HAL-INSU
Not a member yet
203706 research outputs found
Sort by
PHANGS-ML: The Universal Relation between PAH Band and Optical Line Ratios across Nearby Star-forming Galaxies
No full textInternational audienceThe structure and chemistry of the dusty interstellar medium (ISM) are shaped by complex processes that depend on the local radiation field, gas composition, and dust grain properties. Of particular importance are polycyclic aromatic hydrocarbons (PAHs), which emit strong vibrational bands in the mid-infrared, and play a key role in the ISM energy balance. We recently identified global correlations between PAH band and optical line ratios across three nearby galaxies, suggesting a connection between PAH heating and gas ionization throughout the ISM. In this work, we perform a census of the PAH heating–gas ionization connection using ∼700,000 independent pixels that probe scales of 40–150 pc in 19 nearby star-forming galaxies from the PHANGS survey. We find a universal relation between PAH(11.3 μm/7.7 μm) and ([S II]/Hα) with a slope of ∼0.2 and a scatter of ∼0.025 dex. The only exception is a group of anomalous pixels that show unusually high (11.3 μm/7.7 μm) PAH ratios in regions with old stellar populations and high starlight-to-dust emission ratios. Their mid-infrared spectra resemble those of elliptical galaxies. Active galactic nucleus hosts show modestly steeper slopes, with a ∼10% increase in PAH(11.3 μm/7.7 μm) in the diffuse gas on kiloparsec scales. This universal relation implies an emerging simplicity in the complex ISM, with a sequence that is driven by a single varying property: the spectral shape of the interstellar radiation field. This suggests that other properties, such as gas-phase abundances, gas ionization parameter, and grain charge distribution, are relatively uniform in all but specific cases
Kalliope sings rock and metal
No full textInternational audienceAsteroid (22) Kalliope is the densest known asteroid in the main belt, with a density of g cm, suggesting that it is differentiated. Kalliope has recently been identified as the parent body of a family of collisional fragments, which is located in the so-called 'pristine zone' of the outer main belt, between 2.825 and 2.955 au. Kalliope's spectroscopic classification has been uncertain, but it has been broadly associated with iron meteorites. We combined visible reflectance spectra from the Gaia Data Release 3, visible SDSS spectrophotometry, and new near-infrared spectroscopic observations from the SpeX instrument at NASA's Infrared Telescope Facility for 22 Kalliope family members, which were mostly classified as X or Xk-types. Considering the spectral slope and 0.9 absorption band variations, we divided the family members into three spectral groups. By analysing the spectra and geometric visible albedo data, we identified the best matches for Kalliope family members as iron and pallasite meteorites. The absence of crustal material among family members makes the nature of Kalliope's parent body unclear, whether it was a fully or partially differentiated planetesimal and whether it originated in the inner or outer Solar system
exoALMA. IX. Regularized Maximum Likelihood Imaging of Non-Keplerian Features
No full textInternational audienceThe planet-hunting Atacama Large Millimeter/submillimeter Array (ALMA) large program exoALMA observed 15 protoplanetary disks at angular resolution and ∼100 m s‑1 spectral resolution, characterizing disk structures and kinematics in enough detail to detect non-Keplerian features (NKFs) in the gas emission. As these features are often small and low-contrast, robust imaging procedures are critical for identifying and characterizing NKFs, including determining which features may be signatures of young planets. The exoALMA collaboration employed two different imaging procedures to ensure the consistent detection of NKFs: CLEAN, the standard iterative deconvolution algorithm, and regularized maximum likelihood (RML) imaging. This Letter presents the exoALMA RML images, obtained by maximizing the likelihood of the visibility data given a model image and subject to regularizer penalties. Crucially, in the context of exoALMA, RML images serve as an independent verification of marginal features seen in the fiducial CLEAN images. However, best practices for synthesizing RML images of multichanneled (i.e., velocity-resolved) data remain undefined, as prior work on RML imaging for protoplanetary disk data has primarily addressed single-image cases. We used the open-source Python package MPoL to explore RML image validation methods for multichanneled data and synthesize RML images from the exoALMA observations of seven protoplanetary disks with apparent NKFs in the 12CO J = 3–2 CLEAN images. We find that RML imaging methods independently reproduce the NKFs seen in the CLEAN images of these sources, suggesting that the NKFs are robust features rather than artifacts from a specific imaging procedure
Detecting explosive volcanism using global long-range infrasound data
