Initial Mass Function Research Articles

Why should models of dwarf galaxy evolution care about the initial mass function at low star-formation rates?

ABSTRACT When star clusters are formed at low star-formation rates (SFRs), their stellar initial mass function (IMF) can hardly be filled continuously with stars at each mass. This lack holds for massive stars and is verified observationally by the correlation between star-cluster mass and its most massive cluster star. Since galaxy evolution is strongly affected by massive stars, numerical models should account for this lack. Because a filled IMF is mostly applied even when only fractions of massive stars form, here we investigate, by means of 3D chemo-dynamical simulations of isolated dwarf galaxies, how deviations from a standard IMF in star clusters affect the evolution. We compare two different IMF recipes, a filled IMF and one truncated at a maximum mass at which a single complete star forms. Attention is given to energetic and chemical feedback by massive stars. Since their energy release is mass-dependent but steeper than the negative IMF slope, the energetic feedback retains a positive mass dependence, so that a filled IMF regulates star formation (SF) more strongly than truncated IMFs, though only stellar number fractions exist. The higher SFR of the truncated IMF in the simulation leads to more Type II supernovae (SNeII), driving galactic winds. Whether this results from the model-inherent larger SFR is questioned and therefore explored analytically. This shows the expected result for the Lyman continuum, but that the total SNII energy release is equal for both IMF modes, while the power is smaller for the truncated IMF. Reasonably, the different IMFs leave fingerprints in the abundance ratios of massive to intermediate-mass star elements.

The cluster initial mass function of the M82 disc super star clusters

ABSTRACT The presence of a population of a large number (∼400) of almost coeval (100–300 Myr) super star clusters (SSCs) in the disc of M82 offers an opportunity to construct the Cluster Initial Mass Function (CIMF) from the observed present-day Cluster Mass Function (CMF). We carry out the dynamical and photometric evolution of the CMF assuming that the clusters move in circular orbits under the gravitational potential of the host galaxy using the semi-analytical simulation code Evolve Me a Cluster of StarS. We explore power-law and lognormal functions for the CIMFs, and populate the clusters in the disc assuming uniform, power-law, and exponential radial distribution functions. We find that the observed CMF is best produced by a CIMF that is power law in form with an index of 1.8, for a power-law radial distribution function. More importantly, we establish that the observed turn-over in the present-day CMF is the result of observational incompleteness rather than due to dynamically induced effects, or an intrinsically lognormal CIMF, as was proposed for the fossil starburst region B of this galaxy. Our simulations naturally reproduce the mass–radius relation observed for a sub-sample of M82 SSCs.

JADES NIRSpec Spectroscopy of GN-z11: Lyman-α emission and possible enhanced nitrogen abundance in a z = 10.60 luminous galaxy

We present JADES JWST/NIRSpec spectroscopy of GN-z11, the most luminous candidate z > 10 Lyman break galaxy in the GOODS-North field with MUV = −21.5. We derive a redshift of z = 10.603 (lower than previous determinations) based on multiple emission lines in our low and medium resolution spectra over 0.7 − 5.3 μm. We significantly detect the continuum and measure a blue rest-UV spectral slope of β = −2.4. Remarkably, we see spatially extended Lyman-α in emission (despite the highly neutral intergalactic medium expected at this early epoch), offset 555 km s−1 redwards of the systemic redshift. From our measurements of collisionally excited lines of both low and high ionisation (including [O II] λ3727, [Ne III] λ3869, and C III] λ1909), we infer a high ionisation parameter (log U ∼ −2). We detect the rarely seen N IV] λ1486 and N III] λ1748 lines in both our low and medium resolution spectra, with other high ionisation lines seen in the low resolution spectrum, such as He II (blended with O III]) and C IV (with a possible P-Cygni profile). Based on the observed rest-UV line ratios, we cannot conclusively rule out photoionisation from an active galactic nucleus (AGN), although the high C III]/He II and N III]/He II ratios are compatible with a star formation explanation. If the observed emission lines are powered by star formation, then the strong N III] λ1748 observed may imply an unusually high N/O abundance. Balmer emission lines (Hγ, Hδ) are also detected, and if powered by star formation rather than an AGN, we infer a star formation rate of ∼20 − 30 M⊙ yr−1 (depending on the initial mass function) and low dust attenuation. Our NIRSpec spectroscopy confirms that GN-z11 is a remarkable galaxy with extreme properties seen 430 Myr after the Big Bang.

