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Emission-line galaxies at z ∼ 1 from near-IR HST slitless spectroscopy : metallicities, star formation rates, and redshift confirmations from VLT/FORS2 spectroscopy

2025-09-12T09:27:34Z

Title: Emission-line galaxies at z ∼ 1 from near-IR HST slitless spectroscopy : metallicities, star formation rates, and redshift confirmations from VLT/FORS2 spectroscopy Authors: Boyett, K.; Bunker, A. J.; Chevallard, J.; Battisti, A.; Henry, A. L.; Wilkins, Stephen M.; Malkan, M. A.; Caruana, Joseph; Atek, H.; Baronchelli, I.; Colbert, J.; Dai, Y. S.; Gardner, Jonathan P.; Rafelski, M.; Scarlata, C.; Teplitz, H. I.; Wang, X. 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 targeted 85 of 138 line emission objects at identified in WFC3 spectroscopy. Half the galaxies are fainter than mag, and would not have been included in many well-known surveys based on broad-band magnitude selection. We confirm 95 per cent 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 per cent at did not have expected emission lines detected in FORS2 and hence may be spurious (although this false-detection rate improves to 33 per cent using the latest public WISP emission line catalogue). From the Balmer decrement, the extinction of the WISP galaxies is consistent with H mag. From SED fits to multiband photometry including Spitzer m, we find a median stellar mass of ⁠. Our emission-line-selected galaxies tend to lie above the star-forming main sequence (i.e. higher specific star formation rates). Using [O iii], [O ii], and H β lines to derive gas-phase metallicities, we find typically sub-solar metallicities, decreasing with redshift. Our WISP galaxies lie below the 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 α rest-frame equivalent width in this emission-line selected sample, with higher galaxies having larger [O iii]/H β and O32 ratios on average, suggesting lower metallicity or higher ionization parameter in these extreme emission line galaxies.

The next generation deep extragalactic exploratory public near-infrared slitless survey epoch 1 (NGDEEP-NISS1) : extragalactic star-formation and active galactic nuclei at 0.5 < z < 3.6

2025-08-28T07:53:23Z

Title: The next generation deep extragalactic exploratory public near-infrared slitless survey epoch 1 (NGDEEP-NISS1) : extragalactic star-formation and active galactic nuclei at 0.5 < z < 3.6 Authors: Pirzkal, Nor; Rothberg, Barry; Papovich, Casey; Shen, Lu; Leung, Gene C. K.; Bagley, Micaela B.; Finkelstein, Steven L.; Vanderhoof, Brittany N.; Lotz, Jennifer M.; Koekemoer, Anton M.; Hathi, Nimish P.; Cheng, Yingjie; Cleri, Nikko J.; Grogin, Norman A.; Yung, L. Y. Aaron; Dickinson, Mark; Ferguson, Henry C.; Gardner, Jonathan P.; Jung, Intae; Kartaltepe, Jeyhan S.; Ryan, Russell; Simons, Raymond C.; Ravindranath, Swara; Berg, Danielle A.; Backhaus, Bren E.; Casey, Caitlin M.; Castellano, Marco; Chávez Ortiz, Óscar A.; Chworowsky, Katherine; Cox, Isabella G.; Davé, Romeel; Davis, Kelcey; Estrada-Carpenter, Vicente; Fontana, Adriano; Fujimoto, Seiji; Giavalisco, Mauro; Grazian, Andrea; Hutchison, Taylor A.; Jaskot, Anne E.; Kewley, Lisa J.; Kirkpatrick, Allison; Kocevski, Dale D.; Larson, Rebecca L.; Matharu, Jasleen; Natarajan, Priyamvada; Pentericci, Laura; Pérez-González, Pablo G.; Snyder, Gregory F.; Somerville, Rachel S.; Trump, Jonathan R.; Wilkins, Stephen M. Abstract: The Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey program was designed specifically to include Near Infrared Slitless Spectroscopic observations (NGDEEP-NISS) to detect multiple emission lines in as many galaxies as possible and across a wide redshift range using the Near Infrared Imager and Slitless Spectrograph. We present early results obtained from the first set of observations (Epoch 1, 50% of the allocated orbits) of this program (NGDEEP-NISS1). Using a set of independently developed calibration files designed to deal with a complex combination of overlapping spectra, multiple position angles, and multiple cross filters and grisms, in conjunction with a robust and proven algorithm for quantifying contamination from overlapping dispersed spectra, NGDEEP-NISS1 has achieved a 3σ sensitivity limit of 2 × 10−18 erg s−1 cm−2. We demonstrate the power of deep wide field slitless spectroscopy (WFSS) to characterize the star formation rates, and metallicity ([O iii]/Hβ), and dust content, of galaxies at 1 < z < 3.5. The latter showing intriguing initial results on the applicability and assumptions made regarding the use of Case B recombination. Further, we identify the presence of active galactic nuclei and infer the mass of their supermassive black holes using broadened restframe Mg ii and Hβ emission lines. The spectroscopic results are then compared with the physical properties of galaxies extrapolated from fitting spectral energy distribution models to photometry alone. The results clearly demonstrate the unique power and efficiency of WFSS at near-infrared wavelengths over other methods to determine the properties of galaxies across a broad range of redshifts.

