Imaging Fabry-Perot Research Articles

Interferometer response characterization algorithm for multi-aperture Fabry-Perot imaging spectrometers.

In recent years, the demand for hyperspectral imaging devices has grown significantly, driven by their ability of capturing high-resolution spectral information. Among the several possible optical designs for acquiring hyperspectral images, there is a growing interest in interferometric spectral imaging systems based on division of aperture. These systems have the advantage of capturing snapshot acquisitions while maintaining a compact design. However, they require a careful calibration to operate properly. In this work, we present the interferometer response characterization algorithm (IRCA), a robust three-step procedure designed to characterize the transmittance response of multi-aperture imaging spectrometers based on the interferometry of Fabry-Perot. Additionally, we propose a formulation of the image formation model for such devices suitable to estimate the parameters of interest by considering the model under various regimes of finesse. The proposed algorithm processes the image output obtained from a set of monochromatic light sources and refines the results using nonlinear regression after an ad-hoc initialization. Through experimental analysis conducted on four different prototypes from the Image SPectrometer On Chip (ImSPOC) family, we validate the performance of our approach for characterization. The associated source code for this paper is available from Zenodo (http://dx.doi.org/10.5281/zenodo.7978514).

Spectrally-resolved Rayleigh scattering to measure velocity, temperature, density, and density fluctuations in high-speed flows

A new spectroscopic setup to analyze Rayleigh-scattered light from a high-speed jet was created at the NASA Ames Research Center for simultaneous measurement of velocity, temperature, and density. The point-measurement arrangement uses a narrow-linewidth continuous-wave laser and a stabilized, air-spaced, Fabry–Perot etalon to resolve the Rayleigh–Brillouin (RB) spectrum. Light scattered from a 0.4 mm-long and 0.15 mm-diameter probe volume was collected and 10% of the light was split to measure the scattering intensity via a photo-multiplier tube, which provided a measure of the gas density and density fluctuation spectra. The rest was directly imaged through the Fabry–Perot interferometer to an EMCCD camera. A new software program was developed in the Matlab® platform to model the fringes seen in the camera image. At first, a small part of the incident laser light was analyzed to find the instrument function. When Rayleigh-scattered light was passed, a change in the fringe diameter corresponding to the Doppler shift from the air velocity and a thickening of the fringe corresponding to the thermal broadening were observed. A least-squares fit utilizing Tenti’s S6 model of the RB scattering provided velocity and temperature at the probe volume. A high-speed, clean-air jet, operated in the Mach range of 0 ≤ M ≤ 1.2 provided validation of the technique, and demonstrated applicability in shock-containing flows. The compact, transportable, efficient, and affordable setup was fairly accurate: uncertainties were < 7 m/s in velocity, < 5 K in temperature, and < 1% in density. Spectra of density fluctuations were measured over a frequency range of 50 kHz. Principle of Rayleigh scattering technique, (a) schematic representation; (b) superimposed Fabry–Perot images from the present setup, U = 323 m/s, T = 249 K.

First results from SAM-FP: Fabry–Perot observations with ground-layer adaptive optics – the structure and kinematics of the core of 30 Doradus

