arXiv subjects

A. Burkert

Publications and source records attributed to A. Burkert.

At least 37 records · Page 2Linked to original sources

arXiv2021

Stellar feedback in a clumpy galaxy at $z \sim$ 3.4

Giant star-forming regions (clumps) are widespread features of galaxies at $z \approx 1-4$. Theory predicts that they can play a crucial role in galaxy evolution if they survive to stellar feedback for > 50 Myr. Numerical simulations show that clumps' survival depends on the stellar feedback recipes that are adopted. Up to date, observational constraints on both clumps' outflows strength and gas removal timescale are still uncertain. In this context, we study a line-emitting galaxy at redshift $z \simeq 3.4$ lensed by the foreground galaxy cluster Abell 2895. Four compact clumps with sizes $\lesssim$ 280 pc and representative of the low-mass end of clumps' mass distribution (stellar masses $\lesssim 2\times10^8\ {\rm M}_\odot$) dominate the galaxy morphology. The clumps are likely forming stars in a starbursting mode and have a young stellar population ($\sim$ 10 Myr). The properties of the Lyman-$α$ (Ly$α$) emission and nebular far-ultraviolet absorption lines indicate the presence of ejected material with global outflowing velocities of $\sim$ 200-300 km/s. Assuming that the detected outflows are the consequence of star formation feedback, we infer an average mass loading factor ($η$) for the clumps of $\sim$ 1.8 - 2.4 consistent with results obtained from hydro-dynamical simulations of clumpy galaxies that assume relatively strong stellar feedback. Assuming no gas inflows (semi-closed box model), the estimates of $η$ suggest that the timescale over which the outflows expel the molecular gas reservoir ($\simeq 7\times 10^8\ \text{M}_\odot$) of the four detected low-mass clumps is $\lesssim$ 50 Myr.

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arXiv2021

Rotation Curves in z~1-2 Star-Forming Disks: Comparison of Dark Matter Fractions and Disk Properties for Different Fitting Methods

We present a follow-up analysis examining the dynamics and structures of 41 massive, large star-forming galaxies at z~0.67-2.45 using both ionized and molecular gas kinematics. We fit the galaxy dynamics with models consisting of a bulge, a thick, turbulent disk, and a NFW dark matter halo, using code that fully forward models the kinematics, including all observational and instrumental effects. We explore the parameter space using Markov Chain Monte Carlo (MCMC) sampling, including priors based on stellar and gas masses and disk sizes. We fit the full sample using extracted 1D kinematic profiles. For a subset of 14 well-resolved galaxies, we also fit the 2D kinematics. The MCMC approach robustly confirms the results from least-squares fitting presented in Paper I (Genzel et al. 2020): the sample galaxies tend to be baryon-rich on galactic scales (within one effective radius). The 1D and 2D MCMC results are also in good agreement for the subset, demonstrating that much of the galaxy dynamical information is captured along the major axis. The 2D kinematics are more affected by the presence of non-circular motions, which we illustrate by constructing a toy model with constant inflow for one galaxy that exhibits residual signatures consistent with radial motions. This analysis, together with results from Paper I and other studies, strengthens the finding that massive, star-forming galaxies at z~1-2 are baryon-dominated on galactic scales, with lower dark matter fractions towards higher baryonic surface densities. Finally, we present details of the kinematic fitting code used in this analysis.

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arXiv2020

The KMOS$^{\rm 3D}$ Survey: Investigating the Origin of the Elevated Electron Densities in Star-Forming Galaxies at $1\lesssim{z}\lesssim{3}$

