We present deep spectroscopy of 17 very low mass (M ⋆ ≃ 2.0 × 10 6 M ⊙ to 1.4×10 9 M ⊙ ) and low luminosity (M UV ≃ −13.7 to −19.9) gravitationally lensed galaxies in the redshift range z ≃ 1.5 − 3.0. Deep rest-frame ultraviolet spectra reveal large equivalent width emission from numerous emission lines (NIV], OIII], CIV, Si III], CIII]) which are rarely seen in individual spectra of more massive star forming galaxies. CIII] is detected in 16 of 17 low mass star forming systems with rest-frame equivalent widths as large as 13.5Å. Nebular CIV emission is present in the most extreme CIII] emitters, requiring an ionising source capable of producing a substantial component of photons with energies in excess of 47.9 eV. Photoionisation models support a picture whereby the large equivalent widths are driven by the increased electron temperature and enhanced ionising output arising from metal poor gas and stars (0.04 Z ⊙ to 0.13 Z ⊙ ), young stellar populations (6 Myr to 50 Myr), and large ionization parameters (log U = −2.16 to −1.84). The young ages implied by the emission lines and continuum SEDs indicate that the extreme line emitters in our sample are in the midst of a significant upturn in their star formation activity. The low stellar masses, blue UV colours, and large sSFRs of our sample are similar to those of typical z ∼ > 6 galaxies. Given the strong attenuation of Lyα in z ∼ > 6 galaxies, we suggest that CIII] is likely to provide our best probe of early star forming galaxies with ground-based spectrographs and one off the most efficient means of confirming z ∼ > 10 galaxies with the James Webb Space Telescope.

We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628The 1 is consistent with a power-law distribution of slopes~-2 and a truncation of a few times 10 5  M . After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find massindependent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (10 4  M ) clusters, suggesting that a massdependent component is necessary to fully describe the YSC disruption process in NGC 628.Astrophysical Journal, 841:131 (26pp), 2017 June 1 https: