RSS 1.0Astrophysics of Galaxies (astro-ph.GA)
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The HASHTAG project II. Giant molecular cloud properties across the M31 discWe present a study of giant molecular cloud (GMC) properties in the Andromeda galaxy (M31) using CO(3-2) data from the James Clerk Maxwell Telescope (JCMT) in selected regions across the disc and in the nuclear ring, and comparing them with CO(1-0) observations from the IRAM 30m telescope in the same regions. We find that GMCs in the centre of M31 generally exhibit larger velocity dispersions (σ) and sizes (R) compared to those in the disc, while their average surface density (Σ) and turbulent pressure (P<SUB>turb</SUB>) are lower. This low turbulent pressure in the central region is primarily due to the low density of molecular gas. The estimated GMC properties depend on the choice of CO transitions. Compared to CO(1-0), CO(3-2) exhibits smaller velocity dispersion and equivalent radius but higher surface density. These differences highlight the distinct physical conditions probed by different molecular gas tracers. We estimate the virial parameter α<SUB>vir</SUB>∝σ<SUP>2</SUP>R/Σ and find that most molecular clouds exhibit high values (α<SUB>vir</SUB> ~ 4 - 6) for both CO transitions, indicating that they are unbound. Furthermore, clouds in the nuclear ring display even larger α<SUB>vir</SUB> values of ≲ 100, suggesting that they may be highly dynamic, short-lived structures, although they could potentially achieve equilibrium under the external pressure exerted by the surrounding interstellar medium.
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PAMS: The Perseus Arm Molecular Survey-I. Survey description and first resultsThe external environments surrounding molecular clouds vary widely across galaxies such as the Milky Way, and statistical samples of clouds are required to understand them. We present the Perseus Arm Molecular Survey (PAMS), a James Clerk Maxwell Telescope (JCMT) survey combining new and archival data of molecular-cloud complexes in the outer Perseus spiral arm in <inline-formula><tex-math id=TM0001 notation=LaTeX>$^{12}$</tex-math></inline-formula>CO, <inline-formula><tex-math id=TM0002 notation=LaTeX>$^{13}$</tex-math></inline-formula>CO, and C<inline-formula><tex-math id=TM0003 notation=LaTeX>$^{18}$</tex-math></inline-formula>O (J = 3-2). With a survey area of <inline-formula><tex-math id=TM0005 notation=LaTeX>$\sim$</tex-math></inline-formula>8 deg<inline-formula><tex-math id=TM0006 notation=LaTeX>$^2$</tex-math></inline-formula>, PAMS covers well-known complexes such as W3, W5, and NGC 7538 with two fields at <inline-formula><tex-math id=TM0007 notation=LaTeX>$\ell \approx 110^{\circ }$</tex-math></inline-formula> and <inline-formula><tex-math id=TM0008 notation=LaTeX>$\ell \approx 135^{\circ }$</tex-math></inline-formula>. PAMS has an effective resolution of 17 arcsec, and rms sensitivity of <inline-formula><tex-math id=TM0009 notation=LaTeX>$T_\mathrm{mb}= 0.7$</tex-math></inline-formula>-1.0 K in 0.3 km s<inline-formula><tex-math id=TM0010 notation=LaTeX>$^{-1}$</tex-math></inline-formula> channels. Here we present a first look at the data, and compare the PAMS regions in the Outer Galaxy with Inner Galaxy regions from the CO Heterodyne Inner Milky Way Plane Survey (CHIMPS). By comparing the various CO data with maps of H<inline-formula><tex-math id=TM0011 notation=LaTeX>$_2$</tex-math></inline-formula> column density from Herschel, we calculate representative values for the CO-to-H<inline-formula><tex-math id=TM0012 notation=LaTeX>$_2$</tex-math></inline-formula> column-density X-factors, which are <inline-formula><tex-math id=TM0014 notation=LaTeX>$X_\mathrm{^{12}CO\, (3-2)}$</tex-math></inline-formula><inline-formula><tex-math id=TM0015 notation=LaTeX>$\, =4.0\times 10^{20}$</tex-math></inline-formula> and <inline-formula><tex-math id=TM0016 notation=LaTeX>$X_\mathrm{^{13}CO\, (3-2)}$</tex-math></inline-formula><inline-formula><tex-math id=TM0017 notation=LaTeX>$\, =4.0\times 10^{21}$</tex-math></inline-formula> cm<inline-formula><tex-math id=TM0018 notation=LaTeX>$^{-2}$</tex-math></inline-formula> (K km s<inline-formula><tex-math id=TM0019 notation=LaTeX>$^{-1}$</tex-math></inline-formula>)<inline-formula><tex-math id=TM0020 notation=LaTeX>$^{-1}$</tex-math></inline-formula> with a factor of 1.5 uncertainty. We find that the emission profiles, size-linewidth, and mass-radius relationships of <inline-formula><tex-math id=TM0021 notation=LaTeX>$^{13}$</tex-math></inline-formula>CO-traced structures are similar between the Inner and Outer Galaxy. Although PAMS sources are slightly more massive than their Inner Galaxy counterparts for a given size scale, the discrepancy can be accounted for by the Galactic gradient in gas-to-dust mass ratio, uncertainties in the X-factors, and selection biases. We have made the PAMS data publicly available, complementing other CO surveys targeting different regions of the Galaxy in different isotopologues and transitions.
