Initial Mass Function Research Articles

Strong Scatterings Invalidate Proposed Models of Enhanced Tidal Disruption Event Rates in Post-starburst Galaxies

Abstract Stars wandering too close to supermassive black holes (SMBHs) can be ripped apart by the tidal forces of the black hole. Recent optical surveys have revealed that E+A galaxies are over-represented by a factor of ∼30, while green galaxies are over-represented in both optical and IR surveys. Different stellar models have been proposed to explain this tidal disruption event (TDE) preference: ultrasteep stellar densities in the nuclear cluster, radial velocity anisotropies, and a top-heavy initial mass function (IMF). Here, we explore these hypotheses in the framework of our revised loss cone theory that accounts for both weak and strong scattering, i.e., a scattering strong enough to eject a star from the nuclear cluster. We find that when accounting for weak and strong scatterings, both ultrasteep densities and radial velocity anisotropies fail to explain the post-starburst preference of TDEs, except when considering a high anisotropy factor together with a high SMBH mass and a shallow density profile of stellar-mass BHs γ bh = 7/4. Our findings hold when combining either model with top-heavy IMFs. Hence, our work emphasizes both the importance of taking into account strong scatterings and the need for new hypotheses to explain the post-starburst preference of TDEs.

Dual-band Unified Exploration of three CMZ Clouds (DUET). Cloud-wide census of continuum sources showing low spectral indices

The Milky Way's central molecular zone (CMZ) has been measured to form stars ten times less efficiently than in the Galactic disk, based on emission from high-mass stars. However, the CMZ's low-mass (lesssim2 protostellar population, which accounts for most of the initial stellar mass budget and star formation rate (SFR), is poorly constrained observationally due to limited sensitivity and resolution. We aim to perform a cloud-wide census of the protostellar population in three massive CMZ clouds. We present the Dual-band Unified Exploration of three CMZ Clouds (DUET) survey, targeting the and the dust ridge cloud “e” using the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 and 3 mm. The mosaicked observations achieve a comparable resolution of 0 (∼2000 au) and a sky coverage of 8.3--10.4 arcmin^2, respectively. We report 563 continuum sources at 1.3 mm and 330 at 3 mm, respectively, and a dual-band catalog with 450 continuum sources. These sources are marginally resolved at a resolution of 2000 au. We find a universal deviation ($>70$% of the source sample) from commonly used dust modified blackbody (MBB) models, characterized by either low spectral indices or low brightness temperatures. Three possible explanations are discussed for the deviation. (1) Optically thick class 0/I young stellar objects (YSOs) with a very small beam filling factor can lead to lower brightness temperatures than what MBB models predict. (2) Large dust grains with millimeter or centimeter in size have more significant self-scattering, and frequency-dependent albedo could therefore cause lower spectral indices. (3) Free-free emission over 30 μJy can severely contaminate dust emission and cause low spectral indices for milli-Jansky sources, although the number of massive protostars (embedded UCH ii regions) needed is infeasibly high for the normal stellar initial mass function. A reliable measurement of the SFR at low protostellar masses will require future work to distinguish between these possible explanations.

The Impact of Stellar Initial Mass Function on the Epoch of Reionization: Insights from Semi-Analytic Galaxy Modeling

The adequate choice of stellar initial mass function (IMF) is crucial when studying high-z galaxy formation and the epoch of reionization (EoR) models. We employ the semi-analytical galaxy model L-Galaxies2020 and the dark matter simulation Millennium-II, in combination with the BPASS spectral model, to investigate the effects of different stellar IMFs on the properties of high-z galaxies and their ionizing photon budget during EoR. We find that different stellar IMFs lead to different SED of high-z galaxies, and thus different ultraviolet luminosity functions (UVLF) and budgets of ionizing photons for EoR. Specifically, at z<10, the UVLF with Salpeter and Chabrier IMF models are closer to the observed results, while at z>10, the ones with a Top-Heavy model are more consistent with the JWST observations. The increase in the upper limit of star mass within stellar IMF from 100M⊙ to 300M⊙ results in the increase in the UVLF and the ionizing photon number density.

