The WFC3 infrared spectroscopic parallel (WISP) survey

We present the WFC3 Infrared Spectroscopic Parallel (WISP) Survey. WISP is obtaining slitless, near-infrared grism spectroscopy of ∼90 independent, high-latitude fields by observing in the pure-parallel mode with the Wide Field Camera Three on the Hubble Space Telescope for a total of ∼250 orbits. Spectra are obtained with the G₁₀₂ (λ = 0.8-1.17 μm, R ∼ 210) and G₁₄₁ grisms (λ = 1.11-1.67 μm, R ∼ 130), together with direct imaging in the J and H bands (F110W and F140W, respectively). In the present paper, we present the first results from 19 WISP fields, covering approximately 63 arcmin². For typical exposure times (∼6400 s in G₁₀₂ and ∼2700 s in G₁₄₁), we reach 5σ detection limits for emission lines of f ∼ 5 × 10 ^-17 erg s^-1 cm^-2 for compact objects. Typical direct imaging 5σ limits are 26.3 and 26.1 mag. (AB) in F110W and F140W, respectively. Restricting ourselves to the lines measured with the highest confidence, we present a list of 328 emission lines, in 229 objects, in a redshift range 0.3 < z < 3. The single-line emitters are likely to be a mix of Hα and [O III]5007,4959 Å, with Hα predominating. The overall surface density of high-confidence emission-line objects in our sample is approximately 4 per arcmin². These first fields show high equivalent width sources, active galactic nucleus, and post-starburst galaxies. The median observed star formation rate (SFR) of our Hα-selected sample is 4 M_⊙ yr^-1. At intermediate redshifts, we detect emission lines in galaxies as faint as H₁₄₀ ∼ 25, or M _R < - 19, and are sensitive to SFRs down to less than 1M _⊙ yr^-1. The slitless grisms on WFC3 provide a unique opportunity to study the spectral properties of galaxies much fainter than L^* at the peak of the galaxy assembly epoch.