What is the Role of Gravity,Turbulence and Magnetic Fields in High-mass Star Formation Clouds?

To explore the potential role of gravity,turbulence and magnetic fields in high-mass star formation in molecular clouds,this study revisits the velocity dispersion–size(σ–L)and density–size(ρ–L)scalings and the associated turbulent energy spectrum using an extensive data sample.The sample includes various hierarchical density structures in high-mass star formation clouds,across scales of 0.01–100 pc.We observeσ∝L^(0.26)andρ∝L^(-1.54)scalings,converging toward a virial equilibrium state.A nearly flat virial parameter–mass(α_(vir)-M)distribution is seen across all density scales,withα_(vir)values centered around unity,suggesting a global equilibrium maintained by the interplay between gravity and turbulence across multiple scales.Our turbulent energy spectrum(E(k))analysis,based on theσ–L andρ–L scalings,yields a characteristic E(k)∝k^(-1.52).These findings indicate the potential significance of gravity,turbulence,and possibly magnetic fields in regulating dynamics of molecular clouds and high-mass star formation therein.

On the Formation of the Double Neutron Star Binary PSR J1846-0513

The double neutron star PSR J1846-0513 is discovered by the Five-hundred-meter Aperture Spherical radio Telescope(FAST)in Commensal Radio Astronomy FAST Survey.The pulsar is revealed to be harbored in an eccentric orbit with e=0.208 and an orbital period of 0.613 day.The total mass of the system is constrained to b2.6287(35)M_(⊙),with a mass upper limit of 1.3455 M_(⊙)for the pulsar and a mass lower limit of 1.2845 M_(⊙)for th companion star.To reproduce its evolution history,we perform a 1D model for the formation of PSR J1846-0513whose progenitor is assumed to be neutron star—helium(He)star system via MESA code.Since the larg eccentricity is widely believed to originate from an asymmetric supernova explosion,we also investigate th dynamical effects of the supernova explosion.Our simulated results show that the progenitor of PSR J1846-0513could be a binary system consisting of a He star of 3.3-4.0 M_(⊙)and a neutron star in a circular orbit with an initia period of~0.5 day.

Possible Habitats for NH_(3),NH_(2)D,H^(13)CN,HC^(15)N,SO,and C^(18)O in the Initial Conditions of High-mass Star Formation

The initial condition of high-mass star formation is a complex area of study because of the high densities(n_(H_(2))>106cm^(-3))and low temperatures(T_(dust)<18 K)involved.Under such conditions,many molecules become depleted from the gas phase by freezing out onto dust grains.However,the N-bearing and deuterated species could remain gaseous under these extreme conditions,suggesting that they may serve as ideal tracers.In this paper,using the Plateau de Bure Interferometer and Very Large Array observations at 1.3 mm,3.5 mm,and 1.3 cm,we investigate the possible habitats for NH_(3),NH_(2)D,H^(13)CN,HC^(15)N,SO,and C^(18)O in eight massive precluster and protocluster clumps G18.17,G18.21,G23.97N,G23.98,G23.44,G23.97S,G25.38,and G25.71.We found that the NH3cores are in good agreement with the 3.5 mm peak emission,but the NH_(3)is much more extended than the 3.5 mm emission structure.The SO distributions agree well with the 3.5 mm peaks for the evolved star formation stage,but we did not detect any SO emission in the four earliest star formation sources.C^(18)O is a poor tracer in conditions of the cold(■18 K)and dense(■10^(4)cm^(-3))cores,e.g.,the prestellar cores.We also found that the NH_(2)D cores are mainly located in the temperature range of 13.0-20.0 K,and the NH_(2)D lines may be strongly depleted above 20 K.

Does the Redshift Distribution of Swift Long GRBs Trace the Star-Formation Rate?

