Nicholas R. Collins

The On-Orbit Performance of the Space Telescope Imaging Spectrograph

The Space Telescope Imaging Spectrograph (STIS) was successfully installed into the Hubble Space Telescope (HST) in 1997 February, during the second HST servicing mission, STS-82. STIS is a versatile spectrograph, covering the 115-1000 nm wavelength range in a variety of spectroscopic and imaging modes that take advantage of the angular resolution, unobstructed wavelength coverage, and dark sky offered by the HST. In the months since launch, a number of performance tests and calibrations have been carried out and are continuing. These tests demonstrate that the instrument is performing very well. We present here a synopsis of the results to date.

A Pair of Compact Red Galaxies at Redshift 2.38, Immersed in a 100 Kiloparsec Scale Lyα Nebula*

We present Hubble Space Telescope (HST) and ground-based observations of a pair of galaxies at redshift 2.38, which are collectively known as 2142 4420 B1 (Francis et al. 1996). The two galaxies are both luminous extremely red objects (EROs), separated by 0.8 ′′ . They are embedded within a 100 kpc scale diffuse

MEASUREMENT OF COSMIC SHEAR WITH THE SPACE TELESCOPE IMAGING SPECTROGRAPH

Weak lensing by large-scale structure allows a direct measure of the dark matter distribution. We have used parallel images taken with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope to measure weak lensing, or cosmic shear. We measure the shapes of 26,036 galaxies in 1292 STIS fields and measure the shear variance at a scale of 051. The charge transfer efficiency (CTE) of STIS has degraded over time and introduces a spurious ellipticity into galaxy shapes during the readout process. We correct for this effect as a function of signal-to-noise ratio and CCD position. We further show that the detected cosmic shear signal is nearly constant in time over the approximately 4 yr of observation. We detect cosmic shear at the 5.1 σ level, and our measurement of the shear variance is consistent with theoretical predictions in a ΛCDM universe. This provides a measure of the normalization of the mass power spectrum σ8 = 0.46 0.18. The 1 σ error includes noise, cosmic variance, systematics, and the redshift uncertainty of the source galaxies. This is consistent with previous cosmic shear measurements, but tends to favor those with a high value of σ8. It is also consistent with the recent determination of σ8 from the Wilkinson Microwave Anisotropy Probe (WMAP) experiment.

THE ULTRAVIOLET IMAGING TELESCOPE: INSTRUMENT AND DATA CHARACTERISTICS

The Ultraviolet Imaging Telescope (\UIT) was flown as part of the \AstroMiss\ observatory on the Space Shuttle Columbia in December 1990 and again on the Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300A) images of a variety of astronomical objects, with a 40\arcmin\ field of view and a resolution of about 3\arcsec, were recorded on photographic film. The data recorded during the first flight is available to the astronomical community through the National Space Science Data Center (NSSDC); the data recorded during the second flight will soon be available as well. This paper discusses in detail the design, operation, data reduction, and calibration of \UIT, providing the user of the data with information for understanding and using the data. It also provides guidelines for analyzing other astronomical imagery made with image intensifiers and photographic film.

Emission-Line Galaxies in the STIS Parallel Survey. II. Star Formation Density

We present the luminosity function of [O II]-emitting galaxies at a median redshift of z = 0.9, as measured in the deep spectroscopic data in the STIS Parallel Survey (SPS). The luminosity function shows strong evolution from the local value, as expected. By using random lines of sight, the SPS measurement complements previous deep single-field studies. We calculate the density of inferred star formation at this redshift by converting from [O II] to Hα line flux as a function of absolute magnitude and find = 0.043 ± 0.014 M☉ yr-1 Mpc-3 at a median redshift z ~ 0.9 within the range 0.46 < z < 1.415 (H0 = 70 km s-1 Mpc-1, ΩM = 0.3, ΩΛ = 0.7). This density is consistent with a (1 + z)4 evolution in global star formation since z ~ 1. To reconcile the density with similar measurements made by surveys targeting Hα may require substantial extinction correction.