Joint inference of the Milky Way's star formation history and initial mass function from Gaia all-sky G < 13 data

Despite the fundamental importance of the star formation history (SFH) and the initial mass function (IMF) in the description of the Milky Way, their consistent and robust derivation is still elusive. Recent and accurate astrometry and photometry collected by the Gaia satellite provide the natural framework to consolidate these ingredients in our local Galactic environment. We aim to simultaneously infer the IMF and the SFH of the Galactic disc by comparing Gaia data with the mock catalogue resulting from the Besançon population synthesis model (BGM). Our goal is also to estimate the impact of the systematics present in current stellar evolutionary models (SEMs) on this inference. We used a new implementation of the BGM fast approximate simulations (BGM FASt) framework to fit the seven-million-star Gaia DR3 all-sky G<13 colour-magnitude diagram (CMD) to the most up-to-date dynamically self-consistent BGM. Our derived SFH supports an abrupt decrease in star formation approximately 1-1.5 Gyr ago followed by a significant enhancement with a wide plateau in the range of 2-6 Gyr ago. A remarkable hiatus appears around 5-7 Gyr ago, with a ∼1 Gyr shift depending on the set of stellar models. A complex evolution at ages older than 8 Gyr deserves further investigation. Precise but discrepant values using different SEMs are found for the power-law indices of the IMF. In our fiducial execution with PARSEC SEM, the slope takes a value of α_2 = 1.45^ for the range M_⊙, while for masses larger than 1.53 M_⊙ we obtain α_3 = 1.98^ . Using STAREVOL SEM, the inferred values are α_2 = 2.48^ and α_3 = 1.64^ . We find the solution with PARSEC to have a significantly higher likelihood than that obtained with STAREVOL. The current implementation of the BGM FASt framework is ready to address executions fitting all-sky Gaia data up to an apparent limiting magnitude of 14-17. This will naturally allow us to derive both a reliable SFH for the early epochs of the Galactic disc evolution and a precise slope for the IMF at low masses.

Global survey of star clusters in the Milky Way VIII. Cluster formation and evolution

We consider tidal masses and ages of Milky Way open clusters, as well as a simple model of their distribution. This model is presented as part of the Milky Way Star Cluster (MWSC) survey. Our aim is to investigate the space of model parameters and the correspondence between modelled and observed two-dimensional (2D) cluster age-mass distributions. The model for cluster evolution is comprised of a two-section cluster initial mass function, constant cluster formation rate, and a mass loss function. This mass loss function represents a supervirial phase after sudden expulsion of the remaining gas, cluster mass loss due to stellar evolution and gradual cluster dissolution driven by internal dynamics and the Galactic tidal field. We constructed different estimators of model fitness based on χ^2-statistics, the Kullback-Leibler divergence (KLD) and a maximum-likelihood approach, taking into account the uncertainty of our observed cluster parameters. Using these estimators and Markov chain Monte Carlo (MCMC) sampling, we obtained best-fit values and posterior distributions for a selection of model parameters. The KLD returned a superior model compared to the other statistics, because it also reproduced the low-density regions of the observed cluster age-mass distribution. The cluster initial mass function is well constrained and we find a clear signature of an enhanced cluster mass loss in the first 50 Myr. Deviations from a constant cluster formation rate could not be determined due to its strong degeneracy with the shape of the cluster mass loss function. In the KLD best model, clusters lose of their initial mass in the violent relaxation phase after which cluster mass loss slows down, allowing for a relatively low rate of cluster formation of $ kpc^ Gyr^ $. The observed upper limit of cluster ages at approx. 5 Gyr is reflected in the model by a very shallow lifetime-mass relation for clusters with initial masses above 1000msun. The application of the model to an independent cluster sample based on Gaia DR3 data yielded similar results except for a systematic shift in typical age and higher number densities. We conclude that the observed cluster age-mass distribution is compatible with a constant cluster formation rate. Strong correlations between model parameters reflect a sensitive dependence of the cluster age-mass distribution not just on the formation rate and initial mass function, but the details of cluster mass loss and dissolution in particular. The enhanced number of young massive clusters observed requires an early violent relaxation phase of strong mass loss. The cluster age limit cannot be fully explained by an initial mass cutoff.

