Surface Mass Density Research Articles

GALAXY STRUCTURE, STELLAR POPULATIONS, AND STAR FORMATION QUENCHING AT 0.6 ≲ z ≲ 1.2.

We use both photometric and spectroscopic data from the Hubble Space Telescope to explore the relationships among 4000 Å break (D4000) strength, colors, stellar masses, and morphology, in a sample of 352 galaxies with log(M */M ⊙) > 9.44 at 0.6 ≲ z ≲ 1.2. We have identified authentically quiescent galaxies in the UVJ diagram based on their D4000 strengths. This spectroscopic identification is in good agreement with their photometrically-derived specific star formation rates (sSFR). Morphologically, most (that is, 66 out of 68 galaxies, ~ 97 %) of these newly identified quiescent galaxies have a prominent bulge component. However, not all of the bulge-dominated galaxies are quenched. We found that bulge-dominated galaxies show positive correlations among the D4000 strength, stellar mass, and the Sérsic index, while late-type disks do not show such strong positive correlations. Also, bulge-dominated galaxies are clearly separated into two main groups in the parameter space of sSFR vs. stellar mass and stellar surface density within the effective radius, Σe, while late-type disks and irregulars only show high sSFR. This split is directly linked to the 'blue cloud' and the 'red sequence' populations, and correlates with the associated central compactness indicated by Σe. While star-forming massive late-type disks and irregulars (with D4000 < 1.5 and log(M */M ⊙) ≳ 10.5) span a stellar mass range comparable to bulge-dominated galaxies, most have systematically lower Σe ≲ 109 M ⊙kpc-2. This suggests that the presence of a bulge is a necessary but not sufficient requirement for quenching at intermediate redshifts.

Low Surface Brightness Galaxy catalogue selected from the α.40-SDSS DR7 Survey and Tully–Fisher relation

We present a catalogue of an HI-selected sample of 1129 low surface brightness galaxies (LSBGs) searched from the alpha.40-SDSS DR7 survey. This sample, consisting of various types of galaxies in terms of luminosity and morphology, has extended the parameter space covered by the existing LSBG samples. Based on a subsample of 173 LSBGs which are selected from our entire LSBG sample to have the 2-horn shapes of the HI line profiles, minor-to-major axial ratios (b/a) less than 0.6 and signal-to-noise ratio (S/N) of HI detection greater than 6.5, we investigated the Tully-Fisher relation (TFr) of LSBGs in the optical B, g and r bands and near-infrared J, H and K bands as well. In optical bands, the LSBG subsample follows the fundamental TFr which was previously defined for normal spiral galaxies. In NIR bands, the TFrs for our LSBG subsample are slightly different from the TFrs for the normal bright galaxies. This might be due to the internal extinction issue. Furthermore, the mass-to-light ratio (M/L),disk scale length (h) and mass surface density (sigma) for our LSBG subsample were deduced from the optical TFr results. Compared with High Surface Brightness Galaxies(HSBGs), our LSBGs have higher M/L, larger h and lower sigma than HSBGs.

The MOSDEF Survey: Stellar Continuum Spectra and Star Formation Histories of Active, Transitional, and Quiescent Galaxies at 1.4 &lt; z &lt; 2.6

Abstract Using the MOSFIRE Deep Evolution Field (MOSDEF) rest-frame optical spectroscopic survey, we investigate the star formation histories (SFHs) of different galaxy types, ranging from actively star-forming to quiescent at 1.4 ≤ z ≤ 2.6. SFHs are constrained utilizing stellar continuum spectroscopy, specifically through a combination of Balmer absorption lines, the 4000 Å break, and the equivalent width of the Hα emission line. To attain a sufficiently high signal-to-noise ratio (S/N) to conduct these measurements we stack spectra of galaxies with similar spectral types, as determined from their rest-frame U − V and V − J colors. We bin the MOSDEF sample into five spectral types, subdividing the quiescent and star-forming bins to better explore galaxies transitioning between the two. We constrain the average SFHs for each type, finding that quiescent and transitional galaxies in the MOSDEF sample are dominated by an SFH with an average star formation timescale of τ ∼ 0.1–0.2 Gyr. These findings contrast with measurements from the low-redshift Universe where, on average, galaxies form their stars over a more extended time period (τ &gt; 1 Gyr). Furthermore, our spectral index measurements correlate with mass surface density for all spectral types. Finally, we compare the average properties of the galaxies in our transitional bins to investigate possible paths to quiescence, and speculate on the viability of a dusty post-starburst phase.

