Neon Lines Research Articles

EMPRESS. XIV. Strong High-ionization Lines of Young Galaxies at z = 0–8: Ionizing Spectra Consistent with the Intermediate-mass Black Holes with M BH ∼ 103–106 M ⊙

We present ionizing spectra estimated at 13.6–100 eV for 10 dwarf galaxies with strong high-ionization lines of He ii λ4686 and [Ne v] λ3426 ([Ne iv] λ2424) at z = 0 (z = 8) that are identified in our Keck/LRIS spectroscopy and the literature (the JWST Early Release Observations program). With the flux ratios of these high-ionization lines and >10 low-ionization lines of hydrogen, helium, oxygen, neon, and sulfur, we determine ionizing spectra consisting of stellar and nonthermal power-law radiation by photoionization modeling with free parameters of nebular properties, including metallicity and ionization parameter, canceling out abundance ratio differences. We find that all of the observed flux ratios are well reproduced by the photoionization models with the power-law index α EUV of α EUV ∼ (–1) − 0 and the luminosity L EUV of L EUV ∼ 1040–1042 erg s−1 at ∼55–100 eV for six galaxies, while four galaxies include large systematics in α EUV caused by stellar radiation contamination. We then compare α EUV and L EUV of these six galaxies with those predicted by the black hole (BH) accretion disk models and find that α EUV and L EUV are similar to those of the intermediate-mass BHs (IMBHs) in BH accretion disk models, albeit with possibilities of the other scenarios. Confirming these results with a known IMBH having a mass M BH of M BH = 105.75 M ⊙, we find that four local galaxies and one z = 7.665 galaxy have ionizing spectra consistent with those of IMBHs with M BH ∼ 103–105 M ⊙.

Line Profiles of Forbidden Emission Lines and What They Can Tell Us About Protoplanetary Disk Winds

Emission in forbidden lines of oxygen, neon, and other species are commonly used to trace winds from protoplanetary disks. Using Cloudy, we calculate such emission for parametrized wind models of the magnetothermal type, following Bai et al. These models share characteristics with both photoevaporative and magnetocentrifugal winds, which can be regarded as end members, and are favored by recent theoretical research. Both broad and narrow low-velocity components of the lines can be produced with plausible wind parameters, something that traditional wind models have difficulty with. Line luminosities, blueshifts, and widths, as well as trends of these with accretion luminosity and disk inclination, are in general accordance with observations.

Ground-based and JWST Observations of SN 2022pul. I. Unusual Signatures of Carbon, Oxygen, and Circumstellar Interaction in a Peculiar Type Ia Supernova

Nebular-phase observations of peculiar Type Ia supernovae (SNe Ia) provide important constraints on progenitor scenarios and explosion dynamics for both these rare SNe and the more common, cosmologically useful SNe Ia. We present observations from an extensive ground- and space-based follow-up campaign to characterize SN 2022pul, a super-Chandrasekhar mass SN Ia (alternatively “03fg-like” SN), from before peak brightness to well into the nebular phase across optical to mid-infrared (MIR) wavelengths. The early rise of the light curve is atypical, exhibiting two distinct components, consistent with SN Ia ejecta interacting with dense carbon–oxygen (C/O)-rich circumstellar material (CSM). In the optical, SN 2022pul is most similar to SN 2012dn, having a low estimated peak luminosity (M B = −18.9 mag) and high photospheric velocity relative to other 03fg-like SNe. In the nebular phase, SN 2022pul adds to the increasing diversity of the 03fg-like subclass. From 168 to 336 days after peak B-band brightness, SN 2022pul exhibits asymmetric and narrow emission from [O i] λ λ6300, 6364 (FWHM ≈ 2000 km s−1), strong, broad emission from [Ca ii] λ λ7291, 7323 (FWHM ≈ 7300 km s−1), and a rapid Fe iii to Fe ii ionization change. Finally, we present the first ever optical-to-MIR nebular spectrum of an 03fg-like SN Ia using data from JWST. In the MIR, strong lines of neon and argon, weak emission from stable nickel, and strong thermal dust emission (with T ≈ 500 K), combined with prominent [O i] in the optical, suggest that SN 2022pul was produced by a white dwarf merger within C/O-rich CSM.

