Large Equivalent Width Research Articles

Effects of Dust Geometry in Lyα Galaxies atz= 4.41

Equivalent widths (EWs) observed in high-redshift Ly? galaxies could be stronger than the EW intrinsic to the stellar population if dust is present residing in clumps in the interstellar medium (ISM). In this scenario, continuum photons could be extinguished, while the Ly? photons would be resonantly scattered by the clumps, eventually escaping the galaxy. We investigate this radiative transfer scenario with a new sample of six Ly? galaxy candidates in the GOODS CDF-S, selected at -->z = 4.4 with ground-based narrowband imaging obtained at CTIO. Grism spectra from the HST PEARS survey confirm that three objects are at -->z = 4.4, and that another object contains an active galactic nucleus (AGN). If we assume the other five (non-AGN) objects are at -->z = 4.4, they have rest-frame EWs from 47 to 190 ?. We present results of stellar population studies of these objects, constraining their rest-frame UV with HST and their rest-frame optical with Spitzer. Out of the four objects which we analyzed, three objects were best fit to contain stellar populations with ages on the order of 1 Myr and stellar masses from -->3 ? 108 to -->1 ? 109 M?, with dust in the amount of -->A1200 = 0.9?1.8 residing in a quasi-homogeneous distribution. However, one object (with a rest -->EW ~ 150 ?) was best fit by an 800 Myr, -->6.6 ? 109 M? stellar population with a smaller amount of dust ( -->A1200 = 0.4) attenuating the continuum only. In this object, the EW was enhanced ~50% due to this dust. This suggests that large EW Ly? galaxies are a diverse population. Preferential extinction of the continuum in a clumpy ISM deserves further investigation as a possible cause of the overabundance of large-EW objects that have been seen in narrowband surveys in recent years.

Deep Spectroscopy of Systematically Surveyed Extended Lyα Sources atz∼ 3–5

Spatially extended Lyα sources that are faint and/or compact in continuum are candidates for extremely young (107 yr) galaxies at high redshifts. We present medium-resolution ( -->R ~ 2000) VLT/VIMOS spectroscopy of 18 such extended Lyα sources found in our previous study at -->z ~ 3-5. The deep spectroscopy showed that all 18 objects have large equivalent widths (EWs), exceeding 100 A in the rest frame. For about 30% of our sample (five objects), we identified conspicuous asymmetry in the profile of the Lyα line. They show broad wing emission components on the red side, and a sharp cutoff on the blue side of the Lyα line. Such asymmetry is often seen in superwind galaxies, and is also consistent with the theoretical prediction of superwinds. In fact, one of them shows systematic velocity structure in the two-dimensional spectrum, suggesting the existence of superwind activity. There are eight objects ( -->8/18 ~ 40% ) that have very large EWs, exceeding 200 A (rest frame), and no clear signature of superwind activities. Such large EWs cannot be explained in terms of photoionization by a moderately old (>107 yr) stellar population, even with a top-heavy IMF or an extremely low metallicity. These eight objects clearly show a positive correlation between the Lyα line luminosity and the velocity width. This suggests that these eight objects are good candidates for forming galaxies in a gas-cooling phase (cold accretion).

