Emission Line Properties Research Articles

Nebular emission from composite star-forming galaxies – I. A novel modelling approach

Abstract We introduce a novel approach to modelling the nebular emission from star-forming galaxies by combining the contributions from many H ii regions incorporating loose trends in physical properties, random dust attenuation, a predefined Hα luminosity function and a diffuse ionized-gas component. Using a machine-learning-based regression artificial neural network trained on a grid of models generated by the photoionization code CLOUDY, we efficiently predict emission-line properties of individual H ii regions over a wide range of physical conditions. We generate 250,000 synthetic star-forming galaxies composed of up to 3000 H ii regions and explore how variations in parameters affect their integrated emission-line properties. Our results highlight systematic biases in oxygen-abundance estimates derived using traditional methods, emphasizing the importance of accounting for the composite nature of star-forming galaxies when interpreting integrated nebular emission. Future work will leverage this approach to explore in detail its impact on parameter estimates of star-forming galaxies.

A candidate of high-z central tidal disruption event in quasar SDSS J000118.70+003314.0

Abstract We report a high-redshift (z = 1.404) tidal disruption event (TDE) candidate in SDSS J000118.70+003314.0 (SDSS J0001),which is a quasar with apparent broad Mg ii emission line. The long-term variability in its nine-year photometric ugriz-band light curves, obtained from the SDSS Stripe82 and the PHOTOOBJALL databases, can be described by the conventional TDE model. Our results suggest that the TDE is a main-sequence star with mass of $1.905_{-0.009}^{+0.023}{\rm M_\odot }$ tidally disrupted by a black hole (BH) with mass $6.5_{-2.6}^{+3.5}\times 10^7{\rm M_\odot }$. The BH mass is about 7.5 times smaller than the virial BH mass derived from the broad Mg ii emission line, which can be explained by non-virial dynamic properties of broad emission lines from TDEs debris. Furthermore, we examine the probability that the event results from intrinsic variability of quasars, which is about 0.009%, through applications of the DRW/CAR process. Alternative explanations for the event are also discussed, such as the scenarios of dust obscurations, microlensing and accretion. Our results provide clues to support that TDEs could be detectable in broad line quasars as well as in quiescent galaxies, and to indicate the variability of some active galactic nuclei may be partly attributed to central TDEs.

Spatially resolved emission lines in galaxies at 4 ≤ z < 10 from the JADES survey: Evidence for enhanced central star formation

We present the first statistical investigation of spatially resolved emission-line properties in a sample of 63 low-mass galaxies at 4 ≤ z < 10 using James Webb Space Telescope (JWST)/NIRSpec Micro Shutter Assembly (MSA) data from the JWST Advanced Deep Extragalactic (JADES) survey, focusing on deep, spatially resolved spectroscopy in the GOODS-S extragalactic field. By performing a stacking of the 2D spectra of the galaxies in our sample, we find an increasing or flat radial trend with increasing radius for [O III]λ5007/Hβ and a decreasing trend for the blended spectral complex (Hη + [Ne III]λ3869 + He Iλ3889 + Hζ)/[O II]λ3727 (3−4σ significance). These results are still valid when stacking the sample in two redshift bins (i.e. 4 ≤ z < 5.5 and 5.5 ≤ z < 10). The comparison with star-formation photoionisation models suggests that the ionisation parameter increases by ∼0.5 dex with redshift. Under the hypothesis that radial variations in (Hη + [Ne III]λ3869 + He Iλ3889 + Hζ)/[O II]λ3727 are dominated by trends in [Ne III]λ3869/[O II]λ3727, we find a tentative metallicity gradient that increases with radius (i.e. ‘inverted’) in both redshift bins. Moreover, our analysis reveals strong negative gradients for the equivalent width of Hβ (7σ significance). This trend persists even after removing known active galactic nucleus candidates, and is therefore consistent with a radial gradient primarily in stellar age and secondarily in metallicity. Taken together, our results suggest that the sample is dominated by active central star formation, with possibly inverted metallicity gradients sustained by recent episodes of accretion of pristine gas or strong radial flows. Deeper observations and larger samples are needed to confirm these preliminary results and to validate our interpretation.