JWST Detects Neon Line Variability in a Protoplanetary Disk

We report the first detection of variability in the mid-infrared neon line emission of a protoplanetary disk by comparing a JWST Mid-InfraRed Instrument Medium Resolution Spectrometer spectrum of SZ Cha taken in 2023 with a Spitzer Infrared Spectrograph Short-High spectrum of this object from 2008. We measure the [Ne iii]-to-[Ne ii] line flux ratio, which is a diagnostic of the high-energy radiation field, to distinguish between the dominance of EUV- or X-ray-driven disk photoevaporation. We find that the [Ne iii]-to-[Ne ii] line flux ratio changes significantly from ∼1.4 in 2008 to ∼0.2 in 2023. This points to a switch from EUV-dominated to X-ray-dominated photoevaporation of the disk. We present contemporaneous ground-based optical spectra of the Hα emission line that show the presence of a strong wind in 2023. We propose that this strong wind prevents EUV radiation from reaching the disk surface while the X-rays permeate the wind and irradiate the disk. We speculate that at the time of the Spitzer observations, the wind was suppressed and EUV radiation reached the disk. These observations confirm that the MIR neon emission lines are sensitive to changes in high-energy radiation reaching the disk surface. This highlights the [Ne iii]-to-[Ne ii] line flux ratio as a tool to gauge the efficiency of disk photoevaporation in order to provide constraints on the planet formation timescale. However, multiwavelength observations are crucial to interpret the observations and properly consider the star–disk connection.

Stark polarization spectroscopy of neon spectral lines for estimating cathode sheath parameters in Grimm-type glow discharge sources

We present the results of the optical emission spectroscopy (OES) study of the Ne I 503.775 nm and Ne I 508.038 nm atomic spectral lines observed in two DC glow discharge sources (GDS), standard Grimm analytical source and the modified plane cathode Grimm design. The standard Grimm GDS enables OES recording end-on only, i.e. when the radiation is collected from the entire discharge, in the direction perpendicular to the cathode surface. Our modification of Grimm GDS, on the other hand, allows for spectra recording of the complex line shapes from two optical directions, both end-on and side-on, the latter collecting radiation from a narrow slice of the discharge parallel to the cathode surface. Side-on observations enable spatially resolved Stark polarization spectroscopy at different positions along the whole cathode sheath (CS) region of the discharge. This allows the study of the Stark shifts of differently polarized (σ, π, or unpolarized) line components' dependence on the macroscopic CS electric field strength. Stark components of neon lines, encountered in side-on observations in the CS, are preserved in the end-on recordings as characteristic features – wavy wings with intensity maxima corresponding to the distinctly resolved Stark components in the CS. Following OES measurements in a broad range of discharge conditions (pressure, voltage, current), we report on a sustained correlation between the value of the maximum electric field strength Emax in the CS and the end-on recorded wing feature shifts Δλe. This correlation can be extrapolated to estimate the cathode sheath parameters Emax and the CS thickness dc in the standard Grimm-type GDS, with end-on optical access available only.

Collisional broadening and shift coefficients for (n+1)s[3/2]2 → (n+1)p[1/2]1 argon and neon lines in parent and foreign rare gases

Results of simultaneous measurements of pressure shift β and broadening ξ coefficients for 912.3 nm Ar and 703.2 nm Ne spectral lines of the (n+1)s[3/2]2 → (n+1)p[1/2]1 transition are presented. This is a lasing transition in a recently proposed optically pumped rare gas laser. Absorption line shapes fitted to Voigt profiles permitted to assess gas temperature by determining Doppler width components. These coefficients for the Ar 912.3 nm line with He and Ne as the collisional partners were determined for the first time. The values of shift and broadening coefficients in units of 10−10 s-1 cm3, reduced to 300 K are: βAr-Ar = -2.11±0.05, βAr-Ne = -1.21±0.05, βAr-He = 0.37±0.03, βNe-Ne = -0.78±0.05, βNe-He = 0.0±0.05; ξAr-Ar = 2.8±0.1, ξAr-Ne = 1.68±0.05, ξAr-He = 3.7±0.1, ξNe-Ne = 1.94±0.05, ξNe-He = 3.18±0.05.

Application of high precision wavelength calibration method for plasmas rotation measurement based on Fabry-Pérot etalon on experimental advanced superconducting tokamak.

