Mass-size Relation Research Articles

UNCOVER: Illuminating the Early Universe—JWST/NIRSpec Confirmation of z > 12 Galaxies

Observations of high-redshift galaxies provide a critical direct test to the theories of early galaxy formation, yet to date, only three have been spectroscopically confirmed at z > 12. Due to strong gravitational lensing over a wide area, the galaxy cluster field A2744 is ideal for searching for the earliest galaxies. Here we present JWST/NIRSpec observations of two galaxies: a robust detection at , and a plausible candidate at . The galaxies are discovered in JWST/NIRCam imaging and their distances are inferred with JWST/NIRSpec spectroscopy, all from the JWST Cycle 1 UNCOVER Treasury survey. Detailed stellar population modeling using JWST NIRCam and NIRSpec data corroborates the primeval characteristics of these galaxies: low mass (∼108 M ⊙), young, rapidly assembling, metal-poor, and star-forming. Interestingly, both galaxies are spatially resolved, having lensing-corrected rest-UV effective radii on the order of 300–400 pc, which are notably larger than other spectroscopically confirmed systems at similar redshifts. The observed dynamic range of z ≳ 10 sizes spans over 1 order of magnitude, implying a significant scatter in the size–mass relation at early times. Deep into the epoch of reionization, these discoveries elucidate the emergence of the first galaxies.

Low-mass Quiescent Galaxies Are Small in Isolated Environments: Environmental Dependence of the Mass–Size Relation of Low-mass Quiescent Galaxies

We study the mass–size relation of quiescent galaxies across various environments, with a particular focus on its environmental dependence at the low-mass part of . Our sample consists of 13,667 quiescent galaxies with and 0.01 < z < 0.04 from the Sloan Digital Sky Survey. We discover that the mass–size relation of low-mass quiescent galaxies (LQGs) with depends on their environment, with LQGs in the highest-density environments exhibiting an average size ∼70% larger than those in isolated environments. Moreover, the slope of the mass–size relation for LQGs in high-density environments is significantly shallower than that of their counterparts in isolated environments. This is in contrast with high-mass quiescent galaxies with that show a nearly identical mass–size relation across all environments. Combined with additional discoveries that the mass–size relation slopes of LQGs and star-forming galaxies are similar to each other in high-density environments, and that LQGs in higher-density environments exhibit more disk-like structures, our results support the idea that LQGs in high-density environments have evolved from star-forming galaxies through environmental effects, which are capable of causing their quenching and transformation into quiescent galaxies. With the aid of an analysis of merger rates for simulated galaxies from a cosmological galaxy formation simulation, we suggest that the steep slope and low normalization of the mass–size relation of LQGs in the lowest-density environments may originate from recent gas-rich mergers, which occur over 10–30 times more frequently in the progenitors of LQGs in the lowest-density environments than in their counterparts in high-density environments at low redshifts.

Fragmentation and dynamics of dense gas structures in the proximity of massive young stellar object W42-MME

ABSTRACT We present an analysis of the dense gas structures in the immediate surroundings of the massive young stellar object (MYSO) W42-MME, using the high-resolution (0″.31 × 0″.25) Atacama Large Millimetre/submillimetre Array dust continuum and molecular line data. We performed a dendrogram analysis of H13CO+ (4–3) line data to study multiscale structures and their spatio–kinematic properties, and analysed the fragmentation and dynamics of dense structures down to ∼2000 au scale. Our results reveal 19 dense gas structures, out of which 12 are leaves and 7 are branches in dendrogram terminology. These structures exhibit transonic–supersonic gas motions (1$\lt \mathcal {M}\lt 5$) with overvirial states (αvir ≥ 2). The non-thermal velocity dispersion–size relation (σnt–L) of dendrogram structures shows a weak negative correlation, while the velocity dispersion across the sky ($\delta \mathit {V_{\rm lsr}}$) correlates positively with structure size (L). Velocity structure function (S2(l)1/2) analysis of H13CO+ data reveals strong power-law dependences with lag (l) up to a scale length of ≲6000 au. The mass–size (M–R) relation of dendrogram structures shows a positive correlation with power-law index of 1.73 ± 0.23, and the leaf L17 hosting W42-MME meets the mass–size conditions for massive star formation. Blue asymmetry is observed in the H12CO+ (4–3) line profiles of most of the leaves, indicating infall. Overall, our results observationally support the hierarchical and chaotic collapse scenario in the proximity of the MYSO W42-MME.

