Surface Mass Density Research Articles

The contribution ofin situandex situstar formation in early-type galaxies: MaNGA versus IllustrisTNG

ABSTRACTWe compare stellar mass surface density, metallicity, age, and line-of-sight velocity dispersion profiles in massive ($M_*\ge 10^{10.5}\, \mathrm{M_\odot }$) present-day early-type galaxies (ETGs) from the MaNGA survey with simulated galaxies from the TNG100 simulation of the IllustrisTNG suite. We find an excellent agreement between the stellar mass surface density profiles of MaNGA and TNG100 ETGs, both in shape and normalization. Moreover, TNG100 reproduces the shapes of the profiles of stellar metallicity and age, as well as the normalization of velocity dispersion distributions of MaNGA ETGs. We generally also find good agreement when comparing the stellar profiles of central and satellite galaxies between MaNGA and TNG100. An exception is the velocity dispersion profiles of very massive ($M_*\gtrsim 10^{11.5}\, \mathrm{M_\odot }$) central galaxies, which, on average, are significantly higher in TNG100 than in MaNGA ($\approx 50\, \mathrm{km\, s^{-1}}$). We study the radial profiles of in situ and ex situ stars in TNG100 and discuss the extent to which each population contributes to the observed MaNGA profiles. Our analysis lends significant support to the idea that high-mass ($M_*\gtrsim 10^{11}\, \mathrm{M_\odot }$) ETGs in the present-day Universe are the result of a merger-driven evolution marked by major mergers that tend to homogenize the stellar populations of the progenitors in the merger remnant.

Electrical Property of 3D Printed Continuous Fiber Reinforced Thermoplastic Composite Mesh Reflecting Surfaces

Continuous fiber reinforced thermoplastic composites have been widely used in modern aerospace and other high-end manufacturing fields because of their light weight, high strength, fatigue resistance, and corrosion resistance properties. Due to the reinforcement of carbon fiber strands, continuous fiber reinforced thermoplastic composites have good conductivity which makes it a potential material for the preparation of space-borne antennas reflecting surfaces. The reflecting surfaces of common mesh antennas are usually prepared by gold-plated molybdenum wire which is expensive and hard to produce. In this study, the continuous fiber reinforced thermoplastic composites mesh reflecting surfaces are prepared by 3D printing technology. The effect of different mesh shape and mesh size on the electrical properties are investigated systematically. The electrical property of the reflecting surface were tested by waveguide method at the S band with the frequency of 1.9 ~ 2.3GHz. The results show that the reflection loss of the 3D printed continuous fiber reinforced thermoplastic composite mesh reflecting surfaces are lower than 0.25 dB, which can well meet the requirement of space-borne antennas in the S waveband. The reflection loss of the 3D printed continuous fiber reinforced thermoplastic composite mesh reflecting surfaces increases with the increase of mesh size accordingly for both the quadrangular and the triangular mesh reflecting surface. The reflecting property of the mesh reflecting surface tends to be better with a higher surface mass density. The results foresee that the continuous fiber reinforced thermoplastic composites can be used to develop the reflector of large mesh antenna in the future work.

The Effect of a Spiral Density Wave on the Galaxy’s Rotation Curve, as Applied to the Andromeda Galaxy (M31)

The rotational velocity curve, which is the circular velocity profile of the stars and gas in a spiral galaxy as a function of their distance from the galactic center, plays an important role in the kinematic and dynamic investigation of spiral galaxies. There are observations of approximately flat rotation curves (RC) at large distances that have introduced mass discrepancy between the theoretically derived RC and the observed one. In this paper, we derive a rotational velocity expression using a nonlinear spiral density wave solution for the surface mass density (SMD) within the disk. We show that the proposed nonlinear spiral solution is able to support the observed flat rotational velocity curve for large distances with no mass deficiency. The aim of the paper is to confirm the crucial importance of the mass distribution on the rotation curve profile. Although the model is limited by the fluid description of the galactic disk, it provides an improved rotational velocity expression and a rotation curve with no mass discrepancy in the outer part of the disk due to the inclusion of the spiral mass distribution. The disk mass has not been averaged within the exponential disk approximation, but it rather follows the observed spiral pattern given by the analytical solution of the nonlinear equation. The M31 galaxy has been chosen as the closest and well mapped spiral galaxy, similar in many aspects to our host galaxy, in order to apply a rotational velocity expression that accounts for nonlinear effects and derive RC. The obtained result can have a strong influence on large-scale gravity dynamics, as well.

