Spatially resolved cold molecular outflows in ULIRGs
Astronomy and Astrophysics EDP Sciences 616 (2018) A171
Abstract:
We present new CO(2–1) observations of three low-z (d ∼350 Mpc) ultra-luminous infrared galaxy (ULIRG) systems (six nuclei) observed with the Atacama large millimeter/submillimeter array (ALMA) at high spatial resolution (∼500 pc). We detect massive cold molecular gas outflows in five out of six nuclei (Mout ∼ (0.3 − 5) × 108 Mo). These outflows are spatially resolved with deprojected effective radii between 250 pc and 1 kpc although high-velocity molecular gas is detected up to Rmax ∼ 0.5 − 1.8 kpc (1 − 6 kpc deprojected). The mass outflow rates are 12 − 400 Mo yr−1 and the inclination corrected average velocity of the outflowing gas is 350 − 550 km s−1 (vmax = 500 − 900 km s−1 ). The origin of these outflows can be explained by the strong nuclear starbursts although the contribution of an obscured active galactic nucleus cannot be completely ruled out. The position angle (PA) of the outflowing gas along the kinematic minor axis of the nuclear molecular disk suggests that the outflow axis is perpendicular to the disk for three of these outflows. Only in one case is the outflow PA clearly not along the kinematic minor axis, which might indicate a different outflow geometry. The outflow depletion times are 15 − 80 Myr. These are comparable to, although slightly shorter than, the starformation (SF) depletion times (30 − 80 Myr). However, we estimate that only 15 − 30% of the outflowing molecular gas will escape the gravitational potential of the nucleus. The majority of the outflowing gas will return to the disk after 5 − 10 Myr and become available to form new stars. Therefore, these outflows will not likely completely quench the nuclear starbursts. These star-forming powered molecular outflows would be consistent with being driven by radiation pressure from young stars (i.e., momentum-driven) only if the coupling between radiation and dust increases with increasing SF rates. This can be achieved if the dust optical depth is higher in objects with higher SF. This is the case in at least one of the studied objects. Alternatively, if the outflows are mainly driven by supernovae (SNe), the coupling efficiency between the interstellar medium and SNe must increase with increasing SF levels. The relatively small sizes (<1 kpc) and dynamical times (<3 Myr) of the cold molecular outflows suggests that molecular gas cannot survive longer in the outflow environment or that it cannot form efficiently beyond these distances or times. In addition, the ionized and hot molecular phases have been detected for several of these outflows, so this suggests that outflowing gas can experience phase changes and indicates that the outflowing gas is intrinsically multiphase, likely sharing similar kinematics, but different mass and, therefore, different energy and momentum contributions.CO (7-6), [C I] 370 μm, and [N II] 205 μm Line Emission of the QSO BRI1335-0417 at Redshift 4.407
Astrophysical Journal Institute of Physics 864:1 (2018) 38
Abstract:
We present the results from our Atacama Large Millimeter/submillimeter Array (ALMA) imaging observations of the CO(7-6), [C i] 370 μm (hereafter [C i]), and [N ii] 205 μm (hereafter [N ii]) lines and their underlying continuum emission of BRI 1335-0417, an infrared bright quasar at z = 4.407. At the achieved resolutions of ∼1.″1 to 1.″2 (or 7.5-8.2 kpc), the continuum at 205 and 372 μm (rest frame), the CO(7-6), and the [C i] emissions are at best barely resolved whereas the [N ii] emission is well resolved with a beam-deconvolved major axis of 1.″3(±0.″3) or 9(±2) kpc. As a warm dense gas tracer, the CO(7-6) emission shows a more compact spatial distribution and a significantly higher peak velocity dispersion than the other two lines that probe lower density gas, a picture favoring a merger-Triggered star formation (SF) scenario over an orderly rotating SF disk. The CO(7-6) data also indicate a possible QSO-driven gas outflow that reaches a maximum line-of-sight velocity of 500-600 km s-1. The far-infrared (FIR) dust temperature (Tdust) of 41.5 K from a graybody fit to the continuum agrees well with the average Tdustinferred from various line luminosity ratios. The resulting LCO(7-6)/LFIRluminosity ratio is consistent with that of local luminous infrared galaxies powered predominantly by SF. The LCO(7-6)-inferred SF rate is 5.1(±1.5) × 103Moyr-1. The system has an effective star-forming region of kpc in diameter and a molecular gas reservoir of ∼5 × 1011Mo.The MALATANG survey: The L GAS–L IR correlation on sub-kiloparsec scale in six nearby star-forming galaxies as traced by HCN J = 4 → 3 and HCO+ J = 4 → 3