Very massive stars in high-redshift galaxies

A significant fraction of Lyα-emitting galaxies (LAEs) at z ≥ 5.7 have rest-frame equivalent widths (EWs) greater than ∼100 A. However, only a small fraction of the Lyα flux produced by a galaxy is transmitted through the intergalactic medium, which implies intrinsic Lyα EWs that are in excess of the maximum allowed for a Population II stellar population having a Salpeter mass function. In this paper, we study characteristics of the sources powering Lyα emission in high-redshift galaxies. We propose a simple model for Lyα emitters in which galaxies undergo a burst of very massive star formation that results in a large intrinsic EW, followed by a phase of Population II star formation with a lower EW. We confront this model with a range of high-redshift observations and find that the model is able to simultaneously describe the following eight properties of the high-redshift galaxy population with plausible values for parameters like the efficiency and duration of star formation: (i)-(iv) the ultraviolet and Lyα luminosity functions of LAEs at z = 5.7 and 6.5, (v)-(vi) the mean and variance of the EW distribution of Lyα-selected galaxies at z = 5.7, (vii) the EW distribution of i-drop galaxies at z ∼ 6, and (viii) the observed correlation of stellar age with EW. Our modelling suggests that the observed anomalously large intrinsic EWs require a burst of very massive star formation lasting no more than a few to 10 per cent of the galaxy's star-forming lifetime. This very massive star formation may indicate the presence of Population III star formation in a few per cent of i-drop galaxies, and in about half of the Lyα-selected galaxies. © 2007 RAS.

Be stars and binaries in the field of the SMC open cluster NGC 330 with VLT-FLAMES

Observations of hot stars belonging to the young cluster SMC-NGC330 and its surrounding region were obtained with the VLT-GIRAFFE facilities in MEDUSA mode. We investigated the B and Be star properties and proportions in this environment of low metallicity. We also searched for rapid variability in Be stars using photometric databases. With spectroscopic measurements we characterized the emission and properties of Be stars. By cross-correlation with photometric databases such as MACHO and OGLE, we searched for binaries in our sample of hot stars, as well as for short-term variability in Be stars. We report on the global characteristics of the Be star sample (131 objects). We find that the proportion of early Be stars with a large equivalent width of the Halpha emission line is higher in the SMC than in the LMC and MW. We find a slight increase in the proportion of Be stars compared to B-type stars with decreasing metallicity. We also discovered spectroscopic and photometric binaries, and for the latter we give their orbital period. We identify 13 Be stars with short-term variability. We determine their period(s) and find that 9 Be stars are multiperiodic.

The Ages and Masses of Lyα Galaxies atz∼ 4.5

We examine the stellar populations of a sample of 98 redshift 4.5 Lyman alpha emitting galaxies using their broadband colors derived from deep photometry at the MMT. These galaxies were selected by narrowband excess from the Large Area Lyman Alpha survey. Twenty-two galaxies are detected in two or more of our MMT filters (g', r', i' and z'). By comparing broad and narrowband colors of these galaxies to synthetic colors from stellar population models, we determine their ages and stellar masses. The highest equivalent width objects have an average age of 4 Myr, consistent with ongoing star formation. The lowest EW objects show an age of 40 - 200 Myr, consistent with the expectation that larger numbers of stars are causing low EWs. We found masses ranging from 2e7 solar masses for the youngest objects in the sample to 2e9 solar masses for the oldest. It is possible that dust effects could produce large equivalent widths even in older populations by allowing the Lyman alpha photons to escape, even while the continuum is extinguished, and we present models for this scenario also.

High-redshift Ly$\mathsf{\alpha}$ emitters with a large equivalent width

We report new follow-up spectroscopy of -dropout galaxies with an NB921-band depression found in the Subaru Deep Field. The NB921-depressed -dropout selection method is expected to select galaxies with large equivalent-width Lyα emission over a wide redshift range, . Two of four observed targets show a strong emission line with a clear asymmetric profile, identified as Lyα emitters at z = 6.11 and 6.00. Their rest-frame equivalent widths are 153 and 114 , which are lower limits on the intrinsic equivalent widths. Through our spectroscopic observations (including previous ones) of NB921-depressed -dropout galaxies, we identified 5 galaxies in total with a rest-frame equivalent width larger than 100 at out of 8 photometric candidates, which suggests that the NB921-depressed -dropout selection method is possibly an efficient way to search for Lyα emitters with a large Lyα equivalent width, in a wider redshift range than with usual narrow-band excess techniques. By combining these findings with our previous observational results, we infer that the fraction of broad-band selected galaxies having a rest-frame equivalent width larger than 100 is significantly higher at (the cosmic age of ~1 Gyr) than that at (~2 Gyr), being consistent with the idea that the typical stellar population of galaxies is significantly younger at than that at . The NB921-depressed -dropout galaxies may be interesting candidates for hosts of massive, zero-metallicity Population III stars.

