Low Critical Density Research Articles

Generation of skyrmions by combining thermal and spin-orbit torque: breaking half skyrmions into skyrmions.

Skyrmions, swirling spin textures with topologically protected stability and low critical driven-current density, can be generated from the stripe domain with current pulses, bringing them closer to practical applications in racetrack memory. However, the mechanism of this topological transition from the stripe domain to the skyrmion remains unclear because the transition process occurs at a nanosecond timescale, giving rise to difficulties in observing this process using imaging tools. In this study, we controlled the domain wall - skyrmion transition by combining Joule heating with spin-orbit torque (SOT) and experimentally observed the details of this process, by which we confirmed the mechanism: the spatial variation of the topological charge density induces half skyrmions branching from the stripe domains, and these half skyrmions overcome the surface tension and break away from the stripe domain, resulting in the generation of skyrmions. The details were observed by employing Joule heating to overcome the pinning effect and manipulating the strength of the SOT to induce the branching and breaking of half skyrmions. These findings offer new insights into skyrmion generation and serve as an important step towards the development of highly efficient devices for processing and computing based on skyrmionics.

Protonated hydrogen cyanide as a tracer of pristine molecular gas

Context. Protonated hydrogen cyanide, HCNH+, plays a fundamental role in astrochemistry because it is an intermediary in gas-phase ion-neutral reactions within cold molecular clouds. However, the impact of the environment on the chemistry of HCNH+ remains poorly understood. Aims. We aim to study HCNH+, HCN, and HNC, as well as two other chemically related ions, HCO+ and N2H+, in different star formation regions in order to investigate how the environment influences the chemistry of HCNH+. Methods. With the IRAM 30 m and APEX 12 m telescopes, we carried out HCNH+, H13CN, HN13C, H13CO+, and N2H+ imaging observations toward two dark clouds, the Serpens filament and Serpens South, both of which harbor sites of star formation that include protostellar objects and regions that are quiescent. Results. We report the first robust distribution of HCNH+ in the Serpens filament and in Serpens South. Our data suggest that HCNH+ is abundant in cold and quiescent regions but is deficient in active star-forming regions. The observed HCNH+ fractional abundances relative to H2 range from 3.1 × 10−11 in protostellar cores to 5.9 × 10−10 in prestellar cores, and the HCNH+ abundance generally decreases with increasing H2 column density, which suggests that HCNH+ coevolves with cloud cores. Our observations and modeling results suggest that the abundance of HCNH+ in cold molecular clouds is strongly dependent on the H2 number density. The decrease in the abundance of HCNH+ is caused by the fact that its main precursors (e.g., HCN and HNC) undergo freeze-out as the number density of H2 increases. However, current chemical models cannot explain other observed trends, such as the fact that the abundance of HCNH+ shows an anticorrelation with that of HCN and HNC but a positive correlation with that of N2H+ in the southern part of Serpens South’s northern clump. This indicates that additional chemical pathways have to be invoked for the formation of HCNH+ via molecules such as N2 in regions in which HCN and HNC freeze out. Conclusions. Both the fact that HCNH+ is most abundant in molecular cores prior to gravitational collapse and the fact that low-J HCNH+ transitions have very low H2 critical densities make this molecular ion an excellent probe of pristine molecular gas.

Atomic Data Assessment with PyNeb: Radiative and Electron Impact Excitation Rates for [Fe ii] and [Fe iii

We use the PyNeb 1.1.16 Python package to evaluate the atomic datasets available for the spectral modeling of [Fe ii] and [Fe iii], which list level energies, A-values, and effective collision strengths. Most datasets are reconstructed from the sources, and new ones are incorporated to be compared with observed and measured benchmarks. For [Fe iii], we arrive at conclusive results that allow us to select the default datasets, while for [Fe ii], the conspicuous temperature dependency on the collisional data becomes a deterrent. This dependency is mainly due to the singularly low critical density of the 3d7a4F9/2 metastable level that strongly depends on both the radiative and collisional data, although the level populating by fluorescence pumping from the stellar continuum cannot be ruled out. A new version of PyNeb (1.1.17) is released containing the evaluated datasets.