Gamma-ray bursts (GRBs) are extremely powerful explosions that have been traditionally classified into two categories: long bursts (LGRBs) with an observed duration T90 > 2 s, and short bursts (SGRBs) with an observed duration T90 T90 is the time interval during which 90% of the fluence is detected. LGRBs are believed to emanate from the core-collapse of massive stars, while SGRBs are believed to result from the merging of two compact objects, like two neutron stars. Because LGRBs are produced by the violent death of massive stars, we expect that their redshift distribution should trace the star-formation rate (SFR). The purpose of our study is to investigate the extent to which the redshift distribution of LGRBs follows and reflects the SFR. We use a sample of 370 LGRBs taken from the Swift catalog, and we investigate different models for the LGRB redshift distribution. We also carry out Monte Carlo simulations to check the consistency of our results. Our results indicate that the SFR can describe the LGRB redshift distribution well for high redshift bursts, but it needs an evolution term to fit the distribution well at low redshift.

Early Phases of Star Formation: Testing Chemical Tools

Star-forming processes strongly influence the ISM chemistry.Nowadays,many high-quality databases are available at millimeter wavelengths.Using them,it is possible to carry out studies that review and deepen previous results.If these studies involve large samples of sources,it is preferred to use direct tools to study the molecular gas.With the aim of testing these tools such as the use of the HCN/HNC ratio as a thermometer,and the use of H^(13)CO^(+),HC_(3)N,N_(2)H^(+) and C_(2)H as "chemical clocks," we present a molecular line study toward 55 sources representing massive young stellar objects at different evolutionary stages:infrared dark clouds(IRDCs),highmass protostellar objects(HMPOs),hot molecular cores(HMCs) and ultracompact H II regions.We found that the use of the HCN/HNC ratio as a universal thermometer in the ISM should be taken with care because the HCN optical depth is a big issue that can affect the method.Hence,this tool should be utilized only after a careful analysis of the HCN spectrum,checking that no line,neither the main nor the hyperfine ones,presents absorption features.We point out that the analysis of the emission of H^(13)CO^(+),HC_(3)N,N_(2)H^(+) and C_(2)H could be useful to trace and distinguish regions among IRDCs,HMPOs and HMCs.The molecular line widths of these four species increase from the IRDC to the HMC stage,which can be a consequence of the gas dynamics related to the starforming processes taking place in the molecular clumps.Our results not only contribute with more statistics,acting as a probe of such chemical tools,useful to obtain information in large samples of sources,but also complement previous works through the analysis of other types of sources.

115GHz CO Emission from the IRAS Selected Star-Formation Regions

We report here on our search for CO emission in the direction of 70 IRAS sources with colours of star forming regions. CO emission was detected in 47 sources and 16 are newly detected. Emission line profiles that are non Gaussian (showing e. g. possible self absorption or wings) are identified. Line parameters for detected sources and rms for non detections are presented. The data may serve as a basis for future research.

Probing star formation and feedback using CCOSMA and archival data in the CFG028.68–0.28 quasi-sinusoidal filament

We have performed a multi-wavelength study toward a quasi-sinusoidal filament(CFG028.68–0.28). A new large-scale ^12CO J = 3-2 map was obtained from the China-Cologne Observation for Sub Millimeter Astronomy(CCOSMA) 3m radio telescope. Based on the ATLASGAL catalog, we have identified 27 dust clumps in the filament. Through the relationship between the mass and radius of these clumps, 67% of these clumps are dense and massive enough to potentially form massive stars. The obtained CFE is ~11% in the filament. The filament has a linear mass density of ~305 M⊙pc^-1, which is smaller than its critical mass to length ratio. This suggests that the external pressure from the neighboring H Ⅱ regions may help prevent the filament from dispersing under the effects of turbulence. Comparing the energy injection from outflows and H Ⅱ regions in the filament, the ionization feedback from the H Ⅱ regions can help maintain the observed turbulence.

The HI gas and star formation in star-forming galaxies selected from ALFALFA

This paper presents the results of Hαimaging of 169 galaxies randomly selected from the α.40-SDSS catalog.The sample has excluded all low surface brightness galaxies (LSBGs) whose central surface brightness in B band (μ0(B)) fainter than 22.5 mag arcsec-2.It can be used as the counterparts sample to LSBGs.We observed their Hα and R band images by using the 2.16 m telescope at the Xinglong Observatory of the National Astronomical Observatories,Chinese Academy of Sciences (NAOC).The main goal of this work is to present the properties of those galaxies,together with Hαflux and star formation-,gas-,stellar mass-surface density.In addition,we confirm the correlations among HI content,stellar mass and star formation in ALFALFA galaxies.The HI mass increases with stellar mass,and the slope slows down at the higher stellar mass.The overall trend was that the specific star formation rate (s SFR) decreases with stellar mass,and the sSFR dropped sharply when the stellar mass is close to 1010.3~1010.5M⊙.The weak correlation between SFR/MHIand MHIimplies the HI contribute little to star formation.Our sample,which are mostly star-forming galaxies,follows the revisited Kennicutt-Schmidt law as well as the Kennicutt-Schmidt law.

