اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدGlobal mass segregation in hydrodynamical simulations of star formation
155
0
0.0
(
0
)
تأليف
Th. Maschberger
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Recent analyses of mass segregation diagnostics in star forming regions invite a comparison with the output of hydrodynamic simulations of star formation. In this work we investigate the state of mass segregation of stars (i.e. sink particles in the simulations) in the case of hydrodynamical simulations which omit feedback. We first discuss methods to quantify mass segregation in substructured regions, either based on the minimum spanning tree (Allisons Lambda), or through analysis of correlations between stellar mass and local stellar surface number densities. We find that the presence of even a single outlier (i.e. a massive object far from other stars) can cause the Allison Lambda method to describe the system as inversely mass segregated, even where in reality the most massive sink particles are overwhelmingly in the centres of the subclusters. We demonstrate that a variant of the Lambda method is less susceptible to this tendency but also argue for an alternative representation of the data in the plane of stellar mass versus local surface number density. The hydrodynamical simulations show global mass segregation from very early times which continues throughout the simulation, being only mildly influenced during sub-cluster merging. We find that up to approx. 2-3% of the massive sink particles (m > 2.5 Msun) are in relative isolation because they have formed there, although other sink particles can form later in their vicinity. Ejections of massive sinks from subclusters do not contribute to the number of isolated massive sink particles, as the gravitational softening in the calculation suppresses this process.
قيم البحث
اقرأ أيضاً
We analyse a hydrodynamical simulation of star formation. Sink particles in the simulations which represent stars show episodic growth, which is presumably accretion from a core that can be regularly replenished in response to the fluctuating conditi
ons in the local environment. The accretion rates follow $dot{m} propto m^{2/3}$, as expected from accretion in a gas-dominated potential, but with substantial variations over-laid on this. The growth times follow an exponential distribution which is tapered at long times due to the finite length of the simulation. The initial collapse masses have an approximately lognormal distribution with already an onset of a power-law at large masses. The sink particle mass function can be reproduced with a non-linear stochastic process, with fluctuating accretion rates $propto m^{2/3}$, a distribution of seed masses and a distribution of growth times. All three factors contribute equally to the form of the final sink mass function. We find that the upper power law tail of the IMF is unrelated to Bondi-Hoyle accretion.
The mass segregation of stellar clusters could be primordial rather than dynamical. Despite the abundance of studies of mass segregation for stellar clusters, those for stellar progenitors are still scarce, so the question on the origin and evolution
of mass segregation is still open. Our goal is to characterize the structure of the NGC 2264 molecular cloud and compare the populations of clumps and young stellar objects (YSOs) in this region whose rich YSO population has shown evidence of sequential star formation. We separated the Herschel column density map of NGC 2264 in three subregions and compared their cloud power spectra using a multiscale segmentation technique. We identified in the whole NGC 2264 cloud a population of 256 clumps with typical sizes of ~0.1 pc and masses ranging from 0.08 Msun to 53 Msun. Although clumps have been detected all over the cloud, the central subregion of NGC 2264 concentrates most of the massive, bound clumps. The local surface density and the mass segregation ratio indeed indicate a strong degree of mass segregation for the 15 most massive clumps, with a median $Sigma_6$ three time that of the whole clumps population and $Lambda_{MSR}$ about 8. We showed that this cluster of massive clumps is forming within a high-density cloud ridge, itself formed and probably still fed by the high concentration of gas observed on larger scales in the central subregion. The time sequence obtained from the combined study of the clump and YSO populations in NGC 2264 suggests that the star formation started in the northern subregion, that it is now actively developing at the center and will soon start in the southern subregion. Taken together, the cloud structure and the clump and YSO populations in NGC 2264 argue for a dynamical scenario of star formation.
In the disk-mediated accretion scenario for the formation of the most massive stars, gravitational instabilities in the disk can force it to fragment. We investigate the effects of inclination and spatial resolution on observable kinematics and stabi
lity of disks in high-mass star formation. We study a high-resolution 3D radiation-hydrodynamic simulation that leads to the fragmentation of a massive disk. Using RADMC-3D we produce 1.3 mm continuum and CH3CN line cubes at different inclinations. The model is set to different distances and synthetic observations are created for ALMA at ~80 mas resolution and NOEMA at ~0.3. The synthetic ALMA observations resolve all fragments and their kinematics well. The synthetic NOEMA observations at 800 pc (~300 au resolution) are able to resolve the fragments, while at 2000 pc (~800 au resolution) only a single slightly elongated structure is observed. The position-velocity (PV) plots show the differential rotation of material best in the edge-on views. As the observations become less resolved, the inner high-velocity components of the disk become blended with the envelope and the PV plots resemble rigid-body-like rotation. Protostellar mass estimates from PV plots of poorly resolved observations are therefore overestimated. We fit the emission of CH3CN lines and produce maps of gas temperature with values in the range of 100-300 K. Studying the Toomre stability of the disks in the resolved observations, we find Q values below the critical value for stability against gravitational collapse at the positions of the fragments and the arms connecting the fragments. For the poorly resolved observations we find low Q values in the outskirts of the disk. Therefore we are able to predict that the disk is unstable and fragmenting even in poorly resolved observations. This conclusion is true regardless of knowledge about the inclination of the disk.
State-of-the-art cosmological hydrodynamical simulations of galaxy formation have reached the point at which their outcomes result in galaxies with ever more realism. Still, the employed sub-grid models include several free parameters such as the den
sity threshold, $n$, to localize the star-forming gas. In this work, we investigate the possibilities to utilize the observed clustered nature of star formation (SF) in order to refine SF prescriptions and constrain the density threshold parameter. To this end, we measure the clustering strength, correlation length and power-law index of the two-point correlation function of young ($tau<50$ Myr) stellar particles and compare our results to observations from the HST Legacy Extragalactic UV Survey (LEGUS). Our simulations reveal a clear trend of larger clustering signal and power-law index and lower correlation length as the SF threshold increases with only mild dependence on galaxy properties such as stellar mass or specific star formation rate. In conclusion, we find that the observed clustering of SF is inconsistent with a low threshold for SF ($n<1$ cm$^{-3}$) and strongly favours a high value for the density threshold of SF ($n>10$ cm$^{-3}$), as for example employed in the NIHAO project.
We investigate correlations between different physical properties of star-forming galaxies in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological hydrodynamical simulation suite over the redshift range $0le zle 4.5$. A
principal component analysis reveals that neutral gas fraction ($f_{rm gas, neutral}$), stellar mass ($M_{rm stellar}$) and star formation rate (SFR) account for most of the variance seen in the population, with galaxies tracing a two-dimensional, nearly flat, surface in the three-dimensional space of $f_{rm gas, neutral}-M_{rm stellar}-rm SFR$ with little scatter. The location of this plane varies little with redshift, whereas galaxies themselves move along the plane as their $f_{rm gas, neutral}$ and SFR drop with redshift. The positions of galaxies along the plane are highly correlated with gas metallicity. The metallicity can therefore be robustly predicted from $f_{rm gas, neutral}$, or from the $M_{rm stellar}$ and SFR. We argue that the appearance of this fundamental plane of star formation is a consequence of self-regulation, with the planes curvature set by the dependence of the SFR on gas density and metallicity. We analyse a large compilation of observations spanning the redshift range $0lesssim rm zlesssim 2.5$, and find that such a plane is also present in the data. The properties of the observed fundamental plane of star formation are in good agreement with EAGLEs predictions.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
