Strong Emission Lines Research Articles

Census of and Lyα, [Oiii]5007, Hα, and [Ciii]158 μm line emission wiht ∼1000 galaxies atz= 4.9 – 7.0 revealed with Subaru/HSC, Spitzer, and ALMA

AbstractWe investigate rest-frame UV to far-infrared emission lines and SEDs from 1124 galaxies atz= 4.9 – 7.0. Our sample is composed of 1092 Lyα emitters (LAEs) atz= 4.9–7.0 identified by Subaru/Hyper Suprime-Cam (HSC) narrowband surveys and 34 galaxies atz= 5.148–7.508 with deep [Cii]158μm ALMA data. The SEDs clearly show flux excesses in the Spitzer/IRAC 3.6 and 4.5μm bands, suggesting strong rest-frame optical emission lines of [Oiii] and/or Hα. We model the galaxy SEDs with a flexible code combining stellar population and photoionization models (BEAGLE; Chevallard & Charlot 2016), and investigate relations between the emission lines of Lyα, [Oiii], Hα, and [CII]. We find 1) a positive correlation between the rest-frame Hα equivalent width (EW) and the Lyα, EW,${\EW {^0_Ly\alpha}} $, 2) an interesting turn-over trend that the [Oiii]/Hα flux ratio increases in${\EW {^0_Ly\alpha}} $≃ 0–30 Å, and then decreases out to${\EW {^0_Ly\alpha}} $≃ 130 Å, and 3) a > 99% anti-correlation between a [Cii] luminosity to star-formation rate ratioL[Cii]/SFR) and${\EW {^0_Ly\alpha}} $. Modeling with BEAGLE also suggests that a simple anticorrelation between${\EW {^0_Ly\alpha}} $and metallicity explains self-consistently all of the relations of Lyα, Hα, [Oiii]/Hα, and [Cii] in our study, indicative of detections of very metal-poor (∼0.03Z⊙) galaxies with${\EW {^0_Ly\alpha}} $∼200 Å.

Properties of LBGs with [OIII] detection at z > 3: The importance of including nebular emission data in SED fitting

AbstractAt high redshift, the contribution of strong emission lines to the broadband photometry can cause large uncertainties when estimating galaxy physical properties. To examine this effect, we investigate a sample of 54 LBGs at 3 < zspec < 3.8 with detected [OIII] line emissions. We use CIGALE to fit simultaneously the rest-frame UV-to-NIR SEDs of these galaxies and their emission line data. By comparing the results with and without emission line data, we show that spectroscopic data are necessary to constrain the nebular model. We examine the K-band excess, which is usually used to estimate the emissions of [OIII]+Hβ lines when there is no spectral data, and find that the difference between the estimation and observation can reach up to > 1 dex for some galaxies, showing the importance of obtaining spectroscopic measurements of these lines. We also estimate the equivalent width of the Hβ absorption and find it negligible compared to the Hβ emission.

Optical and X-ray studies of three polars: RX J0859.1+0537, RX J0749.1–0549, and RX J0649.8–0737

ABSTRACT We present optical photometric and spectroscopic observations, and an analysis of archival X-ray data of three polars: RX J0859.1+0537, RX J0749.1–0549, and RX J0649.8–0737. Optical light curves of these three polars reveal eclipse-like features that are deep, total, and variable in shape. The optical and X-ray modulations of RX J0859.1+0537, RX J0749.1–0549, and RX J0649.8–0737 are both found to occur at the orbital periods of 2.393 ± 0.003 h, 3.672 ± 0.001 h, and 4.347 ± 0.001 h, respectively. RX J0859.1+0537 is found to be a polar that lies in the region of the period gap, whereas RX J0749.1–0549 and RX J0649.8–0737 are found to be long-period polars above the period gap. The eclipse length is found to be 61 min for RX J0749.1–0549 in the Rband, which is the highest among the long-period eclipsing polars. The radius of the eclipsed light source is found to be more than the actual size of the white dwarf for these three systems, indicating that the eclipsed component is not only the white dwarf but also appears to include the presence of an extended accretion region. Optical spectra of these systems show the presence of high-ionization emission lines along with the strong Balmer emission lines with an inverted Balmer decrement. Cyclotron harmonics are also detected in the optical spectra from which we infer magnetic field strength of the surface of the white dwarf to be 49 ± 2 MG, 43.5 ± 1.4 MG, and 44 ± 1 MG for RX J0859.1+0537, RX J0749.1–0549, and RX J0649.8–0737, respectively.