Bridging the gap in the mass–size relation of compact galaxies with MaNGA

ABSTRACT We present the analysis of the full Mapping Nearby Galaxies at APO (MaNGA) DR17 sample to characterize its population of compact galaxies. We focus on galaxies that fill the stellar mass (M⋆) gap between compact elliptical galaxies (cEs; 8 ≲ log (M⋆/M⊙) ≲ 10) and compact massive galaxies (CMGs; 10 ≲ log (M⋆/M⊙)). We study their stellar populations and kinematics to reveal how their properties depend on stellar mass. We select compact galaxies in the MaNGA DR17 sample according to their effective radius (Re) and stellar mass. 37 galaxies fulfill our selection criteria in the bridging region between cEs and CMGs. We derive their kinematics and stellar population parameters from the stacked spectra at 1 Re using a full spectral fitting routine. We then classify the selected compact galaxies in three main groups based on their stellar population properties. One of the groups shows characteristics compatible with relic galaxies, i.e. galaxies that have remained mostly unchanged since their early formation epoch (z ∼ 2). Another group shows more extended and continuous star formation histories (SFHs). The third group shows a low star-forming rate at initial times, which increases at around ∼4 Gyr. We compare the derived properties of the selected galaxies with those of previously studied compact galaxies at different mass ranges. The selected galaxies successfully fill the mass gap between cEs and CMGs. Their properties are compatible with the assumption that the scaling relations of compact galaxies at different mass ranges are related, although galaxies in the first group are clear outliers in the fundamental plane, suggesting different formation mechanisms for this relic population.

Stellar mass dependence of galaxy size–dark matter halo radius relation probed by Subaru-HSC survey weak lensing measurements

ABSTRACT We investigate the stellar mass dependence of the galaxy size–dark matter halo radius relation for low-redshift galaxies using weak gravitational lensing measurements. Our sample consists of ∼38 000 galaxies more massive than $10^{8}\, {\rm M}_{\odot }\, h^{-2}$ and within z &amp;lt; 0.3 drawn from the overlap of Galaxy And Mass Assembly survey data release 4 and HSC-SSP PDR2. We divide our sample into a number of stellar mass bins and measure stacked weak lensing signals. We model the signals using a conditional stellar mass function to infer the stellar mass–halo mass relation. We fit a single Sérsic model to HSC i-band images of our galaxies and obtain their three-dimensional half-light radii. We use these measurements to construct a median galaxy size–mass relation. We then combine these relations to infer the galaxy size–halo radius relation. We confirm that this relation appears linear, given the statistical errors, i.e. the ratio of galaxy size to halo radius remains constant over two orders of magnitudes in stellar mass above $\sim 10^{9} \, {\rm M}_{\odot }\, h^{-2}$. Extrapolating the stellar mass–halo mass relation below this limit, we see an indication of a decreasing galaxy size–halo radius ratio with the decline in stellar mass. At stellar mass $\sim 10^{8} \, {\rm M}_{\odot }\, h^{-2}$, the ratio becomes 30 per cent smaller than its value in linear regime. The possible existence of a such trend in dwarf galaxy sectors calls for either modification in models employing a constant fraction of halo angular momentum transferred to explain sizes of dwarfs or else points towards our lack of knowledge about dark matter haloes of low-mass galaxies.