The aim of this paper is to present the first data set obtained with SOAR Adaptive Module-Fabry-Parot (SAM-FP), a Fabry-Perot instrument mounted inside the SOAR telescope Adaptive-Optics Module. This is the only existing imaging Fabry-Perot interferometer using laser-assisted ground-layer adaptive optics. SAM-FP was used to observe the ionized gas, traced by Halpha, in the centre of the 30 Doradus starburst (the Tarantula Nebula) in the Large Magellanic Cloud, with high spatial (~0.6" or 0.15 pc) and spectral (R=11200) resolution. Radial velocity, velocity dispersion and monochromatic maps were derived. The region displays a mix of narrow, sigma ~ 20 km/s profiles and multiple broader profiles with sigma ~ 70-80 km/s, indicating the complex nature of the nebula kinematics. A comparison with previously obtained VLT/FLAMES spectroscopy demonstrates that the data agree well in the regions of overlap, but the Fabry-Perot data are superior in spatial coverage. A preliminary analysis of the observations finds a new expanding bubble south of R136, with a projected radius of r=5.6 pc and an expansion velocity of 29 +/- 4 km/s. In addition, the first-time detailed kinematic maps derived here for several complexes and filaments of 30 Doradus allow identification of kinematically independent structures. These data exemplify the power of the combination of a high-order Fabry-Perot with a wide-field imager (3' x 3' GLAO-corrected field of view) for high-resolution spatial and spectral studies. In particular, SAM-FP data cubes are highly advantageous over multifibre or long-slit data sets for nebula structure studies and to search for small-scale bubbles, given their greatly improved spatial coverage. For reference, this paper also presents two appendices with detailed descriptions of the usage of Fabry-Perot devices, including formulae and explanations for understanding Fabry-Perot observations.

Simulations of imaging Fabry–Perot interferometers for measuring upper-atmospheric temperatures and winds

We apply an onion-peeling inversion to simulated imaging Fabry-Perot interferometer (FPI) observations for retrieving altitude profiles of neutral temperatures and winds in the thermosphere in order to investigate the effects of realistic gradients in thermospheric parameters on the retrieved parameters. A forward model is developed that simulates the interference spectrum observed by an FPI using the redline (630.0 nm) and greenline (557.7 nm) emissions simulated based on climatological models. This forward model is applicable to both ground- and satellite-based simulations and generates a two-dimensional interference ring pattern. We simulate both a single-band ground-based FPI and a dual-band satellite-based FPI in order to study the effects of realistic vertical and horizontal gradients on the retrieved parameters.

Neutral thermospheric dynamics observed with two scanning Doppler imagers: 1. Monostatic and bistatic winds

Doppler‐shift measurements of the thermospheric 630.0 nm emission recorded by two spatially separated imaging Fabry‐Perot spectrometers in Alaska have been combined to infer F region horizontal wind vectors at approximately 75 locations across their overlapping fields‐of‐view. These “bistatic” horizontal wind estimates rely only on an assumption regarding the local vertical wind (and assume a common observing volume), and thus represent a more direct measurement of the wind than do the monostatic (single‐station) vector wind fields routinely inferred by these instruments. Here we present comparisons between both the independently derived monostatic wind fields from each instrument and the bistatic wind estimates inferred in their common observing volumes. Data are presented from observations on three nights during 2010. Two principal findings have emerged from this study. First, the monostatic technique was found to be capable of estimating the actual large‐scale wind field reliably under a large range of geophysical conditions, and is well suited to applications requiring only a large‐scale, ‘big picture’ approximation of the wind flow. Secondly, the bistatic (or tristatic) technique is essential for applications requiring detailed knowledge of the small‐scale behavior of the wind, as for example is required when searching for gravity waves.

A 205 μm [N II] MAP OF THE CARINA NEBULA

We present the results of a � 250 arcmin 2 mapping of the 205 �m [NII] fine-structure emission over the northern Carina Nebula, including the Car I and Car II HII regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at South Pole. We supplement the 205 �m data with new reductions of far-IR fine-structure spectra from the Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) in 63 �m [OI], 122 �m [NII], 146 �m [OI], and 158 �m [CII]; the 146 �m [OI] data include 90 raster positions which have not been previously published. Morphological comparisons are made with optical, radio continuum and CO maps. The 122/205 line ratio is used to probe the density of the low-ionization gas, and the 158/205 line ratio is used to probe the fraction of C + arising from photodissociation regions (PDRs). The [OI] and [CII] lines are used to construct a PDR model of Carina. When the PDR properties are compared with other sources, Carina is found to be more akin to 30 Doradus than galactic star-forming regions such as Orion, M17, or W49; this is consistent with the view of Carina as a more evolved region, where much of the parent molecular cloud has been ionized or swept away. These data constitute the first ground-based detection of the 205 �m [NII] line, and the third detection overall since those of the COBE FIRAS and the KAO in the early 1990s. Subject headings: HII regions — infrared: ISM — ISM: individual (Carina nebula) — ISM: lines and bands — photon-dominated region (PDR) — submillimeter: ISM