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Discovery of Metal-poor and Distant Pre–Main Sequence Candidates in WLM with JWSTWe present the discovery of 12 metal-poor and distant pre–main sequence (PMS) candidates in the dwarf irregular galaxy Wolf–Lundmark–Melotte ∼968 kpc away, at a present-day metallicity of [Fe/H] ∼ –0.9. These candidates have masses between 1.25 and 5 M<SUB>⊙</SUB>, with ages <10 Myr, and exhibit significant near-infrared excesses at 2.5 and 4.3 μm. They are concentrated within a cluster roughly 10 pc (2″) across, situated in the H II region [HM95]-9. These are the most distant and metal-poor PMS stars known, and they can offer new quantitative insights into star formation at low metallicities.
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X-Shooting ULLYSES: Massive stars at low metallicity: X. Physical parameters and feedback of massive stars in the LMC N11 B star-forming regionMassive stars drive the ionization and mechanical feedback within young star-forming regions. The Large Magellanic Cloud (LMC) is an ideal galaxy for studying individual massive stars and quantifying their feedback contribution to the environment. We analyze eight exemplary targets in LMC N11 B from the Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program using novel spectra from HST (COS and STIS) in the UV, and from VLT (X-shooter) in the optical. We model the spectra of early to late O-type stars using state-of-the-art PoWR atmosphere models. We determine the stellar and wind parameters (e.g., T<SUB>⋆</SUB>, log g, L<SUB>⋆</SUB>, Ṁ, and v<SUB>∞</SUB>) of the analyzed objects, chemical abundances (C, N, and O), ionizing and mechanical feedback (Q<SUB>H</SUB>, Q<SUB>HeI</SUB>, Q<SUB>He II</SUB>, and L<SUB>mec</SUB>), and X-rays. We report ages of 2–4.5 Myr and masses of 30–60 M<SUB>⊙</SUB> for the analyzed stars in N11 B, which are consistent with a scenario of sequential star formation. We note that the observed wind-momentum–luminosity relation is consistent with theoretical predictions. We detect nitrogen enrichment by up to a factor of seven in most of the stars. However, we do not find a correlation between nitrogen enrichment and projected rotational velocity. Finally, based on their spectral type, we estimate the total ionizing photons injected from the O-type stars in N11 B into its environment. We report log (Σ Q<SUB>H</SUB>) = 50.5 ph s<SUP>‑1</SUP>, log (Σ Q<SUB>He I</SUB>) = 49.6 ph s<SUP>‑1</SUP>, and log (Σ Q<SUB>He II</SUB>)= 44.4 ph s<SUP>‑1</SUP>, consistent with the total ionizing budget in N11.
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Looking into the faintEst WIth MUSE (LEWIS): Exploring the nature of ultra-diffuse galaxies in the Hydra-I cluster: II. Stellar kinematics and dynamical massesContext. This paper focuses on a class of galaxies characterised by an extremely low surface brightness: ultra-diffuse galaxies (UDGs). We used new integral-field (IF) spectroscopic data, obtained with the ESO Large Programme Looking into the faintEst WIth MUSE (LEWIS). It provides the first homogeneous IF spectroscopic survey performed by MUSE at the Very Large Telescope of a complete sample of UDGs and low-surface-brightness galaxies within a virial radius of 0.4 in the Hydra I cluster, according to the UDG abundance-halo mass relation. Aims. Our main goals are addressing the possible formation channels for this class of objects and investigating possible correlations of their observational properties, including the stacked (1D) and spatially resolved (2D) stellar kinematics. In particular, we derive the stellar velocity dispersion from the stacked spectrum integrated within the effective radius (σ<SUB>eff</SUB>) and measure the velocity map of the galaxies in LEWIS. These quantities are used to estimate their dynamical mass (M<SUB>dyn</SUB>). Methods. We extracted the 1D stacked spectrum inside the effective radius (R<SUB>eff</SUB>), which guarantees a high signal-to-noise ratio, to obtain an unbiased measure of σ<SUB>eff</SUB>. To derive the spatially resolved stellar kinematics, we first applied the Voronoi tessellation algorithm to bin the spaxels in the datacube, and then we derived the stellar kinematics in each bin, following the same prescription as adopted for the 1D case. We extracted the velocity profiles along the galaxy major and minor axes and measured the semi-amplitude (ΔV) of the velocity curve. Results. We found that 7 out of 18 UDGs in LEWIS show a mild rotation (ΔV ∼ 25 ‑ 40 km s<SUP>‑1</SUP>), 5 lack evidence of any rotation, and the remaining 6 UDGs are unconstrained cases. This is the first large census of velocity profiles for UDGs. The UDGs in LEWIS are characterised by low values of σ<SUB>eff</SUB> (≤30 km s<SUP>‑1</SUP>) on average, which is comparable with available values from the literature. Two objects show higher values of σ<SUB>eff</SUB> (∼30 ‑ 40 km s<SUP>‑1</SUP>). These higher values might reasonably be due to the fast rotation observed in these galaxies, which affects the values of σ<SUB>eff</SUB>. In the Faber-Jackson relation plane, we found a group of UDGs consistent with the relation within the error bars. Outliers of the Faber-Jackson relation are objects with a non-negligible rotation component. The UDGs and LSB galaxies in the LEWIS sample have a larger dark matter (DM) content on average than dwarf galaxies (M<SUB>dyn</SUB>/L<SUB>V, eff</SUB> ∼ 10 ‑ 100 M<SUB>⊙</SUB>/L<SUB>⊙</SUB>) with a similar total luminosity. We do not find clear correlations between the derived structural properties and the local environment. Conclusions. By mapping the stellar kinematics for a homogenous sample of UDGs in a cluster environment, we found a significant rotation for many galaxies. Therefore, two classes of UDGs are found in the Hydra I cluster based on the stellar kinematics: rotating and non-rotating systems. This result, combined with the DM content and the upcoming analysis of the star formation history and globular cluster population, can help us to distinguish between the several formation scenarios proposed for UDGs.