Assessment of cortical bone material distribution in medial column of proximal humerus with computed tomography

Objective: To evaluate the cortical bone characteristics in the medial column of proximal humerus. Methods: A total of one hundred and three healthy adults who underwent shoulder computed tomography scanning in Tianjing Hospital were included in this study.The subjects were divided into three groups according to the age: group A (20-39 years), group B (40-59 years), and group C (>60 years). Cortical bone mapping (CBM) was used to analyze ordinary clinical CT scans using Stradwin 5.2 software.Colors thickness maps were created for each proximal humerus.The region of interest (ROI) 1-6 were set at three levels of the lateral and medial column of proximal humerus.Cortical thickness (CTh), cortical mass surface density (CMSD), and endocortical trabecular bone mineral density (ECTD) were assessed in the three slices in proximal metaphysis.The impact of age, gender to the cortical bone indices of medial column of proximal humerus were investigated with relative analysis.Cortical indices of the lateral and medial column were compared with independent samples t test. Results: In ROI 2 and 3, men had higher cortical bone values than women, and significant differences in ECTD and CMSD were found in ROI 2, 3 and ROI 2 (t=2.100, 2.238, 2.530, all P<0.05). The lineal regression analysis showed that all cortical indices in ROI 1-3 decreased significantly with age for both women and men (r(2)=0.042-0.248, all P<0.05). In group A-C, the medial columns had higher CTh and CMSD values than lateral sides in plane 1, although significant differences were found only in group A (t=3.696, 3.749, both P<0.05). The highest CTh, CMSD and ECTD of the medial compact bone was detected in ROI 1, followed by ROI 2 and 3 in group A (F=5.867, 6.776, 19.062, all P<0.05). The medial columns had approximately equivalent cortica indices values in ROI 1-3 in group B and C. Conclusion: It indicated that significant regional variation in all cortical parameters exists in the medial column of proximal humerus, and the indices are influenced by gender and age.

The Galactic Census of High- and Medium-mass Protostars. IV. Molecular Clump Radiative Transfer, Mass Distributions, Kinematics, and Dynamical Evolution

Abstract We present 12CO, 13CO, and C18O data as the next major release for the CHaMP project, an unbiased sample of Galactic molecular clouds in l = 280°–300°. From a radiative transfer analysis, we self-consistently compute 3D cubes of optical depth, excitation temperature, and column density for ∼300 massive clumps, and update the -dependent CO → H2 conversion law of Barnes et al. For N ∝ I p , we find p = 1.92 ± 0.05 for the velocity-resolved conversion law aggregated over all clumps. A practical, integrated conversion law is = (4.0 ± 0.3) × 1019 m−2 1.27±0.02, confirming an overall 2× higher total molecular mass for Milky Way clouds, compared to the standard X factor. We use these laws to compare the kinematics of clump interiors with their foreground 12CO envelopes, and find evidence that most clumps are not dynamically uniform: irregular portions seem to be either slowly accreting onto the interiors, or dispersing from them. We compute the spatially resolved mass accretion/dispersal rate across all clumps, and map the local flow timescale. While these flows are not clearly correlated with clump structures, the inferred accretion rate is a statistically strong function of the local mass surface density Σ, suggesting near-exponential growth or loss of mass over effective timescales ∼30–50 Myr. At high enough Σ, accretion dominates, suggesting gravity plays an important role in both processes. If confirmed by numerical simulations, this sedimentation picture would support arguments for long clump lifetimes mediated by pressure confinement, with a terminal crescendo of star formation, suggesting a resolution to the 40 year old puzzle of the dynamical state of molecular clouds and their low star formation efficiency.