The Kyoto Tridimensional Spectrograph II on Subaru and the University of Hawaii 88 in Telescopes

ABSTRACTIn order to investigate physical conditions of ionized gas in galaxies, as well as its kinematics, we have developed the Kyoto tridimensional spectrograph II. It is a multimode optical instrument, including integral field spectrograph (IFS) and Fabry-Perot imager modes. We have designed it compact so that we can mount it on 2 m class telescopes as well as on the 8.2 m Subaru telescope. Special care was taken to obtain high-quality calibrations in the IFS mode. In order to remove the chromatic aberration of micropupil images produced by a lenslet array, we have introduced a corrector lens system behind the lenslet array. The internal calibration system simulates the telescope optics so that the system provides micropupil images identical to those produced by the telescope. The rigidness of the instrument provides the positional stability of micropupil images. We have succeeded in test observations of all the modes on Subaru and the University of Hawaii 88 in (UH88) telescopes and have verified the performance of the instrument. This includes the instrument efficiencies as well as the effective sky background subtraction and the minimization of crosstalk effects in the IFS mode. In the IFS mode a spatial resolution of 0.4″ was obtained in good seeing conditions. Each of 37 × 37 lenslets subtends 0.1″ in Subaru’s case. This samples the image size well. A wider field of view is emphasized in the case of UH88.

Neutral-ion interaction in the auroralEregion obtained from coordinated Fabry-Perot imager and VHF radar observations

[1] It is important to investigate the small-scale dynamics of thermospheric neutrals and ionospheric plasmas at high latitudes since there are local and temporal variations in energy input and transfer processes associated with auroral activities. To clarify these ionosphere-thermosphere interactions in the auroral E region, we examined neutral winds and plasma motions obtained by coordinated Fabry-Perot imager and VHF radar observations at Syowa Station, Antarctica. From case studies on 11 and 12 September 1996, we found a good correlation between temporal variation (period < 1 hr) of E region neutral winds measured by the Fabry-Perot imager and the Doppler velocities of plasmas obtained from the VHF radar echoes. On the other hand, the absolute mean values of the neutral winds were around zero whereas the plasma Doppler velocities were 350–400 m/s, showing a significant discrepancy. Considering that the neutral-ion and ion-neutral momentum transfer collision frequencies in the E region are ∼10−6 Hz and ∼102 Hz, respectively, these good correlations are probably due to ion motions driven by neutral drag force, suggesting a strong coupling between neutrals and ions in the E region. The observed correlation and discrepancy between the radar Doppler velocity and the neutral wind velocity are consistent with the linear theory of E region irregularities that shows the radar Doppler velocity is the sum of two components; one is the E × B drift speed, and another is proportional to the neutral wind velocity.

Thermospheric winds and temperatures above Mawson, Antarctica, observed with an all-sky imaging, Fabry-Perot spectrometer