Astrophysical Journal Institute of Physics 860:2 (2018) 165
Abstract:
We present HCN J = 4→3 and HCO+ J = 4→3 maps of six nearby star-forming galaxies, NGC 253, NGC 1068, IC 342, M82, M83, and NGC 6946, obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey. All galaxies were mapped in the central 2×2 region at 14 (FWHM) resolution (corresponding to linear scales of ∼0.2-1.0 kpc). The LIR-Ldense relation, where the dense gas is traced by the HCN J = 4→3 and the HCO+ J = 4→3 emission, measured in our sample of spatially resolved galaxies is found to follow the linear correlation established globally in galaxies within the scatter. We find that the luminosity ratio, LIR/Ldense, shows systematic variations with LIR within individual spatially resolved galaxies, whereas the galaxy-integrated ratios vary little. A rising trend is also found between LIR/Ldense ratio and the warm-dust temperature gauged by the 70 μm/100 μm flux ratio. We find that the luminosity ratios of IR/HCN (4-3) and IR/HCO+ (4-3), which can be taken as a proxy for the star formation efficiency (SFE) in the dense molecular gas (SFEdense), appear to be nearly independent of the dense gas fraction ( fdense) for our sample of galaxies. The SFE of the total molecular gas (SFEmol) is found to increase substantially with fdensewhen combining our data with those on local (ultra)luminous infrared galaxies and high-z quasars. The mean LHCN(4-3) LHCO+(4-3) line ratio measured for the six targeted galaxies is 0.9±0.6. No significant correlation is found for the L'HCN(4-3) L'HCO+(4-3) ratio with the star formation rate as traced by LIR, nor with the warm-dust temperature, for the different populations of galaxies.Resolving the nuclear obscuring disk in the Compton-thick Seyfert galaxy NGC 5643 with ALMA
Astrophysical Journal American Astronomical Society 859:2 (2018) 144
Abstract:
We present ALMA Band 612CO(2-1) line and rest-frame 232 GHz continuum observations of the nearby Compton-thick Seyfert galaxy NGC 5643 with angular resolutions 0.″11-0.″26 (9-21 pc). The CO(2-1) integrated line map reveals emission from the nuclear and circumnuclear region with a two-arm nuclear spiral extending ∼10″ on each side. The circumnuclear CO(2-1) kinematics can be fitted with a rotating disk, although there are regions with large residual velocities and/or velocity dispersions. The CO(2-1) line profiles of these regions show two different velocity components. One is ascribed to the circular component and the other to the interaction of the AGN outflow, as traced by the [O iii]λ5007 Åemission, with molecular gas in the disk a few hundred parsecs from the AGN. On nuclear scales, we detected an inclined CO(2-1) disk (diameter 26 pc, FWHM) oriented almost in a north-south direction. The CO(2-1) nuclear kinematics can be fitted with a rotating disk that appears to be tilted with respect to the large-scale disk. There are strong non-circular motions in the central 0.″2-0.″3 with velocities of up to 110 km s-1. In the absence of a nuclear bar, these motions could be explained as radial outflows in the nuclear disk. We estimate a total molecular gas mass for the nuclear disk of M(H2) = 1.1 ×107Moand an H2column density toward the location of the AGN of N(H2) ∼ 5 ×1023cm-2, for a standard CO-to-H2conversion factor. We interpret this nuclear molecular gas disk as the obscuring torus of NGC 5643 as well as the collimating structure of the ionization cone.The strong gravitationally lensed Herschel galaxy HLock01: Optical spectroscopy reveals a close galaxy merger with evidence of inflowing gas
Astrophysical Journal Institute of Physics 854:2 (2018) 151