arXiv subjects

G. Wright

Publications and source records attributed to G. Wright.

At least 19 recordsLinked to original sources

arXiv2026

Dust production in the harsh environment of Sgr A* - MIRI/JWST observation of the O-rich asymptotic giant branch star IRS~3

Studies of the interstellar medium (ISM) have frequently revealed signatures of the dust produced in the envelopes of asymptotic giant branch (AGB) stars, demonstrating a connection between the dust composition of the ISM and that of AGB stellar envelopes. Investigating this relationship in the extreme, radiation-dominated environment surrounding Sgr A*, the center of our own galaxy, reveals how such conditions might influence dust composition and the recycling of material in galactic centers. IRS 3, the brightest L band source in the Galactic center and most prominent AGB star within the inner parsec of the Milky Way, is embedded in a dusty envelope with an estimated radius of $\sim$10000 AU. We aim to conduct a comprehensive spectral analysis to more tightly constrain the dust composition and line-emitting species within the envelope of IRS 3 in the immediate vicinity of Sgr A*. In 2025, we observed the inner parsec of the Milky Way with the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) as part of the guaranteed time observations (GTO) program Mid-Infrared Characterisation of Nearby Iconic galaxy Centres (MICONIC). We used the MIRI Medium Resolution Spectrometer (MRS) to study the spectroscopic characteristics of the AGB star IRS 3, located about 0.17 parsecs in projection from Sgr A*.

astro-ph.GA↗

arXiv2026

Understanding Pulsar Magnetospheres with the SKAO

The SKA telescopes will bring unparalleled sensitivity across a broad radio band, a wide field of view across the Southern sky, and the capacity for sub-arraying, all of which make them the ideal instruments for studying the pulsar magnetosphere. This chapter describes the advances that have been made in pulsar magnetosphere physics over the last decade, and details how these have been made possible through the advances of modern radio telescopes, particularly SKA precursors and pathfinders. It explains how the SKA telescopes would transform the field of pulsar magnetosphere physics through a combination of large-scale monitoring surveys and in-depth follow-up observations of unique sources and new discoveries. Finally, it describes how the specific observing opportunities available with the AA* and AA4 configurations will achieve the advances necessary to solve the problem of pulsar radio emission physics in the coming years.

astro-ph.HE↗

arXiv2026

MICONIC: The multiphase circumnuclear region of Centaurus A as seen with JWST/MIRI MRS observations. I. Spectral inventory and properties of the warm molecular disk

Supermassive black holes power Active Galactic Nuclei (AGN), injecting energy that regulates accretion and shapes host galaxies. We investigate the morphology, excitation, and kinematics of molecular hydrogen (H2) in the inner circumnuclear disk of Centaurus A, the nearest radio galaxy. We present JWST/MIRI MRS integral-field spectroscopy of the central 170x100 pc2 at 0.3"-0.7" (5-12 pc) resolution, focusing on pure rotational H2 lines. The spectra show strong nuclear continuum and bright H2 emission from S(1) to S(8), including the first S(8) detection in Centaurus A. Optically thin nuclear lines enable maps of temperature, column density, and ortho-to-para ratio from spaxel-level excitation-diagram fitting. Warm H2 shows a complex morphology, dominating the central region where CO emission is weak or undetected. Low-excitation H2 lines trace an inhomogeneous ring with a 20-pc-radius cavity aligned with the jet's near side, suggesting that the jet affects the morphology of the molecular disk. Higher-excitation lines form filamentary structures around the AGN. Kinematics are rotational with an S-shaped distortion, indicating non-circular motions or a warped disk. A coherent, low-dispersion (70 km/s) streamer spirals inward. A power-law temperature distribution yields a warm (100-2000 K) H2 mass of (5.6+/-1.4)e5 Msun and a dynamical mass of 5e8 Msun within 100 pc. Shock excitation is supported by enhanced H2/continuum and H2/PAH ratios, elevated [Ne III]/[Ne II], and sub-equilibrium ortho-to-para ratios (1.6-2.4). Turbulent dissipation can balance H2 cooling and likely dominates heating beyond 30 pc. In the inner 100 pc of Centaurus A, AGN feeding and feedback are linked: shocks excite H2, regulate the gas temperature, and prevent cooling below 100 K, explaining the weak CO emission and lack of a massive outflow. These shocks may drive angular momentum loss and help fuel the nucleus.