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WISDOM Project - XXII. A 5 per cent precision CO-dynamical supermassive black hole mass measurement in the galaxy NGC 383We present a measurement of the supermassive black hole (SMBH) mass of the nearby lenticular galaxy NGC 383, based on Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the <inline-formula><tex-math id=TM0001 notation=LaTeX>$^{12}$</tex-math></inline-formula>CO(2-1) emission line with an angular resolution of <inline-formula><tex-math id=TM0002 notation=LaTeX>$0.050{\,\rm arcsec}\times 0.024{\,\rm arcsec}$</tex-math></inline-formula> (<inline-formula><tex-math id=TM0003 notation=LaTeX>$\approx 16\times 8$</tex-math></inline-formula> pc<inline-formula><tex-math id=TM0004 notation=LaTeX>$^2$</tex-math></inline-formula>). These observations spatially resolve the nuclear molecular gas disc down to <inline-formula><tex-math id=TM0005 notation=LaTeX>$\approx 41\,300$</tex-math></inline-formula> Schwarzschild radii and the SMBH sphere of influence by a factor of <inline-formula><tex-math id=TM0006 notation=LaTeX>$\approx 24$</tex-math></inline-formula> radially, better than any other SMBH mass measurement using molecular gas to date. The high resolution enables us to probe material with a maximum circular velocity of <inline-formula><tex-math id=TM0007 notation=LaTeX>$\approx 1040$</tex-math></inline-formula> km s<inline-formula><tex-math id=TM0008 notation=LaTeX>$^{-1}$</tex-math></inline-formula>, even higher than those of the highest resolution SMBH mass measurements using megamasers. We detect a clear Keplerian increase (from the outside in) of the line-of-sight rotation velocities, a slight offset between the gas disc kinematic (i.e. the position of the SMBH) and morphological (i.e. the centre of the molecular gas emission) centres, an asymmetry of the innermost rotation velocity peaks and evidence for a mild position angle warp and/or non-circular motions within the central <inline-formula><tex-math id=TM0009 notation=LaTeX>$\approx 0.3\,{\rm arcsec}$</tex-math></inline-formula>. By forward modelling the mass distribution and ALMA data cube, we infer an SMBH mass of <inline-formula><tex-math id=TM0010 notation=LaTeX>$(3.58\pm 0.19)\times 10^9$</tex-math></inline-formula> M<inline-formula><tex-math id=TM0011 notation=LaTeX>$_\odot$</tex-math></inline-formula> (<inline-formula><tex-math id=TM0012 notation=LaTeX>$1\sigma$</tex-math></inline-formula> confidence interval), more precise (5 per cent) but consistent within <inline-formula><tex-math id=TM0013 notation=LaTeX>$\approx 1.4\sigma$</tex-math></inline-formula> with the previous measurement using lower resolution molecular gas data. Our measurement emphasizes the importance of high spatial resolution observations for precise SMBH mass determinations.
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A First Taste of MEAD (Measuring Extinction and Abundances of Dust). I. Diffuse Milky Way Interstellar Dust Extinction Features in JWST Infrared SpectraWe present the initial results of the Measuring Extinction and Abundances of Dust project, with a focus on the dust extinction features observed in our JWST near- and mid-infrared spectra of nine diffuse Milky Way sightlines (1.2 ≤ A(V) ≤ 2.5). For the first time, we find strong correlations between the 10 μm silicate feature strength and the column densities of Mg, Fe, and O in dust. This is consistent with the well-established theory that Mg- and Fe-rich silicates are responsible for this feature. We obtain an average stoichiometry of the silicate grains in our sample of Mg:Fe:O = 1.1:1:11.2, constraining the grain composition. We find variations in the feature properties, indicating that different sightlines contain different types of silicates. In the average spectrum of our sample, we tentatively detect features around 3.4 and 6.2 μm, which are likely caused by aliphatic and aromatic/olefinic hydrocarbons, respectively. If real, to the best of our knowledge, this is the first detection of hydrocarbons in purely diffuse sightlines with A(V) ≤ 2.5, confirming the presence of these grains in diffuse environments. We detected a 3 μm feature toward HD073882 and tentatively in the sample average, likely caused by water ice (or solid-state water trapped on silicate grains). If confirmed, to the best of our knowledge, this is the first detection of ice in purely diffuse sightlines with A(V) ≤ 2.5, supporting previous findings that these molecules can exist in the diffuse interstellar medium.
