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Register a new userMolecular outflows in local galaxies: Method comparison and a role of intermittent AGN driving
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We report new detections and limits from a NOEMA and ALMA CO(1-0) search for molecular outflows in 13 local galaxies with high FIR surface brightness, and combine with results from the literature. CO line ratios and outflow structure provide some constraints on the conversion from observables to quantities such as molecular mass outflow rates. Ratios between outflow emission in higher J CO transitions and in CO(1-0) typically are consistent with excitation Ri1<~1. For IRAS 13120-5453, however, R31=2.10 indicates optically thin CO in the outflow. Like much of the outflow literature, we use alpha(CO) = 0.8, and we present arguments for using C=1 in deriving molecular mass outflow rates Mdot = C*M*v/R. We compare the two main methods for molecular outflow detection: CO mm interferometry and Herschel OH spectroscopy. For 26 sources studied with both methods, we find 80% agreement in detecting vout>~150km/s outflows, and non-matches can be plausibly ascribed to outflow geometry and SNR. For 12 bright ULIRGs with detailed OH-based outflow modeling, CO outflows are detected in all but one. Outflow masses, velocities, and sizes for these 11 sources agree well between the two methods, and modest remaining differences may relate to the different but overlapping regions sampled by CO emission and OH absorption. Outflow properties correlate better with AGN luminosity and with bolometric luminosity than with FIR surface brightness. The most massive outflows are found for systems with current AGN activity, but significant outflows in non-AGN systems must relate to star formation or to AGN activity in the recent past. We report scaling relations for the increase of outflow mass, rate, momentum rate, and kinetic power with bolometric luminosity. Short ~10^6yr flow times and some sources with resolved multiple outflow episodes support a role of intermittent driving, likely by AGN. (abridged)
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We present an analysis of new and archival ALMA observations of molecular gas in twelve central cluster galaxies. We examine emerging trends in molecular filament morphology and gas velocities to understand their origins. Molecular gas masses in these systems span $10^9-10^{11}mathrm{M}_{odot}$, far more than most gas-rich galaxies. ALMA images reveal a distribution of morphologies from filamentary to disk-dominated structures. Circumnuclear disks on kiloparsec scales appear rare. In most systems, half to nearly all of the molecular gas lies in filamentary structures with masses of a few $times10^{8-10}mathrm{M}_{odot}$ that extend radially several to several tens of kpc. In nearly all cases the molecular gas velocities lie far below stellar velocity dispersions, indicating youth, transience or both. Filament bulk velocities lie far below the galaxys escape and free-fall speeds indicating they are bound and being decelerated. Most extended molecular filaments surround or lie beneath radio bubbles inflated by the central AGN. Smooth velocity gradients found along the filaments are consistent with gas flowing along streamlines surrounding these bubbles. Evidence suggests most of the molecular clouds formed from low entropy X-ray gas that became thermally unstable and cooled when lifted by the buoyant bubbles. Uplifted gas will stall and fall back to the galaxy in a circulating flow. The distribution in morphologies from filament to disk-dominated sources therefore implies slowly evolving molecular structures driven by the episodic activity of the AGN.
We perform a joint-analysis of high spatial resolution molecular gas and star-formation rate (SFR) maps in main-sequence star-forming galaxies experiencing galactic-scale outflows of ionised gas. Our aim is to understand the mechanism that determines which galaxies are able to launch these intense winds. We observed CO(1-0) at 1 resolution with ALMA in 16 edge-on galaxies, which also have 2 spatial resolution optical integral field observations from the SAMI Galaxy Survey. Half the galaxies in the sample were previously identified as harbouring intense and large-scale outflows of ionised gas (outflow-types), the rest serve as control galaxies. The dataset is complemented by integrated CO(1-0) observations from the IRAM 30-m telescope to probe the total molecular gas reservoirs. We find that the galaxies powering outflows do not possess significantly different global gas fractions or star-formation efficiencies when compared with a control sample. However, the ALMA maps reveal that the molecular gas in the outflow-type galaxies is distributed more centrally than in the control galaxies. For our outflow-type objects, molecular gas and star-formation is largely confined within their inner effective radius ($rm r_{eff}$), whereas in the control sample the distribution is more diffuse, extending far beyond $rm r_{eff}$. We infer that outflows in normal star-forming galaxies may be caused by dynamical mechanisms that drive molecular gas into their central regions, which can result in locally-enhanced gas surface density and star-formation.
