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Register a new userALMA Imaging of HCN, CS and dust in Arp 220 and NGC 6240
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We report ALMA Band 7 (350 GHz) imaging at 0.4 - 0.6arcsec resolution and Band 9 (696 GHz) at ~0.25arcsec resolution of the luminous IR galaxies Arp 220 and NGC 6240. The long wavelength dust continuum is used to estimate ISM masses for Arp 220 East, West and NGC 6240 of 1.9, 4.2 and 1.6x10^9 msun within radii of 69, 65 and 190 pc. The HCN emission was modeled to derive the emissivity distribution as a function of radius and the kinematics of each nuclear disk, yielding dynamical masses consistent with the masses and sizes derived from the dust emission. In Arp 220, the major dust and gas concentrations are at radii less than 50 pc in both counter-rotating nuclear disks. The thickness of the disks in Arp 220estimated from the velocity dispersion and rotation velocities are 10-20 pc and the mean gas densities are n_H2 ~10^5 cm^-3 at R < 50 pc. We develop an analytic treatment for the molecular excitation (including photon trapping), yielding volume densities for both the HCN and CS emission with n_H2 ~2x10^5 cm^-3. The agreement of the mean density from the total mass and size with that required for excitation suggests that the volume is essentially filled with dense gas, i.e. it is not cloudy or like swiss cheese.
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Aims. We present new IRAM Plateau de Bure Interferometer observations of Arp 220 in HCN, HCO$^{+}$, HN$^{13}$C J=1-0, C$_{2}$H N=1-0, SiO J = 2-1, HNCO J$_{k,k}$ = 5$_{0,4}$ - 4$_{0,4}$, CH$_{3}$CN(6-5), CS J=2-1 and 5-4 and $^{13}$CO J=1-0 and 2-1 and of NGC 6240 in HCN, HCO$^{+}$ J = 1-0 and C$_{2}$H N = 1-0. In addition, we present Atacama Large Millimeter/submillmeter Array science verification observations of Arp 220 in CS J = 4-3 and CH$_{3}$CN(10-9). Various lines are used to analyse the physical conditions of the molecular gas including the [$^{12}$CO]/[$^{13}$CO] and [$^{12}$CO]/[C$^{18}$O] abundance ratios. These observations will be made available to the public. Methods. We create brightness temperature line ratio maps to present the different physical conditions across Arp 220 and NGC 6240. In addition, we use the radiative transfer code RADEX and a Monte Carlo Markov Chain likelihood code to model the $^{12}$CO, $^{13}$CO and C$^{18}$O lines of Arp 220 at ~2 (~700 pc) scales, where the $^{12}$CO and C$^{18}$O measurements were obtained from literature. Results. Line ratios of optically thick lines such as $^{12}$CO show smoothly varying ratios while the line ratios of optically thin lines such as $^{13}$CO show a east-west gradient across Arp 220. The HCN/HCO$^{+}$ line ratio differs between Arp 220 and NGC 6240, where Arp 220 has line ratios above 2 and NGC 6240 below 1. The radiative transfer analysis solution is consistent with a warm (~40 K), moderately dense (~10$^{3.4}$ cm$^{-3}$) molecular gas component averaged over the two nuclei. We find [$^{12}$CO]/[$^{13}$CO] and [$^{12}$CO]/[C$^{18}$O] abundance ratios of ~90 for both. The abundance enhancement of C$^{18}$O can be explained by stellar nucleosynthesis enrichment of the interstellar medium.
We present new images of Arp 220 from the Atacama Large Millimeter/submillimeter Array with the highest combination of frequency (691 GHz) and resolution ($0.36 times 0.20^{primeprime}$) ever obtained for this prototypical ultraluminous infrared galaxy. The western nucleus is revealed to contain warm (200 K) dust that is optically thick ($tau_{434mu m} = 5.3$), while the eastern nucleus is cooler (80 K) and somewhat less opaque ($tau_{434mu m} = 1.7$). We derive full-width half-maximum diameters of $ 76 times le 70$ pc and $123 times 79$ pc for the western and eastern nucleus, respectively. The two nuclei combined account for ($83 ^{+65}_{-38}$ (calibration) $^{+0}_{-34}$ (systematic))% of the total infrared luminosity of Arp 220. The luminosity surface density of the western nucleus ($ log(sigma T^4) = 14.3pm 0.2 ^{+0}_{-0.7}$ in units of L$_odot$ kpc$^{-2}$) appears sufficiently high to require the presence of an AGN or a hot starburst, although the exact value depends sensitively on the brightness distribution adopted for the source. Although the role of any central AGN remains open, the inferred mean gas column densities of $0.6-1.8 times 10^{25}$ cm$^{-2}$ mean that any AGN in Arp 220 must be Compton-thick.
