Continuum Emission Research Articles

Merging Signatures in an Offset Lyman Continuum Emitter at Redshift 3.8

Lyman continuum (LyC) emitters at z > 3 provide critical samples for studying the contribution of galaxies to the ionizing background in the epoch of reionization. We collect a sample of z > 3 LyC emitters, a dominant fraction (∼60%–70%) of which show spatial offsets between LyC emission and the nonionizing continuum. From this sample, especially, we find a case of an offset LyC emitter, CDFS-6664 (z = 3.797), which shows two components in the high-resolution Hubble Space Telescope and James Webb Space Telescope images. The exceptionally rich data set of CDFS-6664 enables us to extract the two components across multiple wavelengths and estimate their physical properties. We show that CDFS-6664 is consistent with a major merger system with boosted star formation in both components and that the offset LyC emission is most likely associated with the bluer and younger component in this merging system. Our result offers an example in which the offset can be caused by a merger. Future observations of more offset LyC emitters would elucidate the role that mergers play in the escape of LyC photons.

Multi-wavelength high-resolution polarimetric imaging of second-generation disc around post-AGB binary IRAS 08544-4431 with SPHERE.

Abstract Exploring the formation and evolution of second-generation circumbinary discs around evolved binary stars, such as post-Asymptotic Giant Branch (post-AGB) and post-Red Giant Branch (post-RGB) binaries, provides valuable insights into the complex binary interaction process that concludes the red-giant phase of evolution in these systems. Additionally, it offers a novel opportunity to investigate the formation of second-generation planets within dusty discs surrounding evolved stars. We present a pilot multi-wavelength polarimetric imaging study of the post-AGB binary system IRAS 08544-4431 using the European Southern Observatory-Very Large Telescope/SPHERE instrument. This study is focused on optical V − and I′ −band ZIMPOL data to complement near-infrared H −band IRDIS data presented previously. The study aims to investigate the dust scattering properties and surface morphology of the post-AGB circumbinary disc as a function of wavelength. We successfully resolved the extended disc structure of IRAS 08544-4431, revealing a complex disc morphology, high polarimetric disc brightness (up to ∼1.5%), and significant forward scattering at optical wavelengths. Additionally, we found that the disc shows a grey polarimetric colour in both optical and near-infrared. The findings highlight similarities between post-AGB circumbinary discs and protoplanetary discs, suggesting submicron-size porous aggregates as the dominant surface dust composition, and indicating potential warping within the disc. However, further expansion of the multi-wavelength analysis to a larger sample of post-AGB binary systems, as well as high-resolution observations of dust continuum and gas emission, is necessary to fully explore the underlying structure of post-AGB circumbinary discs and associated physical mechanisms.

Temperature measurement method with line and continuum emissions in Ar-N2 DC arc

Abstract This study discusses a technique for accurate temperature measurement of thermal plasmas with a high-speed camera. Temperature of thermal plasmas is important parameter for plasma processes. High-speed cameras are useful to measure plasma temperatures in two dimensions. Measurements of plasma emission with a high-speed camera and band-pass filter provide only the spectral intensity of the entire transmitted wavelength range. Temperature measurements with high-speed cameras by Boltzmann plot method or Fowler-Milne method are less accurate. Theoretical consideration of the line and continuum emissions has improved the accuracy of plasma temperature measurement. The measurement target was a free burning arc in an argon and nitrogen atmosphere. Temperature errors were estimated based on the deviation from the true emission coefficient. The calculation and measurement errors were discussed as the factors of the deviation. Error estimation provides important insight into the selection of the measurement wavelength.