Stability Analysis of the New Traffic Flow Lattice Model considering Taillight Effect and Speed Deviation

A new macroscopic traffic flow lattice model is established which considered the taillight effect and velocity deviation. By combining the concept of critical density, the critical condition of taillight triggering is established. The situation of taillight appearing is fully considered, and the influence of taillight effect is analyzed. Through the stability analysis of the model, the stability conditions of the model are obtained. By nonlinear analysis, the mKdV equation is derived which can describe the evolution mechanism of the density wave. From the phase diagram, we can find that the two factors have a positive impact on the stability of traffic flow. Finally, spatiotemporal evolution of the density wave and cross-section view of the density wave are obtained by numerical simulation to verify the theoretical derivation of this paper. The simulation results show that the stability of traffic flow can be improved by considering taillight effect and speed deviation. In addition, by comparing the time-space evolution maps of different parameter values, it can be found that the stability of traffic flow considering the taillight effect and speed deviation is better than that considering one factor alone. However, the stability of traffic flow will be negatively affected by low speed estimate and high critical density.

Loop Quantum Cosmological Model From ADM Hamiltonian

The loop quantum cosmological model from ADM Hamiltonian is studied in this article. We consider the spatially flat homogeneous FRW model. It turns out that the modified Friedmann equation keeps the same form as the APS LQC model. However, the critical matter density for the bounce point is only a quarter of the previous APS model, that is, ρcL=ρc4. This is interesting because the lower critical bounce density means the quantum gravity effects will get involved earlier than the previous LQC model. Besides, the lower critical density also means the detection of quantum gravity effects easier than the previous model.

The cosmic-ray ionisation rate in the pre-stellar core L1544

Context. Cosmic rays (CRs), which are energetic particles mainly composed of protons and electrons, play an important role in the chemistry and dynamics of the interstellar medium. In dense environments, they represent the main ionising agent, hence driving the rich chemistry of molecular ions. Furthermore, they determine the ionisation fraction, which regulates the degree of coupling between the gas and the interstellar magnetic fields, and the heating of the gas. Estimates of the CR ionisation rate of molecular hydrogen (ζ2) span several orders of magnitude, depending on the targeted sources and on the method used. Aims. Recent theoretical models have characterised the CR attenuation with increasing density. We aim to test these models for the attenuation of CRs in the low-mass pre-stellar core L1544. Methods. We used a state-of-the-art gas-grain chemical model, which accepts the CR ionisation rate profile as input, to predict the abundance profiles of four ions: N2H+, N2D+, HC18O+, and DCO+. Non-local thermodynamic equilibrium radiative transfer simulations were run to produce synthetic spectra based on the derived abundances. These were compared with observations obtained with the Institut de Radioastronomie Millimétrique 30 m telescope. Results. Our results indicate that a model with high ζ2 (>10−16 s−1) is excluded by the observations. Also the model with the standard ζ2 = 1.3 × 10−17 s−1 produces a worse agreement with respect to the attenuation model based on Voyager observations, which is characterised by an average ⟨ ζ2 ⟩ = 3 × 10−17 s−1 at the column densities typical of L1544. The single-dish data, however, are not sensitive to the attenuation of the CR profile, which changes only by a factor of two in the range of column densities spanned by the core model (N = 2−50 × 1021 cm−2). Interferometric observations at higher spatial resolution, combined with observations of transitions with lower critical density – hence tracing the low-density envelope – are needed to observe a decrease in the CR ionisation rate with density.

The Structure of Dark Molecular Gas in the Galaxy. II. Physical State of “CO-dark” Gas in the Perseus Arm

