Abstract The unprecedented medium-resolution ( R λ ∼ 1500–3500) near- and mid-infrared (1–18 μ m) spectrum provided by JWST for the young (140 ± 20 Myr) low-mass (12–20 M Jup ) L–T transition (L7) ...companion VHS 1256 b gives access to a catalog of molecular absorptions. In this study, we present a comprehensive analysis of this data set utilizing a forward-modeling approach applying our Bayesian framework, ForMoSA . We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: T eff , log( g ), M/H, C/O, γ , f sed , and R . Our findings reveal that each parameter’s estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS 1256 b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a T eff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log( g ). Despite the exceptional data quality, attaining robust estimates for chemical abundances M/H and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST’s data for VHS 1256 b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.
Abstract We present a sample of 88 candidate z ∼ 8.5–14.5 galaxies selected from the completed NIRCam imaging from the Cosmic Evolution Early Release Science survey. These data cover ∼90 arcmin 2 (10 ...NIRCam pointings) in six broadband imaging filters and one medium-band imaging filter. With this sample we confirm at higher confidence early JWST conclusions that bright galaxies in this epoch are more abundant than predicted by most theoretical models. We construct the rest-frame ultraviolet luminosity functions at z ∼ 9, 11, and 14 and show that the space density of bright ( M UV = −20) galaxies changes only modestly from z ∼ 14 to z ∼ 9, compared to a steeper increase from z ∼ 8 to z ∼ 4. While our candidates are photometrically selected, spectroscopic follow-up has now confirmed 13 of them, with only one significant interloper, implying that the fidelity of this sample is high. Successfully explaining the evidence for a flatter evolution in the number densities of UV-bright z > 10 galaxies may thus require changes to the dominant physical processes regulating star formation. While our results indicate that significant variations of dust attenuation with redshift are unlikely to be the dominant factor at these high redshifts, they are consistent with predictions from models that naturally have enhanced star formation efficiency and/or stochasticity. An evolving stellar initial mass function could also bring model predictions into better agreement with our results. Deep spectroscopic follow-up of a large sample of early galaxies can distinguish between these competing scenarios.
Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability
. However, no unambiguous photochemical products have been detected in ...exoplanet atmospheres so far. Recent observations from the JWST Transiting Exoplanet Community Early Release Science Program
found a spectral absorption feature at 4.05 μm arising from sulfur dioxide (SO
) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 M
) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of around 1,100 K (ref.
). The most plausible way of generating SO
in such an atmosphere is through photochemical processes
. Here we show that the SO
distribution computed by a suite of photochemical models robustly explains the 4.05-μm spectral feature identified by JWST transmission observations
with NIRSpec PRISM (2.7σ)
and G395H (4.5σ)
. SO
is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (H
S) is destroyed. The sensitivity of the SO
feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of about 10× solar. We further point out that SO
also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations.
Recent JWST eclipse spectra of the high-density hot Saturn HD 149026b between 2.35 and 5.08 \(\mu\)m has allowed for in-depth study of its atmosphere. To understand its atmospheric properties, we ...have created a grid of 1D radiative-convective-thermochemical equilibrium atmosphere models and spectra with PICASO 3.0. In agreement with previous work, we find that the presence of gaseous TiO creates a thermal inversion, which is inconsistent with the data. The presence of gaseous VO, however, which condenses at temperatures 200 K cooler, does not cause such inversions but alters the temperature-pressure profile of the atmosphere. We estimate an atmospheric metallicity of \(14^{+12}_{-8}\times\) solar without VO and \(20^{+11}_{-8}\times\) solar with VO, a factor of \(\sim 10\) times smaller than previous work from Bean et al. (2023), who relied on atmosphere retrievals. We attribute this significant difference in metallicity to a larger temperature gradient at low pressures in radiative equilibrium models. Such models with lower metallicities readily fit the strong CO\(_2\) feature at 4.3 \(\mu\)m. Our lower estimated metallicity makes HD 149026b more consistent with the mass-metallicity relationship for other giant planets. We find a C/O ratio of \(0.67^{+0.06}_{-0.27}\) with and without VO. The best-fit heat redistribution factor without VO is \(1.17\), a very high value suggesting very little dayside energy transport and no energy transport to the night side. The heat redistribution factor shrinks to a more plausible value of \(0.91^{+0.05}_{-0.05}\), with VO, which we regard as circumstantial evidence for the molecule in the atmosphere of HD 149026b.
