Aims. The nuclei of active galaxies harbor massive young stars, an accreting central black hole, or both. In order to determine the physical conditions that pertain to molecular gas close to the ...sources of radiation, numerical models are constructed. Methods. These models iteratively determine the thermal and chemical balance of molecular gas that is exposed to X-rays (1-100 keV) and far-ultraviolet radiation (6-13.6 eV), as a function of depth. Results. We present a grid of XDR and PDR models that span ranges in density ( 10 super(2)-10 super(6.5) cm super(-3)), irradiation ( 10 super(0.5)-10 super(5) G sub(0) and F_{\rm X}=1.6\times 10-}160 erg cm super(-2) s super(-1)) and column density ( 3\times 10-}1\times 10cm super(-2)). Predictions are made for the most important atomic fine-structure lines, e.g., CII, OI, CI, SiII, and for molecular species like HCO super(+), HCN, HNC, CS and SiO up to J =4, CO and super(13) CO up to J =16, and column densities for CN, CH, CH super(+), HCO, HOC super(+), NO and N sub(2) H super(+). We find that surface temperatures are higher (lower) in PDRs compared to XDRs for densities >10 super(4) (<10 super(4)) cm super(-3). For the atomic lines, we find that, largely due to the different XDR ionization balance, the fine- structure line ratios of SiII 35 \mum/CII 158 \mum, OI 63 \mum/CII 158 \mum, FeII 26 \mum/CII 158 \mum and CI 369 \mum/CI 609 \mum are larger in XDRs than in PDRs, for a given density, column and irradiation strength. Similarly, for the molecular lines, we find that the line ratios HCN/HCO super(+) and HNC/HCN, as well as the column density ratio CN/HCN, discriminate between PDRs and XDRs. In particular, the HCN/HCO super(+) 1-0 ratio is <1 (>1) for XDRs (PDRs) if the density exceeds 10 super(5) cm super(-3) and if the column density is larger than 10 super(23) cm super(-2). For columns less than 10 super(22.5) cm super(-2) the XDR HCN/HCO super(+) 1-0 ratio becomes larger than one, although the individual HCN 1-0 and HCO super(+) 1-0 line intensities are weaker. For modest densities, n =10 super(4)-10 super(5) cm super(-3), and strong radiation fields (>100 erg s super(-1) cm super(-2)), HCN/HCO super(+) ratios can become larger in XDRs than PDRs as well. Also, the HCN/CO 1- 0 ratio is typically smaller in XDRs, and the HCN emission in XDRs is boosted with respect to CO only for high (column) density gas, with columns in excess of 10 super(23) cm super(-2) and densities larger than 10 super(4) cm super(-3). Furthermore, CO is typically warmer in XDRs than in PDRs, for the same total energy input. This leads to higher CO J = N +1- N /CO 1-0, N\ge 1, line ratios in XDRs. In particular, lines with N\ge 10, like CO(16-15) and CO(10-9) observable with HIFI/Herschel, discriminate very well between XDRs and PDRs. This is crucial since the XDR/AGN contribution will typically be of a much smaller (possibly beam diluted) angular scale and a 10-25% PDR contribution can already suppress XDR distinguishing features involving HCN/HCO+ and HNC/HCN. For possible future observations, column density ratios indicate that CH, CH super(+), NO, HOC super(+) and HCO are good PDR/XDR discriminators.
We present a study of the molecular gas properties in a sample of 98 H i – flux selected spiral galaxies within ∼25 Mpc, using the CO J = 3 − 2 line observed with the James Clerk Maxwell Telescope. ...We use the technique of survival analysis to incorporate galaxies with CO upper limits into our results. Comparing the group and Virgo samples, we find a larger mean H2 mass in the Virgo galaxies, despite their lower mean H i mass. This leads to a significantly higher H2 to H i ratio for Virgo galaxies. Combining our data with complementary Hα star formation rate measurements, Virgo galaxies have longer molecular gas depletion times compared to group galaxies, due to their higher H2 masses and lower star formation rates. We suggest that the longer depletion times may be a result of heating processes in the cluster environment or differences in the turbulent pressure. From the full sample, we find that the molecular gas depletion time has a positive correlation with the stellar mass, indicative of differences in the star formation process between low- and high-mass galaxies, and a negative correlation between the molecular gas depletion time and the specific star formation rate.