Analyzing the radiation spectra of impurity ions is a widely applied diagnostic scheme for plasma ion temperature and rotation measurements on tokamaks. High precision wavelength calibration is a prerequisite for the accurate measurement of plasma parameters, especially for plasma rotation. Furthermore, the sparseness or absence of the standard spectral lines brings calibration challenges due to the narrow wavelength range. A precise wavelength calibration method is demonstrated in which the comb-like spectra generated by the Fabry-Pérot etalon can lock a series of fixed peaks as reference points in a wide wavelength range. The equal frequency intervals of the comb-like spectra are further corrected using several characteristic neon lines of known wavelengths. The experimental results indicate that the wavelength accuracy obtained by this calibration method is less than 0.005 nm, which corresponds to a rotation speed of 2.3 km/s in the toroidal direction for the beam emission spectroscopy spectrometer installed on the experimental advanced superconducting tokamak. Taking the O V(650.024 nm, n = 4 → 3) line as an example, the maximum difference in the oxygen ion rotation velocity is 3.8 km/s for the absolute rotation of ∼25 km/s, when compared with the calibration results of a standard lamp.

The Ionization and Destruction of Polycyclic Aromatic Hydrocarbons in Powerful Quasars

Abstract We reanalyze the mid-infrared (5–40 μm) Spitzer spectra of 86 low-redshift (z < 0.5) Palomar–Green quasars to investigate the nature of polycyclic aromatic hydrocarbon (PAH) emission and its utility as a star formation rate (SFR) indicator for the host galaxies of luminous active galactic nuclei (AGNs). We decompose the spectra with our recently developed template-fitting technique to measure PAH fluxes and upper limits, which we interpret using mock spectra that simulate the effects of AGN dilution. While luminous quasars can severely dilute and affect the detectability of emission lines, PAHs are intrinsically weak in some sources that are otherwise gas-rich and vigorously forming stars, conclusively demonstrating that powerful AGNs destroy PAH molecules. Comparing PAH-based SFRs with independent SFRs derived from the mid-infrared fine-structure neon lines and the total infrared luminosity reveals that PAHs can trace star formation activity in quasars with bolometric luminosities ≲1046 erg s−1, but increasingly underestimate the SFR for more powerful quasars, typically by ∼0.5 dex. Relative to star-forming galaxies and low-luminosity AGNs, quasars have a comparable PAH 11.3 μm/7.7 μm ratio but characteristically lower ratios of 6.2 μm/7.7 μm, 8.6 μm/7.7 μm, and 11.3 μm/17.0 μm. We suggest that these trends indicate that powerful AGNs preferentially destroy small grains and enhance the PAH ionization fraction.

7Be in the outburst of the ONe nova V6595 Sgr

ABSTRACT We report on the search for the 7Be ii isotope in the outbursts of the classical nova V6595 Sgr by means of high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) observations taken at the European Southern Observatory’s Very Large Telescope in 2021 April, about two weeks after its discovery and under difficult circumstances due to the pandemic. Narrow absorption components with velocities at ∼ −2620 and −2820 km s−1, superposed on broader and shallow absorption, are observed in the outburst spectra for the 7Be ii λλ313.0583, 313.1228 nm doublet resonance lines, as well as in several other elements such as Ca ii, Fe i, Mg i, Na i, H i and Li i. Using the Ca ii K line as a reference element, we infer N(7Be)/N(H) ≈ 7.4 × 10−6, or ≈ 9.8 × 10−6 when the 7Be decay is taken into account. The 7Be abundance is about half of the value most frequently measured in novae. The possible presence of overionization in the layers where 7Be ii is detected is also discussed. Observations taken at the Telescopio Nazionale Galileo in La Palma 91 days after discovery showed prominent emission lines of oxygen and neon, which allow us to classify the nova as ONe type. Therefore, although 7Be is expected to be higher in CO novae, it is found at comparable levels in both nova types.

