Single Emission Line Research Articles

The Survey for Ionization in Neutral Gas Galaxies. I. Description and Initial Results

We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG), a census of star formation in HI-selected galaxies. The survey consists of H-alpha and R-band imaging of a sample of 468 galaxies selected from the HI Parkes All Sky Survey (HIPASS). The sample spans three decades in HI mass and is free of many of the biases that affect other star forming galaxy samples. We present the criteria for sample selection, list the entire sample, discuss our observational techniques, and describe the data reduction and calibration methods. This paper focuses on 93 SINGG targets whose observations have been fully reduced and analyzed to date. The majority of these show a single Emission Line Galaxy (ELG). We see multiple ELGs in 13 fields, with up to four ELGs in a single field. All of the targets in this sample are detected in H-alpha indicating that dormant (non-star forming) galaxies with M(HI) > ~3e7 M_sun are very rare. A database of the measured global properties of the ELGs is presented. The ELG sample spans four orders of magnitude in luminosity (H-alpha and R-band), and H-alpha surface brightness, nearly three orders of magnitude in R surface brightness and nearly two orders of magnitude in H-alpha equivalent width (EW). The surface brightness distribution of our sample is broader than that of the Sloan Digital Sky Survey spectroscopic sample, the (EW) distribution is broader than prism-selected samples, and the morphologies found include all common types of star forming galaxies (e.g. irregular, spiral, blue compact dwarf, starbursts, merging and colliding systems, and even residual star formation in S0 and Sa spirals). (abridged)

An ultrasonic analog for a laser

We report measurements on two simple ultrasonic systems analogous to random lasers. One system entails unstable ultrasonic feedback between distinct piezoelectric transducers on an irregularly shaped high-Q solid; another involves a spontaneously emitting piezoelectric device that can also emit by stimulation. Both are found to exhibit some of the behaviors of lasers. Over a wide range of parameters we observe narrow single-emission lines (natural width is estimated at about 0.000<th>000<th>000<th>1 Hz), sensitivity to linear cavity properties, complex multimode emissions, and line narrowing.

Low-resolution VLT spectroscopy of GRBs 991216, 011211 and 021211

We present low-resolution VLT spectroscopy of the afterglow of the gamma-ray bursts (GRBs) 991216, 011211 and 021211. Our spectrum of GRB991216 is the only optical spectrum for this afterglow. It shows two probable absorption systems at z=0.80 and z=1.02, where the highest redshift most likely reflects the distance to the host galaxy. A third system may be detected at z=0.77. HST imaging of the field, obtained 4 months after the burst, has resulted in the detection of two amorphous regions of emission, one at the projected afterglow position, and the other 0.6" away. The spectrum shows a depression in flux in between 4000 A and 5500 A. This could be the result of a 2175 A-type extinction feature in the host of GRB991216, but at a rather red wavelength of 2360 A. If this interpretation is correct, it is the first time the extinction feature is seen in a GRB afterglow spectrum. It is centered at a wavelength similar to that of the ultra-violet (UV) bumps inferred from observations of a few UV-strong, hydrogen-poor stars in the Galaxy. All significant absorption lines (except for one) detected in the spectrum of GRB011211 are identified with lines originating in a single absorption system at z=2.142+/-0.002, the redshift of the GRB011211 host galaxy. We also detect the Lyman alpha absorption line in the host, to which we fit a neutral hydrogen column density of log N(HI)=20.4+/-0.2, which indicates that it is a damped Lyman alpha system. Using a curve-of-growth analysis, we estimate the Si, Fe and Al metallicity at the GRB011211 redshift. For GRB021211, we detect a single emission line in a spectrum obtained tens of days after the burst, which we identify as [OII] 3727 at z=1.006. The corresponding unobscured [OII] star-formation rate is 1.4 Msun/yr.

Discovery of a redshifted X-ray emission line in the symbiotic neutron star binary 4U 1700+24

We present the spectral analysis of an XMM-Newton observation of the X-ray binary 4U 1700+24, performed during an outburst in August 2002. The EPIC-PN spectrum above 1 keV can be modeled by a blackbody plus Comptonization model, as in previous observations. At lower energies, however, we detect a prominent soft excess, which we model with a broad Gaussian centered at ~0.5 keV. In the high resolution RGS spectrum we detect a single emission line, centered at 19.19^{+0.05}_{-0.09} \AA. We discuss two possible interpretations for this line: O VIII at redshift z=0.012^{+0.002}_{-0.004} or Ne IX at redshift z~0.4.

