Circular Velocity Research Articles

Transient Thermal Stresses in FG Porous Rotating Truncated Cones Reinforced by Graphene Platelets

The present work studies an axisymmetric rotating truncated cone made of functionally graded (FG) porous materials reinforced by graphene platelets (GPLs) under a thermal loading. The problem is tackled theoretically based on a classical linear thermoelasticity approach. The truncated cone consists of a layered material with a uniform or non-uniform dispersion of GPLs in a metal matrix with open-cell internal pores, whose effective properties are determined according to the extended rule of mixture and modified Halpin–Tsai model. A graded finite element method (FEM) based on Rayleigh–Ritz energy formulation and Crank–Nicolson algorithm is here applied to solve the problem both in time and space domain. The thermo-mechanical response is checked for different porosity distributions (uniform and functionally graded), together with different types of GPL patterns across the cone thickness. A parametric study is performed to analyze the effect of porosity coefficients, weight fractions of GPL, semi-vertex angles of cone, and circular velocity, on the thermal, kinematic, and stress response of the structural member.

The extended H i halo of NGC 4945 as seen by MeerKAT

ABSTRACT Observations of the neutral atomic hydrogen (H i) in the nuclear starburst galaxy NGC 4945 with MeerKAT are presented. We find a large amount of halo gas, previously missed by H i observations, accounting for 6.8 per cent of the total H i mass. This is most likely gas blown into the halo by star formation. Our maps go down to a 3σ column density level of 5 × 1018 cm−2. We model the H i distribution using tilted-ring fitting techniques and find a warp on the galaxy’s approaching and receding sides. The H i in the northern side of the galaxy appears to be suppressed. This may be the result of ionization by the starburst activity in the galaxy, as suggested by a previous study. The origin of the warp is unclear but could be due to past interactions or ram pressure stripping. Broad, asymmetric H i absorption lines extending throughout the H i emission velocity channels are present towards the nuclear region of NGC 4945. Such broad lines suggest the existence of a nuclear ring moving at a high circular velocity. This is supported by the clear rotation patterns in the H i absorption velocity field. The asymmetry of the absorption spectra can be caused by outflows or inflows of gas in the nuclear region of NGC 4945. The continuum map shows small extensions on both sides of the galaxy’s major axis that might be signs of outflows resulting from the starburst activity.

EMPRESS. VI. Outflows Investigated in Low-mass Galaxies with M ∗ = 104–107 M ⊙: Weak Feedback in Low-mass Galaxies?

We study emission line profiles of 21 nearby low-mass (M * = 104–107 M ⊙) galaxies in deep medium-high resolution spectra taken with Magellan/MagE. These low-mass galaxies are actively star-forming systems with high specific star formation rates of ∼100–1000 Gyr−1 that are well above the star formation main sequence and its extrapolation. We identify broad-line components of Hα and [O iii]λ5007 emission in 14 out of the 21 galaxies that cannot be explained by the MagE instrumental profile or the natural broadening of line emission. We conduct double-Gaussian profile fitting to the emission of the 14 galaxies, and find that the broad-line components have line widths significantly larger than those of the narrow-line components, indicative of galactic outflows. The broad-line components have moderately large line widths of ∼100 km s−1. We estimate the maximum outflow velocities v max and obtain values of ≃60–200 km s−1, which are found to be comparable to or slightly larger than the escape velocities. Positive correlations of v max with star formation rates, stellar masses, and circular velocities extend down into this low-mass regime. Broad- to narrow-line flux ratios (BNRs) are generally found to be smaller than those of massive galaxies. The small v max and BNRs suggest that the mass-loading factors η can be as small as 0.1–1 or below, in contrast to the large η of energy-driven outflows predicted by numerical simulations.

Cosmology with One Galaxy?