We investigate what drives the redshift evolution of the typical electron density ($n_e$) in star-forming galaxies, using a sample of 140 galaxies drawn primarily from KMOS$^{\rm 3D}$ ($0.6\lesssim{z}\lesssim{2.6}$) and 471 galaxies from SAMI ($z<0.113$). We select galaxies that do not show evidence of AGN activity or outflows, to constrain the average conditions within H II regions. Measurements of the [SII]$λ$6716/[SII]$λ$6731 ratio in four redshift bins indicate that the local $n_e$ in the line-emitting material decreases from 187$^{+140}_{-132}$ cm$^{-3}$ at $z\sim$ 2.2 to 32$^{+4}_{-9}$ cm$^{-3}$ at $z\sim$ 0; consistent with previous results. We use the H$α$ luminosity to estimate the root-mean-square (rms) $n_e$ averaged over the volumes of star-forming disks at each redshift. The local and volume-averaged $n_e$ evolve at similar rates, hinting that the volume filling factor of the line-emitting gas may be approximately constant across $0\lesssim{z}\lesssim{2.6}$. The KMOS$^{\rm 3D}$ and SAMI galaxies follow a roughly monotonic trend between $n_e$ and star formation rate, but the KMOS$^{\rm 3D}$ galaxies have systematically higher $n_e$ than the SAMI galaxies at fixed offset from the star-forming main sequence, suggesting a link between the $n_e$ evolution and the evolving main sequence normalization. We quantitatively test potential drivers of the density evolution and find that $n_e$(rms) $\simeq{n_{H_2}}$, suggesting that the elevated $n_e$ in high-$z$ H II regions could plausibly be the direct result of higher densities in the parent molecular clouds. There is also tentative evidence that $n_e$ could be influenced by the balance between stellar feedback, which drives the expansion of H II regions, and the ambient pressure, which resists their expansion.

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arXiv2020

Rotation Curves in z~1-2 Star-Forming Disks: Evidence for Cored Dark Matter Distributions

We report high quality, Halpha or CO rotation curves (RCs) to several Re for 41 large, massive, star-forming disk galaxies (SFGs), across the peak of cosmic galaxy evolution (z~0.67-2.45), taken with the ESO-VLT, the LBT and IRAM-NOEMA. Most RC41 SFGs have reflection symmetric RCs plausibly described by equilibrium dynamics. We fit the major axis position-velocity cuts with beam-convolved, forward modeling with a bulge, a turbulent rotating disk, and a dark matter (DM) halo. We include priors for stellar and molecular gas masses, optical light effective radii and inclinations, and DM masses from abundance matching scaling relations. Two-thirds or more of the z>1.2 SFGs are baryon dominated within a few Re of typically 5.5 kpc, and have DM fractions less than maximal disks ( =0.12). At lower redshift (z<1.2) that fraction is less than one-third. DM fractions correlate inversely with the baryonic angular momentum parameter, baryonic surface density and bulge mass. Inferred low DM fractions cannot apply to the entire disk & halo but more plausibly reflect a flattened, or cored, inner DM density distribution. The typical central 'DM deficit' in these cores relative to NFW distributions is ~30% of the bulge mass. The observations are consistent with rapid radial transport of baryons in the first generation massive gas rich halos forming globally gravitationally unstable disks, and leading to efficient build-up of massive bulges and central black holes. A combination of heating due to dynamical friction and AGN feedback may drive DM out of the initial cusps.

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arXiv2020

The regulation of galaxy growth along the size-mass relation by star-formation, as traced by H$α$ in KMOS$^{3D}$ galaxies at 0.7 < z < 2.7

We present half-light sizes measured from H$α$ emission tracing star-formation in 281 star-forming galaxies from the KMOS3D survey at 0.7 < z < 2.7. Sizes are derived by fitting 2D exponential disk models, with bootstrap errors averaging 20%. H$α$ sizes are a median (mean) of 1.19 (1.26) times larger than those of the stellar continuum, which due to radial dust gradients places an upper limit on the growth in stellar size via star formation, with just 43% intrinsic scatter. At fixed continuum size the H$α$ size shows no residual trend with stellar mass, star formation rate, redshift or morphology. The only significant residual trend is with the excess obscuration of H$α$ by dust, at fixed continuum obscuration. The scatter in continuum size at fixed stellar mass is likely driven by the scatter in halo spin parameters. The stability of the ratio of H$α$ size to continuum size demonstrates a high degree of stability in halo spin and in the transfer of angular momentum to the disk over a wide range of physical conditions and cosmic time. This may require local regulation by feedback processes. The implication of our results, as we demonstrate using a toy model, is that our upper limit on star-formation driven growth is sufficient only to evolve star-forming galaxies approximately along the observed size-mass relation, consistent with the size growth of galaxies at constant cumulative co-moving number density. To explain the observed evolution of the size-mass relation of star-forming disk galaxies other processes, such as the preferential quenching of compact galaxies or galaxy mergers, may be required.