Understanding Lyα Nebulae at Low Redshift. I. The Sizes, Powering, and Kinematics of “Green Bean” Galaxies

Abstract A new but rare sample of spatially extended emission line nebulae, nicknamed “Green Beans,” was discovered at z ≈ 0.3 thanks to strong [O iii] emission, and subsequently shown to be local cousins of the Lyα nebulae found at high redshift. Here we use follow-up APO/DIS spectroscopy to better understand how these low-redshift Lyα nebulae compare to other populations of strong emission line sources. Our spectroscopic data show that low-z Lyα nebulae have active galactic nucleus (AGN)-like emission line ratios, relatively narrow line widths (FWHM ≲ 1000 km s−1), and emission line kinematics resembling those of Type 2 AGN at the same redshift, confirming that they are powered by Type 2 AGN with typical ionizing continua. While low-z Lyα nebulae are larger and less concentrated than compact, star-forming Green Pea galaxies, we find that they resemble typical Type 2 AGN in terms of r-band concentration and size. Based on this pilot study, low-z Lyα nebulae appear to be a subset of Type 2 AGN with bluer optical continua and high [O iii] equivalent widths but with comparable sizes and similar [O iii] kinematics. These characteristics may simply reflect the fact that low-z Lyα nebulae are drawn from the high-luminosity end of the Type 2 AGN distribution, with higher nuclear activity driving higher [O iii] equivalent widths and more central star formation leading to bluer optical continua. Deeper spectroscopic follow-up of the full sample will shed further light on these issues and on the relationship between these low-z Lyα nebulae and the Lyα nebula population at high redshift.

The OTELO survey

Context. The evolution of galaxies through cosmic time is studied observationally by means of extragalactic surveys. The usefulness of these surveys is greatly improved by increasing the cosmological volume, in either depth or area, and by observing the same targets in different wavelength ranges. A multi-wavelength approach using different observational techniques can compensate for observational biases. Aims. The OTELO survey aims to provide the deepest narrow-band survey to date in terms of minimum detectable flux and emission line equivalent width in order to detect the faintest extragalactic emission line systems. In this way, OTELO data will complements other broad-band, narrow-band, and spectroscopic surveys. Methods. The red tunable filter of the OSIRIS instrument on the 10.4 m Gran Telescopio Canarias (GTC) is used to scan a spectral window centred at 9175 Å, which is free from strong sky emission lines, with a sampling interval of 6 Å and a bandwidth of 12 Å in the most deeply explored EGS region. Careful data reduction using improved techniques for sky ring subtraction, accurate astrometry, photometric calibration, and source extraction enables us to compile the OTELO catalogue. This catalogue is complemented with ancillary data ranging from deep X-ray to far-infrared, including high resolution HST images, which allow us to segregate the different types of targets, derive precise photometric redshifts, and obtain the morphological classification of the extragalactic objects detected. Results. The OTELO multi-wavelength catalogue contains 11 237 entries and is 50% complete at AB magnitude 26.38. Of these sources, 6600 have photometric redshifts with an uncertainty δ zphot better than 0.2 (1+zphot). A total of 4336 of these sources correspond to preliminary emission line candidates, which are complemented by 81 candidate stars and 483 sources that qualify as absorption line systems. The OTELO survey results will be released to the public on the second half of 2019.

Multiwavelength Period–Luminosity and Period–Luminosity–Color Relations at Maximum Light for Mira Variables in the Magellanic Clouds

