We present results from near-infrared spectroscopy of 26 emission-line galaxies at z ∼ 2.2 and z ∼ 1.5 obtained with the Folded-port InfraRed Echellette (FIRE) spectrometer on the 6.5-meter Magellan Baade telescope. The sample was selected from the WFC3 Infrared Spectroscopic Parallels (WISP) survey, which uses the near-infrared grism of the Hubble Space Telescope Wide Field Camera 3 to detect emission-line galaxies over 0.3 z 2.3. Our FIRE follow-up spectroscopy (R∼5000) over 1.0-2.5 µm permits detailed measurements of physical properties of the z ∼ 2 emission-line galaxies. Dust-corrected star formation rates for the sample range from ∼5-100 M ⊙ yr −1 with a mean of 29 M ⊙ yr −1 . We derive a median metallicity for the sample of 12 + log(O/H) = 8.34 or ∼0.45 Z ⊙ . The estimated stellar masses range from ∼10 8.5 − 10 9.5 M ⊙ , and a clear positive correlation between metallicity and stellar mass is observed. The average ionization parameter measured for the sample, log U ≈ −2.5, is significantly higher than what is found for most star-forming galaxies in the local universe, but similar to the values found for other star-forming galaxies at high redshift. We derive composite spectra from the FIRE sample, from which we infer typical nebular electron densities of ∼100-400 cm −3 . Based on the location of the galaxies and composite spectra on BPT diagrams, we do not find evidence for significant AGN activity in the sample. Most of the galaxies as well as the composites are offset in the BPT diagram toward higher [O iii]/Hβ at a given [N ii]/Hα, in agreement with other observations of z 1 star-forming galaxies, but composite spectra derived from the sample do not show an appreciable offset from the local star-forming sequence on the [O iii]/Hβ versus [S ii]/Hα diagram. We infer a high nitrogen-to-oxygen abundance ratio from the composite spectrum, which may contribute to the offset of the high-redshift galaxies from the local star-forming sequence in the [O iii]/Hβ versus [N ii]/Hα diagram. We speculate that the elevated nitrogen abundance could result from substantial numbers of Wolf-Rayet stars in starbursting galaxies at z ∼ 2.

The WFC3 Infrared Spectroscopic Parallel Survey uses the Hubble Space Telescope (HST) infrared grism capabilities to obtain slitless spectra of thousands of galaxies over a wide redshift range including the peak of star formation history of the universe. We select a population of very strong emission-line galaxies with rest-frame equivalent widths (EWs) higher than 200 Å. A total of 176 objects are found over the redshift range 0.35 < z < 2.3 in the 180 arcmin 2 area that we have analyzed so far. This population consists of young and low-mass starbursts with high specific star formation rates (sSFR). After spectroscopic follow-up of one of these galaxies with Keck/Low Resolution Imaging Spectrometer, we report the detection at z = 0.7 of an extremely metal-poor galaxy with 12 + log(O/H) = 7.47 ± 0.11. After estimating the active galactic nucleus fraction in the sample, we show that the high-EW galaxies have higher sSFR than normal star-forming galaxies at any redshift. We find that the nebular emission lines can substantially affect the total broadband flux density with a median brightening of 0.3 mag, with some examples of line contamination producing brightening of up to 1 mag. We show that the presence of strong emission lines in low-z galaxies can mimic the color-selection criteria used in the z ∼ 8 dropout surveys. In order to effectively remove low-redshift interlopers, deep optical imaging is needed, at least 1 mag deeper than the bands in which the objects are detected. Without deep optical data, most of the interlopers cannot be ruled out in the wide shallow HST imaging surveys. Finally, we empirically demonstrate that strong nebular lines can lead to an overestimation of the mass and the age of galaxies derived from fitting of their spectral energy distribution (SED). Without removing emission lines, the age and the stellar mass estimates are overestimated by a factor of 2 on average and up to a factor of 10 for the high-EW galaxies. Therefore, the contribution of emission lines should be systematically taken into account in SED fitting of star-forming galaxies at all redshifts.

We present near-infrared emission line counts and luminosity functions from the HST WFC3 Infrared Spectroscopic Parallels (WISP) program for 29 fields (0.037 deg 2 ) observed using both the G102 and G141 grism. Altogether we identify 1048 emission line galaxies with observed equivalent widths greater than 40Å, 467 of which have multiple detected emission lines. We use simulations to correct for significant (>20%) incompleteness introduced in part by the non-dithered, non-rotated nature of the grism parallels. The WISP survey is sensitive to fainter flux levels (3-5×10 −17 ergs s −1 cm −2 ) than the future space near-infrared grism missions aimed at baryonic acoustic oscillation cosmology (1-4 ×10 −16 ergs s −1 cm −2 ), allowing us to probe the fainter emission line galaxies that the shallower future surveys may miss. Cumulative number counts of 0.7

Spectroscopic observations of Hα and Hβ emission lines of 128 star-forming galaxies in the redshift range 0.75 ≤ z ≤ 1.5 are presented. These data were taken with slitless spectroscopy using the G102 and G141 grisms of the Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of the WFC3 Infrared Spectroscopic Parallel (WISP) survey. Interstellar dust extinction is measured from stacked spectra that cover the Balmer decrement (Hα/Hβ). We present dust extinction as a function of Hα luminosity (down to 3 × 10 41 erg s −1 ), galaxy stellar mass (reaching 4 × 10 8 M ), and rest-frame Hα equivalent width. The faintest galaxies are two times fainter in Hα luminosity than galaxies previously studied at z ∼ 1.5. An evolution is observed where galaxies of the same Hα luminosity have lower extinction at higher redshifts, whereas no evolution is found within our error bars with stellar mass. The lower Hα luminosity galaxies in our sample are found to be consistent with no dust extinction. We find an anti-correlation of the [O III]λ5007/Hα flux ratio as a function of luminosity where galaxies with L Hα < 5 × 10 41 erg s −1 are brighter in [O III]λ5007 than Hα. This trend is evident even after extinction correction, suggesting that the increased [O III]λ5007/Hα ratio in low luminosity galaxies is likely due to lower metallicity and/or higher ionization parameters.

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 G 102 (λ = 0.8-1.17 μm, R ∼ 210) and G 141 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 arcmin 2 . For typical exposure times (∼6400 s in G 102 and ∼2700 s in G 141 ), 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 arcmin 2 . 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 H 140 ∼ 25, or M R < −19, and are sensitive to SFRs down to less than 1 M 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.