REBELS-25: Discovery of a dynamically cold disc galaxy at z = 7.31

Abstract We present high resolution (∼0.14” = 710 pc) ALMA [CII] 158μm and dust continuum follow-up observations of REBELS-25, a [CII]-luminous (L[CII] = (1.7 ± 0.2) × 109L⊙) galaxy at redshift z = 7.3065 ± 0.0001. These high resolution, high signal-to-noise observations allow us to study the sub-kpc morphology and kinematics of this massive ($M_* = 8^{+4}_{-2} \times 10^9 \mathrm{{\rm M}_{\odot }}$) star-forming (SFR$_{\mathrm{UV+IR}} = 199^{+101}_{-63} \mathrm{{\rm M}_{\odot }} \mathrm{yr}^{-1}$) galaxy in the Epoch of Reionisation. By modelling the kinematics with 3DBAROLO, we find it has a low velocity dispersion ($\bar{\sigma } = 33^{+9}_{-7}$ km s−1) and a high ratio of ordered-to-random motion ($V_{\mathrm{rot, ~max}}/\bar{\sigma } = 11 ^{+6}_{-5}$), indicating that REBELS-25 is a dynamically cold disc. Additionally, we find that the [CII] distribution is well fit by a near-exponential disc model, with a Sérsic index, n, of 1.3 ± 0.2, and we see tentative evidence of more complex non-axisymmetric structures suggestive of a bar in the [CII] and dust continuum emission. By comparing to other high spatial resolution cold gas kinematic studies, we find that dynamically cold discs seem to be more common in the high redshift Universe than expected based on prevailing galaxy formation theories, which typically predict more turbulent and dispersion-dominated galaxies in the early Universe as an outcome of merger activity, gas accretion and more intense feedback. This higher degree of rotational support seems instead to be consistent with recent cosmological simulations that have highlighted the contrast between cold and warm ionised gas tracers, particularly for massive galaxies. We therefore show that dynamically settled disc galaxies can form as early as 700 Myr after the Big Bang.

Flare heating of the chromosphere: Observations of flare continuum from GREGOR and IRIS

Context. On 2022 May 4, an M5.7 flare erupted in the active region NOAA 13004, which was the target of a coordinated campaign between GREGOR, IRIS, Hinode, and ground-based instruments at the Ondřejov observatory. A flare kernel located at the edge of a pore was co-observed by the IRIS slit and GREGOR HiFI+ imagers. Aims. We investigated the flare continuum enhancement at different wavelength ranges in order to derive the temperature of the chromospheric layer heated during the flare. Methods. All datasets were aligned to IRIS slit-jaw images. We selected a pixel along the IRIS slit where the flare kernel was captured and evaluated multi-wavelength light curves within it. We defined a narrow IRIS near-UV band that comprises only continuum emission. The method, which assumes that the flare continuum enhancement is due to optically thin emission from hydrogen recombination processes, was applied to obtain a lower limit on the temperature in the layer where the continuum enhancement was formed. Results. We determined a lower limit for the temperature and its time evolution in the chromospheric layer heated during the flare in the range of (3–15) ×103 K. The mean electron density in that layer was estimated to be ∼1 × 1013 cm−3. Conlcusions. Multi-wavelength flare co-observations are a rich source of diagnostics. Due to the rapidly evolving nature of flares, the sit-and-stare mode is key to achieving a high temporal cadence that allows one to thoroughly analyse the same flare structure.

Early Planet Formation in Embedded Disks. XI. A High-resolution View Toward the BHR 71 Class 0 Protostellar Wide Binary

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the binary Class 0 protostellar system BHR 71 IRS1 and IRS2 as part of the Early Planet Formation in Embedded Disks (eDisk) ALMA Large Program. We describe the 12CO (J = 2–1), 13CO (J = 2–1), C18O (J = 2–1), H2CO (J = 32,1–22,0), and SiO (J = 5–4) molecular lines along with the 1.3 mm continuum at high spatial resolution (∼0.″08 or ∼5 au). Dust continuum emission is detected toward BHR 71 IRS1 and IRS2, with a central compact component and extended continuum emission. The compact components are smooth and show no sign of substructures such as spirals, rings, or gaps. However, there is a brightness asymmetry along the minor axis of the presumed disk in IRS1, possibly indicative of an inclined geometrically and optically thick disk-like component. Using a position–velocity diagram analysis of the C18O line, clear Keplerian motions were not detected toward either source. If Keplerian rotationally supported disks are present, they are likely deeply embedded in their envelope. However, we can set upper limits of the central protostellar mass of 0.46 M ⊙ and 0.26 M ⊙ for BHR 71 IRS1 and BHR 71 IRS2, respectively. Outflows traced by 12CO and SiO are detected in both sources. The outflows can be divided into two components, a wide-angle outflow and a jet. In IRS1, the jet exhibits a double helical structure, reflecting the removal of angular momentum from the system. In IRS2, the jet is very collimated and shows a chain of knots, suggesting episodic accretion events.