Abstract We present Period–Luminosity and Period–Luminosity–Color relations at maximum light for Mira variables in the Magellanic Clouds using time-series data from the Optical Gravitational Lensing Experiment (OGLE-III) and Gaia data release 2. The maximum-light relations exhibit a scatter typically up to ∼30% smaller than their mean-light counterparts. The apparent magnitudes of oxygen-rich Miras at maximum light display significantly smaller cycle-to-cycle variations than at minimum light. High-precision photometric data for Kepler Mira candidates also exhibit stable magnitude variations at the brightest epochs, while their multi-epoch spectra display strong Balmer emission lines and weak molecular absorption at maximum light. The stability of maximum-light magnitudes for Miras possibly occurs due to the decrease in the sensitivity to molecular bands at their warmest phase. At near-infrared wavelengths, the period–luminosity relations (PLRs) of Miras display similar dispersion at mean and maximum light with limited time-series data in the Magellanic Clouds. A kink in the oxygen-rich Mira PLRs is found at 300 days in the VI-bands, which shifts to longer periods (∼350 days) at near-infrared wavelengths. Oxygen-rich Mira PLRs at maximum light provide a relative distance modulus, Δμ = 0.48 ± 0.08 mag, between the Magellanic Clouds with a smaller statistical uncertainty than the mean-light relations. The maximum-light properties of Miras can be very useful for stellar atmosphere modeling and distance scale studies provided their stability and the universality can be established in other stellar environments in the era of extremely large telescopes.

Dissecting quasars with the J-PAS narrow-band photometric survey

AbstractThe J-PAS survey will soon start observing thousands of square degrees of the Northern Sky with its unique set of 56 narrow band filters covering the entire optical wavelength range, providing, effectively, a low resolution spectra for every object detected. Active galaxies and quasars, thanks to their strong emission lines, can be easily identified and characterized with J-PAS data. A variety of studies can be performed, from IFU-like analysis of local AGN, to clustering of high-z quasars. We also expect to be able to extract intrinsic physical quasar properties from the J-PAS pseudo-spectra, including continuum slope and emission line luminosities. Here we show the first attempts of using the QSFit software package to derive the properties for 22 quasars at 0.8 < z < 2 observed by the miniJPAS survey, the first deg2 of J-PAS data obtained with an interim camera. Results are compared with the ones obtained by applying the same software to SDSS quasar spectra.

Spectrophotometric Redshifts for z ∼ 1 Galaxies and Predictions for Number Densities with WFIRST and Euclid

Abstract We investigate the accuracy of 4000 Å/Balmer-break based redshifts by combining Hubble Space Telescope (HST) grism data with photometry. The grism spectra are from the Probing Evolution And Reionization Spectroscopically survey with HST using the G800L grism on the Advanced Camera for Surveys. The photometric data come from a compilation by the 3D-HST collaboration of imaging from multiple surveys (notably, the Cosmic Assembly Near-infrared Deep Extragalactic Survey (CANDELS) and 3D-HST). We show evidence that spectrophotometric redshifts (SPZs) typically improve the accuracy of photometric redshifts by ∼17%–60%. Our SPZ method is a template-fitting-based routine that accounts for correlated data between neighboring points within grism spectra via the covariance matrix formalism and also accounts for galaxy morphology along the dispersion direction. We show that the robustness of the SPZ is directly related to the fidelity of the D4000 measurement. We also estimate the accuracy of continuum-based redshifts, i.e., for galaxies that do not contain strong emission lines, based on the grism data alone ( ). Given that future space-based observatories like Wide Field InfraRed Survey Telescope and Euclid will spend a significant fraction of time on slitless spectroscopic observations, we estimate number densities for objects with . We predict ∼700–4400 galaxies degree−2 for galaxies with D4000 > 1.1 and to a limiting depth of i AB = 24 mag. This is especially important in the absence of an accompanying rich photometric data set like the existing one for the CANDELS fields, where redshift accuracy from future surveys will rely only on the presence of a feature like the 4000 Å/Balmer breaks or the presence of emission lines within the grism spectra.

HETDEX Pilot Survey. VI. $[{\rm{O}}\,{\rm{III}}]$ Emitters and Expectations for a Local Sample of Star-forming Galaxies in HETDEX