The seven-lobed shape of the outer edge of Saturn’s A ring

Using the complete set of stellar and radio occultation data from the Cassini mission, we fit a multimode model to the outer edge of Saturn’s A ring, similar to that previously applied to the B ring edge by Spitale and Porco (2010) and Nicholson et al. (2014a). Our model takes into account the coorbital libration of the satellite Janus, whose 7:6 Lindblad resonance is believed to be responsible for maintaining the edge at its observed location. Consistent with previous analyses (Spitale and Porco, 2009; El Moutamid et al., 2016), we find that the shape of the ring’s edge is dominated by a 7-lobed radial distortion that rotates with the same angular velocity as Janus during the periods when the satellite is on the inner leg of its 8-yr libration. The amplitude of this distortion is ∼12 km, and one of the seven minima is aligned within a few degrees of the satellite’s mean longitude. At times when Janus is on the outer leg of its libration, however, the 7-lobed pattern disappears completely. In addition to this resonantly-forced distortion, our data reveal the presence of a rich spectrum of normal modes sculpting the ring edge. When the 7-lobed pattern is present, the principal secondary mode has m=5, while when the 7-lobed pattern is absent, the shape of the edge is dominated by modes with m=9 and m=12, all with radial amplitudes of 4–6 km. The data strongly suggest that the m=5 mode actually persists, but at an undetectable level, throughout the latter period. Lower-amplitude modes are also seen with m=3, 4, 6, 8, 10 and 18, though not at all times. The normal mode frequencies are consistent with a simple analytic model whereby each mode exists within a resonant cavity near the edge of the ring (Borderies et al., 1985; Longaretti, 2018), from which we estimate an average surface mass density in this region of ∼20g cm−2, consistent with that derived from weak density waves (Tiscareno and Harris, 2018). Despite the relative complexity of the best-fitting model, the RMS deviations between it and the observed edge radii range from 1.7 to 5.5 km, substantially exceeding the measurement errors of ∼0.3 km and strongly suggesting the existence of additional, as-yet-uncharacterized perturbations. Contrary to previous analyses, we find no evidence for beating between the strong m=7 signature due to Janus and a weaker signature due to its coorbital companion Epimetheus (Spitale and Porco, 2009) and only weak evidence for an m=−3 mode driven by a gravity anomaly within Saturn (El Moutamid et al., 2016).

General-relativistic thin-shell Dyson megaspheres

Loosely inspired by the somewhat fanciful notion of detecting an arbitrarily advanced alien civilization, we consider a general-relativistic thin-shell Dyson mega-sphere completely enclosing a central star-like object, and perform a full general-relativistic analysis using the Israel--Lanczos--Sen junction conditions. We focus attention on the surface mass density, the surface stress, the classical energy conditions, and the forces between hemispheres. We find that in the physically acceptable region the NEC, WEC, and SEC are always satisfied, while the DEC can be violated if the Dyson mega-sphere is sufficiently close to forming a black hole. We also demonstrate that the original quasi-local version of the maximum force conjecture, F <= {1/4} F_{Stoney} = {1/4} F_{Planck}, can easily be violated if the Dyson mega-sphere is sufficiently compact, that is, sufficiently close to forming a black hole. Interestingly there is a finite region of parameter space where one can violate the original quasi-local version of the maximum force conjecture without violating the DEC. Finally, we very briefly discuss the possibility of nested thin-shell mega-spheres (Matrioshka configurations) and thick-shell Dyson mega-spheres.

Are the host galaxies of long gamma-ray bursts more compact than star-forming galaxies of the field?

