Multi-scale observational study of Sagittarius B2

The giant molecular cloud Sagittarius B2 (SgrB2) is the most massive (~ 10^7 Msun) region with ongoing high-mass star formation in the Galaxy. SgrB2 has a higher density (>10^5 cm^{-3}) and dust temperature (~50--70 K) compared to other star forming regions in the Galactic plane. Additionally, SgrB2 is located at a projected distance of only ~100 pc to the Galactic center. These features make SgrB2 an excellent case to study high-mass star formation in an extreme, high-pressure environment. Such an environment resembles nearby starburst galaxies. Understanding the structure of the SgrB2 molecular cloud complex is necessary to comprehend the most massive star forming region in our Galaxy, which at the same time provides an unique opportunity to study in detail the nearest counterpart of the extreme environments that dominate star formation in the Universe. At small scales (0.01--0.1 pc), dense cores appear spread throughout the whole region of SgrB2, embedded within a large scale (~20 pc) envelope with two main sites of high-mass star formation activity at the center of the cloud: SgrB2(M) and SgrB2(N). In order to characterize the properties of SgrB2 from small to large scales, I started an observational project covering spatial scales from 0.004 pc (1000 au) up to 20 pc (the size of the envelope of SgrB2). At small scales, I studied the physical properties of 308 dense cores distributed throughout the entire SgrB2 cloud. I combined mm wavelength data and cm wavelength data to characterize the properties of dense cores and their associated Hii regions. Among the 308 compact dust cores that are identified, 58 are found associated with Hii regions, and 49 are associated with outflows. The cores have a mean mH2 of 150--2500 Msun, by assuming various dust properties and gas temperatures. Most of the 58 Hii regions are ionized by B0 stars. At intermediate scales, I studied the SgrB2(DS) Hii region, which is located in the southern part of the envelope. Using VLA data from 4 to 12 GHz, I derived a spectral index between -1.2 and -0.4, suggesting that SgrB2(DS) is a mixture of thermal and non-thermal emission at radio wavelengths. The thermal free-free emission is likely tracing an Hii region ionized by an O7 star, while the non-thermal emission can be generated by relativistic electrons created through first-order Fermi acceleration. A model of the Sgr B2(DS) region was developed, which reveals that first-order Fermi acceleration can reproduce the observed flux density and spectral index. At the largest scales, I characterized the physical properties of all the Hii regions in the envelope as well as the kinematic structure of the envelope, using newly acquired VLA cm wavelength data and ALMA HC3N line data. The volume filling factor of ionized gas in the envelope of SgrB2 is ~0.03-0.01. The Hii regions in the envelope are more extended than those in SgrB2(M) and SgrB2(N), suggesting that the Hii regions in the envelope may be older than those in the central regions SgrB2(M) and SgrB2(N), and therefore, indicating that high-mass star formation might have started throughout the envelope before than in the central regions. The envelope is also filled with arcs and bubbles, which are traced by HC3N. In summary, this study reveals the properties of SgrB2 from the scale of dense dust cores to the large envelope. The dense cores show various evolutionary stages in terms of high-mass star formation activity. The envelope resembles a ``swiss cheese'' and hosts star forming activities that may have started before those in the central parts of SgrB2. Additionally, for the first time, a model reveals that synchrotron emission from Hii regions can be due to locally produced relativistic electrons accelerated by shocks with moderate velocities