What is the right way to quench star formation in semi-analytic models of galaxy formation?

Semi-analytic models of galaxy formation are powerful tools to study the evolution of a galaxy population in a cosmological context. However, most models overpredict the number of low- mass galaxies at high redshifts and the colors of model galaxies are not right in the sense that low-mass satellite galaxies are too red and centrals are too blue. The recent version of the L-Galaxies model by Henriques et al. （H15） is a step forward to solve these problems by reproducing the evolution of stellar mass function and the overall fraction of red galaxies. In this paper we compare the two model predictions of L-Galaxies （the other is Guo et al., G13） to SDSS data in detail. We find that in the H15 model the red fraction of central galaxies now agrees with the data due to their implementation of strong AGN feedback, but the stellar mass of centrals in massive halos is now slightly lower than what is indicated by the data. For satellite galaxies, the red fraction of low-mass galaxies （log M./M~ 〈 10） also agrees with the data, but the color of massive satellites （10 〈 logM,/M~ 〈 11） is slightly bluer. The correct color of centrals and the bluer color of massive satellites indicate that quenching in massive satellites is not strong enough. We also find that there are too many red spirals and less bulge-dominated galaxies in both H15 and G13 models. Our results suggest that additional mechanisms, such as more minor mergers or disk instability, are needed to slightly increase the stellar mass of the central galaxy in massive galaxies, mainly in the bulge component, and bulge dominated galaxies will be quenched not only by minor mergers, but also by some other mechanisms.

Multi-wavelength study of triggered star formation around 25 H II regions

We investigate 25 H II regions that show bubble morphology in 13CO（1-0） and infrared data, to search for quantitative evidence of triggered star formation by processes described by the collect and collapse （CC） and radiatively driven implosion （RDI） models. These H II regions display the morphology of a complete or partial bubble at 8 μm, and are all associated with the molecular clouds that surround them. We found that the electron temperature ranges from 5627 K to 6839 K in these H II regions, and the average electron temperature is 6083 K. The age of these H II regions is from 3.0× 10^5 yr to 1.7 × 10^6 yr, and the mean age is 7.7 × 10^5 yr. Based on the mor- phology of the associated molecular clouds, we divide these H II regions into three groups, which may support CC and RDI models. We select 23 young IRAS sources which have an infrared luminosity of 〉 10^3 Lo in 19 H II regions. In addition, we iden- tify some young stellar objects （including Class I sources）, which are only concen- trated in H II regions G29.007＋0.076, G44.339-0.827 and G47.028＋0.232. The poly- cyclic aromatic hydrocarbon emissions of the three H II regions all show a cometary globule. Comparing the age of each H II region with the characteristic timescales for star formation, we suggest that the three H II regions can trigger clustered star forma- tion by an RDI process. In addition, we detect seven molecular outflows in the five H II regions for the first time. These outflow sources may be triggered by the corresponding H II regions.

Star Formation in Self-Gravitating Molecular Cloud: The Critical Mass and the Core Accretion Rate

Understanding how stars form in molecular clouds is one of the ongoing research areas in astrophysics. Star formation is the fundamental process to which our current understanding remains incomplete due to the complexity of the physics that drives their formation within molecular clouds. In this article theoretical modelling of the lowest possible mass of the cloud needed for collapse and the core accretion rate has been presented for the molecular cloud collapsing under its gravity. In many of previous studies the critical mass of star forming cloud under its gravity has been modelled using kinetic energy and gravitational potential energy. However, we test the effect of thermodynamic efficiency factor together with other physical processes in describing the critical mass, and controlling or triggering the rate of mass falling onto the central core. Assuming that, the ratio of radiation luminosity to gravitational energy released per unit time of the collapsing MC is less than unity. Following this conceptual framework we have formulated the critical mass and the core accretion rate of the self-gravitating molecular cloud.