astro-ph.GA↗

arXiv2026

JOYS$+$: A JWST/MIRI survey of the evolution of H$_2$ winds and jets from low-mass protostars

Protostellar outflows display wide-angle winds and collimated jets, the magnetocentrifugal launching of which enables accretion onto the protostar. The majority of the outflow mass is likely ejected or entrained molecular H$_2$, which can now be studied in unprecedented detail with JWST. Using JWST MIRI/MRS observations towards 13 single and 20 multiple Class 0 and I protostars, we investigate the nature and evolution of the H$_2$ wind and jet morphology, mass outflow rate, and velocity and temperature structure. We construct line flux and velocity maps of the H$_2$ S(1) and S(7) lines as well as the sub-mm CO traced by ALMA. Low-$J$ ($J\le4$) H$_2$ transitions trace extended wide-angle, low-velocity (0-20 km s$^{-1}$) winds within the contours of the low-velocity ($< 30$ km s$^{-1}$) sub-mm CO emission, while high-$J$ ($J >5$) transitions are associated with shocks and knots. In Class 0 sources with a known high-velocity ($> 30$ km s$^{-1}$) molecular CO or SiO jet, higher H$_2$ velocities are found along the jet axis. The opening angle of the wind traced by the H$_2$ S(1) line broadens from $\sim20^\circ$ to $\sim90^\circ$ through the Class 0 to Class I stage. Near the base of each blue-shifted outflow lobe, we extract representative spectra, where rotation diagram fitting of the H$_2$ lines is combined with the outflow width and H$_2$ line velocity to measure the mass-loss rates. The rotation diagrams show a warm $\sim 600$ K, component with two orders of magnitude more mass than the hot, 1500-3000 K component. The H$_2$ outflow mass-loss rates decline by two orders of magnitude from the Class 0 to Class II stage and are correlated with bolometric luminosity. The declining warm H$_2$ mass loss rates and increasing opening angles from the Class 0 to I stages, and the absence of H$_2$ jets in the Class I sources, are consistent with the predictions of MHD disk wind models.

astro-ph.SR↗

arXiv2026

MICONIC: JWST/MIRI-MRS reveals heavily reprocessed PAH emission in the circum-nuclear disc of Centaurus A

Polycyclic aromatic hydrocarbons (PAHs) are key dust components in galaxies and play a fundamental role in the physics of the interstellar medium (ISM), yet their response to AGN feedback remains debated. We present a spatially resolved analysis of PAHs in the central $7^{\prime\prime}\times12^{\prime\prime}$ ($\sim100\times200$ pc$^2$) of Centaurus A. We use JWST/MIRI-MRS observations at 5-28 $\mu$m from the MIRI European consortium GTO program MICONIC, with angular resolution of $0.35^{\prime\prime}-1^{\prime\prime}$ (about 6-17 pc). We derive PAH moment-0 maps via local continuum subtraction and extract one-dimensional spectra from five regions of interest, including the nucleus, the circumnuclear disc, and a PAH-deficient region. The spectra are decomposed into continuum, emission lines, and PAHs to measure feature intensities and equivalent widths (EWs). PAH emission is primarily distributed in a ring-like structure with localized enhancements at $\sim40$ pc from the nucleus. A distinct PAH-deficient region is observed to the north-west, roughly perpendicular to the jet axis, and coincident with enhanced ionized-gas velocity dispersion and inflowing molecular streamers. The 11.3/7.7 $\mu$m and 6.2/7.7 $\mu$m ratios exceed model predictions for pericondensed PAHs, indicating processed populations with more open structures. The 11.3/12.7 $\mu$m ratio suggests a dominance of solo hydrogen sites and partial dehydrogenation, particularly in the PAH-deficient region, where shocks likely drive erosion. The largest EWs are found in the ring, while reduced values in the deficient region point to partial destruction; in the nucleus, low EWs are mainly due to continuum dilution.