Brown dwarf number density in the JWST COSMOS-Web field

Abstract Brown dwarfs are failed stars with very low mass (13 to 75 Jupiter mass), and an effective temperature lower than 2500 K. Their mass range is between Jupiter and red dwarfs. Thus, they play a key role in understanding the gap in the mass function between stars and planets. However, due to their faint nature, previous searches are inevitably limited to the solar neighbourhood (20 pc). To improve our knowledge of the low mass part of the initial stellar mass function and the star formation history of the MilkyWay, it is crucial to find more distant brown dwarfs. Using JamesWebb Space Telescope (JWST) COSMOS-Web data, this study seeks to enhance our comprehension of the physical characteristics of brown dwarfs situated at a distance of kpc scale. The exceptional sensitivity of the JWST enables the detection of brown dwarfs that are up to 100 times more distant than those discovered in the earlier all-sky infrared surveys. The large area coverage of the JWST COSMOS-Web survey allows us to find more distant brown dwarfs than earlier JWST studies with smaller area coverages. To capture prominent water absorption features around 2.7 μm, we apply two colour criteria, F115W – F277W + 1 < F277W – F444W and F277W – F444W > 0.9. We then select point sources by CLASS_STAR, FLUX_RADIUS, and SPREAD_MODEL criteria. Faint sources are visually checked to exclude possibly extended sources. We conduct SED fitting and MCMC simulations to determine their physical properties and associated uncertainties. Our search reveals 25 T-dwarf candidates and 2 Y-dwarf candidates, more than any previous JWST brown dwarf searches. They are located from 0.3 kpc to 4 kpc away from the Earth. The spatial number density of 900-1050 K dwarf is (2.0 ± 0.9) × 10–6 pc–3, 1050–1200 K dwarf is (1.2 ± 0.7) × 10–6 pc–3, and 1200–1350 K dwarf is (4.4 ± 1.3) × 10–6 pc–3. The cumulative number count of our brown dwarf candidates is consistent with the prediction from a standard double exponential model. Three of our brown dwarf candidates were detected by HST, with transverse velocities 12 ± 5 km s–1, 12 ± 4 km s–1, and 17 ± 6 km s–1. Along with earlier studies, the JWST has opened a new window of brown dwarf research in the MilkyWay thick disk and halo.

The COSMOS-Web ring: Spectroscopic confirmation of the background source at z=5.1

We report the spectroscopic confirmation of the background source of the most distant Einstein ring known to date, the COSMOS-Web ring. This system consists of a complete Einstein ring at z=5.1, which is lensed by a massive early-type galaxy at z∼2. The redshift z=5.1043±0.0004 is unambiguously identified with our NOEMA and Keck/MOSFIRE spectroscopy; the NOEMA observations reveal the CO(4-3) and CO(5-4) lines at $>8,σ$, and the MOSFIRE data detect O ii at ∼ 6,σ. Using multiwavelength photometry spanning near-infrared to radio bands, we find that the lensed galaxy is a dust-obscured starburst ⋆ ∼ 1.8 Msun IR ∼ 60 Msun yr^ $) with a high star formation efficiency (gas depletion time τ_ dep <100 Myr), as indicated by the C i (1-0) non-detection. The redshift confirmation re-validates that the total lens mass budget within the Einstein radius is fully accounted for by the stellar and dark matter components, without the need of modifying the initial mass function or dark matter distribution profile. This work paves the way for detailed studies and future follow-ups of this unique lensing system, which is an ideal laboratory for studying mass distribution at z∼2 and physical conditions of star formation at z∼5.

The SLACS strong lens sample, debiased. II. Lensing-only constraints on the stellar initial mass function and dark matter contraction in early-type galaxies

