Λ5007 Line Research Articles

A Merger-driven Scenario for Clumpy Galaxy Formation in the Epoch of Reionization: Physical Properties of Clumps in the FirstLight Simulation

Recent JWST observations with superb angular resolution have revealed the existence of clumpy galaxies at high redshift through the detection of rest-frame optical emission lines. We use the FirstLight simulation to study the properties of (sub)galactic clumps that are bright in the [O III] λ5007 line with flux greater than ∼10−18 erg s−1 cm−2, to be detected by JWST. For 62 simulated galaxies that have stellar masses of (0.5–6) × 1010 M ⊙ at z = 5, we find clumps in 1828 snapshots in the redshift range z = 9.5–5.5. The clumps are identified by the surface density of the star formation rate (SFR). About one-tenth of the snapshots show the existence of clumpy systems with two or more components. Most of the clumps are formed by mergers and can be characterized by their ages: central clumps dominated by stellar populations older than 50 Myr, and off-centered clumps dominated by younger stellar populations with specific SFRs of ∼50 Gyr−1. The latter type of young clumps is formed from gas debris in the tidal tails of major mergers with baryonic mass ratios of 1 ≤ q < 4. The merger-induced clumps are short-lived and merge within a dynamical time of several tens of million years. The number density of the clumpy systems is estimated to be ∼10−5 cMpc−3, which is large enough to be detected in recent JWST surveys.

VLT/MUSE Detection of Accretion/Ejection Associated with the Close Stellar Companion in the HT Lup System

The accretion/ejection processes in T Tauri stars are fundamental to their physical evolution, while also impacting the properties and evolution of the circumstellar material at a time when planet formation takes place. To date, the characterization of ongoing accretion processes in stellar pairs at 5–50 au scales has been challenging as high-angular resolution spectrographs are required to extract the spectral features of each component. We present the analysis of spectroscopic observations of the tight (160 mas, 25 au) T Tauri system HT Lup A/B, obtained with MUSE at the Very Large Telescope in 2021 March and July. We focus on constraining the accretion/ejection processes and variability of the secondary component HT Lup B by searching for accretion tracers by applying high-resolution spectral differential imaging techniques. We retrieve strong (signal-to-noise ratio > 5) Hα, Hβ, and [O i]λ6300 emission in both epochs. The Hα and Hβ line fluxes showcase high variability, with variations up to 200%–300% between epochs. The fluxes are consistent with accretion rates of 3× 10−9 M ⊙ yr−1 and 8 × 10−10 M ⊙ yr−1 for the first and second epochs, respectively. We attribute the increased accretion activity during the first night to a “burst-like” event, followed by a relaxation period more representative of the common accretion activity of the system. The [O i]λ6300 line profiles remain relatively similar between epochs and suggest ejection rates on the order of 10−9−10−10 M ⊙ yr−1, compatible with moderate disk wind emission. Our results also indicate that the accretion processes of HT Lup B are compatible with Classical T Tauri stars, unlike previous classifications.

Characterizing chemical abundance ratios in extremely metal-poor star-forming galaxies in DESI EDR

We present a search for galaxies in the local Universe with extremely low oxygen abundance, that is, more than 25 times lower than solar, which corresponds to 12 + log(O/H) &lt; 7.3. To determine the oxygen abundance, we apply the direct Te method for objects where the [O III]λ4363 line is detected. We identified 21 extremely metal-poor galaxies in the early data release of the Dark Energy Spectroscopic Instrument (DESI EDR), for some of which we also derived N/O, Ne/O, Ar/O, and S/O ratios. We find that many DESI galaxies with extremely low oxygen abundance exhibit a higher N/O ratio in comparison to the reference low-metallicity sample collected from the literature. We suggest that the elevation in N/O ratio may be explained by a contamination with metal-rich gas caused by gas inflow or a merger event. Moreover, contrary to some recent studies, we find that Ar/O and S/O ratios are enhanced as well, while the Ne/O ratio does not show such elevation. One of the galaxies, J0713+5608, has a remarkably low oxygen abundance of 6.978 ± 0.095 dex. This measurement aligns with the lowest known oxygen abundances in galaxies to date. Given the relatively high uncertainty, this galaxy may have the lowest oxygen abundance ever found. Additionally, J0713+5608 exhibited an enhanced N/O ratio compared to the typical N/O ratio observed in metal-poor galaxies within the local Universe.