Galaxies can be characterized by many internal properties such as stellar mass, gas metallicity, and star formation rate. We quantify the amount of cosmological and astrophysical information that the internal properties of individual galaxies and their host dark matter halos contain. We train neural networks using hundreds of thousands of galaxies from 2000 state-of-the-art hydrodynamic simulations with different cosmologies and astrophysical models of the CAMELS project to perform likelihood-free inference on the value of the cosmological and astrophysical parameters. We find that knowing the internal properties of a single galaxy allows our models to infer the value of Ωm, at fixed Ωb, with a ∼10% precision, while no constraint can be placed on σ 8. Our results hold for any type of galaxy, central or satellite, massive or dwarf, at all considered redshifts, z ≤ 3, and they incorporate uncertainties in astrophysics as modeled in CAMELS. However, our models are not robust to changes in subgrid physics due to the large intrinsic differences the two considered models imprint on galaxy properties. We find that the stellar mass, stellar metallicity, and maximum circular velocity are among the most important galaxy properties to determine the value of Ωm. We believe that our results can be explained by considering that changes in the value of Ωm, or potentially Ωb/Ωm, affect the dark matter content of galaxies, which leaves a signature in galaxy properties distinct from the one induced by galactic processes. Our results suggest that the low-dimensional manifold hosting galaxy properties provides a tight direct link between cosmology and astrophysics.

Galaxy Rotation Parameters from OB2 Stars with Proper Motions and Parallaxes from the Gaia EDR3 Catalog

We have analyzed the kinematics of OB2 stars with proper motions and parallaxes selected by Xu et al. from the Gaia EDR3 catalog. The relative parallax errors for all the stars in this sample do not exceed 10%. Based on a sample of 9750 stars, the group velocity components $${{(U,V,W)}_{ \odot }} = $$ (7.21, 7.46, 8.52) ± (0.13, 0.20, 0.10) km/s were obtained and the parameters of the angular velocity of rotation of the Galaxy: $${{\Omega }_{0}} = 29.712 \pm 0.062$$ km/s/kpc, $$\Omega _{0}^{'} = - 4.014 \pm 0.018$$ km/s/kpc2, and $$\Omega _{0}^{{''}} = 0.674 \pm 0.009$$ km/s/kpc3. The circular velocity of rotation of the solar neighborhood around the center of the Galaxy is $${{V}_{0}} = 240.7 \pm 3.0$$ km/s for the assumed distance of the Sun to the galactic center $${{R}_{0}} = 8.1 \pm 0.1$$ kpc. It is shown that the influence of the systematic correction to the trigonometric parallaxes of the Gaia EDR3 catalog with the value $$\Delta \pi = - 0.040$$ mas does not exceed the $$\sim {\kern 1pt} 1\sigma $$ level of the errors of the sought-for kinematic parameters of the model. Based on the proper motions of OB stars, the following variances of the residual velocities were found: $$({{\sigma }_{1}},{{\sigma }_{2}},{{\sigma }_{3}}) = (11.79,9.66,7.21) \pm (0.06,0.05,0.04)$$ km/s. It is shown that the first axis of this ellipsoid slightly deviates from the direction to the center of the Galaxy $${{L}_{1}} = 12.4^\circ \pm 0.1^\circ $$ , and the third axis is oriented almost exactly to the north pole of the Galaxy, $${{B}_{3}} = 83.7^\circ \pm 0.1^\circ $$ .

LEGA-C: Analysis of Dynamical Masses from Ionized Gas and Stellar Kinematics at z ∼ 0.8

Abstract We compare dynamical mass estimates based on spatially extended stellar and ionized gas kinematics (M dyn,* and M dyn,eml, respectively) of 157 star-forming galaxies at 0.6 ≤ z < 1. Compared with z ∼ 0, these galaxies have enhanced star formation rates, with stellar feedback likely affecting the dynamics of the gas. We use LEGA-C DR3, the highest-redshift data set that provides sufficiently deep measurements of a K s -band limited sample. For M dyn,*, we use Jeans anisotropic multi-Gaussian expansion models. For M dyn,eml, we first fit a custom model of a rotating exponential disk with uniform dispersion, whose light is projected through a slit and corrected for beam smearing. We then apply an asymmetric drift correction based on assumptions common in the literature to the fitted kinematic components to obtain the circular velocity, assuming hydrostatic equilibrium. Within the half-light radius, M dyn,eml is on average lower than M dyn,*, with a mean offset of –0.15 ± 0.016 dex and galaxy-to-galaxy scatter of 0.19 dex, reflecting the combined random uncertainty. While data of higher spatial resolution are needed to understand this small offset, it supports the assumption that the galaxy-wide ionized gas kinematics do not predominantly originate from disruptive events such as star formation–driven outflows. However, a similar agreement can be obtained without modeling from the integrated emission line dispersions for axis ratios q < 0.8. This suggests that our current understanding of gas kinematics is not sufficient to efficiently apply asymmetric drift corrections to improve dynamical mass estimates compared with observations lacking the signal-to-noise ratio required for spatially extended dynamics.