Magnetic Fields in Massive Star-forming Regions (MagMaR). IV. Tracing the Magnetic Fields in the O-type Protostellar System IRAS 16547–4247

The formation of the massive stars, and in particular, the role that the magnetic fields play in their early evolutionary phase is still far from being completely understood. Here, we present the Atacama Large Millimeter/submillimeter Array 1.2 mm full polarized continuum and H13CO+(3−2), CS(5−4), and HN13C(3−2) line observations with a high angular resolution (∼0.″4 or 1100 au). In the 1.2 mm continuum emission, we reveal a dusty envelope surrounding the massive protostars, IRAS16547-E and IRAS16547-W, with dimensions of ∼10,000 au. This envelope has a biconical structure likely carved by the powerful thermal radio jet present in region. The magnetic field vectors follow very well the biconical envelope. The polarization fraction is ∼2.0% in this region. Some of these vectors seem to converge to IRAS 16547-E and IRAS 16547-W, the most massive protostars. Moreover, the velocity fields revealed from the spectral lines H13CO+(3−2) and HN13C(3−2) show velocity gradients with a good correspondence with the magnetic fields, which maybe are tracing the cavities of molecular outflows or maybe infalling in some parts. We derived a magnetic field strength in some filamentary regions that goes from 2 to 6.1 mG. We also find that the CS(5−4) molecular line emission reveals multiple outflow cavities or bow shocks with different orientations, some of which seem to follow the NW–SE radio thermal jet.

The Clearing Timescale for Infrared-selected Star Clusters in M83 with HST

We present an analysis of Hubble Space Telescope data from Wide Field Camera 3 (WFC3)/Ultraviolet Imaging Spectrometer, WFC3/IR, and the Advanced Camera for Surveys, investigating the young stellar cluster (YSC) population in the face-on spiral galaxy M83. Within the field of view of the IR pointings, we identify 454 sources with compact F814W continuum and Paβ line emission with a S/N ≥ 3 as possible YSC candidates embedded in dust. We refine this selection to 97 candidates based on their spectral energy distributions, multiwavelength morphology, and photometric uncertainties. For sources that are detected in all bands and have mass >102.8 M ⊙ (53 sources), we find that by 2 Myr 75% of IR-selected star clusters have an A V ≤ 1 and that by 3 Myr the fraction rises to ∼82%. This evidence of early clearing implies that presupernova (pre-SN) feedback from massive stars is responsible for clearing the majority of the natal gas and dust that surround IR-selected star clusters in M83. Further, this result is consistent with previous estimates based on WFC3 observations and adds to the growing body of literature suggesting pre-SN feedback to be crucial for YSC emergence in normal star-forming galaxies. Finally, we find a weak correlation between the YSC concentration index and age over the first 10 Myr, which matches previous studies and indicates little or no change in the size of YSCs in M83 during their early evolution.

A Nonparametric Morphological Analysis of Hα Emission in Bright Dwarfs Using the Merian Survey

Using medium-band imaging from the newly released Merian Survey, we conduct a nonparametric morphological analysis of Hα emission maps and stellar continua for a sample of galaxies with 8≲log(M⋆/M⊙)<10.3 at 0.064 < z < 0.1. We present a novel method for estimating the stellar continuum emission through the Merian Survey’s N708 medium-band filter, which we use to measure Hα emission and produce Hα maps for our sample of galaxies with seven-band Merian photometry and available spectroscopy. We measure nonparametric morphological statistics for the Hα and stellar continuum images, explore how the morphology of the Hα differs from the continuum, and investigate how the parameters evolve with the galaxies’ physical properties. In agreement with previous results for more massive galaxies, we find that the asymmetry of the stellar continuum increases with specific star formation rate (sSFR), and we extend the trend to lower masses, also showing that it holds for the asymmetry of the Hα emission. We find that the lowest-mass galaxies with the highest sSFR have Hα emission that is consistently heterogeneous and compact, while the less active galaxies in this mass range have Hα emission that appears diffuse. At higher masses, our data do not span a sufficient range in sSFR to evaluate whether similar trends apply. We conclude that high sSFRs in low-mass galaxies likely result from dynamical instabilities that compress a galaxy’s molecular gas to a dense region near the center.

