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Register a new userStellar feedback as the origin of an extended molecular outflow in a starburst galaxy
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J. E. Geach
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Recent observations have revealed that starburst galaxies can drive molecular gas outflows through stellar radiation pressure. Molecular gas is the phase of the interstellar medium from which stars form, so these outflows curtail stellar mass growth in galaxies. Previously known outflows, however, involve small fractions of the total molecular gas content and are restricted to sub-kiloparsec scales. It is also apparent that input from active galactic nuclei is in at least some cases dynamically important, so pure stellar feedback has been considered incapable of aggressively terminating star formation on galactic scales. Extraplanar molecular gas has been detected in the archetype starburst galaxy M82, but so far there has been no evidence that starbursts can propel significant quantities of cold molecular gas to the same galactocentric radius (~10 kpc) as the warmer gas traced by metal absorbers. Here we report observations of molecular gas in a compact (effective radius 100 pc) massive starburst galaxy at z=0.7, which is known to drive a fast outflow of ionized gas. We find that 35 per cent of the total molecular gas is spatially extended on a scale of approximately 10 kpc, and one third of this has a velocity of up to 1000 km/s. The kinetic energy associated with this high-velocity component is consistent with the momentum flux available from stellar radiation pressure. This result demonstrates that nuclear bursts of star formation are capable of ejecting large amounts of cold gas from the central regions of galaxies, thereby strongly affecting their evolution.
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Galactic winds are essential to regulation of star formation in galaxies. To study the distribution and dynamics of molecular gas in a wind, we imaged the nearby starburst galaxy NGC 1482 in CO ($J=1rightarrow0$) at a resolution of 1 ($approx100$ pc) using the Atacama Large Millimeter/submillimeter Array. Molecular gas is detected in a nearly edge-on disk with a radius of 3 kpc and a biconical outflow emerging from the central 1 kpc starburst and extending to at least 1.5 kpc perpendicular to the disk. In the outflow, CO gas is distributed approximately as a cylindrically symmetrical envelope surrounding the warm and hot ionized gas traced by H$alpha$ and soft X-rays. The velocity, mass outflow rate, and kinetic energy of the molecular outflow are $v_mathrm{w}sim100~mathrm{km~s^{-1}}$, $dot{M}_mathrm{w}sim7~M_odot~mathrm{yr}^{-1}$, and $E_mathrm{w}sim7times10^{54}~mathrm{erg}$, respectively. $dot{M}_mathrm{w}$ is comparable to the star formation rate ($dot{M}_mathrm{w}/mathrm{SFR}sim2$) and $E_mathrm{w}$ is $sim1%$ of the total energy released by stellar feedback in the past $1times10^7~mathrm{yr}$, which is the dynamical timescale of the outflow. The results indicate that the wind is starburst driven.
Stellar feedback plays a significant role in modulating star formation, redistributing metals, and shaping the baryonic and dark structure of galaxies -- however, the efficiency of its energy deposition to the interstellar medium is challenging to constrain observationally. Here we leverage HST and ALMA imaging of a molecular gas and dust shell ($M_{H2} sim 2times 10^{5} ~{rm M}_{odot}$) in an outflow from the nuclear star forming ring of the galaxy NGC 3351, to serve as a boundary condition for a dynamical and energetic analysis of the outflowing ionised gas seen in our MUSE TIMER survey. We use texttt{STARBURST99} models and prescriptions for feedback from simulations to demonstrate that the observed star formation energetics can reproduce the ionised and molecular gas dynamics -- provided a dominant component of the momentum injection comes from direct photon pressure from young stars, on top of supernovae, photoionisation heating and stellar winds. The mechanical energy budget from these sources is comparable to low luminosity AGN, suggesting that stellar feedback can be a relevant driver of bulk gas motions in galaxy centres - although here $lesssim 10^{-3}$ of the ionized gas mass is escaping the galaxy. We test several scenarios for the survival/formation of the cold gas in the outflow, including in-situ condensation and cooling. Interestingly, the geometry of the molecular gas shell, observed magnetic field strengths and emission line diagnostics are consistent with a scenario where magnetic field lines aided survival of the dusty ISM as it was initially launched (with mass loading factor $lesssim 1$) from the ring by stellar feedback. This systems unique feedback driven morphology can hopefully serve as a useful litmus test for feedback prescriptions in magnetohydrodynamical galaxy simulations.