Absence of nebular He ii λ4686 constrains the UV emission from the Ultraluminous X-ray pulsar NGC 1313 X–2

Abstract While much has been learned in recent decades about the X-ray emission of the extragalactic Ultraluminous X-ray sources (ULXs), their radiative output in the UV band remains poorly constrained. Understanding of the full ULX spectral energy distribution (SED) is imperative to constrain the accretion flow geometry powering them, as well as their radiative power. Here we present constraints on the UV emission of the pulsating ULX (PULX) NGC 1313 X–2 based on the absence of nebular He ii λ4686 emission in its immediate environment. To this end, we first perform multi-band spectroscopy of the ULX to derive three realistic extrapolations of the SED into the unaccessible UV, each predicting varying levels of UV luminosity. We then perform photo-ionization modelling of the bubble nebula and predict the He ii λ4686 fluxes that should have been observed based on each of the derived SEDs. We then compare these predictions with the derived upper limit on He ii λ4686 from MUSE data, which allows us to infer a UV luminosity LUV ≲ 1 × 1039 erg/s in the PULX NGC 1313 X–2. Comparing the UV luminosity inferred with other ULXs, our work suggests there may be an intrinsic difference between hard and soft ULXs, either related to different mass-transfer rates and/or the nature of the accretor. However, a statistical sample of ULXs with inferred UV luminosities is needed to fully determine the distinguishing features between hard and soft ULXs. Finally, we discuss ULXs ionising role in the context of the nebular He ii λ4686 line observed in star-forming, metal-poor galaxies.

JWST and ALMA Multiple-line Study in and around a Galaxy at z = 8.496: Optical to Far-Infrared Line Ratios and the Onset of an Outflow Promoting Ionizing Photon Escape

We present Atacama Large Millimeter/submillimeter Array (ALMA) deep spectroscopy for a lensed galaxy at z spec = 8.496 with log(Mstar/M⊙)∼7.8 whose optical nebular lines and stellar continuum are detected by JWST/NIRSpec and NIRCam Early Release Observations in the field of SMACS J0723.3–7327. Our ALMA spectrum shows [O iii] 88 μm and [C ii] 158 μm line detections at 4.0σ and 4.5σ, respectively. The redshift and position of the [O iii] line coincide with those of the JWST source, while the [C ii] line is blueshifted by 90 km s−1 with a spatial offset of 0.″5 (≈0.5 kpc in the source plane) from the centroid of the JWST source. The NIRCam F444W image, including [O iii] λ5007 and Hβ line emission, spatially extends beyond the stellar components by a factor of >8. This indicates that the z = 8.5 galaxy has already experienced strong outflows as traced by extended [O iii] λ5007 and offset [C ii] emission, which would promote ionizing photon escape and facilitate reionization. With careful slit-loss corrections and the removal of emission spatially outside the galaxy, we evaluate the [O iii] 88 μm/λ5007 line ratio, and derive the electron density n e by photoionization modeling to be 220−130+230 cm−3, which is comparable with those of z ∼ 2–3 galaxies. We estimate an [O iii] 88 μm/[C ii] 158 μm line ratio in the galaxy of >4, as high as those of known z ∼ 6–9 galaxies. This high [O iii] 88 μm/[C ii] 158 μm line ratio is generally explained by the high n e as well as the low metallicity ( Zgas/Z⊙=0.04−0.02+0.02 ), high ionization parameter ( logU>−2.27 ), and low carbon-to-oxygen abundance ratio (log(C/O) = [−0.52: −0.24]) obtained from the JWST/NIRSpec data; further [C ii] follow-up observations will constrain the covering fraction of photodissociation regions.

