Temperature Sensitive Emission Line Research Articles

Ionized gas in quiescent galaxies: Temperature measurement and constraint on the ionization source

In non-star-forming, passively evolving galaxies, regions with emission lines dominated by low-ionization species are classified as low-ionization emission regions (LIERs). The ionization mechanism behind such regions has long been a mystery. Active galactic nuclei (AGNs), which were once believed to be the source, have been found not to be the dominant mechanism, especially in regions distant from the galaxy nuclei. The remaining candidates, photoionization by post-asymptotic giant branch (pAGB) stars and interstellar shocks can only be distinguished with in-depth analysis. As the temperature predictions of these two models differ, temperature measurements can provide strong constraints on this puzzle. We selected a sample of 2795 quiescent red-sequence galaxies from the Sloan Digital Sky Survey IV (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. We divided the sample spectra into three groups based on the flux ratio, and utilized stacking techniques to improve the signal-to-noise ratio of the observed spectra. We determined the temperature of and through their temperature-sensitive emission line ratios. Subsequently, we compared the measured temperatures with predictions from different models. The results demonstrate consistency with the interstellar shock model with pre-shock density n = 1 $ and solar metallicity, thus supporting shocks as the dominant ionization source of LIERs. Additionally, we also find that the interstellar dust extinction value measured through the Balmer decrement appears to be larger than that implied by the forbidden line ratios of low-ionization lines.

Searching for metal-deficient emission-line galaxy candidates: the final sample of the SDSS DR12 galaxies

We present a spectroscopic study of metal-deficient dwarf galaxy candidates, selected from the SDSS DR12. The oxygen abundances were derived using the direct method in galaxies with the electron temperature-sensitive emission line [OIII]4363A measured with an accuracy better than 30%. The oxygen abundances for the remaining galaxies with larger uncertainties of the [OIII]4363A line fluxes were calculated using a strong-line semi-empirical method by Izotov and Thuan. The resulting sample consists of 287 low-metallicity candidates with oxygen abundances below 12+logO/H=7.65 including 23 extremely metal-deficient (XMD) candidates with 12+log O/H<7.35. Ten out of sixteen XMDs known so far (or ~60%) have been discovered by our team using the direct method. Three XMDs were found in the present study. We study relations between global parameters of low-metallicity galaxies, including absolute optical magnitudes, Hbeta luminosities (or equivalently star formation rates), stellar masses, mid-infrared colours, and oxygen abundances. Low-metallicity and XMD galaxies strongly deviate to lower metallicities in L-Z, L(Hbeta)-Z and Mstar-Z diagrams than in relations obtained for large samples of low-redshift, star-forming galaxies with non-restricted metallicities. These less chemically evolved galaxies with stellar masses ~10^6-10^8Msun, Hbeta luminosities ~10^38-10^41 erg/s, SFR~0.01-1.0Msun/yr, and sSFR~50 Gyr^-1 have physical conditions which may be characteristic of high-redshift low-mass star-forming galaxies which are still awaiting discovery.

New candidates for extremely metal-poor emission-line galaxies in the SDSS/BOSS DR10

We present a spectroscopic study of eight extremely low-metallicity candidate emission-line galaxies with oxygen abundances possibly below 12 +log O/H = 7.35. These galaxies were selected from Data Release 10 of the Sloan Digital Sky Survey/Baryon Oscillation Spectroscopic Survey (SDSS/BOSS DR10). We will call these extremely metal-deficient galaxies XMD galaxies. The electron temperature-sensitive emission line [O~{\sc iii}] $\lambda$4363 is detected in three galaxies and marginally detected in two galaxies, allowing for abundance determination by a "direct" method. Because of large uncertainties in the [O {\sc iii}]$\lambda$4363\AA\ line fluxes, we also calculated oxygen abundance in these galaxies together with the remaining three galaxies using a strong-line semi-empirical method. This method gives oxygen abundances higher than 7.35 for three galaxies with detected [O {\sc iii}]$\lambda$4363\AA\ line and lower than 7.35 for the remaining five objects of the sample. The newly-discovered galaxies represent excellent targets for follow-up spectroscopic observations with the largest telescopes to improve the oxygen abundance determination and to increase the number of these very rare low-metallicity objects. The extreme location of the most massive and luminous XMD galaxies and XMD candidates in the stellar mass-metallicity diagram implies that these galaxies may be genuine young objects. With stellar masses of up to $\sim$ 10$^7$ - 10$^8$$M_{\odot}$, the galaxies are not chemically enriched and strongly deviate to lower metallicity as compared to the relation obtained for a large sample of low-redshift, star-forming galaxies.