astro-ph.GA↗

arXiv2026

MIDIS: The identification of deep MIRI-red sources as candidates for extreme Balmer-break and line emitting galaxies at high-z

We investigate the detection and nature of 5.6~\mu m MIRI-red sources in the MIRI Deep Imaging Survey (MIDIS), covering 2.4~arcmin$^2$ in the Hubble Ultra Deep Field. MIDIS is the deepest JWST/MIRI survey to date, probing faint limits and enabling studies of rare high-redshift galaxy populations. We define MIRI-red sources as those detected at 5$\sigma$ significance in MIRI/F560W with red colors: $m_{\rm F444W} - m_{\rm F560W} \ge 0.5$. Using an empirical methodology, we estimate the purity and completeness of MIRI detections and find that a 5-sigma detection at 28.75 mag has a purity of 92\% and completeness of 54\%. We identify seven MIRI-red galaxy candidates, including an F115W dropout consistent with a high-redshift galaxy candidate. We explore possible physical origins for the MIRI-red population, including active galactic nuclei, dust-obscured galaxies, extreme emission-line galaxies, evolved stellar populations, and Little Red Dots (LRDs). Given the proximity of the F444W and F560W filters and the depth of MIDIS, MIRI-red galaxies are consistent with emission-line galaxies with $EW_0(H\alpha) \ge 750$ \AA\ or $EW_0(H\beta + [OIII]) \ge 600$ \AA, or high-redshift Balmer breaks of at least 1.6. We also discuss an extreme MIRI-red galaxy undetected in F444W, a potential MIRI-only source, for which we derive $EW_0(H\alpha) \sim 6000$ \AA\ and $EW_0(H\beta + [OIII]) \sim 4000$ \AA, or high-$z$ LRD analogs with Balmer breaks of 6.3. Finally, we find fewer MIRI-red detections than expected from extrapolations of the H$\alpha$ or H$\beta$+[OIII] line luminosity functions, consistent with previous deep searches, while the absence of $z>10$ LRD candidates agrees with theoretical expectations for the MIDIS volume.

astro-ph.GA↗

arXiv2026

PRISMS. U37126, a very blue, ISM-naked starburst at z=10.255 with nearly 100% Lyman continuum escape fraction

We present very deep (~11h) JWST/MIRI low-resolution spectroscopy of the rest-frame optical emission of U37126, a UV-bright (M_UV ~ -20), mildly lensed ($\mu\simeq 2.2$) galaxy at z=10.255. The continuum emission is well detected in both NIRSpec and MIRI spectra, yet no nebular recombination or metal emission lines are observed (EW(Hbeta+[OIII])<300A and EW(Halpha)<400A, at 3sigma). Combined with the exceptionally blue UV continuum slope, beta_UV ~ -2.9, and weak/flat Balmer break, these constraints indicate a stellar population dominated by very young and massive stars with a strongly suppressed nebular contribution. Comparisons with synthetic stellar population models indicate that U37126 requires both a very high ionizing photon production efficiency, log(Xi_ion / Hz erg^-1) ~ 25.75, and a nearly unit LyC escape fraction, of fesc>86% (3sigma) based on Halpha flux limit and fesc=0.94+/-0.06 derived independently from SED fitting. The best-fit SED yields a (de-lensed) stellar mass of Mstar ~ 10^7.8 Msun and a star-formation rate of SFR~10Msun/yr (sSFR~160 Gyr^-1), that along with its very compact size, reff~61pc, yields very high stellar mass and star-formation-rate surface densities, Sigma_M ~ 3x10^3 Msun/pc^2 and Sigma_SFR ~ 400 Msun/yr/kpc^2. Together with the lack of detectable nebular emission, these properties suggest that U37126 is undergoing an ``ISM-naked'' starburst phase, possibly driven by an extremely efficient gas-to-star conversion followed by strong feedback that has cleared the remaining gas from its stellar core, allowing most LyC photons to escape. Finally, we show that even a small fraction of galaxies like U37126 (~ 3%-6%), with extreme LyC production and escape, could contribute disproportionately (~ 50%-100%) to the ionizing photon budget during cosmic reionization.