The XMM-Newton/INTEGRAL monitoring campaign of IGR J16318-4848

IGR J16318-4848 is the prototype and one of the more extreme examples of the new class of highly obscured Galactic X-ray sources discovered by INTEGRAL. A monitoring campaign on this source has been carried out by XMM-Newton and INTEGRAL, consisting in three simultaneous observations performed in February, March and August 2004. The long-term variability of the Compton-thick absorption and emission line complexes will be used to probe the properties of the circumstellar matter. A detailed timing and spectral analysis of the three observations is performed, along with the reanalysis of the XMM-Newton observation performed in February 2003. The results are compared with predictions from numerical radiative transfer simulations to derive the parameters of the circumstellar matter. Despite the large flux dynamic range observed (almost a factor 3 between observations performed a few months apart), the source remained bright (suggesting it is a persistent source) and Compton-thick (NH >1.2x10^24 cm-2). Large Equivalent Width (EW) emission lines from Fe Kalpha, Fe Kbeta and Ni Kalpha were present in all spectra. The addition of a Fe Kalpha Compton Shoulder improves the fits, especially in the 2004 observations. Sporadic occurrences of rapid X-ray flux risings were observed in three of the four observations. The Fe Kalpha light curve followed the continuum almost instantaneously, suggesting that the emission lines are produced by illumination of small-scale optically-thick matter around the high-energy continuum source. Using the iron line EW and Compton Shoulder as diagnostic of the geometry of the matter, we suggest that the obscuring matter is in a flattened configuration seen almost edge-on.

Systematic Survey of Extended Lyα Sources overz∼ 3–5

Spatially extended Ly-alpha sources which are faint and compact in coninuum are candidates for extremely young galaxies (age of ~<10e+7 yrs) at high redshifts. We carried out a systematic survey for extended Ly-alpha sources, using deep intermediate-band imaging data taken with the Suprime-Cam on the Subaru Telescope. Our survey covers a field of view of 33' * 25' and a redshift range of 3.24<z<4.95, down to a Ly-alpha flux of ~1e-17 ergs/cm^2/s. We identified 41 extended Ly-alpha sources. The redshift distribution of these sources shows that this kind of objects are common in the early universe over the surveyed redshift range. The identified objects have typical sizes of \~10-15 kpc and luminosities of ~10^42 ergs/s. Follow-up spectroscopy made for 7 of the 41 objects showed that our sample suffers from little contamination. All 7 objects have large equivalent widths of Ly-alpha emission line, all but one exceeding 240A in the rest frame. The large equivalent widths suggest that their extended Ly-alpha emissions are unlikely to be due to normal starbursts, but possibly originated from very young galaxies. All 41 objects in our sample have much smaller Ly-alpha luminosities than the two Ly-alpha Blobs (LABs) found by Steidel et al. (2000) in spite of our much larger survey volume. This suggests that large and luminous extended Ly-alpha objects like the two LABs are very rare and are clustered in overdense regions.

An observational pursuit for Pop III stars in a Lyα emitter at z&gt;6 through He II emission

AbstractWe report our on-going observational project to search for population III (Pop III) stars in high-z galaxies. We searched Lyα emitters (LAEs) with a large equivalent width (EW), by our new selection technique ‘NB921-depressed i′-dropout selection’. We found eight photometric candidates and spectroscopically identified five LAEs with EW0(Lyα) &gt; 100 Å. We then carried out a very deep near-infrared spectroscopy for a LAE among the above five, to search for the redshifted He iiλ1640 emission from Pop III stars in the galaxy, but obtained only an upper limit.