MATLAB codes for generating dispersion images for ground exploration using different multichannel analysis of surface wave transforms

A set of codes has been developed in MATLAB for generating multimodal dispersion images by using three different transformation techniques. While performing the multichannel analysis of surface waves (MASW), the field data obtained by using multiple geophones, in the distance and time domain, become the required input data for these developed programs. The dispersion images have been evaluated by generating synthetic data and performing field tests using a 20 lb hammer at two different chosen sites with 48 geophones. The dispersion plots from the three different transformation techniques are found to match each other closely. In general, the circular frequency-phase velocity ([Formula: see text]- c) transform provides the best clarity. An increase in the spread length, however, without increasing the number of sensors, often leads to the appearance of aliased modes in the dispersion images.

The Origin of Exponential Star-forming Disks

Abstract The disk components of galaxies generally show an exponential profile extending over several scale lengths, both in mass and star formation rate, but the physical origin is not well understood. We explore a physical model in which the galactic gas disk is viewed as a “modified accretion disk” in which coplanar gas inflow, driven by viscous stresses in the disk, provides the fuel for star formation, which progressively removes gas as it flows inward. We show that magnetic stresses from magneto-rotational instability are the most plausible source of the required viscosity, and construct a simple physical model to explore this. A key feature is to link the magnetic field strength to the local star formation surface density, B tot ∝ Σ SFR α . This provides a feedback loop between star formation and the flow of gas. We find that the model naturally produces stable steady-state exponential disks, as long as α ∼ 0.15, the value indicated from spatially resolved observations of nearby galaxies. The disk scale length h R is set by the rate at which the disk is fed, by the normalization of the B tot–ΣSFR relation and by the circular velocity of the halo. The angular momentum distribution of the gas and stars within the disk is a consequence of the transfer of angular momentum that is inherent to the operation of an accretion disk, rather than the initial angular momentum of the inflowing material. We suggest that magnetic stresses likely play a major role in establishing the stable exponential form of galactic disks.

Finding Universal Relations in Subhalo Properties with Artificial Intelligence

Abstract We use a generic formalism designed to search for relations in high-dimensional spaces to determine if the total mass of a subhalo can be predicted from other internal properties such as velocity dispersion, radius, or star formation rate. We train neural networks using data from the Cosmology and Astrophysics with MachinE Learning Simulations project and show that the model can predict the total mass of a subhalo with high accuracy: more than 99% of the subhalos have a predicted mass within 0.2 dex of their true value. The networks exhibit surprising extrapolation properties, being able to accurately predict the total mass of any type of subhalo containing any kind of galaxy at any redshift from simulations with different cosmologies, astrophysics models, subgrid physics, volumes, and resolutions, indicating that the network may have found a universal relation. We then use different methods to find equations that approximate the relation found by the networks and derive new analytic expressions that predict the total mass of a subhalo from its radius, velocity dispersion, and maximum circular velocity. We show that in some regimes, the analytic expressions are more accurate than the neural networks. The relation found by the neural network and approximated by the analytic equation bear similarities to the virial theorem.