astro-ph.GA↗

arXiv2026

PRISMS. UNCOVER-26185, a metal-poor SFG at z=10.05 with no evidence for a X-ray-luminous AGN

This work presents the first results of the PRImordial galaxy Survey with MIRI Spectroscopy (PRISMS), a JWST cycle 4 program (PID 8051) aimed at the characterization of a relatively large sample of ten galaxies about 500 Myr after the Big Bang. Here, we present deep (13.9 hours) spectroscopy with the MIRI LRS of the lensed galaxy UNCOVER-26185 at a redshift of z=10.054. It is a faint UV galaxy (UV absolut magnitude of -18.83 mag) previously identified as a X-ray luminous AGN. MIRI LRS detects the H$\beta$+[OIII]4960,5008 complex and H$\alpha$ emission line with a significance of 10$\sigma$ and 8$\sigma$, respectively, as well as the optical continuum emission at rest-frame 0.45 $\mu$m and 0.57 $\mu$m with a signal-to-noise ratio of 6-7. The UV-to-optical spectral energy distribution, combining continuum and emission lines, is compatible with: (i) a low stellar (A$_V$= 0.2) and nebular (A$_V$=0.0) extinction, (ii) a SFH composed by a young (7 Myr) starburst and an intermediate-age (65 Myr) stellar population, and (iii) a total stellar mass of 1.7$\times$10$^{8}$ M$_{\odot}$. The H$\alpha$-derived star-formation rate is 1.3 M$_{\odot}$ yr$^{-1}$. The low optical emission line ratios locate UNCOVER-26185 as the most metal-poor (Z = 0.04 Z$_{\odot}$), and as outlier with the lowest ionization (logU=-2.5) galaxy identified so far at redshifts above 9. With no evidence of an active galactic nuclei in the rest-frame UV-to-optical spectrum, UNCOVER-26185 has the properties of a metal-poor, main-sequence star-forming galaxy at redshift 10, with ISM and ionization properties very different than those of the already studied UV-bright galaxies at redshifts beyond 10. PRISMS is starting to explore the population of intermediate-UV luminosity galaxies at z=10, covering UV absolute magnitudes in the range of -17.9 to -20.5, fainter than those of UV-bright galaxies studied so far.

astro-ph.GA↗

arXiv2025

Understanding pulsar magnetospheres with the SKAO

The SKA telescopes will bring unparalleled sensitivity across a broad radio band, a wide field of view across the Southern sky, and the capacity for sub-arraying, all of which make them the ideal instruments for studying the pulsar magnetosphere. This paper describes the advances that have been made in pulsar magnetosphere physics over the last decade, and details how these have been made possible through the advances of modern radio telescopes, particularly SKA precursors and pathfinders. It explains how the SKA telescopes would transform the field of pulsar magnetosphere physics through a combination of large-scale monitoring surveys and in-depth follow-up observations of unique sources and new discoveries. Finally, it describes how the specific observing opportunities available with the AA* and AA4 configurations will achieve the advances necessary to solve the problem of pulsar radio emission physics in the coming years.

astro-ph.HE↗

arXiv2025

MIDIS: Unveiling the Star Formation History in massive galaxies at $1<z<4.5$ with spectro-photometric analysis