Exploring the spectroscopic diversity of Type Ia supernovae

The velocities and equivalent widths (EWs) of a set of absorption features are measured for a sample of 28 well-observed Type Ia supernovae (SNe Ia) covering a wide range of properties. The values of these quantities at maximum are obtained through interpolation/extrapolation and plotted against the decline rate, and so are various line ratios. The SNe are divided according to their velocity evolution into three classes defined in a previous work of Benetti et al.: low velocity gradient (LVG), high velocity gradient (HVG) and FAINT. It is found that all the LVG SNe have approximately uniform velocities at B maximum, while the FAINT SNe have values that decrease with increasing Δm 15 (B) and the HVG SNe have a large spread. The EWs of the Fe-dominated features are approximately constant in all SNe, while those of intermediate mass element (IME) lines have larger values for intermediate decliners and smaller values for brighter and FAINT SNe. The HVG SNe have stronger Si II 60355-A lines, with no correlation with Δm 15 (B). It is also shown that the Si II 5972 A EW and three EW ratios, including one analogous to the R(Si II) ratio introduced by Nugent et al., are good spectroscopic indicators of luminosity. The data suggest that all LVG SNe have approximately constant kinetic energy, since burning to IME extends to similar velocities. The FAINT SNe may have somewhat lower energies. The large velocities and EWs of the IME lines of HVG SNe appear correlated with each other, but are not correlated with the presence of high-velocity features in the Ca II infrared triplet in the earliest spectra for the SNe for which such data exist.

Deficiency of Large Equivalent Width Lyα Emission in Luminous Lyman Break Galaxies at z ~ 5-6?

We report a deficiency of luminous Lyman break galaxies (LBGs) with a large rest-frame equivalent width (EWrest) of Lyα emission at z ~ 5-6. Combining our spectroscopic sample of LBGs at z ~ 5 and those from the literature, we found that luminous LBGs at z ~ 5-6 generally show weak Lyα emissions, while faint LBGs show a wide range of Lyα EWrest and tend to have strong (EWrest 20 A) Lyα emissions; i.e., there is a deficiency of strong Lyα emission in luminous LBGs. There seems to be a threshold UV luminosity for the deficiency; it is M1400 = -21.5 to -21.0 mag, which is close to or somewhat brighter than the M* of the UV luminosity function at z ~ 5 and 6. Since the large EWrest of Lyα emission can be seen among the faint LBGs, the ratio of Lyα emitters to LBGs may change rather abruptly with the UV luminosity. If the weakness of Lyα emission is due to dust absorption, the deficiency suggests that luminous LBGs at z = 5-6 tend to be in dusty and more chemically evolved environments and that they begin star formation earlier than faint LBGs, although other causes cannot be ruled out.

X‐Ray Emission from Megamaser Galaxy IC 2560

Observation of the H{sub 2}O megamaser galaxy IC 2560 with the Chandra Observatory reveals a complex spectrum composed of soft X-ray emission due to multi-temperature thermal plasma, and a hard continuum with strong emission lines. The continuum is most likely a Compton reflection (reprocessing) of primary emission that is completely absorbed at least up to 7 keV. The lines can be identified with fluorescence from Si, S and Fe in the lowest ionization stages. The equivalent widths of the Si and S lines are broadly compatible with those anticipated for reprocessing by optically thick cold plasma of Solar abundances, while the large equivalent width of the Fe line requires some overabundance of iron. A contribution to the line from a transmitted component cannot be ruled out, but the limits on the strength of the Compton shoulder make it less likely. From the bolometric luminosity of the nuclear region, we infer that the source radiates at 1-10% of its Eddington luminosity, for an adopted central mass of 3 x 10{sup 6} M{sub {circle_dot}}. The overall spectrum is consistent with the hypotheses that the central engines powering the detected megamsers in accretion disks are obscured from direct view by the associated accretion disk material itself, and that there is a correlation between the occurrence of megamaser emission and Compton-thick absorption columns. For the 11 known galaxies with both column density measurements and maser emission believed to arise from accretion disks, eight AGN are Compton thick.

