arXiv subjects

E. Rosolowsky

Publications and source records attributed to E. Rosolowsky.

At least 37 records · Page 2Linked to original sources

arXiv2021

ALMA-IMF I -- Investigating the origin of stellar masses: Introduction to the Large Program and first results

The ALMA-IMF Large Program imaged a total noncontiguous area of 53pc2, covering 15 extreme, nearby protoclusters of the Milky Way. They were selected to span relevant early protocluster evolutionary stages. Our 1.3mm and 3mm observations provide continuum images that are homogeneously sensitive to point-like cores with masses of 0.2 and 0.6Msun, respectively, with a matched spatial resolution of 2000au. We also detect lines that probe the protocluster structure, kinematics, chemistry, and feedback over scales from clouds to filaments to cores. We classify ALMA-IMF protoclusters as Young, Intermediate, or Evolved based on the amount of dense gas in the cloud that has potentially been impacted by HII regions. The ALMA-IMF catalog contains 700 cores that span a mass range of 0.15-250Msun at a typical size of 2100au. We show that this core sample has no significant distance bias and can be used to build core mass functions at similar physical scales. Significant gas motions, which we highlight here in the G353.41 region, are traced down to core scales and can be used to look for inflowing gas streamers and to quantify the impact of the possible associated core mass growth on the shape of the CMF with time. Our first analysis does not reveal any significant evolution of the matter concentration from clouds to cores or from the youngest to more evolved protoclusters, indicating that cloud dynamical evolution and stellar feedback have for the moment only had a slight effect on the structure of high-density gas in our sample. Furthermore, the first-look analysis of the line richness toward bright cores indicates that the survey encompasses several tens of hot cores, of which we highlight the most massive in the G351.77 cloud. Their homogeneous characterization can be used to constrain the emerging molecular complexity in protostars of high to intermediate masses.

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arXiv2021

Comparing the pre-SNe feedback and environmental pressures for 6000 HII regions across 19 nearby spiral galaxies

The feedback from young stars (i.e. pre-supernova) is thought to play a crucial role in molecular cloud destruction. In this paper, we assess the feedback mechanisms acting within a sample of 5810 HII regions identified from the PHANGS-MUSE survey of 19 nearby ($<$ 20 Mpc) star-forming, main sequence spiral galaxies (log($M_\star$/M$_\odot$)= 9.4 $-$ 11). These optical spectroscopic maps are essential to constrain the physical properties of the HII regions, which we use to investigate their internal pressure terms. We estimate the photoionised gas ($P_\mathrm{therm}$), direct radiation ($P_\mathrm{rad}$), and mechanical wind pressure ($P_\mathrm{wind}$), which we compare to the confining pressure of their host environment ($P_\mathrm{de}$). The HII regions remain unresolved within our ${\sim}50{-}100$ pc resolution observations, so we place upper ($P_\mathrm{max}$) and lower ($P_\mathrm{min}$) limits on each of the pressures by using a minimum (i.e. clumpy structure) and maximum (i.e. smooth structure) size, respectively. We find that the $P_\mathrm{max}$ measurements are broadly similar, and for $P_\mathrm{min}$ the $P_\mathrm{therm}$ is mildly dominant. We find that the majority of HII regions are over-pressured, $P_\mathrm{tot}/P_\mathrm{de} = (P_\mathrm{therm}+P_\mathrm{wind}+P_\mathrm{rad})/P_\mathrm{de} > 1$, and expanding, yet there is a small sample of compact HII regions with $P_\mathrm{tot,max}/P_\mathrm{de} < 1$ ($\sim$1% of the sample). These mostly reside in galaxy centres ($R_\mathrm{gal}<1$kpc), or, specifically, environments of high gas surface density; log($Σ_\mathrm{gas}/\mathrm{M_\odot} \mathrm{pc}^{-2}$)$\sim$2.5 (measured on kpc-scales). Lastly, we compare to a sample of literature measurements for $P_\mathrm{therm}$ and $P_\mathrm{rad}$ to investigate how dominant pressure term transitions over around 5dex in spatial dynamic range and 10 dex in pressure.