We assemble an unbiased sample of 29 galaxies with [O II] $\lambda 3727$ and/or [O III] $\lambda 5007$ detections at $z < 0.15$ from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Pilot Survey (HPS). HPS finds galaxies without pre-selection based on their detected emission lines via integral field spectroscopy. Sixteen of these objects were followed up with the second-generation, low resolution spectrograph (LRS2) on the upgraded Hobby-Eberly Telescope. Oxygen abundances were then derived via strong emission lines using a Bayesian approach. We find most of the galaxies fall along the mass-metallicity relation derived from photometrically selected star forming galaxies in the Sloan Digital Sky Survey (SDSS). However, two of these galaxies have low metallicity (similar to the very rare green pea galaxies in mass-metallicity space). The star formation rates of this sample fall in an intermediate space between the SDSS star forming main sequence and the extreme green pea galaxies. We conclude that spectroscopic selection fills part of the mass-metallicity-SFR phase space that is missed in photometric surveys with pre-selection like SDSS, i.e., we find galaxies that are actively forming stars but are faint in continuum. We use the results of this pilot investigation to make predictions for the upcoming unbiased, large spectroscopic sample of local line emitters from HETDEX. With the larger HETDEX survey we will determine if galaxies selected spectroscopically without continuum brightness pre-selection have metallicities that fall on a continuum that bridges typical star forming and rarer, more extreme systems like green peas.

A Sparkler in the Fireworks Galaxy: Discovery of an Ultraluminous X-Ray Transient with a Strong Oxygen Line in NGC 6946

Abstract We discovered and studied an ultraluminous X-ray source (CXOU J203451.1+601043) that appeared in the spiral galaxy NGC 6946 at some point between 2008 February and 2012 May and has remained at luminosities ≈2–4 × 1039 erg s−1 in all observations since then. Our spectral modeling shows that the source is generally soft but with spectral variability from epoch to epoch. Using standard empirical categories of the ultraluminous regimes, we found that CXOU J203451.1+601043 was consistent with a broadened disk state in 2012 but was in a transitional state approaching the supersoft regime in 2016, with substantial down-scattering of the hard photons (similar, for example, to the ultraluminous X-ray source in NGC 55). It has since hardened again in 2018–2019 without any significant luminosity change. The most outstanding property of CXOU J203451.1+601043 is a strong emission line at an energy of of (0.66 ± 0.01) keV, with an equivalent width of ≈100 eV and de-absorbed line luminosity of ≈2 × 1038 erg s−1, seen when the continuum spectrum was softest. We identify the line as O viii Lyα (rest-frame energy of 0.654 keV); we interpret it as a strong indicator of a massive outflow. Our finding supports the connection between two independent observational signatures of the wind in super-Eddington sources: a lower temperature of the Comptonized component and the presence of emission lines in the soft X-ray band. We speculate that the donor star is oxygen-rich: a CO or O–Ne–Mg white dwarf in an ultracompact binary. If that is the case, the transient behavior of CXOU J203451.1+601043 raises intriguing theoretical questions.

HSC16aayt: A Slowly Evolving Interacting Transient Rising for More than 100 Days

We report our observations of HSC16aayt (SN 2016jiu), which was discovered by the Subaru/Hyper Suprime-Cam (HSC) transient survey conducted as part of Subaru Strategic Program (SSP). It shows very slow photometric evolution and its rise time is more than 100 days. The optical magnitude change in 400 days remains within 0.6 mag. Spectra of HSC16aayt show a strong narrow emission line and we classify it as a Type IIn supernova. The redshift of HSC16aayt is 0.6814 +/- 0.0002 from the spectra. Its host galaxy center is at 5 kpc from the supernova location and HSC16aayt might be another example of isolated Type IIn supernovae, although the possible existence of underlying star forming activity of the host galaxy at the supernova location is not excluded.

Unfolding Overlapped Slitless Imaging Spectrometer Data for Extended Sources

Abstract Slitless spectrometers can provide simultaneous imaging and spectral data over an extended field of view, thereby allowing rapid data acquisition for extended sources. In some instances, when the object is greatly extended or the spectral dispersion is too small, there may be locations in the focal plane where emission lines at different wavelengths contribute. It is then desirable to unfold the overlapped regions in order to isolate the contributions from the individual wavelengths. In this paper, we describe a method for such an unfolding, using an inversion technique developed for an extreme ultraviolet imaging spectrometer and coronagraph named the COronal Spectroscopic Imager in the EUV (COSIE). The COSIE spectrometer wavelength range (18.6–20.5 nm) contains a number of strong coronal emission lines and several density sensitive lines. We focus on optimizing the unfolding process to retrieve emission measure maps at constant temperature, maps of spectrally pure intensity in the Fe xii and Fe xiii lines, and density maps based on both Fe xii and Fe xiii diagnostics.