Modeling the JWST High-redshift Galaxies with a General Formation Scenario and the Consistency with the ΛCDM Model

Early results from the James Webb Space Telescope (JWST) observations have hinted at two traces beyond the standard cosmological framework. One is the extraordinarily high stellar masses and their density at z = 7.5 ∼ 9.1; another is the unexpected abundance of ultraviolet (UV) bright galaxies at z ≥ 10. Nevertheless, both pieces of evidence are not statistically robust yet. In this work, we construct rest-frame UV luminosity functions (LFs) based on a general formation model for these high-redshift galaxy candidates, since UV LFs always carry the information of stellar formation efficiency (SFE), initial mass function (IMF), dust attenuation, and other crucial elements for galaxy evolution. By updating the massive galaxies candidates with spectroscopic observations and exploring the parameter space of SFE, we are able to reasonably explain the cumulative stellar mass density within the redshift range of 7.5–9.1, with only one galaxy exhibiting unusual characteristics. We also reveal a potential nonmonotonic trend of SFE with the increasing redshift. At higher redshift (z ∼ 13), bright UV LFs can be well fitted with non–dust attenuation or top-heavy IMF for Population III stars. The Population III star scenario can also naturally account for the possible dip of the peak SFE evolution curve at z ∼ 9.

Correction to ‘The impact of carbon and oxygen abundances on the metal-poor initial mass function'

Correction to ‘The impact of carbon and oxygen abundances on the metal-poor initial mass function'

Universal Upper End of the Stellar Initial Mass Function in the Young and Compact LEGUS Clusters

We investigate the variation in the upper end of the stellar initial mass function (uIMF) in 375 young and compact star clusters in five nearby galaxies within ∼5 Mpc. All the young stellar clusters (YSCs) in the sample have ages ≲ 4 Myr and masses above 500 M ⊙, according to standard stellar models. The YSC catalogs were produced from Hubble Space Telescope images obtained as part of the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. They are used here to test whether the uIMF is universal or changes as a function of the cluster’s stellar mass. We perform this test by measuring the Hα luminosity of the star clusters as a proxy for their ionizing photon rate, and charting its trend as a function of cluster mass. Large cluster numbers allow us to mitigate the stochastic sampling of the uIMF. The advantage of our approach relative to previous similar attempts is the use of cluster catalogs that have been selected independently of the presence of Hα emission, thus removing a potential sample bias. We find that the uIMF, as traced by the Hα emission, shows no dependence on cluster mass, suggesting that the maximum stellar mass that can be produced in star clusters is universal, in agreement with previous findings.

Spectroscopic substellar initial mass function of NGC 2244

Context. The dominant formation channel of brown dwarfs (BDs) is not well constrained yet and a promising way to discriminate between scenarios is to test the environment-dependent efficiency in forming BDs. So far, the outcome of star formation, studied through the initial mass function, has been found to be very similar in all clusters that have been inspected. Aims. We aim to characterize the low-mass (sub)stellar population of the central portion (2.4 pc2) of the ∼2 Myr old cluster NGC 2244 using near-infrared spectroscopy. By studying this cluster, characterized by a low stellar density and numerous OB stars, we aim to explore the effect that OB stars may have on the production of BDs. Methods. We obtained near-infrared HK spectroscopy of 85 faint candidate members of NGC 2244. We derived the spectral type and extinction by comparison with spectral templates. We evaluated cluster membership using three gravity-sensitive spectral indices based on the shape of the H-band. Furthermore, we evaluated the infrared excess from Spitzer of all the candidate members of the cluster. Finally, we estimated the mass of all the candidate members of the cluster and derived the initial mass function, star-to-BD number ratio, and disk fraction. Results. The initial mass function is well represented by a power law (dN/dM ∝ M−α) below 0.4 M⊙, with a slope α = 0.7–1.1 depending on the fitted mass range. We calculated a star-to-BD number ratio of 2.2–2.8. We find the low-mass population of NGC 2244 to be consistent with nearby star-forming regions, although it is at the high end of BD production. We find BDs in NGC 2244 to be, on average, closer to OB stars than to low-mass stars, which could potentially be the first piece of evidence that OB stars affect the formation of BDs. We find a disk fraction of all the members with a spectral type later than K0 of 39 ± 9% which is lower than typical values found in nearby star-forming regions of similar ages.

