| 1. |
- Barrado, David, et al.
(författare)
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15NH3 in the atmosphere of a cool brown dwarf
- 2023
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 624:7991, s. 263-266
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Tidskriftsartikel (refereegranskat)abstract
- Brown dwarfs serve as ideal laboratories for studying the atmospheres of giant exoplanets on wide orbits, as the governing physical and chemical processes within them are nearly identical. Understanding the formation of gas-giant planets is challenging, often involving the endeavour to link atmospheric abundance ratios, such as the carbon-to-oxygen (C/O) ratio, to formation scenarios. However, the complexity of planet formation requires further tracers, as the unambiguous interpretation of the measured C/O ratio is fraught with complexity. Isotope ratios, such as deuterium to hydrogen and 14N/15N, offer a promising avenue to gain further insight into this formation process, mirroring their use within the Solar System. For exoplanets, only a handful of constraints on 12C/13C exist, pointing to the accretion of 13C-rich ice from beyond the CO iceline of the disks. Here we report on the mid-infrared detection of the 14NH3 and 15NH3 isotopologues in the atmosphere of a cool brown dwarf with an effective temperature of 380 K in a spectrum taken with the Mid-Infrared Instrument (MIRI) of JWST. As expected, our results reveal a 14N/15N value consistent with star-like formation by gravitational collapse, demonstrating that this ratio can be accurately constrained. Because young stars and their planets should be more strongly enriched in the 15N isotope, we expect that 15NH3 will be detectable in several cold, wide-separation exoplanets.
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| 2. |
- Dyrek, Achrène, et al.
(författare)
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SO2, silicate clouds, but no CH4 detected in a warm Neptune
- 2024
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 625, s. 51-54
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Tidskriftsartikel (refereegranskat)abstract
- WASP-107b is a warm (approximately 740 K) transiting planet with a Neptune-like mass of roughly 30.5 M⊕ and Jupiter-like radius of about 0.94 RJ (refs. 1,2), whose extended atmosphere is eroding3. Previous observations showed evidence for water vapour and a thick, high-altitude condensate layer in the atmosphere of WASP-107b (refs. 4,5). Recently, photochemically produced sulfur dioxide (SO2) was detected in the atmosphere of a hot (about 1,200 K) Saturn-mass planet from transmission spectroscopy near 4.05 μm (refs. 6,7), but for temperatures below about 1,000 K, sulfur is predicted to preferably form sulfur allotropes instead of SO2 (refs. 8,9,10). Here we report the 9σ detection of two fundamental vibration bands of SO2, at 7.35 μm and 8.69 μm, in the transmission spectrum of WASP-107b using the Mid-Infrared Instrument (MIRI) of JWST. This discovery establishes WASP-107b as the second irradiated exoplanet with confirmed photochemistry, extending the temperature range of exoplanets exhibiting detected photochemistry from about 1,200 K down to about 740 K. Furthermore, our spectral analysis reveals the presence of silicate clouds, which are strongly favoured (around 7σ) over simpler cloud set-ups. Furthermore, water is detected (around 12σ) but methane is not. These findings provide evidence of disequilibrium chemistry and indicate a dynamically active atmosphere with a super-solar metallicity.
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| 3. |
- Gasman, Danny, et al.