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arXiv2021

The EDGE-CALIFA survey: The resolved star formation efficiency and local physical conditions

We measure the star formation rate (SFR) per unit gas mass and the star formation efficiency (SFE$_{\rm gas}$ for total gas, SFE$_{\rm mol}$ for the molecular gas) in 81 nearby galaxies selected from the EDGE-CALIFA survey, using $^{12}$CO(J=1-0) and optical IFU data. For this analysis we stack CO spectra coherently by using the velocities of H$α$ detections to detect fainter CO emission out to galactocentric radii $r_{\rm gal} \sim 1.2 r_{25}$ ($\sim 3 R_{\rm e}$), and include the effects of metallicity and high surface densities in the CO-to-H$_2$ conversion. We determine the scale lengths for the molecular and stellar components, finding a close to 1:1 relation between them. This result indicates that CO emission and star formation activity are closely related. We examine the radial dependence of SFE$_{\rm gas}$ on physical parameters such as galactocentric radius, stellar surface density $Σ_{\star}$, dynamical equilibrium pressure $P_{\rm DE}$, orbital timescale $τ_{\rm orb}$, and the Toomre $Q$ stability parameter (including star and gas $Q_{\rm star+gas}$). We observe a generally smooth, continuous exponential decline in the SFE$_{\rm gas}$ with $r_{\rm gal}$. The SFE$_{\rm gas}$ dependence on most of the physical quantities appears to be well described by a power-law. Our results also show a flattening in the SFE$_{\rm gas}$-$τ_{\rm orb}$ relation at $\log[τ_{\rm orb}]\sim 7.9-8.1$ and a morphological dependence of the SFE$_{\rm gas}$ per orbital time, which may reflect star formation quenching due to the presence of a bulge component. We do not find a clear correlation between SFE$_{\rm gas}$ and $Q_{\rm star+gas}$.

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arXiv2021

Star formation scaling relations at ~100 pc from PHANGS: Impact of completeness and spatial scale

Aims: The complexity of star formation at the physical scale of molecular clouds is not yet fully understood. We investigate the mechanisms regulating the formation of stars in different environments within nearby star-forming galaxies from the PHANGS sample. Methods: Integral field spectroscopic data and radio-interferometric observations of 18 galaxies were combined to explore the existence of the resolved star formation main sequence (rSFMS), resolved Kennicutt-Schmidt relation (rKS), and resolved molecular gas main sequence (rMGMS), and we derived their slope and scatter at spatial resolutions from 100 pc to 1 kpc (under various assumptions). Results: All three relations were recovered at the highest spatial resolution (100 pc). Furthermore, significant variations in these scaling relations were observed across different galactic environments. The exclusion of non-detections has a systematic impact on the inferred slope as a function of the spatial scale. Finally, the scatter of the $Σ_\mathrm{mol. gas + stellar}$ versus $Σ_\mathrm{SFR}$ correlation is smaller than that of the rSFMS, but higher than that found for the rKS. Conclusions: The rMGMS has the tightest relation at a spatial scale of 100 pc (scatter of 0.34 dex), followed by the rKS (0.41 dex) and then the rSFMS (0.51 dex). This is consistent with expectations from the timescales involved in the evolutionary cycle of molecular clouds. Surprisingly, the rKS shows the least variation across galaxies and environments, suggesting a tight link between molecular gas and subsequent star formation. The scatter of the three relations decreases at lower spatial resolutions, with the rKS being the tightest (0.27 dex) at a spatial scale of 1 kpc. Variation in the slope of the rSFMS among galaxies is partially due to different detection fractions of $Σ_\mathrm{SFR}$ with respect to $Σ_\mathrm{stellar}$.

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arXiv2021

Dense molecular gas properties on 100 pc scales across the disc of NGC 3627

It is still poorly constrained how the densest phase of the interstellar medium varies across galactic environment. A large observing time is required to recover significant emission from dense molecular gas at high spatial resolution, and to cover a large dynamic range of extragalactic disc environments. We present new NOrthern Extended Millimeter Array (NOEMA) observations of a range of high critical density molecular tracers (HCN, HNC, HCO+) and CO isotopologues (13CO, C18O) towards the nearby (11.3 Mpc), strongly barred galaxy NGC 3627. These observations represent the current highest angular resolution (1.85"; 100 pc) map of dense gas tracers across a disc of a nearby spiral galaxy, which we use here to assess the properties of the dense molecular gas, and their variation as a function of galactocentric radius, molecular gas, and star formation. We find that the HCN(1-0)/CO(2-1) integrated intensity ratio does not correlate with the amount of recent star formation. Instead, the HCN(1-0)/CO(2-1) ratio depends on the galactic environment, with differences between the galaxy centre, bar, and bar end regions. The dense gas in the central 600 pc appears to produce stars less efficiently despite containing a higher fraction of dense molecular gas than the bar ends where the star formation is enhanced. In assessing the dynamics of the dense gas, we find the HCN(1-0) and HCO+(1-0) emission lines showing multiple components towards regions in the bar ends that correspond to previously identified features in CO emission. These features are co-spatial with peaks of Halpha emission, which highlights that the complex dynamics of this bar end region could be linked to local enhancements in the star formation.