Developing an Advanced Prototype of the Acousto-Optical Radio-Wave Spectrometer for Studying Star Formation in the Milky Way

The designed practically prototype of an advanced acousto-optical radio-wave spectrometer is presented in a view of its application to investigating the Milky Way star formation problems. The potential areas for observations of the cold interstellar medium, wherein such a spectrometer can be exploited successfully at different approximations, are: 1) comparison of the Milky Way case with extragalactic ones at scale of the complete galactic disk;2) global studies of the Galactic spiral arms;and 3) characterization of specific regions like molecular clouds or star clusters. These aspects allow us to suggest that similar instrument will be really useful. The developed prototype of spectrometer is able to realize multi-channel wideband parallel spectrum analysis of very-high-frequency radio-wave signals with an improved resolution power exceeding 103. It includes the 1D-acousto-optic wide-aperture cell as the input device for real-time scale data processing. Here, the current state of developing this acousto-optical spectrometer in frames of the astrophysical instrumentation is briefly discussed, and the data obtained experimentally with a tellurium dioxide crystalline acousto-optical cell are presented. Then, we describe a new technique for more precise spectrum analysis within an algorithm of the collinear wave heterodyning. It implies a two-stage integrated processing, namely, the wave heterodyning of a signal in an acoustically square-law nonlinear medium and then the optical processing in the same solid-state cell. Technical advantage of this approach lies in providing a direct multi-channel parallel processing of ultra-high-frequency radio-wave signals with the resolution power exceeding 104. This algorithm can be realized on a basis of exploiting a large-aperture effective acousto-optical cell, which operates in the Bragg regime and performs the ultra-high-frequency co-directional collinear acoustic wave heterodyning. The general concept and basic conclusions here are confirmed by proof-of-principle experiments with the specially designed cell of a new type based on a lead molybdate crystal.

Information from the Kinematics of F and G Stars in the Solar Neighborhood

We have calculated the orbital parameters for 90 stars in Chen et al. and updated the kinematic data for stars in Edvardsson et al. by using the accurate Hipparcos parallaxes and proper motions, and recalculated the α-element abundances in Edvardsson et al. in a way consistent with Chen et al. The two sets of data are combined in a study of stellar populations and characteristics of F & G stars in the solar neighborhood. We confirm the result of Chen et al. that a distinguishable group of stars may belong to the thick disk rather than the thin disk. The ages for the stars are determined using the theoretical isochrones of VandenBerg et al. The age-metallicity relation is investigated for different subgroups according to distance from the sun and galactic orbital parameters. It is found that a mixing of stars with different orbital parameters significantly affect the age-metallicity relation for the disk. Stars with orbits confined to the solar circle all have metallicities [Fe/H] > -0.3 irrespective of their distances from the sun or from the Galactic plane.

Disks and outflows in the S255IR area of high mass star formation from ALMA observations

We describe the general structure of the well known S255IR high mass star forming region, as revealed by our recent ALMA observations. The data indicate a physical relation exists between the major clumps SMA1 and SMA2. The driving source of the extended high velocity, well collimated bipolar outflow, is not the most pronounced disk-like SMA1 clump harboring a 20M⊙ young star （S255 NIRS3）, as was assumed earlier. Apparently, it is the less evolved SMA2 clump, which drives the outflow and contains a compact rotating structure （probably a disk）. At the same time, the SMA 1 clump drives another outflow, with a larger opening angle. The molecular line data do not show an outflow from the SMA3 clump （NIRS 1）, which was suggested by IR studies of this region.

History of Star Formation and Chemical Enrichment in the Milky Way Disk

Based on a physical treatment of the star formation law similar to that given by Efstathiou, we have improved our two-component chemical evolution model for the Milky Way disk. Two gas infall rates are compared, one exponential, one Gaussian. It is shown that the star formation law adopted in this paper depends more strongly on the gas surface density than that in Chang et al. It has large effects on the history of star formation and gas evolution of the whole disk. In the solar neighborhood, the history of chemical evolution and star formation is not sensitive to whether the infall rate is Gaussian or exponential. For the same infall time scale, both forms predict the same behavior for the current properties of the Galactic disk. The model predictions do depend on whether or not the infall time scale varies with the radius, but current available observations cannot decide which case is the more realistic. Our results also show that it would be inadequate to describe the gradient evolution along the Galactic disk by only one word "flatter" or "steeper", as was suggested by Hou et al. and Chiapinni et al. We point out that both the absolute value and the evolution of the abundance gradient may be different in the inner and outer regions.