Host Galaxy and Nuclear Properties of IR-selected AGNs with and without Outflow Signatures

Active galactic nucleus (AGN) driven outflows can have a significant impact on the evolution of the host galaxy. In this work, we compare the properties of galaxies that host AGNs with and without outflows. Our sample consists of 103 AGNs identified by mid-IR color–color selection and confirmed with optical spectroscopy at a redshift range of 0.3 ≲ z ≲ 0.9. We fit the [O iii] λ5007 line using spectra from the zCOSMOS survey to identify and study the occurrence of outflows. We find that ionized outflows are present in ∼25% of our sample, with the largest incidence at the highest [O iii] and X-ray luminosity bins. The fastest outflows are found in the more extended and massive galaxies. We do not observe a difference in the star formation rate of AGNs with outflows compared to AGNs without outflows. From visual inspection and nonparametric morphological studies, we obtain that outflows are preferentially observed in galaxies with disk-type and elliptical morphologies.

A Large Sample of Extremely Metal-poor Galaxies at z < 1 Identified from the DESI Early Data

Extremely metal-poor galaxies (XMPGs) at relatively low redshift are excellent laboratories for studying galaxy formation and evolution in the early universe. Much effort has been spent on identifying them from large-scale spectroscopic surveys or spectroscopic follow-up observations. Previous work has identified a few hundred XMPGs. In this work, we obtain a large sample of 223 XMPGs at z < 1 from the early data of the Dark Energy Spectroscopic Instrument (DESI). The oxygen abundance is determined using the direct T e method based on the detection of the [O iii]λ4363 line. The sample includes 95 confirmed XMPGs based on the oxygen abundance uncertainty; the remaining 128 galaxies are regarded as XMPG candidates. These XMPGs are only 0.01% of the total DESI observed galaxies. Their coordinates and other properties are provided in the paper. The most XMPGs have an oxygen abundance of ∼1/34 Z ⊙, a stellar mass of about 1.5 × 107 M ⊙, and a star formation rate of 0.22 M ⊙ yr−1. The two most XMPGs present distinct morphologies suggesting different formation mechanisms. The local environmental investigation shows that XMPGs preferentially reside in relatively low-density regions. Many of them fall below the stellar mass–metallicity relations (MZRs) of normal star-forming galaxies. From a comparison of the MZR with theoretical simulations, it appears that XMPGs are good analogs to high-redshift star-forming galaxies. The nature of these XMPG populations will be further investigated in detail with larger and more complete samples from the ongoing DESI survey.

Testing He ii Emission from Wolf–Rayet Stars as a Dust Attenuation Measure in Eight Nearby Star-forming Galaxies

The ability to determine galaxy properties such as masses, ages, and star formation rates robustly is critically limited by the ability to measure dust attenuation accurately. Dust reddening is often characterized by comparing observations to models of either nebular recombination lines or the UV continuum. Here, we use a new technique to measure dust reddening by exploiting the He ii λ1640 and λ4686 emission lines originating from the stellar winds of Wolf–Rayet stars. The intrinsic line ratio is determined by atomic physics, enabling an estimate of the stellar reddening similar to how the Balmer lines probe gas-emission reddening. The He ii line ratio is measured from UV and optical spectroscopy using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope for eight nearby galaxies hosting young massive star clusters. We compare our results to dust reddening values estimated from UV spectral slopes and from Balmer line ratios and find tentative evidence for systematic differences. The reddening derived from the He ii lines tends to be higher, whereas that from the UV continuum tends to be lower. A larger sample size is needed to confirm this trend. If confirmed, this may indicate an age sequence probing different stages of dust clearing. Broad He ii lines have also been detected in galaxies more distant than in our sample, providing the opportunity to estimate the dust reddening of the youngest stellar populations out to distances of ∼100 Mpc.

