| 1. |
- Ferreras, Ignacio, et al.
(författare)
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FIGS : spectral fitting constraints on the star formation history of massive galaxies since the cosmic noon
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 486:1, s. 1358-1376
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Tidskriftsartikel (refereegranskat)abstract
- We constrain the stellar population properties of a sample of 52 massive galaxies - with stellar mass log (M-s/M-circle dot) greater than or similar to 10.5 - over the redshift range 0.5 < z < 2 by use of observer-frame optical and near-infrared slitless spectra from Hubble Space Telescope's ACS and WFC3 grisms. The deep exposures (similar to 100 ks) allow us to target individual spectra of massive galaxies to F160W = 22.5AB. Our spectral fitting approach uses a set of six base models adapted to the redshift and spectral resolution of each observation, and fits the weights of the base models, including potential dust attenuation, via a Markov Chain Monte Carlo method. Our sample comprises a mixed distribution of quiescent (19) and star-forming galaxies (33). We quantify the width of the age distribution (Delta t) that is found to dominate the variance of the retrieved parameters according to principal component analysis. The population parameters follow the expected trend towards older ages with increasing mass, and Delta t appears to weakly anticorrelate with stellar mass, suggesting a more efficient star formation at the massive end. As expected, the redshift dependence of the relative stellar age (measured in units of the age of the Universe at the source) in the quiescent sample rejects the hypothesis of a single burst (aka monolithic collapse). Radial colour gradients within each galaxy are also explored, finding a wider scatter in the star-forming subsample, but no conclusive trend with respect to the population parameters.
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| 2. |
- Pharo, John, et al.
(författare)
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Emission-line Metallicities from the Faint Infrared Grism Survey and VLT/MUSE
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 874:2
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Tidskriftsartikel (refereegranskat)abstract
- We derive direct-measurement gas-phase metallicities of 7.4 < 12 + log (O/H) < 8.4 for 14 low-mass emissionline galaxies at 0.3 < z < 0.8 identified in the Faint Infrared Grism Survey. We use deep slitless G102 grism spectroscopy of the Hubble Ultra Deep Field, dispersing light from all objects in the field at wavelengths between 0.85 and 1.15 mu m. We run an automatic search routine on these spectra to robustly identify 71 emission-line sources, using archival data from Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) to measure additional lines and confirm redshifts. We identify 14 objects with 0.3 < z < 0.8 with measurable [O Iota Iota Iota] lambda 4363 angstrom emission lines in matching VLT/MUSE spectra. For these galaxies, we derive direct electron-temperature gas-phase metallicities with a range of 7.4 < 12 + log (O/H) < 8.4. With matching stellar masses in the range of 10(7.9) M-circle dot < M* < 10(10.4) M-circle dot, we construct a mass-metallicity (MZ) relation and find that the relation is offset to lower metallicities compared to metallicities derived from alternative methods (e.g., R-23,O3N2, N2O2) and continuum selected samples. Using star formation rates derived from the H alpha emission line, we calculate our galaxies' position on the Fundamental Metallicity Relation, where we also find an offset toward lower metallicities. This demonstrates that this emission-line-selected sample probes objects of low stellar masses but even lower metallicities than many comparable surveys. We detect a trend suggesting galaxies with higher Specific Star Formation (SSFR) are more likely to have lower metallicity. This could be due to cold accretion of metal-poor gas that drives star formation, or could be because outflows of metal-rich stellar winds and SNe ejecta are more common in galaxies with higher SSFR.
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