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arXiv2019

A contribution of star-forming clumps and accreting satellites to the mass assembly of z ~ 2 galaxies

We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analyzed spatially-resolved Hubble Space Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z ~ 1 - 3. We created continuum and emission line maps and pinpointed residual "blobs" detected after subtracting the galaxy disk. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes ~ 2 kpc and comparable stellar mass and age as the galaxy disks, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the disks. Furthermore the extended blobs are typically found at larger distances from the galaxy barycenter than the compact ones. Prompted by these observations and by the comparison with simulations, we suggest that compact blobs are in-situ formed clumps, whereas the extended ones are accreting satellites. Clumps and satellites enclose respectively ~ 20% and ~< 80% of the galaxy stellar mass, ~ 30% and ~ 20% of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (Mstar >~ 10^9 Msun) have lifetimes of ~ 650 Myr, and the less massive ones (10^8 < Mstar < 10^9 Msun) of ~ 145 Myr. This supports simulations predicting long-lived clumps (lifetime > 100 Myr). Finally, ~< 30% (13%) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation ~< 10 kpc, and the typical mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1), in agreement with literature results for close pair galaxies.

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arXiv2019

The possible hierarchical scales of observed clumps in high-redshift disc galaxies

Giant clumps on ~kpc scales and with masses of 10^8-10^9 Msol are ubiquitous in observed high-redshift disc galaxies. Recent simulations and observations with high spatial resolution indicate the existence of substructure within these clumps. We perform high-resolution simulations of a massive galaxy to study the substructure formation within the framework of gravitational disc instability. We focus on an isolated and pure gas disk with an isothermal equation of state with T=10^4 K that allows capturing the effects of self-gravity and hydrodynamics robustly. The main mass of the galaxy resides in rotationally supported clumps which grow by merging to a maximum clump mass of 10^8 Msol with diameter ~120 pc for the dense gas. They group to clump clusters (CCs) within relatively short times (<< 50 Myr), which are present over the whole simulation time. We identify several mass and size scales on which the clusters appear as single objects at the corresponding observational resolution between ~10^8 - 10^9 Msol. Most of the clusters emerge as dense groups and for larger beams they are more likely to be open structures represented by a single object. In the high resolution runs higher densities can be reached, and the initial structures can collapse further and fragment to many clumps smaller than the initial Toomre length. In our low resolution runs, the clumps directly form on larger scales 0.3-1 kpc with 10^8-10^9 Msol. Here, the artificial pressure floor which is typically used to prevent spurious fragmentation strongly influences the initial formation of clumps and their properties at very low densities.

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arXiv2019

The KMOS^3D Survey: Demographics and Properties of Galactic Outflows at z = 0.6 - 2.7

We present a census of ionized gas outflows in 599 normal galaxies at redshift 0.6 11.2 galaxies. The incidence, strength, and velocity of AGN-driven winds strongly correlates with stellar mass and central concentration. Their outflowing ionized gas appears denser (n_e~1000 cm^-3), and possibly compressed and shock-excited. These winds have comparable mass loading factors as the SF-driven winds but carry ~10 (~50) times more momentum (energy). The results confirm our previous findings of high duty cycle, energy-driven outflows powered by AGN above the Schechter mass, which may contribute to star formation quenching.

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arXiv2019

PHIBSS2: survey design and z=0.5-0.8 results. Molecular gas reservoirs during the winding-down of star formation

Following the success of the Plateau de Bure high-z Blue Sequence Survey (PHIBSS), we present the PHIBSS2 legacy program, a survey of the molecular gas properties of star-forming galaxies on and around the star formation main sequence (MS) at different redshifts using NOEMA. This survey significantly extends the existing sample of star-forming galaxies with CO molecular gas measurements, probing the peak epoch of star formation (z=1-1.6) as well as its building-up (z=2-3) and winding-down (z=0.5-0.8) phases. The targets are drawn from the GOODS, COSMOS, and AEGIS deep fields and uniformly sample the MS in the stellar mass (M*) - star formation rate (SFR) plane with log(M*/Msun) = 10-11.8. We describe the survey strategy and sample selection before focusing on the results obtained at z=0.5-0.8, where we report 60 CO(2-1) detections out of 61 targets. We determine their molecular gas masses and separately obtain disc sizes and bulge-to-total (B/T) luminosity ratios from HST I-band images. The median molecular gas-to-stellar mass ratio, gas fraction, and depletion time as well as their dependence with M* and offset from the MS follow published scaling relations for a much larger sample of galaxies spanning a wider range of redshifts. The galaxy-averaged Kennicutt-Schmidt (KS) relation between molecular gas and SFR surface densities is strikingly linear, pointing towards similar star formation timescales within galaxies at any given epoch. In terms of morphology, the molecular gas content, the SFR, the disc stellar mass, and the disc molecular gas fraction do not seem to correlate with B/T and the stellar surface density, which suggests an ongoing supply of fresh molecular gas to compensate for the build-up of the bulge. Our measurements do not yield any significant variation of the depletion time with B/T and hence no strong evidence for morphological quenching within the scatter of the MS.