The Sloan Lens ACS (SLACS) is the best studied sample of strong lenses to date. Much of our knowledge of the SLACS lenses has been obtained by combining strong lensing with stellar kinematics constraints. However, interpreting stellar kinematics data is difficult, as it requires reconstructing the three-dimensional structure of a galaxy and the orbits of its stars. For SLACS, the problem is exacerbated by its selection function, which caused lenses with a larger observed velocity dispersion to be overrepresented. In this work, we pursue an alternative approach to the study of galaxy structure with SLACS, based purely on gravitational lensing data. The primary goal of this study is to constrain the stellar population synthesis mismatch parameter asps, quantify the ratio between the true stellar mass of a galaxy and that obtained with a reference stellar population synthesis model, and identify the efficiency of the dark matter response to the infall of baryons, eps. We combined Einstein radius measurements from the SLACS lenses with weak lensing information from their parent sample, while accounting for selection effects. The data can be fit comparatively well by a model with log asps =0.22 and eps=0, corresponding to an initial mass function (IMF) slightly lighter than Salpeter and no dark matter contraction, or log asps =0 and eps=0.8, equivalent to a Chabrier IMF and almost maximal contraction. Selection effects, if not modelled, produce a shift in the joint posterior probability that is larger than the uncertainty. The degeneracy between asps and eps could be broken with lensing-only measurements of the projected density slope, but existing data are completely inconsistent with our model. We suspect systematic errors in the measurements to be at the origin of this discrepancy. Number density constraints would also help break the degeneracy. Because of selection effects, SLACS lenses have a larger velocity dispersion than galaxies with the same projected mass distribution, and their velocity dispersion is overestimated. These two biases combined produce a $5%$ upward shift in the observed velocity dispersion.

Stars as cosmic scales: measuring stellar mass with microlensed supernovae

Abstract Gravitational microlensing is a unique probe of the stellar content in strong lens galaxies. Flux ratio anomalies from gravitationally lensed supernovae (glSNe), just like lensed quasars, can be used to constrain the stellar mass fractions at the image positions. Type Ia supernovae are of particular interest as knowledge of the intrinsic source brightness helps constrain the amount of (de)magnification from the macromodel predictions that might be due to microlensing. In addition, the presence or absence of caustic crossings in the light curves of glSNe can be used to constrain the mass of the microlenses. We find that a sample of 50 well-modeled glSNe Ia systems with single epoch observations at peak intrinsic supernova luminosity should be able to constrain an average stellar mass-to-light ratio to within ∼ 15%. A set of systems with light curve level information providing the location (or absence) of caustic crossing events can also constrain the mass of the microlenses to within ∼50%. Much work is needed to make such a measurement in practice, but our results demonstrate the feasibility of microlensing to place constraints on astrophysical parameters related to the initial mass function of lensing galaxies without any prior assumptions on the stellar mass.

Measuring Resolved Star Formation Histories from High-precision Color–Magnitude Diagrams with StarFormationHistories.jl

Abstract Understanding how and when galaxies formed stars over the history of the Universe is fundamental to the study of galaxy evolution. The star formation histories (SFHs) of galaxies in the local Universe can be measured with high precision using deep imaging with space telescopes. Such resolved SFHs are based on modeling the observed color–magnitude diagram (CMD) with stellar evolution models and rely on age-sensitive features like the main-sequence turnoff to measure a galaxy’s star formation rate as a function of time. There are many other population-level parameters that factor into these measurements, such as the stellar initial mass function (IMF), binary fraction, and metallicity, to name a few. We present and release StarFormationHistories.jl, a modular, open-source Julia package for measuring resolved SFHs with a focus on model flexibility for these types of population parameters. The code can model unresolved photometric binaries and supports arbitrary IMFs. Random uncertainties in the SFH measurements can be quantified with Monte Carlo posterior sampling methods. We illustrate the performance of the package on JWST/NIRCAM data of the Local Group dwarf irregular galaxy Wolf–Lundmark–Melotte M v ≈ − 14.2 mag , which exhibits a complex, well-sampled CMD, and Hubble Space Telescope/Advanced Camera for Surveys data of the ultrafaint Milky Way satellite dwarf galaxy Horologium I M v ≈ − 3.7 mag , which has a much simpler but sparser CMD.

JADES: The star formation and chemical enrichment history of a luminous galaxy at z∼9.43 probed by ultra-deep JWST/NIRSpec spectroscopy