Context. Long gamma-ray bursts (GRBs) offer a promising tool for tracing the cosmic history of star formation, especially at high redshift, where conventional methods are known to suffer from intrinsic biases. Previous studies of GRB host galaxies at low redshift showed that high surface density of stellar mass and high surface density of star formation rate (SFR) can potentially enhance the GRB production. Evaluating the effect of such stellar densities at high redshift is therefore crucial to fully control the ability of long GRBs for probing the activity of star formation in the distant Universe. Aims. We assess how the size, stellar mass, and star formation rate surface densities of distant galaxies affect the probability of their hosting a long GRB, using a sample of GRB hosts at z &gt; 1 and a control sample of star-forming sources from the field. Methods. We gathered a sample of 45 GRB host galaxies at 1 &lt; z &lt; 3.1 observed with the Hubble Space Telescope WFC3 camera in the near-infrared. Our subsample at 1 &lt; z &lt; 2 has cumulative distributions of redshift and stellar mass consistent with the host galaxies of known unbiased GRB samples, while our GRB host selection at 2 &lt; z &lt; 3.1 has lower statistics and is probably biased toward the high end of the stellar mass function. Using the GALFIT parametric approach, we modeled the GRB host light profile with a Sérsic component and derived the half-light radius for 35 GRB hosts, which we used to estimate the star formation rate and stellar mass surface densities of each object. We compared the distribution of these physical quantities to the SFR-weighted properties of a complete sample of star-forming galaxies from the 3D-HST deep survey at a comparable redshift and stellar mass. Results. We show that similarly to z &lt; 1, GRB hosts are smaller in size and they have higher stellar mass and star formation rate surface densities than field galaxies at 1 &lt; z &lt; 2. Interestingly, this result is robust even when separately considering the hosts of GRBs with optically bright afterglows and the hosts of dark GRBs, as the two subsamples share similar size distributions. At z &gt; 2, however, GRB hosts appear to have sizes and stellar mass surface densities more consistent with those characterizing the field galaxies. This may reveal an evolution with redshift of the bias between GRB hosts and the overall population of star-forming sources, although we cannot exclude that our result at z &gt; 2 is also affected by the prevalence of dark GRBs in our selection. Conclusions. In addition to a possible trend toward a low-metallicity environment, other environmental properties such as stellar density appear to play a role in the formation of long GRBs, at least up to z ∼ 2. This might suggest that GRBs require special environments to enhance their production.

Lack of influence of the environment in the earliest stages of massive galaxy formation

ABSTRACT We investigate how the environment affects the assembly history of massive galaxies. For that purpose, we make use of Survey for High-z Absorption Red and Dead Sources (SHARDS) and HST spectrophotometric data, whose depth, spectral resolution, and wavelength coverage allow to perform a detailed analysis of the stellar emission as well as obtaining unprecedentedly accurate photometric redshifts. This expedites a sufficiently accurate estimate of the local environment and a robust derivation of the star formation histories of a complete sample of 332 massive galaxies (&amp;gt;1010M⊙) at redshift 1 ≤ z ≤ 1.5 in the GOODS-N field. We find that massive galaxies in this redshift range avoid the lowest density environments. Moreover, we observed that the oldest galaxies in our sample with mass-weighted formation redshift $\mathrm{\overline{z}_{M-w} \ge 2.5}$, avoid the highest density regions, preferring intermediate environments. Younger galaxies, including those with active star formation, tend to live in denser environments ($\Sigma = \mathrm{5.0_{1.1}^{24.8}\times 10^{10}\, M_{\odot }\, Mpc^{-2}}$). This behaviour could be expected if those massive galaxies starting their formation first would merge with neighbours and sweep their environment earlier. On the other hand, galaxies formed more recently ($\overline{z}_{M-w} \lt 2.5$) are accreted into large-scale structures at later times and we are observing them before sweeping their environment or, alternatively, they are less likely to affect their environment. However, given that both number and mass surface densities of neighbour galaxies is relatively low for the oldest galaxies, our results reveal a very weak correlation between environment and the first formation stages of the earliest massive galaxies.

