ABSTRACT
Galaxy clusters are the most massive virialized structures in the Universe and are formed through the gravitational accretion of matter over cosmic time1. The discovery2 of an evolved galaxy cluster at redshift z = 2, corresponding to a look-back time of 10.4 billion years, provides an opportunity to study its properties. The galaxy cluster XLSSC 122 was originally detected as a faint, extended X-ray source in the XMM Large Scale Structure survey and was revealed to be coincident with a compact over-density of galaxies2 with photometric redshifts of 1.9 ± 0.2. Subsequent observations3 at millimetre wavelengths detected a Sunyaev-Zel'dovich decrement along the line of sight to XLSSC 122, thus confirming the existence of hot intracluster gas, while deep imaging spectroscopy from the European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton) revealed4 an extended, X-ray-bright gaseous atmosphere with a virial temperature of 60 million Kelvin, enriched with metals to the same extent as are local clusters. Here we report optical spectroscopic observations of XLSSC 122 and identify 37 member galaxies at a mean redshift of 1.98, corresponding to a look-back time of 10.4 billion years. We use photometry to determine a mean, dust-free stellar age of 2.98 billion years, indicating that star formation commenced in these galaxies at a mean redshift of 12, when the Universe was only 370 million years old. The full range of inferred formation redshifts, including the effects of dust, covers the interval from 7 to 13. These observations confirm that XLSSC 122 is a remarkably mature galaxy cluster with both evolved stellar populations in the member galaxies and a hot, metal-rich gas composing the intracluster medium.
ABSTRACT
In the cores of some clusters of galaxies the hot intracluster plasma is dense enough that it should cool radiatively in the cluster's lifetime, leading to continuous 'cooling flows' of gas sinking towards the cluster centre, yet no such cooling flow has been observed. The low observed star-formation rates and cool gas masses for these 'cool-core' clusters suggest that much of the cooling must be offset by feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical and infrared observations of the galaxy cluster SPT-CLJ2344-4243 (ref. 11) at redshift z = 0.596. These observations reveal an exceptionally luminous (8.2 × 10(45) erg s(-1)) galaxy cluster that hosts an extremely strong cooling flow (around 3,820 solar masses a year). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (formation of around 740 solar masses a year), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool-core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star-formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form through accretion of the intracluster medium, rather than (as is currently thought) assembling entirely via mergers.
ABSTRACT
We have constructed a stabilized low temperature infrared absorption cell cooled by an open cycle refrigerator, which can run with liquid nitrogen from 250 to 80K or with liquid helium from 80K to a few kelvin. Several CO infrared spectra were recorded at low temperature using a tunable diode laser spectrometer. These spectra were analyzed taking into account the detailed effects of collisions on the line profile when the pressure increases. We also recorded spectra at very low pressure to accurately model the diode laser emission. Spectra of the R(2) line in the fundamental band of 13CO cooled by collisions with helium buffer gas at 10.5K and at pressures near 1 Torr have been recorded. The He-pressure broadening parameter (gamma(0) = 0.3 cm(-1) atm(-1)) has been derived from the simultaneous analysis of four spectra at different pressures.
Subject(s)
Chemistry Techniques, Analytical/instrumentation , Argon , Carbon Isotopes , Carbon Monoxide/chemistry , Cold Temperature , Helium , Spectrophotometry, Infrared/instrumentationABSTRACT
We studied the R(0) line profile in the CH4 v4 band from room temperature to 188 K with N2 as a perturber, to 100 K with O2 as perturber, and from room temperature to 15 K using He as a perturber. The N2 and O2 measurements were performed over a total pressure range of 15-110 mbar, and for the He measurements the maximum sample pressure at 15 K was 1.10 mbar. Broadening parameters were determined, taking into account the confinement narrowing (Dicke effect), and narrowing parameters, deduced from the soft or hard collision model, are compared with the dynamic friction coefficient calculated values. We also obtained preliminary values for the temperature dependence of the N2, O2 and He line broadening parameters for this transition.
Subject(s)
Cold Temperature , Methane/analysis , Spectrophotometry/methods , Helium/chemistry , Nitrogen/chemistry , Oxygen/chemistry , Pressure , Spectrophotometry/instrumentationABSTRACT
Three different thermal transpiration models have been tested for a range of pressures and temperatures normally encountered in collisional cooling experiments. The calculated corrections for two of these models follow similar patterns and differ only in magnitude at a fixed sample temperature for sample pressures between 0 and 8 Torr. Corrections calculated from the third model follow a pattern similar to the other two models only at pressures above about two Torr.
Subject(s)
Cold Temperature , Spectrophotometry/methods , PressureABSTRACT
We determined accurate He-broadening parameters and collisional cross sections for the P(2) line in the fundamental band of CO at room temperature and at intermediate temperatures down to 11.5 K. We also determined a precise value for the temperature dependence of the line-broadening parameter on (T)(-n) with n equal to 0.548+/-0.010. Our results validate the microwave results for the J=1 to J=2 rotational transitions measured over the same range of temperatures which were reported previously by Beaky et al. (1996, J. Chem. Phys. 105, 3994-4004). Copyright 2001 Academic Press.