A population of Optically Quiescent Quasars from WISE and SDSS

ABSTRACT The growth of active galactic nuclei (AGNs) occurs under some form of obscuration in a large fraction of the population. The difficulty in constraining this population leads to high uncertainties in cosmic X-ray background and galaxy evolution models. Using an SDSS–WISE cross-match, we target infrared luminous AGN (W1 − W2 &amp;gt; 0.8, and monochromatic rest-frame luminosity above λLλ(12 μm) ≈ 3 × 1044 erg s−1), but with passive galaxy-like optical spectra (Optically Quiescent Quasars; OQQs). We find 47 objects that show no significant [O iii]λ5007 emission, a typically strong AGN optical emission line. As a comparison sample, we examine SDSS-selected Type 2 quasars (QSO2s), which show a significant [O iii]λ5007 line by definition. We find a 1:16 ratio of OQQs compared to QSO2s, suggesting that the OQQ duty cycle is likely much shorter than that of QSO2s (though selection biases are not fully quantified). We consider observed properties in comparison with other galaxy types, and examine them for consistency with theories on their intrinsic nature: chiefly (a) a high covering factor for surrounding obscuring matter, preventing the detection of high-ionisation emission lines – ‘cocooned AGN’; or (b) ionized gas being absent on the kpc scales of the Narrow Line Region (NLR), perhaps due to a ‘switching on’ or ‘young’ AGN. OQQs do not obviously fit the standard paradigm for merger-driven AGN and host galaxy evolution, implying we may be missing part of the flow of AGN evolution.

Dwarfs in nearby voids: results of SALT spectroscopy

ABSTRACT In the framework of the ongoing project, aimed at the systematical studying galaxies in nearby voids, we conducted spectroscopy with the Southern African Large Telescope (SALT) of 62 objects from the Nearby Void Galaxy (NVG) sample. They include 8 remaining objects of the 60 pre-selected candidates to eXtremely Metal-Poor (XMP) dwarfs, two known void XMP dwarfs and 52 void dwarfs residing within the Local Volume. For 47 galaxies residing in the nearby voids, we obtained spectra of the diverse quality. For 42 of them, we detected the Hydrogen and Oxygen lines that allowed us to get estimates of O/H in the observed H ii regions. For 12 of the 42 objects, we detected the faint line [O iii]λ4363, that allowed us to directly derive the electron temperature Te and obtain their gas O/H by the direct method. 14 objects with the undetected [O iii]λ4363 line fall to the lowest metallicities range (12+log(O/H) ≲ 7.5 dex). For them, we use a carefully checked new empirical ‘Strong line’ method of Izotov et al. For 14 other objects with only strong lines detected and with 12+log(O/H) of ∼7.5–8.0 dex, we used the modified version of ‘semi-empirical’ method of Izotov and Thuan. It accounts for effect of the excitation parameter O32 on Te. 16 new galaxies are found with parameter 12+log(O/H) ≲ 7.39 dex. Of them, four have 12+log(O/H) = 7.07–7.20 dex. Of the 60 observed NVG objects, 15 have mistaken radial velocities in HyperLEDA. They do not reside in the nearby voids.