First light and reionization epoch simulations (FLARES) IX: the physical mechanisms driving compact galaxy formation and evolution

ABSTRACT In the First Light And Reionization Epoch Simulations (Flares) suite of hydrodynamical simulations, we find the high-redshift (z &amp;gt; 5) intrinsic size–luminosity relation is, surprisingly, negatively sloped. However, after including the effects of dust attenuation, we find a positively sloped UV observed size–luminosity relation in good agreement with other simulated and observational studies. In this work, we extend this analysis to probe the underlying physical mechanisms driving the formation and evolution of the compact galaxies driving the negative size–mass/size–luminosity relation. We find the majority of compact galaxies (R1/2, ⋆ &amp;lt; 1 pkpc, which drive the negative slope of the size–mass relation, have transitioned from extended to compact sizes via efficient centralized cooling, resulting in high specific star formation rates in their cores. These compact stellar systems are enshrouded by non-star-forming gas distributions as much as 100 times larger than their stellar counterparts. By comparing with galaxies from the Eagle simulation suite, we find that these extended gas distributions ‘turn on’ and begin to form stars between z = 5 and 0 leading to increasing sizes, and thus the evolution of the size–mass relation from a negative to a positive slope. This explicitly demonstrates the process of inside-out galaxy formation in which compact bulges form earlier than the surrounding discs.

Beyond Ultra-diffuse Galaxies. I. Mass–Size Outliers among the Satellites of Milky Way Analogs

Large diffuse galaxies are hard to find, but understanding the environments where they live, their numbers, and ultimately their origins, is of intense interest and importance for galaxy formation and evolution. Using Subaru’s Hyper Suprime-Cam Strategic Survey Program, we perform a systematic search for low surface brightness galaxies and present novel and effective methods for detecting and modeling them. As a case study, we surveyed 922 Milky Way analogs in the nearby Universe (0.01 < z < 0.04) and built a large sample of satellite galaxies that are outliers in the mass–size relation. These “ultra-puffy” galaxies (UPGs), defined to be 1.5σ above the average mass–size relation, represent the tail of the satellite size distribution. We find that each MW analog hosts N UPG = 0.31 ± 0.05 UPGs on average, which is consistent with but slightly lower than the observed abundance at this halo mass in the Local Volume. We also construct a sample of ultra-diffuse galaxies (UDGs) in MW analogs and find an abundance of N UDG = 0.44 ± 0.05 per host. With literature results, we confirm that the UDG abundance scales with the host halo mass following a sublinear power law. We argue that our definition of UPGs, which is based on the mass–size relation, is more physically motivated than the common definition of UDGs, which depends on the surface brightness and size cuts and thus yields different surface mass density cuts for quenched and star-forming galaxies.

A stochastic model leading to various particle mass distributions including the RRSB distribution

Modern particle size statistics uses many different statistical distributions, but these distributions are empirical approximations for theoretically unknown relationships. This also holds true for the famous RRSB (Rosin-Rammler-Sperling-Bennett) distribution. Based on the compound Poisson process, this paper introduces a simple stochastic model that leads to a general product form of particle mass distributions. The beauty of this product form is that its two factors characterize separately the two main components of samples of particles, namely, individual particle masses and total particle number. The RRSB distribution belongs to the class of distributions following the new model. Its simple product form can be a starting point for developing new particle mass distributions. The model is applied to the statistical analysis of samples of blast-produced fragments measured by hand, which enables a precise investigation of the mass-size relationship. This model-based analysis leads to plausible estimates of the mass and size factors and helps to understand the influence of blasting conditions on fragment-mass distributions.

KURVS: the outer rotation curve shapes and dark matter fractions of z ∼ 1.5 star-forming galaxies

ABSTRACT We present first results from the KMOS Ultra-deep Rotation Velocity Survey (KURVS), aimed at studying the outer rotation curves shape and dark matter content of 22 star-forming galaxies at z ∼ 1.5. These galaxies represent ‘typical’ star-forming discs at z ∼ 1.5, being located within the star-forming main sequence and stellar mass-size relation with stellar masses 9.5 ≤ log(M⋆/M⊙) ≤ 11.5. We use the spatially resolved H α emission to extract individual rotation curves out to 4 times the effective radius, on average, or ∼10–15 kpc. Most rotation curves are flat or rising between three and six disc scale radii. Only three objects with dispersion-dominated dynamics (vrot/σ0 ∼ 0.2) have declining outer rotation curves at more than 5σ significance. After accounting for seeing and pressure support, the nine rotation-dominated discs with vrot/σ0 ≥ 1.5 have average dark matter fractions of $50 \pm 20{{\ \rm per\ cent}}$ at the effective radius, similar to local discs. Together with previous observations of star-forming galaxies at cosmic noon, our measurements suggest a trend of declining dark matter fraction with increasing stellar mass and stellar mass surface density at the effective radius. Measurements of simulated EAGLE galaxies are in quantitative agreement with observations up to log$(M_{\star } R_{\rm eff}^{-2} /\mathrm{M_{\odot } kpc^{-2}}) \sim 9.2$, and overpredict the dark matter fraction of galaxies with higher mass surface densities by a factor of ∼3. We conclude that the dynamics of typical rotationally-supported discs at z ∼ 1.5 is dominated by dark matter from effective radius scales, in broad agreement with cosmological models. The tension with observations at high stellar mass surface density suggests that the prescriptions for baryonic processes occurring in the most massive galaxies (such as bulge growth and quenching) need to be reassessed.