ALMA Detection of Masers and Dasars in the Hydrogen Recombination Lines of the Planetary Nebula Mz3

The hydrogen recombination lines H30α, H40α, H42α, H50β, and H57γ and the underlying bremsstrahlung continuum emission were detected with ALMA in the bipolar nebula Mz3. The source was not spatially resolved, but the velocity profile of the H30α line shows clear indication of maser amplification, confirming previous reports of laser amplification in the far-infrared H recombination lines observed with Herschel Space Observatory. Comparison between the flux densities of the H50β, H40α, and H42α lines show overcooling, or darkness amplification by stimulated absorption (dasar effect) at the LSR velocity of about −25 km s−1, which constrains the density of the absorbing region to about 103 cm−3. The H30α line, on the other hand, presents maser lines at LSR velocities of −69 and −98 km s−1, which indicates ionized gas with densities close to 107 cm−3. Although the source of emission was not resolved, it was possible to find the central position of the images for each velocity interval, which resulted in a well defined position–velocity distribution.

Hints of Planet Formation Signatures in a Large-cavity Disk Studied in the AGE-PRO ALMA Large Program

Detecting planet signatures in protoplanetary disks is fundamental to understanding how and where planets form. In this work, we report dust and gas observational hints of planet formation in the disk around 2MASS J16120668-301027, as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Large Program “AGE-PRO: ALMA survey of Gas Evolution in Protoplanetary disks.” The disk was imaged with the ALMA at Band 6 (1.3 mm) in dust continuum emission and four molecular lines: 12CO(J = 2–1), 13CO(J = 2–1), C18O(J = 2–1), and H2CO(J = 3(3,0)–2(2,0)). Resolved observations of the dust continuum emission (angular resolution of ∼150 mas, 20 au) show a ring-like structure with a peak at 0.″57 (75 au), a deep gap with a minimum at 0.″24 (31 au), an inner disk, a bridge connecting the inner disk and the outer ring, along with a spiral arm structure, and a tentative detection (to 3σ) of a compact emission at the center of the disk gap, with an estimated dust mass of ∼2.7−12.9 Lunar masses. We also detected a kinematic kink (not coincident with any dust substructure) through several 12CO channel maps (angular resolution ∼200 mas, 30 au), located at a radius of ∼0.″875 (115.6 au). After modeling the 12CO velocity rotation around the protostar, we identified a purple tentative rotating-like structure at the kink location with a geometry similar to that of the disk. We discuss potential explanations for the dust and gas substructures observed in the disk and their potential connection to signatures of planet formation.

The ALMA-CRISTAL survey

We present the morphological parameters and global properties of dust-obscured star formation in typical star-forming galaxies at z = 4–6. Among 26 galaxies composed of 20 galaxies observed by the Cycle-8 ALMA Large Program, CRISTAL, and 6 galaxies from archival data, we individually detect rest-frame 158 μm dust continuum emission from 19 galaxies, 9 of which are reported for the first time. The derived far-infrared luminosities are in the range log10LIR [L⊙] = 10.9 − 12.4, an order of magnitude lower than previously detected massive dusty star-forming galaxies (DSFGs). We find the average relationship between the fraction of dust-obscured star formation (fobs) and the stellar mass to be consistent with previous results at z = 4–6 in a mass range of log10M* [M⊙]∼9.5 − 11.0 and to show potential evolution from z = 6 − 9. The individual fobs exhibits significant diversity, and we find a potential correlation with the spatial offset between the dust and UV continuum, suggesting that inhomogeneous dust reddening may cause the source-to-source scatter in fobs. The effective radii of the dust emission are on average ∼1.5 kpc and are about two times more extended than those seen in rest-frame UV. The infrared surface densities of these galaxies (ΣIR ∼ 2.0 × 1010 L⊙ kpc−2) are one order of magnitude lower than those of DSFGs that host compact central starbursts. On the basis of the comparable contribution of dust-obscured and dust-unobscured star formation along with their similar spatial extent, we suggest that typical star-forming galaxies at z = 4 − 6 form stars throughout the entirety of their disks.