We investigate the star formation histories (SFHs) of a sample of massive galaxies ($M_\star \geq 10^{10} \, M_\odot$) in the redshift range $1 < z < 4.5$. We analyze spectro-photometric data combining broadband photometry from HST and JWST with low-resolution grism spectroscopy from JWST/NIRISS, obtained as part of the MIDIS (MIRI Deep Imaging Survey) program. SFHs are derived through spectral energy distribution (SED) fitting using two independent codes, BAGPIPES and Synthesizer, under various SFH assumptions. This approach enables a comprehensive assessment of the biases introduced by different modeling choices. The inclusion of NIRISS spectroscopy, even with its low resolution, significantly improves constraints on key physical parameters, such as the mass-weighted stellar age ($t_M$) and formation redshift ($z_{\mathrm{form}}$), by narrowing their posterior distributions. The massive galaxies in our sample exhibit rapid stellar mass assembly, forming 50\% of their mass between $3 \leq z \leq 9$. The highest inferred formation redshifts are compatible with elevated star formation efficiencies ($\epsilon$) at early epochs. Non-parametric SFHs generally imply an earlier and slower mass assembly compared to parametric forms, highlighting the sensitivity of inferred formation timescales to the chosen SFH model, particularly for galaxies at $z < 2$. Quiescent galaxies are, on average, older ($t_M \sim 1.1$ Gyr) and assembled more rapidly at earlier times than their star-forming counterparts. These findings support the ``downsizing'' scenario, in which more massive and passive systems form earlier and more efficiently.

astro-ph.GA↗

arXiv2025

Main and interpulse interaction in PSRs J1842+0358 and J1926+0737: evidence for interpole communication

Our understanding of the elusive radio-pulsar emission mechanism would be deepened by determining the locality of the emission. Pulsars in which the two poles interact can potentially help solve this challenge. We here report the discovery of interaction of emission between the main and the interpulse in two pulsars -- J1842+0358 and J1926+0737, based on FAST and MeerKAT data. When emission is bright in one pulse, it is dim in the other. Even when split in just 2 groups (strong versus weak) the anti-correlated brightness can change by a factor $\gtrsim$2. Both sources furthermore show the same quasi-periodic modulation from the main and interpulse, at timescales exceeding 100 pulse periods. The longitude stationary modulation from at least one pulse suggests that it is a key signature for interpulse pulsars showing main and interpulse interaction. If the interaction happens within an isolated magnetosphere, without external influences, either communication between the opposite poles is required, or global changes drive both. This detailed study of these two sources was only made possible by improved sensitivity. The fact that both show two-pole modulation strongly suggests this is a general phenomenon in interpulse pulsars. In regular pulsars only one pole is visible, and a number of these show correlated changes between the profile and spin-down rate, that are also thought to be caused by global magnetospheric changes. Our results strengthen the case that such interactive magnetospheres are common to all pulsars.

astro-ph.HE↗

arXiv2025

JWST/MIRI observations of the young TWA 27 system: hydrocarbon disk chemistry, silicate clouds, evidence for a CPD

The Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) enables the characterisation of young self-luminous gas giants at previously inaccessible wavelengths, revealing physical processes in gas, dust, and clouds. We characterise the young planetary system TWA 27 (2M1207) in the mid-infrared (MIR), studying the atmosphere and disk spectra of the M9 brown dwarf TWA 27A and its L6 planetary-mass companion TWA 27b. We obtained data with the MIRI Medium Resolution Spectrometer (MRS) from 4.9 to 20 um, and MIRI Imaging in the F1000W and F1500W filters. We applied high-contrast imaging methods to extract the companion's spectral energy distribution up to 15 um at 0.78 arcsec separation and a contrast of 60. Combining these with published JWST/NIRSpec spectra, we analysed the 1-20 um range using self-consistent atmospheric grids and 0D slab models for molecular disk emission. The atmosphere of TWA 27A is well fitted by a BT-SETTL model with Teff 2780 K, log g 4.3, plus a 740 K blackbody for the inner disk rim. The disk shows at least 11 organic molecules, with no water or silicate dust emission detected. The atmosphere of TWA 27b is matched by a Teff 1400 K low-gravity model with extinction, best fit by the ExoREM grid. MIRI spectra and photometry for TWA 27b reveal a silicate cloud absorption feature between 8-10 um and significant (>5 sigma) infrared excess at 15 um consistent with circumplanetary disk emission. These MIRI observations provide new insights into TWA 27, revealing diverse features to study the formation and evolution of circumplanetary disks and young dusty atmospheres.