Abstract. A new all-sky imaging Fabry-Perot spectrometer has been installed at Mawson station (67°36' S, 62°52' E), Antarctica. This instrument is capable of recording independent spectra from many tens of locations across the sky simultaneously. Useful operation began in March 2007, with spectra recorded on a total of 186 nights. Initial analysis has focused on the large-scale daily and average behavior of winds and temperatures derived from observations of the 630.0 nm airglow line of atomic oxygen, originating from a broad layer centered around 240 km altitude, in the ionospheric F-region. The 1993 Horizontal Wind Model (HWM93), NRLMSISE-00 atmospheric model, and the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model were used for comparison. During the geomagnetically quiet period studied, observed winds and temperatures were generally well modelled, although temperatures were consistently higher than NRLMSISE-00 predicted, by up to 100 K. CTIP temperatures better matched our data, particularly later in the night, but predicted zonal winds which were offset from those observed by 70–180 ms−1 westward. During periods of increased activity both winds and temperatures showed much greater variability over time-scales of less than an hour. For the active night presented here, a period of 45 min saw wind speeds decrease by around 180 ms−1, and temperatures increase by approximately 100 K. Active-period winds were poorly modelled by HWM93 and CTIP, although observed median temperatures were in better agreement with NRLMSISE-00 during such periods. Average behavior was found to be generally consistent with previous studies of thermospheric winds above Mawson. The collected data set was representative of quiet geomagnetic and solar conditions. Geographic eastward winds in the afternoon/evening generally continued until around local midnight, when winds turned equatorward. Geographic meridional and zonal winds in the afternoon were approximately 50 ms−1 weaker than expected from HWM93, as was the transition to equatorward flow around midnight. There was also a negligible geographic zonal component to the post-midnight wind where HWM93 predicted strong westward flow. Average temperatures between 19:00 and 04:00 local solar time were around 60 K higher than predicted by NRLMSISE-00.

New results on equatorial thermospheric winds and the midnight temperature maximum

Abstract. Optical observations of thermospheric winds and temperatures determined with high resolution measurements of Doppler shifts and Doppler widths of the OI 630-nm equatorial nightglow emission have been made with improved accuracy at Arequipa, Peru (16.4° S, 71.4° W) with an imaging Fabry-Perot interferometer. An observing procedure previously used at Arecibo Observatory was applied to achieve increased spatial and temporal sampling of the thermospheric wind and temperature with the selection of eight azimuthal directions, equally spaced from 0 to 360°, at a zenith angle of 60°. By assuming the equivalence of longitude and local time, the data obtained using this technique is analyzed to determine the mean neutral wind speeds and mean horizontal gradients of the wind field in the zonal and meridional directions. The new temperature measurements obtained with the improved instrumental accuracy clearly show the midnight temperature maximum (MTM) peak with amplitudes of 25 to 200 K in all directions observed for most nights. The horizontal wind field maps calculated from the mean winds and gradients show the MTM peak is always preceded by an equatorward wind surge lasting 1–2 h. The results also show for winter events a meridional wind abatement seen after the MTM peak. On one occasion, near the September equinox, a reversal was observed during the poleward transit of the MTM over Arequipa. Analysis inferring vertical winds from the observed convergence yielded inconsistent results, calling into question the validity of this calculation for the MTM structure at equatorial latitudes during solar minimum. Comparison of the observations with the predictions of the NCAR general circulation model indicates that the model fails to reproduce the observed amplitude by a factor of 5 or more. This is attributed in part to the lack of adequate spatial resolution in the model as the MTM phenomenon takes place within a scale of 300–500 km and ~45 min in local time. The model shortcoming is also attributed in part to the need for the model to include a hydrodynamical mechanism to describe the merging of the zonal wind with the meridional tidal winds that converge onto the geographical equator. Finally, a conclusion of this work is that the MTM compressional heating takes place along the perimeter of the pressure bulge rather than within the bulge, an issue previously not appreciated.