Exciton-controlled magnetization in single magnetic quantum dots

We report on low temperature polarization-resolved imaging of single magnetic self-assembled CdMnTe quantum dots (QDs) in the absence of magnetic field. Using longitudinal optical phonon-assisted absorption to photoexcite spin-polarized excitons into a QD ground state, we find that the magnetic impurities within CdMnTe QDs can be aligned ferromagnetically with a single emission lines exhibiting a circular polarization as large as 65%. These results demonstrate that the magnetization of a single magnetic QD can be optically controlled with a suitably polarized laser.

Comparative investigation of quantum-dot-like localization centers in InGaN quantum well and quantum dot structures

AbstractWe present comparative micro-photoluminescence measurements on InGaN/GaN quantum well and quantum dot samples. Single sharp emission lines were investigated for both kinds of samples as a function of temperature and excitation density. For the sharp emission lines of the quantum dots and the strong localization centers in the quantum well samples comparable experimental findings were obtained such as the independence of their spectral position of the excitation density and the observation of binding and antibinding multiexcitonic states giving clear evidence for the quantum dot nature of localization centers.

Nanoindentation and near-field spectroscopy of single semiconductor quantum dots

Low-temperature near-field scanning optical microscopy was used to study the dependence of the emission spectra of single self-organized InAs on GaAs, InAs on AlAs and InP on GaInP quantum dots (QDs) on contact pressure exerted by a near-field optical fiber tip (nanoindentation). A large energy shift (up to 150 meV), broadening (up to 10 meV), and intensity increase (up to one order of magnitude) of single QD emission lines have been observed at tip compressions up to 70 nm. Ground state energy shift rates from 0.5 to 3.5 meV/nm have been measured for different aperture types (rounded and flat, metal coated and uncoated) and sizes (50--300 nm) in agreement with numerical calculations using Picus--Bir orbital-strain Hamiltonian. A reduction of the hydrostatic pressure coefficient due to a nonuniform In distribution in self-organized QDs has been observed. Anomalously strong lateral inhomogeneity of the local stress field has been observed.

Keck spectroscopy of Cosmic Lens All-Sky Survey gravitational lenses

We present the optical spectra of four newly discovered gravitational lenses from the Cosmic Lens All-Sky Survey (CLASS). These observations were carried out using the Low-Resolution Imaging Spectrograph on the W. M. Keck-I Telescope as part of a programme to study galaxy-scale gravitational lenses. From our spectra, we found the redshift of the background source in CLASS B0128+437 (z s = 3.1240 ± 0.0042) and the lensing galaxy redshifts in CLASS B0445+123 (z 1 = 0.5583 ± 0.0003) and CLASS B0850+054 (z 1 = 0.5883 ± 0.0006). Intriguingly, we also discovered that CLASS B0631+519 may have two lensing galaxies (z 1,1 = 0.0896 ± 0.0001, z 1,2 = 0.6196 ± 0.0004). We also found a single unidentified emission line from the lensing galaxy in CLASS B0128+437 and the lensed source in CLASS B0850+054. We find the lensing galaxies in CLASS B0445+123 and CLASS B0631+519 (1, 2) to be early-type galaxies with Einstein radii of 2.8-3.0 h -1 kpc. The deflector in CLASS B0850+054 is a late-type galaxy with an Einstein radius of 1.6 h -1 kpc.

Single quantum dot electroluminescence near [formula omitted

We present the first electroluminescence spectra to resolve individual single quantum dot emission lines to the telecommunications transmission window at 1.3 μm . The dot is embedded within the i-region of a p– i– n diode to enable electrical excitation. Detection is performed using a cooled InGaAs array detector. Photoluminescence spectra of single quantum dots in small mesas (∼1 μm) reveal the complex emission line structure of these dots for the first time. Initial time-resolved electroluminescence measurements at wavelengths above 1 μm indicate lifetimes similar to those commonly measured in dots emitting around 900 nm .

Micro-photoluminescence studies of excitonic and multiexcitonic states of quantum dot-like localization centers in InGaN/GaN structures

ABSTRACTWe present micro-photoluminescence measurements on unstructured InGaN/GaN quantum well samples. Single sharp emission lines were observed and their optical properties were studied as a function of temperature and excitation density. The experimental findings such as the independence of their spectral position on the excitation density and the observation of binding and antibinding multiexcitonic states give clear evidence for the existence of strong localization centers in the InGaN quantum well, which exhibit the same characteristics as they are known for quantum dot structures.