Improved strong lensing modelling of galaxy clusters using the Fundamental Plane: Detailed mapping of the baryonic and dark matter mass distribution of Abell S1063

Aims. From accurate photometric and spectroscopic information, we build the Fundamental Plane (FP) relation for the early-type galaxies of the cluster Abell S1063. We use this relation to develop an improved strong lensing model of the cluster, and we decompose the cluster’s cumulative projected total mass profile into its stellar, hot gas, and dark matter mass components. We compare our results with the predictions of cosmological simulations. Methods. We calibrate the FP using Hubble Frontier Fields photometry and data from the Multi Unit Spectroscopic Explorer on the Very Large Telescope. The FP allows us to determine the velocity dispersions of all 222 cluster members included in the model from their measured structural parameters. As for their truncation radii, we test a proportionality relation with the observed half-light radii. Fixing the mass contribution of the hot gas component from X-ray data, the mass density distributions of the diffuse dark matter haloes are optimised by comparing the observed and model-predicted positions of 55 multiple images of 20 background sources distributed over the redshift range 0.73 − 6.11. We determine the uncertainties on the model parameters with Monte Carlo Markov chains. Results. We find that the most accurate predictions of the positions of the multiple images are obtained when the truncation radii of the member galaxies are approximately 2.3 times their effective radii. Compared to earlier work on the same cluster, our model allows for the inclusion of some scatter on the relation between the total mass and the velocity dispersion of the cluster members. We notice a lower statistical uncertainty on the value of some model parameters. For instance, the main dark matter halo of the cluster has a core radius of 86 ± 2 kpc: the uncertainty on this value decreases by more than 30% with respect to previous work. Taking advantage of a new estimate of the stellar mass of all cluster members from the HST multi-band data, we measure the cumulative two-dimensional mass profiles out to a radius of 350 kpc for all baryonic and dark matter components of the cluster. At the outermost radius of 350 kpc, we obtain a baryon fraction of 0.147 ± 0.002. We study the stellar-to-total mass fraction of the high-mass cluster members in our model, finding good agreement with the observations of wide galaxy surveys and some disagreement with the predictions of halo occupation distribution studies based on N-body simulations. Finally, we compare the features of the sub-haloes as described by our model with those predicted by high-resolution hydrodynamical simulations. We obtain compatible results in terms of the stellar over total mass fraction. On the other hand, we report some discrepancies both in terms of the maximum circular velocity, which is an indication of the halo compactness, and the sub-halo total mass function in the central cluster regions.

Structure and kinematics of tidally limited satellite galaxies in LCDM

ABSTRACT We use N-body simulations to model the tidal evolution of dark matter-dominated dwarf spheroidal galaxies embedded in cuspy Navarro-Frenk-White subhaloes. Tides gradually peel off stars and dark matter from a subhalo, trimming it down according to their initial binding energy. This process strips preferentially particles with long orbital times, and comes to an end when the remaining bound particles have crossing times shorter than a fraction of the orbital time at pericentre. The properties of the final stellar remnant thus depend on the energy distribution of stars in the progenitor subhalo, which in turn depends on the initial density profile and radial segregation of the initial stellar component. The stellar component may be completely dispersed if its energy distribution does not extend all the way to the subhalo potential minimum, although a bound dark remnant may remain. These results imply that ‘tidally limited’ galaxies, defined as systems whose stellar components have undergone substantial tidal mass-loss, neither converge to a unique structure nor follow a single tidal track. On the other hand, tidally limited dwarfs do have characteristic sizes and velocity dispersions that trace directly the characteristic radius (rmx) and circular velocity (Vmx) of the subhalo remnant. This result places strong upper limits on the size of satellites whose unusually low velocity dispersions are often ascribed to tidal effects. In particular, the large size of kinematically cold ‘feeble giant’ satellites like Crater 2 or Antlia 2 cannot be explained as due to tidal effects alone in the Lambda Cold Dark Matter scenario.

