Small Equivalent Width Research Articles

The Energetics of the Central Engine in the Powerful Quasar 3C 298

Abstract The compact steep-spectrum radio source 3C 298 (redshift of 1.44) has the largest 178 MHz luminosity in the Third Cambridge Revised Catalogue (3CR); its radio lobes are among the most luminous in the universe. The plasma state of the radio lobes is modeled with the aid of interferometric radio observations (in particular, the new Low Frequency Array observation and archival MERLIN data) and archival single-station data. It is estimated that the long-term time-averaged jet power required to fill these lobes with leptonic plasma is Q ¯ ≈ 1.28 ± 0.51 × 10 47 erg s − 1 , rivaling the largest time-averaged jet powers from any quasar. Supporting this notion of extraordinary jet power is a 0.5–10 keV luminosity of ≈ 5.2 × 1046 erg s−1, comparable to luminous blazars, yet there is no other indication of strong relativistic beaming. We combine two new high signal-to-noise ratio optical spectroscopic observations from the Hobby-Eberly Telescope with archival Hubble Space Telescope, Two Micron All Sky Survey, and Galaxy Evolutionary Explorer data to compute a bolometric luminosity from the accretion flow of L bol ≈ 1.55 ± 0.15 × 1047 erg s−1. The ratio, Q ¯ / L bol ≈ 1 , is the approximate upper limit for quasars. Characteristic of a large Q ¯ / L bol , we find an extreme-ultraviolet (EUV) spectrum that is very steep (the “EUV deficit” of powerful radio quasars relative to radio-quiet quasars), and this weak ionizing continuum is likely a contributing factor to the relatively small equivalent widths of the broad emission lines in this quasar.

A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with the Lyman Break Technique

Abstract We report a discovery of a z = 4.72 radio galaxy, HSC J083913.17+011308.1, using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) catalog for Very Large Array Faint Images of the Radio Sky at Twenty centimeter radio sources. The number of known high-z radio galaxies (HzRGs) at z > 3 is quite small to constrain the evolution of HzRGs so far. The deep and wide-area optical survey by HSC-SSP enables us to apply the Lyman break technique to a large search for HzRGs. For an HzRG candidate among pre-selected r-band dropouts with a radio detection, a follow-up optical spectroscopy with the Gemini Multi-Object Spectrographs (GMOS)/Gemini has been performed. The obtained spectrum presents a clear Lyα emission line redshifted to z = 4.72. The spectral energy distribution fitting analysis with the rest-frame UV and optical photometries suggests the massive nature of this HzRG with . The small equivalent width of Lyα and the moderately red UV colors indicate its dusty host galaxy, implying a chemically evolved and dusty system. The radio spectral index does not meet a criterion for an ultra-steep spectrum, of −1.1 and of −0.9, demonstrating that the HSC-SSP survey compensates for a subpopulation of HzRGs that are missed in surveys focusing on an ultra-steep spectral index.

Big Three Dragons: A z = 7.15 Lyman-break galaxy detected in [O iii] 88 μm, [C ii] 158 μm, and dust continuum with ALMA

Abstract We present new ALMA observations and physical properties of a Lyman break galaxy at z = 7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, MUV ≈ −22.4, and has been spectroscopically identified in Lyα with a small rest-frame equivalent width of ≈4 Å. A previous Hubble Space TElescope (HST) image has shown that the target is composed of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [O iii] 88 μm, [C ii] 158 μm, and their underlying dust continuum emission. In the whole system of B14-65666, the [O iii] and [C ii] lines have consistent redshifts of 7.1520 ± 0.0003, and the [O iii] luminosity, (34.4 ± 4.1) × 108 L⊙, is about three times higher than the [C ii] luminosity, (11.0 ± 1.4) × 108 L⊙. With our two continuum flux densities, the dust temperature is constrained to be Td ≈ 50–60 K under the assumption of a dust emissivity index of βd = 2.0–1.5, leading to a large total infrared luminosity of LTIR ≈ 1 × 1012 L⊙. Owing to our high spatial resolution data, we show that the [O iii] and [C ii] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by ≈200 km s−1. We also find these two clumps have comparable UV, infrared, [O iii], and [C ii] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major merger. The merger interpretation is also supported by the large specific star formation rate (defined as the star formation rate per unit stellar mass), sSFR $= 260^{+119}_{-57}\:$Gyr−1, inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [O iii]-to-[C ii] luminosity ratio.