SN 2016iet: The Pulsational or Pair Instability Explosion of a Low-metallicity Massive CO Core Embedded in a Dense Hydrogen-poor Circumstellar Medium

Abstract We present optical photometry and spectroscopy of SN 2016iet (=Gaia16bvd=PS17brq), an unprecedented Type I supernova (SN I) at z = 0.0676 with no obvious analog in the existing literature. SN 2016iet exhibits a peculiar light curve, with two roughly equal brightness peaks (≈ −19 mag) separated by about 100 days, and a subsequent slow decline by about 5 mag in 650 rest-frame days. The spectra are dominated by strong emission lines of calcium and oxygen, with a width of only 3400 km s−1, superposed on a strong blue continuum in the first year. There is no clear evidence for hydrogen or helium associated with the SN at any phase. The nebular spectra exhibit a ratio of , much larger than for core-collapse SNe and Type I superluminous SNe. We model the light curves with several potential energy sources: radioactive decay, a central engine, and ejecta–circumstellar medium (CSM) interaction. Regardless of the model, the inferred progenitor mass near the end of its life (i.e., the CO core mass) is ≳55 M ⊙ and potentially up to 120 M ⊙, clearly placing the event in the regime of pulsational pair instability supernovae (PPISNe) or pair instability supernovae (PISNe). The models of CSM interaction provide the most consistent explanation for the light curves and spectra, and require a CSM mass of ≈35 M ⊙ ejected in the final decade before explosion. We further find that SN 2016iet is located at an unusually large projected offset (16.5 kpc, 4.3 effective radii) from its low-metallicity dwarf host galaxy (Z ≈ 0.1 Z ⊙, L ≈ 0.02 L *, M ≈ 108.5 M ⊙), supporting the interpretation of a PPISN/PISN explosion. In our final spectrum at a phase of about 770 rest-frame days we detect weak and narrow Hα emission at the location of the SN, corresponding to a star formation rate of ≈3 × 10−4 M ⊙ yr−1, which is likely due to a dim underlying galaxy host or an H ii region. Despite the overall consistency of the SN and its unusual environment with PPISNe and PISNe, we find that the inferred properties of SN 2016iet challenge existing models of such events.

Advances in neutral tungsten ultraviolet spectroscopy for the potential benefit to gross erosion diagnosis

A spectral survey of tungsten emission in the ultraviolet region has been completed in the DIII-D tokamak and the CTH torsatron to assess the potential benefit of UV emission for the diagnosis of gross W erosion. A total of 29 W I spectral lines are observed from the two experiments using survey spectrometers between 200 and 400 nm with level identifications provided based on a structure calculation for many of the excited states that produce strong emission lines. Of the 29 observed lines, 20 have not previously been reported in fusion relevant plasmas, including an intense line at 265.65 nm which could be important for benchmarking the frequently exploited line at 400.88 nm. Nearly all of the observed spectral lines decay down to one of the six lowest energy levels for neutral W, which are likely to be long-lived metastable states. The impact of metastable level populations on the W I emission spectrum and any erosion measurement utilizing a spectroscopic technique is potentially significant. Nevertheless, the high density of W I emission in the UV region allows for the possibly of determining the relative metastable fractions and plasma parameters local to the erosion region. Additionally, the lines observed in this work could be used to perform multiple independent gross erosion measurements, leading to more accurate diagnosis of gross tungsten erosion.

Photometric and Spectroscopic Follow-up of the Recently Activated Asteroid 6478 Gault

Abstract 6478 Gault, a main-belt asteroid, was detected of cometary activity recently and has been recognized as an active asteroid since 2018 December. We present imaging and spectroscopic observations of 6478 Gault, to probe its properties since activation and to shed light on the how Gault became an active asteroid. We obtain V-band imaging and optical spectra using the Alhambra Faint Object Spectrograph and Camera on board the 2.5 m Nordic Optical Telescope. Our V-band imaging shows a long tail spanning more than 3′, but there is no trace of possible fragmentation or debris in our imaging. A close look at the asteroid also shows a precursor of a second tail. Our spectrum shows that Gault is a C-type asteroid, indicating it belongs to the carbonaceous Tamara family in the Phocaea family region. In addition, we also investigate possible emission lines of CN and C2 that are commonly seen in comets. However, they are not detected in our optical spectrum. As CN and C2 are strong emission lines and can be used as alternate indicators of water, the nondetection of CN and C2 evinces no trace of water production from ice sublimation.