Properties of Fast and Slow Bars Classified by Epicyclic Frequency Curves from Photometry of Barred Galaxies

Abstract We test the idea that bar pattern speeds decrease with time owing to angular momentum exchange with a dark matter halo. If this process actually occurs, then the radii of the corotation resonance and other resonances should generally increase with time. We therefore derive the angular velocity Ω and epicyclic frequency κ as functions of galactocentric radius for 85 barred galaxies using photometric data. Mass maps are constructed by assuming a dynamical mass-to-light ratio and then solving the Poisson equation for the gravitational potential. The locations of Lindblad resonances and the corotation resonance radius are then derived using the standard precession frequency curves in conjunction with bar pattern speeds recently estimated from the Tremaine–Weinberg method as applied to integral field spectroscopy data. Correlations between physical properties of bars and their host galaxies indicate that bar length and the corotation radius depend on the disk circular velocity while bar strength and pattern speed do not. As the bar pattern speed decreases, bar strength, length, and corotation radius increase, but when bars are subclassified into fast, medium, and slow domains, no significant change in bar length is found. Only a hint of an increase in bar strength from fast to slow bars is found. These results suggest that bar length in a galaxy undergoes little evolution, and is determined instead mainly by the size of the host galaxy.

The CGM–GRB Study. II. Outflow–Galaxy Connection at z ∼ 2–6

Abstract We use a sample of 27 gamma-ray bursts (GRBs) at redshift z = 2–6 to probe the outflows in their respective host galaxies (log(M */M ⊙) ∼ 9–11) and search for possible relations between the outflow properties and those of the host galaxies, such as M *, the star formation rate (SFR), and the specific SFR (sSFR). First, we consider three outflow properties: outflow column density (N out), maximum outflow velocity (V max), and normalized maximum velocity (V norm = V max/V circ,halo, where V circ,halo is the halo circular velocity). We observe clear trends of N out and V max with increasing SFR in high-ion-traced outflows, with a stronger (>3σ) V max–SFR correlation. We find that the estimated mass outflow rate and momentum flux of the high-ion outflows scale with SFR and can be supported by the momentum imparted by star formation (supernovae and stellar winds). The kinematic correlations of high-ion-traced outflows with SFR are similar to those observed for star-forming galaxies at low redshifts. The correlations with SFR are weaker in low-ion outflows. This, along with the lower detection fraction in low-ion outflows, indicates that the outflow is primarily high-ion dominated. We also observe a strong (>3σ) trend of normalized velocity (V norm) decreasing with halo mass and increasing with sSFR, suggesting that outflows from low-mass halos and high-sSFR galaxies are most likely to escape and enrich the outer circumgalactic medium (CGM) and intergalactic medium with metals. By comparing the CGM–GRB stacks with those of starbursts at z ∼ 2 and z ∼ 0.1, we find that over a broad redshift range, the outflow strength strongly depends on the main-sequence offset at the respective redshifts, rather than simply the SFR.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ГЕОМЕТРИЧЕСКИХ ОСОБЕННОСТЕЙ ТОПЛИВНЫХ ФОРСУНОК ГАЗОТУРБИННОГО АВИАЦИОННОГО ДВИГАТЕЛЯ НА ХАРАКТЕРИСТИКИ РАСПЫЛА С ПОМОЩЬЮ БЕСКОНТАКТНЫХ МЕТОДОВ

The experimental research of the peripheral unevenness of air-blast atomizer with different fuel sprayers has been con-ducted on a hydraulic stand. The experimental research of fuel atomizers based on laser anemometer’s readings has been con-ducted. Parameters of atomization characteristics and circular velocity have been analyzed. Based of those findings and relevant research information, hypotheses have been made that is capable to properly describe experimental results. Basic guidance’s to future investigations has been given.

Kinematics of the Galaxy from Young Open Star Clusters with Data from the Gaia EDR3 Catalogue