Spatially Resolved MaNGA Observations of the Host Galaxy of Superluminous Supernova 2017egm

Abstract Superluminous supernovae (SLSNe) are found predominantly in dwarf galaxies, indicating that their progenitors have a low metallicity. However, the most nearby SLSN to date, SN 2017egm, occurred in the spiral galaxy NGC 3191, which has a relatively high stellar mass and correspondingly high metallicity. In this Letter, we present detailed analysis of the nearby environment of SN 2017egm using MaNGA IFU data, which provides spectral data on kiloparsec scales. From the velocity map we find no evidence that SN 2017egm occurred within some intervening satellite galaxy, and at the SN position most metallicity diagnostics yield a solar and above solar metallicity ( ). Additionally, we measure a small Hα equivalent width (EW) at the SN position of just 34 Å, which is one of the lowest EWs measured at any SLSN or gamma-ray burst position, and indicative of the progenitor star being comparatively old. We also compare the observed properties of NGC 3191 with other SLSN host galaxies. The solar-metallicity environment at the position of SN 2017egm presents a challenge to our theoretical understanding, and our spatially resolved spectral analysis provides further constraints on the progenitors of SLSNe.

Statistical properties of diffuse Lyα haloes around star-forming galaxies atz∼ 2

We present statistical properties of diffuse Lyman-alpha halos (LAHs) around high-$z$ star-forming galaxies with large Subaru samples of Lyman-alpha emitters (LAEs) at $z=2.2$. We make subsamples defined by the physical quantities of LAEs' central Lyman-alpha luminosities, UV magnitudes, Lyman-alpha equivalent widths, and UV slopes, and investigate LAHs' radial surface brightness (SB) profiles and scale lengths $r_n$ as a function of these physical quantities. We find that there exist prominent LAHs around LAEs with faint Lyman-alpha luminosities, bright UV luminosities, and small Lyman-alpha equivalent widths in cumulative radial Lyman-alpha SB profiles. We confirm this trend with the anti-correlation between $r_n$ and Lyman-alpha luminosities (equivalent widths) based on the Spearman's rank correlation coefficient that is $\rho=-0.9$ ($-0.7$) corresponding to the $96\%$ ($93\%$) confidence level, although the correlation between $r_n$ and UV magnitudes is not clearly found in the rank correlation coefficient. Our results suggest that LAEs with properties similar to typical Lyman-break galaxies (with faint Lyman-alpha luminosities and small equivalent widths) possess more prominent LAHs. We investigate scenarios for the major physical origins of LAHs with our results, and find that the cold stream scenario is not preferred, due to the relatively small equivalent widths up to $77$\AA\ in LAHs that include LAEs' central components. There remain two possible scenarios of Lyman-alpha scattering in circum-galactic medium and satellite galaxies that cannot be tested with our observational data.

An exploration of Pluto’s environment through stellar occultations

Context. Pluto has five known satellites with diameters ranging from ~1200 km down to ~40 km, a possible outcome of a collisional origin. Smaller objects probably exist and may maintain tenuous rings, thus representing hazards during the New Horizons flyby of July 2015. Aims. The goal is to provide an upper limit for the numbers of unseen small bodies and/or equivalent widths of putative Pluto rings. Methods. We use a Pluto stellar appulse on April 10, 2006, and a stellar occultation by the dwarf planet on June 14, 2007, to scan Pluto’s surroundings. Results. Our best data set places a 3σ upper limit of 0.3 km for the radius of isolated moonlets that we can detect. In the absence of detection, we derive an upper limit of 15 000 for the number of such bodies at distances smaller than ~70 000 km from Pluto’s system barycenter. We place a 3σ upper limit of typically 30−100 m for the equivalent width of ring material at barycentric distances ranging from 13 000 to 70 000 km. This limit applies for narrow rings only, i.e. less than about 10 km in width