Accelerated Structural Evolution of Galaxies in a Starbursting Cluster at z = 2.51

Structural properties of cluster galaxies during their peak formation epoch, z ∼ 2–4 provide key information on whether and how the environment affects galaxy formation and evolution. Based on deep Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) imaging toward the z = 2.51 cluster, J1001, we explore environmental effects on the structure, color gradients, and stellar populations of a statistical sample of cluster star-forming galaxies (SFGs). We find that the cluster SFGs are on average smaller than their field counterparts. This difference is most pronounced at the high-mass end (M ⋆ > 1010.5 M ⊙), with nearly all of them lying below the mass–size relation of field galaxies. The high-mass cluster SFGs are also generally old, with a steep negative color gradient, indicating an early formation time likely associated with strong dissipative collapse. For low-mass cluster SFGs, we unveil a population of compact galaxies with steep positive color gradients that are not seen in the field. This suggests that the low-mass compact cluster SFGs may have already experienced strong environmental effects, e.g., tidal/ram pressure stripping, in this young cluster. These results provide evidence on the environmental effects at work in the earliest formed clusters with different roles in the formation of low- and high-mass galaxies.

Initial sizes of star clusters: implications for cluster dissolution during galaxy evolution

ABSTRACT Massive star clusters are often used as tracers of galaxy formation and assembly. In order to do so, we must understand their properties at formation, and how those properties change with time, galactic environment, and galaxy assembly history. The two most important intrinsic properties that govern star cluster evolution are mass and radius. In this paper, we investigate 10 theoretically and observationally motivated initial size–mass relations for star clusters, and evolve populations of clusters through galaxy formation models. We compare our results to each other and to observations of cluster populations in M83, M31, and the Milky Way. We find that none of our size–mass relations agree with the observations after 6–10 Gyr of evolution. We can successfully reproduce the cluster mass functions with models that have a small range of initial radii, and which do not allow cluster radii to change with time. However, these models do not agree with our understanding of cluster evolution, which does involve radius evolution, and do not match the observed distributions of radii. We note that there is a region of parameter space where clusters are optimally protected from both tidal shocks and evaporation due to two-body relaxation. Clusters that are allowed to evolve into this parameter space will likely survive. An improved understanding of both mass and radius evolution of star clusters in realistic, time-varying galactic potentials is necessary to appropriately make the connection between present-day cluster properties and their use as tracers of galaxy formation and assembly.

Unveiling the gravitationally unstable disc of a massive star-forming galaxy using NOEMA and MUSE

ABSTRACT Using new high-resolution data of CO (2–1), H$\alpha$ and H$\beta$ obtained with the Northern Extended Millimeter Array (NOEMA) and the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope, we have performed a Toomre Q disc stability analysis and studied star formation, gas depletion times and other environmental parameters on sub-kpc scales within the z ∼ 0 galaxy SDSS J125013.84+073444.5 (LARS 8). The galaxy hosts a massive, clumpy disc and is a proto-typical analogue of main-sequence galaxies at z ∼ 1 − 2. We show that the massive (molecular) clumps in LARS 8 are the result of an extremely gravitationally unstable gas disc, with large scale instabilities found across the whole extent of the rotating disc, with only the innermost 500 pc being stabilized by its bulge-like structure. The radial profiles further reveal that – contrary to typical disc galaxies – the molecular gas depletion time decreases from more than 1 Gyr in the centre to less than ∼100 Myr in the outskirts of the disc, supporting the findings of a Toomre-unstable disc. We further identified and analysed 12 individual massive molecular clumps. They are virialized and follow the mass–size relation, indicating that on local (cloud/clump) scales the stars form with efficiencies comparable to those in Milky Way clouds. The observed high star formation rate must thus be the result of triggering of cloud/clump formation over large scales due to disc instability. Our study provides evidence that ‘in-situ’ massive clump formation (as also observed at high redshifts) is very efficiently induced by large-scale instabilities.