Discovery of Six Low-z, High-luminosity, and High-mass Quasars

This study presents the discovery of six low-redshift quasars, identified through spectral observations conducted with the RTT-150 telescope. These quasars, with redshifts ranging from 0.3 to 0.6, were selected incorporating their placement in the color–color diagrams and detection by ROSAT 2RXS, focusing on those resembling the spectral energy distribution of a quasar. Our analysis includes detailed modeling of their continuum and emission line properties, which allowed us to estimate their bolometric luminosities, central black hole masses, and Eddington ratios. The findings reveal that these quasars exhibit exceptionally high luminosities and high masses for their redshift values, making them rare examples in the low-redshift quasar population. The results contribute to our understanding of quasar characteristics and their role in probing the structure and evolution of the nearby universe. This research underscores the importance of continued exploration of low-redshift quasars to enhance our knowledge of cosmic evolution and the dynamics of supermassive black holes in the early universe.

JWST/NIRSpec Observations of Lyman α Emission in Star-forming Galaxies at 6.5 ≲ z ≲ 13

We present an analysis of JWST Lyα spectroscopy of z ≳ 6.5 galaxies, using observations in the public archive covering galaxies in four independent fields: Great Observatories Origins Deep Survey (GOODS)-N, GOODS-S, A2744, and the Extended Groth Strip (EGS). We measure the Lyα emission line properties for a sample of 210 z ≃ 6.5–13 galaxies, with redshifts confirmed independently of Lyα in all cases. We present three new detections of Lyα emission in JWST spectra, including a large equivalent width (EW; =143 Å) Lyα emitter (LAE) with strong C iv emission (EW = 21 Å) at z = 7.1 in GOODS-N. We measure the redshift-dependent Lyα EW distribution across our sample. We find that strong Lyα emission (EW > 25 Å) becomes increasingly rare at earlier epochs, suggesting that the transmission of Lyα photons decreases by 4× between z ≃ 5 and z ≃ 9. We describe potential implications for the intergalactic medium neutral fraction. There is significant field-to-field variance in the LAE fraction. In contrast to the three other fields, the EGS shows no evidence for reduced transmission of Lyα photons at z ≃ 7–8, suggesting a significantly ionized sight line may be present in the field. We use available NIRCam grism observations from the First Reionization Epoch Spectroscopically Complete Observations survey to characterize overdensities on large scales around known LAEs in the GOODS fields. The strongest overdensities appear linked with extremely strong Lyα detections (EW > 50 Å) in most cases. Future Lyα spectroscopy with JWST has the potential to constrain the size of ionized regions around early galaxy overdensities, providing a new probe of the reionization process.

Stacking and Analyzing MOSDEF Galaxies by Spectral Types: Implications for Dust Geometry and Galaxy Evolution

We examine star formation and dust properties for a sample of 660 galaxies at 1.37 ≤ z ≤ 2.61 in the MOSDEF survey by dividing them into groups with similarly shaped spectral energy distributions (SEDs). For each group, we combine the galaxy photometry into a finely sampled composite SED, and stack their spectra. This method enables the study of more complete galaxy samples, including galaxies with very faint emission lines. We fit these composite SEDs with Prospector to measure the stellar attenuation and SED-based star formation rates (SFRs). We also derive emission-line properties from the spectral stacks, including Balmer decrements, dust-corrected SFRs, and metallicities. We find that stellar attenuation correlates most strongly with mass, while nebular attenuation correlates strongly with both mass and SFR. Furthermore, the excess of nebular compared to stellar attenuation correlates most strongly with SFR. The highest SFR group has 2 mag of excess nebular attenuation. Our results are consistent with a model in which star-forming regions become more dusty as galaxy mass increases. To explain the increasing excess nebular attenuation, we require a progressively larger fraction of star formation to occur in highly obscured regions with increasing SFR. This highly obscured star formation could occur in dusty clumps or central starbursts. Additionally, as each galaxy group represents a different evolutionary stage, we study their locations on the UVJ and SFR-mass diagrams. As mass increases, metallicity and dust attenuation increase, while sSFR decreases. However, the most massive group moves towards the quiescent region of the UVJ diagram, while showing less obscuration, potentially indicating removal of dust.