Radiation pressure limits on the star formation efficiency and surface density of compact stellar systems

The large columns of dusty gas enshrouding and fuelling star-formation in young, massive stellar clusters may render such systems optically thick to radiation well into the infrared. This raises the prospect that both "direct" radiation pressure produced by absorption of photons leaving stellar surfaces and "indirect" radiation pressure from photons absorbed and then re-emitted by dust grains may be important sources of feedback in such systems. Here we evaluate this possibility by deriving the conditions under which a spheroidal, self-gravitating, mixed gas-star cloud can avoid catastrophic disruption by the combined effects of direct and indirect radiation pressure. We show that radiation pressure sets a maximum star cluster formation efficiency of $\epsilon_{\rm max} \sim 0.9$ at a (very large) gas surface density of $\sim 10^5 M_\odot$ pc$^{-2} (Z_\odot/Z) \simeq 20$ g cm$^{-2} (Z_\odot/Z)$, but that gas clouds above this limit undergo significant radiation-driven expansion during star formation, leading to a maximum stellar surface density very near this value for all star clusters. Data on the central surface mass density of compact stellar systems, while sparse and partly confused by dynamical effects, are broadly consistent with the existence of a metallicity-dependent upper-limit comparable to this value. Our results imply that this limit may preclude the formation of the progenitors of intermediate-mass black holes for systems with $Z \gtrsim 0.2 Z_\odot$.

Color gradients of the galaxies at 0.5 < z < 1 I. Dependence on galaxy global properties

We investigate the color gradients of galaxies at 0.5 < z < 1.0, using a sample of ∼35 000 galaxies with both spectroscopy from the final data release of the VIMOS Public Extragalactic Redshift Survey (VIPERS), and photometry in ultraviolet/optical/near-infrared bands from the VIPERS-Multi-Lambda Survey (VIPERS-MLS) and the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We estimate rest-frame colors, stellar mass, star formation rate from fitting the Spectral Energy Distribution (SED) for each galaxy, as well as a two-zone color Δ(u − r), defined as the difference in rest-frame (u − r) color between the outer and inner region of the galaxy. We find that the two-zone color shows weak or no correlations with all galaxy properties considered except stellar mass. On average, Δ(u − r) decreases with increasing stellar mass, indicating relatively red colors in galactic centers of more massive galaxies. We then compare the properties of “red-cored” and “blue-cored” galaxies, defined to have either a negative or a positive Δ(u − r) respectively. Although the two types of galaxies show similar distributions in most properties, we find massive red-cored galaxies with M* > 1010.5 M⊙ to have larger sizes at given stellar mass (thus lower surface mass densities), and less massive red-cored galaxies with M* < 1010.5 M⊙ to have lower central galaxy fraction. These findings can be understood if one assumes that the star formation process happens from inside out, in the same way as recently emphasized in studies of low-z galaxies. The similarity between the galaxies at intermediate redshifts and those at low redshifts supports the idea that galaxy evolution since z ∼ 1 has been mainly driven by secular processes internal to galaxies rather than galaxy mergers or external environment.

Connecting Compact Star-forming and Extended Star-forming Galaxies at Low Redshift: Implications for Galaxy Compaction and Quenching