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A Tale of Three: Magnetic Fields along the Orion Integral-shaped Filament as Revealed by the JCMT BISTRO SurveyAs part of the B-fields In Star-forming Region Observations survey, we present James Clerk Maxwell Telescope (JCMT) 850 μm polarimetric observations toward the Orion integral-shaped filament (ISF) that covers three portions known as OMC-1, OMC-2, and OMC-3. The magnetic field threading the ISF seen in the JCMT POL-2 map appears as a tale of three: pinched for OMC-1, twisted for OMC-2, and nearly uniform for OMC-3. A multiscale analysis shows that the magnetic field structure in OMC-3 is very consistent at all the scales, whereas the field structure in OMC-2 shows no correlation across different scales. In OMC-1, the field retains its mean orientation from large to small scales but shows some deviations at small scales. Histograms of relative orientations between the magnetic field and filaments reveal a bimodal distribution for OMC-1, a relatively random distribution for OMC-2, and a distribution with a predominant peak at 90<SUP>∘</SUP> for OMC-3. Furthermore, the magnetic fields in OMC-1 and OMC-3 both appear to be aligned perpendicular to the fibers, which are denser structures within the filament, but the field in OMC-2 is aligned along with the fibers. All these suggest that gravity, turbulence, and magnetic field are each playing a leading role in OMC-1, 2, and 3, respectively. While OMC-2 and 3 have almost the same gas mass, density, and nonthermal velocity dispersion, there are on average younger and fewer young stellar objects in OMC-3, providing evidence that a stronger magnetic field will induce slower and less efficient star formation in molecular clouds.
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ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Nested Morphological and Kinematic Structures of Outflows Revealed in SiO and CO EmissionThe Atacama Large Millimeter/submillimeter Array Survey of Orion Planck Galactic Cold Clumps (ALMASOP) reveals complex nested morphological and kinematic features of molecular outflows through the CO (J = 2‑1) and SiO (J = 5‑4) emission. We characterize the jet and outflow kinematics of the ALMASOP sample in four representative sources (HOPS 10, 315, 358, and G203.21-11.20W2) through channel maps and position–velocity diagrams (PVDs) parallel and transverse to the outflow axes. The combined CO and SiO emission exhibits the coexistence of the conventional extremely high-velocity jets and shell-like low-velocity cavity walls and new features. More complex, nested bubble-like and filamentary structures in the images and channel maps, triangle-shaped regions near the base of the parallel PVDs, and regions composed of rhombus/oval shapes in the transverse PVDs are also evident. Such features find natural explanations within the bubble structure of the unified model of jet, wind, and ambient medium. The reverse shock cavity is revealed on the PVD base regions, and other features naturally arise within the dynamic postshock region of magnetic interaction. The finer nested shells observed within the compressed wind region reveal previously unnoticed shocked emission between the jet and the conventional large cavity walls. These pseudopulse-produced filamentary features connect to the jetlike knotty blobs, creating an impression of episodicity in mass ejection. SiO emission is enhanced downstream of the reverse shock boundary, with jetlike excitation conditions. Combined, these observed features reveal the extended structures induced by the magnetic interplay between a jet-bearing magnetized wide-angle wind and its ambient magnetized surrounding medium.
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X-Shooting ULLYSES: Massive stars at low metallicity: VII. Stellar and wind properties of B supergiants in the Small Magellanic CloudContext. With the aim of understanding massive stars and their feedback in the early epochs of our Universe, the ULLYSES and XShootU collaborations collected the biggest homogeneous dataset of high-quality hot star spectra at low metallicity. Within the rich zoo of massive star stellar types, B supergiants (BSGs) represent an important connection between the main sequence and more extreme evolutionary stages. Additionally, lying toward the cool end of the hot star regime, determining their wind properties is crucial to gauging our expectations on the evolution and feedback of massive stars as, for instance, they are implicated in the bi-stability jump phenomenon. Aims. Here, we undertake a detailed analysis of a representative sample of 18 Small Magellanic Cloud (SMC) BSGs within the ULLYSES dataset. Our UV and optical analysis samples early- and late-type BSGs (from B0 to B8), covering the bi-stability jump region. Our aim is to evaluate their evolutionary status and verify what their wind properties say about the bi-stability jump at a low-metallicity environment. Methods. We used the stellar atmosphere code CMFGEN to model the UV and optical spectra of the sample BSGs as well as photometry in different bands. The optical range encodes photospheric properties, while the wind information resides mostly in the UV. Further, we compare our results with different evolutionary models, with previous determinations in the literature of OB stars, and with diverging mass-loss prescriptions at the bi-stability jump. Additionally, for the first time we provide BSG models in the SMC including X-rays. Results. Our analysis yielded the following main results: (i) From a single-stellar evolution perspective, the evolutionary status of early BSGs appear less clear than late BSGs, which are agree reasonably well with H-shell burning models. (ii) Ultraviolet analysis shows evidence that the BSGs contain X-rays in their atmospheres, for which we provide constraints. In general, higher X-ray luminosity (close to the standard log(L<SUB>X</SUB>/L) ~ ‑7) is favored for early BSGs, despite associated degeneracies. For later-type BSGs, lower values are preferred, log(L<SUB>X</SUB>/L) ~ ‑8.5. (iii) The obtained mass-loss rates suggest neither a jump nor an unperturbed monotonic decrease with temperature. Instead, a rather constant trend appears to happen, which is at odds with the increase found for Galactic BSGs. (iv) The wind velocity behavior with temperature shows a sharp drop at ~19 kK, very similar to the bi-stability jump observed for Galactic stars.