Stellar Metallicities and Elemental Abundance Ratios of z ∼ 1.4 Massive Quiescent Galaxies*

Abstract The chemical composition of galaxies has been measured out to z ∼ 4. However, nearly all studies beyond z ∼ 0.7 are based on strong-line emission from H ii regions within star-forming galaxies. Measuring the chemical composition of distant quiescent galaxies is extremely challenging, as the required stellar absorption features are faint and shifted to near-infrared wavelengths. Here, we present ultradeep rest-frame optical spectra of five massive quiescent galaxies at z ∼ 1.4, all of which show numerous stellar absorption lines. We derive the abundance ratios [Mg/Fe] and [Fe/H] for three out of five galaxies; the remaining two galaxies have too young luminosity-weighted ages to yield robust measurements. Similar to lower-redshift findings, [Mg/Fe] appears positively correlated with stellar mass, while [Fe/H] is approximately constant with mass. These results may imply that the stellar mass–metallicity relation was already in place at z ∼ 1.4. While the [Mg/Fe]−mass relation at z ∼ 1.4 is consistent with the z &lt; 0.7 relation, [Fe/H] at z ∼ 1.4 is ∼0.2 dex lower than at z &lt; 0.7. With a [Mg/Fe] of the most massive galaxy may be more α-enhanced than similar-mass galaxies at lower redshift, but the offset is less significant than the [Mg/Fe] of 0.6 previously found for a massive galaxy at z = 2.1. Nonetheless, these results combined may suggest that [Mg/Fe] in the most massive galaxies decreases over time, possibly by accreting low-mass, less α-enhanced galaxies. A larger galaxy sample is needed to confirm this scenario. Finally, the abundance ratios indicate short star formation timescales of 0.2–1.0 Gyr.

Mineral carbonate dissolution with increasing CO2 pressure measured by underwater laser induced breakdown spectroscopy and its application in carbon sequestration

In this study, the ability of laser-induced breakdown spectroscopy (LIBS) to measure the in situ aqueous dissolution of various mineral carbonates with increasing CO2 pressure was examined. Dissolution experiments included four geologically common mineral carbonates (CaCO3, MgCO3, MnCO3, SrCO3) and the CO2 pressure ranged from ambient to 250 bar. The ensuing plasma emission was spectrally analyzed, and the intensities of Ca, Mg, Mn, and Sr emission lines were used to monitor the respective metal cations released to the aqueous solution. The strong emission lines of Ca (Ca II 393.36, Ca II 396.84, Ca I 422.67 nm), Mg (unresolved magnesium doublet: Mg I 383.230, Mg I 383.829 nm), Mn (unresolved manganese triplet: Mn I 403.076, Mn I 403.307, Mn I 403.449 nm), and Sr (Sr II 407.77, Sr II 421.55, Sr I 460.73 nm) were identified in the spectra. The amounts of metals released from their respective carbonates were estimated at different time intervals following the CO2 injection (5 m, 1, 2, 3, 4, 24 h) and at different pressures (50, 100, 150, 200, 250 bar) using calibration models developed at corresponding pressure settings. The results demonstrated that the pressure-induced dissolution of all carbonates was consistent with their expected and selective pH-dependent solubility. The dissolution rate of CaCO3, MgCO3, and SrCO3 was found to be higher than that of MnCO3. The dissolution of constituents in a Mt. Simon sandstone associated with a deep saline reservoir at elevated CO2 pressure was also studied and Ca release was quantified. The results demonstrated that real-time monitoring of carbonate dissolution by LIBS may provide a useful indirect detection system indicative of CO2 leakage from geologic carbon storage sites.