XGASS: the connection between angular momentum, mass, and atomic gas fraction in nearby galaxies

ABSTRACT We use a sample of 559 disc galaxies extracted from the eXtended GALEX Arecibo SDSS Survey to study the connection between baryonic angular momentum, mass, and atomic gas fraction in the local Universe. Baryonic angular momenta are determined by combining H i and H2 integrated profiles with 2D stellar mass surface density profiles. In line with previous work, we confirm that specific angular momentum and atomic gas fraction are tightly correlated, but we find a larger scatter than previously observed. This is most likely due to the wider range of galaxy properties covered by our sample. We compare our findings with the predictions of the analytical stability model developed by Obreschkow et al. and find that, while the model provides a very good first-order approximation for the connection between baryonic angular momentum, mass, and gas fraction, it does not fully match our data. Specifically, we find that at fixed baryonic mass, the dependence of specific angular momentum on gas fraction is significantly weaker, and at fixed gas fraction, the slope of the angular momentum versus mass relation is shallower than what was predicted by the model. The reasons behind this tension remain unclear, but we speculate that multiple factors may simultaneously play a role, all related to the fact that the model is not able to encapsulate the full diversity of galaxy properties in our sample.

CLEAR: The Evolution of Spatially Resolved Star Formation in Galaxies between 0.5 ≲ z ≲ 1.7 Using Hα Emission Line Maps

Using spatially resolved Hα emission line maps of star-forming galaxies, we study the spatial distribution of star formation over a wide range in redshift (0.5 ≲ z ≲ 1.7). Our z ∼ 0.5 measurements come from deep Hubble Space Telescope (HST) Wide Field Camera 3 G102 grism spectroscopy obtained as part of the CANDELS Lyα Emission at Reionization Experiment. For star-forming galaxies with log(M */M ⊙) ≥ 8.96, the mean Hα effective radius is 1.2 ± 0.1 times larger than that of the stellar continuum, implying inside-out growth via star formation. This measurement agrees within 1σ with those measured at z ∼ 1 and z ∼ 1.7 from the 3D-HST and KMOS3D surveys, respectively, implying no redshift evolution. However, we observe redshift evolution in the stellar mass surface density within 1 kpc (Σ1kpc). Star-forming galaxies at z ∼ 0.5 with a stellar mass of log(M */M ⊙) = 9.5 have a ratio of Σ1kpc in Hα relative to their stellar continuum that is lower by (19 ± 2)% compared to z ∼ 1 galaxies. Σ1kpc,Hα /Σ1kpc,Cont decreases toward higher stellar masses. The majority of the redshift evolution in Σ1kpc,Hα /Σ1kpc,Cont versus stellar mass stems from the fact that log(Σ1kpc,Hα ) declines twice as much as log(Σ1kpc,Cont) from z ∼ 1 to 0.5 (at a fixed stellar mass of log(M */M ⊙) = 9.5). By comparing our results to the TNG50 cosmological magneto-hydrodynamical simulation, we rule out dust as the driver of this evolution. Our results are consistent with inside-out quenching following in the wake of inside-out growth, the former of which drives the significant drop in Σ1kpc,Hα from z ∼ 1 to z ∼ 0.5.

Incorporating baryon-driven contraction of dark matter halos in rotation curve fits

The condensation of baryons within a dark matter (DM) halo during galaxy formation should result in some contraction of the halo as the combined system settles into equilibrium. We quantify this effect on the cuspy primordial halos predicted by DM-only simulations for the baryon distributions observed in the galaxies of the SPARC database. We find that the DM halos of high surface brightness galaxies (with Σeff ≳ 100 L⊙ pc−2 at 3.6 μm) experience strong contraction. Halos become more cuspy as a result of compression: the inner DM density slope increases with the baryonic surface mass density. We iteratively fit rotation curves to find the balance between initial halo parameters (constrained by abundance matching), compression, and stellar mass-to-light ratio. The resulting fits often require lower stellar masses than expected for stellar populations, particularly in galaxies with bulges: stellar mass must be reduced to make room for the DM it compresses. This trade off between dark and luminous mass is reminiscent of the cusp-core problem in dwarf galaxies, but occurs in more massive systems: the present-epoch DM halos cannot follow from cuspy primordial halos unless (1) the stellar mass-to-light ratios are systematically smaller than expected from standard stellar population synthesis models, and/or (2) there is a net outward mass redistribution from the initial cusp, even in massive galaxies widely considered to be immune from such effects.