Polycyclic Aromatic Hydrocarbon Emission in the Central Regions of Three Seyferts and the Implication for Underlying Feedback Mechanisms

We analyze JWST Mid-Infrared Instrument/Medium Resolution Spectrograph integral field unit observations of three Seyferts from the Galactic Activity, Torus, and Outflow Survey (GATOS) and showcase the intriguing polycyclic aromatic hydrocarbon (PAH) and emission-line characteristics in regions of ∼500 pc scales over or around their active galactic nuclei (AGN). Combing the measurements and model predictions, we find that the central regions containing a high fraction of neutral PAHs with small sizes, e.g., those in ESO137-G034, are in highly heated environments, due to collisional shock heating, with hard and moderately intense radiation fields. Such environments are proposed to result in inhibited growth or preferential erosion of PAHs, decreasing their average size and overall abundance. We additionally find that the central regions containing a high fraction of ionized PAHs with large sizes, e.g., those in MCG-05-23-016, are likely experiencing severe photoionization because of the radiative effects from the radiative shock precursor besides the AGN. The severe photoionization can contribute to the ionization and further destruction of PAHs. Overall, different Seyferts, even different regions in the same galaxy, e.g., those in NGC 3081, can contain PAH populations of different properties. Specifically, Seyferts that exhibit similar PAH characteristics to ESO137-G034 and MCG-05-23-016 also tend to have similar emission-line properties to them, suggesting that the explanations for PAH characteristics of ESO137-G034 and MCG-05-23-016 may also apply generally. These results have promising application in the era of JWST, especially in diagnosing different (i.e., radiative and kinetic) AGN feedback modes.

Short-term variability of the transitional pulsar candidate CXOU J110926.4−650224 from X-rays to infrared

CXOU J110926.4−650224 is a candidate transitional millisecond pulsar (tMSP) with X-ray and radio emission properties reminiscent of those observed in confirmed tMSPs in their X-ray ‘subluminous’ disc state. We present the results of observing campaigns that, for the first time, characterise the optical and near-infrared variability of this source and establish a connection with the mode-switching phenomenon observed in X-rays. The optical emission exhibited flickering activity, frequent dipping episodes where it appeared redder, and a multi-peaked flare where it was bluer. The variability pattern was strongly correlated with that of the X-ray emission. Each dip matched an X-ray low-mode episode, indicating that a significant portion of the optical emission originates from nearly the same region as the X-ray emission. The near-infrared emission also displayed remarkable variability, including a dip of 20 min in length during which it nearly vanished. Time-resolved optical spectroscopic observations reveal significant changes in the properties of emission lines from the disc and help infer the spectral type of the companion star to be between K0 and K5. We compare the properties of CXOU J110926.4−650224 with those of other tMSPs in the X-ray subluminous disc state and discuss our findings within the context of a recently proposed scenario that explains the phenomenology exhibited by the prototypical tMSP PSR J1023+0038.

Spectroscopic Observations of the GALEX Nearby Young Star Survey Sample. I. Nearby Moving Group Candidates