We report the results from a new, highly sensitive ($\Delta T_{mb} \sim 3 $mK) survey for thermal OH emission at 1665 and 1667 MHz over a dense, 9 x 9-pixel grid covering a $1\deg$ x $1\deg$ patch of sky in the direction of $l = 105\deg, b = +2.50\deg$ towards the Perseus spiral arm of our Galaxy. We compare our Green Bank Telescope (GBT) 1667 MHz OH results with archival CO J=1-0 observations from the Five College Radio Astronomy Observatory (FCRAO) Outer Galaxy Survey within the velocity range of the Perseus Arm at these galactic coordinates. Out of the 81 statistically-independent pointings in our survey area, 86% show detectable OH emission at 1667 MHz, and 19% of them show detectable CO emission. We explore the possible physical conditions of the observed features using a set of diffuse molecular cloud models. In the context of these models, both OH and CO disappear at current sensitivity limits below an A$_{\rm v}$ of 0.2, but the CO emission does not appear until the volume density exceeds 100-200 cm$^{-3}$. These results demonstrate that a combination of low column density A$_{\rm v}$ and low volume density $n_{H}$ can explain the lack of CO emission along sight lines exhibiting OH emission. The 18-cm OH main lines, with their low critical density of $n^{*}$ $ \sim 1 $ cm$^{-3}$, are collisionally excited over a large fraction of the quiescent galactic environment and, for observations of sufficient sensitivity, provide an optically-thin radio tracer for diffuse H$_2$.

Molecular line emission in NGC 4945, imaged with ALMA

NGC 4945 is one of the nearest (D ≈ 3.8 Mpc; 1″ ≈ 19 pc) starburst galaxies. To investigate the structure, dynamics, and composition of the dense nuclear gas of this galaxy, ALMA band 3 (λ ≈ 3−4 mm) observations were carried out with ≈2″ resolution. Three HCN and two HCO+ isotopologues, CS, C3H2, SiO, HCO, and CH3C2H were measured. Spectral line imaging demonstrates the presence of a rotating nuclear disk of projected size 10″ × 2″ reaching out to a galactocentric radius of r ≈ 100 pc with position angle PA = 45° ± 2°, inclination i = 75° ± 2° and an unresolved bright central core of size ≲2″. The continuum source, representing mostly free-free radiation from star forming regions, is more compact than the nuclear disk by a linear factor of two but shows the same position angle and is centered 0.′′39 ± 0.′′14 northeast of the nuclear accretion disk defined by H2O maser emission. Near the systemic velocity but outside the nuclear disk, both HCN J = 1 → 0 and CS J = 2 → 1 delineate molecular arms of length ≳15″ (≳285 pc) on opposite sides of the dynamical center. These are connected by a (deprojected) ≈ 0.6 kpc sized molecular bridge, likely a dense gaseous bar seen almost ends-on, shifting gas from the front and back side into the nuclear disk. Modeling this nuclear disk located farther inside (r ≲100 pc) with tilted rings provides a good fit by inferring a coplanar outflow reaching a characteristic deprojected velocity of ≈50 km s−1. All our molecular lines, with the notable exception of CH3 C2H, show significant absorption near the systemic velocity (≈571 km s−1), within the range ≈500–660 km s−1. Apparently, only molecular transitions with low critical H2 density (ncrit ≲ 104 cm−3) do not show absorption. The velocity field of the nuclear disk, derived from CH3 C2H, provides evidence for rigid rotation in the inner few arcseconds and a dynamical mass of Mtot = (2.1 ± 0.2) × 108 M⊙ inside a galactocentric radius of 2.′′45 (≈45 pc), with a significantly flattened rotation curve farther out. Velocity integrated line intensity maps with most pronounced absorption show molecular peak positions up to ≈1.′′5 (≈30 pc) southwest of the continuum peak, presumably due to absorption, which appears to be most severe slightly northeast of the nuclear maser disk. A nitrogen isotope ratio of 14N/15N ≈ 200–450 is estimated. This range of values is much higher then previously reported on a tentative basis. Therefore, because 15N is less abundant than expected, the question for strong 15N enrichment by massive star ejecta in starbursts still remains to be settled.

Dynamical Violation of Scale Invariance and the Dilaton in a Cold Fermi Gas.

We use the large-N approximation to find an exotic phase of a cold, two-dimensional, N-component Fermi gas which exhibits dynamically broken approximate scale symmetry. We identify a particular weakly damped collective excitation as the dilaton, the pseudo-Goldstone boson associated with the broken approximate scale symmetry. We argue that the symmetry breaking phase is stable for a range of parameters of the theory and there is a fluctuation induced first order quantum phase transition between the normal and the scale symmetry breaking phases which can be driven by tuning the chemical potential. We find that the compressibility of the gas at its lower critical density is anomalously large, 2N times that of a perfect gas at the same density.