3D Modeling of the Molecular Gas Kinematics in Optically Selected Jellyfish Galaxies

Cluster galaxies are subject to the ram pressure exerted by the intracluster medium, which can perturb or even strip away their gas while leaving the stars undisturbed. We model the distribution and kinematics of the stars and the molecular gas in four late-type cluster galaxies (JO201, JO204, JO206, and JW100), which show tails of atomic and ionized gas indicative of ongoing ram pressure stripping. We analyze MUSE@VLT data and CO data from the Atacama Large Millimeter Array searching for signatures of radial gas flows, ram pressure stripping, and other perturbations. We find that all galaxies, with the possible exception of JW100, host stellar bars. Signatures of ram pressure are found in JO201 and JO206, which also shows clear indications of ongoing stripping in the molecular disk outskirts. The stripping affects the whole molecular gas disk of JW100. The molecular gas kinematics in JO204 is instead dominated by rotation rather than ram pressure. We also find indications of enhanced turbulence of the molecular gas compared to field galaxies. Large-scale radial flows of molecular gas are present in JO204 and JW100, but more uncertain in JO201 and JO206. We show that our sample follows the molecular gas mass–size relation, confirming that it is essentially independent of environment even for the most extreme cases of stripping. Our findings are consistent with the molecular gas being affected by the ram pressure on different timescales and less severely than the atomic and ionized gas phases, likely because the molecular gas is denser and more gravitationally bound to the galaxy.

Melting of fractal snowflakes: Experiments and modeling

Numerical simulations of snow accretion on aircraft or weather phenomena require an accurate prediction of the melting of snowflakes. In the present study, an experimental setup for the investigation of snowflake melting is presented, which utilizes an acoustic levitator holding a snowflake in a warm airflow. Based on the experimental findings, a theoretical model for the melting process is developed. This theoretical model takes into account that the generated liquid water is driven into the porous ice structure by capillary forces and does not accumulate at the outer surface of the snowflake. This enables the use of a mass–size relationship in form of a power law, which is common in atmospheric sciences. The model prediction of the evolution of the maximum dimension during melting agrees well with the experiments. Moreover, the snowflake melting durations are also estimated well, if an accurate value is available for the particle mass fractal dimension, i.e., the exponent in the mass–size power law.

IMaNGA: mock MaNGA galaxies based on IllustrisTNG and MaStar SSPs – II. The catalogue

ABSTRACT Strengthening the synergy between simulations and observations is essential to test galaxy formation and evolution theories. To achieve this goal, in the first paper of this series, we presented a method to generate mock SDSS-IV/Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) integral-field spectroscopic galaxy observations from cosmological simulations. In this second paper, we build the iMaNGA catalogue consisting of ∼1000 unique galaxies from the TNG50 cosmological simulations, selected to mimic the SDSS-IV/MaNGA-Primary sample selection. Here, we present and discuss the iMaNGA sample and its comparison to the MaNGA Primary catalogue. The iMaNGA sample well recovers the MaNGA-Primary sample in terms of stellar mass versus angular size relation and spatial resolution. The Sérsic index versus angular size relation, instead, is not reproduced well by the simulations, mostly because of a paucity of high-mass elliptical galaxies in TNG50. We also investigate our ability to recover the galaxy kinematics and stellar population properties with full-spectral fitting. We demonstrate that ‘intrinsic’ and ‘recovered’ stellar kinematics, stellar ages, and metallicities are consistent, with residuals compatible with zero within 1σ. Also ‘intrinsic’ and ‘recovered’ star formation histories display a great resemblance. We conclude that our mock generation and spectral fitting processes do not distort the ‘intrinsic’ galaxy properties. Therefore, in the third paper of this series, we can meaningfully test the cosmological simulations, comparing the stellar population properties and kinematics of the iMaNGA mock galaxies and the MaNGA observational results.