ATOMS: ALMA three-millimeter observations of massive star-forming regions – XII: Fragmentation and multiscale gas kinematics in protoclusters G12.42+0.50 and G19.88−0.53

ABSTRACT We present new continuum and molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey for the two protoclusters, G12.42+0.50 and G19.88−0.53. The 3 mm continuum maps reveal seven cores in each of the two globally contracting protoclusters. These cores satisfy the radius–mass relation and the surface mass density criteria for high-mass star formation. Similar to their natal clumps, the virial analysis of the cores suggests that they are undergoing gravitational collapse ($\rm \alpha _{vir} \lt \lt 2$). The clump to core scale fragmentation is investigated and the derived core masses and separations are found to be consistent with thermal Jeans fragmentation. We detect large-scale filamentary structures with velocity gradients and multiple outflows in both regions. Dendrogram analysis of the H13CO+ map identifies several branch and leaf structures with sizes ∼ 0.1 and 0.03 pc, respectively. The supersonic gas motion displayed by the branch structures is in agreement with the Larson power law indicating that the gas kinematics at this spatial scale is driven by turbulence. The transition to transonic/subsonic gas motion is seen to occur at spatial scales of ∼0.1 pc indicating the dissipation of turbulence. In agreement with this, the leaf structures reveal gas motions that deviate from the slope of Larson’s law. From the large-scale converging filaments to the collapsing cores, the gas dynamics in G12.42+0.50 and G19.88−0.53 show scale-dependent dominance of turbulence and gravity and the combination of these two driving mechanisms needs to be invoked to explain massive star formation in the protoclusters.

Menopause-related cortical loss of the humeral head region mainly occurred in the greater tuberosity.

AimsProximal humerus fractures are commonly observed in postmenopausal women. The goal of this study was to investigate menopause-related changes in cortical structure of the humeral head.Materials and methodsClinical computed tomography (CT) scans of 75 healthy women spanning a wide range of ages (20–72 years) were analyzed. For each subject, cortical bone mapping (CBM) was applied to create a color three-dimensional (3D) thickness map for the proximal humerus. Nine regions of interest (ROIs) were defined in three walls of the humeral head. Cortical parameters, including the cortical thickness (CTh), cortical mass surface density (CM), and the endocortical trabecular density (ECTD), were measured.ResultsCompared to premenopausal women, postmenopausal women were characterized by a significantly lower CTh and CM value in the lateral part of the greater tuberosity. Similar changes were only found in ROI 4, but not in ROIs 5–6 in the lesser tuberosity. Linear regression analysis revealed that the CTh and CM value of ROIs 1, 3, and 4 were negatively associated with age. These results showed that menopause-related loss in CTh and CM was mainly in the greater tuberosity besides the proximal part of the lesser tuberosity. Trabecular bone variable measured as ECTD showed a notably lower value in ROIs 1–9 in postmenopausal vs. premenopausal group. Inverse linear associations for ECTD and age were found in ROIs 2, 3, 5, 6, 7, and 9, indicating no site-specific differences of endocortical trabecular bone loss between the greater and lesser tuberosity.ConclusionsMenopause-related cortical loss of the humeral head mainly occurred in the lateral part of the greater tuberosity. The increased rate of humeral bone loss in the greater tuberosity may contribute materially to complex proximal humerus fractures.