Star Formation in Self-gravitating Disks in Active Galactic Nuclei. III. Efficient Production of Iron and Infrared Spectral Energy Distributions

Strong iron lines are a common feature of the optical spectra of active galactic nuclei (AGNs) and quasars from z ∼ 6−7 to the local universe, and [Fe/Mg] ratios do not show cosmic evolution. During active episodes, accretion disks surrounding supermassive black holes (SMBHs) inevitably form stars in the self-gravitating part, and these stars accrete with high accretion rates. In this paper, we investigate the population evolution of accretion-modified stars (AMSs) to produce iron and magnesium in AGNs. The AMSs, as a new type of star, are allowed to have any metallicity but without significant loss from stellar winds, since the winds are choked by the dense medium of the disks and return to the core stars. Mass functions of the AMS population show a pile-up or cutoff pile-up shape in top-heavy or top-dominant forms if the stellar winds are strong, consistent with the narrow range of supernovae (SNe) explosions driven by the known pair-instability. This provides an efficient way to produce metals. Meanwhile, SN explosions support an inflated disk as a dusty torus. Furthermore, the evolving top-heavy initial mass functions lead to bright luminosity in infrared bands in dusty regions. This contributes a new component in infrared bands, which is independent of the emissions from the central part of accretion disks, appearing as a long-term trending of the NIR continuum compared to optical variations. Moreover, the model can be further tested through reverberation mapping of emission lines, including LIGO/LISA detections of gravitational waves and signatures from spatially resolved observations of GRAVITY+/VLTI.

A Value-added COSMOS2020 Catalog of Physical Properties: Constraining Temperature-dependent Initial Mass Function

This work presents and releases a catalog of new photometrically derived physical properties for the ∼105 most well-measured galaxies in the COSMOS field on the sky. Using a recently developed technique, spectral energy distributions are modeled assuming a stellar initial mass function (IMF) that depends on the temperature of gas in star-forming regions. The method is applied to the largest current sample of high-quality panchromatic photometry, the COSMOS2020 catalog, that allows for testing this assumption. It is found that the galaxies exhibit a continuum of IMF and gas temperatures, most of which are bottom-lighter than measured in the Milky Way. As a consequence, the stellar masses and star formation rates of most galaxies here are found to be lower than those measured by traditional techniques in the COSMOS2020 catalog by factors of ∼1.6–3.5 and 2.5–70.0, respectively, with the change being the strongest for the most active galaxies. The resulting physical properties provide new insights into variation of the IMF-derived gas temperature along the star-forming main sequence and at quiescence, produce a sharp and coherent picture of downsizing, as seen from the stellar mass functions, and hint at a possible high-temperature and high-density stage of early galactic evolution.

Free-floating Planet Mass Function from MOA-II 9 yr Survey toward the Galactic Bulge

We present the first measurement of the mass function of free-floating planets (FFPs), or very wide orbit planets down to an Earth mass, from the MOA-II microlensing survey in 2006–2014. Six events are likely to be due to planets with Einstein radius crossing times t E < 0.5 days, and the shortest has t E = 0.057 ± 0.016 days and an angular Einstein radius of θ E = 0.90 ± 0.14 μas. We measure the detection efficiency depending on both t E and θ E with image-level simulations for the first time. These short events are well modeled by a power-law mass function, dex−1 star−1 with for M/M ⊙ < 0.02. This implies a total of FFPs or very wide orbit planets of mass 0.33 < M/M ⊕ < 6660 per star, with a total mass of star−1. The number of FFPs is times the number of planets in wide orbits (beyond the snow line), while the total masses are of the same order. This suggests that the FFPs have been ejected from bound planetary systems that may have had an initial mass function with a power-law index of α ∼ 0.9, which would imply a total mass of star−1. This model predicts that Roman Space Telescope will detect FFPs with masses down to that of Mars (including with 0.1 ≤ M/M ⊕ ≤ 1). The Sumi et al. large Jupiter-mass FFP population is excluded.

Massive binary black holes from Population II and III stars

ABSTRACT Population III stars, born from the primordial gas in the Universe, lose a negligible fraction of their mass via stellar winds and possibly follow a top-heavy mass function. Hence, they have often been regarded as the ideal progenitors of massive black holes (BHs), even above the pair instability mass gap. Here, we evolve a large set of Population III binary stars (metallicity Z = 10−11) with our population-synthesis code sevn, and compare them with Population II binary stars (Z = 10−4). In our models, the lower edge of the pair-instability mass gap corresponds to a BH mass of ≈86 (≈91) M⊙ for single Population III (II) stars. Overall, we find only mild differences between the properties of binary BHs (BBHs) born from Population III and II stars, especially if we adopt the same initial mass function and initial orbital properties. Most BBH mergers born from Population III and II stars have primary BH mass below the pair-instability gap, and the maximum secondary BH mass is &amp;lt;50 M⊙. Only up to ≈3.3 per cent (≈0.09 per cent) BBH mergers from Population III (II) progenitors have primary mass above the gap. Unlike metal-rich binary stars, the main formation channel of BBH mergers from Population III and II stars involves only stable mass transfer episodes in our fiducial model.