X-ray obscuration and obscured AGN in the local universe

We discuss the X-ray properties of 49 local ($z Chandra and XMM-Newton observations, which yield 25 (22) new X-ray detections in the 0.5–2 keV (2–10 keV) energy band. Our sample covers a range in the 2–10 keV observed flux, F 2-10 , from $3 \times 10^{-11}$ to $6 \times 10^{-15}$ erg cm -2 s -1 . The percentage of objects that are likely obscured by Compton-thick matter (column density, $N_{\rm H} \ge \sigma_t^{-1} \simeq 1.6 \times 10^{24}$ cm -2 ) is $\simeq$50%, and reaches $\simeq$80% for $\log\, (F_{2-10}) α fluorescent iron lines with large Equivalent Width (${\it EW} > 0.6$ keV) are common in our sample (6 new detections at a confidence level ≥ 2 σ ). They are explained as due to reflection off the illuminated side of optically thick material. We confirm a correlation between the presence of a ~100-pc scale nuclear dust in the WFC2 images and Compton-thin obscuration. We interpret this correlation as due to the large covering fraction of gas associated with the dust lanes. The X-ray spectra of highly obscured AGN invariably present a prominent soft excess emission above the extrapolation of the hard X-ray component. This soft component can account for a very large fraction of the overall X-ray energy budget. As this component is generally unobscured – and therefore likely produced in extended gas structures – it may lead to a severe underestimation of the nuclear obscuration in $z \sim 1$ absorbed AGN, if standard X-ray colors are used to classify them. As a by-product of our study, we report the discovery of a soft X-ray, luminous ($\simeq$7$\,\times\, 10^{40}$ erg s -1 ) halo embedding the interacting galaxy pair Mkn 266.

Dust properties of UV bright galaxies atz~ 2

We investigate the properties of the extinction curve in the rest-frame UV for a sample of 34 UV-luminous galaxies at $2 -0.4$ a significant 2175 A absorption feature (or “UV bump”) is inferred, indicating an LMC-like extinction curve. On the other hand, the UV continua of the least reddened objects are mostly consistent with SMC-like extinction curves, lacking a significant UV bump, as for the sample of local starbursts investigated by Calzetti and collaborators. Furthermore, the most opaque ($\beta \sim 0$) and, thus (for our models), dustiest UV-luminous FDF galaxies tend to be among the most metal-rich, most massive, and largest systems at $z \sim 2$, indicating $\langle Z \rangle \sim 0.5 {-} 1$ $Z_{\odot}$, $\langle M_{\rm stars} \rangle \sim 6 \times 10^{10}$ $M_{\odot}$, and $\langle R_{\rm eff} \rangle \sim 4$ kpc, respectively. The presence of the UV bump does not seem to depend on the total metallicity, as given by the equivalent width (EW) of the C IV doublet. Conversely, it seems to be associated with a large average EW of the six most prominent interstellar low-ionisation absorption lines falling in the FORS spectra. The average EW of these saturated lines offers a proxy for the ISM topology. We interpret these results as the evidence for a difference in the properties of the dusty ISM among the most evolved UV-luminous, massive galaxies at $z \sim 2$.

Spectroscopy of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $i^{\prime }$ \end{document} ‐Dropout Galaxies with an NB921‐Band Depression in the Subaru Deep Field