The GALEX Nearby Young Star Search (GALNYSS) yielded the identification of more than 2000 late-type stars that, based on their ultraviolet and infrared colors and pre-Gaia proper motions, are potentially of age<200 Myr and lie within ~120 pc of Earth. We present the results of a campaign of medium- and high-resolution optical spectroscopy of 471 GALNYSS stars aimed at confirming their youth and their potential membership in nearby young stellar moving groups. We present radial velocity (RV), Li absorption, and H-alpha emission measurements for these spectroscopically observed GALNYSS stars, and assess their Li absorption and optical emission-line properties and infrared excesses. Our RV measurements are combined with literature and Gaia DR3 RV measurements and Gaia DR3 astrometry and photometry to obtain the spatiokinematics and color-magnitude positions of GALNYSS stars. We use these results to assess membership in the TW Hya, Tuc-Hor, Carina, Columba, and Argus Associations and the β Pic and AB Dor moving groups. We have identified 132 stars as candidate members of these seven groups; roughly half of these candidates are newly identified on the basis of data presented here. At least one-third of the 132 candidates are spectroscopic and/or photometric binaries and/or have comoving (visual) binary companions in Gaia DR3. The contingent of young, low-mass stars in the solar vicinity we identify here should provide excellent subjects for future direct imaging exoplanet surveys and studies of the early evolution of low-mass stars and their planetary progeny.

High-temporal-resolution optical spectroscopic observations of the transitional millisecond pulsar PSR J1023+0038

Transitional millisecond pulsars (tMSPs) represent a dynamic category of celestial sources that establish a crucial connection between low-mass X-ray binaries and millisecond radio pulsars. These systems exhibit transitions from rotation-powered states to accretion-powered ones and vice versa, highlighting the tight evolutionary link expected by the so-called recycling scenario. In their active phase, these sources manifest two distinct emission modes named high and low, occasionally punctuated by sporadic flares. Here, we present high-time-resolution spectroscopic observations of the binary tMSP J1023+0038, in the sub-luminous disc state. This is the first short-timescale (sim 1 min) optical spectroscopic campaign ever conducted on a tMSP. The campaign was carried out over the night of June 10, 2021 using the Gran Telescopio Canarias. The optical continuum shows erratic variability, without clear evidence of high and low modes or of orbital modulation. Besides, the analysis of these high-temporal-cadence spectroscopic observations reveals, for the first time, evidence for a significant (up to a factor of $ 2$) variability in the emission line properties (equivalent width and full width half maximum) over a timescale of minutes. Intriguingly, the variability episodes observed in the optical continuum and in the emission line properties seem uncorrelated, making their origin unclear.

O iii] emission in z ≈ 2 quasars with and without broad absorption lines

ABSTRACT Understanding the links between different phases of outflows from active galactic nuclei is a key goal in extragalactic astrophysics. Here, we compare [O iii] $\lambda \lambda$4960, 5008 outflow signatures in quasars with and without broad absorption lines (BALs), aiming to test how the broad absorption troughs seen in the rest-frame ultraviolet are linked to the narrow line region outflows seen in the rest-frame optical. We present new near-infrared spectra from Magellan/FIRE that cover [O iii] in 12 quasars with $2.1\lt z\lt 2.3$, selected to have strong outflow signatures in C iv$\lambda$1550. Combining with data from the literature, we build a sample of 73 BAL, 115 miniBAL, and 125 non-BAL quasars with $1.5\lt z\lt 2.6$. The strength and velocity width of [O iii] correlate strongly with the C iv emission properties, but no significant difference is seen in the [O iii] emission-line properties between the BALs, non-BALs, and miniBALs once the dependence on C iv emission is taken into account. A weak correlation is observed between the velocities of C iv BALs and [O iii] emission, which is accounted for by the fact that both outflow signatures correlate with the underlying C iv emission properties. Our results add to the growing evidence that BALs and non-BALs are drawn from the same parent population and are consistent with a scenario wherein BAL troughs are intermittent tracers of persistent quasar outflows, with a part of such outflow becoming optically thick along our line of sight for sporadic periods of time within which BALs are observed.