Origin and evolution of ultradiffuse galaxies in different environments

ABSTRACT We study the formation of ultradiffuse galaxies (UDGs) using the cosmological hydrodynamical simulation TNG50 of the Illustris-TNG suite. We define UDGs as dwarf galaxies in the stellar mass range $\rm {7.5 \le log (M_{\star } / {\rm M}_{\odot }) \le 9 }$ that are in the 5 per cent most extended tail of the simulated mass–size relation. This results in a sample of UDGs with half-mass radii $\rm {r_{h \star } \gtrsim 2 \ kpc}$ and surface brightness between $\rm {24.5}$ and $\rm {28 \ mag \ arcsec^{-2}}$, similar to definitions of UDGs in observations. The large cosmological volume in TNG50 allows for a comparison of UDGs properties in different environments, from the field to galaxy clusters with virial mass $\rm {M_{200} \sim 2 \times 10^{14} ~ {\rm M}_{\odot }}$. All UDGs in our sample have dwarf-mass haloes ($\rm {M_{200}\sim 10^{11} ~ {\rm M}_{\odot } }$) and show the same environmental trends as normal dwarfs: field UDGs are star-forming and blue while satellite UDGs are typically quiescent and red. The TNG50 simulation predicts UDGs that populate preferentially higher spin haloes and more massive haloes at fixed $\rm {M_{\star }}$ compared to non-UDG dwarfs. This applies also to most satellite UDGs, which are actually ‘born’ UDGs in the field and infall into groups and clusters without significant changes to their size. We find, however, a small subset of satellite UDGs ($\lesssim 10~{{\ \rm per\ cent}}$) with present-day stellar size a factor ≥1.5 larger than at infall, confirming that tidal effects, particularly in the lower mass dwarfs, are also a viable formation mechanism for some of these dwarfs, although sub-dominant in this simulation.

Galactic scaling rules in a modified dynamical model

Schulz (2017) galactic scaling rules , which include baryonic Tully–Fisher relation, have been surveyed in this work within the context of a modified dynamical model. These scaling relations are derived by employing the virial theorem and applying equilibrium and stability conditions. The scaling rules are also obtained by dimensional analysis of an integral relation between surface density and circular velocity of disk galaxies. To check the validity of the scaling relations based on observational data, we have defined, based on the properties of the model, the proper equilibrium size Req and equilibrium velocity Veq of systems. By employing these measures of length and velocity, SPARC data (Lelli et al., 2016a) is used to analyze the results. The viability of the scaling relations is tested and it is shown that, compared to some other measures of length and velocity, Req and Veq provide the closest fits to the theoretical predictions. We have compared our results with prior works and have concluded that the set of baryonic Tully–Fisher relation plus mass–size relation ( or mass–velocity) provides an appropriate description of the general characteristics of the systems. Lastly, it is shown that these scaling relations predict a certain evolution of galactic properties with redshift. This behavior provides a chance to examine the cosmic evolution of the present modified dynamical model in future works.

Size and Spectroscopic Evolution of HectoMAP Quiescent Galaxies

The HectoMAP survey provides a complete, mass-limited sample of 30,231 quiescent galaxies with i-band Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) imaging that spans the redshift range 0.2 < z < 0.6. We combine half-light radii based on HSC SSP imaging with redshifts and D n 4000 to explore the size–mass relation, , and its evolution for the entire HectoMAP quiescent population and for two subsets of the data. Newcomers with 1.5 < D n 4000 < 1.6 at each redshift show a steeper increase in A as the universe ages than the population that descends from galaxies that are already quiescent at the survey limit, z ∼ 0.6 (the resident population). In broad agreement with previous studies, evolution in the size–mass relation both for the entire HectoMAP sample and for the resident population (but not for the newcomers alone) is consistent with minor merger driven growth. For the resident population, the evolution in the size–mass relation is independent of the population age at z ∼ 0.6. The contrast between the sample of newcomers and the resident population provides insight into the role of commonly termed “progenitor bias” on the evolution of the size–mass relation.