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arXiv2019

Simulating the impact of the Smith Cloud

We investigate the future evolution of the Smith Cloud by performing hydrodynamical simulations of the cloud impact onto the gaseous Milky Way Galactic disk. We assume a local origin for the cloud and thus do not include a dark matter component to stabilize it. Our main focus is the cloud's influence on the local and global star formation rate (SFR) of the Galaxy and whether or not it leads to an observable event in the far future. Our model assumes two extremes for the mass of the Smith Cloud, an upper mass limit of 10$^7$ M$_{\odot}$ and a lower mass limit of 10$^6$ M$_{\odot}$, compared to the observational value of a few 10$^6$ M$_{\odot}$. In addition, we also make the conservative assumption that the entirety of the cloud mass of the extended Smith Cloud is concentrated within the tip of the cloud. We find that the impact of the low-mass cloud produces no noticeable change in neither the global SFR nor the local SFR at the cloud impact site within the galactic disk. For the high-mass cloud we find a short-term (roughly 5 Myr) increase of the global SFR of up to 1 M$_{\odot}$ yr$^{-1}$, which nearly doubles the normal Milky Way SFR. This highly localized starburst should be observable.

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arXiv2018

Detection of a drag force in G2's orbit: Measuring the density of the accretion flow onto Sgr A* at 1000 Schwarzschild radii

The Galactic Center black hole Sgr A* is the archetypical example of an underfed massive black hole. The extremely low accretion rate can be understood in radiatively inefficient accretion flow models. Testing those models has proven to be difficult due to the lack of suitable probes. Radio and submm polarization measurements constrain the flow very close to the event horizon. X-ray observations resolving the Bondi radius yield an estimate roughly four orders of magnitude further out. Here, we present a new, indirect measurement of the accretion flow density at intermediate radii. We use the dynamics of the gas cloud G2 to probe the ambient density. We detect the presence of a drag force slowing down G2 with a statistical significance of approx 9 σ. This probes the accretion flow density at around 1000 Schwarzschild radii and yields a number density of approx. 4 x 10^3 cm^-3. Self-similar accretion models where the density follows a power law radial profile between the inner zone and the Bondi radius have predicted similar values.

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arXiv2018

Simulating the pericentre passage of the Galactic centre star S2

The so-called S2 star reached its closest approach to the massive black hole (BH) at around 1500 $R_\mathrm{s}$ in May 2018. It has been proposed that the interaction of its stellar wind with the high-density accretion flow at this distance from Sgr A* will lead to a detectable, month-long X-ray flare. Our goal is to verify whether or not the S2 star wind can be used as a diagnostic tool to infer the properties of the accretion flow towards Sgr A* at its pericentre (an unprobed distance regime), putting important constraints on BH accretion flow models. We run a series of three-dimensional adaptive mesh refinement simulations with the help of the Ramses code which include the realistic treatment of the interaction of S2's stellar wind with the accretion flow along its orbit and - apart from hydrodynamical and thermodynamical effects - include the tidal interaction with the massive BH. These are post-processed to derive the X-ray emission in the observable 2-10 keV window. No significant excess of X-ray emission from Sgr A* is found for typical accretion flow models. A measurable excess is produced for a significantly increased density of the accretion flow. This can, however, be ruled out for standard power-law accretion flow models as in this case the thermal X-ray emission without the S2 wind interaction would already exceed the observed quiescent luminosity. Only a significant change of the wind parameters (increased mass loss rate and decreased wind velocity) might lead to an (marginally) observable X-ray flaring event. Even the detection of an (month-long) X-ray flare during the pericentre passage of the S2 star would not allow for strict constraints to be put on the accretion flow around Sgr A* due to the degeneracy caused by the dependence on multiple parameters (of the accretion flow model as well as the stellar wind).