astro-ph.EP↗

arXiv2025

MICONIC: JWST/MIRI MRS reveals a fast ionized gas outflow in the central region of Centaurus A

We present a kinematical study of the ionized and molecular gas in the central region (~7-14"~100-200pc) of the nearby radio galaxy Cen A. We used JWST/MIRI MRS 5-28$\mu$m observations taken as part of the MIR Characterization of Nearby Iconic galaxy Centers (MICONIC) of the MIRI EC. The two gas phases present contrasting morphologies and kinematics. The brightest emission from the ionized gas, traced with a range of IP lines ([Fe II] to [Ne VI]), is extended along the direction of the radio jet. We also detected emission from low IP emission lines and H$_2$ transitions in the galaxy disk. Both gas phases present rotational motions but also complex kinematics. The observations reveal several ionized gas kinematical features that are consistent with simulation predictions of a jet-driven bubble and outflow interacting with the galaxy ISM. These include broad components in the nuclear line profiles ($\sigma$~600km/s), high velocities (~ +1000, -1400km/s) confined within the nuclear region, velocities of hundreds of km/s in several directions in the central 2", and enhanced velocity dispersions perpendicular to the radio jet. Moreover, we find evidence of shock excitation in the nuclear region based on MIR line ratios. We compared the ionized gas mass outflow rate with Cen A's AGN luminosity and radio jet power and demonstrate that both mechanisms provide sufficient energy to launch the outflow. The noncircular motions observed in the H$_2$ lines can be reproduced with either a warped rotating disk model or a radial component. The latter might be to related to gas streamers detected in cold molecular gas. There is no clear indication of a fast nuclear H$_2$ outflow, only a weak blueshifted component. This could be due to a relatively low nuclear warm H$_2$ column density and/or the limited geometrical coupling of Cen A's inner radio jet with the circumnuclear disk of the galaxy. (Abridged)

astro-ph.GA↗

arXiv2025

The Thousand-Pulsar-Array programme on MeerKAT XVII: Discovery of beating radio emission variability in PSR J1514-4834

We present a comprehensive analysis of the complex subpulse modulation patterns in PSR J1514-4834 (B1510-48) using L-band data from the Thousand-Pulsar-Array (TPA) programme, complemented with further MeerKAT UHF-band data. We demonstrate that periodic drifting subpulses and rapid amplitude modulation with a period of about 2 pulse periods coexist. It is established that these two periodic emission patterns interfere in the form of a beat system, giving rise to multiple spectral features. We develop a new methodology which confirms the expected correlations in the complex phase of the beat features in a 2D Fourier Transform of the data. Therefore, a relatively simple beat system can explain the complex single-pulse behaviour of this pulsar. The simultaneous coexistence of multiple subpulse modulation periodicities is rare in the population and points to poorly understood intricate dynamics within pulsar magnetospheres. A comparison with PSR B0943+10 is made, for which the coexistence of multiple periodicities has been argued to be a natural consequence of a rotating carousel. However, our observations of PSR J1514-4834 require a different explanation, involving time-delayed interactions between separate regions of the magnetosphere. The developed phase correlation methodology opens up the route for underlying beat systems in the modulation patterns of more pulsars.