MULTI-WAVELENGTH GOALS OBSERVATIONS OF STAR FORMATION AND ACTIVE GALACTIC NUCLEUS ACTIVITY IN THE LUMINOUS INFRARED GALAXY IC 883

New optical HST, Spitzer, GALEX, and Chandra observations of the single-nucleus, luminous infrared galaxy (LIRG) merger IC 883 are presented. The galaxy is a member of the Great Observatories All-sky LIRG Survey (GOALS), and is of particular interest for a detailed examination of a luminous late-stage merger due to the richness of the optically-visible star clusters and the extended nature of the nuclear X-ray, mid-IR, CO and radio emission. In the HST ACS images, the galaxy is shown to contain 156 optically visible star clusters distributed throughout the nuclear regions and tidal tails of the merger, with a majority of visible clusters residing in an arc ~ 3-7 kpc from the position of the mid-infrared core of the galaxy. The luminosity functions of the clusters have an alpha_F435W ~ -2.17+/-0.22 and alpha_F814W ~ -2.01+/-0.21. Further, the colors and absolute magnitudes of the majority of the clusters are consistent with instantaneous burst population synthesis model ages in the range of a few x10^7 - 10^8 yrs (for 10^5 M_sun clusters), but may be as low as few x10^6 yrs with extinction factored in. The X-ray and mid-IR spectroscopy are indicative of predominantly starburst-produced nuclear emission, and the star formation rate is ~ 80 M_sun / yr. The kinematics of the CO emission and the morphology of both the CO and radio emission are consistent with the nuclear starburst being situated in a highly inclined disk 2 kpc in diameter with an infrared surface brightness mu_IR ~ 2x10^11 L_sun kpc^-2, a factor of 10 less than that of the Orion star-forming region. Finally, the detection of the [Ne V] 14.32 um emission line is evidence that an AGN is present. The faintness of the line (i.e., [Ne V] / [Ne II] um ~ 0.01) and the small equivalent width of the 6.2 um PAH feature ($= 0.39\mu$m) are both indicative of a relatively weak AGN. (abridged)

Radio and X-ray emission from disc winds in radio-quiet quasars

It has been proposed that the radio spectra of radio-quiet quasars is produced by free-free emission in the optically thin part of an accretion disc wind. An important observational constraint on this model is the observed X-ray luminosity. We investigate this constraint using a sample of PG radio-quiet quasars for which XMM-Newton EPIC spectra are available. Comparing the predicted and measured luminosities for 0.5, 2 and 5 keV, we conclude that all of the studied PG quasars require a large hydrogen column density absorber, requiring these quasars to be close to or Compton-thick. Such a large column density can be directly excluded for PG 0050+124, for which a high-resolution RGS spectrum exists. Further constraint on the column density for a further 19 out of the 21 studied PG quasars comes from the EPIC spectrum characteristics such as hard X-ray power-law photon index and the equivalent width of the Fe Kalpha line; and the small equivalent width of the C IV absorber present in UV spectra. For 2 sources: PG 1001+054 and PG 1411+442 we cannot exclude that they are indeed Compton-thick, and the radio and X-ray luminosity are due to a wind originating close to the super-massive black hole. We conclude that for 20 out of 22 PG quasars studied free-free emission from a wind emanating from the accretion disc cannot mutually explain the observed radio and X-ray luminosity.