NEATH − III. A molecular line survey of a simulated star-forming cloud

ABSTRACT We present synthetic line observations of a simulated molecular cloud, utilizing a self-consistent treatment of the dynamics and time-dependent chemical evolution. We investigate line emission from the three most common CO isotopologues (12CO, 13CO, C18O) and six supposed tracers of dense gas (NH3, HCN, N2H+, HCO+, CS, HNC). Our simulation produces a range of line intensities consistent with that observed in real molecular clouds. The HCN-to-CO intensity ratio is relatively invariant with column density, making HCN (and chemically similar species such as CS) a poor tracer of high-density material in the cloud. The ratio of N2H+ to HCN or CO, on the other hand, is highly selective of regions with densities above $10^{22} \, {\rm cm}^{-2}$, and the N2H+ line is a very good tracer of the dynamics of high volume density ($\gt 10^4 \, {\rm cm}^{-3}$) material. Focusing on cores formed within the simulated cloud, we find good agreement with the line intensities of an observational sample of prestellar cores, including reproducing observed CS line intensities with an undepleted elemental abundance of sulphur. However, agreement between cores formed in the simulation, and models of isolated cores which have otherwise-comparable properties, is poor. The formation from and interaction with the large-scale environment has a significant impact on the line emission properties of the cores, making isolated models unsuitable for interpreting observational data.

Exploring the Properties of Photosphere and Emission Lines for Tidal Disruption Events Based on the Global Solution of Slim Disk and Winds

The theoretical debris supply rate from a tidal disruption of stars can exceed about 100 times of Eddington accretion rate for a 106−7 M ⊙ supermassive black hole. It is believed that a strong wind will be launched from the disk surface due to the radiation pressure in the case of super-Eddington accretion, which may be one of the mechanisms for the formation of the envelope, as observed in tidal disruption events (TDEs). In this work, we explore the evolution of the envelope that formed from the optical thick winds by solving the global solution of the slim-disk model. Our model can roughly reproduce the typical temperature, luminosity, and size of the photosphere for TDEs. Based on Cloudy modeling, we find that, if only considering the radiation-driven disk wind, the emission line luminosities are normally much lower than the typical observational results, due to the limited atmosphere mass outside the envelope. We propose that the ejection of the outflow from the self-collision of the stellar debris during the circularization may provide enough matter outside the disk-wind photosphere. Our calculated spectra can roughly reproduce the main properties of several typical emission lines (e.g., Hα, Hβ, and He ii), which was applied well to a TDE candidate AT2018dyb.

A MUSE view of the core of the giant low-surface-brightness galaxy Malin 1

Aims. The central region of the giant low-surface-brightness galaxy Malin 1 has long been known to have a complex morphology, with evidence of a bulge, disc, and potentially a bar hosting asymmetric star formation. In this work, we use VLT/MUSE data to resolve the central region of Malin 1 in order to determine its structure. Methods. We used careful light profile fitting in every image slice of the datacube to create wavelength-dependent models of each morphological component, from which we were able to cleanly extract their spectra. We then used the kinematics and emission line properties from these spectra to better understand the nature of each component extracted from our model fitting. Results. We report the detection of a pair of distinct sources at the centre of this galaxy with a separation of ∼1.05″, which corresponds to a separation on sky of ∼1.9 kpc. The radial velocity data of each object confirm that they both lie in the kinematic core of the galaxy. An analysis of the emission lines reveals that the central compact source is more consistent with being ionised through star formation and/or a LINER, while the off-centre compact source lies closer to the separation between star-forming galaxies and active galactic nuclei. Conclusions. This evidence suggests that the centre of Malin 1 hosts either a bar with asymmetric star formation or two distinct components. In the latter scenario, we propose two hypotheses for the nature of the off-centre compact source-it could either be a star-forming clump, containing one or more star clusters, that is in the process of falling into the core of the galaxy and eventually merging with the central nuclear star cluster, or it could be a clump of gas falling into the centre of the galaxy from either outside or from the disc and triggering star formation there.