Analytic models of dust temperature in high-redshift galaxies

ABSTRACT We investigate physical reasons for high-dust temperatures (Tdust ≳ 40K) observed in some high-redshift ($z$ &amp;gt; 5) galaxies using analytic models. We consider two models that can be treated analytically: the radiative transfer (RT) model, where a broad distribution of values for Tdust is considered, and the one-tempearture (one-T) model, which assumes uniform Tdust. These two extremes serve to bracket the most realistic scenario. We adopt the Kennicutt–Schmidt (KS) law to relate stellar radiation field to gas surface density, and vary the dust-to-gas ratio. As a consequence, our model is capable of predicting the relation between the surface density of star formation rate (ΣSFR) or dust mass (Σdust) and Tdust. We show that the high Tdust observed at $z$ ≳ 5 favour low dust-to-gas ratios (≲ 10−3). An enhanced star formation compared with the KS law gives an alternative explanation for the high Tdust. The dust temperatures are similar between the two (RT and one-T) models as long as we use ALMA Bands 6–8. We also examine the relation among ΣSFR, Σdust, and Tdust without assuming the KS law, and confirm the consistency with the actual observational data at $z$ &amp;gt; 5. In the one-T model, we also examine a clumpy dust distribution, which predicts lower Tdust because of the leakage of stellar radiation. This enhances the requirement of low-dust abundance or high-star formation efficiency to explain the observed high Tdust.

Multiply lensed star forming clumps in the A521-sys1 galaxy at redshift 1

ABSTRACT We study the population of star-forming clumps in A521-sys1, a $z=1.04$ system gravitationally lensed by the foreground ($z=0.25$) cluster Abell 0521. The galaxy presents one complete counter-image with a mean magnification of $\rm \mu \sim 4$ and a wide arc containing two partial images of A521-sys1 with magnifications reaching $\mu &amp;gt; 20$, allowing the investigations of clumps down to scales of ${\rm R}_{\rm eff} &amp;lt; 50$ pc. We identify 18 unique clumps with a total of 45 multiple images. Intrinsic sizes and UV magnitudes reveal clumps with elevated surface brightnesses comparable to similar systems at redshifts $z\gtrsim 1.0$. Such clumps account for ${\sim}40\,\rm{per\ cent}$ of the galaxy UV luminosity implying a significant fraction of the recent star-formation activity is taking place there. Clump masses range from 106 to $10^9\,{\rm M}_\odot$ and sizes from tens to hundreds of parsec resulting in mass surface densities from 10 to $10^3\,{\rm M}_\odot\,{\rm pc}^{-2}$ with a median of ${\sim}10^2\,{\rm M}_\odot\,{\rm pc}^{-2}$. These properties suggest that we detect star formation taking place across a wide range of scale from cluster aggregates to giant star-forming complexes. We find ages of less than 100 Myr consistent with clumps being observed close to their natal region. The lack of galactocentric trends with mass, mass density, or age and the lack of old migrated clumps can be explained either by dissolution of clumps after few ∼100 Myr or by stellar evolution making them fall below the detectability limits of our data.

Dust emissivity in resolved spiral galaxies

Context. The far-infrared (FIR) and sub-millimeter (submm) emissivity, ϵν, of the Milky Way (MW) cirrus is an important benchmark for dust grain models. Dust masses in other galaxies are generally derived from the FIR/submm using the emission properties of these MW-calibrated models. Aims. We seek to derive the FIR/submm ϵν in nine nearby spiral galaxies to check its compatibility with MW cirrus measurements. Methods. We obtained values of ϵν at 70–500 μm, using maps of dust emission from the Herschel satellite and of gas surface density from the THINGS and HERACLES surveys on a scale generally corresponding to 440 pc. We studied the variation of ϵν with the surface brightness ratio Iν(250 μm)/Iν(500 μm), a proxy for the intensity of the interstellar radiation field heating the dust. Results. We find that the average value of ϵν agrees with MW estimates for pixels sharing the same color as the cirrus, namely, for Iν(250 μm)/Iν(500 μm)=4.5. For Iν(250 μm)/Iν(500 μm)&gt; 5, the measured emissivity is instead up to a factor ∼2 lower than predicted from MW dust models heated by stronger radiation fields. Regions with higher Iν(250 μm)/Iν(500 μm) are preferentially closer to the galactic center and have a higher overall (stellar+gas) surface density and molecular fraction. The results do not depend strongly on the adopted CO-to-molecular conversion factor and do not appear to be affected by the mixing of heating conditions. Conclusions. Our results confirm the validity of MW dust models at low density, but are at odds with predictions for grain evolution in higher density environments. If the lower-than-expected ϵν at high Iν(250 μm)/Iν(500 μm) is the result of intrinsic variations in the dust properties, it would imply an underestimation of the dust mass surface density of up to a factor ∼2 when using current dust models.