(författare)
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MINDS Abundant water and varying C/O across the disk of Sz 98 as seen by JWST/MIRI
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 679
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) on board the James Webb Space Telescope (JWST) allows us to probe the inner regions of protoplanetary disks, where the elevated temperatures result in an active chemistry and where the gas composition may dictate the composition of planets forming in this region. The disk around the classical T Tauri star Sz 98, which has an unusually large dust disk in the millimetre with a compact core, was observed with the MRS, and we examine its spectrum here.Aims. We aim to explain the observations and put the disk of Sz 98 in context with other disks, with a focus on the H2O emission through both its ro-vibrational and pure rotational emission. Furthermore, we compare our chemical findings with those obtained for the outer disk from Atacama Large Millimeter/submillimeter Array (ALMA) observations.Methods. In order to model the molecular features in the spectrum, the continuum was subtracted and local thermodynamic equilibrium (LTE) slab models were fitted. The spectrum was divided into different wavelength regions corresponding to H2O lines of different excitation conditions, and the slab model fits were performed individually per region.Results. We confidently detect CO, H2O, OH, CO2, and HCN in the emitting layers. Despite the plethora of H2O lines, the isotopo-logue (H2O)-O-18 is not detected. Additionally, no other organics, including C2H2, are detected. This indicates that the C/O ratio could be substantially below unity, in contrast with the outer disk. The H2O emission traces a large radial disk surface region, as evidenced by the gradually changing excitation temperatures and emitting radii. Additionally, the OH and CO2 emission is relatively weak. It is likely that H2O is not significantly photodissociated, either due to self-shielding against the stellar irradiation, or UV shielding from small dust particles. While H2O is prominent and OH is relatively weak, the line fluxes in the inner disk of Sz 98 are not outliers compared to other disks.Conclusions. The relative emitting strength of the different identified molecular features points towards UV shielding of H2O in the inner disk of Sz 98, with a thin layer of OH on top. The majority of the organic molecules are either hidden below the dust continuum, or not present. In general, the inferred composition points to a sub-solar C/O ratio (<0.5) in the inner disk, in contrast with the larger than unity C/O ratio in the gas in the outer disk found with ALMA.
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| 4. |
- Perotti, G., et al.
(författare)
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Water in the terrestrial planet-forming zone of the PDS 70 disk
- 2023
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 620:7974, s. 516-520
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial and sub-Neptune planets are expected to form in the inner (less than 10 AU) regions of protoplanetary disks1. Water plays a key role in their formation2,3,4, although it is yet unclear whether water molecules are formed in situ or transported from the outer disk5,6. So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks7, similar to PDS 70, the first system with direct confirmation of protoplanet presence8,9. Here we report JWST observations of PDS 70, a benchmark target to search for water in a disk hosting a large (approximately 54 AU) planet-carved gap separating an inner and outer disk10,11. Our findings show water in the inner disk of PDS 70. This implies that potential terrestrial planets forming therein have access to a water reservoir. The column densities of water vapour suggest in-situ formation via a reaction sequence involving O, H2 and/or OH, and survival through water self-shielding5. This is also supported by the presence of CO2 emission, another molecule sensitive to ultraviolet photodissociation. Dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir12. Our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry.
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| 5. |
- Álvarez-Márquez, J., et al.
(författare)
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MIRI/JWST observations reveal an extremely obscured starburst in the z = 6.9 system SPT0311-58
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 671
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Tidskriftsartikel (refereegranskat)abstract