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arXiv2018

The Molecular and Ionized Gas Phases of an AGN-driven Outflow in a Typical Massive Galaxy at z=2

Nuclear outflows driven by accreting massive black holes are one of the main feedback mechanisms invoked at high-z to reproduce the distinct separation between star-forming, disk galaxies and quiescent spheroidal systems. Yet, our knowledge of feedback at high-z remains limited by the lack of observations of the multiple gas phases in galaxy outflows. In this work we use new deep, high-spatial resolution ALMA CO(3-2) and archival VLT/SINFONI H$α$ observations to study the molecular and ionized components of the AGN-driven outflow in zC400528 ---a massive, main sequence galaxy at z=2.3 in the process of quenching. We detect a powerful molecular outflow that shows a positive velocity gradient and extends for at least ~10 kpc from the nuclear region, about three times the projected size of the ionized wind. The molecular gas in the outflow does not reach velocities high enough to escape the galaxy and is therefore expected to be reaccreted. Keeping in mind the various assumptions involved in the analysis, we find that the mass and energetics of the outflow are dominated by the molecular phase. The AGN-driven outflow in zC400528 is powerful enough to deplete the molecular gas reservoir on a timescale at least twice shorter than that needed to exhaust it by star formation. This suggests that the nuclear outflow is one of the main quenching engines at work in the observed suppression of the central star-formation activity in zC400528.

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arXiv2018

The extended Planetary Nebula Spectrograph (ePN.S) early-type galaxy survey. The kinematic diversity of stellar halos and the relation between halo transition scale and stellar mass

In the hierarchical two-phase formation scenario, the extended halos of early type galaxies (ETGs) are expected to have different physical properties from those of the galaxies' central regions. This work aims at characterizing the kinematic properties of ETG halos using planetary nebulae (PNe) as tracers, which allow us to overcome the limitations of absorption line spectroscopy of continuum at low surface brightness. We present two-dimensional velocity and velocity dispersion fields for 33 ETGs, including both fast (FRs) and slow rotators (SRs), making this the largest kinematic survey to-date of extragalactic PNe. The velocity fields extend out to a median 5.6 effective radii (Re), with a range [3Re-13Re] for the PN.S ETGs. We complemented the PN kinematics with absorption line data from the literature. We find that ETGs typically show a kinematic transition between inner regions and halo. Estimated transition radii in units of Re anticorrelate with stellar mass. SRs have increased but still modest rotational support at large radii, while most of the FRs show a decrease in rotation, due to the fading of the stellar disk in the outer, more slowly rotating spheroid. 30% of the FRs are dominated by rotation also at large radii. Most ETGs have flat or slightly falling halo velocity dispersion profiles, but 15% of the sample have steeply falling profiles. 40% of the FRs show kinematic twists, misalignments, or rotation along two axes, indicating that they turn from oblate at the center to triaxial in the halo, consistently with the distribution of isophote twists from extended photometry. ETGs have more diverse kinematic properties in their halos than in the central regions. The observed kinematic transition to the halo and its dependence on stellar mass is consistent with LambdaCDM simulations and supports a two-phase formation scenario. [abridged]

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arXiv2018

Compact dusty clouds and efficient H$_2$ formation in diffuse ISM

The formation of compact dusty clouds in diffuse interstellar medium (ISM) has been recently proposed and studied by Tsytovich et al. (2014). In the present paper, an effect of the clouds on the rate of H$\to$H$_2$ transition in the ISM is examined. We discuss the mechanisms leading to the formation of the clouds and the creation of gaseous clumps around them, analyze the main processes determining the efficiency of the recombination of atomic hydrogen on dust grains, and estimate the expected enhancement of the global H$_2$ formation due to the presence of the clouds. In conclusion, we argue that the compact dusty clouds provide optimum conditions for the atomic recombination in diffuse ISM, and point out some astrophysical implications of the resulting H$_2$ formation enhancement.

