We present a luminosity function for Hα emission from galaxies at redshifts between 0.7 and 1.9 based on slitless spectroscopy with NICMOS on HST. The luminosity function is well fit by a Schechter function over the range 6 × 10 41 < L(Hα) < 2 × 10 43 erg sec −1 with L * = 7 × 10 42 erg sec −1 and φ * = 1.7 × 10 −3 Mpc −3 for H 0 = 50 km s −1 Mpc −1 and q 0 = 0.5. We derive a volume averaged star formation rate at z = 1.3 ± 0.5 of 0.13 M ⊙ yr −1 Mpc −3 without correction for extinction. The SFR that we derive at ∼ 6500Å is a factor of 3 higher than that deduced from 2800Å continua. If this difference is due entirely to reddening, the extinction correction at 2800Å is quite significant. The precise magnitude of the total extinction correction at rest-frame UV wavelengths (e.g. 2800Å and 1500Å) is sensitive to the relative spatial distribution of the stars, gas and dust, as well as on the extinction law. In the extreme case of a homogeneous foreground dust screen and a MW or LMC extinction law, we derive a total extinction at 2800Å of 2.1 magnitudes, or a factor of 7 correction to the UV luminosity density. If we use the Calzetti reddening curve, which was derived for the model where stars, gas and dust are well mixed and nebular gas suffers more extinction than stars, our estimate of A 2800 is increased by more than one magnitude.

We investigate the environment of the nearest Herbig Ae star, HD 104237, with a multiwavelength combination of optical coronagraphic, near-IR, and mid-IR imaging supported by optical, UV, and far-ultraviolet spectroscopy. We confirm the presence of T Tauri stars associated with the Herbig Ae star HD 104237, noted by Feigelson et al. We find that two of the stars within 15 00 of HD 104237 have IR excesses, potentially indicating the presence of circumstellar disks, in addition to the Herbig Ae star itself. We derive a new spectral type of A7.5Ve-A8Ve for HD 104237 and find log (L=L ) ¼ 1:39. With these data, HD 104237 has an age of t % 5 Myr, in agreement with the estimates for the other members of the association. HD 104237 is still actively accreting, with a conspicuous UV/far-UV excess seen down to 1040 8, and is driving a bipolar microjet termed HH 669. This makes it the second, older Herbig Ae star now known to have a microjet. The presence of the microjet enables us to constrain the circumstellar disk to r 0B6 (70 AU) with an inclination angle of i ¼ 18 þ14 À11 from pole-on. The absence of a spatially extended continuum and fluorescent H 2 emission near Ly is in agreement with the prediction of shadowed disk models for the IR spectral energy distribution. With the high spatial density of disks in this group of stars, proximity, and minimal reddening, HD 104237 and its companions should serve as ideal laboratories for probing the comparative evolution of planetary systems.

We have used the F160W filter (1.4-1.8 um) and the coronagraph on the Near-InfraRed Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope (HST) to survey 45 single stars with a median age of 0.15 Gyr, an average distance of 30 pc, and an average H-magnitude of 7 mag. For the median age we were capable of detecting a 30 M_Jup companion at separations between 15 and 200 AU. A 5 M_Jup object could have been detected at 30 AU around 36% of our primaries. For several of our targets that were less than 30 Myr old, the lower mass limit was as low as a Jupiter mass, well into the high mass planet region. Results of the entire survey include the proper motion verification of five low-mass stellar companions, two brown dwarfs (HR7329B and TWA5B) and one possible brown dwarf binary (Gl 577B/C).Comment: 11 figures, accepted by A

We present Hubble Space T elescope and ground-based observations of a pair of galaxies at a redshift of 2.38, which are collectively known as 2142[4420 B1. Both galaxies are luminous extremely red objects (EROs) and are separated by They are embedded within a 100 kpc scale di †use Lya nebula 0A .8. (or blob) of luminosity D1044 ergs s~1. The radial proÐles and colors of both red objects are most naturally explained if they are young elliptical galaxies, the most distant galaxies of this type found to date. It is not possible, however, to rule out a model in which they are abnormally compact, extremely dusty starbursting disk galaxies. If they are elliptical galaxies, their stellar populations have inferred masses of D1011 and ages of D7 ] 108 yr. Both galaxies have color gradients : their centers are signiÐcantly M _ bluer than their outer regions. The surface brightness of both galaxies is roughly 1 order of magnitude greater than would be predicted by the Kormendy relation. A chain of di †use star formation extending 1A from the galaxies may be evidence that they are interacting or merging. The Lya nebula surrounding the galaxies shows apparent velocity substructure of amplitude D700 km s~1. We propose that the Lya emission from this nebula may be produced by fast shocks that are powered either by a galactic superwind or by the release of gravitational potential energy.

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.

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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.

We compare mid-infrared emission-line properties, from high-resolutionSpitzer spectra of a hard X-ray (14 -195 keV) selected sample of nearby (z < 0.05) AGN detected by the Burst Alert Telescope (BAT) aboard Swift. The luminosity distribution for the mid-infrared emission-lines, [O IV] 25.89 µm, [Ne II] 12.81 µm, [Ne III] 15.56 µm and [Ne V] 14.32/24.32 µm, and hard X-ray continuum show no differences between Seyfert 1 and Seyfert 2 populations, however six newly discovered BAT AGNs are under-luminous in [O IV], most likely the result of dust extinction in the host galaxy. The overall tightness of the midinfrared correlations and BAT fluxes and luminosities suggests that the emission lines primarily arise in gas ionized by the AGN. We also compare the mid-infrared emission-lines in the BAT AGNs with those from published studies of ULIRGs, PG QSOs, star-forming galaxies and LINERs. We find that the BAT AGN sample fall into a distinctive region when comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] ratios. These line ratios are lower in sources that have been previously classified in the mid-infrared/optical as AGN than those found for the BAT AGN, suggesting that, in our X-ray selected sample, the AGN represents the main contribution to the observed line emission. These ratios represent a new emission line diagnostic for distinguishing between AGN and star forming galaxies.