A JWST/NIRSpec First Census of Broad-line AGNs at z = 4–7: Detection of 10 Faint AGNs with M BH ∼ 106–108 M ⊙ and Their Host Galaxy Properties

We present the first statistical sample of faint type 1 AGNs at z > 4 identified by JWST/NIRSpec deep spectroscopy. Among the 185 galaxies at z spec = 3.8–8.9 confirmed with NIRSpec, our systematic search for broad-line emission reveals 10 type 1 AGNs at z = 4.015–6.936 whose broad component is only seen in the permitted Hα line and not in the forbidden [O iii]λ5007 line that is detected with greater significance than Hα. The broad Hα line widths of FWHM ≃ 1000–6000 km s−1 suggest that the AGNs have low-mass black holes with M BH ∼ 106–108 M ⊙, remarkably lower than those of low-luminosity quasars previously identified at z > 4 with ground-based telescopes. JWST and Hubble Space Telescope high-resolution images reveal that the majority of them show extended morphologies indicating significant contribution to the total lights from their host galaxies, except for three compact objects two of which show red spectral energy distributions, probably in a transition phase from faint AGNs to low luminosity quasars. Careful AGN-host decomposition analyses show that their host’s stellar masses are systematically lower than the local relation between the black hole mass and the stellar mass, implying a fast black hole growth consistent with predictions from theoretical simulations. A high fraction of the broad-line AGNs (∼5%), higher than z ∼ 0, indicates that the number density of such faint AGNs is higher than an extrapolation of the quasar luminosity function, implying a large population of AGNs in the early universe. Such faint AGNs contribute to cosmic reionization, while the total contribution is not large, up to ∼50% at z ∼ 6, because of their faint nature.

Faint [C i](1–0) emission in z ∼ 3.5 radio galaxies

ABSTRACT We present Atacama Large Millimeter/sub-millimeter Array neutral carbon, [${\rm C\, \small {\rm I}}$](1–0), line observations that probe molecular hydrogen gas (H2) within seven radio galaxies at z = 2.9−4.5 surrounded by extended (≳100 kpc) Ly α nebulae. We extract [${\rm C\, \small {\rm I}}$](1–0) emission from the radio-active galactic nuclei (AGNs) host galaxies whose positions are set by near-infrared detections and radio detections of the cores. Additionally, we place constraints on the galaxies’ systemic redshifts via ${\rm He\, \small {\rm II}}$ λ1640 lines seen with the Multi-Unit Spectroscopic Explorer. We detect faint [${\rm C\, \small {\rm I}}$] emission in four out of seven sources. In two of these galaxies, we discover narrow-line emission of full width at half-maximum ≲100 km s−1 that may trace emission from bright kpc-scale gas clouds within the interstellar medium (ISM). In the other two [${\rm C\, \small {\rm I}}$]-detected galaxies, line dispersions range from ∼100−600 km s−1 and may be tracing the rotational component of the cold gas. Overall, the [${\rm C\, \small {\rm I}}$] line luminosities correspond to H2 masses of $M_{\rm H_2,[{\rm C\, \small {\rm I}}]} \simeq (0.5{\!-\!}3) \times 10^{10}$ M⊙ for the detections and $M_{\rm H_2,[{\rm C\, \small {\rm I}}]}\lt 0.65\times 10^{10}$ M⊙ for the [${\rm C\, \small {\rm I}}$] non-detections in three out of seven galaxies within the sample. The molecular gas masses in our sample are relatively low in comparison to previously reported measures for similar galaxies that are $M_{\rm H_2,[{\rm C\, \small {\rm I}}]} \simeq (3{\!-\!}4) \times 10^{10}$ M⊙. Our results imply that the observed faintness in carbon emission is representative of a decline in molecular gas supply from previous star formation epochs and/or a displacement of molecular gas from the ISM due to jet-powered outflows.

First Sample of Hα+[O iii]λ5007 Line Emitters at z > 6 Through JWST/NIRCam Slitless Spectroscopy: Physical Properties and Line-luminosity Functions