Abstract Previous findings show that the existence of dense cores or bulges is the prerequisite for quenching a galaxy, leading to a proposed two-step quenching scenario: compaction and quenching. In this scenario, galaxies first grow their cores to a stellar mass surface density threshold, and subsequently quenching occurs, suggesting that galaxies evolve from extended star-forming galaxies (eSFGs), through compact star-forming galaxies (cSFGs), to a quenched population. In this work, we aim at examining the possible evolutionary link between eSFGs and cSFGs by identifying the trends in star formation rate (SFR), gas-phase metallicity, and H I content, since one would naturally expect that galaxies evolve along the track of cold gas consumption and metal enhancement. We select a volume-limited sample of 15,933 galaxies with stellar mass above and redshift of from the NASA Sloan Atlas catalog within the ALFALFA footprint. The cSFGs on average exhibit similar or slightly higher SFRs of ∼0.06 dex and significantly higher gas-phase metallicity (up to 0.2 dex at low mass) with respect to the eSFGs, while the cSFGs dominate the galaxy population of the most intense star formation activities. More importantly, overall the median H i content and gas depletion time of cSFGs are about half of eSFGs. Our result supports the compaction and quenching scenario that galaxies evolve and grow their cores along the track of cold gas consumption and metal enhancement. The environments of eSFGs and cSFGs are indistinguishable, suggesting that the compaction process is independent of any environmental effects at least for the low-redshift universe.

Nonlinear secondary resonance of nanobeams under subharmonic and superharmonic excitations including surface free energy effects

• Size-dependent nonlinear hard oscillation of nanobeams. • Surface free energy effects on the nonlinear secondary resonance of nanobeam with various end supports. • Size-dependent frequency-response of a nanobeam for the both of subharmonic and superharmonic excitations. • Size-dependent amplitude-response of a nanobeam for the both of subharmonic and superharmonic excitations. The main objective of this study is to predict both the subharmonic and superharmonic resonances of the nonlinear oscillation of nanobeams in the presence of surface free energy effects. To this purpose, Gurtin–Murdoch elasticity theory is adopted to the classical beam theory in order to consider the surface Lame constants , surface mass density, and residual surface stress within the differential equations of motion. The Galerkin method together with the method of multiple scales is utilized to investigate the size-dependent response of nanobeams under hard excitations corresponding to various boundary conditions. A parametric analysis is carried out to indicate the influence of the surface elastic parameters on the frequency-response as well as amplitude-response of the nonlinear secondary resonance including multiple vibration modes and interactions between them. It is seen that for the superharmonic excitation, except for the clamped–free boundary condition, the jump phenomenon is along the hardening direction, while in the clamped–free end supports, it is along the softening direction. Moreover, it is revealed that for the subharmonic excitation, within a specific range of the excitation amplitude, the nanobeam is excited, and this range shifts to lower external force by incorporating the surface free energy effects. It is found that in the case of superharmonic excitation, the value of the excitation frequency associated with the bifurcation point at the peak of the frequency-response curve increases by taking the surface free energy effect into consideration.

ALMA Observations toward the Starburst Dwarf Galaxy NGC 5253. I. Molecular Cloud Properties and Scaling Relations

Abstract We present high-spatial-resolution (∼0.″2, or ∼3 pc) CO(2–1) observations of the nearest young starburst dwarf galaxy, NGC 5253, taken with the Atacama Large Millimeter/submillimeter Array. We have identified 118 molecular clouds with average values of 4.3 pc in radius and 2.2 km s−1 in velocity dispersion, which comprise the molecular cloud complexes observed previously with ∼100 pc resolution. We derive for the first time in this galaxy the I(CO)–N(H2) conversion factor, cm−2(K km s−1)−1, based on the virial method. The line width and mass-to-size relations of the resolved molecular clouds present an offset on average toward higher line widths and masses with respect to quiescent regions in other nearby spiral galaxies and our Galaxy. The offset in the scaling relation reaches its maximum in regions close to the central starburst, where velocity dispersions are ∼0.5 dex higher and gas mass surface densities are as high as . These central clouds are gravitationally bound despite the high internal pressure. A spatial comparison with star clusters found in the literature enables us to identify six clouds that are associated with young star clusters. Furthermore, the star formation efficiencies (SFEs) of some of these clouds exceed those found in star-cluster-forming clouds within our Galaxy. We conclude that once a super star cluster is formed, the parent molecular clouds are rapidly dispersed by the destructive stellar feedback, which results in such a high SFE in the central starburst of NGC 5253.