Molecular Hydrogen Outflows in the Central Arcseconds of the T Tauri System

We present new, near-infrared, adaptive optics observations of the enigmatic pre-main-sequence object T Tauri, using broadband filter imagery, long-slit spectroscopy, and Fabry-Perot imaging spectra. The broadband filter images spatially resolve the three stellar components of T Tau in the H, Ks, and L' photometric bands. We clearly detect T Tau Sb in the J band, and place upper limits on the J brightness of the infrared companion, T Tau Sa. The K-band spectrum of the T Tau S binary also resolves both components, and confirms strong Brγ emission in both stars and photospheric features in Sb. We also report 2.058 μm helium recombination radiation associated with T Tau Sb. The Fabry-Perot channel map centered on the v = 1-0 S(1) line of molecular hydrogen shows a number of spatially extended structures, including a loop of emission north of the stars that is also visible in continuum frames taken at ±900 km s-1 from the line center. The continuum-subtracted H2 image displays bow shock structures associated with the southeast-northwest and east-west outflows. The east-west jet system also shows bright, oblique shocks lining the flow channel. The part of the long-slit spectrum that overlaps this channel wall displays H2 line ratios consistent with shock heating. This region also corresponds to the brightest knot of UV fluorescent emission reported by Saucedo and coworkers. The Fabry-Perot images unambiguously identify T Tau S binary as the source of the east-west outflow, although we cannot yet determine which of the two components produces the jet.

Detection of the 205 μm [N ii ] Line from the Carina Nebula

We report the first detection of the 205 μm 3P1 P0 [N II] line from a ground-based observatory using a direct detection spectrometer. The line was detected from the Carina star formation region using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) on the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. The [N II] 205 μm line strength indicates a low-density (n ~ 32 cm-3) ionized medium, similar to the low-density ionized halo previously reported in its [O III] 52 and 88 μm line emission. When compared with the Infrared Space Observatory [C II] observations of this region, we find that 27% of the [C II] line emission arises from this low-density ionized gas, but the large majority (~73%) of the observed [C II] line emission arises from the neutral interstellar medium. This result supports and underpins prior conclusions that most of the observed [C II] 158 μm line emission from Galactic and extragalactic sources arises from the warm, dense photodissociated surfaces of molecular clouds. The detection of the [N II] line demonstrates the utility of Antarctic sites for THz spectroscopy.

Imaging Fabry‐Perot Spectroscopy of NGC 5775: Kinematics of the Diffuse Ionized Gas Halo

We present imaging Fabry-Perot observations of Hα emission in the nearly edge-on spiral galaxy NGC 5775. We have derived a rotation curve and a radial density profile along the major axis by examining position-velocity (PV) diagrams from the Fabry-Perot data cube, as well as a CO 2-1 data cube from the literature. PV diagrams constructed parallel to the major axis are used to examine changes in azimuthal velocity as a function of height above the midplane. The results of this analysis reveal the presence of a vertical gradient in azimuthal velocity. The magnitude of this gradient is approximately 1 km s-1 arcsec-1, or about 8 km s-1 kpc-1, although a higher value of the gradient may be appropriate in localized regions of the halo. The evidence for an azimuthal velocity gradient is much stronger for the approaching half of the galaxy, although earlier slit spectra are consistent with a gradient on both sides. There is evidence for an outward radial redistribution of gas in the halo. The form of the rotation curve may also change with height, but this is not certain. We compare these results with those of an entirely ballistic model of a disk-halo flow. The model predicts a vertical gradient in azimuthal velocity that is shallower than the observed gradient, indicating that an additional mechanism is required to further slow the rotation speeds in the halo.

Exploring the Kinematics of the Oxygen‐rich Supernova Remnant G292.0+1.8: Ejecta Shells, Fast‐moving Knots, and Shocked Circumstellar Material