The galaxy mass-size relation in CARLA clusters and proto-clusters at 1.4 &lt; z &lt; 2.8: Larger cluster galaxy sizes

We study the galaxy mass-size relation in 15 spectroscopically confirmed clusters at 1.4 &lt; z &lt; 2.8 from the CARLA survey. Our clusters span a total stellar mass in the range 11.3 &lt; log(M*c/M⊙) &lt; 12.6 (with an approximate halo mass in the range 13.5 ≲ log(Mhc/M⊙) ≲ 14.5). Our main finding is that cluster passive early-type galaxies (ETGs) at z ≳ 1.5 with a mass log(M/M⊙) &gt; 10.5 are systematically ≳0.2 − 0.3dex larger (≳3σ) than field ETGs at a similar redshift and mass from the CANDELS survey. The passive ETG average size evolution with redshift is slower at 1 &lt; z &lt; 2 when compared to the field. This could be explained by early-epoch differences in the formation and early evolution of galaxies in haloes of a different mass, as predicted by models. It does not exclude that other physical mechanisms, such as strong compaction and gas dissipation in field galaxies, followed by a sequence of mergers may have also played a significant role in the field ETG evolution, but not necessarily in the evolution of cluster galaxies. Our passive ETG mass-size relation shows a tendency to flatten at 9.6 &lt; log(M/M⊙) &lt; 10.5, where the average size is log(Re/kpc) = 0.05 ± 0.22, which is broadly consistent with galaxy sizes in the field and in the local Universe. This implies that galaxies in the low end of the mass-size relation do not evolve much from z ∼ 2 to the present, and that their sizes evolve in a similar way in clusters and in the field. Brightest cluster galaxies lie on the same mass-size relation as satellites, suggesting that their size evolution is not different from satellites at redshift z ≳ 2. Half of the active early-type galaxies, which are 30% of our ETG sample, follow the field passive galaxy mass-size relation, and the other half follow the field active galaxy mass-size relation. These galaxies likely went through a recent merger or neighbor galaxy interaction, and would most probably quench at a later epoch and increase the fraction of passive ETGs in clusters. We do not observe a large population of compact galaxies (only one), as is observed in the field at these redshifts, implying that the galaxies in our clusters are not observed in an epoch close to their compaction.

A Microphysics-Scheme-Consistent Snow Optical Parameterization for the Community Radiative Transfer Model

Abstract The satellite observational data assimilation community requires consistent hydrometer descriptions—including mass–size relation and particle size distribution—to be used in both the forecast model and observation operator. We develop a microphysics-scheme-consistent snow and graupel single-scattering property database to meet this requirement. In this database, snowflakes are modeled as a mixture of small column and large aggregated ice particles, the mixing ratios of which may be adjusted to satisfy a given mass–size relation. Snow single-scattering properties are computed for four different mass–size relations. Subsequently, the snow description in the Thompson microphysics scheme is used as an example to demonstrate how microphysics-scheme-consistent snow bulk optical properties are derived. The Thompson-scheme-consistent snow bulk optical properties are added to the Community Radiative Transfer Model (CRTM), version 2.4.0. With CloudSat Cloud Profiling Radar (CPR) snow and liquid precipitation retrievals as the inputs, CRTM simulations are performed over global oceans and compared with four collocated Global Precipitation Measurement (GPM) Microwave Imager (GMI) high-frequency channel observations. The CRTM simulated brightness temperatures show agreement with the GMI observed brightness temperatures in cases of light-to-moderate precipitation over extratropical and polar ice-free oceans, with root-mean-square errors of 4.3, 13.0, 1.8, and 3.3 K in the 166-GHz (vertical polarization), 166-GHz (horizontal polarization), 183 ± 3-GHz (vertical polarization), and 183 ± 7-GHz (vertical polarization) channels, respectively. The result demonstrates the potential of using the newly developed microphysics-scheme-consistent snow optical parameterization in data assimilation applications.