DUST PROCESSING AND GRAIN GROWTH IN PROTOPLANETARY DISKS IN THE TAURUS-AURIGA STAR-FORMING REGION

Mid-infrared spectra of 65 T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope are modeled using dust at two temperatures to probe the radial variation in dust composition in the uppermost layers of protoplanetary disks. Most spectra indicating crystalline silicates require Mg-rich minerals and silica, but a few suggest otherwise. Spectra indicating abundant enstatite at higher temperatures also require crystalline silicates at temperatures lower than those required for spectra showing high abundance of other crystalline silicates. A few spectra show 10 micron complexes of very small equivalent width. They are fit well using abundant crystalline silicates but very few large grains, inconsistent with the expectation that low peak-to-continuum ratio of the 10 micron complex always indicates grain growth. Most spectra in our sample are fit well without using the opacities of large crystalline silicate grains. If large grains grow by agglomeration of submicron grains of all dust types, the amorphous silicate components of these aggregates must typically be more abundant than the crystalline silicate components. Crystalline silicate abundances correlate positively with other such abundances, suggesting that crystalline silicates are processed directly from amorphous silicates and that neither forsterite, enstatite, nor silica are intermediate steps when producing either of the other two. Disks with more dust settling typically have greater crystalline abundances. Large-grain abundance is somewhat correlated with greater settling of disks. The lack of strong correlation is interpreted to mean that settling of large grains is sensitive to individual disk properties. Lower-mass stars have higher abundances of large grains in their inner regions.

Modeling of RO/NF membrane rejections of PhACs and organic compounds: a statistical analysis

Abstract. Rejections of pharmaceutical compounds (Ibuprofen, Diclofenac, Clofibric acid, Naproxen, Primidone, Phenacetin) and organic compounds (Dichloroacetic acid, Trichloroacetic acid, Chloroform, Bromoform, Trichloroethene, Perchloroethene, Carbontetrachloride, Carbontetrabromide) by NF (Filmtec, Saehan) and RO (Filmtec, Saehan, Toray, Koch) membranes were studied. Chloroform presented the lowest rejection due to small molar volume, equivalent width and length. Diclofenac and Primidone showed high rejections related to high molar volume and length. Dichloroacetic acid and Trichloroacetic acid presented good rejections caused by charge exclusion instead of steric hindrance mechanism influencing rejection. Bromoform and Trichloroethene showed low rejections due to small length and equivalent width. Carbontetrabromide, Perchloroethene and Carbontetrachloride with higher equivalent width than BF and TCE presented better rejections. A qualitative analysis of variables using Principal Component Analysis was successfully implemented for reduction of physical-chemical compound properties that influence membrane rejection of PhACs and organic compounds. Properties such as dipole moment, molar volume, hydrophobicity/hydrophilicity, molecular length and equivalent width were found to be important descriptors for simulation of membrane rejection. For membranes used in the experiments, we may conclude that charge repulsion was an important mechanism of rejection for ionic compounds. After analysis with Multiple Linear Regression, we also may conclude that membrane rejection of neutral compounds was well predicted by molar volume, length, equivalent width, hydrophobicity/hydrophilicity and dipole moment. Molecular weight was a poor descriptor variable for rejection modelling. We were able to provide acceptable statistical significance for important results.

Spectroscopy of the hot pulsating star β Cephei. Velocities and EWs from C, N, O and Si lines

Frequencies in oscillating β Cephei stars are usually inferred by means of radial velocities measured from the Si iii triplet λλ 4552–4574 Å. These lines, relatively insensitive to the variation of T eff through a pulsation cycle, show small equivalent width variations. In this study, we aimed to verify if the behavior of radial velocities and equivalent widths measured from other ions are compatible with the one observed from Si iii lines and than to verify the possible vertical stratification along the stellar atmosphere. For this reason we selected from our spectra a number of, unblended and well isolated, C ii, N ii and O ii lines besides the famous Si iii triplet. All those lines cover the range in optical depth between −2.1 and −0.5. Unfortunately, we did not find any differences in the radial velocities behavior line-by-line and then we derived the frequency of the principal radial mode combining all the velocities derived from each spectral line separately. The inferred frequency was f 1 = 5.249677 ± 0.000007 c d −1. Another important task we would like to accomplish with this paper is to make available to the community our large sample of spectroscopic data, that is 932 velocities and equivalent widths measured from our sample of C, N, O and Si lines. All the spectra were acquired at the 1-m class telescope of the stellar station of the INAF – Osservatorio Astrofisico di Catania, in the period starting from July, the 27th 2005 to November, the 1st 2006.