We present the first JWST spectral energy distribution of a Y dwarf. This spectral energy distribution of the Y0 dwarf WISE J035934.06\(-\)540154.6 consists of low-resolution ...(\(\lambda\)/\(\Delta\lambda\) \(\sim\) 100) spectroscopy from 1\(-\)12 \(\mu\)m and three photometric points at 15, 18, and 21 \(\mu\)m. The spectrum exhibits numerous fundamental, overtone, and combination rotational-vibrational bands of H\(_2\)O, CH\(_4\), CO, CO\(_2\), and NH\(_3\), including the previously unidentified \(\nu_3\) band of NH\(_3\) at 3 \(\mu\)m. Using a Rayleigh-Jeans tail to account for the flux emerging at wavelengths greater than 21 \(\mu\)m, we measure a bolometric luminosity of \(1.523\pm0.090\times10^{20}\) W. We determine a semi-empirical effective temperature estimate of \(467^{+16}_{-18}\) K using the bolometric luminosity and evolutionary models to estimate a radius. Finally, we compare the spectrum and photometry to a grid of atmospheric models and find reasonably good agreement with a model having \(T_{\mathrm{eff}}\)=450 K, log \(g\)=3.25 cm s\(^{-2}\), M/H=\(-0.3\). However, the low surface gravity implies an extremely low mass of 1 \(M_{\rm{Jup}}\) and a very young age of 20 Myr, the latter of which is inconsistent with simulations of volume-limited samples of cool brown dwarfs.
We reanalyze near-infrared spectra of the young extrasolar giant planet 51 Eridani b which was originally presented in (Macintosh et al. 2015) and (Rajan et al. 2017) using modern atmospheric models ...which include a self-consistent treatment of disequilibrium chemistry due to turbulent vertical mixing. In addition, we investigate the possibility that significant opacity from micrometeors or other impactors in the planet's atmosphere may be responsible for shaping the observed spectral energy distribution (SED). We find that disequilibrium chemistry is useful for describing the mid-infrared colors of the planet's spectra, especially in regards to photometric data at M band around 4.5 \(\mu\)m which is the result of super-equilibrium abundances of carbon monoxide, while the micrometeors are unlikely to play a pivotal role in shaping the SED. The best-fitting, micrometeroid-dust-free, disequilibrium chemistry, patchy cloud model has the following parameters: effective temperature \(T_\textrm{eff} = 681\) K with clouds (or without clouds, i.e. the grid temperature \(T_\textrm{grid}\) = 900 K), surface gravity \(g\) = 1000 m/s\(^2\), sedimentation efficiency \(f_\textrm{sed}\) = 10, vertical eddy diffusion coefficient \(K_\textrm{zz}\) = 10\(^3\) cm\(^2\)/s, cloud hole fraction \(f_\textrm{hole}\) = 0.2, and planet radius \(R_\textrm{planet}\) = 1.0 R\(_\textrm{Jup}\).
Future space-based direct imaging missions will perform low-resolution (R\(<\)100) optical (0.3-1~\(\mu\)m) spectroscopy of planets, thus enabling reflected spectroscopy of cool giants. Reflected ...light spectroscopy is encoded with rich information about the scattering and absorbing properties of planet atmospheres. Given the diversity of clouds and hazes expected in exoplanets, it is imperative we solidify the methodology to accurately and precisely retrieve these scattering and absorbing properties that are agnostic to cloud species. In particular, we focus on determining how different cloud parameterizations affect resultant inferences of both cloud and atmospheric composition. We simulate mock observations of the reflected spectra from three top priority direct imaging cool giant targets with different effective temperatures, ranging from 135 K to 533 K. We perform retrievals of cloud structure and molecular abundances on these three planets using four different parameterizations, each with increasing levels of cloud complexity. We find that the retrieved atmospheric and scattering properties strongly depend on the choice of cloud parameterization. For example, parameterizations that are too simplistic tend to overestimate the abundances. Overall, we are unable to retrieve precise/accurate gravity beyond \(\pm\)50\%. Lastly, we find that even low SNR=5, low R=40 reflected light spectroscopy gives cursory zeroth order insights into cloud deck position relative to molecular and Rayleigh optical depth level.
The sensitivity and spectral coverage of JWST is enabling us to test our
assumptions of ultracool dwarf atmospheric chemistry, especially with regards
to the abundances of phosphine (PH$_3$) and ...carbon dioxide (CO$_2$). In this
paper, we use NIRSpec PRISM spectra ($\sim$0.8$-$5.5 $\mu$m, $R\sim$100) of
four late T and Y dwarfs to show that standard substellar atmosphere models
have difficulty replicating the 4.1$-$4.4 $\mu$m wavelength range as they
predict an overabundance of phosphine and an underabundance of carbon dioxide.