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Stellar expansion or inflation?While stellar expansion after core-hydrogen exhaustion related to thermal imbalance has been documented for decades, the physical phenomenon of stellar inflation that occurs close to the Eddington limit has only come to the fore in recent years. We aim to elucidate the differences between these physical mechanisms for stellar radius enlargement, especially given that additional terms such as 'bloated' and 'puffed-up' stars have been introduced in the recent massive star literature. We employ single and binary star MESA structure and evolution models for constant mass, as well as models allowing the mass to change due to winds or binary interaction. We find cases that were previously attributed to stellar inflation in fact to be due to stellar expansion. We also highlight that while the opposite effect of expansion is contraction, the removal of an inflated zone should not be referred to as contraction but rather deflation, as the star is still in thermal balance.
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Cataclysmic Variables and AM CVn Binaries in SRG/eROSITA + Gaia: Volume Limited Samples, X-Ray Luminosity Functions, and Space DensitiesWe present volume-limited samples of cataclysmic variables (CVs) and AM CVn binaries jointly selected from SRG/eROSITA eRASS1 and Gaia DR3 using an X-ray + optical color–color diagram (the X-ray Main Sequence). This tool identifies all CV subtypes, including magnetic and low-accretion rate systems, in contrast to most previous surveys. We find 23 CVs, 3 of which are AM CVns, out to 150 pc in the Western Galactic Hemisphere. Our 150 pc sample is spectroscopically verified and complete down to L<SUB>X</SUB> = 1.3 × 10<SUP>29</SUP> erg s<SUP>‑1</SUP> in the 0.2–2.3 keV band, and we also present CV candidates out to 300 pc and 1000 pc. We discovered two previously unknown systems in our 150 pc sample: the third nearest AM CVn and a magnetic period bouncer. We find the mean L<SUB>X</SUB> of CVs to be <L<SUB>X</SUB>> ≈ 4.6 × 10<SUP>30</SUP> erg s<SUP>‑1</SUP>, in contrast to previous surveys which yielded <L<SUB>X</SUB>> ∼ 10<SUP>31</SUP>‑10<SUP>32</SUP> erg s<SUP>‑1</SUP>. We construct X-ray luminosity functions that, for the first time, flatten out at L<SUB>X</SUB> ∼ 10<SUP>30</SUP> erg s<SUP>‑1</SUP>. We infer average number, mass, and luminosity densities of ρ<SUB>N,CV</SUB> = (3.7 ± 0.7) × 10<SUP>‑6</SUP>pc<SUP>‑3</SUP>, <inline-formula> <mml:math overflow=scroll><mml:msub><mml:mrow><mml:mi>ρ</mml:mi></mml:mrow><mml:mrow><mml:mi>M</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mo stretchy=false>(</mml:mo><mml:mn>5.0</mml:mn><mml:mo>±</mml:mo><mml:mn>1.0</mml:mn><mml:mo stretchy=false>)</mml:mo><mml:mo>×</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>5</mml:mn></mml:mrow></mml:msup><mml:msubsup><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula>, and <inline-formula> <mml:math overflow=scroll><mml:msub><mml:mi>ρ</mml:mi><mml:msub><mml:mi>L</mml:mi><mml:mi mathvariant=normal>X</mml:mi></mml:msub></mml:msub><mml:mo>=</mml:mo><mml:mo stretchy=false>(</mml:mo><mml:mn>2.3</mml:mn><mml:mo>±</mml:mo><mml:mn>0.4</mml:mn><mml:mo stretchy=false>)</mml:mo><mml:mo>×</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mn>0</mml:mn><mml:mn>26</mml:mn></mml:msup><mml:mspace width=0.25em></mml:mspace><mml:mi>erg</mml:mi><mml:mspace width=0.25em></mml:mspace><mml:msup><mml:mi mathvariant=normal>s</mml:mi><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup><mml:msubsup><mml:mi>M</mml:mi><mml:mo>⊙</mml:mo><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula>, respectively, in the solar neighborhood. Our uniform selection method also allows us to place meaningful estimates on the space density of AM CVns, ρ<SUB>N,AM CVn</SUB> = (5.5 ± 3.7) × 10<SUP>‑7</SUP> pc<SUP>‑3</SUP>. Magnetic CVs and period bouncers make up 35% and 25% of our sample, respectively. This work, through a novel discovery technique, shows that the observed number densities of CVs and AM CVns, as well as the fraction of period bouncers, are still in tension with population synthesis estimates.