Photoluminescence of single InGaN quantum dots grown at low surface densities by MOVPE

We report the observation of photoluminescence due to single InGaN dots using samples containing very low surface dot densities. InGaN dot samples were grown by metalorganic vapour phase epitaxy with varying surface dot densities, the lowest being below 1 per μm2. The dots are typically 30–40 nm in diameter and 4–6 nm in height. Photoluminescence spectra taken from large dot ensembles indicate a low energy tale to the InGaN layer emission, which increases in intensity as the dot density increases. The energy resolved photoluminescence lifetime indicates that low energy feature is long lived, a significant rise time for the low energy photoluminescence also indicates slow carrier relaxation. The use of 400 nm apertures in aluminium shadow masks allows the observation of sharp line features due to individual exciton localisation centres. Under low excitation powers the broadband InGaN epilayer emission is found to break up into very large number of sharp line features consistent with the presence of strong localisation excitons within the InGaN epilayer due to alloy fluctuations. In addition, on the low energy wing of the quantum well band, strong, isolated sharp emission lines are observed. Many such apertures containing single line emission spectra have been observed. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A star-forming galaxy atz= 5.78 in theChandraDeep Field South

We report the discovery of a luminous z=5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an `i-drop' from the GOODS public survey imaging with HST/ACS (object 3 in Stanway, Bunker & McMahon 2003, astro-ph/0302212). The large colour of (i'-z')_AB=1.6 indicated a spectral break consistent with the Lyman-alpha forest absorption short-ward of Lyman-alpha at z~6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08arcsec, so r_hl<0.5kpc/h_70). We have obtained a deep (5.5-hour) spectrum of this z'(AB)=24.7 galaxy with the DEIMOS optical spectrograph on Keck, and here we report the discovery of a single emission line centred on 8245Ang detected at 20sigma with a flux of f~2E-17 ergs/s/cm^2. The line is clearly resolved with detectable structure at our resolution of better than 55km/s, and the only plausible interpretation consistent with the ACS photometry is that we are seeing Lyman-alpha emission from a z=5.78 galaxy. This is the highest redshift galaxy to be discovered and studied using HST data. The velocity width Delta(v)_FWHM=260km/s and rest-frame equivalent width (W=20Ang) indicate that this line is most probably powered by star formation, as an AGN would typically have larger values. The starburst interpretation is supported by our non-detection of the high-ionization NV1240Ang emission line, and the absence of this source from the deep Chandra X-ray images. The star formation rate inferred from the rest-frame UV continuum is 34M_sun/yr/h^2_70 (Omega_M=0.3, Omega_Lambda=0.7). This is the most luminous starburst known at z>5. Our spectroscopic redshift for this object confirms the validity of the i'-drop technique of Stanway, Bunker & McMahon (2003) to select star-forming galaxies at z~6.

A multi-colour study of the dark GRB 000210 host galaxy and its environment

We present UBVRIZJsHKs broad band photometry of the host galaxy of the dark gamma-ray burst (GRB) of February 10, 2000. These observations represent the most exhaustive photometry given to date of any GRB host galaxy. A grid of spectral templates have been fitted to the Spectral Energy Distribution (SED) of the host. The derived photometric redshift is z=0.842^+0.054_-0.042, which is in excellent agreement with the spectroscopic redshift (z=0.8463+/-0.0002) proposed by Piro et al. (2002) based on a single emission line. Furthermore, we have determined the photometric redshift of all the galaxies in an area of 6'x6' around the host galaxy, in order to check for their overdensity in the environment of the host. We find that the GRB 000210 host galaxy is a subluminous galaxy (L ~ 0.5+/-0.2 L*), with no companions above our detection threshold of 0.18+/-0.06 L*. Based on the restframe ultraviolet flux a star formation rate of 2.1+/-0.2 Solar Masses per year is estimated. The best fit to the SED is obtained for a starburst template with an age of 0.181^+0.037_-0.026 Gyr and a very low extinction (Av~0). We discuss the implications of the inferred low value of Av and the age of the dominant stellar population for the non detection of the GRB 000210 optical afterglow.

The luminescence of Sm 2+ in alkaline earth borophosphates

The temperature-dependent luminescence of Sm 2+ ions in MBPO 5 ( M= Ca 2+, Sr 2+, Ba 2+) was studied. At low temperature, Sm 2+ in this series shows 4f 6→4f 6 luminescence with only a single emission line observed for the 5 D 0→ 7 F 0 transition, revealing that only one crystallographic cationic site is available for Sm 2+ in all the hosts. With increasing temperature, the emission intensity of the 5 D 0→ 7 F 0 transition increases whereas that of the 5 D 0→ 7 F 1 transitions decreases. The 5 D 1→ 7 F 0 transitions of Sm 2+ were observed in BaBPO 5 and its intensity increases with increasing temperature. At 450 K , a broad band of the 4f 55d→4f 6 luminescent transition of Sm 2+ in SrBPO 5 and BaBPO 5 with maximum at ∼600 nm appears due to the thermal population. The lifetime of the 5 D 0→ 7 F 0 transition was recorded at different temperatures, showing a single exponential decay for Sm 2+ in SrBPO 5 and BaBPO 5 but a non-single-exponential decay in CaBPO 5.