Constraints on the Physical Origin of Large Cavities in Transition Disks from Multiwavelength Dust Continuum Emission

The physical origin of the large cavities observed in transition disks is to date still unclear. Different physical mechanisms (e.g., a companion, dead zones, enhanced grain growth) produce disk cavities of different depth, and the expected spatial distribution of gas and solids in each mechanism is not the same. In this work, we analyze the multiwavelength interferometric visibilities of dust continuum observations obtained with Atacama Large Millimeter/submillimeter Array and Very Large Array for six transition disks: CQTau, UXTau A, LkCa15, RXJ1615, SR24S, and DMTau, and calculate brightness radial profiles, where diverse emission morphology is revealed at different wavelengths. The multiwavelength data are used to model the spectral energy distribution and compute constraints on the radial profile of the dust surface density, maximum grain size, and dust temperature in each disk. They are compared with the observational signatures expected from various physical mechanisms responsible for disk cavities. The observational signatures suggest that the cavities observed in the disks around UXTau A, LkCa15, and RXJ1615 could potentially originate from a dust trap created by a companion. Conversely, in the disks around CQTau, SR24S, DMTau, the origin of the cavity remains unclear, although it is compatible with a pressure bump and grain growth within the cavity.

The Spatial Correlation between CN-line- and Dust-continuum-emitting Regions in High-mass Star-forming Clouds

Measuring the strength of a three-dimensional (3D) magnetic field vector is challenging as it is not easy to recognize whether its line-of-sight (LOS) and plane-of-sky (POS) components are obtained from the same region. CN (N = 1–0) emission has been used to get the LOS component of a magnetic field (B LOS) from its Zeeman splitting lines, while dust continuum emission has been used to get the POS component of a magnetic field (B POS). We use the CN (N = 1–0) data observed with the Taeduk Radio Astronomy Observatory 14 m telescope and the dust continuum data from the Herschel archive toward six high-mass star-forming regions in order to test whether CN line and dust continuum emission can trace a similar region and thus can be used for inferring 3D magnetic field strength. Our comparison between CN and H2 column densities for all targets indicates that CN line emission tends to be strong toward bright continuum regions. The positions of peak CN column densities are particularly well correlated with those of peak H2 column densities, at least over the H2 column density of 8.0 × 1022 cm−2 within one or two telescope beam sizes in all targets, implying that CN-line- and dust-continuum-emitting regions are likely spatially coincident. This enabled us to make the reliable measurement of the 3D magnetic field strengths of five targets by taking a vector sum of their B LOS and B POS, helping to decide the magnetical criticality of the targets as supercritical or transcritical.

Early Planet Formation in Embedded Disks (eDisk)

We present the results of the observations made within the ALMA Large Program called Early Planet Formation in Embedded disks of the Class 0 protostar GSS30 IRS3. Our observations included the 1.3 mm continuum with a resolution of 0″.05 (7.8 au) and several molecular species, including 12CO, 13CO, C18O, H2CO, and c-C3H2. The dust continuum analysis unveiled a disk-shaped structure with a major axis of ~200 au. We observed an asymmetry in the minor axis of the continuum emission suggesting that the emission is optically thick and the disk is flared. On the other hand, we identified two prominent bumps along the major axis located at distances of 26 and 50 au from the central protostar. The origin of the bumps remains uncertain and might be an embedded substructure within the disk or the temperature distribution and not the surface density because the continuum emission is optically thick. The 12CO emission reveals a molecular outflow consisting of three distinct components: a collimated component, an intermediate-velocity component exhibiting an hourglass shape, and a wider angle low-velocity component. We associate these components with the coexistence of a jet and a disk wind. The C18O emission traces both a circumstellar disk in Keplerian rotation and the infall of the rotating envelope. We measured a stellar dynamical mass of 0.35 ±0.09 M⊙.