We present a sample of four emission-line galaxies at z = 6.11–6.35 that were serendipitously discovered using the commissioning data for the James Webb Space Telescope (JWST)/NIRCam wide-field slitless spectroscopy mode. One of them (at z = 6.11) has been reported previously, while the others are new discoveries. These sources are selected by the secure detections of both [O iii] λ5007 and Hα lines with other fainter lines, which were tentatively detected in some cases (e.g., [O ii] λ3727, [O iii] λ4959). In the [O iii]/Hβ–[N ii]/Hα Baldwin–Phillips–Terlevich diagram, these galaxies occupy the same parameter space as that of z ∼ 2 star-forming galaxies, indicating that they have been enriched rapidly to subsolar metallicities (∼0.4 Z ⊙), similar to galaxies with comparable stellar masses at much lower redshifts. The detection of strong Hα lines suggests a higher ionizing photon production efficiency within galaxies in the early universe. We find brightening of the [O iii] λ5007 line-luminosity function (LF) from z = 3 to 6, and weak or no redshift evolution of the Hα line LF from z = 2 to 6. Both LFs are underpredicted at z ∼ 6 by a factor of ∼10 in certain cosmological simulations. This further indicates a global Lyα photon escape fraction of 7%–10% at z ∼ 6, which is slightly lower than previous estimates through the comparison of the UV-derived star formation rate density and Lyα luminosity density. Our sample recovers % of z = 6.0–6.6 galaxies in the survey volume with stellar masses greater than 5 × 108 M ⊙, suggesting the ubiquity of strong Hα and [O iii] line emitters in the Epoch of Reionization, which will be further uncovered in the era of JWST.

The [O iii] Profiles of Far-infrared Active and Inactive Optically Selected Green Valley Galaxies

We present a study of the [O iii] λ5007 line profile in a subsample of eight active galactic nuclei (AGNs) and six non-AGNs in the optically selected green valley at z < 0.5 using long-slit spectroscopic observations obtained with the 11 m Southern African Large Telescope. Gaussian decomposition of the line profile was performed to study its different components. We observe that the AGN profiles are more complex than the non-AGN ones. In particular, in most AGNs (5/8) we detect a blue wing of the line. We derive the FWHM velocities of the wing and systemic component, and find that the AGNs show higher FWHM velocities than the non-AGNs in their core component. We also find that the AGNs show blue wings with a median velocity width of approximately 600 km s−1, and a velocity offset from the core component in the range −90 to −350 km s−1, in contrast to the non-AGN galaxies, where we do not detect blue wings in any of their [O iii] λ5007 line profiles. Using the spatial information in our spectra, we show that at least three of the outflow candidate galaxies have centrally driven gas outflows extending across the whole galaxy. Moreover, these are also the galaxies which are located on the main sequence of star formation, raising the possibility that the AGNs in our sample are influencing the star formation of their host galaxies (such as positive feedback). This is in agreement with our previous work where we studied the star formation, morphology, and stellar population properties of a sample of green valley AGNs and non-AGN galaxies.

A radio-jet-driven outflow in the Seyfert 2 galaxy NGC 2110?

We present a spatially resolved study of the ionized gas in the central 2 kpc of the Seyfert 2 galaxy NGC 2110 and investigate the role of its moderate-luminosity radio jet (kinetic radio power of Pjet = 2.3 × 1043 erg s−1). We used new optical integral-field observations taken with the MEGARA spectrograph at the Gran Telescopio Canarias, which cover the 4300 − 5200 Å and 6100 − 7300 Å ranges with a spectral resolution of R ≃ 5000 − 5900. We fitted the emission lines with a maximum of two Gaussian components, except at the position of the active galactic nucleus (AGN), where we used three. Aided by existing stellar kinematics, we used the observed velocity and velocity dispersion (σ) of the emission lines to classify the different kinematic components. The disk component is characterized by lines with σ ≃ 60 − 200 km s−1. The outflow component has typical values of σ ≃ 700 km s−1 and is confined to the central 2.5″ ≃ 400 pc, which is coincident with the linear part of the radio jet detected in NGC 2110. At the AGN position, the [O III]λ5007 line shows high velocity components that reach at least 1000 km s−1. This and the high velocity dispersions indicate the presence of outflowing gas outside the galaxy plane. Spatially resolved diagnostic diagrams reveal mostly low ionization (nuclear) emitting region-like excitation in the outflow and some regions in the disk, which could be due to the presence of shocks. However, there is also Seyfert-like excitation beyond the bending of the radio jet, which probably traces the edge of the ionization cone that intercepts with the disk of the galaxy. NGC 2110 follows the observational trends between the outflow properties and the jet radio power found for a few nearby Seyfert galaxies. All these pieces of information suggest that part of the observed ionized outflow in NGC 2110 might be driven by the radio jet. However, the radio jet was bent at radial distances of ∼200 pc (in projection) from the AGN, and beyond there, most of the gas in the galaxy disk is rotating.