No full textInternational audienceVolcanoes have the potential to erupt abruptly, ejecting ash into the atmosphere and posing risks, among others, to civil aviation. Such explosive eruptions often occur unnoticed, complicating the air traffic management efforts of Volcanic Ash Advisory Centres (VAACs) of the International Civil Aviation Organization. Explosive eruptions are efficient sources of infrasound that, thanks to the low attenuation in the atmosphere, allow volcano monitoring at long (up to >1000 km) distances. The Volcanic Information System (VIS) is a recent framework for detecting eruptive events in near real-time (considering the slow propagation of infrasound), based on infrasound observations from one or several arrays of infrasound sensors. Several studies have already proved the efficiency of long-range infrasound monitoring and VIS in particular, but a systematic and global validation has not yet been done. In the current study, we investigate the reliability of VIS based on 10 years (2010–2019) of data provided by 16 infrasound arrays of the International Monitoring System operated by the Comprehensive Nuclear-Test-Ban Treaty Organization. The dataset contains eruptions with a Volcanic Explosivity Index (VEI) of 2 (mild explosions) to 4 (very energetic explosions with a high ash column). In order to estimate the rate of false positives, VIS records are compared with reports from the Global Volcanism Program. Our results show that VIS is well designed for large (VEI ≥3) and long-lasting (Sub-Plinian/Plinian) events, as well as for highly repeated Vulcanian/Strombolian explosions. On the other hand, it typically misses single explosive, transient (few seconds) eruptive events. Good results on true detected events are obtained within 1000 km and up to 2000 km range under downwind propagation conditions. Unresolved ambiguity often remains for cases with small angular separation between volcanoes with respect to the infrasound array. We tackle the issue of azimuth resolution by considering volcanic sectors rather than single edifices. This approach can still provide critical information to the VAACs for triggering independent and extended analysis on ongoing volcanic eruptions
Clues on the Australasian impact crater site inferred from detailed mineralogical study of a monazite inclusion in a Muong Nong tektite: REPLY
No full textInternational audienc
Large Cold Dust Reservoir Revealed in Transitional SN Ib 2014C by James Webb Space Telescope Mid-Infrared Spectroscopy
No full textInternational audienceSupernova (SN) 2014C is a rare transitional event that exploded as a hydrogen-poor, helium-rich Type Ib SN and subsequently interacted with a hydrogen-rich circumstellar medium (CSM) a few months post explosion. This unique interacting object provides an opportunity to probe the mass-loss history of a stripped-envelope SN progenitor. Using the James Webb Space Telescope (JWST), we observed SN 2014C with the Mid-InfraRed Instrument Medium Resolution Spectrometer at 3477 days post explosion (rest frame), and the Near-InfraRed Spectrograph Integral Field Unit at 3568 days post explosion, covering 1.7 to 25 m. The bolometric luminosity indicates that the SN is still interacting with the same CSM that was observed with the Spitzer Space Telescope 40--1920 days post explosion. JWST spectra and near-contemporaneous optical and near-infrared spectra show strong [Ne II] 12.831 m, He 1.083 m, H, and forbidden oxygen ([O I] 6300, 6364, [O II] 7319, 7330, and [O III] 4959, 5007) emission lines with asymmetric profiles, suggesting a highly asymmetric CSM. The mid-IR continuum can be explained by ~0.036 of carbonaceous dust at ~300 K and ~0.043 of silicate dust at 200 K. The observed dust mass has increased tenfold since the last Spitzer observation 4 yr ago, with evidence suggesting that new grains have condensed in the cold dense shell between the forward and reverse shocks. This dust mass places SN 2014C among the dustiest SNe in the mid-IR and supports the emerging observational trend that SN explosions produce enough dust to explain the observed dust mass at high redshifts
[C II]-deficit caused by self-absorption in an ionized carbon-filled bubble in RCW79
No full textInternational audienceRecent spectroscopic observations of the [C II] 158 fine-structure line of ionized carbon (C), using the Stratospheric Observatory for Infrared Astronomy (SOFIA), have revealed expanding [C II] shells in Galactic H II regions. We report the discovery of a bubble-shaped source (S144 in RCW79), associated with a compact H II region, excited by a single O7.5--9.5V/III star, which is consistent with a scenario that the bubble is still mostly ``filled'' with C. This indicates most likely a very early evolutionary state, in which the stellar wind has not yet blown material away, as it is the case for more evolved H II regions. Using the SimLine non-LTE radiative transfer code, the [C II] emission can be modeled to originate from three regions. First, a central H II region with little C in the fully ionized phase, followed by two layers with gas density around of partially photo-dissociated gas. The second layer is a slowly expanding [C II] shell with an expansion velocity of . The outermost layer exhibits a temperature and velocity gradient that produces the observed self-absorption features in the optically thick [C II] line () leading to an apparent deficit in [C II] emission and a low ratio of [C II] to total far-infrared (FIR) emission. We developed a procedure to approximate the missing [C II] flux and find a linear correlation between [C II] and FIR without a [C II]-deficit. This demonstrates that at least some of the [C II]-deficit found in Galactic H II bubbles can be attributed to self-absorption
Sediment and organic carbon discharges to the coastal oceans by badlands (English Channel, Normandy, France)