In this paper we present fluxes in the CI lines of neutral carbon at the centers of some 76 galaxies with far-infrared luminosities ranging from 109 to 1012L, as obtained with the Herschel Space ...Observatory and ground-based facilities, along with the line fluxes of the J = 7-6, J = 4-3, J = 2-112CO, and J = 2-113CO transitions. With this data-set, we determine the behavior of the observed lines with respect to each other and then investigate whether they can be used to characterize the molecular interstellar medium (ISM) of the parent galaxies in simple ways and how the molecular gas properties define the model results. In particular, so-called X(CI) conversion factors are not superior to X(12CO) factors. The methods and diagnostic diagrams outlined in this paper also provide a new and relatively straightforward means of deriving the physical characteristics of molecular gas in high-redshift galaxies up to z = 5, which are otherwise hard to determine.
We present a systematic survey of multiple velocity-resolved H2O spectra using Herschel/Heterodyne Instrument for the Far Infrared (HIFI) toward nine nearby actively star-forming galaxies. The ...ground-state and low-excitation lines (Eup ≤ 130 K) show profiles with emission and absorption blended together, while absorption-free medium-excitation lines (130 K ≤ Eup ≤ 350 K) typically display line shapes similar to CO. We analyze the HIFI observation together with archival SPIRE/PACS H2O data using a state-of-the-art 3D radiative transfer code that includes the interaction between continuum and line emission. The water excitation models are combined with information on the dust and CO spectral line energy distribution to determine the physical structure of the interstellar medium (ISM). We identify two ISM components that are common to all galaxies: a warm ( K), dense ( ) phase that dominates the emission of medium-excitation H2O lines. This gas phase also dominates the far-IR emission and the CO intensities for . In addition, a cold ( K), dense ( ), more extended phase is present. It outputs the emission in the low-excitation H2O lines and typically also produces the prominent line absorption features. For the two ULIRGs in our sample (Arp 220 and Mrk 231) an even hotter and more compact (Rs ≤ 100 pc) region is present, which is possibly linked to AGN activity. We find that collisions dominate the water excitation in the cold gas and for lines with K and K in the warm and hot component, respectively. Higher-energy levels are mainly excited by IR pumping.
We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J = 4-3 through J = 13-12, 6 H sub(2)O rotational lines, and ...CI and NII fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H sub(2) upsilon = 1-0 S(1) and nu = 2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity nu sub(s) = 10 km s super(-1) and a pre-shock density n sub(H) = 5 x 10 super(4) cm super(-3). We find that the solution best fitting the H sub(2) lines is degenerate. The shock velocities and number densities range between nu sub(s) = 17-47 km s super(-1) and n sub(H) = 10 super(7)-5 x 10 super(4) cm super(-3), respectively. The H sub(2) lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s super(-1)) shocks while only a small fraction (<, ~1%) of the interstellar medium is exposed to the high-velocity shocks. This implies that the gas is rapidly losing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.