VLA multi-wavelength microwave observations of Saturn's C and B rings

We present multi-wavelength VLA observations in the microwave of Saturn's rings. The data were obtained over two observational windows and cover a range from the Q to S bands (0.7–13 cm). Key ring particle properties are determined in the C and B rings such as particle porosity and non-icy material fraction in order to compare them directly with previously derived results using the 2-cm Cassini RADAR radiometry data (Zhang et al., 2017a, b). We confirm that these new data are consistent with the particles in the C ring being quite porous with porosity values of roughly 75–90% depending on different scattering phase functions, as well as the presence of a “hot band” in the middle C ring which is associated with both an anomalously high non-icy material fraction and low opacity relative to the rest of the C ring. Furthermore, with our multi-wavelength study we find that the amount of intrinsic thermal emission is almost constant with wavelength, which is unexpected since particles tend to become more absorbing at higher frequencies. If we assume that the non-icy material in the rings is intramixed within the ring particles, this result suggests a corresponding decrease in the imaginary part of the non-icy material dielectric constant at higher frequencies, which is most noticeable in the middle C ring. We do not see evidence for such decrease in the B ring particles. If true, this supports the idea that the non-icy material in the middle C ring has a different origin, and that the larger particles in the middle C ring may be composed of a rocky core covered by a porous, icy mantle. If the non-icy materials in the middle C ring are embedded as large chunks, a core-mantle model for the ring particles there naturally explains this almost constant intrinsic thermal emission. Furthermore, because the VLA has more complete azimuthal angle coverage than the Cassini radiometry observations, we are able to investigate the ring brightness in more detail. In particular, we notice a flatter scattering profile than that predicted by using a pure Mie phase function at higher frequencies (Q and K bands; 0.7–1.3 cm) for azimuthal angles between |40|o and |60|o. We can match the observed scattering profile better by introducing a semi-empirical phase function for large particles to account for nonsphericity effects. Finally, the non-icy material fraction in the B ring is less than 1%, which is in agreement with that derived from Cassini observations. The frequency-dependence of the B ring thermal emission sets the lower limit of B ring particle porosity. We confirm that the B ring particles are likely over 80% porous, which at the same time explains the high opacity in the B ring as measured from density waves. Because we are limited by the signal-to-noise ratio, the optical depth of the middle B ring could be higher than the currently accepted values. However, we found that even if the middle B ring is six times more optically thick than the value measured from UVIS occultations, the surface mass density is still likely to be less than 300 g/cm2, while the exposure time to non-icy pollutants due to micrometeoroid bombardment is less than 200 Myr.

Delayed Stellar Mass Assembly in the Low Surface Brightness Dwarf Galaxy KDG 215∗

Abstract We present H i spectral line and optical broadband images of the nearby low surface brightness dwarf galaxy KDG 215. The H i images, acquired with the Karl G. Jansky Very Large Array, reveal a dispersion-dominated interstellar medium with only weak signatures of coherent rotation. The H i gas reaches a peak mass surface density of 6 M ⊙ pc−2 at the location of the peak surface brightness in the optical and the ultraviolet. Although KDG 215 is gas-rich, the Hα non-detection implies a very low current massive star formation rate. In order to investigate the recent evolution of this system, we have derived the recent and lifetime star formation histories from archival Hubble Space Telescope images. The recent star formation history shows a peak star formation rate ∼1 Gyr ago, followed by a decreasing star formation rate to the present day quiescent state. The cumulative star formation history indicates that a significant fraction of the stellar mass assembly in KDG 215 has occurred within the last 1.25 Gyr. KDG 215 is one of only a few known galaxies that demonstrates such a delayed star formation history. While the ancient stellar population (predominantly red giants) is prominent, the look-back time by which 50% of the mass of all stars ever formed had been created is among the youngest of any known galaxy.