astro-ph.HE↗

arXiv2024

MICONIC: Dual active galactic nuclei, star formation, and ionised gas outflows in NGC 6240 seen with MIRI/JWST

As part of the guaranteed time observations program Mid-Infrared Characterization Of Nearby Iconic galaxy Centers (MICONIC), we used the medium-resolution spectrometer (MRS) of the Mid-Infrared Instrument (MIRI) on board of the JWST to study the nearby merger NGC6240. We aim to characterise the dual active galactic nuclei (AGN), the ionised gas outflows and the main properties of the interstellar medium over a mapped area of 6.6"x7.7". We obtained integral field spectroscopic mid-infrared data of NGC6240, resolving both nuclei for the first time in the full 5-28{\mu}m spectral range. We modelled the emission lines through a kinematic decomposition, finding that the fine-structure lines in the southern (S) nucleus are broader than for the northern (N) nucleus (full width at half maximum of $\geq$1500 vs ~700 km s^{-1} on average). High excitation lines, such as [NeV], [NeVI], and [MgV], are clearly detected in the N nucleus. In the S nucleus, the same lines can be detected but only after a decomposition of the PAH features in the integrated spectrum, due to a combination of a strong mid-IR continuum, the broad emission lines, and the intense star formation (SF). The SF is distributed all over the mapped FoV of 3.5kpc x 4.1kpc (projected), with the maximum located around the S nucleus. Both nuclear regions appear to be connected by a bridge region detected with all the emission lines. Based on the observed MRS line ratios and the high velocity dispersion ({\sigma}~600 km s^{-1}), shocks are also dominating the emission in this system. We detected the presence of outflows as a bubble north-west from the N nucleus and at the S nucleus. We estimated a ionised mass outflow rate of 1.4$\pm$0.3 M yr^{-1} and 1.8$\pm$0.2 M yr^{-1}, respectively. Given the derived kinetic power of these outflows, both the AGN and the starburst could have triggered them. [Abridged]

astro-ph.GA↗

arXiv2024

Insight into the Starburst Nature of Galaxy GN-z11 with JWST MIRI Spectroscopy

This paper presents a deep MIRI/JWST medium resolution spectroscopy (MRS) covering the rest-frame optical spectrum of the GN-z11 galaxy. The [OIII]5008 and H$\alpha$ emission lines are detected and spectroscopically resolved. The line profiles are well-modeled by a narrow Gaussian component with intrinsic FWHMs of 189$\pm$25 and 231$\pm$52 kms$^{-1}$, respectively. We do not find any evidence of a dominant broad H$\alpha$ emission line component tracing a Broad Line Region in a type 1 active galactic nuclei (AGN). However, a broad ($\sim$430-470 kms$^{-1}$) and weak ($<$ 20-30%) H$\alpha$ line component, tracing a minor AGN contribution in the optical, cannot be ruled out completely with the sensitivity of the present data. The physical and excitation properties of the ionized gas are consistent with a low-metallicity starburst forming stars at a rate of SFR(H$\alpha$)$=$24 $\pm$3$M_{\odot}$yr$^{-1}$. The electron temperature of the ionized gas is $T_{\mathrm{e}}$(O$^{++}$)$=$14000$\pm$2100K, while the direct-$T_{\mathrm{e}}$ gas-phase metallicity is 12+$\log$(O/H)$=$7.91$\pm$0.07 (Z=0.17$\pm$0.03Z$_{\odot}$). The optical line ratios locate GN-z11 in the starburst or AGN region but more consistent with those of local low-metallicity starbursts and high-$z$ luminous galaxies detected at redshifts similar to GN-z11. We conclude that the MRS optical spectrum of GN-z11 is consistent with that of a massive, compact, and low-metallicity starburst galaxy. Due to its high SFR and stellar mass surface densities, close to that of the densest stellar clusters, we speculate that GN-z11 could be undergoing a feedback-free, highly efficient starburst phase. Additional JWST data are needed to validate this scenario, and other recently proposed alternatives, to explain the existence of bright compact galaxies in the early Universe.