Equation-of-state and melting curve of solid neon and argon up to 100 GPa

Equation-of-state and melting curve of neon and argon solids at high pressure are investigated based on the statistical moment method taking into account the anharmonicity contributions of thermal lattice vibrations. We have derived the analytical expression of equation-of-state and proposed a procedure to calculate melting temperature of materials at high pressure. We perform numerical calculations for neon and argon solids up to 100 GPa by using the Buckingham function (exp-6) to model the interaction between atoms. Our theoretical calculations reveal the strong dependence of the lattice constant and melting temperature on pressure of rare-gas solids, in particular at below 10 GPa. The derived equation-of-states of neon and argon go along with earlier experiments up to pressure 100 GPa. The present argon melting curve is in good agreement with previous measurements up to pressure 80 GPa. Our melting line of neon can reproduce well melting data points using W absorbers with thickness 8 μm and 6–8 μm up to pressure nearly 80 GPa, and differs from the measurements using W absorbers with thickness 4–6 μm.

Calibration of mid- to far-infrared spectral lines in galaxies

Context. Mid- to far-infrared (IR) lines are suitable in the study of dust-obscured regions in galaxies because dust extinction strongly decreases with wavelength, and therefore IR spectroscopy allows us to explore the most hidden regions of galaxies, where heavily obscured star formation as well as accretion onto supermassive black holes at the nuclei of galaxies occur. This is mostly important for the so-called cosmic noon (i.e. at redshifts of 1 < z < 3), at which point most of the baryonic mass in galaxies has been assembled. Aims. Our goal is to provide reliable calibrations of the mid- to far-IR ionic fine-structure lines, the brightest H2 pure rotational lines, and the polycyclic aromatic hydrocarbon (PAH) features, which we used to analyse current and future observations in the mm-submm range from the ground, as well as mid-IR spectroscopy from the upcoming James Webb Space Telescope. Methods. We used three samples of galaxies observed in the local Universe: star-forming galaxies (SFGs, 196), active galactic nuclei (AGN; 90−150 for various observables), and low-metallicity dwarf galaxies (40). For each population, we derive different calibrations of the observed line luminosities versus the total IR luminosities. Results. Through the resulting calibrations, we derive spectroscopic measurements of the star formation rate (SFR) and of the black hole accretion rate (BHAR) in galaxies using mid- and far-IR fine-structure lines, H2 pure rotational lines and PAH features. In particular, we derive robust star formation tracers based on the following: the [CII]158 μm line; the sum of the two far-IR oxygen lines, the [OI]63 μm line, and the [OIII]88 μm line; a combination of the neon and sulfur mid-IR lines; the bright PAH features at 6.2 and 11.3 μm; as well as – for the first time – the H2 rotational lines at 9.7, 12.3, and 17 μm. We propose the [CII]158 μm line, the combination of the two neon lines ([NeII]12.8 μm and [NeIII]15.5 μm), and, for solar-like metallicity galaxies that may harbour an AGN, the PAH 11.3 μm feature as the best SFR tracers. On the other hand, a reliable measure of the BHAR can be obtained using the [OIV]25.9 μm and the [NeV]14.3 and 24.3 μm lines. For the most commonly observed fine-structure lines in the far-IR, we compare our calibration with the existing ALMA observations of high-redshift galaxies. We find an overall good agreement for the [CII]158 μm line for both AGN and SFGs, while the [OIII]88 μm line in high-z galaxies is in better agreement with the low-metallicity local galaxies (dwarf galaxy sample) than with the SFGs, suggesting that high-z galaxies might have strong radiation fields due to low metal abundances, as expected.