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ALMASOP. The Localized and Chemically Rich Features near the Bases of the Protostellar Jet in HOPS 87HOPS 87 is a Class 0 protostellar core known to harbor an extremely young bipolar outflow and a hot corino. We report the discovery of localized, chemically rich regions near the bases of the two-lobe bipolar molecular outflow in HOPS 87 containing molecules such as H<SUB>2</SUB>CO, <SUP>13</SUP>CS, H<SUB>2</SUB>S, OCS, and CH<SUB>3</SUB>OH, the simplest complex organic molecule (COM). The locations and kinematics suggest that these localized features are due to jet-driven shocks rather than being part of the hot-corino region encasing the protostar. The COM compositions of the molecular gas in these jet-localized regions are relatively simpler than those in the hot-corino zone. We speculate that this simplicity is due to either the liberation of ice with a less complex chemical history or the effects of shock chemistry. Our study highlights the dynamic interplay between the protostellar bipolar outflow, disk, inner-core environment, and the surrounding medium, contributing to our understanding of molecular complexity in solar-like young stellar objects.
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X-Shooting ULLYSES: Massive stars at low metallicity: VIII. Stellar and wind parameters of newly revealed stripped stars in Be binariesOn the route toward merging neutron stars and stripped-envelope supernovae, binary population synthesis predicts a large number of post-interaction systems with massive stars that have been stripped of their outer layers. However, observations of such stars in the intermediate-mass regime below the Wolf-Rayet masses are rare. Using X-Shooting ULLYSES (XShootU) data, we have discovered three partially stripped star + Be/Oe binaries in the Magellanic Clouds. We analyzed the UV and optical spectra using the Potsdam Wolf-Rayet (PoWR) model atmosphere code by superimposing model spectra that correspond to each component. The estimated current masses of the partially stripped stars fall within the intermediate-mass range of ≈4 ‑ 8 M<SUB>⊙</SUB>. These objects are found to be over-luminous for their corresponding stellar masses, which aligns with the luminosities during core He-burning. Their accompanying Be/Oe secondaries are found to have much higher masses than their stripped primaries (mass ratio ≳2). The surfaces of all three partially stripped stars exhibit clear indications of significant nitrogen enrichment as well as a depletion of carbon and oxygen. Furthermore, one of our sample stars shows signs of substantial helium enrichment. Our study provides the first comprehensive determination of the wind parameters of partially stripped stars in the intermediate-mass range. The wind mass-loss rates of these stars are estimated to be on the order of 10<SUP>‑7</SUP> M<SUB>⊙</SUB> yr<SUP>‑1</SUP>, which is more than ten times higher than that of OB stars with the same luminosity. The current mass-loss recipes commonly employed in evolutionary models to characterize this phase are based on OB or WR mass-loss rates, and they significantly underestimate or overestimate the observed mass-loss rates of (partially) stripped stars by an order of magnitude. Binary evolution models suggest that the observed primaries had initial masses in the range of 12‑17 M<SUB>⊙</SUB>, and are potential candidates for stripped-envelope supernovae resulting in the formation of a neutron star. If these systems survive the explosion, they will likely evolve to become Be X-ray binaries and later double neutron stars.
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X-Shooting ULLYSES: Massive Stars at low metallicity: IX. Empirical constraints on mass-loss rates and clumping parameters for OB supergiants in the Large Magellanic CloudContext. Current implementations of mass loss for hot, massive stars in stellar evolution models usually include a sharp increase in mass loss when blue supergiants become cooler than T<SUB>eff</SUB> ∼ 20 ‑ 22 kK. Such a drastic mass-loss jump has traditionally been motivated by the potential presence of a so-called bistability ionisation effect, which may occur for line-driven winds in this temperature region due to recombination of important line-driving ions. Aims. We perform quantitative spectroscopy using UV (ULLYSES program) and optical (XShootU collaboration) data for 17 OB-supergiant stars in the LMC (covering the range T<SUB>eff</SUB> ∼ 14 ‑ 32 kK), deriving absolute constraints on global stellar, wind, and clumping parameters. We examine whether there are any empirical signs of a mass-loss jump in the investigated region, and we study the clumped nature of the wind. Methods. We used a combination of the model atmosphere code FASTWIND and the genetic algorithm (GA) code Kiwi-GA to fit synthetic spectra of a multitude of diagnostic spectral lines in the optical and UV. Results. We find an almost monotonic decrease of mass-loss rate with effective temperature, with no signs of any upward mass loss jump anywhere in the examined region. Standard theoretical comparison models, which include a strong bistability jump thus severely overpredict the empirical mass-loss rates on the cool side of the predicted jump. Another key result is that across our sample we find that on average about 40% of the total wind mass seems to reside in the more diluted medium in between dense clumps. Conclusions. Our derived mass-loss rates suggest that for applications such as stellar evolution one should not include a drastic bistability jump in mass loss for stars in the temperature and luminosity region investigated here. The derived high values of interclump density further suggest that the common assumption of an effectively void interclump medium (applied in the vast majority of spectroscopic studies of hot star winds) is not generally valid in this parameter regime.