We report new spectroscopy of two star-forming galaxies with strong Lyα emission at z = 6.03 and 6.04 in the Subaru Deep Field. These two objects are originally selected as i'-dropouts (i' - z' > 1.5) showing an interesting photometric property, the "NB921 depression." The NB921-band (centered at 9196 Å) magnitude is significantly depressed with respect to the z'-band magnitude. The optical spectra of these two objects exhibit asymmetric emission lines at λobs ~ 8540 and ~8560 Å, suggesting that these objects are Lyα emitters at z ~ 6. The rest-frame equivalent widths of the Lyα emission of the two objects are 94 and 236 Å; the latter is the Lyα emitter with the largest Lyα equivalent width at z ≳ 6 ever spectroscopically confirmed. The spectroscopically measured Lyα fluxes of these two objects are consistent with the interpretation that the NB921 depression is caused by the contribution of the strong Lyα emission to the z'-band flux. Most of the NB921-depressed i'-dropout objects are thought to be strong Lyα emitters at 6.0 ≲ z ≲ 6.5; Galactic L and T dwarfs and NB921-dropout galaxies at z > 6.6 do not dominate the NB921-depressed i'-dropout sample. Thus, the NB921-depression method is very useful for finding high-z Lyα emitters with a large Lyα equivalent width over a large redshift range, 6.0 ≲ z ≲ 6.5. Although the broadband-selected sample at z ~ 3 contains only a small fraction of objects with a Lyα equivalent width larger than 100 Å, the i'-dropout sample of the Subaru Deep Field contains a much larger fraction of such strong Lyα emitters. This may imply a strong evolution of the Lyα equivalent width from z ≳ 6 to z ~ 3.

X‐Ray Observations of V4641 SGR (SAX J1819.3−2525) during the Brief and Violent Outburst of 2003

We present the results of detailed analysis of pointed X-ray observations by RXTE of the black hole X-ray binary (BHXRB) system V4641 Sgr (SAX J1819.3-2525) during its outburst of 2003 August. Soft X-ray (3-20 keV) flux variations by factors of 10 or more on timescales of minutes or shorter were seen. The rapid and strong variability of this source sets it apart from typical XRBs. In spite of large luminosity fluctuations, the spectral state of the source did not change significantly during the dwells, which suggests that the physical emission processes did not change much during the observations. The energy spectra during the dwells were dominated by a hard Comptonized power-law component, indicative of the canonical low/hard state observed in other BHXRBs. No soft thermal component was found in three out of the four RXTE pointings. However, spectral deconvolution of the observation with the largest average luminosity suggests an obscured, hot accretion disk. During one of the observations, we detected a short-term (~100 s) soft X-ray dropout, which is apparently due to variability in the observed column density. A strong Fe Kα fluorescent emission line near 6.5 keV was detected with large equivalent widths in the range 700-1000 eV. In the temporal domain, the Fourier power spectra were dominated by red noise below a few hertz. Poisson noise dominated at higher frequencies, and no high-frequency features were detected. The strong Comptonized spectra, broad iron emission line, absence of a disk component in the spectra, absence of any timing variability above a few hertz, and occasional large changes in the column density along the line of sight all support an enshrouded black hole with occasional outflow and a very dynamic environment.

Ly+ and ultraviolet emission from high-redshift gamma-ray burst hosts: to what extent do gamma-ray bursts trace star formation?

We report the result of a search for Lyα emission from the host galaxies of the gamma-ray bursts (GRBs) 030226 (z= 1.986), 021004 (z= 2.335) and 020124 (z= 3.198). We find that the host galaxy of GRB 021004 is an extended (around 8 kpc) strong Lyα emitter with a rest-frame equivalent width (EW) of 68+12−11Å, and a star formation rate of 10.6 ± 2.0 M⊙ yr−1. We do not detect the hosts of GRB 030226 and GRB 020124, but the upper limits on their Lyα fluxes do not rule out large rest-frame EWs. In the fields of GRB 021004 and GRB 030226 we find seven and five other galaxies, respectively, with excess emission in the narrow-band filter. These galaxies are candidate Lyα-emitting galaxies in the environment of the host galaxies. We have also compiled a list of all z≳ 2 GRB hosts, and demonstrate that a scenario where they trace star formation in an unbiased way is compatible with current observational constraints. Fitting the z= 3 luminosity function (LF) under this assumption results in a characteristic luminosity of R*= 24.6 and a faint-end slope of α=−1.55, consistent with the LF measured for Lyman-break galaxies.