Outflows from starburst galaxies can be driven by thermal pressure, radiation and cosmic rays. We present an analytic phenomenological model that accounts for these contributions simultaneously to investigate their effects on the hydrodynamical properties of outflows. We assess the impact of energy injection, wind opacity, magnetic field strength and the mass of the host galaxy on flow velocity, temperature, density and pressure profiles. For an M82-like wind, a thermally-dominated driving mechanism is found to deliver the fastest and hottest wind. Radiation-driven winds in typical starburst-galaxy configurations are unable to attain the higher flow velocities and temperatures associated with thermal and cosmic ray-driven systems, leading to higher wind densities which would be more susceptible to cooling and fragmentation at lower altitudes. High opacity winds are more sensitive to radiative driving, but terminal flow velocities are still lower than those achieved by other driving mechanisms at realistic opacities. We demonstrate that variations in the outflow magnetic field can influence its coupling with cosmic rays, where stronger fields enable greater streaming but less driving near the base of the flow, instead with cosmic rays redirecting their driving impact to higher altitudes. The gravitational potential is less important in M82-like wind configurations, and substantial variations in the flow profiles only emerge at high altitude in massive haloes. This model offers a more generalised approach to examine the large scale hydrodynamical properties for a wide variety of starburst galaxies.
We analyse the 2-dimensional distribution and kinematics of the stars as well as molecular and ionised gas in the central few hundred parsecs of 5 active and 5 matched inactive galaxies. The equivalent widths of the Br-gamma line indicate there is no on-going star formation in their nuclei, although recent (terminated) starbursts are possible in the active galaxies. The stellar velocity fields show no signs of non-circular motions, while the 1-0S(1) H_2 kinematics exhibit significant deviations from simple circular rotation. In the active galaxies the H_2 kinematics reveal inflow and outflow superimposed on disk rotation. Steady-state circumnuclear inflow is seen in three AGN, and hydrodynamical models indicate it can be driven by a large scale bar. In three of the five AGN, molecular outflows are spatially resolved. The outflows are oriented such that they intersect, or have an edge close to, the disk - which may be the source of molecular gas in the outflow. The relatively low speeds imply the gas will fall back onto the disk; and with moderate outflow rates, they will have only a local impact on the host galaxy. H_2 was detected in two inactive galaxies. These exhibit chaotic circumnuclear dust morphologies and have molecular structures that are counter-rotating with respect to the main gas component, which could lead to gas inflow in the near future. In our sample, all four galaxies with chaotic dust morphology in the circumnuclear region exist in moderately dense groups with 10-15 members where accretion of stripped gas can easily occur.
We present 1.3mm Submillimeter Array (SMA) observations at $sim$3$^{primeprime}$ resolution towards the brightest section of the intermediate/massive star forming cluster NGC 2264-C. The millimetre continuum emission reveals ten 1.3mm continuum peaks, of which four are new detections. The observed frequency range includes the known molecular jet/outflow tracer SiO (5-4), thus providing the first high resolution observations of SiO towards NGC 2264-C. We also detect molecular lines of twelve additional species towards this region, including CH$_3$CN, CH$_3$OH, SO, H$_2$CO, DCN, HC$_3$N, and $^{12}$CO. The SiO (5-4) emission reveals the presence of two collimated, high velocity (up to 30kms$^{-1}$ with respect to the systemic velocity) bi-polar outflows in NGC 2264-C. In addition, the outflows are traced by emission from $^{12}$CO, SO, H$_2$CO, and CH$_3$OH. We find an evolutionary spread between cores residing in the same parent cloud. The two unambiguous outflows are driven by the brightest mm continuum cores, which are IR-dark, molecular line weak, and likely the youngest cores in the region. Furthermore, towards the RMS source AFGL 989-IRS1, the IR-bright and most evolved source in NGC 2264-C, we observe no molecular outflow emission. A molecular line rich ridge feature, with no obvious directly associated continuum source, lies on the edge of a low density cavity and may be formed from a wind driven by AFGL 989-IRS1. In addition, 229GHz class I maser emission is detected towards this feature.
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