The Ultraviolet Imaging Telescope - Design and performance

The instrumental configuration, calibration, and operations during the first flight of the Ultraviolet Imaging Telescope on the Astro-1 mission, December 2-10, 1990, are described. The UV images of a wide variety of astronomical objects were recorded with a 40-arcmin diameter field of view. Images of targets as faint as magnitude 21 (UV) were secured with a resolution of about 3 arcsec. The optics, light baffling, and image motion compensation system are summarized, and detectors and electronic subsystems are described.

Far-ultraviolet Color Gradients in Early-Type Galaxies

We discuss far-UV (FUV) (1500 ?) surface photometry and FUV-B color profiles for eight E/S0 galaxies from images taken with the Ultraviolet Imaging Telescope, primarily during the Astro-2 mission. In three cases, the FUV radial profiles are more consistent with an exponential than a de Vaucouleurs function, but there is no other evidence for the presence of a disk or of young, massive stars. In all cases except M32, the FUV-B color becomes redder at larger radii. There is a wide range of internal radial FUV-B color gradients. However, we find no correlation between the FUV-B color gradients and internal metallicity gradients based on Mg absorption features. We conclude that metallicity is not the sole parameter controlling the UV upturn component in old populations.

Ultraviolet imaging of old population in nearby galaxies

We analyze UV imagery of two Sb bulges and two E galaxies obtained with the Ultraviolet Imaging Telescope during the Astro-1 mission. The UV brightness of these systems is not produced by recent massive star formation. Instead it must originate in relatively low-luminosity objects, probably low-mass, post-giant-branch stars. We find extended, large-amplitude UV color gradients, which are probably related to abundance gradients within the galaxies. M32 has a color gradient opposite to the other three objects, possibly because of an intermediate-age population.

Measurements of the Diffuse Ultraviolet Background and the Terrestrial Airglow with the Space Telescope Imaging Spectrograph

Far-UV observations in and near the Hubble Deep Fields demonstrate that the Space Telescope Imaging Spectrograph (STIS) may obtain unique and precise measurements of the diffuse far-ultraviolet background. Although STIS is not the ideal instrument for such measurements, high-resolution images allow Galactic and extragalactic objects to be masked to very faint magnitudes, thus ensuring a measurement of the truly diffuse UV signal. The programs we have analyzed were not designed for this scientific purpose, but they would be sufficient to obtain a very sensitive measurement if it were not for a weak but larger than expected signal from airglow in the STIS 1450?1900 ? bandpass. Our analysis shows that STIS far-UV crystal quartz observations taken near the limb during orbital day can detect a faint airglow signal, most likely from N I ?1493, that is comparable to the dark rate and inseparable from the far-UV background. Discarding all but the night data from these data sets yields the diffuse far-ultraviolet background measurement 501 ? 103 photons cm-2 s-1 sr-1 ?-1, along a line of sight with very low Galactic neutral hydrogen column (NH I = 1.5 ? 1020 cm-2) and extinction [E(B-V) = 0.01 mag]. This result is in good agreement with earlier measurements of the far-UV background and should not include any significant contribution from airglow. We present our findings as a warning to other groups who may use the STIS far-UV camera to observe faint extended targets and to demonstrate how this measurement may be properly obtained with STIS.

Wide-Field Imaging of the Hubble Deep Field-South Region. II. The Evolution of Galaxy Clustering at z < 1*

We present the galaxy-galaxy angular correlations as a function of photometric redshift in a deep, wide galaxy survey centered on the Hubble Deep Field-South (HDF-S). Images were obtained with the Big Throughput Camera on the Blanco 4 m telescope at CTIO, of square degree in broadband uBVRI, reaching ~24 mag. Approximately 40,000 galaxies are detected in the survey. We determine photometric redshifts using galaxy template fitting to the photometry. Monte Carlo simulations show that redshifts from these data should be reliable out to z ~ 1, where the 4000 A break shifts into the I band. The inferred redshift distribution, n(z), shows good agreement with the distribution of galaxies measured in the Hubble Deep Field-North (HDF-N) and the Canada-France Redshift Survey. After assigning galaxies to redshift bins with width Δz = 0.33, we determine the two-point angular correlation function in each bin. We find that the amplitude of the correlation, Aw, drops across the three bins to redshift z ~ 1. Simple models of clustering evolution fit this result, with the best agreement for = 0. Hierarchical cold dark matter models best fit in a low-density, Λ-dominated universe.