The black hole masses of high-redshift QSOs

ABSTRACT Observations of high-redshift quasars frequently promote suggestions of large black hole masses, whose presence so early in cosmic time is not easily explicable. I consider the parallel with ultraluminous X-ray sources (ULXs) – now known to be stellar-mass black hole (and neutron star) binaries apparently radiating far above their Eddington luminosities LEdd. The true luminosity in ULXs is actually only of order LEdd, for stellar-mass accretors, but has a very anisotropic (‘beamed’) component, plus a near-isotropic component of similar luminosity but much lower specific intensity. Observers viewing ULXs from within the beam but assuming spherical symmetry deduce a luminosity ≫LEdd. These features appear because the accretors are fed mass at highly super-Eddington rates, most of it expelled in high-speed (v > 0.2c) outflows from the accretion disc. I show that in similarly beamed AGN, emission-line properties would be essentially the same as in unbeamed sources, but standard virial mass indicators unusable because velocity widths are dominated by the outflows, not bound motions about the black holes. In an ensemble of this kind the apparently most luminous systems are always the most distant, but have the lowest black hole masses. Interpreting observations of this ensemble without knowing that they are beamed leads instead to very high black hole mass estimates. The analogy with ULXs therefore suggests that high-redshift quasars might actually have central black hole masses which could have grown from stellar values within the lookback time. I consider how one might test these ideas observationally.

Changing-look Active Galactic Nuclei. I. Tracking the Transition on the Main Sequence of Quasars

This paper is the first in a series of papers that prepare and analyze spectral and other properties for a database of already-discovered changing-look active galactic nuclei (CL AGNs). Here we focus on the spectral fitting and analysis of broad emission lines in a sample of 93 CL AGNs collected from the literature with existing Sloan Digital Sky Survey (SDSS)/Baryon Oscillation Spectroscopic Survey (BOSS)/extended-BOSS spectroscopy where the Hβ emission-line profile does not completely disappear in any epochs. Additionally, we have gathered older/newer spectral epochs from all the available SDSS data releases to make the database more complete. We use PyQSOFit and perform a homogeneous spectral decomposition of all of our SDSS spectra and tabulate the AGN continuum and emission-line properties per epoch per source, chronologically. This further allows us to categorize the sources in our sample as Turn-On or Turn-Off and subsequently check for repeated occurrences of such phases. We then estimate the black hole mass (M BH) and the Eddington ratio (λ Edd) per epoch per source where the required parameters are available and well estimated. We demonstrate the movement of the source in the M BH–λ Edd plane, allowing us to check for systematic changes in the source’s fundamental properties. We then track their transition along the optical plane of the Eigenvector 1 schema and categorize sources that either stay within the same population (A or B) or make an interpopulation movement as a function of spectral epoch. We also test the Balmer decrement (Hα/Hβ) of a subset of our sample of CL AGNs as a function of time and AGN luminosity.

The Weakness of Soft X-Ray Intensity: Possible Physical Reason for Weak-line Quasars

Weak-line quasars (WLQs) are a notable group of active galactic nuclei (AGNs) that show unusually weak UV lines even though their optical-UV continuum shapes are similar to those of typical quasars. The physical mechanism for WLQs is an unsolved puzzle in the AGN unified model. We explore the properties of UV emission lines by performing extensive photoionization calculations based on Cloudy simulations with different spectral energy distributions (SEDs) of AGNs. The AGN continua are built from several observational empirical correlations, where the blackbody emission from the cold disk, the power-law emission from the hot corona, and a soft X-ray excess component are considered. We find that the equivalent width (EW) of C iv from our models is systematically lower than observational values if the component of soft X-ray excess is neglected. The EW will increase several times and is roughly consistent with the observations after considering the soft X-ray excess component as constrained from normal type I AGNs. We find that the UV lines are weak for QSOs with quite large black hole mass (e.g., M BH > 109 M ⊙) and weak soft X-ray emission due to the deficit of ionizing photons. As an example, we present the strength of C iv based on the multiband SEDs for three nearby weak-line AGNs, where the weaker soft X-ray emission normally predicts the weaker lines.