Measuring chemical abundances with infrared nebular lines: HII-CHI-MISTRY-IR

We provide a new method for deriving heavy element abundances taking advantage of the unique suite of fine-structure lines in the mid- to far-infrared (IR) range. Using grids of photo-ionisation models that cover a wide range in O/H and N/O abundances and ionisation parameter, our code HII-CHI-MISTRY-IR (HCM-IR) provides model-based abundances based on extinction-free and temperature-insensitive tracers. These are two significant advantages over optical diagnostics when they are applied to dust-obscured regions or unresolved (stratified) nebulae, typical conditions found in high-z galaxies. The performance of the code is probed using three different samples of galaxies that extend over a wide range in metallicity, 7.2 ≲ 12 + log(O/H) ≲ 8.9, with available mid- to far-IR spectroscopic observations from Spitzer and Herschel, respectively. The samples correspond to 28 low-metallicity dwarf galaxies, 19 nearby starbursts, and 9 luminous IR galaxies. The IR model-based metallicities obtained are robust within a scatter of 0.03 dex when the hydrogen recombination lines, which are typically faint transitions in the IR range, are not available. When compared to the optical abundances obtained with the direct method, model-based methods, and strong-line calibrations, HCM-IR estimates show a typical dispersion of ∼ 0.2 dex. This is in line with previous studies comparing IR and optical abundances and does not introduce a noticeable systematic above 12 + log(O/H) ≳ 7.6. This accuracy can be achieved by measuring the sulphur ([S IV]10.5 μm and [S III]18.7, 33.5 μm) and the neon lines ([Ne III]15.6 μm and [Ne II]12.8 μm). Additionally, HCM-IR provides an independent N/O measurement when the oxygen ([O III]52, 88 μm) and nitrogen ([N III]57 μm) transitions are measured. The derived abundances in this case do not rely on particular assumptions on the N/O ratio. Large uncertainties (∼ 0.4 dex) may affect the abundance determinations of galaxies at sub- or over-solar metallicities when a solar-like N/O ratio is adopted. Finally, the code has been applied to 8 galaxies located at 1.8 < z < 7.5 with ground-based detections of far-IR lines redshifted in the submillimetre range, revealing solar-like N/O and O/H abundances in agreement with recent studies. A script to derive chemical abundances with HCM-IR has been made publicly available online.

Measurement of the first Townsend’s ionization coefficient for atmospheric pressure neon by a dielectric barrier discharge

Fast photography and optical emission spectroscopy are implemented in a 5 mm neon gap dielectric barrier discharge (DBD) at atmospheric pressure with quartz glass used as the dielectric layer. Results show that it starts with a Townsend discharge and ends at a sub-normal glow discharge in neon DBD. Based on the Townsend discharge, the first ionization coefficient of neon is measured. The measurements are consistent with those at low pressure. Optical emission spectroscopy indicates that the spectra are mainly composed of atomic lines of neon, molecular bands and molecular ion bands originating from inevitable gas impurities (mainly nitrogen). Moreover, spectral lines emitted from atomic neon corresponding to the transitions (2p5 3p → 2p5 3s) are predominant. Although the second positive system of N2(C3Πu → B3Πg) is observed, their intensities are too weak compared with neon’s spectrum. The molecular nitrogen ion line of 391.4 nm is observed. It reveals that Penning ionization between high energy neon excited states and the inevitable gas impurities plays an important role in the value of the α coefficient.

Complex UV Ne II line shapes in the cathode sheath of an abnormal glow discharge

We report results of an experimental and theoretical study of complex UV line shapes of Ne II 369.421 nm, Ne II 371.308 nm and Ne II 372.711 nm lines in the cathode sheath (CS) region of an abnormal glow discharge in pure neon. The experimental profiles were studied by means of the optical emission spectroscopy (OES) in conjunction with an iterative CS kinetic model. It is shown that our theoretical model describes the experimental line shapes and that, with the aid of the measured Stark shifts of atomic neon lines, it can be used for the determination of the most important CS parameters (e.g. the thickness of the CS region, distribution of electric field, and the gas temperature). We draw attention to the possibility of determining the electric field strength in CS from the width of the pedestal of the complex line profiles.

Theoretical ISM Pressure and Electron Density Diagnostics for Local and High-redshift Galaxies

Abstract We derive new self-consistent theoretical UV, optical, and IR diagnostics for the interstellar medium (ISM) pressure and electron density in the ionized nebulae of star-forming galaxies. Our UV diagnostics utilize the intercombination, forbidden, and resonance lines of silicon, carbon, aluminum, neon, and nitrogen. We also calibrate the optical and IR forbidden lines of oxygen, argon, nitrogen, and sulfur. We show that line ratios used as ISM pressure diagnostics depend on the gas-phase metallicity with a residual dependence on the ionization parameter of the gas. In addition, the traditional electron density diagnostic [S ii] λ6731/[S ii] λ6717 is strongly dependent on the gas-phase metallicity. We show how different emission-line ratios are produced in different ionization zones in our theoretical nebulae. The [S ii] and [O ii] ratios are produced in different zones and should not be used interchangeably to measure the electron density of the gas unless the electron temperature is known to be constant. We review the temperature and density distributions observed within H ii regions and discuss the implications of these distributions on measuring the electron density of the gas. Many H ii regions contain radial variations in density. We suggest that the ISM pressure is a more meaningful quantity to measure in H ii regions or galaxies. Specific combinations of line ratios can cover the full range of ISM pressures (4 < log(P/k) < 9). As H ii regions become resolved at increasingly high redshift through the next generation of telescopes, we anticipate that these diagnostics will be important for understanding the conditions around the young, hot stars from the early universe to the present day.