The Orbital and Physical Properties of Five Southern Be+sdO Binary Systems

Close binary interactions may play a critical role in the formation of the rapidly rotating Be stars. Mass transfer can result in a mass gainer star spun up by the accretion of mass and angular momentum, while the mass donor is stripped of its envelope to form a hot and faint helium star. Far-UV spectroscopy has led to the detection of about 20 such binary Be+sdO systems. Here we report on a 3 yr program of high-quality spectroscopy designed to determine the orbital periods and physical properties of five Be binary systems. These binaries are long orbital period systems with P = 95–237 days and small semiamplitude K 1 < 11 km s−1. We combined the Be star velocities with prior sdO measurements to obtain mass ratios. A Doppler tomography algorithm shows the presence of the He ii λ4686 line in the faint spectrum of the hot companion in four of the targets. We discuss the observed line variability and show evidence of phase-locked variations in the emission profiles of HD 157832, suggesting a possible disk spiral density wave due to the presence of the companion star. The stripped companions in HD 113120 and HD 137387 may have a mass larger than 1.4 M ⊙, indicating that they could be progenitors of Type Ib and Ic supernovae.

A High-resolution Optical Survey of Upper Sco: Evidence for Coevolution of Accretion and Disk Winds

Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. Here, we analyze high-resolution (Δv ∼ 7 km s−1) optical spectra from a sample of 115 T Tauri stars in the ∼5–10 Myr Upper Sco association and focus on the [O i] λ6300 and Hα lines to trace disk winds and accretion, respectively. Our sample covers a large range of spectral types and we divide it into warm (G0-M3) and cool (later than M3) to facilitate comparison with younger regions. We detect the [O i] λ6300 line in 45 out of 87 Upper Sco sources with protoplanetary disks and 32 out of 45 are accreting based on Hα profiles and equivalent widths. All [O i] λ6300 Upper Sco profiles have low-velocity (centroid < −30 km s−1; low-velocity component (LVC)) emission and most (36/45) can be fit by a single Gaussian (SC). The single-component (SC) distribution of centroid velocities and FWHMs is consistent with MHD disk winds. We also find that the Upper Sco sample follows the same accretion luminosity−LVC [O i] λ6300 relation and the same anticorrelation between SC FWHM and Wide-field Infrared Survey Explorer W3-W4 spectral indices as the younger samples. These results indicate that accretion and disk winds coevolve and that, as inner disks clear out, wind emission arises further away from the star. Finally, our large spectral range coverage reveals that cool stars have larger FWHMs normalized by stellar mass than warm stars indicating that [O i] λ6300 emission arises closer in toward lower-mass/lower luminosity stars.