Protostellar cores in Sagittarius B2 N and M

We present 500 AU and 700 AU resolution 1 mm and 3 mm ALMA observations, respectively, of protostellar cores in protoclusters Sagittarius B2 (Sgr B2) North (N) and Main (M), parts of the most actively star-forming cloud in our Galaxy. Previous lower resolution (5000 AU) 3 mm observations of this region detected $\sim$150 sources inferred to be young stellar objects (YSOs) with $M>8\mathrm{\,M}_\odot$. With a tenfold increase in resolution, we detect 371 sources at 3 mm and 218 sources in the smaller field of view at 1 mm. The sources seen at low resolution are observed to fragment into an average of two objects. About a third of the observed sources fragment. Most of the sources we report are marginally resolved and are at least partially optically thick. We determine that the observed sources are most consistent with Stage 0/I YSOs, i.e., rotationally supported disks with an active protostar and an envelope, that are warmer than those observed in the solar neighborhood. We report source-counting-based inferred stellar mass and the star formation rate of the cloud: 2800$\mathrm{\,M}_\odot$, 0.0038$\mathrm{\,M}_\odot$ yr$^{-1}$ for Sgr B2 N and 6900$\mathrm{\,M}_\odot$, 0.0093$\mathrm{\,M}_\odot$ yr$^{-1}$ for Sgr B2 M respectively.Comment: 31 pages, 18 figures. Accepted for publication in ApJ (September 15, 2023

Non-thermal emission from cosmic rays accelerated in H II regions

Context. Radio observations at metre-centimetre wavelengths shed light on the nature of the emission of H II regions. Usually this category of objects is dominated by thermal radiation produced by ionised hydrogen, namely protons and electrons. However, a number of observational studies have revealed the existence of H II regions with a mixture of thermal and non-thermal radiation. The latter represents a clue as to the presence of relativistic electrons. However, neither the interstellar cosmic-ray electron flux nor the flux of secondary electrons, produced by primary cosmic rays through ionisation processes, is high enough to explain the observed flux densities. Aims: We investigate the possibility of accelerating local thermal electrons up to relativistic energies in H II region shocks. Methods: We assumed that relativistic electrons can be accelerated through the first-order Fermi acceleration mechanism and we estimated the emerging electron fluxes, the corresponding flux densities, and the spectral indexes. Results: We find flux densities of the same order of magnitude of those observed. In particular, we applied our model to the "deep south" (DS) region of Sagittarius B2 and we succeeded in reproducing the observed flux densities with an accuracy of less than 20% as well as the spectral indexes. The model also gives constraints on magnetic field strength (0.3-4 mG), density (1-9 × 104 cm-3), and flow velocity in the shock reference frame (33-50 km s-1) expected in DS. Conclusions: We suggest a mechanism able to accelerate thermal electrons inside H II regions through the first-order Fermi acceleration. The existence of a local source of relativistic electrons can explain the origin of both the observed non-thermal emission and the corresponding spectral indexes

Call for papers for IET special issue: Emerging technologies in analogue and RF integrated circuits and systems enabling 5/6G communication

Since its renaissance, the 5G technologies deliver tremendous new and advanced electronic products and tools to the public and industries. It must attribute to the invention, optimization, and designs of varies advanced Analogue and RF integrated circuits and systems, both from academia, industry, and government. 6G follows the footsteps of 5G. Recently, the 5/6G millimetre-wave (mmW) and terahertz (THz) frequency bands are developing rapidly, facing the demand for ultra-high capacity and transmission rate of 5/6G networks in near future. It becomes essential to continuously dig into the Analogue and RF integrated circuits for the dedicated mmW and THz systems

Research on multi-energy cooperative participation of grid frequency inertia response control strategy for energy storage type doubly-fed wind turbine considering wind speed disturbance

With the proposal of carbon peaking and carbon neutralization, the penetration rate of wind power generation continues to increase. This paper focuses on the problem that doubly fed induction wind turbines are vulnerable to input “source” disturbances and have weak frequency modulation ability, which reduces the stability of the power grid. Based on the structural model of energy storage system embedded in doubly fed wind power generation system, it is compared the ability of super capacitor energy storage and releasing rotor kinetic energy to provide inertia response power and energy, and the feasibility of multi-energy coordinated inertia response is analyzed. Based on the inertia time constant of conventional synchronous generator set, the inertia time constant and actual inertia constant of energy storage doubly fed wind power generation system under variable wind speed are defined. An extended state observer is used to estimate the change of captured mechanical power caused by the change of wind speed, and a control strategy for doubly fed induction generator with super capacitor to participate in power grid frequency regulation is designed. Finally, considering the aggregation of wind power and the difference of the state of charge during the operation of distributed energy storage, the 3*3*3 wind farm model is established using Matlab/Simulink simulation software. The feasibility and advantages of the frequency modulation control strategy proposed in this paper are verified by building a power grid frequency modulation simulation involving wind farms and traditional generators

