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1226 ATLASGAL clumps with H iiregions (H ii-clumps) were matched with radio sources in the CORNISH-North/South surveys, and 392 of them have corresponding radio sources. We determined the stellar luminosity L*,T84according to the Lyman continuum flux NLy. When the bolometric luminosity of H ii-clumps is less than log10(Lbol,obs/L⊙) ≈3.7, corresponding to a clump mass log10(Mcl/M⊙) ≈ 2.55, the values of L*,T84derived from NLyoverestimate the actual stellar luminosities, because the accretion onto the protostars contributes significantly to the radio emission. After subtracting the accretion luminosity from L*,T84, we obtained reasonable estimates of the stellar luminosity. Using the 0.5 Myr isochrone, we calculated the stellar masses according to the stellar luminosities, and found that they roughly follow the mmax−Meclrelation of embedded clusters, consistent with the ionizing sources representing the most massive stars in the embedded clusters of H ii-clumps. We also studied the contribution of the possible flaring activity to the observed stellar luminosity and found that they can be neglected. We further studied the change of SFE with the clump mass. According to the derived mass of the most massive star in each HII-clump, using the theoretical mmax−Meclrelation, we calculated the mass of the corresponding embedded cluster and then the SFE of the clump. The SFE decreases with increasing clump mass, with a median value of ≈0.3. We also independently derived the SFE for each H ii-clump based on the model developed in our previous work. The SFEs of H ii-clumps derived from the observation and the model are in good agreement. Concerning the star formation histories of the ATLASGAL clumps, low-mass clumps may reach the peak of star formation earlier than high-mass clumps, consistent with the shorter free-fall time of low-mass clumps.

Using the optimal sampling model, we synthesized the embedded clusters of ATLASGAL clumps with Hiiregions (Hii-clumps). The 0.1 Myr isochrone was used to estimate the bolometric luminosity of each star in an embedded cluster, we also added the accretion luminosity of each star in the embedded cluster. The total bolometric luminosity of synthetic embedded clusters can well fit the observed bolometric luminosity of Hii-clumps. More realistically, we considered the age spread in the young star and protostar populations in embedded clusters of Hii-clumps by modeling both constant and time-varying star formation histories (SFHs). According to the age distribution of the stellar population, we distributed the appropriate isochrones to each star, and sorted out the fraction of stellar objects that are still protostars (Class 0 and Class I phases) to properly add their accretion luminosities. Compared to a constant SFH, burst-like and time-dependent SFHs can better fit the observational data. We found that as long as 20% of the stars within the embedded cluster are still accreting, the contribution of accretion luminosity will be significant to the total bolometric luminosity of low-mass Hii-clumps with mass log10(Mcl/M⊙) < 2.8. Variations in the accretion rate, the SFE and the initial mass function and more physical processes like the external heating from Hiiregions and the flaring from pre-main sequence stars and protostars need to be investigated to further explain the excess luminosity of low-mass Hii-clumps.

We study the instantaneous virial balance of CCs in numerical models of MCs. The models represent a range of magnetic field strengths in MCs from subcritical to nonmagnetic regimes. We identify CCs at different density thresholds and calculate, for each object, the terms that enter the EVT. A CC is gravitationally bound when the gravitational term in the EVT is larger than the amount for the system to be virialized, which is more stringent than the condition that it be large enough to make the total volume energy negative. We also calculate other quantities used to indicate the state of gravitational boundedness: Jeans number Jc, mass-to-magnetic flux ratio mc, and virial parameter avir. Our results suggest the following: (1) CCs are dynamical out-of-equilibrium structures. (2) The surface energies are of the same order as their volume counterparts. (3) CCs are either in the process of being compressed or dispersed by the velocity field. Yet, not all CCs that have a compressive net kinetic energy are gravitationally bound. (4) There is no one-to-one correspondence between the states of gravitational boundedness as described by the virial analysis or by the other indicators. In general, in the virial analysis, only the inner regions of the objects are gravitationally bound, whereas Jc, avir, and mc estimates tend to show that they are more bound at the lowest threshold levels and more magnetically supercritical. (5) We observe, in the nonmagnetic simulation, the existence of a bound core with structural and dynamical properties that resemble those of Barnard 68. This suggests that such cores can form in a larger MC and then be confined by the warm gas of a newly formed, nearby H II region.