Confirmation and refutation of very luminous galaxies in the early Universe.

During the first 500 million years of cosmic history, the first stars and galaxies formed, seeding the Universe with heavy elements and eventually reionizing the intergalactic medium1-3. Observations withtheJames Webb Space Telescope (JWST) have uncovered a surprisingly high abundance of candidates for early star-forming galaxies, with distances (redshifts, z), estimated from multiband photometry, as large as z ≈ 16, far beyond pre-JWST limits4-9. Althoughsuch photometric redshifts are generally robust, they can suffer from degeneracies and occasionally catastrophic errors. Spectroscopic measurements are required to validate these sources and to reliably quantify physical properties that can constrain galaxy formation models and cosmology10. Here we present JWST spectroscopy that confirms redshifts for two very luminous galaxies with z > 11, and also demonstrates that another candidate with suggested z ≈ 16 instead has z = 4.9, with an unusual combination of nebular line emission and dust reddening that mimics the colours expected for much more distant objects. These results reinforce evidence for the early, rapid formation of remarkably luminous galaxies while also highlighting the necessity of spectroscopic verification. The large abundance of bright, early galaxies may indicate shortcomings in current galaxy formation models or deviations from physical properties (such as the stellar initial mass function) that are generally believed to hold at later times.

Evolved massive stars at low-metallicity

The mass-loss rate (MLR) is one of the most important parameters in astrophysics, because it impacts many areas of astronomy, such as ionizing radiation, wind feedback, star-formation rates, initial mass functions, stellar remnants, supernovae, and so on. However, the most important modes of mass loss are also the most uncertain, as the dominant physical mechanisms that lead to this phenomenon are stull largely unknown. Here we assemble the most complete and clean red supergiant (RSG) sample (2121 targets) so far in the Small Magellanic Cloud (SMC) with 53 different bands of data to study the MLR of RSGs. In order to match the observed spectral energy distributions (SEDs), we created a theoretical grid of 17 820 oxygen-rich models (“normal” and “dusty” grids are half-and-half) using the radiatively driven wind model of the DUSTY code, covering a wide range of dust parameters. We select the best model for each target by calculating the minimal modified chi-square and visual inspection. The resulting MLRs from DUSTY are converted to real MLRs based on the scaling relation, for which a total MLR of 6.16 × 10−3 M⊙ yr−1 is measured (corresponding to a dust-production rate of ∼6 × 10−6 M⊙ yr−1), with a typical MLR of ∼10−6 M⊙ yr−1 for the general population of the RSGs. The complexity of mass-loss estimations based on the SED is fully discussed for the first time, and our results indicate large uncertainties based on the photometric data (potentially up to one order of magnitude or more). The Hertzsprung-Russell (HR) and luminosity versus median-absolute-deviation (MAD) diagrams of the sample indicate the positive relation between luminosity and MLR. Meanwhile, the luminosity versus MLR diagrams show a “knee-like” shape with enhanced mass loss occurring above log10(L/L⊙)≈4.6, which may be due to the degeneracy of luminosity, pulsation, low surface gravity, convection, and other factors. We derive our MLR relation using a third-order polynomial to fit the sample and compare our results with previous empirical MLR prescriptions. Given that our MLR prescription is based on a much larger sample than previous determinations, it provides a more accurate relation at the cool and luminous region of the HR diagram at low metallicity compared to previous studies. Finally, nine targets in our sample were detected in the UV, which could be an indicator of OB-type companions of binary RSGs.

Diffuse Neutrino Flux Based on the Rates of Core-collapse Supernovae and Black Hole Formation Deduced from a Novel Galactic Chemical Evolution Model

Fluxes of the diffuse supernova neutrino background (DSNB) are calculated based on a new modeling of galactic chemical evolution, where a variable stellar initial mass function (IMF), depending on the galaxy type, is introduced and black hole (BH) formation from the failed supernova is considered for progenitors heavier than 18M ⊙. The flux calculations are performed for different combinations of the star formation rate, nuclear equation of state, and neutrino mass hierarchy, to examine the systematic effects from these factors. In any case, our new model predicts the enhanced DSNB flux at E ν ≳ 30 MeV and E ν ≲ 10 MeV, due to more frequent BH formation and a larger core-collapse rate at high redshifts in early-type galaxies, respectively. Event rate spectra of the DSNB at a detector from the new model are shown, and the detectability at water-based Cherenkov detectors, Super-Kamiokande with a gadolinium dissolution and Hyper-Kamiokande, is discussed. In order to investigate the impacts of the assumptions in the new model, we prepare alternative models, based on different IMF forms and treatments of BH formation, and estimate the discrimination capabilities between the new and alternative models at these detectors.

