IC 860. We detect compact (r ∼ 10 pc), luminous, 3 to 0.8 mm continuum emission in the core of IC 860, with brightness temperatures TB >  160 K. The 45 GHz continuum is equally compact but significantly fainter in flux. We suggest that the 3 to 0.8 mm continuum emerges from hot dust with radius r ∼ 8 pc and temperature Td ∼ 280 K, and that it is opaque at millimetre wavelengths, implying a very large H2 column density N(H2)≳1026 cm−2. Vibrationally excited lines of HCN ν2 = 1f J = 4 − 3 and 3–2 (HCN-VIB) are seen in emission and spatially resolved on scales of 40–50 pc. The line-to-continuum ratio drops towards the inner r = 4 pc, resulting in a ring-like morphology. This may be due to high opacities and matching HCN-VIB excitation- and continuum temperatures. The HCN-VIB emission reveals a north–south nuclear velocity gradient with projected rotation velocities of ν = 100 km s−1 at r = 10 pc. The brightest emission is oriented perpendicular to the velocity gradient, with a peak HCN-VIB 3–2 TB of 115 K (above the continuum). Vibrational ground-state lines of HCN 3–2 and 4–3, HC15N 4–3, HCO+ 3–2 and 4–3, and CS 7–6 show complex line absorption and emission features towards the dusty nucleus. Redshifted, reversed P-Cygni profiles are seen for HCN and HCO+ consistent with gas inflow with νin ≲ 50 km s−1. Foreground absorption structures outline the flow, and can be traced from the north-east into the nucleus. In contrast, CS 7–6 has blueshifted line profiles with line wings extending out to −180 km s−1. We suggest that a dense and slow outflow is hidden behind a foreground layer of obscuring, inflowing gas. The centre of IC 860 is in a phase of rapid evolution where an inflow is building up a massive nuclear column density of gas and dust that feeds star formation and/or AGN activity. The slow, dense outflow may be signaling the onset of feedback. The inner, r = 10 pc, IR luminosity may be powered by an AGN or a compact starburst, which then would likely require a top-heavy initial mass function.