Unveiling hidden active nuclei in MaNGA star-forming galaxies with He ii λ4686 line emission

ABSTRACT Nebular He ii λ4686 Å line emission is useful to unveil active galactic nuclei (AGN) residing in actively star-forming (SF) galaxies, typically missed by the standard BPT classification. Here, we adopt the He ii diagnostic to identify hidden AGN in the Local Universe using for the first time spatially resolved data from the Data Release 15 of the Mapping Nearby Galaxies at APO survey (MaNGA DR15). By combining results from He ii and BPT diagnostics, we overall select 459 AGN host candidates (∼10 per cent in MaNGA DR15), out of which 27 are identified as AGN by the He ii diagram only. The He ii-only AGN population is hosted by massive (M* ≳ 1010 M⊙) SF Main Sequence galaxies and on average less luminous than the BPT-selected AGN. Given the He ii line faintness, we revisit our census accounting for incompleteness effects due to the He ii sensitivity limit of MaNGA. We thus obtain an overall increased fraction (11 per cent) of AGN in MaNGA compared to the BPT-only census (9 per cent), which further increases to 14 per cent for galaxies more massive than 1010 M⊙; interestingly, on the SF Main Sequence the increase is by about a factor of 2. A substantial number of AGN in SF galaxies points to significant, coeval star formation and black hole accretion, consistently with results from hydrodynamical simulations and with important implications on quenching scenarios. In view of exploring unprecedented high redshifts with JWST and new ground-based facilities, revisiting the standard BPT classification through novel emission-line diagnostics is fundamental to discover AGN in highly SF environments.

Solar Flare Ribbon Fronts. I. Constraining Flare Energy Deposition with IRIS Spectroscopy

Spectral lines formed at lower atmospheric layers show peculiar profiles at the “leading edge” of ribbons during solar flares. In particular, increased absorption of the BBSO/GST He i λ10830 line, as well as broad and centrally reversed profiles in the spectra of the Mg ii and C ii lines observed by the IRIS satellite, has been reported. In this work, we aim to understand the physical origin of such peculiar IRIS profiles, which seem to be common of many, if not all, flares. To achieve this, we quantify the spectral properties of the IRIS Mg ii profiles at the ribbon leading edge during four large flares and perform a detailed comparison with a grid of radiative hydrodynamic models using the RADYN+FP code. We also studied their transition region (TR) counterparts, finding that these ribbon front locations are regions where TR emission and chromospheric evaporation are considerably weaker compared to other parts of the ribbons. Based on our comparison between the IRIS observations and modeling, our interpretation is that there are different heating regimes at play in the leading edge and the main bright part of the ribbons. More specifically, we suggest that bombardment of the chromosphere by more gradual and modest nonthermal electron energy fluxes can qualitatively explain the IRIS observations at the ribbon leading front, while stronger and more impulsive energy fluxes are required to drive chromospheric evaporation and more intense TR emission in the bright ribbon. Our results provide a possible physical origin for the peculiar behavior of the IRIS chromospheric lines in the ribbon leading edge and new constraints for the flare models.

A Census of the Low Accretors. II. Accretion Properties

Much is known about the processes driving accretion from protoplanetary disks onto low-mass pre-main-sequence stars (T Tauri stars). Nevertheless, it is unclear how accretion stops. To determine the accretion properties and their relation to stellar properties and gain insight into the last stages of accretion, we present a detailed analysis of 24 low and possible accretors, previously identified using the He i λ10830 line. We model moderate-resolution Hα profiles of these stars using magnetospheric accretion flow models that account for the chromospheric contribution at the line center. Based on parameters derived from the fits of 20 stars that can be reproduced with the models, we find a power-law relation between the disk truncation radius and the mass accretion rate consistent with predictions from theory and simulations. Comparing the corotation and truncation radii, we find that most of our targets are accreting in the unstable regime and rule out the propeller as the main process stopping accretion. For the truncation radius to be the same as the magnetic radius, the dipole magnetic field and/or the efficiency parameter ξ need to be smaller than previously determined, suggesting that higher-order fields dominate in low accretion rates. Lastly, we determine that the lowest accretion rates that can be detected by Hα line modeling are (1–3) × 10−11 M ☉ yr−1 for M3 stars and (3–5) × 10−11 M ☉ yr−1 for K5 stars. These limits are lower than the observed accretion rates in our sample, suggesting that we have reached a physical lower limit. This limit, , is consistent with EUV-dominated photoevaporation.