A model for GN-z11: top-heavy stellar initial mass functions in forming galactic nuclei and ultra-compact dwarfs

ABSTRACT Recent JWST observations of the z = 10.6 galaxy GN-z11 have revealed a very high gas-phase nitrogen abundance (higher than four times the solar value), a very small half-light radius (≈60 pc), and a large stellar mass (Ms ≈ 109 M⊙) for its size. We consider that this object is a forming galactic nucleus or ultra-compact dwarf galaxy rather than a proto globular cluster, and thereby investigate the chemical abundance pattern using one-zone chemical evolution models. The principal results of the models are as follows. The observed log (N/O) &amp;gt; −0.24, log (C/O) &amp;gt; −0.78, and 12 + log (O/H) ≈ 7.8 can be self-consistently reproduced by the models both with very short star formation time-scales (&amp;lt;107 yr) and with top-heavy stellar initial mass functions. The adopted assumption of no chemical enrichment by massive (m &amp;gt; 25 M⊙) core collapse supernovae (CCSNe) is also important for the reproduction of high gas-phase log (N/O), because such CCSNe can decrease high log (N/O) of gas polluted by OB and Wolf–Rayet stars. GN-z11 can have a significant fraction (&amp;gt;0.5) of nitrogen-rich ([N/Fe] &amp;gt; 0.5) stars, which implies a possible link between nitrogen-rich stellar populations of the inner Galaxy and giant elliptical galaxies and high-z objects with high gas-phase log (N/O) like GN-z11.

The energy distribution of the first supernovae

ABSTRACT The nature of the first Pop III stars is still a mystery and the energy distribution of the first supernovae is completely unexplored. For the first time we account simultaneously for the unknown initial mass function (IMF), stellar mixing, and energy distribution function (EDF) of Pop III stars in the context of a cosmological model for the formation of a MW-analogue. Our data-calibrated semi-analytic model is based on a N-body simulation and follows the formation and evolution of both Pop III and Pop II/I stars in their proper time-scales. We discover degeneracies between the adopted Pop III unknowns, in the predicted metallicity and carbonicity distribution functions and the fraction of C-enhanced stars. None the less, we are able to provide the first available constraints on the EDF, $dN/dE_\star \propto E_{\star }^{-\alpha _e}$ with 1 ≤ αe ≤ 2.5. In addition, the characteristic mass of the Pop III IMF should be mch &amp;lt; 100 M⊙, assuming a mass range consistent with hydrodynamical simulations (0.1–1000 M⊙). Independent of the assumed Pop III properties, we find that all $\rm [C/Fe]\gt +0.7$ stars (with $\rm [Fe/H]\lt -2.8$) have been enriched by Pop III supernovae at a $\gt 20~{{\ \rm per\ cent}}$ level, and all $\rm [C/Fe]\gt +2$ stars at a $\gt 95~{{\ \rm per\ cent}}$ level. All very metal-poor stars with $\rm [C/Fe]\lt 0$ are predicted to be predominantly enriched by Pop III hypernovae and/or pair instability supernovae. To better constrain the primordial EDF, it is absolutely crucial to have a complete and accurate determination of the metallicity distribution function, and the properties of C-enhanced metal-poor stars (frequency and [C/Fe]) in the Galactic halo.