We have analyzed the kinematics of open star clusters (OSCs) with the proper motions and distances calculated by Hao et al. based on Gaia EDR3 data. The mean line-of-sight velocities are known for a number of clusters from this list. We show that the Galactic rotation parameters determined from samples of OSCs with various ages are in good agreement between themselves. The most interesting results have been obtained from a sample of 967 youngest OSCs with a mean age of 18 Myr. In particular, we have found the following parameters of the angular velocity of Galactic rotation using only their proper motions and distances: $\Omega_0 =28.01\pm0.15$ km s$^{-1}$ kpc$^{-1},$ $\Omega^{'}_0=-3.674\pm0.040$ km s$^{-1}$ kpc$^{-2},$ and $\Omega^{''}_0=0.565\pm0.023$ km s$^{-1}$ kpc$^{-3}$. The circular rotation velocity of the solar neighborhood around the Galactic center here is $V_0=226.9\pm3.1$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.1\pm0.1$ kpc. The parameters of the spiral density wave have been determined from the space velocities of 233 young clusters. The amplitudes of the radial and tangential velocity perturbations produced by the spiral density wave are $f_R=9.1\pm0.8$ km s$^{-1}$ and $f_\theta=4.6\pm1.2$ km s$^{-1}$, respectively; the perturbation wavelengths are $\lambda_R=3.3\pm0.5$ kpc and $\lambda_\theta=2.6\pm0.6$ kpc for the the adopted four-armed spiral pattern. The Sun's phase in the spiral density wave has been found to be $(\chi_\odot)_R\approx-180^\circ$.

Simulating Globular Clusters in Dark Matter Subhalos

Abstract A cosmological zoom-in simulation that develops into a Milky Way-like halo begins at redshift 7. The initial dark matter distribution is seeded with dense star clusters of median mass 5 × 105 M ⊙, placed in the largest subhalos present, which have a median peak circular velocity of 25 km s−1. Three simulations are initialized using the same dark matter distribution with the star clusters starting on approximately circular orbits having initial median radii 6.8, 0.14 kpc, and, at the exact center of the subhalos. The simulations are evolved to the current epoch at which time the median galactic orbital radii of the three sets of clusters are 30, 5, and 16 kpc, with the clusters losing about 2%, 50%, and 15% of their mass, respectively. Clusters beginning at small orbital radii have so much tidal forcing that they are often not in equilibrium. Clusters that start at larger subhalo radii have a velocity dispersion that declines smoothly to ≃20% of the central value at ≃20 half-mass radii. The clusters that begin in the subhalo centers can show a rise in velocity dispersion beyond 3–5 half-mass radii. That is, the clusters that form without local dark matter always have stellar-mass-dominated kinematics at all radii, whereas about 25% of the clusters that begin in subhalo centers have remnant local dark matter.

Scaling relations and baryonic cycling in local star-forming galaxies

Gas accretion and stellar feedback processes link metal content, star formation, and gas and stellar mass (and the potential depth) in star-forming galaxies. Constraining this hypersurface has been challenging because of the need for measurements of H I and H2 gas masses spanning a broad parameter space. A recent step forward has been achieved through the Metallicity And Gas for Mass Assembly sample of local star-forming galaxies, which consists of homogeneously determined parameters and a significant quantity of dwarf galaxies, with stellar masses as low as ∼105 − 106 M⊙. Here, in the third paper of a series, we adopt a standard galactic chemical evolution model, with which we can quantify stellar-driven outflows. In particular, we constrain the difference between the mass-loading in accretion and outflows and the wind metal-loading factor. The resulting model reproduces very well the local mass–metallicity relation, and the observed trends of metallicity with gas fraction. Although the difference in mass loading between accreted and expelled gas is extremely difficult to constrain, we find indications that, on average, the amount of gas acquired through accretion is roughly the same as the gas lost through bulk stellar outflows, a condition roughly corresponding to a “gas equilibrium” scenario. In agreement with previous work, the wind metal-loading factor shows a steep increase toward lower mass and circular velocity, indicating that low-mass galaxies are more efficient at expelling metals, thus shaping the mass–metallicity relation. Effective yields are found to increase with mass up to an inflection mass threshold, with a mild decline at larger masses and circular velocities. A comparison of our results for metal loading in outflows with the expectations for their mass loading favors momentum-driven winds at low masses, rather than energy-driven ones.