Dissociation Energy and Dissociative Recombination of $${\text{Ne}}_{2}^{ + }$$ and HeNe+ Ions

We present the results of our study of a weakly ionized decaying helium plasma with a small admixture of neon by means of kinetic spectroscopy. The experimental conditions are a helium pressure of 10–38 Torr, an electron density [e] ≤ 2 × 1011 cm–3, and a neon density [Ne] ≤ 2 × 10–4 [He]. The recombination processes of $${\text{Ne}}_{2}^{ + }$$ , $${\text{He}}_{2}^{ + }$$ , HeNe+, and Ne+ ions with electrons have been identified by the decaying-plasma radiation. The neon afterglow spectrum at [e] ≤ 1011 cm–3 is shown to be formed mainly by dissociative recombination of $${\text{Ne}}_{2}^{ + }$$ and HeNe+ ions in the ground vibrational state $${v}$$ = 0. The early afterglow of a number of atomic neon lines is formed by the well-known process of excitation transfer from helium atoms in metastable states He(23S1, 21S0). At [e] > 1011 cm–3, the afterglow spectrum is enriched due to the collisional-radiation recombination of Ne+ ions. In the recombination stage of the afterglow at room electron temperature, the existence of a clear upper bound on the excitation energy of the atomic neon levels being populated is characteristic of the dissociative recombination of both molecular ions. For $${\text{Ne}}_{2}^{ + }$$ this is the 3p1 level (in Paschen notation) with an energy of 20.369 eV, with the levels closest to $${\text{Ne}}_{2}^{ + }$$ ( $${v}$$ = 0) in energy being 3p3 and 3p2 with energies of 20.26 and 20.3 eV, respectively; for HeNe+, this is the 5 $$d_{1}^{'}$$ level with an energy of about 21.02 eV. These values are proposed to be taken as the energies of $${\text{Ne}}_{2}^{ + }$$ and HeNe+ ions in the ground vibrational state.

CO-Dark Star Formation and Black Hole Activity in 3C 368 at z = 1.131: Coeval Growth of Stellar and Supermassive Black Hole Masses∗ †

Abstract We present the detection of four far-infrared fine-structure oxygen lines, as well as strong upper limits for the CO(2–1) and [N ii] 205 μm lines, in 3C 368, a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in conjunction with previously observed neon and carbon fine-structure lines, suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and extended star formation. A starburst dominated by O8 stars, with an age of ∼6.5 Myr, provides a good fit to the fine-structure line data. This estimated age of the starburst makes it nearly concurrent with the latest episode of AGN activity, suggesting a link between the growth of the supermassive black hole and stellar population in this source. We do not detect the CO(2–1) line, down to a level twelve times lower than the expected value for star-forming galaxies. This lack of CO line emission is consistent with recent star formation activity if the star-forming molecular gas has low metallicity, is highly fractionated (such that CO is photodissociated throughout much of the clouds), or is chemically very young (such that CO has not yet had time to form). It is also possible, although we argue it is unlikely, that the ensemble of fine-structure lines is emitted from the region heated by the AGN.

THE MOSDEF SURVEY: DETECTION OF [O III]λ4363 AND THE DIRECT-METHOD OXYGEN ABUNDANCE OF A STAR-FORMING GALAXY AT z = 3.08*