Stellar Mass Distribution and Star Formation History of the Galactic Disk Revealed by Mono-age Stellar Populations from LAMOST

We present a detailed determination and analysis of 3D stellar mass distribution of the Galactic disk for mono-age populations using a sample of 0.93 million main-sequence turn-off and subgiant stars from the LAMOST Galactic Surveys. Our results show (1) all stellar populations younger than 10\,Gyr exhibit strong disk flaring, which is accompanied with a dumpy vertical density profile that is best described by a $sech^n$ function with index depending on both radius and age; (2) Asymmetries and wave-like oscillations are presented in both the radial and vertical direction, with strength varying with stellar populations; (3) As a contribution by the Local spiral arm, the mid-plane stellar mass density at solar radius but 400--800\,pc (3--6$^\circ$) away from the Sun in the azimuthal direction has a value of $0.0594\pm0.0008$\,$M_\odot$/pc$^3$, which is 0.0164\,$M_\odot$/pc$^3$ higher than previous estimates at the solar neighborhood. The result causes doubts on the current estimate of local dark matter density; (4) The radial distribution of surface mass density yields a disk scale length evolving from $\sim$4\,kpc for the young to $\sim$2\,kpc for the old populations. The overall population exhibits a disk scale length of $2.48\pm0.05$\,kpc, and a total stellar mass of $3.6(\pm0.1)\times10^{10}$\,$M_\odot$ assuming $R_{\odot}=8.0$\,kpc, and the value becomes $4.1(\pm0.1)\times10^{10}$\,$M_\odot$ if $R_{\odot}=8.3$\,kpc; (5) The disk has a peak star formation rate ({\rm SFR}) changing from 6--8\,Gyr at the inner to 4--6\,Gyr ago at the outer part, indicating an inside-out assemblage history. The 0--1\,Gyr population yields a recent disk total {\rm SFR} of $1.96\pm0.12$\,$M_\odot$/yr.

Numerical computation of gravitational field of infinitely-thin axisymmetric disc with arbitrary surface mass density profile and its application to preliminary study of rotation curve of M33

AbstractWe developed a numerical method[-70pt] to compute the gravitational field of an infinitely-thin axisymmetric disc with an arbitrary surface mass density profile. We evaluate the gravitational potential by a split quadrature using the double exponential rule and obtain the acceleration vector by numerically differentiating the potential by Ridders’ algorithm. By using the new method, we show the rotation curves of some non-trivial discs: (i) truncated power-law discs, (ii) discs with a non-negligible center hole, (iii) truncated Mestel discs with edge-softening, (iv) double power-law discs, (v) exponentially-damped power-law discs, and (vi) an exponential disc with a sinusoidal modulation of the density profile. Also, we present a couple of model fittings to the observed rotation curve of M33: (i) the standard deconvolution by assuming a spherical distributin of the dark matter and (ii) a direct fit of infinitely-thin disc mass with a double power-law distribution of the surface mass density.

The Relation between H I Gas and Star Formation Properties in Nearby Galaxies

In this paper, we present some correlations of neutral hydrogen (H i) gas and physical properties of galaxies to investigate the role of atomic gas in governing galaxy evolution. We build a H i-detected sample including 70 galaxies that are detected by ALFALFA in a 15 deg2 region, and derive their star formation distribution based on the images of Hα narrowband observed here. In general, H i-detected galaxies have low surface density of stellar mass and active star formation. Additionally, most of the galaxies are in good agreement with the star-forming main sequence, consistent with the previous findings. We confirm the dependence of star formation (SF) in galaxies on H i gas at least on global scale, i.e., star formation rate (SFR) generally increases with H i mass, specific star formation rate (SSFR ≡ SFR/M*) increases with H i fraction (fH i) even for a given stellar mass, and H i-based star formation efficiency (SFE) mildly increases with the stellar mass and SFR surface density. Based on the distribution of stellar mass and star formation, we calculate the morphology indices of the sample, and analyze the dependence of fH i and SFE on them. The weak correlations between SFE and morphological indexes imply a weak physical link between H i and star formation in small scale. We find that fH i mildly increases with the asymmetry and decreases with the concentration of galaxies, suggesting that the H i gas supply and its effect are likely correlated with external processes in the extended disks of galaxies.