THERMAL STRUCTURE OF CORONAL LOOPS AS SEEN WITH NORIKURA CORONAGRAPH

The thermal structure of a coronal loop, both along and across the loop, is vital in determining the exact plasma heating mechanism. High resolution spectroscopic observations of the off-limb corona were made using 25 cm Norikura coronagraph, located at Norikura, Japan. Observations on a number of days, were made simultaneously in four forbidden iron emission lines namely, [Fe XI] 7892 \AA\ line, [Fe XIII] 10747 \AA & 10798 \AA\ lines and [Fe XIV] 5303 \AA\ line and on some days made only in [Fe XI] 7892 \AA\ and [Fe X] 6374 \AA\ lines. Using the temperature sensitive emission line ratios [Fe XIV] 5303 \AA/[Fe XIII] 10747 \AA, and [Fe XI] 7892 \AA/[Fe X] 6374 \AA\ we compute the electron temperatures along 18 different loop structures observed on different days. We find a significant negative temperature gradient in all the structures observed in Fe XIV and Fe XIII and a positive temperature gradient in the structures observed in Fe XI and Fe X. Combining these results with the previous investigations by Singh and his collaborators, we infer that the loop tops, in general, appear hotter when observed in colder lines and colder when observed in relatively hotter lines as compared to their coronal foot points. We suggest that this contrasting trend observed in the temperature variation along the loop structures can be explained by a gradual interaction of different temperature plasma. The exact mechanism responsible for this interaction needs further quest and has potential to constrain loop heating models.

Hunting for extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey: MMT and 3.5 m APO observations

We present 6.5-meter MMT and 3.5m APO spectrophotometry of 69 H II regions in 42 low-metallicity emission-line galaxies, selected from the Data Release 7 of the Sloan Digital Sky Survey to have mostly [O III]4959/Hbeta < 1 and [N II]6583/Hbeta < 0.1. The electron temperature-sensitive emission line [O III] 4363 is detected in 53 H II regions allowing a direct abundance determination. The oxygen abundance in the remaining 16 H II regions is derived using a semi-empirical method. The oxygen abundance of the galaxies in our sample ranges from 12 + log O/H ~ 7.1 to ~ 7.9, with 14 H II regions in 7 galaxies with 12 +log O/H < 7.35. In 5 of the latter galaxies, the oxygen abundance is derived here for the first time. Including other known extremely metal-deficient emission-line galaxies from the literature, e.g. SBS 0335-052W, SBS 0335-052E and I Zw 18, we have compiled a sample of the 17 most metal-deficient (with 12 +log O/H < 7.35) emission-line galaxies known in the local universe. There appears to be a metallicity floor at 12 +log O/H ~ 6.9, suggesting that the matter from which dwarf emission-line galaxies formed was pre-enriched to that level by e.g. Population III stars.

The M33 Metallicity Project: Resolving the Abundance Gradient Discrepancies in M33

We present a new determination of the metallicity gradient in M33, based on Keck LRIS measurements of oxygen abundances using the temperature-sensitive emission line [O III] λ4363 in 61 H II regions. These data approximately triple the sample of direct oxygen abundances in M33. We find a central abundance of 12 + log (O/H) = 8.36 ± 0.04 and a slope of –0.027 ± 0.012 dex kpc^−1, in agreement with infrared measurements of the neon abundance gradient but much shallower than most previous oxygen gradient measurements. There is substantial intrinsic scatter of 0.11 dex in the metallicity at any given radius in M33, which imposes a fundamental limit on the accuracy of gradient measurements that rely on small samples of objects. We also show that the ionization state of neon does not follow the ionization state of oxygen as is commonly assumed, suggesting that neon abundance measurements from optical emission lines require careful treatment of the ionization corrections.