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arXiv2021

New Constraints on the $^{12}$CO(2-1)/(1-0) Line Ratio Across Nearby Disc Galaxies

Both the CO(2-1) and CO(1-0) lines are used to trace the mass of molecular gas in galaxies. Translating the molecular gas mass estimates between studies using different lines requires a good understanding of the behaviour of the CO(2-1)-to-CO(1-0) ratio, $R_{21}$. We compare new, high quality CO(1-0) data from the IRAM 30-m EMPIRE survey to the latest available CO(2-1) maps from HERACLES, PHANGS-ALMA, and a new IRAM 30-m M51 Large Program. This allows us to measure $R_{21}$ across the full star-forming disc of nine nearby, massive, star-forming spiral galaxies at 27" (${\sim} 1{-}2$ kpc) resolution. We find an average $R_{21} = 0.64\pm0.09$ when we take the luminosity-weighted mean of all individual galaxies. This result is consistent with the mean ratio for disc galaxies that we derive from single-pointing measurements in the literature, $R_{\rm 21, lit}~=~0.59^{+0.18}_{-0.09}$. The ratio shows weak radial variations compared to the point-to-point scatter in the data. In six out of nine targets the central enhancement in $R_{21}$ with respect to the galaxy-wide mean is of order $\sim 10{-}20\%$. We estimate an azimuthal scatter of $\sim$20% in $R_{21}$ at fixed galactocentric radius but this measurement is limited by our comparatively coarse resolution of 1.5 kpc. We find mild correlations between $R_{21}$ and CO brightness temperature, IR intensity, 70-to-160$ μ$m ratio, and IR-to-CO ratio. All correlations indicate that $R_{21}$ increases with gas surface density, star formation rate surface density, and the interstellar radiation field.

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arXiv2021

The EDGE-CALIFA survey: The local and global relations between $Σ_\ast$ , $Σ_{SFR}$ and $Σ_{mol}$ that regulate star-formation

We present a new characterization of the relations between star-formation rate, stellar mass and molecular gas mass surface densities at different spatial scales across galaxies (from galaxy wide to kpc-scales). To do so we make use of the largest sample combining spatially-resolved spectroscopic information with CO observations, provided by the EDGE-CALIFA survey, together with new single dish CO observations obtained by APEX. We show that those relations are the same at the different explored scales, sharing the same distributions for the explored data, with similar slope, intercept and scatter (when characterized by a simple power-law). From this analysis, we propose that these relations are the projection of a single relation between the three properties that follows a distribution well described by a line in the three-dimension parameter space. Finally, we show that observed secondary relations between the residuals and the considered parameters are fully explained by the correlation between the uncertainties, and therefore have no physical origin. We discuss these results in the context of the hypothesis of self-regulation of the star-formation process.

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arXiv2021

Star formation quenching stages of active and non-active galaxies

The mechanisms that bring galaxies to strongly reduce their star formation activity (star-formation quenching) is still poorly understood. To better study galaxy evolution, we propose a classification based on the maps of the ionised hydrogen distribution, traced by kpc-resolved, equivalent width of H$α$ maps, and the nuclear activity of the galaxies using information from the BPT diagnostic diagrams. Using these tools, we group a sample of 238 galaxies from the CALIFA survey in six quenching stages (QS): objects dominated by recent star formation; systems that present a quiescent-nuclear-ring structure in their centre; galaxies that are centrally-quiescent; galaxies with no clear pattern in their ionisation gas distribution - mixed; systems that posses only a few star-forming regions - nearly-retired, or galaxies that are completely quiescent - fully-retired. Regarding their nuclear activity, we further divide the galaxies into two groups - active systems that host a weak or strong AGN in their centre, and non-active objects. Galaxies grouped into quenching stage classes occupy specific locations on the star-formation-rate versus stellar mass diagram. The "Blue cloud" is populated by the star-forming and the quiescent-nuclear-ring galaxies, the "Green valley" is populated by centrally-quiescent and mixed systems, "Red sequence" by the nearly- and fully-retired objects. Generally, galaxies that host a weak or strong AGN show properties, comparable to the non-active counterparts at the same quenching stages, except for the AGN-hosting star-forming systems. The degree of the star-formation quenching increases along the present emission-line pattern sequence from star-forming to fully-retired. The proposed emission-line classes reinforce the "inside-out" quenching scenario, which foresees that the suppression of the star-formation begins from the central regions of the galaxies.