The galaxy–halo size relation of low-mass galaxies in FIRE

ABSTRACT Galaxy sizes correlate closely with the sizes of their parent dark matter haloes, suggesting a link between halo formation and galaxy growth. However, the precise nature of this relation and its scatter remains to be understood fully, especially for low-mass galaxies. We analyse the galaxy–halo size relation (GHSR) for low-mass ($M_\star \sim 10^{7-9}\, {\rm M}_\odot$) central galaxies over the past 12.5 billion years with the help of cosmological volume simulations (FIREbox) from the Feedback in Realistic Environments (FIRE) project. We find a nearly linear relationship between the half-stellar mass galaxy size R1/2 and the parent dark matter halo virial radius Rvir. This relation evolves only weakly since redshift z = 5: $R_{1/2}\, [{\rm kpc}] = (0.053\pm 0.002)(R_{\rm vir}/35\, {\rm kpc})^{0.934\pm 0.054}$, with a nearly constant scatter $\langle \sigma \rangle = 0.084\, [{\rm dex}]$. While this ratio is similar to what is expected from models where galaxy disc sizes are set by halo angular momentum, the low-mass galaxies in our sample are not angular momentum supported, with stellar rotational to circular velocity ratios vrot/vcirc ∼ 0.15. Introducing redshift as another parameter to the GHSR does not decrease the scatter. Furthermore, this scatter does not correlate with any of the halo properties we investigate – including spin and concentration – suggesting that baryonic processes and feedback physics are instead critical in setting the scatter in the GHSR. Given the relatively small scatter and the weak dependence of the GHSR on redshift and halo properties for these low-mass central galaxies, we propose using galaxy sizes as an independent method from stellar masses to infer halo masses.

Crosstalk between protein kinases A and C regulates sea urchin sperm motility.

Fertilization, a crucial event for species preservation, in sea urchins, as in many other organisms, requires sperm motility regulation. In Strongylocentrotus purpuratus sea urchins, speract, a sperm chemoattractant component released to seawater from the outer egg layer, attracts sperm after binding to its receptor in the sperm flagellum. Previous experiments performed in demembranated sperm indicated that motility regulation in these cells involved protein phosphorylation mainly due to the cAMP-dependent protein kinase (PKA). However, little information is known about the involvement of protein kinase C (PKC) in this process. In this work, using intact S. purpuratus sea urchin sperm, we show that: (i) the levels of both phosphorylated PKA (PKA substrates) and PKC (PKC substrates) substrates change between immotile, motile and speract-stimulated sperm, and (ii) the non-competitive PKA (H89) and PKC (chelerythrine) inhibitors diminish the circular velocity of sperm and alter the phosphorylation levels of PKA substrates and PKC substrates, while the competitive inhibitors Rp-cAMP and bisindolylmaleimide (BIM) do not. Altogether, our results show that both PKA and PKC participate in sperm motility regulation through a crosstalk in the signalling pathway. These results contribute to a better understanding of the mechanisms that govern motility in sea urchin sperm.

Crucial Factors for Lyα Transmission in the Reionizing Intergalactic Medium: Infall Motion, H ii Bubble Size, and Self-shielded Systems

Abstract Using the CoDa II simulation, we study the Lyα transmissivity of the intergalactic medium (IGM) during reionization. At z > 6, a typical galaxy without an active galactic nucleus fails to form a proximity zone around itself due to the overdensity of the surrounding IGM. The gravitational infall motion in the IGM makes the resonance absorption extend to the red side of Lyα, suppressing the transmission up to roughly the circular velocity of the galaxy. In some sight lines, an optically thin blob generated by a supernova in a neighboring galaxy results in a peak feature, which can be mistaken for a blue peak. Redward of the resonance absorption, the damping-wing opacity correlates with the global IGM neutral fraction and the UV magnitude of the source galaxy. Brighter galaxies tend to suffer lower opacity because they tend to reside in larger H ii regions, and the surrounding IGM transmits redder photons, which are less susceptible to attenuation, owing to stronger infall velocity. The H ii regions are highly nonspherical, causing both sight-line-to-sight-line and galaxy-to-galaxy variation in opacity. Also, self-shielded systems within H ii regions strongly attenuate the emission for certain sight lines. All these factors add to the transmissivity variation, requiring a large sample size to constrain the average transmission. The variation is largest for fainter galaxies at higher redshift. The 68% range of the transmissivity is similar to or greater than the median for galaxies with M UV ≥ −21 at z ≥ 7, implying that more than a hundred galaxies would be needed to measure the transmission to 10% accuracy.