Near-infrared Spectroscopy of Galaxies During Reionization: Measuring C iii] in a Galaxy at z = 7.5

Abstract We present Keck/MOSFIRE H-band spectroscopy targeting C iii] λ1907, 1909 in a z = 7.5056 galaxy previously identified via Lyα emission. We detect strong line emission at with a line flux of (2.63 ± 0.52) × 10−18 erg s−1 cm−2. We tentatively identify this line as [C iii] λ1907, but we are unable to detect C iii] λ1909 owing to sky emission at the expected location. This gives a galaxy systemic redshift, , with a velocity offset to Lyα of = 88 ± 27 km s−1. The ratio of combined C iii]/Lyα is 0.30–0.45, one of the highest values measured for any z &gt; 2 galaxy. We do not detect Si iii] λλ1883, 1892, and place an upper limit on Si iii]/C iii] &lt; 0.35 (2σ). Comparing our results to photoionization models, the C iii] equivalent width (W C iii] = 16.23 ± 2.32 Å), low Si iii]/C iii] ratio, and high implied [O iii] equivalent width (from the Spitzer/IRAC [3.6]–[4.5] ≃ 0.8 mag color) require subsolar metallicities (Z ≃ 0.1–0.2 Z ⊙) and a high ionization parameter, log U ≳ −1.5. These results favor models that produce higher ionization, such as the bpass models for the photospheres of high-mass stars, and that include both binary stellar populations and/or an IMF that extends to 300 M ⊙. The combined C iii] equivalent width and [3.6]–[4.5] color are more consistent with ionization from young stars than active galactic nuclei (AGNs); however, we cannot rule out ionization from a combination of an AGN and young stars. We make predictions for James Webb Space Telescope spectroscopy using these different models, which will ultimately test the nature of the ionizing radiation in this source.

Orbital parameters and period variation studies of the short-period eclipsing binaries FG Sct, VZ Lib and VZ Psc

We present eight sets of new light curves for binaries FG Sct, VZ Lib and VZ Psc, which are all contact eclipsing binaries with short orbital periods. We carried out our observations from 2016 to 2017 using the 60-cm telescope administered by National Astronomical Observatories, Chinese Academy of Sciences, the Holcomb Observatory at Butler University and the SARA-CT telescope in Chile. We firstly determined the orbital parameters of FG Sct using the O − C method and obtained photometric solutions utilizing the updated W-D program. We also studied its period variation and discovered that its orbital period is decreasing at a rate of 6.39(±0.24) × 10−8 d yr−1, which was likely caused by mass transfer from the primary component to the secondary component or angular momentum interchange between the two components via magnetic interactions. For VZ Lib and VZ Psc, we simultaneously analyzed their BV RI light curves in conjunction with the published radial velocities. In order to obtain the orbital parameters of VZ Lib, we also analyzed its period variation and revised cyclic change, which could be attributed to either the light-time effect due to a tertiary companion or magnetic activity cycle mechanism. We derived the periods of the tertiary component of VZ Lib to be 48.7(±0.1) yr or magnetic cycle to be 46.9(±1.9) yr. Strong emission lines at Ca ii H+K, Hα, Hβ, Hγ and Ca ii IRT were detected in the LAMOST spectra of VZ Psc, which imply chromospheric activities in this binary system.

X-Ray Observations of an Intermediate Polar V2400 Oph

Abstract Based on the X-ray observations from XMM-Newton and Suzaku satellites at four different epochs, we present temporal and spectral properties of an intermediate polar (IP) V2400 Oph (=RX J1712.6-2414). The X-ray variations are found to occur at the spin and synodic periods and are derived to be 929 s and 1003 s, respectively. The X-ray spectrum is strongly absorbed by a dense material with an average equivalent hydrogen column density of ∼5 × 1022 cm−2, which partially covers ∼46% of the X-ray source. Suzaku spectra in the 0.3–50 keV energy range are well explained by two temperature collisional equilibrium plasma emission models with its reflection from the cold matter. A soft X-ray emission is also seen in the X-ray spectrum of V2400 Oph and is well modeled by the blackbody with an average temperature of ∼98 eV. The partial covering absorbers and softness ratio are spin phase dependent indicating that the coverage of accretion curtains is variable. A strong emission line of fluorescent Fe Kα at 6.4 keV is also detected in the X-ray spectra. The central energy of Fe Kα appears to be redshifted and found to be modulated with the white dwarf (WD) rotation, where modulations are at minimum around the spin minimum, indicating that the redshifted line is originated from pre-shock accreting material via fluorescence. An attempt is also made to characterize the system and to understand the magnetic accretion flows using the present data of V2400 Oph.