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arXiv2021

EDGE-CALIFA survey: Self-regulation of Star formation at kpc scales

We present the relation between the star formation rate surface density, $Σ_{\rm SFR}$, and the hydrostatic mid-plane pressure, P$_{\rm h}$, for 4260 star-forming regions of kpc size located in 96 galaxies included in the EDGE-CALIFA survey covering a wide range of stellar masses and morphologies. We find that these two parameters are tightly correlated, exhibiting smaller scatter and strong correlation in comparison to other star-forming scaling relations. A power-law, with a slightly sub-linear index, is a good representation of this relation. Locally, the residuals of this correlation show a significant anti-correlation with both the stellar age and metallicity whereas the total stellar mass may also play a secondary role in shaping the $Σ_{\rm SFR}$ - P$_{\rm h}$ relation. For our sample of active star-forming regions (i.e., regions with large values of H$α$ equivalent width), we find that the effective feedback momentum per unit stellar mass ($p_\ast/m_\ast$),measured from the P$_{\rm h}$ / $Σ_{\rm SFR}$ ratio increases with P$_{\rm h}$. The median value of this ratio for all the sampled regions is larger than the expected momentum just from supernovae explosions. Morphology of the galaxies, including bars, does not seem to have a significant impact in the $Σ_{\rm SFR}$ - P$_{\rm h}$ relation. Our analysis suggests that self regulation of the $Σ_{\rm SFR}$ at kpc scales comes mainly from momentum injection to the interstellar medium from supernovae explosions. However, other mechanism in disk galaxies may also play a significant role in shaping the $Σ_{\rm SFR}$ at local scales. Our results also suggest that P$_{\rm h}$ can be considered as the main parameter that modulates star formation at kpc scales, rather than individual components of the baryonic mass.

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arXiv2020

The EDGE-CALIFA survey: exploring the role of the molecular gas on the galaxy star formation quenching

Understanding how galaxies cease to form stars represents an outstanding challenge for galaxy evolution theories. This process of "star formation quenching" has been related to various causes, including Active Galactic Nuclei (AGN) activity, the influence of large-scale dynamics, and the environment in which galaxies live. In this paper, we present the first results from a follow-up of CALIFA survey galaxies with observations of molecular gas obtained with the APEX telescope. Together with EDGE survey CARMA observations, we collect $^{12}$CO observations that cover approximately one effective radius in 472 CALIFA galaxies. We observe that the deficit of galaxy star formation with respect to the star formation main sequence (SFMS) increases with the absence of molecular gas and with a reduced efficiency of conversion of molecular gas into stars, in line with results of other integrated studies. However, by dividing the sample into galaxies dominated by star formation and galaxies quenched in their centres (as indicated by the average value of the H$α$ equivalent width), we find that this deficit increases sharply once a certain level of gas consumption is reached, indicating that different mechanisms drive separation from the SFMS in star-forming and quenched galaxies. Our results indicate that differences in the amount of molecular gas at a fixed stellar mass are the primary driver for the dispersion in the SFMS, and the most likely explanation for the start of star-formation quenching. However, once a galaxy is quenched, changes in star formation efficiency drive how much a retired galaxy separates in star formation rate from star-forming ones of similar masses. In other words, once a paucity of molecular gas has significantly reduced star formation, changes in the star formation efficiency are what drives a galaxy deeper into the red cloud, retiring it.