We investigate the relationship between the velocity dispersion of the gas and the supernova (SN) rate and feedback efficiency with three-dimensional numerical simulations of SN-driven turbulence in the interstellar medium (ISM). Our simulations aim to explore the constancy of the velocity dispersion profiles in the outer parts of galactic disks at ~6-8 km s-1 and the transition to the starburst regime, i.e., high star formation rates (SFRs) associated with high velocity dispersions. With our fiducial value of the SN feedback efficiency (i.e., [?] = 0.25, corresponding to an injected energy per SN of 0.25 x 1051 ergs), our results show that (1) SN driving leads to constant velocity dispersions of s ~ 6 km s-1 for the total gas and simg1.gif ~ 3 km s-1 for the H I gas, independent of the SN rate, for values of the rate between 0.01 and 0.5 the Galactic value (eG); (2) the position of the transition to the starburst regime (i.e., location of sharp increase in the velocity dispersion) at around SFR/area [?] 5 x 10-3 to 10-2 M yr-1 kpc-2 observed in the simulations is in good agreement with the transition to the starburst regime in the observations (e.g., NGC 628 and NGC 6949); (3) for the high SN rates, no H I gas is present in the simulations box; however, for the total gas velocity dispersion, there is good agreement between the models and the observations; (4) at the intermediate SN rates (e/eG ~ 0.5-1), taking into account the thermal broadening of the H I line helps reach a good agreement in that regime between the models and the observations; and (5) for e/eG < 0.5, s and simg1.gif fall below the observed values by a factor of ~2. However, a set of simulations with different values of [?] indicates that, for larger values of the SN feedback efficiencies, velocity dispersions of the H I gas of the order of 5-6 km s-1 can be obtained, in closer agreement with the observations. The fact that for e/eG < 0.5, the H I gas velocity dispersions are a factor of ~2 smaller than the observed values could result from the fact that we might have underestimated the SN feedback efficiency. On the other hand, it might also be an indication that other physical processes couple to the stellar feedback in order to produce the observed level of turbulence in galactic disks.

We suggest that large H I holes observed in the interstellar medium (ISM) of galaxies such as the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), and Holmberg II (Ho II, DDO 50, UGC 4305) can form as the combined result of turbulence coupled with thermal and gravitational instabilities. We investigate this problem with three-dimensional hydrodynamic simulations, taking into account cooling and heating processes and the action of the self-gravity of the gas. We construct an algorithm for radiative transfer to postprocess the simulated data and build emission maps in the 21 cm neutral hydrogen line. With this approach, we are able to reproduce the structure of the shells and holes as observed in regions of the ISM where no stellar activity is detected. In order to quantify the comparison of our synthetic maps to the observations, we calculate the physical scale-autocorrelation length relation (L-Lcr relation) both on the synthetic H I maps and the H I map of Ho II. The L-Lcr relation shows a linear increase of the autocorrelation length with the physical scale up to the scale of energy injection and flattens for larger scales. The comparison of the L-Lcr relation between the observations and the synthetic maps suggests that turbulence is driven in the ISM of Ho II on large scales (~6 kpc). The slope of the L-Lcr relation in the linear regime in Ho II is better reproduced by models where turbulence is coupled with a low-efficiency cooling of the gas. These results demonstrate the importance of the interplay between turbulence and the thermodynamics of the gas for structure formation in the ISM. Our analysis can be used to determine the scale on which kinetic energy is injected into the ISM of dwarf irregular galaxies and to derive, in a first approximation, the cooling rate of the gas.