Thermal Properties of the Hot Core Population in Sagittarius B2 Deep South

We report the discovery of 9 new hot molecular cores in the Deep South (DS) region of Sagittarius B2 using Atacama Large Millimeter/submillimeter Array Band 6 observations. We measure the rotational temperature of CH$_3$OH and derive the physical conditions present within these cores and the hot core Sgr B2(S). The cores show heterogeneous temperature structure, with peak temperatures between 252 and 662 K. We find that the cores span a range of masses (203-4842 M$_\odot$) and radii (3587-9436 AU). CH$_3$OH abundances consistently increase with temperature across the sample. Our measurements show the DS hot cores are structurally similar to Galactic Disk hot cores, with radii and temperature gradients that are comparable to sources in the Disk. They also show shallower density gradients than Disk hot cores, which may arise from the Central Molecular Zone's higher density threshold for star formation. The hot cores have properties which are consistent with those of Sgr B2(N), with 3 associated with Class II CH$_3$OH masers and one associated with an UCHII region. Our sample nearly doubles the high-mass star forming gas mass near Sgr B2(S) and suggest the region may be a younger, comparably massive counterpart to Sgr B2(N) and (M). The relationship between peak CH$_3$OH abundance and rotational temperature traced by our sample and a selection of comparable hot cores is qualitatively consistent with predictions from chemical modeling. However, we observe constant peak abundances at higher temperatures ($T \gtrsim 250$ K), which may indicate mechanisms for methanol survival that are not yet accounted for in models.Comment: 39 pages, 24 figures, 4 tables. Accepted for publication in ApJ (December 11, 2023

The physical and chemical structure of Sagittarius B2 -- VI. UCHII regions in Sgr B2

The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. Two ultra-compact HII (UCHII) regions were identified in SgrB2's central hot cores, SgrB2(M) and SgrB2(N). Our aim is to characterize the properties of the HII regions in the entire SgrB2 cloud. Comparing the HII regions and the dust cores, we aim to depict the evolutionary stages of different parts of SgrB2. We use the Very Large Array in its A, CnB, and D configurations, and in the frequency band C (~6 GHz) to observe the whole SgrB2 complex. Using ancillary VLA data at 22.4 GHz and ALMA data at 96 GHz, we calculated the physical parameters of the UCHII regions and their dense gas environment. We identify 54 UCHII regions in the 6 GHz image, 39 of which are also detected at 22.4 GHz. Eight of the 54 UCHII regions are newly discovered. The UCHII regions have radii between $0.006 {\rm pc}$ and $0.04 {\rm pc}$, and have emission measure between $10^{6} {\rm pc\,cm^{-6}}$ and $10^{9} {\rm pc\,cm^{-6}}$. The UCHII regions are ionized by stars of types from B0.5 to O6. We found a typical gas density of $\sim10^6-10^9 {\rm cm^{-3}}$ around the UCHII regions. The pressure of the UCHII regions and the dense gas surrounding them are comparable. The expansion timescale of these UCHII regions is determined to be $\sim10^4-10^5 {\rm yr}$. The percentage of the dust cores that are associated with HII regions are 33%, 73%, 4%, and 1% for SgrB2(N), SgrB2(M), SgrB2(S), and SgrB2(DS), respectively. Two-thirds of the dust cores in SgrB2(DS) are associated with outflows. The electron densities of the UCHII regions we identified are in agreement with that of typical UCHII regions, while the radii are smaller than those of the typical UCHII regions. The dust cores in SgrB2(N) are more evolved than in SgrB2(DS) but younger than in SgrB2(M).Comment: 17 pages, 15 figure, accepted to A&