Correlation spectroscopy of excitons and biexcitons on a single quantum dot

We report the observation of antibunched emission from single self-assembled InAs quantum dots under various conditions. We have measured the correlation function of the photon emission pertaining to single emission lines from single quantum dots under continuous and pulsed laser excitation, as well as under continuous white light excitation. The measurements were performed under different excitation intensities at liquid helium temperatures on two samples with distinct structures. At higher temperatures (30 K), an antibunching dip was still observed. We have also observed antibunching on a second emission line in the quantum dot spectrum, attributed to the biexciton, demonstrating the possibility of generating photon pairs with a single quantum dot. Polarization correlations on the biexciton and exciton line were also measured in an attempt to generate entangled photon pairs.

Discovery of X–rays from Mars with Chandra

On 4 July 2001, X–rays from Mars were detected for the first time. The observation was performed with the ACIS–I detector onboard Chandra and yielded data of high spatial and temporal resolution, together with spectral information. Mars is clearly detected as an almost fully illuminated disk, with an indication of limb brightening at the sunward side, accompanied by some fading on the opposite side. The morphology and the X–ray luminosity of ~ are fully consistent with fluorescent scattering of solar X–rays in the upper Mars atmosphere. The X–ray spectrum is dominated by a single narrow emission line, which is most likely caused by O–Kα fluorescence. No evidence for temporal variability is found. This is in agreement with the solar X–ray flux, which was almost constant during the observation. In addition to the X–ray fluorescence, there is evidence for an additional source of X–ray emission, indicated by a faint X–ray halo which can be traced to about three Mars radii, and by an additional component in the X–ray spectrum of Mars, which has a similar spectral shape as the halo. Within the available limited statistics, the spectrum of this component can be characterized by 0.2 keV thermal bremsstrahlung emission. This is indicative of charge exchange interactions between highly charged heavy ions in the solar wind and exospheric hydrogen and oxygen around Mars. Although the observation was performed at the onset of a global dust storm, no evidence for dust–related X–ray emission was found.

The Redshift of the Lensed Object in the Einstein Ring B0218+357

We present a secure redshift of z = 0.944 ± 0.002 for the lensed object in the Einstein ring gravitational lens B0218+357 based on five broad emission lines, in good agreement with our preliminary value announced several years ago based solely on the detection of a single emission line.

Terahertz Emission Spectra of Optically Pumped Silicon Lasers

The emission spectra of terahertz Si lasers measured with a resolution up to 0.3 cm -1 are presented. The laser mechanism is based on intracenter transitions of optically excited Si doped by phosphor or bismuth. The laser transitions and the involved intracenter impurity levels have been identified. For Si:P a single emission line originating from the 2p 0 → 1s(T 2 ) transition was observed while for Si:Bi two emission lines originating from 2p ± → 1s(E) and 2p ± → 1s(T 2 :Γ 8 ) transitions were observed.

The Unusually Long Duration Gamma‐Ray Burst GRB 000911: Discovery of the Afterglow and Host Galaxy

Of all the well-localized gamma-ray bursts, GRB 000911 has the longest duration (T90 = 500 s) and ranks in the top 1% of BATSE bursts for fluence. Here we report the discovery of the afterglow of this unique burst. In order to simultaneously fit our radio and optical observations, we are required to invoke a model involving a hard electron distribution, p ~ 1.5, and a jet-break time less than 1.5 days. A spectrum of the host galaxy taken 111 days after the burst reveals a single emission line, interpreted as [O II] at a redshift z = 1.0585, and a continuum break that we interpret as the Balmer limit at this redshift. Despite the long T90, the afterglow of GRB 000911 is not unusual in any other way when compared to the set of afterglows studied to date. We conclude that the duration of the GRB plays little part in determining the physics of the afterglow.

Phonon-Assisted Luminescence of Magnetoexcitons in Semiconductor Quantum Wells

We consider a line-shape of magnetoexciton photoluminescence from quantum wells when the disorder is sufficiently small. In this case the phonon-assisted optical transitions become important for the line formation. We study both inter-band and intra-band excitons. For inter-band excitons the width of a single peak emission line is calculated as a function of temperature and quantum well width. For intra-band excitons the double peak of the emission line is predicted when the electron filling factor is odd and greater or equal to three. In the latter case the lowest magnetoexciton dispersion curve has a minimum at non-zero momentum. Then the higher-energy peak results from the direct optical emission of zero-momentum excitons. The origin of the lower-energy peak is the phonon-assisted transitions from the non-zero momentum exciton states. With increasing temperature, the higher-energy peak becomes more pronounced and the lower-energy peak vanishes.