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arXiv2018

The SINS/zC-SINF survey of z~2 galaxy kinematics: SINFONI adaptive optics-assisted data and kiloparsec-scale emission line properties

We present the "SINS/zC-SINF AO survey" of 35 star-forming galaxies, the largest sample with deep adaptive optics-assisted (AO) near-infrared integral field spectroscopy at z~2. The observations, taken with SINFONI at the Very Large Telescope, resolve the Ha and [NII] line emission and kinematics on scales of ~1.5 kpc. In stellar mass, star formation rate, rest-optical colors and size, the AO sample is representative of its parent seeing-limited sample and probes the massive (M* ~ 2x10^9 - 3x10^11 Msun), actively star-forming (SFR ~ 10-600 Msun/yr) part of the z~2 galaxy population over a wide range in colors ((U-V)_rest ~ 0.15-1.5 mag) and half-light radii (R_e,H ~ 1-8.5 kpc). The sample overlaps largely with the "main sequence" of star-forming galaxies in the same redshift range to a similar K_AB = 23 magnitude limit; it has ~0.3 dex higher median specific SFR, ~0.1 mag bluer median (U-V)_rest color, and ~10% larger median rest-optical size. We describe the observations, data reduction, and extraction of basic flux and kinematic properties. With typically 3-4 times higher resolution and 4-5 times longer integrations (up to 23hr) than the seeing-limited datasets of the same objects, the AO data reveal much more detail in morphology and kinematics. The now complete AO observations confirm the majority of kinematically-classified disks and the typically elevated disk velocity dispersions previously reported based on subsets of the data. We derive typically flat or slightly negative radial [NII]/Ha gradients, with no significant trend with global galaxy properties, kinematic nature, or the presence of an AGN. Azimuthal variations in [NII]/Ha are seen in several sources and are associated with ionized gas outflows, and possible more metal-poor star-forming clumps or small companions. [Abridged]

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arXiv2018

PHIBSS: Unified Scaling Relations of Gas Depletion Time and Molecular Gas Fractions

This paper provides an update of our previous scaling relations (Genzel et al.2015) between galaxy integrated molecular gas masses, stellar masses and star formation rates, in the framework of the star formation main-sequence (MS), with the main goal to test for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and ~1mm dust photometry, in a large sample of 1444 star forming galaxies (SFGs) between z=0 and 4. The sample covers the stellar mass range log(M*/M_solar)=9.0-11.8, and star formation rates relative to that on the MS, delta_MS=SFR/SFR(MS), from 10^{-1.3} to 10^{2.2}. Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t_depl, defined as the ratio of molecular gas mass to star formation rate, scales as (1+z)^{-0.6}x(delta_MS)^{-0.44}, and is only weakly dependent on stellar mass. The ratio of molecular-to-stellar mass mu_gas depends on (1+z)^{2.5}x (delta_MS)^{0.52}x(M*)^{-0.36}, which tracks the evolution of the specific star formation rate. The redshift dependence of mu_gas requires a curvature term, as may the mass-dependences of t_depl and mu_gas. We find no or only weak correlations of t_depl and mu_gas with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high-z.

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arXiv2017

Squeezed between shells? On the origin of the Lupus I molecular cloud. - II. APEX CO and GASS HI observations

[Abridged] The Lupus I cloud is found between the Upper-Scorpius and the Upper-Centaurus-Lupus sub-groups, where the expanding USco HI shell appears to interact with a bubble currently driven by the winds of the remaining B-stars of UCL. We investigate if the Lupus I molecular could have formed in a colliding flow, and how the kinematics of the cloud might have been influenced by the larger scale gas dynamics. We performed APEX 13CO and C18O observations of three parts of Lupus. We compare these results to the atomic hydrogen data from the GASS HI survey and our dust emission results presented in the previous paper. Based on the velocity information, we present a geometric model for the interaction zone between the USco shell and the UCL wind bubble. We present evidence that the molecular gas of Lupus I is tightly linked to the atomic material of the USco shell. The CO emission in Lupus I is found mainly at velocities in the same range as the HI velocities. Thus, the molecular cloud is co-moving with the expanding USco atomic Hi shell. The gas in the cloud shows a complex kinematic structure with several line-of-sight components that overlay each other. The non-thermal velocity dispersion is in the transonic regime in all parts of the cloud and could be injected by external compression. Our observations and the derived geometric model agree with a scenario where Lupus I is located in the interaction zone between the USco shell and the UCL wind bubble. The kinematics observations are consistent with a scenario where the Lupus I cloud formed via shell instabilities. The particular location of Lupus I between USco and UCL suggests that counter-pressure from the UCL wind bubble and pre-existing density enhancements, perhaps left over from the gas stream that formed the stellar subgroups, may have played a role in its formation.

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