Gas emissions in Planck cold dust clumps---A Survey of the J=1-0 Transitions of 12^{12}CO, 13^{13}CO, and C18^{18}O

A survey toward 674 Planck cold clumps of the Early Cold Core Catalogue (ECC) in the J=1-0 transitions of $^{12}$CO, $^{13}$CO and C$^{18}$O has been carried out using the PMO 13.7 m telescope. 673 clumps were detected with the $^{12}$CO and $^{13}$CO, and 68% of the samples have C$^{18}$O emission. Additional velocity components were also identified.A close consistency of the three line peak velocities was revealed for the first time. Kinematic distances are given out for all the velocity components and half of the clumps are located within 0.5 and 1.5 kpc. Excitation temperatures range from 4 to 27 K, slightly larger than those of $T_d$. Line width analysis shows that the majority of ECC clumps are low mass clumps. Column densities N$_{H_{2}}$ span from 10$^{20}$ to 4.5$\times10^{22}$ cm$^{-2}$ with an average value of (4.4$\pm$3.6)$\times10^{21}$ cm$^{-2}$. N$_{H_{2}}$ cumulative fraction distribution deviates from the lognormal distribution, which is attributed to optical depth. The average abundance ratio of the $^{13}$CO to C$^{18}$O in these clumps is 7.0$\pm$3.8, higher than the terrestrial value. Dust and gas are well coupled in 95% of the clumps. Blue profile, red profile and line asymmetry in total was found in less than 10% of the clumps, generally indicating star formation is not developed yet. Ten clumps were mapped. Twelve velocity components and 22 cores were obtained. Their morphologies include extended diffuse, dense isolated, cometary and filament, of which the last is the majority. 20 cores are starless.Only 7 cores seem to be in gravitationally bound state. Planck cold clumps are the most quiescent among the samples of weak-red IRAS, infrared dark clouds, UC H{\sc ii} region candidates, EGOs and methanol maser sources, suggesting that Planck cold clumps have expanded the horizon of cold Astronomy.Comment: Accepted to Ap

Dietary organic zinc promotes growth, immune response and antioxidant capacity by modulating zinc signaling in juvenile Pacific white shrimp (Litopenaeus vannamei)

An 8-week feeding trial was conducted to evaluate effects of dietary organic zinc (zinc amino acid chelate) on growth performance, mineral bioaccumulation in whole body, hepatopancreas and carapace, innate immune response and antioxidant capacity of juvenile Pacific white shrimp Litopenaeus vannamei. Five isonitrogenous and isolipidic diets were formulated to contain different zinc levels of 46.4 (basal diet), 65.5, 85.9, 108.4 and 130.6 mg kg−1. Dietary zinc level significantly influenced growth and feed utilization, with the lowest weight gain and highest feed conversion ratio observed in shrimp fed the basal diet. The optimal dietary zinc requirement was estimated to be 104.8 mg kg-1 for juvenile Pacific white shrimp. Shrimp fed the diet containing 130.6 mg kg−1 Zn had the highest zinc concentration in hepatopancreas and carapace, but there were no significant differences in calcium or phosphorus concentration in tissues. Dietary Zn increased the activities of lysozyme, alkaline phosphatase and polyphenol oxidase in hepatopancreas. Shrimp fed the diets supplemented with zinc had significantly higher activity of Cu/Zn SOD and lower content of malondialdehyde in hepatopancreas. The expression levels of toll, imd, lzm, proPO and alp involved in immunity and Cu/Zn sod related to oxidation resistance were up-regulated. Zinc also promoted the expression levels of mt and mtf-1, and up-regulated the expression of SLC39 family genes (zip3, zip9, zip11, zip14) in hepatopancreas. These data provided novel insights in the potential mechanism of organic zinc-induced enhancement of immunity and antioxidant capacity in Pacific white shrimp