A multiwavelength observation and investigation of six infrared dark clouds

Context. Infrared dark clouds (IRDCs) are ubiquitous in the Milky Way, yet they play a crucial role in breeding newly-formed stars. Aims. With the aim of further understanding the dynamics, chemistry, and evolution of IRDCs, we carried out multi-wavelength observations on a small sample. Methods. We performed new observations with the IRAM 30 m and CSO 10.4 m telescopes, with tracers ${\rm HCO^+}$, HCN, ${\rm N_2H^+}$, ${\rm C^{18}O}$, DCO$^+$, SiO, and DCN toward six IRDCs G031.97+00.07, G033.69-00.01, G034.43+00.24, G035.39-00.33, G038.95-00.47, and G053.11+00.05. Results. We investigated 44 cores including 37 cores reported in previous work and seven newly-identified cores. Toward the dense cores, we detected 6 DCO$^+$, and 5 DCN lines. Using pixel-by-pixel spectral energy distribution (SED) fits of the $\textit{Herschel}$ 70 to 500 $\mu$m, we obtained dust temperature and column density distributions of the IRDCs. We found that ${\rm N_2H^+}$ emission has a strong correlation with the dust temperature and column density distributions, while ${\rm C^{18}O}$ showed the weakest correlation. It is suggested that ${\rm N_2H^+}$ is indeed a good tracer in very dense conditions, but ${\rm C^{18}O}$ is an unreliable one, as it has a relatively low critical density and is vulnerable to freezing-out onto the surface of cold dust grains. The dynamics within IRDCs are active, with infall, outflow, and collapse; the spectra are abundant especially in deuterium species. Conclusions. We observe many blueshifted and redshifted profiles, respectively, with ${\rm HCO^+}$ and ${\rm C^{18}O}$ toward the same core. This case can be well explained by model "envelope expansion with core collapse (EECC)".

Core collapse supernovae in the QCD phase diagram

We compare two classes of hybrid equations of state with a hadron-to-quark matter phase transition in their application to core collapse supernova simulations. The first one uses the quark bag model and describes the transition to three-flavor quark matter at low critical densities. The second one employs a Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model with parameters describing a phase transition to two-flavor quark matter at higher critical densities. These models possess a distinctly different temperature dependence of their transition densities which turns out to be crucial for the possible appearance of quark matter in supernova cores. During the early post bounce accretion phase quark matter is found only if the phase transition takes place at sufficiently low densities as in the study based on the bag model. The increase critical density with increasing temperature, as obtained for our PNJL parametrization, prevents the formation of quark matter. The further evolution of the core collapse supernova as obtained applying the quark bag model leads to a structural reconfiguration of the central proto-neutron star where, in addition to a massive pure quark matter core, a strong hydrodynamic shock wave forms and a second neutrino burst is released during the shock propagation across the neutrinospheres. We discuss the severe constraints in the freedom of choice of quark matter models and their parametrization due to the recently observed 2 solar mass pulsar and their implications for further studies of core collapse supernovae in the QCD phase diagram.

Strange matter in core-collapse supernovae

We discuss the possible impact of strange quark matter on the evolution of core-collapse supernovae with emphasis on low critical densities for the quark-hadron phase transition. For such cases the hot proto-neutron star can collapse to a more compact hybrid star configuration hundreds of milliseconds after core-bounce. The collapse triggers the formation of a second shock wave. The latter leads to a successful supernova explosion and leaves an imprint on the neutrino signal. These dynamical features are discussed with respect to their compatibility with recent neutron star mass measurements which indicate a stiff high density nuclear matter equation of state.

Electronic transport in dopedSrTiO3: Conduction mechanisms and potential applications