To help quantify this discrepancy, we generate a grid of models using PICASO
based on the Elf Owl chemical and temperature profiles where we include the
abundances of these two molecules as parameters. The fits to these PICASO
models show a consistent preference for orders of magnitude higher CO$_2$
abundances and a reduction in PH$_3$ abundance as compared to the nominal
models. This tendency means that the claimed phosphine detection in
UNCOVER$-$BD$-$3 could instead be explained by a CO$_2$ abundance in excess of
standard atmospheric model predictions; however the signal-to-noise of the
spectrum is not high enough to discriminate between these cases. We discuss
atmospheric mechanisms that could explain the observed underabundance of PH$_3$
and overabundance of CO$_2$, including a vertical eddy diffusion coefficient
($K_{\mathrm{zz}}$) that varies with altitude, incorrect chemical pathways, or
elements condensing out in forms such as NH$_4$H$_2$PO$_4$. However, our
favored explanation for the required CO$_2$ enhancement is that the quench
approximation does not accurately predict the CO$_2$ abundance, as CO$_2$
remains in chemical equilibrium with CO after CO quenches.
We present infrared spectral energy distributions of 23 late-type T and Y dwarfs obtained with the James Webb Space Telescope. The spectral energy distributions consist of NIRSpec PRISM and MIRI LRS ...spectra covering the \(\sim\)1--12 \(\mu\)m wavelength range at \(\lambda/ \Delta \lambda \approx 100\) and broadband photometry at 15, 18, and 21 \(\mu\)m. The spectra exhibit absorption features common to these objects including H\(_2\)O, CH\(_4\), CO, CO\(_2\), and NH\(_3\). Interestingly, while the spectral morphology changes relatively smoothly with spectral type at \(\lambda < 3\) \(\mu\)m and \(\lambda > 8\) \(\mu\)m, it shows no clear trend in the 5 \(\mu\)m region where a large fraction of the flux emerges. The broad wavelength coverage of the data enables us to compute the first accurate measurements of the bolometric fluxes of cool brown dwarfs. Combining these bolometric fluxes with parallaxes from Spitzer and HST, we also obtain the first accurate bolometric luminosities of these cool dwarfs. We then used the Sonora Bobcat solar metallicity evolutionary models to estimate the radii of the dwarfs which results in effective temperature estimates ranging from \(\sim\)1000 to 350 K with a median uncertainty of \(\pm\)20 K which is nearly an order of magnitude improvement over previous work. We also discuss how various portions of the spectra either do or do not exhibit a clear sequence when ordered by their effective temperatures.
We present an atmospheric retrieval analysis of the Y0 brown dwarf WISE J035934.06\(-\)540154.6 using the low-resolution 0.96--12 \(\mu\)m JWST spectrum presented in \citet{Beiler_2023}. We obtain ...volume number mixing ratios of the major gas-phase absorbers (H\(_2\)O, CH\(_4\), CO, CO\(_2\), PH\(_3\), and H\(_2\)S) that are 3--5\(\times\) more precise than previous work that used HST spectra. We also find an order-of-magnitude improvement in the precision of the retrieved thermal profile, a direct result of the broad wavelength coverage of the JWST data. We used the retrieved thermal profile and surface gravity to generate a grid of chemical forward models with varying metallicity, (C/O)\(_\textrm{atm}\), and strengths of vertical mixing as encapsulated by the eddy diffusion coefficient \(K_\textrm{zz}\). Comparison of the retrieved abundances with this grid of models suggests that the deep atmosphere of WISE 0359\(-\)54 shows signs of vigorous vertical mixing with \(K_\textrm{zz}=10^9\) cm\(^{2}\) s\(^{-1}\). To test the sensitivity of these results to our 5-knot spline thermal profile model, we performed a second retrieval using the \citet{Madhusudhan_2009} thermal profile model. While the results of the two retrievals generally agree well, we do find differences between the retrieved values of mass and volume number mixing ratio of H\(_2\)S with fractional differences of the median values of \(-\)0.64 and \(-\)0.10, respectively. In addition, the 5-knot thermal profile is consistently warmer at pressure between 1 and 70 bar. Nevertheless, our results underscore the power that the broad-wavelength infrared spectra obtainable with the James Webb Space Telescope have to characterize the atmospheres of cool brown dwarfs.