Infrared 3–4 μm Spectroscopic Investigations of a Large Sample of Nearby Ultraluminous Infrared Galaxies

We present infrared L-band (3-4 μm) nuclear spectra of a large sample of nearby ultraluminous infrared galaxies (ULIRGs). ULIRGs classified optically as non-Seyfert galaxies (LINERs, H II regions, and unclassified) are our main targets. Using the 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission and absorption features at 3.1 μm due to ice-covered dust and at 3.4 μm produced by bare carbonaceous dust, we search for signatures of powerful AGNs deeply buried along virtually all lines of sight. The 3.3 μm PAH emission, the signatures of starbursts, is detected in all but two non-Seyfert ULIRGs, but the estimated starburst magnitudes can account for only a small fraction of the infrared luminosities. Three LINER ULIRGs show spectra typical of almost pure buried AGNs, namely, strong absorption features with very small equivalent width PAH emission. Besides these three sources, 14 LINER and three H II ULIRGs' nuclei show strong absorption features whose absolute optical depths suggest an energy source more centrally concentrated than the surrounding dust, such as a buried AGN. In total, 17 out of 27 (63%) LINER and 3 out of 13 (23%) H II ULIRGs' nuclei show some degree of evidence for powerful buried AGNs, suggesting that powerful buried AGNs may be more common in LINER ULIRGs than in H II ULIRGs. The evidence of AGNs is found in non-Seyfert ULIRGs with both warm and cool far-infrared colors. These spectra are compared with those of 15 ULIRGs' nuclei with optical Seyfert signatures taken for comparison. The overall spectral properties suggest that the total amount of dust around buried AGNs in non-Seyfert ULIRGs is systematically larger than that around AGNs in Seyfert 2 ULIRGs. We argue that the optical (non)detectability of Seyfert signatures in ULIRGs is highly dependent on how deeply buried the AGNs are, and that it is essential to properly evaluate the energetic importance of buried AGNs in non-Seyfert ULIRGs.

Resolving the Fe xx v Triplet with Chan d r a in Centaurus X-3

We present the results of a 45 ks Chandra observation of the high-mass X-ray binary Cen X-3 at orbital phases between 0.13 and 0.40 (in the eclipse post-egress phases). Here we concentrate on the study of discrete features in the energy spectrum at energies between 6 and 7 keV, that is, on the iron Kα line region, using the High Energy Transmission Grating Spectrometer (HETGS) on board the Chandra satellite. We clearly see a Kα neutral iron line at ~6.40 keV and were able to distinguish the three lines of the Fe XXV triplet at 6.61, 6.67, and 6.72 keV, with equivalent widths of 6, 9, and 5 eV, respectively. The equivalent width of the Kα neutral iron line is 13 eV, an order of magnitude lower than previous measures. We discuss the possibility that the small equivalent width is due to a decrease of the solid angle subtended by the reflector.

Black hole mass estimation using a relation between the BLR size and emission line luminosity of AGN

An empirical relation between the broad line region (BLR) size and optical continuum luminosity is often adopted to estimate the BLR size and then the black hole mass of AGNs. However, optical luminosity may not be a good indicator of photoionizing luminosity for extremely radio-loud AGNs because the jets usually contribute significantly to the optical continuum. Therefore, the black hole masses derived for blazar-type AGNs with this method are probably overestimated. Here we first derived a tight empirical relation between the BLR size and the Hp emission line luminosity, R(light - days) = 24.05(L Hβ /10 42 ergs s -1 ) 0.68 , from a sample of 34 AGNs with the BLR size estimated with the reverberation mapping technique. Then we applied this relation to estimate the black hole masses of some AGNs and found that for many extremely radio-loud AGNs the black hole masses obtained with the R - L Hβ relation are systematically lower than those derived previously with the R - L 5100 A relation, while for radio-quiet and slightly radio-loud AGNs the results obtained with these two methods are almost the same. The difference of black hole masses estimated with these two relations increases with the radio-loudness for extremely radio-loud AGNs, which is consistent with the fact that their equivalent widths of the H β emission line become smaller at greater radio-loudness. If the small Hp equivalent widths of extremely radio-loud AGNs are indeed caused by the beaming effect, we argue that the optical emission line luminosity may be a better tracer of ionizing luminosity for blazar-type AGNs and the black hole masses derived with the R - L Hβ relation are probably more accurate.