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X-Shooting ULLYSES: Massive stars at low metallicity: VI. Atmosphere and mass-loss properties of O-type giants in the Small Magellanic CloudContext. Mass loss through a stellar wind is an important physical process that steers the evolution of massive stars and controls the properties of their end-of-life products, such as the supernova type and the mass of compact remnants. To probe its role in stellar evolution over cosmic time, mass loss needs to be studied as function of metallicity. For mass loss to be accurately quantified, the wind structure needs to be established jointly with the characteristics of small-scale inhomogeneities in the outflow, which are known as wind clumping. Aims. We aim to improve empirical estimates of mass loss and wind clumping for hot main-sequence massive stars, study the dependence of both properties on the metal content, and compare the theoretical predictions of mass loss as a function of metallicity to our findings. Methods. Using the model atmosphere code FASTWIND and the genetic algorithm fitting method KIWI-GA, we analyzed the optical and ultraviolet spectra of 13 O-type giant to supergiant stars in the Small Magellanic Cloud galaxy, which has a metallicity of approximately one-fifth of that of the Sun. We quantified the stellar global outflow properties, such as the mass-loss rate and terminal wind velocity, and the wind clumping properties. To probe the role of metallicity, our findings were compared to studies of Galactic and Large Magellanic Cloud samples that were analyzed with similar methods, including the description of clumping. Results. We find significant variations in the wind clumping properties of the target stars, with clumping starting at flow velocities 0.01–0.23 of the terminal wind velocity and reaching clumping factors f<SUB>cl</SUB> = 2–30. In the luminosity (log L/L<SUB>⊙</SUB> = 5.0–6.0) and metallicity (Z/Z<SUB>⊙</SUB> = 0.2–1) range we considered, we find that the scaling of the mass loss M<SUP>˙</SUP> with metallicity Z varies with luminosity. At log L/L<SUB>⊙</SUB> = 5.75, we find M<SUP>˙</SUP> ∝ Z<SUP>m</SUP> with m = 1.02 ± 0.30, in agreement with pioneering work in the field within the uncertainties. For lower luminosities, however, we obtain a significantly steeper scaling of m > 2. Conclusions. The monotonically decreasing m(L) behavior adds a complexity to the functional description of the mass-loss rate of hot massive stars. Although the trend is present in the predictions, it is much weaker than we found here. However, the luminosity range for which m is significantly larger than previously assumed (at log L/L<SUB>⊙</SUB> ≲ 5.4) is still poorly explored, and more studies are needed to thoroughly map the empirical behavior, in particular, at Galactic metallicity.
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The JCMT BISTRO Survey: The Magnetic Fields of the IC 348 Star-forming RegionWe present 850 μm polarization observations of the IC 348 star-forming region in the Perseus molecular cloud as part of the B-fields In STar-forming Region Observation survey. We study the magnetic properties of two cores (HH 211 MMS and IC 348 MMS) and a filamentary structure of IC 348. We find that the overall field tends to be more perpendicular than parallel to the filamentary structure of the region. The polarization fraction decreases with intensity, and we estimate the trend by power law and the mean of the Rice distribution fittings. The power indices for the cores are much smaller than 1, indicative of possible grain growth to micron size in the cores. We also measure the magnetic field strengths of the two cores and the filamentary area separately by applying the Davis–Chandrasekhar–Fermi method and its alternative version for compressed medium. The estimated mass-to-flux ratios are 0.45–2.20 and 0.63–2.76 for HH 211 MMS and IC 348 MMS, respectively, while the ratios for the filament are 0.33–1.50. This result may suggest that the transition from subcritical to supercritical conditions occurs at the core scale (∼0.05 pc) in the region. In addition, we study the energy balance of the cores and find that the relative strength of turbulence to the magnetic field tends to be stronger for IC 348 MMS than for HH 211 MMS. The result could potentially explain the different configurations inside the two cores: a single protostellar system in HH 211 MMS and multiple protostars in IC 348 MMS.