We present the results of an in-depth optical study of the core-collapse supernova remnant G292.0+1.8 using the Rutgers Fabry-Perot (RFP) imaging spectrometer. Our observations provide a detailed picture of the supernova remnant in the emission lines of [O III] λ5007, Hα, and [N II] λ6548. The [O III] Fabry-Perot scans reveal a bright crescent-shaped spur of previously known high-velocity (Vradial ~ 1500 km s-1) O-rich ejecta located on the eastern side of the remnant. The spur consists of a semicoherent structure of mostly redshifted material, along with several clumps that have apparently broken out of the more orderly shell-like expansion. The high-velocity (600 km s-1) component of the spur also displays a scalloped morphology characteristic of Rayleigh-Taylor instabilities. We also find a large number of fast-moving knots (FMKs) of O-rich ejecta undetected in prior photographic plate images and similar to features seen in Cas A. The FMKs are distributed sparsely in the interior of G292.0+1.8 and are seen mostly in blueshifted emission out to Vradial ≈ -1700 km s-1. The position-velocity distribution of the FMKs can be kinematically described as a shell 34 in radius expanding at a velocity of 1700 km s-1. Another feature apparent in the [O III] scans is an equatorial belt consisting of both a barlike structure at zero radial velocity and a clumpy, high-velocity ejecta component seen in projection along the line of sight. Portions of the zero-velocity bar are spatially well correlated with a similar structure seen in the Chandra X-ray image of G292.0+1.8. The bar is also detected in our Hα RFP images at zero radial velocity, providing further evidence that this structure is of circumstellar origin. We find that the optical and X-ray properties of the bar are consistent with incomplete (partially radiative) shocks in material of moderate densities. There are also a number of faint, elongated structures seen in Hα at zero radial velocity across the interior of G292.0+1.8 that lack [O III] and X-ray counterparts. These filaments may be low-density H I clouds photoionized by hard radiation from the interior of the remnant. Overall, these results suggest that G292.0+1.8 is currently interacting with a low-density environment. We find no evidence for high-velocity Hα or [N II] emission over the dynamical range sampled by the RFP. Assuming a distance of 6 kpc for G292.0+1.8, we estimate a kinematic age of (3000-3400)d6 yr for this remnant.

The metallicity-luminosity relation at medium redshift based on faint CADIS emission line galaxies

The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects galaxies with very low continuum brightness by using an imaging Fabry-Perot interferometer. With spectroscopic follow-up observations of MB>~-19 CADIS galaxies using FORS2 at the VLT and DOLORES at TNG we obtained oxygen abundances of 5 galaxies at z~0.4 and 10 galaxies at z~0.64. Combining these measurements with published oxygen abundances of galaxies with MB<~-19 we find evidence that a metallicity-luminosity relation exists at medium redshift, but it is displaced to lower abundances and higher luminosities compared to the metallicity-luminosity relation in the local universe. Comparing the observed metallicities and luminosities of galaxies at z<3 with Pegase2 chemical evolution models we have found a favoured scenario in which the metallicity of galaxies increases by a factor of ~2 between z~0.7 and today, and their luminosity decreases by ~0.5-0.9mag.

A Spatiokinematic Study of the Planetary Nebula NGC 1514

New spatiokinematic observations were undertaken of the planetary nebula NGC 1514 in the [O III] line at 5007 A using an imaging Fabry-Perot spectrometer. Our results show an inner ellipsoidal shell and polar blobs that do not conform to bipolar morphology. It is argued that the nebula is a descendant of a common envelope binary system the periodicity of which is estimated to be about 10 days, with a progenitor mass of 4.5 M⊙.

The Physics of Supernova Blast Waves. I. Kinematics of DEM L71 in the Large Magellanic Cloud

We present the results from Fabry-Perot imaging spectroscopy of the Balmer-dominated supernova remnant DEM L71 (0505-67.9) in the LMC. Spectra extracted from the entire circumference of the blast wave reveal the broad- and narrow-component Hα line emission characteristic of nonradiative shocks in partially neutral gas. The new spectra of DEM L71 include portions of the rim that have not been previously observed. We find that the broad-component width varies azimuthally along the edge of DEM L71, ranging from 450 ± 60 km s-1 along the eastern edge to values as high as 985 km s-1 along the faint western edge. The latter width is nearly 60% larger than the value determined by earlier spectroscopy of the brightest Balmer-dominated filaments. In part of the faint northern rim the broad component is not detected, possibly indicating a lower density in these regions and/or a broad-component width in excess of 1000 km s-1. Between the limits of zero and full electron-ion temperature equilibration at the shock front, the allowed range of shock velocities is 430-560 km s-1 along the east rim and 700-1250 km s-1 along other parts of the blast wave. The Hα broad-to-narrow flux ratios vary considerably around the remnant, ranging from 0.4 to 0.8. These ratios lie below the values predicted by our shock models. We find that narrow-component Hα emission from a cosmic-ray precursor may be the cause of the discrepancy. The least decelerated portions of the blast wave (i.e., regions excluding the brightest filaments) are well characterized by Sedov models with a kinetic energy E51 = (0.37 ± 0.06)D, where D50 is the LMC distance in units of 50 kpc. The corresponding age for DEM L71 is (4360 ± 290)D50 yr. This is the first time that velocity information from the entire blast wave has been utilized to study the global kinematics of a nonradiative supernova remnants at a known distance.