ABSTRACT
The refractive index is measured for PbEuTe alloys in the 3.3-12-microm spectral region. Each alloy is grown with a different Eu concentration. The range of Eu concentrations studied is between 0.76 and 6.5 at. %. All measurements are performed on samples maintained at room temperature. We use a classical dispersion relation to establish a simple empirical relationship that describes the dependence of the refractive index as a function of both the percentage of the Eu concentration and the infrared wave number.
ABSTRACT
A wavelength-stabilized tunable diode laser and a reflective optical system can produce fringe-free spectra with a noise level of 10(-5) absorbance units and a precision of 10(-5) cm(-1) in the wave-number scale.
ABSTRACT
This paper describes the design and performance of a tunable diode laser system, incorporating a multipass absorption cell to allow determination of water concentration below 10 ppb and carbon dioxide concentration below 1 ppb in nitrogen semiconductor gas. The cell is used with a tunable Pb-salt diode laser spectrometer frequency locked to a first derivative error signal from an intense vibration-rotation molecular absorption line. Sample concentrations are monitored in the second derivative mode, and the system automatically compensates for laser intensity fluctuations. A flowing gas method is used to minimize adsorption/desorption effects from the sample cell walls.
ABSTRACT
An infrared diode laser is frequency stabilized to a tunable internally coupled Fabry-Perot interferometer (icFPI). Diode laser spectra are digitally recorded utilizing a step-by-step tuning and stabilization sequence of the icFPI. Fringes from a frequency stabilized reference He-Ne laser are used to control digital sampling steps. While improving significantlythe spectral SNR, this method is combined with a confocal Fabry-Perot etalon, thus providing a frequency scale accuracy of ~3.5 x 10(-5) cm(-1) over a 1-cm(-1) scan. The method is shown to be consistent with high resolution Fourier transform and heterodyne spectroscopy results.
ABSTRACT
A tunable diode laser beam is sent through a Michelson interferometer and is locked to a fringe of the diode laser interference pattern by controlling the diode laser polarization current. The path difference change of the Michelson interferometer is controlled step by step by a stabilized He-Ne red laser. When the interferometer path difference increases or decreases, the polarization current of the diode is forced to change in order to preserve the interference order of the diode beam. At every step the diode frequency is accurately fixed and its phase noise significantly reduced.
ABSTRACT
The output and transmission characteristics of both single and double (tandem) integrating spheres have been studied with a lead-salt diode laser in the 2000-cm(-1) spectral region. For an f/20 input beam, the effective length is about eight times the diameter of the sphere. The corresponding transmittance is ~10(-5) for the tandem spheres. The output beam has a Gaussian profile.
ABSTRACT
A diode-laser dual-beam spectrometer using reflective optics and a special lock-in amplifier has a 100 +/- 0.25% base line flatness and a long-term base line drift of <0.25%. The system is highly immune to fringe interference occurring before the ratioing system.
ABSTRACT
The low-frequency noise characteristics of several stripe-geometry Pb-salt semiconductor diode lasers were investigated in the 4-11-microm spectral region. Excess noise is observed to vary as the ratio of I/I(t), where I is the injection current and I(t) is the threshold value at which lasing action begins. The magnitude of the diode laser excess noise has been measured to be 24 dB above shot noise at threshold.
ABSTRACT
A tunable diode laser has been incorporated as a source in an operating high resolution vacuum grating spectrometer. The advantages of such a system for recording molecular spectra have been elaborated. In the process of developing this system, several practical problems came about, and it has been considered useful to document the manner in which they have been resolved. In particular, for work in the region of 15 microm, it was advantageous to develop an air-spaced Fabry-Perot etalon to record fringes simultaneously with the scanning of molecular spectra. This was successfully done, and the upsilon(2) band lines of the HCN molecule at 14 microm have proved to be ideally suited for determining the fringe spacing spectroscopically.
ABSTRACT
The detection sensitivity of a long-path atmospheric pollutant monitor using tunable diode lasers has been greatly improved to about 0.1%. These improvements directly result from measurements made on the low frequency noise characteristics of several diode lasers and the temporal spectrum of atmospheric turbulence. Optimum modulation frequencies are given, and an improved optical design is recommended.
ABSTRACT
Fourier transform spectroscopy has been demonstrated to provide outstanding results in astronomical and high resolution spectral studies of cw sources. However, techniques for the study of reacting or transient systems have been less than satisfactory in cases where one is seriously interested in obtaining detailed spectroscopic data. It has been demonstrated that Fourier transform techniques can also be utilized in the study of systems which are transient as well. This paper discusses the use of Michelson interferometers in the study of transients, and new results will be presented.
