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arXiv · 2404.07497

Emission-line galaxies at $z\sim1$ from near-IR HST Slitless Spectroscopy: metallicities, star formation rates and redshift confirmations from VLT/FORS2 spectroscopy

K. Boyett·A. J. Bunker·J Chevallard·A. J. Battisti·A. L. Henry·S. Wilkins·M. A. Malkan·J. Caruana·H. Atek·I. Baronchelli·J. Colbert·Y. S. Dai·Jonathan. P. Gardner·M. Rafelski·C. Scarlata·H. I. Teplitz·X. Wang
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Abstract

We follow up emission line galaxies identified through the near-infrared slitless HST/WFC3 WISP survey with VLT/FORS2 optical spectroscopy. Over 4 WISP fields, we targetted 85 of 138 line emission objects at $0.4<z<2$ identified in WFC3 spectroscopy. Half the galaxies are fainter than $H_{AB}=24$mag, and would not have been included in many well-known surveys based on broad-band magnitude selection. We confirm 95% of the initial WFC3 grism redshifts in the 38 cases where we detect lines in FORS2 spectroscopy. However, for targets which exhibited a single emission line in WFC3, up to 65% at $z<1.28$ did not have expected emission lines detected in FORS2 and hence may be spurious (although this false-detection rate improves to 33% using the latest public WISP emission line catalogue). From the Balmer decrement the extinction of the WISP galaxies is consistent with $A($H$\alpha)=1$mag. From SED fits to multi-band photometry including Spitzer $3.6\mu$m, we find a median stellar mass of $\log_{10}(M/M_{\odot})=8.94$. Our emission-line-selected galaxies tend to lie above the star-forming main sequence (i.e. higher specific star formation rates). Using [OIII], [OII] and H$\beta$ lines to derive gas-phase metallicities, we find typically sub-solar metallicities, decreasing with redshift. Our WISP galaxies lie below the $z=0$ mass-metallicity relation, and galaxies with higher star formation rates tend to have lower metallicity. Finally, we find a strong increase with redshift of the H$\alpha$ rest-frame equivalent width in this emission-line selected sample, with higher $EW_0$ galaxies having larger [OIII]/H$\beta$ and O32 ratios on average, suggesting lower metallicity or higher ionisation parameter in these extreme emission line galaxies.

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K. Boyett, A. J. Bunker, J Chevallard, A. J. Battisti, A. L. Henry, S. Wilkins, M. A. Malkan, J. Caruana, H. Atek, I. Baronchelli, J. Colbert, Y. S. Dai, Jonathan. P. Gardner, M. Rafelski, C. Scarlata, H. I. Teplitz, X. Wang. 2024-04-11. Emission-line galaxies at $z\sim1$ from near-IR HST Slitless Spectroscopy: metallicities, star formation rates and redshift confirmations from VLT/FORS2 spectroscopy. https://arxiv.org/abs/2404.07497

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