Discovery of Extremely Embedded X‐Ray Sources in the R Coronae Australis Star‐forming Core

We detected three extremely embedded X-ray sources in the R Corona Australis (R CrA) star forming core, IRS 7 region. Two weak X-ray sources are associated with the VLA centimeter radio sources 10E & W, whereas the third brightest source detected in the two XMM-Newton observations on March 2003 has no counterpart at any wavelengths. The large K-band upper-limit (19.4m) measured with the University of Hawaii 88-inch Telescope and strong absorption derived in X-rays (N(sub H) approx. 2.8 x 10(exp 23)/sq cm equivalent to A(sub v) approx. 180 m) indicate that the source is younger than typical Class I protostars, i.e. a Class 0 protostar or an intermittent phase between Class 0 and Class I protostars. The X-ray luminosity was less than one thirtieth (log L(sub x) less than or approx. equals 29.3 ergs/s) in the former Chandra observation in October 2000, which suggests that the X-ray activity, probably generated by magnetic activity, is triggered by an intermittent mass accretion episode such as FU Ori type outbursts. Because the source was detected at high significance in the XMM-Newton observations (approx. 2,000 cnts), X-ray properties of such young protostars can be well investigated for the first time. The light curves were constant in the 1st observation and increased linearly by a factor of two during 30 ksec in the 2nd observation. Both spectra showed iron K lines originated in hot thin-thermal plasma and fluorescence by cold gas. They can be reproduced by an absorbed thin-thermal plasma model with a Gaussian component at 6.4 keV (kT approx. 3-4 keV, L(sub x) approx. 7-20 x 10(exp 30) ergs/s). The rising timescale of the light curves in the 2nd observation was too slow for magnetically generated X-ray flares, whereas large equivalent width of the fluorescence iron K line in the 1st observation (approx. 810 eV) requires strong partial covering of the X-ray source. These results suggest that a confined hot (perhaps accretion) spot on the protostellar core was behind the star in the 1st observation and just appeared in the 2nd observation due to the core rotation with period of greater than or approx. 22.8 days, which is much slower than the break-up velocity previously assumed for young protostars. This means that the source had quiescent X-ray activity during the observations with an order of magnitude stronger level than Class I (older) protostars. We also consider whether the X-ray source associated with 10E could be shock heated plasma by a collision of a jet emanating from the tentative Class 0 object.

Spectroscopic Properties of thez≈ 4.5 Lyα Emitters

We present Keck Low Resolution Imaging Spectrometer optical spectra of 17 Lyα-emitting galaxies and one Lyman break galaxy at z ≈ 4.5 discovered in the Large Area Lyman Alpha survey. The survey has identified a sample of ~350 candidate Lyα-emitting galaxies at z ≈ 4.5 in a search volume of 1.5 × 106 comoving Mpc3. We targeted 25 candidates for spectroscopy; hence, the 18 confirmations presented herein suggest a selection reliability of 72%. The large equivalent widths (median W ≈ 80 A) but narrow physical widths (Δv 240 A, exceeding the maximum Lyα equivalent width predicted for normal stellar populations. Nonetheless, we find no evidence for He II λ1640 emission in either individual or composite spectra, indicating that although these galaxies are young, they are not truly primitive, Population III objects.

Spectral Features in the Thermal Emission from Isolated Neutron Stars: Dependence on Magnetic Field Strengths

We study several effects that influence the strength of the proton cyclotron and atomic features in the thermal spectra of magnetic neutron stars. We show that it is possible for vacuum polarization to strongly suppress the spectral lines when the magnetic field B 1014 G. For weaker fields (B 7 × 1013 G), the surface spectrum is unaffected by vacuum polarization; thus, the proton cyclotron absorption line can have a large equivalent width. Using an approximate calculation of the synthetic spectra, we show that variation of magnetic fields over the neutron star surface leads to broadening of the line. The recently detected absorption features from the isolated neutron stars RX J1308.6+2127, RX J1605.3+3249, and RX J0720.4-3125 can plausibly be explained by the proton cyclotron resonance, with possible blending due to atomic transitions, in the atmosphere of the star.