The MillenniumTNG project: the galaxy population at z ≥ 8

ABSTRACT The early release science results from JWST have yielded an unexpected abundance of high-redshift luminous galaxies that seems to be in tension with current theories of galaxy formation. However, it is currently difficult to draw definitive conclusions form these results as the sources have not yet been spectroscopically confirmed. It is in any case important to establish baseline predictions from current state-of-the-art galaxy formation models that can be compared and contrasted with these new measurements. In this work, we use the new large-volume ($L_\mathrm{box}\sim 740 \, \mathrm{cMpc}$) hydrodynamic simulation of the MillenniumTNG project, suitably scaled to match results from higher resolution – smaller volume simulations, to make predictions for the high-redshift (z ≳ 8) galaxy population and compare them to recent JWST observations. We show that the simulated galaxy population is broadly consistent with observations until z ∼ 10. From z ≈ 10–12, the observations indicate a preference for a galaxy population that is largely dust-free, but is still consistent with the simulations. Beyond z ≳ 12, however, our simulation results underpredict the abundance of luminous galaxies and their star-formation rates by almost an order of magnitude. This indicates either an incomplete understanding of the new JWST data or a need for more sophisticated galaxy formation models that account for additional physical processes such as Population III stars, variable stellar initial mass functions, or even deviations from the standard ΛCDM model. We emphasize that any new process invoked to explain this tension should only significantly influence the galaxy population beyond z ≳ 10, while leaving the successful galaxy formation predictions of the fiducial model intact below this redshift.

A Number Estimate of Detectable Detached Black Hole-star Binaries using a Photometric Telescope

Detached and wide-orbit black hole-star binaries (BHSBs) can generate three types of periodic photometric signals: Ellipsoidal Variation, Doppler beaming and Self-Lensing (SL), providing a proxy to discover these black holes. We estimate the relative amplitude of the three signals for such systems and the detectability for black holes of a photometric telescope like Kepler in several steps. We estimate the searchable star number by assuming every star has a black hole companion, and apply the occurrence of BHSBs in field stars to estimate the detectable black hole signals. We consider three types of Initial Mass Function (IMF) model with different high end exponential slopes. “When spot and white noise are both considered, there is about one detectable signal for SL and less than one event is expected for beaming and Ellipsoidal Variation signal in Kepler Input Catalog stars with the standard IMF model.” to “Due to contamination by stellar spots and white noise, one may expect one detectable signal for SL and less than one detectable signal for both beaming and Ellipsoidal Variation in Kepler Input Catalog stars with the standard IMF model.” On the other hand, if we assume that only white noise affects the detection efficiency of the BHSBs, we expect about 10 Ellipsoidal Variation signals and 17 beaming signals to be detectable while the number of SL signals remains unchanged.

A Novel Survey for Young Substellar Objects with the W-band Filter. VI. Spectroscopic Census of Substellar Members and the IMF of the σ Orionis Cluster

Low-mass stars and substellar objects are essential in tracing the initial mass function (IMF). We study the nearby young σ Orionis cluster (d ∼ 408 pc, age ∼ 1.8 Myr) using deep near-infrared (NIR) photometric data in the J, W, and H bands from WIRCam on the Canada–France–Hawaii Telescope. We use the water absorption feature to select brown dwarfs photometrically and confirm their nature spectroscopically with IRTF-SpeX. Additionally we select candidate low-mass stars for spectroscopy and analyze their membership and those of literature sources using astrometry from Gaia DR3. We obtain NIR spectra for 28 very-low-mass stars and brown dwarfs and estimate their spectral type between M3 and M8.5 (masses ranging between 0.3 and 0.01 M ⊙). Apart from these, we also identify five new planetary-mass candidates which require further spectroscopic confirmation of youth. We compile a comprehensive catalog of 170 spectroscopically confirmed members in the central region of the cluster, for a wide mass range of ∼19–0.004 M ☉. We estimate the star-to-brown-dwarf ratio to be ∼4, within the range reported for other nearby star-forming regions. With the updated catalog of members we trace the IMF down to 4 M Jup and we find that a two-segment power law fits the substellar IMF better than a log-normal distribution.

Templates for Fitting Photometry of Ultra-high-redshift Galaxies

Recent data from the James Webb Space Telescope allow a first glimpse of galaxies at z ≳ 11. The most successful tool for identifying ultra-high-redshift candidates and inferring their properties is photometric template fitting. However, current methods rely on templates derived from much lower-redshift conditions, including stellar populations older than the age of the Universe at z > 12, a stellar initial mass function that is physically disallowed at z > 6, and weaker emission lines than currently observed at z > 7.5. Here, two sets of synthetic templates, optimized for the expected astrophysics of galaxies at 8 < z < 12 and z > 12, are developed and used to fit three galaxies at z > 12 from the SMACS0723 field. Using these improved templates, quantitative estimates are produced of the bias in inferred properties from JWST observations at z > 8 due to these effects. The best-fit redshifts are similar to those found with previous template sets, but the inferred stellar masses drop by as much as 1–1.6 dex, such that stellar masses are no longer seemingly inconsistent with ΛCDM. The two new template sets are released in formats compatible with EAZY and LePhare.