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A resolved, multiwavelength study of gas-rich dwarf galaxies in the Fornax cluster using MUSE, MeerKAT, and ALMAWe combine new and archival Multi-unit spectroscopic explorer (MUSE) observations with data from the MeerKAT Fornax Survey and the ALMA Fornax Cluster Survey to study the ionized, atomic, and molecular gas in six gas-rich dwarf galaxies in the Fornax cluster in detail. We compare the distributions and velocity fields of the three gas phases with each other, with MUSE white-light images, and with the stellar velocity fields. Additionally, we derive the resolved molecular Kennicutt-Schmidt relation for each object, and compare these with existing relations for field galaxies and for the Fornax and Virgo clusters. Finally, we explore global measurements such as gas deficiencies and star formation rates to paint as complete a picture of their evolutionary state as possible. We find that all six gas-rich dwarf galaxies have very disturbed interstellar medium, with all three gas phases being irregular both in terms of spatial distribution and velocity field. Most objects lie well below the Kennicutt-Schmidt relations from the literature. Furthermore, they are quite deficient in H I (with def<inline-formula><tex-math id=TM0001 notation=LaTeX>$_{{\rm{H}{\small I}}}$</tex-math></inline-formula> between <inline-formula><tex-math id=TM0002 notation=LaTeX>$\sim$</tex-math></inline-formula>1 and <inline-formula><tex-math id=TM0003 notation=LaTeX>$\sim$</tex-math></inline-formula>2 dex), and moderately deficient in H<inline-formula><tex-math id=TM0004 notation=LaTeX>$_2$</tex-math></inline-formula> (with def<inline-formula><tex-math id=TM0005 notation=LaTeX>$_{\mathrm{ H}_{2}}$</tex-math></inline-formula> between <inline-formula><tex-math id=TM0006 notation=LaTeX>$\sim$</tex-math></inline-formula>0 and <inline-formula><tex-math id=TM0007 notation=LaTeX>$\sim$</tex-math></inline-formula>1), suggesting that, while both cold gas phases are affected simultaneously, H I is removed in significant quantities before H<inline-formula><tex-math id=TM0008 notation=LaTeX>$_2$</tex-math></inline-formula>. We suggest that these dwarfs are on their first infall into the cluster, and are in the process of transitioning from star-forming to passive. A combination of tidal interactions, mergers/pre-processing, and ram pressure stripping is likely responsible for these transformations.
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Disruption of a massive molecular cloud by a supernova in the Galactic Centre: Initial results from the ACES projectThe Milky Way's Central Molecular Zone (CMZ) differs dramatically from our local solar neighbourhood, both in the extreme interstellar medium conditions it exhibits (e.g. high gas, stellar, and feedback density) and in the strong dynamics at play (e.g. due to shear and gas influx along the bar). Consequently, it is likely that there are large-scale physical structures within the CMZ that cannot form elsewhere in the Milky Way. In this paper, we present new results from the Atacama Large Millimeter/submillimeter Array (ALMA) large programme ACES (ALMA CMZ Exploration Survey) and conduct a multi-wavelength and kinematic analysis to determine the origin of the M0.8–0.2 ring, a molecular cloud with a distinct ring-like morphology. We estimate the projected inner and outer radii of the M0.8–0.2 ring to be 79″ and 154″, respectively (3.1 pc and 6.1 pc at an assumed Galactic Centre distance of 8.2 kpc) and calculate a mean gas density >10<SUP>4</SUP> cm<SUP>‑3</SUP>, a mass of ~10<SUP>6</SUP> M<SUB>⊙</SUB>, and an expansion speed of ~20 km s<SUP>‑1</SUP>, resulting in a high estimated kinetic energy (>10<SUP>51</SUP> erg) and momentum (>10<SUP>7</SUP> M<SUB>⊙</SUB> km s<SUP>‑1</SUP>). We discuss several possible causes for the existence and expansion of the structure, including stellar feedback and large-scale dynamics. We propose that the most likely cause of the M0.8–0.2 ring is a single high-energy hypernova explosion. To viably explain the observed morphology and kinematics, such an explosion would need to have taken place inside a dense, very massive molecular cloud, the remnants of which we now see as the M0.8–0.2 ring. In this case, the structure provides an extreme example of how supernovae can affect molecular clouds.
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JCMT 850 μm Continuum Observations of Density Structures in the G35 Molecular ComplexFilaments are believed to play a key role in high-mass star formation. We present a systematic study of the filaments and their hosting clumps in the G35 molecular complex using James Clerk Maxwell Telescope SCUBA-2 850 μm continuum data. We identified five clouds in the complex and 91 filaments within them, some of which form 10 hub–filament systems (HFSs), each with at least three hub-composing filaments. We also compiled a catalog of 350 dense clumps, 183 of which are associated with the filaments. We investigated the physical properties of the filaments and clumps, such as mass, density, and size, and their relation to star formation. We find that the global mass–length trend of the filaments is consistent with a turbulent origin, while the hub-composing filaments of high line masses (m <SUB>l</SUB> > 230 M <SUB>⊙</SUB> pc<SUP>‑1</SUP>) in HFSs deviate from this relation, possibly due to feedback from massive star formation. We also find that the most massive and densest clumps (R > 0.2 pc, M > 35 M <SUB>⊙</SUB>, Σ > 0.05 g cm<SUP>‑2</SUP>) are located in the filaments and in the hubs of HFSs, with the latter bearing a higher probability of the occurrence of high-mass star-forming signatures, highlighting the preferential sites of HFSs for high-mass star formation. We do not find significant variation in the clump mass surface density across different evolutionary environments of the clouds, which may reflect the balance between mass accretion and stellar feedback.