We present ALMA observations of the CO(2-1) and CO(3-2) molecular gas transitions and associated (sub)-mm continua of the nearby Seyfert 1.5 galaxy NGC3227 with angular resolutions 0.085-0.21 (7-15pc). On large scales the cold molecular gas shows circular motions as well as streaming motions on scales of a few hundred parsecs associated with a large scale bar. We fitted the nuclear ALMA 1.3mm emission with an unresolved component and an extended component. The 850$mu$m emission shows at least two extended components, one along the major axis of the nuclear disk and the other along the axis of the ionization cone. The molecular gas in the central region (1 ~73pc) shows several CO clumps with complex kinematics which appears to be dominated by non-circular motions. While we cannot demonstrate conclusively the presence of a warped nuclear disk, we also detected non-circular motions along the kinematic minor axis. They reach line-of-sight velocities of v-vsys =150-200km/s. Assuming that the radial motions are in the plane of the galaxy, then we interpret them as a nuclear molecular outflow due to molecular gas in the host galaxy being entrained by the AGN wind. We derive molecular outflow rates of $5,M_odot,{rm yr}^{-1}$ and $0.6,M_odot,{rm yr}^{-1}$ at projected distances of up to 30pc to the northeast and southwest of the AGN, respectively. At the AGN location we estimate a mass in molecular gas of $5times 10^{5},M_odot$ and an average column density $N({rm H}_2) = 2-3times 10^{23},{rm cm}^{-2}$ in the inner 15pc. The nuclear molecular gas and sub-mm continuum emission of NGC3227 do not resemble the classical compact torus. Rather, these emissions extend for several tens of parsecs and appear connected with the circumnuclear ring in the host galaxy disk, as found in other local AGN. (Abridged)
We analyze new high spatial resolution (~60 pc) ALMA CO(2-1) observations of the isolated luminous infrared galaxy ESO 320-G030 (d=48 Mpc) in combination with ancillary HST optical and near-IR imaging as well as VLT/SINFONI near-IR integral field spectroscopy. We detect a high-velocity (~450 km/s) spatially resolved (size~2.5 kpc; dynamical time ~3 Myr) massive (~10^7 Msun; mass rate~2-8 Msun/yr) molecular outflow originated in the central ~250 pc. We observe a clumpy structure in the outflowing cold molecular gas with clump sizes between 60 and 150 pc and masses between 10^5.5 and 10^6.4 Msun. The mass of the clumps decreases with increasing distance, while the velocity is approximately constant. Therefore, both the momentum and kinetic energy of the clumps decrease outwards. In the innermost (~100 pc) part of the outflow, we measure a hot-to-cold molecular gas ratio of 7x10^-5, which is similar to that measured in other resolved molecular outflows. We do not find evidence of an ionized phase in this outflow. The nuclear IR and radio properties are compatible with strong and highly obscured star-formation (A_k ~ 4.6 mag; SFR~15 Msun/yr). We do not find any evidence for the presence of an active galactic nucleus. We estimate that supernova explosions in the nuclear starburst ( u(SN) ~ 0.2 yr^-1) can power the observed molecular outflow. The kinetic energy and radial momentum of the cold molecular phase of the outflow correspond to about 2% and 20%, respectively, of the supernovae output. The cold molecular outflow velocity is lower than the escape velocity, so the gas will likely return to the galaxy disk. The mass loading factor is ~0.1-0.5, so the negative feedback due to this star-formation powered molecular outflow is probably limited.
We use high (0.65 x 0.52,(65x52pc)) resolution SubMillimeter Array (SMA) observations to image the CO and 13CO 2-1 line emission of the extreme FIR-excess galaxy NGC 1377. We find bright, complex CO 2-1 line emission in the inner 400 pc of the galaxy. The CO 2-1 line has wings that are tracing a kinematical component which appears perpendicular to that of the line core. Together with an intriguing X-shape of the integrated intensity and dispersion maps, this suggests that the molecular emission of NGC 1377 consists of a disk-outflow system. Lower limits to the molecular mass and outflow rate are M_out(H2)>1e7 Msun and dM/dt>8 Msun/yr. The age of the proposed outflow is estimated to 1.4Myrs, the extent to 200pc and the outflow speed to 140 km/s. The total molecular mass in the SMA map is estimated to M_tot(H2)=1.5e8 Msun (on a scale of 400 pc) while in the inner r=29 pc the molecular mass is M_core(H2)=1.7e7 Msun with a corresponding H2 column density of N(H2)=3.4e23 cm-2 and an average CO 2-1 brightness temperature of 19K. Observing the molecular properties of the FIR-excess galaxy NGC 1377 allows us to probe the early stages of nuclear activity and the onset of feedback in active galaxies. The age of the outflow supports the notion that the current nuclear activity is young - a few Myrs. The outflow may be powered by radiation pressure from a compact, dust enshrouded nucleus, but other driving mechanisms are possible. The buried source may be an AGN or an extremely young (1Myr) compact starburst. Limitations on size and mass lead us to favour the AGN scenario, but further studies are required to settle the issue. In either case, the wind with its implied mass outflow rate will quench the nuclear power source within a very short time of 5-25 Myrs. It is however possible that the gas is unable to escape the galaxy and may eventually fall back onto NGC 1377 again.
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