[en] We report the first systematic study of the submillimeter water vapor rotational emission lines in infrared (IR) galaxies based on the Fourier Transform Spectrometer (FTS) data of Herschel SPIRE. Among the 176 galaxies with publicly available FTS data, 45 have at least one H₂O emission line detected. The H₂O line luminosities range from ∼1 × 10⁵ L_☉ to ∼5 × 10⁷ L_☉ while the total IR luminosities (L_IR) have a similar spread (∼1-300 × 10¹⁰ L_☉). In addition, emission lines of H₂O⁺ and H₂¹⁸O are also detected. H₂O is found, for most galaxies, to be the strongest molecular emitter after CO in FTS spectra. The luminosity of the five most important H₂O lines is near-linearly correlated with L_IR, regardless of whether or not strong active galactic nucleus signature is present. However, the luminosity of H₂O(2₁₁-2₀₂) and H₂O(2₂₀-2₁₁) appears to increase slightly faster than linear with L_IR. Although the slope turns out to be slightly steeper when z ∼ 2-4 ULIRGs are included, the correlation is still closely linear. We find that L_H2O/L_IR decreases with increasing f₂₅/f₆₀, but see no dependence on f₆₀/f₁₀₀, possibly indicating that very warm dust contributes little to the excitation of the submillimeter H₂O lines. The average spectral line energy distribution (SLED) of the entire sample is consistent with individual SLEDs and the IR pumping plus collisional excitation model, showing that the strongest lines are H₂O(2₀₂-1₁₁) and H₂O(3₂₁-3₁₂).

[en] We present new Herschel-SPIRE imaging spectroscopy (194-671 μm) of the bright starburst galaxy M82. Covering the CO ladder from J = 4 → 3 to J = 13 → 12, spectra were obtained at multiple positions for a fully sampled ∼3 × 3 arcmin map, including a longer exposure at the central position. We present measurements of ¹²CO, ¹³CO, [C I], [N II], HCN, and HCO⁺ in emission, along with OH⁺, H₂O⁺, and HF in absorption and H₂O in both emission and absorption, with discussion. We use a radiative transfer code and Bayesian likelihood analysis to model the temperature, density, column density, and filling factor of multiple components of molecular gas traced by ¹²CO and ¹³CO, adding further evidence to the high-J lines tracing a much warmer (∼500 K), less massive component than the low-J lines. The addition of ¹³CO (and [C I]) is new and indicates that [C I] may be tracing different gas than ¹²CO. No temperature/density gradients can be inferred from the map, indicating that the single-pointing spectrum is descriptive of the bulk properties of the galaxy. At such a high temperature, cooling is dominated by molecular hydrogen. Photon-dominated region (PDR) models require higher densities than those indicated by our Bayesian likelihood analysis in order to explain the high-J CO line ratios, though cosmic-ray-enhanced PDR models can do a better job reproducing the emission at lower densities. Shocks and turbulent heating are likely required to explain the bright high-J emission.

[en] We present our initial results on the CO rotational spectral line energy distribution (SLED) of the J to J–1 transitions from J = 4 up to 13 from Herschel SPIRE spectroscopic observations of 65 luminous infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey. The observed SLEDs change on average from one peaking at J ≤ 4 to a broad distribution peaking around J ∼ 6 to 7 as the IRAS 60-to-100 μm color, C(60/100), increases. However, the ratios of a CO line luminosity to the total infrared luminosity, L _IR, show the smallest variation for J around 6 or 7. This suggests that, for most LIRGs, ongoing star formation (SF) is also responsible for a warm gas component that emits CO lines primarily in the mid-J regime (5 ≲ J ≲ 10). As a result, the logarithmic ratios of the CO line luminosity summed over CO (5–4), (6–5), (7–6), (8–7) and (10–9) transitions to L _IR, log R _midCO, remain largely independent of C(60/100), and show a mean value of –4.13 (≡log R_midCO^SF) and a sample standard deviation of only 0.10 for the SF-dominated galaxies. Including additional galaxies from the literature, we show, albeit with a small number of cases, the possibility that galaxies, which bear powerful interstellar shocks unrelated to the current SF, and galaxies, in which an energetic active galactic nucleus contributes significantly to the bolometric luminosity, have their R _midCO higher and lower than R_midCO^SF, respectively

[en] We present, for the first time, a statistical study of [N II] 205 μm line emission for a large sample of local luminous infrared galaxies using Herschel Spectral and Photometric Imaging Receiver Fourier Transform Spectrometer (SPIRE FTS) data. For our sample of galaxies, we investigate the correlation between the [N II] luminosity (L_[NII]) and the total infrared luminosity (L_IR), as well as the dependence of L_[NII]/L_IR ratio on L_IR, far-infrared colors (IRAS f₆₀/f₁₀₀), and the [O III] 88 μm to [N II] luminosity ratio. We find that L_[NII] correlates almost linearly with L_IR for non-active galactic nucleus galaxies (all having L_IR < 10¹² L_☉) in our sample, which implies that L_[NII] can serve as a star formation rate tracer which is particularly useful for high-redshift galaxies that will be observed with forthcoming submillimeter spectroscopic facilities such as the Atacama Large Millimeter/submillimeter Array. Our analysis shows that the deviation from the mean L_[NII]-L_IR relation correlates with tracers of the ionization parameter, which suggests that the scatter in this relation is mainly due to the variations in the hardness, and/or ionization parameter, of the ambient galactic UV field among the sources in our sample.

[en] (Ultra) luminous infrared galaxies ((U)LIRGs) are objects characterized by their extreme infrared (8-1000 μm) luminosities (L _L_I_R_G > 10"1"1 L _☉ and L _U_L_I_R_G > 10"1"2 L _☉). The Herschel Comprehensive ULIRG Emission Survey (PI: van der Werf) presents a representative flux-limited sample of 29 (U)LIRGs that spans the full luminosity range of these objects (10"1"1 L _☉ ≤ L _I_R ≤ 10"1"3 L _☉). With the Herschel Space Observatory, we observe [C II] 157 μm, [O I] 63 μm, and [O I] 145 μm line emission with Photodetector Array Camera and Spectrometer, CO J = 4-3 through J = 13-12, [C I] 370 μm, and [C I] 609 μm with SPIRE, and low-J CO transitions with ground-based telescopes. The CO ladders of the sample are separated into three classes based on their excitation level. In 13 of the galaxies, the [O I] 63 μm emission line is self absorbed. Comparing the CO excitation to the InfraRed Astronomical Satellite 60/100 μm ratio and to far infrared luminosity, we find that the CO excitation is more correlated to the far infrared colors. We present cooling budgets for the galaxies and find fine-structure line flux deficits in the [C II], [Si II], [O I], and [C I] lines in the objects with the highest far IR fluxes, but do not observe this for CO 4 ≤ J _u_p_p ≤ 13. In order to study the heating of the molecular gas, we present a combination of three diagnostic quantities to help determine the dominant heating source. Using the CO excitation, the CO J = 1-0 linewidth, and the active galactic nucleus (AGN) contribution, we conclude that galaxies with large CO linewidths always have high-excitation CO ladders, and often low AGN contributions, suggesting that mechanical heating is important