Cassini-VIMS observations of Saturn’s main rings: II. A spectrophotometric study by means of Monte Carlo ray-tracing and Hapke’s theory

This work is the second in a series of manuscripts devoted to the investigation of the spectrophotometric properties of Saturn’s rings from Cassini-VIMS (Visible and Infrared Mapping Spectrometer) observations. The dataset used for this analysis is represented by ten radial spectrograms of the rings which have been derived in Filacchione et al. (2014) by radial mosaics produced by VIMS. Spectrograms report the measured radiance factor I/F of the main rings of Saturn as a function of both radial distance (from 73500 to 141375 km) and wavelength (0.35–5.1 µm) for different observation geometries (phase angle ranging in the 2°–132° interval). We take advantage of a Monte Carlo ray-tracing routine (Ciarniello et al., 2014) to characterize the photometric behavior of the rings at each wavelength and derive the spectral Bond albedo of ring particles. This quantity is used to infer the composition of the regolith covering ring particles by applying Hapke’s theory. Four different regions, characterized by different optical depths, and respectively located in the C ring, inner B ring, mid B ring and A ring, have been investigated. Results from photometric modeling indicate that, in the VIS-NIR spectral range, B ring particles are intrinsically brighter than A and C ring particles, with the latter having the lowest albedo, while the single particle phase function of the ring’s particles is compatible with an Europa-like or Callisto-like formulation, depending on the investigated region. Spectral modeling of the inferred Bond albedo indicates that ring spectrum can be reproduced by water ice grains with inclusion of organic materials (tholin) as a UV absorber intimately mixed with variable amounts of other compounds in pure form (carbon, silicates) or embedded in water ice grains (nanophase hydrated iron oxides, carbon, silicates, crystalline hematite, metallic iron, troilite). The abundance of tholin decreases with radial distance from C ring (0.2–0.6%) to A ring (0.06%) for the selected regions. Its distribution is compatible with an intrinsic origin and is possibly related to the different plasma environment of the different ring regions. The identification of the other absorber(s) and its absolute volumetric abundance is uncertain, depending on the adopted grain size and mixing modality (intraparticle or intimate). However, assuming a common composition of the other absorber in the ring plane, we find that its abundance anti-correlates with the optical depth of the investigated regions, being maximum in the thinnest C ring and minimum in the thickest mid B ring. In the case of the C ring, an additional population of low-albedo grains is required to match the positive spectral slope of the continuum in the 0.55–2.2 µm interval, represented by an intraparticle mixture of water ice and a spectrum similar to troilite or metallic iron. The distribution of the darkening compounds is interpreted as the result of a contamination by exogenous material, which is more effective in the less dense regions of the rings because of their lower surface mass density of pure water ice.

Quantifying Embolism: Label‐Free Volumetric Mapping of Thrombus Structure and Kinesis in a Microfluidic System with Optical Holography

AbstractEmbolization of thrombotic material may lead to acute events such as ischemia and myocardial infarction. The embolus is the physical detachment from a primary thrombus that has developed under fluid shear rates. The physical characteristics (surface area coverage, volume, mass, and packing density) of a thrombus influence the overall flow dynamics of an occluding blood vessel. Here, the effectiveness of holographic quantitative phase microscopy (QPM) in identifying multiple morphological parameters of a thrombus (volume, surface area, and height) formed over collagen‐coated microfluidic channels by exerting a range of shear rates with anticoagulated platelet‐rich plasma (PRP) and whole blood is demonstrated. QPM enables the recording of entire thrombus volumes in real‐time using PRP and observed both growth and contraction trends of thrombi, without need for biochemical labeling. The process of emboli detachment in a microfluidic channel under pathophysiological shear rates (7500 and 12 500 s−1) is quantified. Rapid and direct quantification of an embolizing thrombus can enable the study of events during undesirable vessel occlusion and lead to targeting and early diagnosis of acute coronary and venous events.

