Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMass Assembly of Stellar Systems and Their Evolution with the SMA (MASSES). Multiplicity and the Physical Environment in L1448N
61
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present continuum and molecular line observations at 230 GHz and 345 GHz from the Sub-millimeter Array (SMA) toward three protostars in the Perseus L1448N region. The data are from the large project Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES). Three dust continuum sources, Source B, Source NW, and Source A, are detected at both frequencies. These sources have corresponding emission peaks in C18O (J=2-1), 13CO (J=2-1), and HCO+ (J=4-3), and have offsets with N2D+ (J=3-2) peaks. High angular resolution data from a complimentary continuum survey with the Karl G. Jansky Very Large Array show that Source B is associated with three 8 mm continuum objects, Source NW with two, and Source A remains single. These results suggest that multiplicity in L1448N exists at different spatial scales from a few thousand AU to < 100 AU. Velocity gradients in each source obtained from two-dimensional fits to the SMA C18O emission are found to be perpendicular to within 20 degrees of the outflow directions as revealed by 12CO (J=2-1). We have observed that Sources B and NW with multiplicity have higher densities than Source A without multiplicity. This suggests that thermal Jeans fragmentation can be relevant in the fragmentation process. However, we have not observed a difference in the ratio between rotational and gravitational energy between sources with and without multiplicity. We also have not observed a trend between non-thermal velocity dispersions and the level of fragmentation. Our study has provided the first direct and comprehensive comparison between multiplicity and core properties in low-mass protostars, although based on small number statistics.
rate research
Read More
We present and release the full dataset for the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey. This survey used the Submillimeter Array (SMA) to image the 74 known protostars within the Perseus molecular cloud. The SMA was used in two array configurations to capture outflows for scales $>$30$^{primeprime}$ ($>$9000 au) and to probe scales down to $sim$1$^{primeprime}$ ($sim$300 au). The protostars were observed with the 1.3 mm and 850 $mu$m receivers simultaneously to detect continuum at both wavelengths and molecular line emission from CO(2-1), $^{13}$CO(2-1), C$^{18}$O(2-1), N$_2$D$^+$(3-2), CO(3-2), HCO$^+$(4-3), and H$^{13}$CO$^+$(4-3). Some of the observations also used the SMAs recently upgraded correlator, SWARM, whose broader bandwidth allowed for several more spectral lines to be observed (e.g., SO, H$_2$CO, DCO$^+$, DCN, CS, CN). Of the main continuum and spectral tracers observed, 84% of the images and cubes had emission detected. The median C$^{18}$O(2-1) linewidth is $sim$1.0 km s$^{-1}$, which is slightly higher than those measured with single-dish telescopes at scales of 3000-20000 au. Of the 74 targets, six are suggested to be first hydrostatic core candidates, and we suggest that L1451-mm is the best candidate. We question a previous continuum detection toward L1448 IRS2E. In the SVS13 system, SVS13A certainly appears to be the most evolved source, while SVS13C appears to be hotter and more evolved than SVS13B. The MASSES survey is the largest publicly available interferometric continuum and spectral line protostellar survey to date, and is largely unbiased as it only targets protostars in Perseus. All visibility ($uv$) data and imaged data are publicly available at https://dataverse.harvard.edu/dataverse/full_MASSES/.
We use a large $N$-body simulation to study the relation of the structural properties of dark matter halos to their assembly history and environment. The complexity of individual halo assembly histories can be well described by a small number of principal components (PCs), which, compared to formation times, provide a more complete description of halo assembly histories and have a stronger correlation with halo structural properties. Using decision trees built with the random ensemble method, we find that about $60%$, $10%$, and $20%$ of the variances in halo concentration, axis ratio, and spin, respectively, can be explained by combining four dominating predictors: the first PC of the assembly history, halo mass, and two environment parameters. Halo concentration is dominated by halo assembly. The local environment is found to be important for the axis ratio and spin but is degenerate with halo assembly. The small percentages of the variance in the axis ratio and spin that are explained by known assembly and environmental factors suggest that the variance is produced by many nuanced factors and should be modeled as such. The relations between halo intrinsic properties and environment are weak compared to their variances, with the anisotropy of the local tidal field having the strongest correlation with halo properties. Our method of dimension reduction and regression can help simplify the characterization of the halo population and clarify the degeneracy among halo properties.
We introduce the Virgo Consortiums EAGLE project, a suite of hydrodynamical simulations that follow the formation of galaxies and black holes in representative volumes. We discuss the limitations of such simulations in light of their finite resolution and poorly constrained subgrid physics, and how these affect their predictive power. One major improvement is our treatment of feedback from massive stars and AGN in which thermal energy is injected into the gas without the need to turn off cooling or hydrodynamical forces, allowing winds to develop without predetermined speed or mass loading factors. Because the feedback efficiencies cannot be predicted from first principles, we calibrate them to the z~0 galaxy stellar mass function and the amplitude of the galaxy-central black hole mass relation, also taking galaxy sizes into account. The observed galaxy mass function is reproduced to $lesssim 0.2$ dex over the full mass range, $10^8 < M_*/M_odot lesssim 10^{11}$, a level of agreement close to that attained by semi-analytic models, and unprecedented for hydrodynamical simulations. We compare our results to a representative set of low-redshift observables not considered in the calibration, and find good agreement with the observed galaxy specific star formation rates, passive fractions, Tully-Fisher relation, total stellar luminosities of galaxy clusters, and column density distributions of intergalactic CIV and OVI. While the mass-metallicity relations for gas and stars are consistent with observations for $M_* gtrsim 10^9 M_odot$, they are insufficiently steep at lower masses. The gas fractions and temperatures are too high for clusters of galaxies, but for groups these discrepancies can be resolved by adopting a higher heating temperature in the subgrid prescription for AGN feedback. EAGLE constitutes a valuable new resource for studies of galaxy formation.
In this chapter, we review some historical understanding and recent advances on the Initial Mass Function (IMF) and the Core Mass Function (CMF), both in terms of observations and theories. We focus mostly on star formation in clustered environment since this is suggested by observations to be the dominant mode of star formation. The statistical properties and the fragmentation behaviour of turbulent gas is discussed, and we also discuss the formation of binaries and small multiple systems.
We summarize some of the compelling new scientific opportunities for understanding stars and stellar systems that can be enabled by sub-mas angular resolution, UV/Optical spectral imaging observations, which can reveal the details of the many dynamic processes (e.g., variable magnetic fields, accretion, convection, shocks, pulsations, winds, and jets) that affect their formation, structure, and evolution. These observations can only be provided by long-baseline interferometers or sparse aperture telescopes in space, since the aperture diameters required are in excess of 500 m - a regime in which monolithic or segmented designs are not and will not be feasible - and since they require observations at wavelengths (UV) not accessible from the ground. Two mission concepts which could provide these invaluable observations are NASAs Stellar Imager (SI; http://hires.gsfc.nasa.gov/si/) interferometer and ESAs Luciola sparse aperture hypertelescope, which each could resolve hundreds of stars and stellar systems. These observatories will also open an immense new discovery space for astrophysical research in general and, in particular, for Active Galactic Nuclei (Kraemer et al. Decadal Survey Science Whitepaper). The technology developments needed for these missions are challenging, but eminently feasible (Carpenter et al. Decadal Survey Technology Whitepaper) with a reasonable investment over the next decade to enable flight in the 2025+ timeframe. That investment would enable tremendous gains in our understanding of the individual stars and stellar systems that are the building blocks of our Universe and which serve as the hosts for life throughout the Cosmos.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