Formation of Superthin Galaxies in IllustrisTNG

Superthin galaxies are observed to have stellar disks with extremely small minor-to-major axis ratios.In this work,we investigate the formation of superthin galaxies in the TNG100 simulation.We trace the merger history and investigate the evolution of galaxy properties of a selected sample of superthin galaxies and a control sample of galaxies that share the same joint probability distribution in the stellar-mass and color diagram.Through making comparisons between the two galaxy samples,we find that present-day superthin galaxies had similar morphologies as the control sample counterparts at higher redshifts,but have developed extended flat“superthin”morphologies since z~1.During this latter evolution stage,superthin galaxies undergo an overwhelmingly higher frequency of prograde mergers(with orbit-spin angleθ_(orb)≤40°).Accordingly the spins of their dark matter halos have grown significantly and become noticeably higher than those of their normal disk counterparts.This further results in the buildup of their stellar disks at larger distances much beyond the regimes of normal disk galaxies.We also discuss the formation scenario of those superthin galaxies that live in larger dark matter halos as satellite galaxies therein.

Investigation of star formation toward the Sharpless 155 H II region

We present a comprehensive study of star formation toward the H II re- gion Sharpless 155 （$155）. Star-formation activities therein were investigated based on multi-wavelength data from optical to the far-infrared. The surface density distri- bution of selected 2MASS sources toward S 155 indicates the existence of a compact cluster, which is spatially consistent with the position of the exciting source of the Htt region, HD 217086. A sample of more than 200 sources with excessive emission in the infrared were selected based on their 2MASS color indices. The spatial distri- bution of the sample sources reveals the existence of three young subclusters in this region, among which subcluster A is spatially coincident with the bright rim of the H II region. In addition, photometric data from the WISE survey were used to identify and classify young stellar objects （YSOs）. To further explore the evolutionary stages of the candidate YSOs, we fit the spectral energy distributions of 44 sources, which led to the identification of 14 Class I, 27 Class II and 3 Class Ⅲ YSOs. The spatial distribu- tion of the classified YSOs at different evolutionary stages presents a spatiotemporal gradient, which is consistent with a scenario of sequential star formation. On the other hand, Herschel PACS observations toward the interface between S 155 and the ambi- ent molecular cloud disclose an arc-shaped dust layer, the origin of which could be attributed to the UV dissipation from early type stars, e.g. HD 217061, in S155. Four dusty cores were revealed by the Herschel data, which hints at new generations of star formation.

The ALMA-QUARKS Survey.Ⅱ.The ACA 1.3 mm Continuum Source Catalog and the Assembly of Dense Gas in Massive Star-Forming Clumps

Leveraging the high resolution,sensitivity,and wide frequency coverage of the Atacama Large Millimeter/submillimeter Array(ALMA),the QUARKS survey,standing for“Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures”,is observing 139 massive starforming clumps at ALMA Band 6(λ~1.3 mm).This paper introduces the Atacama Compact Array(ACA)7 m data of the QUARKS survey,describing the ACA observations and data reduction.Combining multiwavelength data,we provide the first edition of QUARKS atlas,offering insights into the multiscale and multiphase interstellar medium in high-mass star formation.The ACA 1.3 mm catalog includes 207 continuum sources that are called ACA sources.Their gas kinetic temperatures are estimated using three formaldehyde transitions with a non-LTE radiation transfer model,and the mass and density are derived from a dust emission model.The ACA sources are massive(16–84 percentile values of 6–160 M_(⊙)),gravity-dominated(M∝R^(1.1))fragments within massive clumps,with supersonic turbulence(M>1)and embedded star-forming protoclusters.We find a linear correlation between the masses of the fragments and the massive clumps,with a ratio of 6%between the two.When considering fragments as representative of dense gas,the ratio indicates a dense gas fraction(DGF)of 6%,although with a wide scatter ranging from 1%to 10%.If we consider the QUARKS massive clumps to be what is observed at various scales,then the size-independent DGF indicates a self-similar fragmentation or collapsing mode in protocluster formation.With the ACA data over four orders of magnitude of luminosity-to-mass ratio(L/M),we find that the DGF increases significantly with L/M,which indicates clump evolutionary stage.We observed a limited fragmentation at the subclump scale,which can be explained by a dynamic global collapse process.