Physical properties of extreme emission-line galaxies at z ∼ 4-9 from the JWST CEERS survey

2025-08-27T06:02:50Z

Title: Physical properties of extreme emission-line galaxies at z ∼ 4-9 from the JWST CEERS survey Authors: Llerena, M.; Amorín, R.; Pentericci, L.; Arrabal Haro, P.; Backhaus, B. E.; Bagley, M. B.; Calabrò, A.; Cleri, N. J.; Davis, K.; Dickinson, M.; Finkelstein, S. L.; Gawiser, E.; Grogin, N. A.; Hathi, N. P.; Hirschmann, M.; Kartaltepe, J. S.; Koekemoer, A. M.; McGrath, E. J.; Mobasher, B.; Napolitano, L.; Papovich, C.; Pirzkal, N.; Trump, J. R.; Wilkins, Stephen M.; Yung, L. Y. A. Abstract: Context. Extreme emission line galaxies (EELGs) are typically characterized by high equivalent widths (EWs) which are driven by elevated specific star formation rates (sSFRs) in low-mass galaxies with subsolar metallicities and little dust. Such extreme systems are exceedingly rare in the local universe, but the number density of EELGs increases with increasing redshift. Such starburst galaxies are currently strongly presumed to be the main drivers of hydrogen reionization over 5.5 < z < 15, which serves to motivate many of the searches for high-z EELGs. Aims. We aim to characterize the physical properties of a sample of ∼730 EELGs at 4 ≤ z < 9 photometrically selected from the CEERS survey using JWST/NIRCam. We validate our method and demonstrate the main physical properties of a subset of EELGs using NIRSpec spectra. Methods. We create synthetic NIRCam observations of EELGs using empirical templates based on ∼2000 local metal-poor starbursts to select EELGs based on color-color criteria. We study their properties based on SED fitting and flux excess from emission lines in the photometric filters. Results. Our sample of EELGs has a mean stellar mass of 107.84 M with high sSFRs from SED fitting with a mean value of 10−7.03 yr−1 . We consider a delayed-τ model for the star formation history and find our sample of EELGs are young with a mean value of the time after the onset of star formation of 45 Myr. We find that they have similar line ratios to local metal-poor starburst galaxies with high log([OIII]/Hβ) & 0.4−1 which indicates that star formation may be the dominant source of ionization in these galaxies. Based on the photometric fluxes and morphologies, we find an increase of EW([OIII]+Hβ) with sSFR and ΣSFR, and a decrease with age and stellar mass. The sample of EELGs can reach ΣSFR > 10 M yr−1 kpc−2 which indicate they are strong candidates of LyC leakers. Another indirect indicator is the high values of O32 > 5 that can be reached for some galaxies in the sample. This indicates that they may have the conditions to facilitate the escape of ionizing photons.

Characterizing the average interstellar medium conditions of galaxies at z ∼ 5.6–9 with ultraviolet and optical nebular lines

2025-08-26T07:18:59Z

Title: Characterizing the average interstellar medium conditions of galaxies at z ∼ 5.6–9 with ultraviolet and optical nebular lines Authors: Hu, Weida; Papovich, Casey; Dickinson, Mark; Kennicutt, Robert; Shen, Lu; Amorín, Ricardo O.; Arrabal Haro, Pablo; Bagley, Micaela B.; Bhatawdekar, Rachana; Cleri, Nikko J.; Cole, Justin W.; Dekel, Avishai; de la Vega, Alexander; Finkelstein, Steven L.; Grogin, Norman A.; Hathi, Nimish P.; Hirschmann, Michaela; Holwerda, Benne W.; Hutchison, Taylor A.; Jung, Intae; Koekemoer, Anton M.; Kartaltepe, Jeyhan S.; Lucas, Ray A.; Llerena, Mario; Mascia, S.; Mobasher, Bahram; Napolitano, L.; Newman, Jeffrey A.; Pentericci, Laura; Pérez-González, Pablo G.; Trump, Jonathan R.; Wilkins, Stephen M.; Yung, L. Y. Aaron Abstract: Ultraviolet (UV; rest-frame ∼1200–2000 Å) spectra provide a wealth of diagnostics to characterize fundamental galaxy properties, such as their chemical enrichment, the nature of their stellar populations, and their amount of Lyman-continuum (LyC) radiation. In this work, we leverage publicly released JWST data to construct the rest-frame UV-to-optical composite spectrum of a sample of 63 galaxies at 5.6 < z < 9, spanning a wavelength range from 1500 to 5200 Å. Based on the composite spectrum, we derive an average dust attenuation from Hβ/Hγ, an electron density cm−3 from the [O ii] doublet ratio, an electron temperature K from the [O iii] λ4363/[O iii] λ5007 ratio, and an ionization parameter from the [O iii]/[O ii] ratio. Using a direct Te method, we calculate an oxygen abundance and a carbon-to-oxygen (C/O) abundance ratio . This C/O ratio is smaller than compared to z = 0 and z = 2–4 star-forming galaxies, albeit with moderate significance. This indicates the reionization-era galaxies might be undergoing a rapid buildup of stellar mass with high specific star formation rates. A UV diagnostic based on the ratios of C iii] λλ1907, 1909/He iiλ1640 versus O iii] λ1666/He iiλ1640 suggests that the star formation is the dominant source of ionization, similar to the local extreme dwarf galaxies and z ∼ 2–4 He ii–detected galaxies. The [O iii]/[O ii] and C iv/C iii] ratios of the composite spectrum are marginally larger than the criteria used to select galaxies as LyC leakers, suggesting that some of the galaxies in our sample are strong contributors to the reionizing radiation.