ABSTRACT We present measurements of the electron-temperature-based oxygen abundance for a highly star-forming galaxy at z = 3.08, COSMOS-1908. This is the highest redshift at which [O iii]λ4363 has been detected and the first time that this line has been measured at z > 2 . We estimate an oxygen abundance of 12 + log ( O / H ) = 8.00 − 0.14 + 0.13 . This galaxy is a low-mass ( 10 9.3 M ⊙ ), highly star-forming (∼50 M ⊙ yr−1) system that hosts a young stellar population (∼160 Myr). We investigate the physical conditions of the ionized gas in COSMOS-1908 and find that this galaxy has a high ionization parameter, little nebular reddening ( E ( B − V ) gas < 0.14 ), and a high electron density ( n e ∼ 500 cm−3). We compare the ratios of strong oxygen, neon, and hydrogen lines to the direct-method oxygen abundance for COSMOS-1908 and additional star-forming galaxies at z = 0 − 1.8 with [O iii]λ4363 measurements and show that galaxies at z ∼ 1 – 3 follow the same strong-line correlations as galaxies in the local universe. This agreement suggests that the relationship between ionization parameter and O/H is similar for z ∼ 0 and high-redshift galaxies. These results imply that metallicity calibrations based on lines of oxygen, neon, and hydrogen do not strongly evolve with redshift and can reliably estimate abundances out to z ∼ 3 , paving the way for robust measurements of the evolution of the mass–metallicity relation to high redshift.

POLYCYCLIC AROMATIC HYDROCARBON EMISSION IN SPITZER/IRS MAPS. I. CATALOG AND SIMPLE DIAGNOSTICS

ABSTRACT We present a sample of resolved galactic H ii regions and photodissociation regions (PDRs) observed with the Spitzer infrared spectrograph in spectral mapping mode between the wavelengths of 5–15 μm. For each object we have spectral maps at a spatial resolution of ∼4″ in which we have measured all of the mid-infrared emission and absorption features. These include the polycyclic aromatic hydrocarbon (PAH) emission bands, primarily at 6.2, 7.7, 8.6, 11.2, and 12.7 μm, as well as the spectral emission lines of neon and sulfur and the absorption band caused by silicate dust at around 9.8 μm. In this work we describe the data in detail, including the data reduction and measurement strategies, and subsequently present the PAH emission band intensity correlations for each of the objects and the sample as a whole. We find that there are distinct differences between the sources in the sample, with two main groups: the first comprising the H ii regions and the second the reflection nebulae (RNe). Three sources—the reflection nebula NGC 7023, the Horsehead nebula PDR (an interface between the H ii region IC 434 and the Orion B molecular cloud), and M17—resist this categorization, with the Horsehead PDR points mimicking the RNe and the NGC 7023 fluxes displaying a unique bifurcated appearance in our correlation plots. These discrepancies seem to be due to the very low radiation field experienced by the Horsehead PDR and the very clean separation between the PDR environment and a diffuse environment in the NGC 7023 observations.

UVES and X-Shooter spectroscopy of the emission line AM CVn systems GP Com and V396 Hya

We present time-resolved spectroscopy of the AM CVn-type binaries GP Com and V396 Hya obtained with VLT/X-Shooter and VLT/UVES. We fully resolve the narrow central components of the dominant helium lines and determine radial velocity semi-amplitudes of $K_{\rm spike} = 11.7\pm0.3$ km s$^{-1}$ for GP Com and $K_{\rm spike} = 5.8\pm0.3$ km s$^{-1}$ for V396 Hya. The mean velocities of the narrow central components show variations from line to line. Compared to calculated line profiles that include Stark broadening we are able to explain the displacements, and the appearance of forbidden helium lines, by additional Stark broadening of emission in a helium plasma with an electron density $n_e\simeq 5\times 10^{15}$ cm$^{-3}$. More than $30$ nitrogen and more than $10$ neon lines emission lines were detected in both systems. Additionally, $20$ nitrogen absorption lines are only seen in GP Com. The radial velocity variations of these lines show the same phase and velocity amplitude as the central helium emission components. The small semi-amplitude of the central helium emission component, the consistency of phase and amplitude with the absorption components in GP Com as well as the measured Stark effect shows that the central helium emission component, the so-called central-spike, is consistent with an origin on the accreting white dwarf. We use the dynamics of the bright spot and the central spike to constrain the binary parameters for both systems and find a donor mass of $9.6$ - $42.8$ M$_{\rm Jupiter}$ for GP Com and $6.1$ - $30.5$ M$_{\rm Jupiter}$ for V396 Hya. We find an upper limit for the rotational velocity of the accretor of $v_{\rm rot}<46$ km s$^{-1}$ for GP Com and $v_{\rm rot}<59$ km s$^{-1}$ for V396 Hya which excludes a fast rotating accretor in both systems.