Emission-line velocity, metallicity, and extinction maps of the Large Magellanic Cloud

ABSTRACT We measure the properties of optical emission lines in multiple locations across the Large Magellanic Cloud (LMC) using the Australian National University 2.3-m telescope and the Wide-Field Spectrograph (WiFeS). From these measurements, we interpolate maps of the gas-phase metallicity, extinction, Hα radial velocity, and Hα velocity dispersion across the LMC. The LMC metallicity maps show a complex structure that cannot be explained by a simple radial gradient. The bright H ii region 30 Doradus stands out as a region of high extinction. The Hα and H i gas radial velocities are mostly consistent except for a region to the south and east of the LMC centre. The Hα velocity dispersion is almost always higher than the H i velocity dispersion, except in the region that shows the divergence in radial velocity, where the H i velocity dispersion is greater than the Hα velocity dispersion. This suggests that the H i gas is diverging from the stellar radial velocity, perhaps as a result of inflow or outflow of H i gas. The study of dwarf galaxies like the LMC is important as they are the building blocks of larger galaxies like our own Milky Way. The maps provided in this work show details not accessible in the study of more distant dwarf galaxies.

Testing AGN outflow and accretion models with SDSS quasar demographics

AbstractOne commonly-invoked launching mechanism for AGN outflows is radiation line driving. This mechanism depends closely on the SED of the ionizing continuum, and so is inherently linked to the structure of the accretion flow. Theories of radiation line-driven winds therefore provide testable predictions as a function of black hole (BH) mass and accretion rate. In this work we confront these predictions using the ultraviolet emission line properties of 190,000 quasars from SDSS DR17. We quantify how the shape of CIV 1549Å and the equivalent width (EW) of HeII 1640Å depend on the BH mass and Eddington ratio inferred from MgII 2800Å. The blueshift of the CIV emission line is commonly interpreted as a tracer of quasar outflows, while the HeII EW traces the strength of the 10-100 eV continuum which photo-ionizes the ultraviolet emission line regions. Above L/LEdd > 0.2, there is a strong mass dependence in both CIV blueshift and HeII EW. Large CIV blueshifts are observed only in regions with both high BH mass and high accretion rate, consistent with predictions for radiation line driven winds. The observed trends in HeII and 2 keV X-ray strength are broadly consistent with theoretical models of AGN SEDs, where the ionizing SED depends on the accretion disc temperature and the strength of the soft excess. At L/LEdd < 0.2, we find a dramatic switch in behaviour: the ultraviolet emission properties show much weaker trends, and no longer agree with SED models, hinting at changes in the structure of the broad line region. Overall the observed emission line properties are generally consistent with the radiation line driving scenario, where quasar winds are governed by the SED, which itself results from the accretion flow and hence depends on both the SMBH mass and accretion rate.

Nebular emission from young stellar populations including binary stars

ABSTRACT We investigate the nebular emission produced by young stellar populations using the new galsevn model based on the combination of the sevn population-synthesis code including binary-star processes and the galaxev code for the spectral evolution of stellar populations. Photoionization calculations performed with the cloudy code confirm that accounting for binary-star processes strongly influences the predicted emission-line properties of young galaxies. In particular, we find that our model naturally reproduces the strong He ii λ4686/H β ratios commonly observed at high H β equivalent widths in metal-poor, actively star-forming galaxies, which have proven challenging to reproduce using previous models. Including bursty star formation histories broadens the agreement with observations, while the most extreme He ii λ1640 equivalent widths can be reproduced by models dominated by massive stars. galsevn also enables us to compute, for the first time in a way physically consistent with stellar emission, the emission from accretion discs of X-ray binaries (XRBs) and radiative shocks driven by stellar winds and supernova explosions. We find that these contributions are unlikely to prominently affect the predicted He ii λ4686/H β ratio, and that previous claims of a significant contribution by XRBs to the luminosities of high-ionization lines are based on models predicting improbably high ratios of X-ray luminosity to star formation rate, inconsistent with the observed average luminosity function of XRBs in nearby galaxies. The results presented here provide a solid basis for a more comprehensive investigation of the physical properties of observed galaxies with galsevn using Bayesian inference.