Intensive Broadband Reverberation Mapping of Fairall 9 with 1.8 yr of Daily Swift Monitoring

We present 1.8 yr of near-daily Swift monitoring of the bright, strongly variable Type 1 active galactic nucleus (AGN) Fairall 9. Totaling 575 successful visits, this is the largest such campaign reported to date. Variations within the UV/optical are well correlated, with longer wavelengths lagging shorter wavelengths in the direction predicted by thin-disk/lamppost models. The correlations are improved by “detrending,” subtracting a second-order polynomial fit to the UV/optical light curves to remove long-term trends that are not of interest to this study. Extensive testing indicates detrending with higher-order polynomials removes too much intrinsic variability signal on reverberation timescales. These data provide the clearest detection to date of interband lags within the UV, indicating that neither emission from a large disk nor diffuse continuum emission from the broad-line region (BLR) can independently explain the full observed lag spectrum. The observed X-ray flux variations are poorly correlated with those in the UV/optical. Further, subdivision of the data into four ∼160 days light curves shows that the UV/optical lag spectrum is highly stable throughout the four periods, but the X-ray to UV lags are unstable, significantly changing magnitude and even direction from one period to the next. This indicates the X-ray to UV relationship is more complex than predicted by the simple reprocessing model often adopted for AGN. A “bowl” model (lamppost irradiation and blackbody reprocessing on a disk with a steep rim) fit suggests the disk thickens at a distance (∼10 lt-day) and temperature (∼8000 K) consistent with the inner edge of the BLR.

The Far-ultraviolet Spectrum of FU Ori South

The eruptive young stellar object FU Ori is the eponym of its variable class. FU Ori stars are known to undergo outbursts with amplitudes of >4 mag in the V band and durations of several decades. Interaction with a binary companion is one proposed outburst trigger, so understanding both components of the FU Ori system is crucial. A recent Hubble Space Telescope/Space Telescope Imaging Spectrograph observation of the FU Ori system clearly resolves its North and South components. We report here on the spectrum of FU Ori South. We detect near-ultraviolet continuum emission but no far-ultraviolet continuum, although several bright emission lines consistent with those seen in T Tauri stars are present. The presence of the C ii] 2325 multiplet and many H2 lines indicate active accretion. We estimate the extinction to the source and find that the UV spectrum favors A V < 4, contrary to past estimates based on the near-infrared spectrum.

CO spectra of the ISM in the Host Galaxies of the most luminous WISE-selected AGNs

Abstract We present observations of mid-J (J = 4–3 or J = 5–4) carbon monoxide (CO) emission lines and continuum emission from a sample of ten of the most luminous (Lbol ≥ 1014 L$\rm \odot$) Hot Dust-Obscured Galaxies (Hot DOGs) discovered by the Wide-field Infrared Survey Explorer (WISE) with redshifts up to 4.6. We uncover broad spectral lines (FWHM ≥ 400 km s−1) in these objects, suggesting a turbulent molecular interstellar medium (ISM) may be ubiquitous in Hot DOGs. A halo of molecular gas, extending out to a radius of 5 kpc is observed in W2305–0039, likely supplied by 940 km s−1 molecular outflows. W0831+0140 is plausibly the host of a merger between at least two galaxies, consistent with observations made using ionized gas. These CO(4–3) observations contrast with previous CO(1–0) studies of the same sources: the CO(4–3) to CO(1–0) luminosity ratios exceed 300 in each source, suggesting that the lowest excited states of CO are underluminous. These findings show that the molecular gas in Hot DOGs is consistently turbulent, plausibly a consequence of AGN feedback, triggered by galactic mergers.