We analysed ultra-deep observations of the galaxy at z=9.4327, and derived detailed stellar and interstellar medium (ISM) properties of this luminous UV =--20.43) high-redshift system. Complementary information from NIRCam imaging and NIRSpec spectroscopy (both low and medium resolution) reveal a compact system (R_ e ∼110 pc) characterised by a steeply rising star formation history, which is reflected in the inferred young stellar age (t ∼3 Myr, light-weighted), high star formation rate surface density (Σ_ SFR ∼72 yr^-1 kpc^-2), high ionisation parameter (log(U) ∼-1.5), low metallicity (12+log(O/H) ∼7.5), and low carbon-to-oxygen abundance C/O $=-0.64$). Leveraging the detection of we derived a nitrogen-to-oxygen abundance N/O ∼0) higher than the plateau followed by low-redshift galaxies of similar metallicity, possibly revealing the imprint from (very) massive stars on the ISM enrichment and favouring a top-heavy initial mass function (IMF) scenario. Massive stars powering a hard radiation field are also required to explain the rest-frame UV line ratios, though the presence of the high-excitation emission line possibly hints at additional ionisation from an active galactic nucleus (AGN). We also report the tentative detection of emission in the G140M spectrum, shifted by ∼450 km/s redwards of the systemic redshift. Combined with a modelling of the spectral break, we rule out the presence of very high column densities of neutral gas pertaining to local absorbers, as well as any extended surrounding ionised bubbles, suggesting that has not yet significantly contributed to cosmic reionisation.

The S stars’ zone of avoidance in the Galactic center

This paper investigates the origin and orbital evolution of S stars in the Galactic center using models of binary disruption and relaxation processes. We focus on explaining the recently discovered “zone of avoidance” in S-star orbital parameters, defined as a region where no S stars are observed with pericenters of log(rp/AU) ≤ 1.57 + 2.6(1 − e) pc. We demonstrate that the observed S-star orbital distributions, including this zone of avoidance and their thermal eccentricity distribution, can be largely explained by the continuous disruption of binaries near the central supermassive black hole, followed by orbital relaxation. Our models consider binaries originating from large scales (5–100 pc) and incorporate empirical distributions of binary properties. We simulate close encounters between binaries and the black hole, tracking the remnant stars’ orbits. The initially highly eccentric orbits of disrupted binary remnants evolve due to nonresonant and resonant relaxation in the Galactic center potential. While our results provide insights into the formation mechanism of S stars, there are limitations, such as uncertainties in the initial binary population and mass function and simplifications in our relaxation models. Despite these caveats, our study demonstrates the power of using S-star distributions to probe the dynamical history and environment of the central parsec of our Galaxy.

Synergising semi-analytical models and hydrodynamical simulations to interpret JWST data from the first billion years

The field of high redshift galaxy formation has been revolutionised by the James Webb Space Telescope (JWST), which is yielding unprecedented insights into galaxy assembly at early times. In addition to global statistics, including the redshift evolution of the ultraviolet luminosity function (UV LF) and stellar mass function (SMF), new datasets are providing information on galaxy properties, including the mass-metallicity relation, UV spectral slopes (β), and ionising photon production efficiencies. In this work our key aim is to understand the physical mechanisms that can simultaneously explain the unexpected abundance of bright galaxies at z 11 as well as the metal enrichment and observed spectral properties of galaxies in the early Universe. We also aim to determine the key sources of reionisation in light of recent data. We incorporated interstellar medium physics - namely, cold gas fractions and star formation efficiencies - derived from the sphinx ^20 high-resolution radiation-hydrodynamics simulation into delphi a semi-analytic model that tracks the assembly of dark matter halos and their baryonic components from z ∼ 4.5-40. In addition, we explored two methodologies to boost galaxy luminosities at z 11: a stellar initial mass function (IMF) that becomes increasingly top-heavy with decreasing metallicity and increasing redshift (eIMF model), and star formation efficiencies that increase with increasing redshift (eSFE model). Our key findings are the following: (i) Both the eIMF and eSFE models can explain the abundance of bright galaxies at z (ii) Dust attenuation plays an important role in determining the bright end (MUV -21) of the UV LF at z 11. At higher redshifts, dust is too dispersed to have an impact on the UV luminosity. (iii) The mass-metallicity relation is in place as early as z ∼ 17 in all models, although its slope is model-dependent. (iv) Within the spread of both the models and observations, all of our models are in good agreement with current estimates of β slopes at z ∼ 5-17 and Balmer break strengths at z ∼ 6-10. (v) In the eIMF model, galaxies at z or with MUV show typical values of xion ∼ Hz erg^ a factor two larger than in other models. (vi) Star formation in low-mass galaxies (M_* is the key reionisation driver, providing the bulk (∼ 85%) of ionising photons down to its midpoint at z ∼ 7.