Effects of the environment and feedback physics on the initial mass function of stars in the STARFORGE simulations

ABSTRACT One of the key mysteries of star formation is the origin of the stellar initial mass function (IMF). The IMF is observed to be nearly universal in the Milky Way and its satellites, and significant variations are only inferred in extreme environments, such as the cores of massive elliptical galaxies and the Central Molecular Zone. In this work, we present simulations from the STARFORGE project that are the first cloud-scale radiation-magnetohydrodynamic simulations that follow individual stars and include all relevant physical processes. The simulations include detailed gas thermodynamics, as well as stellar feedback in the form of protostellar jets, stellar radiation, winds, and supernovae. In this work, we focus on how stellar radiation, winds, and supernovae impact star-forming clouds. Radiative feedback plays a major role in quenching star formation and disrupting the cloud; however, the IMF peak is predominantly set by protostellar jet physics. We find that the effect of stellar winds is minor, and supernovae ‘occur too late’ to affect the IMF or quench star formation. We also investigate the effects of initial conditions on the IMF. We find that the IMF is insensitive to the initial turbulence, cloud mass, and cloud surface density, even though these parameters significantly shape the star formation history of the cloud, including the final star formation efficiency. Meanwhile, the characteristic stellar mass depends weakly on metallicity and the interstellar radiation field, which essentially set the average gas temperature. Finally, while turbulent driving and the level of magnetization strongly influence the star formation history, they only influence the high-mass slope of the IMF.

Extreme giant molecular clouds in the luminous infrared galaxy NGC 3256

ABSTRACT We present a cloud decomposition of 12CO (2–1) observations of the merger and nearest luminous infrared galaxy, NGC 3256. 185 spatially and spectrally resolved clouds are identified across the central ≈130 kpc2 at 90 pc resolution and completeness is estimated. We compare our cloud catalogue from NGC 3256 to ten galaxies observed in the PHANGS-ALMA survey. Distributions in NGC 3256 of cloud velocity dispersions (median 23 km s−1), luminosities (1.5 × 107 K km s−1 pc2), CO-estimated masses (2.1 × 107 M⊙), mass surface densities (470 M⊙ pc−2), virial masses (5.4 × 107 M⊙), virial parameters (4.3), size-linewidth coefficients (6.3 km2 s−2 pc−1), and internal turbulent pressures ( 1.0 × 10 7K cm−3$\, k_{\mathrm{B}}^{-1}$) are significantly higher than in the PHANGS-ALMA galaxies. Cloud radii (median 88 pc) are slightly larger in NGC 3256 and free-fall times (4.1 Myr) are shorter. The distribution of cloud eccentricities in NGC 3256 (median of 0.8) is indistinguishable from many PHANGS-ALMA galaxies, possibly because the dynamical state of clouds in NGC 3256 is similar to that of nearby spiral galaxies. However, the narrower distribution of virial parameters in NGC 3256 may reflect a narrower range of dynamical states than in PHANGS-ALMA galaxies. No clear picture of cloud alignment is detected, despite the large eccentricities. Correlations between cloud properties point to high external pressures in NGC 3256 keeping clouds bound and collapsing given such high velocity dispersions and star-formation rates. A fit to the cloud mass function gives a high-mass power-law slope of $-2.75^{+0.07}_{-0.01}$, near the average from PHANGS-ALMA galaxies. We also compare our results to a pixel-based analysis of these observations and find molecular-gas properties agree qualitatively, though peak brightness temperatures are somewhat higher and virial parameters and free-fall times are somewhat lower in this cloud-based analysis.