Study of Complex Nitrogen and Oxygen-bearing Molecules toward the High-mass Protostar IRAS 18089–1732

The observation of oxygen(O)-and nitrogen(N)-bearing molecules gives an idea about the complex prebiotic chemistry in the interstellar medium.Recent millimeter and submillimeter wavelength observations have shown the presence of complex O-and N-bearing molecules in the star formation regions.So,the investigation of those molecules is crucial to understanding the chemical complexity in the star-forming regions.In this article,we present the identification of the rotational emission lines of N-bearing molecules ethyl cyanide(C_(2)H_(5)CN)and cyanoacetylene(HC_(3)N),and O-bearing molecule methyl formate(CH_(3)OCHO)toward high-mass protostar IRAS18089–1732 using the Atacama Compact Array.We also detected the emission lines of both the N-and O-bearing molecule formamide(NH_(2)CHO)in the envelope of IRAS 18089–1732.We have detected the v=0 and 1 state rotational emission lines of CH_(3)OCHO.We also detected the two vibrationally excited states of HC_(3)N(v7=1 and v7=2).The estimated fractional abundances of C_(2)H_(5)CN,HC_(3)N(v7=1),HC_(3)N(v7=2),and NH_(2)CHO toward IRAS 18089–1732 are(1.40±0.5)×10^(-10),(7.5±0.7)×10^(-11),(3.1±0.4)×10^(-11),and(6.25±0.82)×10^(-11)respectively.Similarly,the estimated fractional abundances of CH_(3)OCHO(v=0)and CH_(3)OCHO(v=1)are(1.90±0.9)×10^(-9)and(8.90±0.8)×10^(-10),respectively.We also created the integrated emission maps of the detected molecules,and the observed molecules may have originated from the extended envelope of the protostar.We show that C_(2)H_(5)CNand HC_(3)N are most probably formed via the subsequential hydrogenation of the CH_(2)CHCNand the reaction between C_(2)H_(2)and CN on the grain surface of IRAS 18089–1732.We found that NH_(2)CHO is probably produced due to the reaction between NH_(2)and H_(2)CO in the gas phase.Similarly,CH_(3)OCHO is possibly created via the reaction between radical CH_(3)O and radical HCO on the grain surface of IRAS 18089–1732.

Fracture prediction in the tight-oil reservoirs of the Triassic Yanchang Formation in the Ordos Basin,northern China

It is important to predict the fracture distribution in the tight reservoirs of the Ordos Basin because fracturing is very crucial for the reconstruction of the low-permeability reservoirs. Three-dimensional finite element models are used to predict the fracture orientation and distribution of the Triassic Yanchang Formation in the Longdong area, southern Ordos Basin. The numerical modeling is based on the distribution of sand bodies in the Chang 7a and 72 members, and the different forces that have been exerted along each boundary of the basin in the Late Mesozoic and the Cenozoic. The calculated results demonstrate that the fracture orientations in the Late Mesozoic and the Ceno- zoic are NW-EW and NNE-ENE, respectively. In this paper, the two-factor method is applied to analyze the distribution of fracture density. The distribution maps of predicted fracture density in the Chang 71 and 72 members are obtained, indicating that the tectonic movement in the Late Mesozoic has a greater influence on the fracture development than that in the Cenozoic. The average fracture densities in the Chang 71 and 72 members are similar, but there are differences in their distributions. Compared with other geological elements, the lithology and the layer thickness are the primary factors that control the stress distribution in the study area, which further determine the fracture distribution in the stable Ordos Basin. The predicted fracture density and the two-factor method can be utilized to guide future exploration in the tight-sand reservoirs.