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arXiv2020

CHIMPS2: Survey description and $^{12}$CO emission in the Galactic Centre

The latest generation of Galactic-plane surveys is enhancing our ability to study the effects of galactic environment upon the process of star formation. We present the first data from CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). CHIMPS2 is a survey that will observe the Inner Galaxy, the Central Molecular Zone (CMZ), and a section of the Outer Galaxy in $^{12}$CO, $^{13}$CO, and C$^{18}$O $(J = 3\rightarrow2)$ emission with the Heterodyne Array Receiver Program on the James Clerk Maxwell Telescope (JCMT). The first CHIMPS2 data presented here are a first look towards the CMZ in $^{12}$CO J = 3$\rightarrow$2 and cover $-3^{\circ}\leq\,\ell\,\leq\,5^{\circ}$ and $\mid$b$\mid \leq 0.5^{\circ}$ with angular resolution of 15 arcsec, velocity resolution of 1 km s$^{-1}$, and rms $ΔT_A ^\ast =$ 0.58 K at these resolutions. Such high-resolution observations of the CMZ will be a valuable data set for future studies, whilst complementing the existing Galactic Plane surveys, such as SEDIGISM, the Herschel infrared Galactic Plane Survey, and ATLASGAL. In this paper, we discuss the survey plan, the current observations and data, as well as presenting position-position maps of the region. The position-velocity maps detect foreground spiral arms in both absorption and emission.

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arXiv2020

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

The density structure of the interstellar medium (ISM) determines where stars form and release energy, momentum, and heavy elements, driving galaxy evolution. Density variations are seeded and amplified by gas motion, but the exact nature of this motion is unknown across spatial scale and galactic environment. Although dense star-forming gas likely emerges from a combination of instabilities, convergent flows, and turbulence, establishing the precise origin is challenging because it requires quantifying gas motion over many orders of magnitude in spatial scale. Here we measure the motion of molecular gas in the Milky Way and in nearby galaxy NGC 4321, assembling observations that span an unprecedented spatial dynamic range ($10^{-1}{-}10^3$ pc). We detect ubiquitous velocity fluctuations across all spatial scales and galactic environments. Statistical analysis of these fluctuations indicates how star-forming gas is assembled. We discover oscillatory gas flows with wavelengths ranging from $0.3{-}400$ pc. These flows are coupled to regularly-spaced density enhancements that likely form via gravitational instabilities. We also identify stochastic and scale-free velocity and density fluctuations, consistent with the structure generated in turbulent flows. Our results demonstrate that ISM structure cannot be considered in isolation. Instead, its formation and evolution is controlled by nested, interdependent flows of matter covering many orders of magnitude in spatial scale.

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arXiv2019

The Karl G. Jansky Very Large Array Sky Survey (VLASS). Science case and survey design

The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution ($\approx$2.5"), sensitivity (a 1$σ$ goal of 70 $μ$Jy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in September 2017, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hours of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (Declination $>-40^{\circ}$), a total of 33,885 deg$^2$. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an "on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.

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arXiv2019

Rotation of molecular clouds in M~51

The grand-design spiral galaxy M~51 was observed at 40pc resolution in CO(1--0) by the PAWS project. A large number of molecular clouds were identified and we search for velocity gradients in two high signal-to-noise subsamples, containing 682 and 376 clouds. The velocity gradients are found to be systematically prograde oriented, as was previously found for the rather flocculent spiral M~33. This strongly supports the idea that the velocity gradients reflect cloud rotation, rather than more random dynamical forces, such as turbulence. Not only are the gradients prograde, but their $\frac{\partial v}{\partial x}$ and $\frac{\partial v}{\partial y}$ coefficients follow galactic shear in sign, although with a lower amplitude. No link is found between the orientation of the gradient and the orientation of the cloud. The values of the cloud angular momenta appear to be an extension of the values noted for galactic clouds despite the orders of magnitude difference in cloud mass. Roughly 30\% of the clouds show retrograde velocity gradients. For a strictly rising rotation curve, as in M~51, gravitational contraction would be expected to yield strictly prograde rotators within an axisymmetric potential. In M~51, the fraction of retrograde rotators is found to be higher in the spiral arms than in the disk as a whole. Along the leading edge of the spiral arms, a majority of the clouds are retrograde rotators. While this work should be continued on other nearby galaxies, the M~33 and M~51 studies have shown that clouds rotate and that they rotate mostly prograde, although the amplitudes are not such that rotational energy is a significant support mechanism against gravitation. In this work, we show that retrograde rotation is linked to the presence of a spiral gravitational potential.