Comparison of methods used to derive the Galactic star formation history from white dwarf samples

Abstract We compare three methods of deriving the local Galactic star formation history, using as a benchmark the Gaia-defined 40 pc white dwarf sample, currently the largest volume complete sample of stellar remnants with medium-resolution spectroscopy. We create a population synthesis model to (1) reproduce the observed white dwarf luminosity function, (2) reproduce the observed absolute Gaia G magnitude distribution, and (3) directly calculate the ages of all individual white dwarfs in the 40 pc volume. We then compare the star formation histories determined from each method. Previous studies using these methods were based on different white dwarf samples and as such were difficult to compare. Uncertainties in each method such as the initial mass function, initial-final mass relation, main sequence lifetimes, stellar metallicity, white dwarf cooling ages and binary evolution are accounted for to estimate the precision and accuracy of each method. We conclude that no method is quantitatively better at determining the star formation history and all three produce star formation histories that agree within uncertainties of current external astrophysical relations.

Inversely synthesizing the core mass function of high-mass star-forming regions from the canonical initial mass function

Many studies have revealed that the core mass function (CMF) in high-mass star-forming regions is top-heavy. In this work, we start from the canonical initial mass function (IMF) to inversely synthesize the observed CMFs of high-mass star formation regions, taking into account variations in multiplicity and mass conversion efficiency from core to star (ε_ core). To match the observed CMFs, cores of different masses should have varying ε_ core, with ε_ core increasing as the core mass decreases. However, the multiplicity fraction does not affect the synthesized CMFs. To accurately fit the high-mass end of the CMF, it is essential to determine whether the CMF shows a slope transition from the low-mass end to the high-mass one. If the CMF truly undergoes a slope transition but observational biases obscure it, leading to a combined fit with a shallower slope, this could artificially create a top-heavy CMF.

Identification of a Turnover in the Initial Mass Function of a Young Stellar Cluster Down to 0.5 MJ

Abstract A successful theory of star formation should predict the number of objects as a function of their mass produced through star-forming events. Previous studies in star-forming regions and the solar neighborhood have identified a mass function increasing from the hydrogen-burning limit down to about 10 M J. Theory predicts a limit to the fragmentation process, providing a natural turnover in the mass function down to the opacity limit of turbulent fragmentation, thought to be near 1–10 M J. Programs to date have not been sensitive enough to probe the hypothesized opacity limit of fragmentation. We present the first identification of a turnover in the initial mass function below 12 M J within NGC 2024, a young star-forming region. With JWST/NIRCam deep exposures across 0.7–5 μm, we identified several free-floating objects down to roughly 3 M J with sensitivity to 0.5 M J. We present evidence for a double power-law model increasing from about 60 M J to roughly 12 M J, consistent with previous studies, followed by a decrease down to 0.5 M J. Our results support the predictions of star and brown dwarf formation theory, identifying the theoretical turnover in the mass function and suggesting the fundamental limit of turbulent fragmentation to be near 3 M J.

Detectability of accretion-induced bosenovae in the Milky Way

We estimate collapse rates of axion stars in our galaxy based on the axion minicluster mass function of the Milky Way dark matter halo. We consider axionlike particles (ALP) with different temperature evolution of the axion mass, including the QCD axion with ma=50 μeV. Combining estimates for the present-day axion star mass function from our previous work with the axion star accretion model predicted by self-similar growth, we can infer the expected number of bosenovae occurring within the Milky Way. Our estimates suggest that for an observation time of tobs=1 yr, the majority of the up to ∼1013 bosenovae per galaxy occur in the densest miniclusters with initial overdensity parameter Φ≲104. We discuss the detectability of such recurring axion bursts within our galactic vicinity and find that, for models with derivative couplings including axion-fermion interactions, potential broadband axion dark matter experiments can probe a large range of ALP masses ma≲10−6 eV and with moderate improvements even the quantum chromodynamics axion case. For axions with nonderivative-type interactions like the axion-photon coupling, our analysis suggests that optimistic predictions with order-one dark matter abundance of axion stars f⋆∼1 can be probed by dedicated burst searches. Published by the American Physical Society 2025

The FLAMINGO project: cosmology with the redshift dependence of weak gravitational lensing peaks