The metallicity gradient of M 33: chemical abundances of H ii regions

Context. We present spectroscopic observations of a sample of 72 emission-line objects, including mainly H ii regions, in the spiral galaxy M 33. Spectra were obtained with the multi-object, wide field spectrograph AF2/WYFFOS at the 4.2 m WHT telescope. Line intensities, extinction, and electron density were determined for the whole sample of objects. Aims. The aim of the present work was to derive chemical and physical parameters of a set of H ii regions, and from them the metallicity gradient. Methods. Electron temperatures and chemical abundances were derived for the 14 H ii regions where both [O ii ]a nd [Oiii ]e mission line fluxes were measured, including the electron temperature sensitive emission line [O iii] 436.3 nm and in a few cases [N ii] 575.5 nm. The ionization correction factor (ICF) method was used to derive the total chemical abundances. Results. The presence of abundance gradients was inferred from the radial behaviour of several emission-line ratios, and accurately measured from chemical abundances directly derived in 14 H ii regions. The oxygen abundances of our H ii regions, located in the radial region from ∼ 2t o∼7.2 kpc, gave an oxygen gradient −0.054 ± 0.011 dex kpc −1 Conclusions. The overall oxygen gradient for M 33 obtained using ours and previous oxygen determinations in a large number of H ii regions with direct electron temperature determination as well as abundance in young stars presented a two slope shape: −0.19 dex kpc −1 for the central regions (R < 3 kpc), and −0.038 dex kpc −1 for the outer regions (R ≥ 3 kpc).

FORBIDDEN LINES OF [O I] IN THE HIGH-RESOLUTION OPTICAL SPECTRA OF PLANETARY NEBULAE

ABSTRACT Electron impact excitation rates for transitions in O I, calculated with the R-matrix code, are used to derive the electron temperature sensitive emission line ratio R = I(2s2p4 1D - 2s2 2p4 1S)/I(2s2 2p4 3P1,2 - 2x2 2p4 1D) = I(5577 A)/I(6300 + 6365 A), for a range of electron temperatures (Te = 5000 - 20000 K) and d 2ensities (ne = 104 - 106 cm-3) applicable to planetary nebulae. Experimental values of R for a number of planetaries have been measured from high resolution (~0.6 A FWHM) spectra obtained with the Hamilton Echelle spectrograph on the 3 m telescope at the Lick Observatory. These measurements should be particularly reliable, as the sample of planetaries was restricted to those with large enough radial velocities for the nebular [O I] 5577 A emission to be red- or blue-shifted from the atmospheric airglow feature by a sufficient amount for the former to be reliably determined. Electron temperatures deduced from the observed values of R are generally in good agreement with those derived from Te sensitive line ratios in other species, providing observational support for the accuracy of the atomic data adopted in the calculations.

Ca X line ratios in solar flares

Theoretical Ca X electron temperature sensitive emission line ratios, derived using electron excitation rates interpolated from accurateR-matrix calculations, are presented forR 1 =I(419.74 A)/I(574.02 A,),R 2 =I(411.65 A)/I(574.02 A),R 3 =I(419.74 A)/I(557.75 A), andR 4 =I(411.65 A)/I(557.75 A). A comparison of these with observational data for three solar flares, obtained by the Naval Research Laboratory's S082A slitless spectrograph on boardSkylab, reveals good agreement between theory and observation forR 1 andR 3 in one event, which provides limited support for the accuracy of the atomic data adopted in the analysis. However, in the other flares the observed values ofR 1 –R 4 are much larger than the theoretical high-temperature limits, which is probably due to blending of the 419.74 A line with Civ 419.71 A, and 411.65 A with possibly Ciii 411.70 A.

Electron temperature and density sensitive X-ray emission line ratios for CI XVI

Recently calculated electron impact excitation rates for transitions in helium-like CI XVI are used to derive the electron temperature sensitive emission line ratio G = [(x + y + z)/w] and the electron density sensitive ratio R = [z/(x + y)] where w, x, y and z are the resonance 1s2 1S0-1s2p 1P1, intercombination 1s2 1S0-1s2p 3P2,1 and forbidden 1s2 1S0-1s2s 3S1 transitions, respectively. These calculations, which differ from those of previous authors, are compared with experimental R and G ratios obtained from X-ray spectra from the JET (Joint European Torus) plasma, for which the electron temperature and density have been measured by independent methods. The R ratio is approximately in its low density limit (Ro) for this device and is therefore not electron density sensitive. However it does function as an electron temperature diagnostic as does the G ratio. A comparison is also made with the previously reported results from the Alcator-C tokamak, where the experimental results lie in the electron density sensitive region. The current results show good agreement between theory and observation, with discrepancies of typically 7% in Ro and 10% in G for JET, implying that the theoretical results may be applied to the analysis of remote plasma sources in order to derive values for these parameters, where no independent measurements exist. A departure from coronal equilibrium due to diffusion effects is taken into account for the JET plasma conditions, and the resulting non-coronal ionization balance is found to produce changes to the theoretical ratios at temperatures exceeding Tm.