Is there a disc in the superluminal quasars?

We look for the expected signature of an accretion disc by examining the properties of the Hα emission line versus viewing angle in a sample of 22 superluminal (SL) quasars. The Doppler factor δ, jet velocity γ and viewing angle θ towards the jet are derived from published radio and X-ray data. Most of the Hα spectra (14) have been observed at the United Kingdom Infrared Telescope (UKIRT) and are reported here. About a quarter of the SL objects have weak or absent Hα emission lines, with small equivalent widths (EW). These have high optical polarization, radio core dominance and Doppler factor, and most of them have high apparent SL velocity and low viewing angles. Therefore these weak-EW objects almost certainly have relativistically beamed optical continua. The strong-EW objects also show a clear beaming effect, but a much weaker one, with line EW varying by only a factor of 3 while radio core dominance varies by a factor of several hundred. The correlation of EW with θ is quantitatively in good agreement with the prediction of a flat accretion disc with limb darkening. The weak- and strong-EW sources also show an anticorrelation of line velocity width with the various beaming indicators. Again, the correlation with the derived viewing angle θ shows a quantitative agreement with the effect expected for an axisymmetric structure with velocity dominated by rotation. The line emission cannot come from the surface of the disc, or the line beaming would cancel the continuum beaming. However, it could come from an axisymmetric system of clouds corotating with the accretion disc.

The Effect of Vacuum Polarization and Proton Cyclotron Resonances on Photon Propagation in Strongly Magnetized Plasmas

We consider the effects of vacuum polarization and proton cyclotron resonances on the propagation of radiation through a strongly magnetized plasma. We analyze the conditions under which the photons evolve adiabatically through the resonant density and find that the adibaticity condition is satisfied for most photon energies of interest, allowing for a normal-mode treatment of the photon propagation. We then construct radiative equilibrium atmosphere models of strongly magnetized neutron stars that includes these effects, employing a new numerical method that resolves accurately the sharp changes of the absorption and mode-coupling cross sections at the resonant densities. We show that the resulting spectra are modified by both resonances and are harder at all field strengths than a blackbody at the effective temperature. We also show that the narrow absorption features introduced by the proton cyclotron resonance have small equivalent widths. We discuss the implications of our results for properties of thermal emission from the surfaces of young neutron stars.

Near-infrared line imaging of the starburst galaxies NGC 520, NGC 1614 and NGC 7714

We present high spatial resolution (0: 00 6) near{infrared broad{band JHK images and Br 2.1661 m and H2 1{0 S(1) 2.122 m emission line images of the nuclear regions in the interacting starburst galaxies NGC 520, NGC 1614 and NGC 7714. The near{infrared emission line and radio morphologies are in general agreement, although there are dierences in details. In NGC 1614, we detect a nuclear double structure in Br, in agreement with the radio double structure. We derive average extinctions of AK =0 .41 andAK =0 .18 toward the nuclear regions of NGC 1614 and NGC 7714, respectively. For NGC 520, the extinction is much higher, AK =1 :2 1:6. The observed H2/Br ratios indicate that the main excitation mechanism of the molecular gas is fluorescence by intense UV radiation from clusters of hot young stars, while shock excitation can be ruled out. The starburst regions in all galaxies exhibit small Br equivalent widths. Assuming a constant star formation model, even with a lowered upper mass cuto of Mu =3 0M, results in rather old ages (10 40 Myr), in disagreement with the clumpy near{infrared morphologies. We prefer a model of an instantaneous burst of star formation with Mu = 100 M, occurring6{7 Myr ago, in agreement with previous determinations and with the detection of W{R features in NGC 1614 and NGC 7714. Finally, we note a possible systematic dierence in the amount of hot molecular gas between starburst and Seyfert galaxies.