We have previously shown that 21-benzylidene digoxin (21-BD) increases the total cholesterol and phospholipid content on the membrane of HeLa cells. Lipid modulation caused by cardiotonic steroids ...(CTS) is still unexplored. Therefore, the aim of the present study was to evaluate the cholesterol and phospholipid modulation of the cell membrane caused by ouabain and 21-BD and the possible involvement of the caveolae on this modulation. For this, one cell line containing caveolae (HeLa) and other not containing (Caco-2) were used. The modulation of the lipid profile was evaluated by total cholesterol and phospholipids measurements, and identification of membrane phospholipids by HPTLC. The cholesterol distribution was evaluated by filipin staining. The caveolin-1 expression was evaluated by Western Blotting. Ouabain had no effect on the total membrane lipid content in both cell lines. However, 21-BD increased total membrane phospholipid content and had no effect on the membrane cholesterol content in Caco-2 cells. CTS were not able to alter the specific phospholipids content. In the filipin experiments, 21-BD provoked a remarkable redistribution of cholesterol to the perinuclear region of HeLa cells. In Caco-2 cells, it was observed only a slight increase in cholesterol, especially as intracellular vesicles. The caveolin-1 expression was not altered by any of the compounds. Our data mainly show different effects of two cardiotonic steroids. Ouabain had no effect on the lipid profile of cells, whereas 21-BD causes important changes in cholesterol and phospholipid content. Therefore, the modulation of cholesterol content in the plasma membrane of HeLa cells is not correlated with the expression of caveolin-1.
Graphic Abstract
We report on four radio-detected cosmic-ray (CR) or CR-like events observed with the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload. Two of the four ...were previously identified as stratospheric CR air showers during the ANITA-I flight. A third stratospheric CR was detected during the ANITA-II flight. Here, we report on characteristics of these three unusual CR events, which develop nearly horizontally, 20-30 km above the surface of Earth. In addition, we report on a fourth steeply upward-pointing ANITA-I CR-like radio event which has characteristics consistent with a primary that emerged from the surface of the ice. This suggests a possible τ-lepton decay as the origin of this event, but such an interpretation would require significant suppression of the standard model τ-neutrino cross section.
Recently, the ANITA collaboration reported on two upward-going extensive air shower events consistent with a primary particle that emerges from the surface of the Antarctic ice sheet. These events ...may be of ν τ origin, in which the neutrino interacts within the Earth to produce a τ lepton that emerges from the Earth, decays in the atmosphere, and initiates an extensive air shower. In this paper we estimate an upper bound on the ANITA acceptance to a diffuse ν τ flux detected via τ -lepton-induced air showers within the bounds of standard model uncertainties. By comparing this estimate with the acceptance of Pierre Auger Observatory and IceCube and assuming standard model interactions, we conclude that a ν τ origin of these events would imply a neutrino flux at least two orders of magnitude above current bounds.
We present the first complete CO J = 3-2 map of the nearby grand-design spiral galaxy M51 (NGC 5194), at a spatial resolution of ∼600 pc, obtained with the HARP-B instrument on the James Clerk ...Maxwell Telescope. The map covers the entire optical galaxy disc and out to the companion NGC 5195, with CO J = 3-2 emission detected over an area of ∼9 arcmin × 6 arcmin (∼21 × 14 kpc). We describe the CO J = 3-2 integrated intensity map and combine our results with maps of CO J = 2-1, CO J = 1-0 and other data from the literature to investigate the variation of the molecular gas, atomic gas and polycyclic aromatic hydrocarbon (PAH) properties of M51 as a function of distance along the spiral structure on sub-kiloparsec scales. We find that for the CO J = 3-2 and CO J = 2-1 transitions, there is a clear difference between the variation of arm and interarm emission with galactocentric radius, with the interarm emission relatively constant with radius and the contrast between arm and interarm emission decreasing with radius. For the CO J = 1-0 line and H i emission, the variation with radius shows a similar trend for the arm and interarm regions, and the arm-interarm contrast appears relatively constant with radius. We investigate the variation of CO line ratios (J = 3-2/2-1, J = 2-1/1-0 and J = 3-2/1-0) as a function of distance along the spiral structure. Line ratios are consistent with the range of typical values for other nearby galaxies in the literature. The highest CO J = 3-2/J = 2-1 line ratios are found in the central ∼1 kiloparsec and in the spiral arms and the lowest line ratios in the interarm regions. We find no clear evidence of a trend with radius for the spiral arms, but for the interarm regions there appears to be a trend for all CO line ratios to increase with radius. We find a strong relationship between the ratio of CO J = 3-2 intensity to stellar-continuum-subtracted 8 μm PAH surface brightness and the CO J = 3-2 intensity that appears to vary with radius.
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