No full text(IF 2.8;Q2)International audienceAbstract Determining sedimentary and organic carbon fluxes and sources within the sedimentary continuum from land to sea is crucial for improving the understanding of Earth system dynamics, global carbon budgets and associated biogeochemical cycles, especially in the context of Global Change. Among continental sources, marly badlands, characterized by high erosion rates and significant Total Organic Carbon (TOC) contents, are potential contributors of material to the sea. However, data on sediment and TOC yields, fluxes and the contribution of badlands to the marine environment are still limited, particularly in NW Europe and oceanic regions. In this context, the instrumented sites of Vaches Noires cliffs on the western Normandy coast, France, were studied over three years. Suspended Particulate Matter (SPM) and source samples were collected along the eastern part of the cliff. Geochemical analyses, sediment fluxes and yields were obtained and compared with those from local rivers, European badlands and worldwide Small Mountain River systems (SMRs). These first results show that the cliffs exhibited high productivity in terms of sediment and organic carbon (OC) yields, like other studied badlands. Reaching the English Channel, material from badlands can enter and sediment within the Seine estuary, contributing to the Turbidity Maximal Zone and mixing with other OC sources (such as primary productivity and continental OC). Although the contribution of this material to the carbon (C) budget of this interface remains uncertain, it could be significant, especially with the increase in global sea level and major rainfall events
Millimeter emission from supermassive black hole coronae
No full textInternational audienceActive Galactic Nuclei (AGN) host accreting supermassive black holes (SMBHs). The accretion can lead to the formation of a hot, X-ray emitting corona close to the SMBH capable of accelerating relativistic electrons. Observations in the millimetre (mm) band can probe its synchrotron emission. We provide a framework to derive physical information of SMBH coronae by modelling their spectral energy distribution (SED) from radio to far infrared frequencies. We also explore the possibilities of deriving additional information from mm observations, such as the SMBH mass, and studying high-redshift lensed sources. We introduce a corona emission model based on a one-zone spherical region with a hybrid thermal and non-thermal plasma. We investigate in detail how the corona SED depends on different parameters such as size, opacity, and magnetic field strength. Other galactic emission components from dust, ionised gas and diffuse relativistic electrons are also included in the SED fitting scheme. We apply our code consistently to a sample of radio-quiet AGN with strong indications of a coronal component in the mm. The detected mm emission from SMBH coronae is consistent with having a non-thermal relativistic particle population with an energy density that is ~0.5-10% of that in the thermal plasma. This requires magnetic energy densities close to equipartition with the thermal gas, and corona sizes of 60-250 gravitational radii. The model can also reproduce the observed correlation between mm emission and SMBH mass when accounting for uncertainties in the corona size. The mm band offers a unique window into the physics of SMBH coronae, enabling the study of highly dust-obscured sources and high-redshift lensed quasars. Gaining a deeper understanding of the relativistic particle population in SMBH coronae can provide key insights into their potential multiwavelength and neutrino emission
The Pristine Dwarf-Galaxy survey:VI. A VLT/FLAMES spectroscopic study of the dwarf galaxy Boötes II
No full textInternational audienceAims. The Milky Way has a large population of dwarf galaxy satellites. Their properties are sensitive to both cosmology and the physical processes underlying galaxy formation, but these properties are still not properly characterised for the entire satellite population. Methods. We aim to provide the most accurate systemic dynamical and metallicity properties of the dwarf galaxy Boötes II (Boo II). Results. We use a new spectroscopic sample of 39 stars in the field of Boo II (heliocentric distance of ∼66 kpc) with data from the Fiber Large Array Multi Element Spectrograph (FLAMES) mounted on the Very Large Telescope (VLT). The target selection is based on a combination of broadband photometry, proper motions from Gaia, and the metallicity-sensitive narrow-band photometry from the Pristine survey that is ideal for removing obvious Milky Way contaminants. Conclusions. We found nine new members, including five also found by recent works in the literature, and the farthest member to date (5.7 half-light radii from Boo II centroid), extending the spectroscopic spatial coverage of this system. Our metallicity measurements based on the Calcium triplet lines leads to the detection of the two first Extremely Metal-poor stars ([Fe/H] < -3.0) in Boo II. Combining this new dataset with literature data refines Boo II's velocity dispersion (5.6 +1.8 -1.1 km s -1 ), systemic velocity (-126.8 +2.0 -1.5 km s -1 ), and shows that it does not show any sign of a significant velocity gradient (d v /dχ = 0.6 +0.6 -0.4 km s -1 arcmin -1 , or -0.5/1.9 km s -1 arcmin -1 as 3σ upper limits). We are thus able to confirm the kinematic and metallicity properties of the satellite as well as identify new members for future high-resolution analyses.</div