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arXiv2019

Mapping metallicity variations across nearby galaxy disks

The distribution of metals within a galaxy traces the baryon cycle and the buildup of galactic disks, but the detailed gas phase metallicity distribution remains poorly sampled. We have determined the gas phase oxygen abundances for 7,138 HII regions across the disks of eight nearby galaxies using VLT/MUSE optical integral field spectroscopy as part of the PHANGS-MUSE survey. After removing the first order radial gradients present in each galaxy, we look at the statistics of the metallicity offset (Delta O/H) and explore azimuthal variations. Across each galaxy, we find low (sigma=0.03-0.05 dex) scatter at any given radius, indicative of efficient mixing. We compare physical parameters for those HII regions that are 1 sigma outliers towards both enhanced and reduced abundances. Regions with enhanced abundances have high ionization parameter, higher Halpha luminosity, lower Halpha velocity dispersion, younger star clusters and associated molecular gas clouds show higher molecular gas densities. This indicates recent star formation has locally enriched the material. Regions with reduced abundances show increased Halpha velocity dispersions, suggestive of mixing introducing more pristine material. We observe subtle azimuthal variations in half of the sample, but can not always cleanly associate this with the spiral pattern. Regions with enhanced and reduced abundances are found distributed throughout the disk, and in half of our galaxies we can identify subsections of spiral arms with clearly associated metallicity gradients. This suggests spiral arms play a role in organizing and mixing the ISM.

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arXiv2019

Dense gas is not enough: environmental variations in the star formation efficiency of dense molecular gas at 100pc scales in M51

It remains unclear what sets the efficiency with which molecular gas transforms into stars. Here we present a new VLA map of the spiral galaxy M51 in 33GHz radio continuum, an extinction-free tracer of star formation, at 3" scales (~100pc). We combined this map with interferometric PdBI/NOEMA observations of CO(1-0) and HCN(1-0) at matched resolution for three regions in M51 (central molecular ring, northern and southern spiral arm segments). While our measurements roughly fall on the well-known correlation between total infrared and HCN luminosity, bridging the gap between Galactic and extragalactic observations, we find systematic offsets from that relation for different dynamical environments probed in M51, e.g. the southern arm segment is more quiescent due to low star formation efficiency (SFE) of the dense gas, despite having a high dense gas fraction. Combining our results with measurements from the literature at 100pc scales, we find that the SFE of the dense gas and the dense gas fraction anti-correlate and correlate, respectively, with the local stellar mass surface density. This is consistent with previous kpc-scale studies. In addition, we find a significant anti-correlation between the SFE and velocity dispersion of the dense gas. Finally, we confirm that a correlation also holds between star formation rate surface density and the dense gas fraction, but it is not stronger than the correlation with dense gas surface density. Our results are hard to reconcile with models relying on a universal gas density threshold for star formation and suggest that turbulence and galactic dynamics play a major role in setting how efficiently dense gas converts into stars.

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arXiv2019

Comparing the Properties of GMCs in M33 from Simulations and Observations

We compare the properties of clouds in simulated M33 galaxies to those observed in the real M33. We apply a friends of friends algorithm and CPROPS to identify clouds, as well as a pixel by pixel analysis. We obtain very good agreement between the number of clouds, and maximum mass of clouds. Both are lower than occurs for a Milky Way-type galaxy and thus are a function of the surface density, size and galactic potential of M33. We reproduce the observed dependence of molecular cloud properties on radius in the simulations, and find this is due to the variation in gas surface density with radius. The cloud spectra also show good agreement between the simulations and observations, but the exact slope and shape of the spectra depends on the algorithm used to find clouds, and the range of cloud masses included when fitting the slope. Properties such as cloud angular momentum, velocity dispersions and virial relation are also in good agreement between the simulations and observations, but do not necessarily distinguish between simulations of M33 and other galaxy simulations. Our results are not strongly dependent on the level of feedback used here (10 and 20%) although they suggest that 15% feedback efficiency may be optimal. Overall our results suggest that the molecular cloud properties are primarily dependent on the gas and mass surface density, and less dependent on the localised physics such as the details of stellar feedback, or the numerical code used.

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arXiv2018

A 50 pc scale view of star formation efficiency across NGC 628

Star formation is a multi-scale process that requires tracing cloud formation and stellar feedback within the local ( 1 Gyr, significantly longer than previously reported for individual star-forming clouds in the Milky Way. Finally, we find no clear trends that relate variations in the depletion time observed on 500 pc scales to physical drivers (metallicity, molecular and stellar mass surface density, molecular gas boundedness) on 50 pc scales.

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