MINDS

Context. The majority of young stars form in multiple systems, the properties of which can significantly impact the evolution of any circumstellar disks. Aims. We investigate the physical and chemical properties of the equal-mass, small-separation (~66 milliarcsecond, ~9 au) binary system DF Tau. Previous spatially resolved observations indicate that only DF Tau A has a circumstellar disk, while DF Tau B does not, as concluded by a lack of accretion signatures and a near-infrared excess. Methods. We present JWST-MIRI MRS observations of DF Tau. The MIRI spectrum shows emission from a forest of H2O lines and emission from CO, C2H2, HCN, CO2, and OH. Local thermodynamic equilibrium slab models were used to determine the properties of the gas. The binary system is not spatially or spectrally resolved in the MIRI observations; therefore, we analyzed high spatial and spectral resolution observations from ALMA, VLTI-GRAVITY, and IRTF-iSHELL to aid in the interpretation of the molecular emission observed with JWST. Results. The 1.3 mm ALMA observations show two equal-brightness sources of compact (R ≲ 3 au) continuum emission that are detected at high significance, with separations consistent with astrometry from VLTI-GRAVITY and movement consistent with the known orbital parameters of the system. We interpret this as a robust detection of the disk around DF Tau B, which we suggest may host a small (~1 au) cavity; such a cavity would reconcile all of the observations of this source. In contrast, the disk around DF Tau A is expected to be a full disk, and spatially and spectrally resolved dust and gas emission traced by ground-based infrared observations point to hot, close-in (≲0.2 au) material around this star. High-temperature emission (~500–1000 K) from H2O, HCN, and potentially C2H2 in the MIRI data likely originates in the disk around DF Tau A, while a cold H2O component (≲200 K) with an extended emitting area is consistent with an origin from both disks. Conclusions. Given the unique characteristics of this binary pair, complementary observations are critical for constraining the properties of these disks. Despite the very compact outer disk properties, the inner disk composition and the conditions of the DF Tau disks are remarkably similar to those of isolated systems, suggesting that neither the outer disk evolution nor the close binary nature are driving factors in setting the inner disk chemistry in this system. However, constraining the geometry of the disk around DF Tau B, via higher angular resolution ALMA observations for instance, would provide additional insight into the properties of the mid-infrared gas emission observed with MIRI. JWST observations of spatially resolved binaries, at a range of separations, will be important for understanding the impact of binarity on inner disk chemistry more generally.

A spatially resolved radio spectral study of the galaxy M 51

Context. Radio continuum emission from galaxies at gigahertz frequencies can be used as an extinction-free tracer of star formation. However, at frequencies of a few hundred megahertz, there is evidence for low-frequency spectral flattening. Aims. We wish to understand the origin of this low-frequency flattening better, and to this end, we performed a spatially resolved study of the nearby spiral galaxy M51. We explored the different effects that can cause a flattening of the spectrum towards lower frequencies, such as free–free absorption and cosmic-ray ionisation losses. Methods. We used radio continuum intensity maps between 54 and 8350 MHz at eight different frequencies, with observations at 240 MHz from the Giant Metrewave Radio Telescope presented for the first time. We corrected for the contribution from thermal free–free emission using an H α map that was corrected for extinction with 24 μm data. We fitted free–free absorption models to the radio spectra to determine the emission measure (EM) as well as polynomial functions to measure the non-thermal spectral curvature. We also obtained a new extinction-corrected H α intensity map from the Metal-THINGS survey using integral field unit spectroscopy. Results. The non-thermal low-frequency radio continuum spectrum between 54 and 144 MHz is very flat and even partially inverted, particularly in the spiral arms; in contrast, the spectrum at higher frequencies is typical for a non-thermal radio continuum spectrum. However, we did not find any correlation between the EMs calculated from radio and from H α observations; instead, the non-thermal spectral curvature weakly correlates with the H I gas-mass surface density. This suggests that cosmic-ray ionisation losses play an important role in the low-frequency spectral flattening. Conclusions. The observed spectral flattening towards low frequencies in M51 is caused by a combination of ionisation losses and free–free absorption. The reasons for this flattening need to be understood in order to use sub-gigahertz frequencies as a tracer of star formation.