Star forming rates between z = 0.25 and z = 1.2 from the CADIS emission line survey

The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects emission line galaxies by a scan with an imaging Fabry-Perot interferometer. It covers 5 fields of each in three wavelengths windows centered on , 820, and 920 nm, and reaches to a typical limiting line flux of W m-2. This is the deepest emission line survey covering a field of several 100 . Galaxies between and are detected by prominent emission lines (from Hα to [O ii]372.7) falling into the FP scans. Additional observations with a dozen medium band filters allow to establish the line identification and thus the redshift of the galaxies to better than . On the basis of a total of more than 400 emission line galaxies detected in Hα (92 galaxies), [O iii]500.7 (124 galaxies), or [O ii]372.7 (222 galaxies) we measure the instantaneous star formation rate (SFR) in the range . With this purely emission line selected sample we are able to reach much fainter emission line galaxies than previous, continuum-selected samples. Thus completeness corrections are much less important. Although the relative [O iii] emission line strength depends on excitation and metallicity and shows strong variation, the mean line ratios yield SFR[O iii] values consistent with the SFR evolution. Our results substantiates the indications from previous studies (based on small galaxy samples) that the SFR decreases by a factor of ~20 between and today. In fact, for a cosmology, we find an exponential decline Gyr). This decrease of the SFR with time follows an exponential law which is compatible with the decreasing galaxy merger rate as expected from model calculations. The inferred SF density is in perfect agreement with that deduced from the FIR emission of optically selected galaxies which is explained by a large overlap between both populations. We show that self-consistent extinction corrections of both our emission lines and the UV continua lead to consistent results for the SF density.

Constraints to the evolution of Ly-αbright galaxies betweenz= 3 andz= 6

Galaxies at high redshift with a strong Ly-α emission line trace massive star formation in the absence of dust, and can therefore be regarded as a prime signature of the first major starburst in galaxies. We report results of the Ly-α search within the Calar Alto Deep Imaging Survey (CADIS). With the imaging Fabry-Perot interferometer, CADIS can detect emission lines in three waveband windows free of night-sky emission lines at 700 nm, 820 nm, and 920 nm. The typical flux detection limit for Ly-α emission redshifted into these windows, Flim > 3 × 10 −20 Wm −2 , corresponds to (unobscured) star formation rates of >10 M� /yr at z = 6. Candidate Ly-α-emitting galaxies are selected from the total emission line sample, which contains more than 97% of objects at z 5 than the assumption of a non-evolving population would predict. Therefore we conclude that the Ly-α bright phase of primeval star formation episodes reached its peak at redshifts 3 < z < 6.

The Collimated Wind in NGC 253

Near-infrared Fabry-Perot imaging has revealed H2 emission extended to about 130 pc from the disk of NGC 253. It is closely related to the hot plasma observed in soft X-rays: filamentary H2 features are found at the edges of the hot plasma. These are the places of direct interaction between a superwind and its surrounding molecular gas. We suggest that the filamentary features actually trace a more or less conical shell-like structure, whose tangential line of sight to us is intensely observed. The H2 emission shell is most likely from the molecular gas blown out or swept to the side by the hot plasma outflow. Dust is associated with this molecular gas structure. The outflow is tilted with respect to the disk, possibly suggesting the inhomogeneous nature of the interstellar medium in which the starburst takes place.