Near–Infrared Line Imaging of the Circumnuclear Starburst Ring in NGC 7771

We present high spatial resolution near-infrared broadband JHK images and, for the first time, Brγ 2.1661 μm and H2 1-0 S(1) 2.122 μm emission-line images of the circumnuclear star-forming ring (major axis diameter 7'' = 2 kpc) in the starburst galaxy NGC 7771. These data are used to investigate the morphology and extinction of the starburst ring and to study its star-forming properties and history by comparing the observed quantities with an evolutionary population synthesis model. The clumpy morphology of NGC 7771 varies strongly with wavelength, as a result of the combination of extinction (for which we derive an average value of AV = 2.8), emission from hot dust and red supergiants, and several stellar generations in the ring. Also, the ellipticity and the position angle of the ring depend on the wavelength. The starburst ring in NGC 7771 exhibits small Brγ equivalent widths. Assuming a constant star formation model with Mu = 100 M☉ results in very long lifetimes of the star-forming regions (up to 1 Gyr), in disagreement with the clumpy near-infrared morphology and the observed radio spectral index of NGC 7771. This situation is only slightly remedied by assuming a reduced upper mass cutoff (Mu = 30 M☉), resulting in ages between 8 and 180 Myr. We prefer an instantaneous star formation model with Mu = 100 M☉, which can explain the derived Brγ equivalent widths if a single starburst occurred 6-7 Myr ago. The main excitation mechanism of the molecular gas, based on the observed S(1)/Brγ ratio, appears to be excitation by UV radiation from hot young stars. We derive M 1900 M☉ for the mass of the excited H2.

SimultaneousEUVE/ASCA/RXTEObservations of NGC 5548

We present simultaneous observations by EUVE, ASCA, and RXTE of the type?1 Seyfert galaxy NGC?5548. These data indicate that variations in the EUV emission (at ~0.2 keV) appear to lead similar modulations in higher energy (1 keV) X-rays by ~10-30 ks. This is contrary to popular models which attribute the correlated variability of the EUV, UV and optical emission in type?1 Seyferts to reprocessing of higher energy radiation. This behavior instead suggests that the variability of the optical through EUV emission is an important driver for the variability of the harder X-rays which are likely produced by thermal Comptonization. We also compute the power density spectra at the various energy bands probed by these observations. Over 10-300 ks timescales, the emission in EUV shows about a factor of two greater rms variability than that of the 2-20 keV RXTE-PCA band?18. ? 1.4% versus 7.4 ? 0.6%. On longer timescales, we construct a PDS from 1-12 keV RXTE-ASM data which shows evidence for a break at about 6 ? 10-8 Hz. Furthermore, we find that the combined RXTE-ASM/PCA power spectrum is remarkably similar in shape to PDSs found for the low/hard states of Galactic black hole candidates such as Cygnus X-1. The implied scaling factor of ~106 is comparable to the expected mass ratio for these two objects. In addition, we investigate the spectral characteristics of the fluorescent iron K? line and Compton reflection emission. In contrast to prior measurements of these spectral features, we find that the iron K? line has a relatively small equivalent width (WK? ~ 100 eV) and that the reflection component is consistent with a covering factor which is significantly less than unity (?/2? ~ 0.4-0.5). Notably, although the 2-10?keV X-ray flux varies by ~?25% and the derived reflection fraction appears to be constant throughout our observations, the flux in the iron K? line is also constant. This behavior is difficult to reconcile in the context of standard Compton reflection models.

A Galaxy at [ITAL]z[/ITAL] = 5.34

We report the discovery of Lyman alpha emission from a galaxy at z=5.34, the first object at z>5 with a spectroscopically confirmed redshift. The faint continuum emission (m(8000A)=27 AB mag), relatively small rest-frame equivalent width of the emission line (rest equivalent width of 95A), and limits on the NV/Lya ratio suggest that this is a star-forming galaxy and not an AGN. The star-formation rates implied by the UV continuum emission and the Lyman alpha emission are (in the absence of dust extinction) fairly modest (about 6 Msun/yr for q0=0.5, H0=50). The continuum luminosity is similar to that of sub-L*(1500) star-forming galaxies at z~3, and the width of the Lyman alpha line yields an upper limit to the mass of < 2.6 x 10^{10} Msun. The strong emission line detected in this low-luminosity galaxy provides hope for the discovery of higher luminosity primeval galaxies at redshifts z>5.