A comparison of theoretical Sv emission line strengths with extreme ultraviolet observations of a sunspot

Electron impact excitation rates for transitions in the S v ion, calculated with theR-matrix code, are used to derive the electron temperature sensitive emission line ratiosR 1 =I(854.8 A)/I(786.9 A),R 2 =I(852.2 A)/I(786.9 A),R 3 =I(849.2 A)/I(786.9 A), andR 4 =I(1199.1 A)/I(786.9 A), which are found to be significantly different from previous estimates. A comparison of the present results with observational data for a sunspot obtained with the Harvard S-055 spectrometer on boardSkylab reveals generally good agreement between theory and experiment, except in the case ofR 1, which is probably due to blending in the 854.8 A feature. The possible effects of Lyman continuum absorption on the observed line ratios is briefly discussed.

The Comparison of Helium-Like Ion Emission Line Ratios with Solar X-Ray Spectral Data

AbstractElectron impact excitation rates recently calculated by Keenan, McCann and Kingston for transitions in the He-like ions Al XII, Si XIII and S XV are used to derive the electron temperature sensitive emission line ratio G and the density sensitive ratio R in its low density limit (Ro). These ratios are compared with those calculated by other authors and with the values obtained for solar flares using instruments on board the P78-1 and Solar Maximum Mission satellites. In general it is found that our results resolve discrepancies which currently exist between observation and theory, which provides experimental support for the methods and atonic data adopted in the present analysis.

Theoretical emission line strengths for the beryllium-like ion Sxiii compared to XUV observations of solar flares

A comparison of Skylab S082A observations for several solar flares with calculations of the electron temperature sensitive emission line ratio R1 = I(2s2p1P − 2s21S)/I(2s2p3P1 - 2s21S) = = I(256.68 A)/I(491.45 A) in Be-like SXIII reveals good agreement between theory and experiment, which provides observational support for the accuracy of the adopted atomic data. However, observed values of the electron density sensitive ratio R2 = I(2s2p1P − 2s21S)/I(2p23P2 - 2s2p3P2) = = I(256.68 A)/I(308.96 A) all lie below the theoretical high density limit, which is probably due to blending in the 308.96 A line.

Theoretical Siiv line ratios compared to extreme ultraviolet solar observations

New theoretical electron temperature sensitive emission line ratios in Siiv involving the 3d2D − 3p2P and 4s2S − 3p2P multiplets at ∼1125 and 816 A, respectively, are derived using recent R-matrix electron excitation rate calculations. A comparison of these with observational data for a solar active region at the limb obtained with the Harvard S-055 spectrometer on board Skylab reveals that there is good agreement between theory and observation for ratios that include the 2D3/2, 5/2 − 2P3/2 transition at 1128.3 A. This is in contrast to the findings of Keenan, Dufton, and Kingston (1986) and provides support for the atomic data adopted in the calculations. However, the 2D3/2 − 2P1/2 line at 1122.5 A appears to be severely blended, as suggested previously by Burton and Ridgeley (1970) and Feldman and Doschek (1977), as it leads to electron temperature estimates that differ significantly from that expected in ionisation equilibrium. The fact that the I(1122.5 A)/I(1128.3 A) intensity ratios determined from several flare spectra are closer to theory than that for the active region indicates that the blending is probably due to species with relatively low ionization potentials, as noted by Flower and Nussbaumer (1975). Electron temperatures deduced for a sunspot are much lower than that predicted from ionisation balance calculations, in agreement with earlier results, and imply that a cooling flow may be present.

Euv Emission Line Ratios for Si IV in the Solar Transition Region

AbstractTheoretical electron temperature sensitive emission line ratios in Si IV involving the 3d2D − 3p2P and 4s2S - 3p2P multiplets at ~1125A and 816A respectively are derived using R-matrix electron excitation rate calculations. A comparison of these with observational data for a solar active region obtained with the Harvard S-055 spectrometer on board Skylab reveals that there is good agreement between theory and observation for the ratio that includes the2D3/2, 5/2 −2p3/2 transition at 1128.3A. This is in contrast to the findings of Keenan, Dufton and Kingston, and provides support for the atomic data adopted in the calculations. However the2D3/2 −2pl/2 line at 1122.5A appears to be severely blended, as it leads to electron temperature estimates that differ significantly from that expected in ionisation equilibrium. The fact that the I(1122.5A)/I(1128.3A) intensity ratios determined from several flare spectra are closer to theory than that for the active region indicates that the blending is probably due to species with relatively low ionisation potentials, such as an Fe III transition at 1122.53A, as suggested previously by Burton and Ridgeley, and Feldman and Doschek. Electron temperatures deduced for a sunspot are much lower than that predicted from ionisation balance calculations, in agreement with earlier results, and imply that a cooling flow may be present.