Resistivity, Hall effect, and magnetoresistance are reported on a large set of semiconducting ${\text{SrTiO}}_{3\ensuremath{-}\ensuremath{\delta}}$ single crystals doped $n$-type (by reduction or Nb substitution) over a broad range of carrier density (the ${10}^{15}$ to mid ${10}^{20}\text{ }{\text{cm}}^{\ensuremath{-}3}$ range). Temperature-independent carrier densities, strongly temperature-dependent mobilities (up to $22\text{ }000\text{ }{\text{cm}}^{2}\text{ }{\text{V}}^{\ensuremath{-}1}\text{ }{\text{s}}^{\ensuremath{-}1}$ at 4.2 K), and a remarkably low critical carrier density for the metal-insulator transition are observed, and interpreted in terms of the known quantum paraelectricity of the host. We argue that an unusual, high mobility, low density, metallic state is thus established at carrier densities at least as low as $8.5\ifmmode\times\else\texttimes\fi{}{10}^{15}\text{ }{\text{cm}}^{\ensuremath{-}3}$, in contrast to some prior conclusions. At low temperatures, the temperature dependence of the mobility and resistivity exhibit a nonmonotonic carrier density dependence and an abrupt change in character near $2\ifmmode\times\else\texttimes\fi{}{10}^{16}\text{ }{\text{cm}}^{\ensuremath{-}3}$, indicating a distinct crossover in conduction mechanism, perhaps associated with a transition from impurity-band to conduction-band transport. The results provide a simple framework for the understanding of the global transport behavior of doped ${\text{SrTiO}}_{3}$. Finally, it is proposed that the large residual resistivity ratios $(>3000)$, and large, temperature independent, Hall coefficients $(>1700\text{ }{\text{cm}}^{3}\text{ }{\text{C}}^{\ensuremath{-}1})$, demonstrate considerable potential for high-sensitivity resistive thermometry and Hall sensing applications.

Математическая модель сообщества хищник - жертва с нижним порогом численности жертвы

Математическая модель сообщества хищник - жертва с нижним порогом численности жертвы

Is H+3cooling ever important in primordial gas?

Studies of the formation of metal-free Population III stars usually focus primarily on the role played by H2 cooling, on account of its large chemical abundance relative to other possible molecular or ionic coolants. However, while H2 is generally the most important coolant at low gas densities, it is not an effective coolant at high gas densities, owing to the low critical density at which it reaches local thermodynamic equilibrium (LTE) and to the large opacities that develop in its emission lines. It is therefore possible that emission from other chemical species may play an important role in cooling high-density primordial gas. A particularly interesting candidate is the H + molecular ion. This ion has an LTE cooling rate that is roughly a billion times larger than that of H2, and unlike other primordial molecular ions such as H + or HeH + , it is not easily removed from the gas by collisions with H or H2 .I t is already known to be an important coolant in at least one astrophysical context – the upper atmospheres of gas giants – but its role in the cooling of primordial gas has received little previous study. In this paper, we investigate the potential importance of H + cooling in primordial gas using a newly developed H + cooling function and the most detailed model of primordial chemistry published to date. We show that although H + is, in most circumstances, the third most important coolant in dense primordial gas (after H2 and HD), it is nevertheless unimportant, as it contributes no more than a few per cent of the total cooling. We also show that in gas irradiated by a sufficiently strong flux of cosmic rays or X-rays, H + can become the dominant coolant in the gas, although the size of the flux required renders this scenario unlikely to occur.

Mating success and its consequences for population growth in an estuarine copepod

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 377:183-191 (2009) - DOI: https://doi.org/10.3354/meps07819 Mating success and its consequences for population growth in an estuarine copepod Keun-Hyung Choi, Wim Kimmerer* Romberg Tiburon Center for Environmental Studies, San Francisco State University, 3152 Paradise Drive, Tiburon, California 94920, USA *Corresponding author: Email: kimmerer@sfsu.edu ABSTRACT: We conducted experiments on mating success of the estuarine copepod Eurytemora affinis in the San Francisco Estuary, USA. The experimental approach was to isolate virgin pairs (one male and one female) in containers varying in volume from 0.03 to 32 l for 2, 4, or 8 h. Mating was considered successful if viable eggs were produced by individual females subsequently incubated for up to 5 d. The experimental data were analyzed by fitting a 3-parameter model to the data to determine the volume search rate of males. Mating frequencies indicated a volume search rate for E. affinis males of 7.2 ± 4.0 l h–1 (172 ± 96 l d–1, 95% CL), about 20-fold higher than that for Acartia hudsonica previously determined by a similar method. A simple population model showed that the critical population density needed to maintain the E. affinis population can be well below the seasonally low abundance of this copepod in the San Francisco Estuary. The low critical density may allow population persistence in an estuary without the production of resting eggs. KEY WORDS: Copepod mating · Allee effects · Population growth · Volume search rate Full text in pdf format PreviousNextCite this article as: Choi K, Kimmerer W (2009) Mating success and its consequences for population growth in an estuarine copepod. Mar Ecol Prog Ser 377:183-191. https://doi.org/10.3354/meps07819 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 377. Online publication date: February 26, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Exact solutions of systems describing interacting populations with low critical densities

The generalization of the simplest equation method to look for exact solutions of systems of nonlinear differential equations is presented. The exact solutions of NDE systems describing the evolution of two interacting populations in two cases (both populations have the low critical density or low critical density is typical for only one of populations) are obtained.