astro-ph.GA↗

arXiv2024

Water depletion and 15NH3 in the atmosphere of the coldest brown dwarf observed with JWST/MIRI

With a temperature of $\sim 285$ K WISE0855 is the coldest brown dwarf observed so far. Using the James Webb Space Telescope (JWST) we obtained observations that allow us to characterize WISE0855s atmosphere focusing on vertical variation in the water steam abundance, measuring trace gas abundances and receiving bulk parameters for this cold object. We observed the ultra cool dwarf WISE0855 using the Mid-Infrared Instrument Medium Resolution Spectrometer (MIRI/MRS) onboard JWST at a spectral resolution of up to 3750. We combined the observation with published data from the Near Infrared Spectrograph (NIRSpec) G395M and PRISM modes yielding a spectrum ranging from 0.8 to 22 um. We apply atmospheric retrievals using petitRADTRANS to measure atmospheric abundances, the pressure-temperature structure, radius and gravity of the brown dwarf. We also employ publicly available clear and cloudy self-consistent grid models to estimate bulk properties of the atmosphere such as the effective temperature, radius, gravity and metallicity. Atmospheric retrievals constrain a variable water abundance profile in the atmosphere, as predicted by equilibrium chemistry. We detect the 15NH3 isotopologue and infer a ratio of mass fraction of 14NH3/15NH3 = 332+63-43 for the clear retrieval. We measure the bolometric luminosity by integrating the presented spectrum and obtain a value of log(L/L$_{\odot}$) = -7.291+/-0.008. The detected water depletion indicates that water condenses out in the upper atmosphere due to the very low effective temperature of WISE0855. The height in the atmosphere where this occurs is covered by the MIRI/MRS data, and thus demonstrates the potential of MIRI to characterize cold gas giants atmospheres. Comparing the data to retrievals and self-consistent grid models, we do not detect signs for water ice clouds, although their spectral features have been predicted in previous studies.

astro-ph.EP↗

arXiv2024

JWST Observations of Young protoStars (JOYS). Overview of gaseous molecular emission and absorption in low-mass protostars

The MIRI-MRS instrument onboard JWST allows for probing the molecular gas composition at mid-IR wavelengths at unprecedented resolution and sensitivity. It is important to study these features in low-mass embedded protostellar systems since the formation of planets is thought to start in this phase. We present JWST/MIRI-MRS data of 18 low-mass protostellar systems in the JOYS program, focusing on gas-phase molecular lines in spectra extracted from the central protostellar positions. Besides H2, the most commonly detected molecules are H2O, CO2, CO, and OH. Other molecules such as 13CO2, C2H2, 13CCH, HCN, C4H2, CH4, and SO2 are detected only toward at most three of the sources. The JOYS data also yield the surprising detection of SiO gas toward two sources (BHR71-IRS1, L1448-mm) and for the first time CS and NH3 at mid-IR wavelengths toward a low-mass protostar (B1-c). The temperatures derived for the majority of the molecules are 100-300 K, much lower than what is typically derived toward more evolved Class II sources (>500 K). Toward three sources (e.g., TMC1-W), hot (~1000 K) H2O is detected, indicative of the presence of hot molecular gas in the embedded disks, but such warm emission from other molecules is absent. The agreement in abundance ratios with respect to H2O between ice and gas point toward ice sublimation in a hot core for a few sources (e.g., B1-c) whereas their disagreement and velocity offsets hint at high-temperature (shocked) conditions toward other sources (e.g., L1448-mm, BHR71-IRS1). The typical temperatures of the gas-phase molecules of 100-300 K are consistent with both ice sublimation in hot cores as well as high-temperature gas phase chemistry. Molecular features originating from the inner embedded disks are not commonly detected, likely because they are too extincted even at mid-IR wavelengths by small not-settled dust grains in upper layers of the disk.

astro-ph.SR↗