- Luminous infrared starbursts in the early Universe are thought to be the progenitors of massive quiescent galaxies identified at redshifts 2–4. Using the Mid-IRfrared Instrument (MIRI) on board the James Webb Space Telescope (JWST), we present mid-infrared sub-arcsec imaging and spectroscopy of such a starburst: the slightly lensed hyper-luminous infrared system SPT0311-58 at z = 6.9. The MIRI IMager (MIRIM) and Medium Resolution Spectrometer (MRS) observations target the stellar (rest-frame 1.26 μm emission) structure and ionised (Paα and Hα) medium on kpc scales in the system. The MIRI observations are compared with existing ALMA far-infrared continuum and [C II]158μm imaging at a similar angular resolution. Even though the ALMA observations imply very high star formation rates (SFRs) in the eastern (E) and western (W) galaxies of the system, the Hα line is, strikingly, not detected in our MRS observations. This fact, together with the detection of the ionised gas phase in Paα, implies very high internal nebular extinction with lower limits (AV) of 4.2 (E) and 3.9 mag (W) as well as even larger values (5.6 (E) and 10.0 (W)) by spectral energy distribution (SED) fitting analysis. The extinction-corrected Paα lower limits of the SFRs are 383 and 230 M⊙ yr−1 for the E and W galaxies, respectively. This represents 50% of the SFRs derived from the [C II]158 μm line and infrared light for the E galaxy and as low as 6% for the W galaxy. The MIRIM observations reveal a clumpy stellar structure, with each clump having 3–5×109 M⊙ mass in stars, leading to a total stellar mass of 2.0 and 1.5×1010 M⊙ for the E and W galaxies, respectively. The specific star formation (sSFR) in the stellar clumps ranges from 25 to 59 Gyr−1, assuming a star formation with a 50–100 Myr constant rate. This sSFR is three to ten times larger than the values measured in galaxies of similar stellar mass at redshifts 6–8. Thus, SPT0311-58 clearly stands out as a starburst system when compared with typical massive star-forming galaxies at similar high redshifts. The overall gas mass fraction is Mgas/M∗ ∼ 3, similar to that of z ∼ 4.5–6 star-forming galaxies, suggesting a flattening of the gas mass fraction in massive starbursts up to redshift 7. The kinematics of the ionised gas in the E galaxy agrees with the known [C II] gas kinematics, indicating a physical association between the ionised gas and the cold ionised or neutral gas clumps. The situation in the W galaxy is more complex, as it appears to be a velocity offset by about +700 km s−1 in the Paα relative to the [C II] emitting gas. The nature of this offset and its reality are not fully established and require further investigation. The observed properties of SPT0311-58, such as the clumpy distribution at sub(kpc) scales and the very high average extinction, are similar to those observed in low- and intermediate-z luminous (E galaxy) and ultra-luminous (W galaxy) infrared galaxies, even though SPT0311-58 is observed only ∼800 Myr after the Big Bang. Such massive, heavily obscured clumpy starburst systems as SPT0311-58 likely represent the early phases in the formation of a massive high-redshift bulge, spheroids and/or luminous quasars. This study demonstrates that MIRI and JWST are, for the first time, able to explore the rest-frame near-infrared stellar and ionised gas structure of these galaxies, even during the Epoch of Reionization.
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| 6. |
- Amorín, R. O., et al.
(författare)
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Ubiquitous broad-line emission and the relation between ionized gas outflows and Lyman continuum escape in Green Pea galaxies
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 682
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Tidskriftsartikel (refereegranskat)abstract
- We report observational evidence of highly turbulent ionized gas kinematics in a sample of 20 Lyman continuum (LyC) emitters (LCEs) at low redshift (z ∼ 0.3). Detailed Gaussian modeling of optical emission line profiles in high-dispersion spectra consistently shows that both bright recombination and collisionally excited lines can be fitted as one or two narrow components with intrinsic velocity dispersion of σ ∼ 40 − 100 km s−1, in addition to a broader component with σ ∼ 100 − 300 km s−1, which contributes up to ∼40% of the total flux and is preferentially blueshifted from the systemic velocity. We interpret the narrow emission as highly ionized gas close to the young massive star clusters and the broader emission as a signpost of unresolved ionized outflows, resulting from massive stars and supernova feedback. We find a significant correlation between the width of the broad emission and the LyC escape fraction, with strong LCEs exhibiting more complex and broader line profiles than galaxies with weaker or undetected LyC emission. We provide new observational evidence supporting predictions from models and simulations; our findings suggest that gas turbulence and outflows resulting from strong radiative and mechanical feedback play a key role in clearing channels through which LyC photons escape from galaxies. We propose that the detection of blueshifted broad emission in the nebular lines of compact extreme emission-line galaxies can provide a new indirect diagnostic of Lyman photon escape, which could be useful to identify potential LyC leakers in the epoch of reionization with the JWST.
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| 7. |
- Bortolini, Giacomo, 1996-, et al.