We present 0.97 $times$ 0.53 (470 pc $times$ 250 pc) resolution CO ($J$ = 2-1) observations toward the nearby luminous merging galaxy NGC 6240 with the Atacama Large Millimeter/submillimeter Array. We confirmed a strong CO concentration within the central 700 pc, which peaks between the double nuclei, surrounded by extended CO features along the optical dust lanes ($sim$11 kpc). We found that the CO emission around the central a few kpc has extremely broad velocity wings with full width at zero intensity $sim$ 2000 km s$^{-1}$, suggesting a possible signature of molecular outflow(s). In order to extract and visualize the high-velocity components in NGC 6240, we performed a multiple Gaussian fit to the CO datacube. The distribution of the broad CO components show four extremely large linewidth regions ($sim$1000 km s$^{-1}$) located 1-2 kpc away from both nuclei. Spatial coincidence of the large linewidth regions with H$alpha$, near-IR H$_2$, and X-ray suggests that the broad CO (2-1) components are associated with nuclear outflows launched from the double nuclei.
We present results from Atacama Large Millimeter/submillimeter Array (ALMA) observations of CS from the nearby galaxy NGC 1068 ($sim14$ Mpc). This Seyfert 2 barred galaxy possesses a circumnuclear disc (CND, $rsim200$ pc) and a starburst ring (SB ring, $rsim1.3$ kpc). These high-resolution maps ($sim0.5$, $sim35$ pc) allow us to analyse specific sub-regions in the galaxy and investigate differences in line intensity ratios and physical conditions, particularly those between the CND and SB ring. Local thermodynamic equilibrium (LTE) analysis of the gas is used to calculate CS densities in each sub-region, followed by non-LTE analysis conducted using the radiative transfer code RADEX to fit observations and constrain gas temperature, CS column density and hydrogen density. Finally, the chemical code UCLCHEM is used to reconstruct the gas, allowing an insight into its origin and chemical history. The density of hydrogen in the CND is found to be $geq10^5$ cm$^{-2}$, although exact values vary, reaching $10^6$ cm$^{-2}$ at the AGN. The conditions in the two arms of the SB ring appear similar to one another, though the density found ($sim10^4$ cm$^{-2}$) is lower than in the CND. The temperature in the CND increases from east to west, and is also overall greater than found in the SB ring. These modelling methods indicate the requirement for multi-phase gas components in order to fit the observed emission over the galaxy. A larger number of high resolution transitions across the SLED may allow for further constraining of the conditions, particularly in the SB ring.
We report the results of HCN(J=4-3) and HCO+(J=4-3) observations of two luminous infrared galaxies (LIRGs), NGC 4418 and Arp 220, made using the Atacama Submillimeter Telescope Experiment (ASTE). The ASTE wide-band correlator provided simultaneous observations of HCN(4-3) and HCO+(4-3) lines, and a precise determination of their flux ratios. Both galaxies showed high HCN(4-3) to HCO+(4-3) flux ratios of >2, possibly due to AGN-related phenomena. The J = 4-3 to J = 1-0 transition flux ratios for HCN (HCO+) are similar to those expected for fully thermalized (sub-thermally excited) gas in both sources, in spite of HCNs higher critical density. If we assume collisional excitation and neglect an infrared radiative pumping process, our non-LTE analysis suggests that HCN traces gas with significantly higher density than HCO+. In Arp 220, we separated the double-peaked HCN(4-3) emission into the eastern and western nuclei, based on velocity information. We confirmed that the eastern nucleus showed a higher HCN(4-3) to HCN(1-0) flux ratio, and thus contained a larger amount of highly excited molecular gas than the western nucleus.
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