Abstract Weak gravitational lensing (WL) convergence peaks contain valuable cosmological information in the regime of non-linear collapse. Using the FLAMINGO suite of cosmological hydrodynamical simulations, we study the physical origin and redshift distributions of the objects generating WL peaks selected from a WL convergence map mimicking a Euclid signal. We match peaks to individual haloes and show that the high signal-to-noise ratio (SNR > 5) WL peaks measured by Stage IV WL surveys primarily trace M200c > 1014 M⊙ haloes. We find that the WL peak sample can compete with the purity and completeness of state-of-the-art X-ray and Sunyaev-Zel’dovich cluster abundance inferences. By comparing the distributions predicted by simulation variations that have been calibrated to the observed gas fractions of local clusters and the present-day galaxy stellar mass function, or shifted versions of these, we illustrate that the shape of the redshift distribution of SNR > 5 peaks is insensitive to baryonic physics while it does change with cosmology. The difference highlights the potential of using WL peaks to constrain cosmology. As the WL convergence and redshift number densities of WL peaks scale differently with cosmology and baryonic feedback, WL peak statistics can simultaneously calibrate baryonic feedback and constrain cosmology.

Modeling the UV to Radio Spectral Energy Distribution of NGC 6946: Star Formation Rates and Dust Attenuation Properties

Abstract In this paper, we perform an ultraviolet (UV) to radio spectral energy distribution fitting analysis of star-forming regions in the nearby galaxy NGC 6946 by means of the Graphite and Silicates (GRASIL) population synthesis and radiative transfer model to which the first version of the thoroughly updated Padova and Trieste Stellar Evolutionary Code (PARSEC v1.2s) database of evolutionary nonrotating tracks of massive stars is incorporated. The tracks span a wide range of initial chemical compositions (Z = 0.0001–0.04) and stellar initial mass function (IMF) upper mass limits (M up = 40 M ⊙–350 M ⊙). We obtain from our best-fit models consistent and robust estimates of star formation rate calibrations at wavelengths ranging from UV to radio and as a function of IMF upper mass limit. We investigate the properties of dust attenuation curves that also result from the best-fit models by exploiting the realistic treatment of dust performed by GRASIL. This resulted in new relations between optical emission fluxes that are subject to attenuation and fluxes that are not prone to attenuation. These relations, which we show to be almost independent of IMF upper mass limits, can be extremely useful in estimating attenuations in young high redshift galaxies.

Sloan Digital Sky Survey IV MaStar: Quantification and Abatement of Interstellar Absorption in the Largest Empirical Stellar Spectral Library

We assess the impact of Ca ii λ λ3934, 3969 and Na i λ λ5891, 5897 absorption arising in the interstellar medium (ISM) on the Sloan Digital Sky Survey-IV MaNGA Stellar Library (MaStar) and produce corrected spectroscopy for 80% of the 24,162-star catalog. We model the absorption strength of these transitions as a function of the stellar distance, Galactic latitude, and dust reddening based on high-spectral resolution studies. With this model, we identify 6342 MaStar stars that have negligible ISM absorption (W ISM(Ca ii K) < 0.07 Å and W ISM(Na i 5891) < 0.05 Å). For 12,110 of the remaining stars, we replace their Na i D profile (and their Ca ii profile for effective temperatures T eff > 9000 K) with a coadded spectrum of low-ISM stars with similar T eff, surface gravity, and metallicity. For 738 additional stars with T eff > 9000 K, we replace these spectral regions with a matching ATLAS9-based BOSZ model. This results in a mean reduction in W(Ca ii K) (W(Na i D)) of 0.4–0.7 Å (0.6–1.1 Å) for hot stars (T eff > 7610 K), and a mean reduction in W(Na i D) of 0.1–0.2 Å for cooler stars. We show that interstellar absorption in the simple stellar population (SSP) model spectra constructed from the original library artificially enhances W(Ca ii K) by ≳20% at young ages (<400 Myr); dramatically enhances the strength of stellar Na i D in starbursting systems (by ≳50%); and enhances stellar Na i D in older stellar populations (≳10 Gyr) by ≳10%. We provide SSP spectra constructed from the cleaned library and discuss the implications of these effects for stellar population synthesis analyses constraining the stellar age, [Na/Fe] abundance, and initial mass function.