(författare)
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The spatially resolved star formation history of the dwarf spiral galaxy NGC 5474
- 2024
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 527:3, s. 5339-5355
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Tidskriftsartikel (refereegranskat)abstract
- We study the resolved stellar populations and derive the star formation history of NGC 5474, a peculiar star-forming dwarf galaxy at a distance of ∼7 Mpc, using Hubble Space Telescope Advanced Camera for Surveys data from the Legacy Extragalactic UV Survey (LEGUS) programme. We apply an improved colour–magnitude diagram fitting technique based on the code SFERA and use the latest PARSEC–COLIBRI stellar models. Our results are the following. The off-centre bulge-like structure, suggested to constitute the bulge of the galaxy, is dominated by star formation (SF) activity initiated 14 Gyr ago and lasted at least up to 1 Gyr ago. Nevertheless, this component shows clear evidence of prolonged SF activity (lasting until ∼10 Myr ago). We estimate the total stellar mass of the bulge-like structure to be (5.0 ± 0.3) × 108 M⊙. Such a mass is consistent with published suggestions that this structure is in fact an independent system orbiting around and not within NGC 5474’s disc. The stellar overdensity located to the South–West of the bulge-like structure shows a significant SF event older than 1 Gyr, while it is characterized by two recent peaks of SF, around ∼10 and ∼100 Myr ago. In the last Gyr, the behaviour of the stellar disc is consistent with what is known in the literature as ‘gasping’. The synchronized burst at 10–35 Myr in all components might hint to the recent gravitational interaction between the stellar bulge-like structure and the disc of NGC 5474.
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| 8. |
- Bouchet, P., et al.
(författare)
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JWST MIRI Imager Observations of Supernova SN 1987A
- 2024
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 965:1
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Tidskriftsartikel (refereegranskat)abstract
- There exist very few mid-infrared (IR) observations of supernovae (SNe) in general. Therefore, SN 1987A, the closest visible SN in 400 yr, gives us the opportunity to explore the mid-IR properties of SNe, the dust in their ejecta, and the surrounding medium and to witness the birth of an SN remnant (SNR). The James Webb Space Telescope, with its high spatial resolution and extreme sensitivity, gives a new view on these issues. We report on the first imaging observations obtained with the Mid-InfraRed Instrument (MIRI). We build temperature maps and discuss the morphology of the nascent SNR. Our results show that the temperatures in the equatorial ring (ER) are quite nonuniform. This could be due to dust destruction in some parts of the ring, as had been assumed in some previous works. We show that the IR emission extends beyond the ER, illustrating the fact that the shock wave has now passed through this ring to affect the circumstellar medium on a larger scale. Finally, while submillimeter Atacama Large Millimeter Array observations have hinted at the location of the compact remnant of SN 1987A, we note that our MIRI data have found no such evidence.