On the dynamic response of bi-directional functionally graded nanobeams under moving harmonic load accounting for surface effect

This paper presents an investigation of the dynamic behavior of bi-directionally functionally graded (BDFG) micro/nanobeams excited by a moving harmonic load. The formulation is established in the context of the surface elasticity theory and the modified couple stress theory to incorporate the effects of surface energy and microstructure, respectively. Based on the generalized elasticity theory and the parabolic shear deformation beam theory, the nonclassical governing equations of the problem are obtained using Lagrange’s equation accounting for the physical neutral plane concept. The material properties of the beam smoothly change along both the axial and thickness directions according to power-law distribution, accounting for the gradation of the material length scale parameter and the surface parameters, i.e., residual surface stress, two surface elastic constants, and surface mass density. Using trigonometric Ritz method (TRM), the trial functions denoting transverse, axial deflections, and rotation of the cross sections of the beam are expressed in sinusoidal form. Then, with the aid of Lagrange’s equation, the system of equations of motion are derived. Finally, Newmark method is employed to find the dynamic responses of BDFG subjected to a moving harmonic load. To validate the present formulation and solution method, some comparisons of the obtained fundamental frequency and dynamic response with those available in the literature are performed. A parametric study is performed to extensively explore the impact of the key parameters such as the gradient indices in both directions, moving speed, and excitation frequency of the acting load on the dynamic response of BDFG nanobeams. The obtained results can serve as a guideline for assessing the multi-functional and optimal design of micro/nanobeams acted upon by a moving load.

Variations in the ΣSFR − Σmol − Σ⋆ plane across galactic environments in PHANGS galaxies

Aims. There exists some consensus that the stellar mass surface density (Σ⋆) and molecular gas mass surface density (Σmol) are the main quantities responsible for locally setting the star formation rate. This regulation is inferred from locally resolved scaling relations between these two quantities and the star formation rate surface density (ΣSFR), which have been extensively studied in a wide variety of works. However, the universality of these relations is debated. Here, we probe the interplay between these three quantities across different galactic environments at a spatial resolution of 150 pc. Methods. We performed a hierarchical Bayesian linear regression to find the best set of parameters C⋆, Cmol, and Cnorm that describe the star-forming plane conformed by Σ⋆, Σmol, and ΣSFR, such that logΣSFR = C⋆logΣ⋆ + CmollogΣmol + Cnorm. We also explored variations in the determined parameters across galactic environments, focusing our analysis on the C⋆ and Cmol slopes. Results. We find signs of variations in the posterior distributions of C⋆ and Cmol across different galactic environments. The dependence of ΣSFR on Σ⋆ spans a wide range of slopes, with negative and positive values, while the dependence of ΣSFR on Σmol is always positive. Bars show the most negative value of C⋆ (−0.41), which is a sign of longer depletion times, while spiral arms show the highest C⋆ among all environments (0.45). Variations in Cmol also exist, although they are more subtle than those found for C⋆. Conclusions. We conclude that systematic variations in the interplay of Σ⋆, Σmol, and ΣSFR across different galactic environments exist at a spatial resolution of 150 pc, and we interpret these variations to be produced by an additional mechanism regulating the formation of stars that is not captured by either Σ⋆ or Σmol. Studying environmental variations in single galaxies, we find that these variations correlate with changes in the star formation efficiency across environments, which could be linked to the dynamical state of the gas that prevents it from collapsing and forming stars, or to changes in the molecular gas fraction.

Inferring the Gas-to-Dust Ratio in the Main Planet-forming Region of Disks

Measuring the amount of gas and dust in protoplanetary disks is a key challenge in planet formation studies. Here we provide a new set of dust depletion factors and relative mass surface densities of gas and dust for the innermost regions of a sample of protoplanetary disks. We do this by combining stellar theory with observed refractory element abundances in both disk hosts and open cluster stars. Our results are independent of, and complementary to, those obtained from spatially resolved disk observations.