A detection of the environmental dependence of the sizes and stellar haloes of massive central galaxies

We use ~100 square deg of deep (>28.5 mag arcsec$^{-2}$ in i-band), high-quality (median 0.6 arcsec seeing) imaging data from the Hyper Suprime-Cam (HSC) survey to reveal the halo mass dependence of the surface mass density profiles and outer stellar envelopes of massive galaxies. The i-band images from the HSC survey reach ~4 magnitudes deeper than Sloan Digital Sky Survey and enable us to directly trace stellar mass distributions to 100 kpc without requiring stacking. We conclusively show that, at fixed stellar mass, the stellar profiles of massive galaxies depend on the masses of their dark matter haloes. On average, massive central galaxies with $\log M_{\star, 100\ \mathrm{kpc}}>11.6$ in more massive haloes at 0.3 < z < 0.5 have shallower inner stellar mass density profiles (within ~10-20 kpc) and more prominent outer envelopes. These differences translate into a halo mass dependence of the mass-size relation. Central galaxies in haloes with $\log M_{\rm{Halo}}>14.0$ are ~20% larger in $R_{\mathrm{50}}$ at fixed stellar mass. Such dependence is also reflected in the relationship between the stellar mass within 10 and 100 kpc. Comparing to the mass--size relation, the $\log M_{\star, 100\ \rm{kpc}}$-$\log M_{\star, 10\ \rm{kpc}}$ relation avoids the ambiguity in the definition of size, and can be straightforwardly compared with simulations. Our results demonstrate that, with deep images from HSC, we can quantify the connection between halo mass and the outer stellar halo, which may provide new constraints on the formation and assembly of massive central galaxies.

The Stellar Halo of the Spiral Galaxy NGC 1560

Abstract We report on the detection of a stellar halo around NGC 1560, a 109 M ⊙ spiral galaxy member of the Maffei group. We obtained deep images in the r- and i-bands using the 10.4 m Gran Telescopio Canarias in a field centered at ∼3.7 arcmin (projected distance of 3.5 kpc) from the center of this galaxy. The luminosity function and the color–magnitude diagram show a clear excess of stars with respect to the expected foreground level at magnitudes fainter than the red giant branch tip at the distance of NGC 1560. The colors of the halo stars imply a metallicity of Z ∼ Z ⊙/50, while their counts correspond to a stellar mass of ∼107 M ⊙ in the sampled region. Assuming a power-law profile for the surface mass density of the halo, our data suggest a total stellar mass of 108 M ⊙ for the halo of NGC 1560.

SEAGLE – I. A pipeline for simulating and modelling strong lenses from cosmological hydrodynamic simulations

In this paper we introduce the SEAGLE (i.e. Simulating EAGLE LEnses) program, that approaches the study of galaxy formation through strong gravitational lensing, using a suite of high-resolution hydrodynamic simulations, Evolution and Assembly of GaLaxies and their Environments (EAGLE) project. We introduce the simulation and analysis pipeline and present the first set of results from our analysis of early-type galaxies. We identify and extract an ensemble of simulated lens galaxies and use the GLAMER ray-tracing lensing code to create mock lenses similar to those observed in the SLACS and SL2S surveys, using a range of source parameters and galaxy orientations, including observational effects such as the Point-Spread-Function (PSF), pixelization and noise levels, representative of single-orbit observations with the Hubble Space Telescope (HST) using the ACS-F814W filter. We subsequently model these mock lenses using the code LENSED, treating them in the same way as observed lenses. We also estimate the mass model parameters directly from the projected surface mass density of the simulated galaxy, using an identical mass model family. We perform a three-way comparison of all the measured quantities with real lenses. We find the average total density slope of EAGLE lenses, $t=2.26\; (0.25\; \rm{rms})$ to be higher than SL2S, $t=2.16$ or SLACS, $t=2.08$. We find a very strong correlation between the external shear ($\gamma$) and the complex ellipticity ($\epsilon$), with $\gamma \sim \epsilon/4$. This correlation indicates a degeneracy in the lens mass modeling. We also see a dispersion between lens modeling and direct fitting results, indicating systematical biases.