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| 9. |
- Ejdetjärn, Timmy
(författare)
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Exploring the nature of ISM turbulencein disc galaxies
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Galaxy formation is a continuous process that started only a few hundred million yearsafter the Big Bang. The first galaxies were very volatile, with bursts of star formationand disorganised gas motions. However, even as these galaxies evolved to have orderlyrotating gas discs, the gas within the disc, referred to as the interstellar medium (ISM),still remained highly turbulent. In fact, the ISM is supersonically turbulent, meaning thatthe disorganised gas motion exceeds the speed of sound in the medium. This supersonicturbulence has been connected to several crucial properties related to galaxy evolution; forexample, increasing (and decreasing in some regions) the ISM gas density, star formation,and gas mixing.Many observation have shown that all of the gas phases in the ISM experience su-personic levels of turbulence, with line widths (an observational method to quantify theamount of turbulence) as high as σg ≲ 100 km s−1 in high-redshift (younger) disc galaxies,while local quiescent discs have σg ≲ 40 km s−1 . However, the ISM contains a variety ofgas phases that cover a wide range of temperatures and densities, which exhibit differentlevels of turbulence. For example, the warm ionised gas phase represents the upper limitsquoted above, while colder denser gas only reaches σg ≲ 40 km s−1 and σg ≲ 15 km s−1 inhigh-redshift and local galaxies, respectively.The physical processes driving this turbulence are not fully understood, but a combi-nation of stellar feedback (e.g. supernova) and gravitational instability (e.g. during cloudcollapse) have been suggested to provide a majority of the turbulent energy. In particular,stellar feedback is crucial in the formation of warm ionised gas and may therefore have asignificant contribution on the turbulence within ionised gas. Furthermore, heterogeneousdata of widely different galaxies (in terms of e.g. mass and size) at different resolutions(which causes artificial line broadening) complicates understanding the underlying cause.A commonly used tracer of ionised gas is the Hα emission line and has been usedextensively in high-redshift surveys. However, the contribution of the Hα signal comesfrom two primary sources: the radiatively ionised regions around massive newborn starsembedded in molecular gas (called H II regions) and diffuse ionised gas (DIG) filling theentire galactic disc. Observations have found that these two sources contribute, on average,roughly the same amount to the Hα signal (although with a large spread), but the levelsof turbulence is starkly different; with the DIG being roughly 2-3 times more turbulethan the gas in H II regions.Numerical simulations have come a long way and are now able to simulate entire discgalaxies at parsec-scale resolution (in regions of interest). Furthermore, galaxy simulationshave been able to reproduce the level of turbulence observed in local and high-redshiftgalaxies. Direct comparisons between numerical and observational studies are crucial tounderstand the relevant physics driving observed correlations. However, numerical andobservational work have different data available and the reduction/analysis varies betweenauthors, and so diligence is required to perform qualitative comparisons.In this work, I perform numerical simulations to investigate ISM turbulence in differentgas phases. My simulations model a Milky Way-like galaxy at two different redshifts(using gas fraction as a proxy for redshift) and with/without stellar feedback physics, toevaluate its impact. I perform mock observations to explore the relation between the starformation rate and turbulence, and investigate what is driving this relation. Additionally, Ianalyse the Hα emission line and compare the contribution in intensity and line broadening(turbulence) from H II regions and DIG.
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| 10. |
- Ejdetjärn, Timmy
(författare)
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The origin of the Hα line profiles in simulated disc galaxies
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Observations of ionised Hα gas in disc galaxies with high star formation rates have ubiquitous and significant line broadening with widths σHα≳50−100 km s−1. To understand whether this broadening reflects gas turbulence within the interstellar medium (ISM) of galactic discs, or arises from off-the-plane emission in mass-loaded galactic winds, we perform radiation hydrodynamic (RHD) simulations of isolated Milky Way-mass disc galaxies in a gas-poor (low-redshift) and gas rich (high-redshift) condition and create mock Hα emission line profiles. We find that the vast majority of the Hα emission is confined within the ISM, with extraplanar gas contributing mainly to the extended profile wings. This substantiates the \Halpha emission line as a tracer of mid-plane disc dynamics. We investigate the relative contribution of diffuse and dense Hα emitting gas, corresponding to DIG (ρ≲0.1 cm−3, T∼8 000 K) and HII regions (ρ≳10 cm−3, T∼10 000 K), respectively, and find that DIG contributes ≲10% of the total LHα. However, the DIG can reach upwards of σHα∼60−80 km s−1 while the HII regions are much less turbulent σHα∼10−40 km s−1. This implies that the σHα observed using the full Hα emission line is dependent on the relative Hα contribution from DIG/HII regions and a larger fDIG would shift σHα to higher values. Finally, we show that σHα evolves, in both the DIG and HII regions, with the galaxy gas fraction. Our high-redshift equivalent galaxy is roughly twice as turbulent, except for in the DIG which has a more shallow evolution.
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