Is there quark matter in (low-mass) pulsars?

The effect of the QCD phase transition is studied for the mass–radius relation of compact stars and for hot and dense matter at a given proton fraction used as input in core-collapse supernova simulations. The phase transitions to the 2SC and CFL colour superconducting phases lead to stable hybrid star configurations with a pure quark matter core. In supernova explosions quark matter could be easily produced due to β equilibrium, small proton fractions and nonvanishing temperatures. A low critical density for the phase transition to quark matter is compatible with present pulsar mass measurements.

Molecular Star Formation Rate Indicators in Galaxies

We derive a physical model for the observed relations between star formation rate (SFR) and molecular line (CO and HCN) emission in galaxies and show how these observed relations are reflective of the underlying star formation law. We do this by combining 3D non-LTE radiative transfer calculations with hydrodynamic simulations of isolated disk galaxies and galaxy mergers. We demonstrate that the observed SFR-molecular line relations are driven by the relationship between molecular line emission and gas density and anchored by the index of the underlying Schmidt law controlling the SFR in the galaxy. Lines with low critical densities (e.g., CO J = 1–0) are typically thermalized and trace the gas density faithfully. In these cases, the SFR will be related to line luminosity with an index similar to the Schmidt law index. Lines with high critical densities greater than the mean density of most of the emitting clouds in a galaxy (e.g., CO J = 3–2, HCN J = 1–0) will have only a small amount of thermalized gas and consequently a superlinear relationship between molecular line luminosity (Lmol) and mean gas density (). This results in an SFR-line luminosity index less than the Schmidt index for high critical density tracers. One observational consequence of this is a significant redistribution of light from the small pockets of dense, thermalized gas to diffuse gas along the line of sight, and prodigious emission from subthermally excited gas. At the highest star formation rates, the SFR-Lmol slope tends to the Schmidt index, regardless of the molecular transition. The fundamental relation is the Kennicutt-Schmidt law, rather than the relation between SFR and molecular line luminosity. Our model for SFR-molecular line relations quantitatively reproduces the slopes of the observed SFR-CO (J = 1–0), CO (J = 3–2), and HCN (J = 1–0) relations when a Schmidt law with index of ~1.5 describes the SFR. We use these results to make imminently testable predictions for the SFR-molecular line relations of unobserved transitions.

The Relationship between Molecular Gas Tracers and Kennicutt‐Schmidt Laws

We provide a model for how Kennicutt-Schmidt (KS) laws, which describe the correlation between star formation rate and gas surface or volume density, depend on the molecular line chosen to trace the gas. We show that, for lines that can be excited at low temperatures, the KS law depends on how the line critical density compares to the median density in a galaxy's star-forming molecular clouds. High critical density lines trace regions with similar physical properties across galaxy types, and this produces a linear correlation between line luminosity and star formation rate. Low critical density lines probe regions whose properties vary across galaxies, leading to a star formation rate that varies superlinearly with line luminosity. We show that a simple model in which molecular clouds are treated as isothermal and homogenous can quantitatively reproduce the observed correlations between galactic luminosities in far-infrared and in the CO(1→0) and HCN(1→0) lines, and naturally explains why these correlations have different slopes. We predict that IR-line luminosity correlations should change slope for galaxies in which the median density is close to the line critical density. This prediction may be tested by observations of lines such as HCO+(1→0) with intermediate critical densities, or by HCN(1 → 0) observations of intensely star-forming high-redshift galaxies with very high densities. Recent observations by Gao et al. hint at just such a change in slope. We argue that deviations from linearity in the HCN(1→0)-IR correlation at high luminosity are consistent with the assumption of a constant star formation efficiency.