The BPT Diagram in Cosmological Galaxy Formation Simulations: Understanding the Physics Driving Offsets at High Redshift
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The BPT Diagram in Cosmological Galaxy Formation Simulations : Understanding the Physics Driving Offsets at High Redshift. / Garg, Prerak; Narayanan, Desika; Byler, Nell; Sanders, Ryan L.; Shapley, Alice E.; Strom, Allison L.; Davé, Romeel; Hirschmann, Michaela; Lovell, Christopher C.; Otter, Justin; Popping, Gergö; Privon, George C.
I: Astrophysical Journal, Bind 926, Nr. 1, 80, 15.02.2022.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
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TY - JOUR
T1 - The BPT Diagram in Cosmological Galaxy Formation Simulations
T2 - Understanding the Physics Driving Offsets at High Redshift
AU - Garg, Prerak
AU - Narayanan, Desika
AU - Byler, Nell
AU - Sanders, Ryan L.
AU - Shapley, Alice E.
AU - Strom, Allison L.
AU - Davé, Romeel
AU - Hirschmann, Michaela
AU - Lovell, Christopher C.
AU - Otter, Justin
AU - Popping, Gergö
AU - Privon, George C.
PY - 2022/2/15
Y1 - 2022/2/15
N2 - The Baldwin, Philips, & Terlevich diagram of [O iii]/Hβ versus [N ii]/Hα (hereafter N2-BPT) has long been used as a tool for classifying galaxies based on the dominant source of ionizing radiation. Recent observations have demonstrated that galaxies at z ∼2 reside offset from local galaxies in the N2-BPT space. In this paper, we conduct a series of controlled numerical experiments to understand the potential physical processes driving this offset. We model nebular line emission in a large sample of galaxies, taken from the simba cosmological hydrodynamic galaxy formation simulation, using the cloudy photoionization code to compute the nebular line luminosities from H ii regions. We find that the observed shift toward higher [O iii]/Hβ and [N ii]/Hα values at high redshift arises from sample selection: when we consider only the most massive galaxies M ∗ ∼1010-11 M ⊙, the offset naturally appears, due to their high metallicities. We predict that deeper observations that probe lower-mass galaxies will reveal galaxies that lie on a locus comparable to z ∼0 observations. Even when accounting for samples-selection effects, we find that there is a subtle mismatch between simulations and observations. To resolve this discrepancy, we investigate the impact of varying ionization parameters, H ii region densities, gas-phase abundance patterns, and increasing radiation field hardness on N2-BPT diagrams. We find that either decreasing the ionization parameter or increasing the N/O ratio of galaxies at fixed O/H can move galaxies along a self-similar arc in N2-BPT space that is occupied by high-redshift galaxies.
AB - The Baldwin, Philips, & Terlevich diagram of [O iii]/Hβ versus [N ii]/Hα (hereafter N2-BPT) has long been used as a tool for classifying galaxies based on the dominant source of ionizing radiation. Recent observations have demonstrated that galaxies at z ∼2 reside offset from local galaxies in the N2-BPT space. In this paper, we conduct a series of controlled numerical experiments to understand the potential physical processes driving this offset. We model nebular line emission in a large sample of galaxies, taken from the simba cosmological hydrodynamic galaxy formation simulation, using the cloudy photoionization code to compute the nebular line luminosities from H ii regions. We find that the observed shift toward higher [O iii]/Hβ and [N ii]/Hα values at high redshift arises from sample selection: when we consider only the most massive galaxies M ∗ ∼1010-11 M ⊙, the offset naturally appears, due to their high metallicities. We predict that deeper observations that probe lower-mass galaxies will reveal galaxies that lie on a locus comparable to z ∼0 observations. Even when accounting for samples-selection effects, we find that there is a subtle mismatch between simulations and observations. To resolve this discrepancy, we investigate the impact of varying ionization parameters, H ii region densities, gas-phase abundance patterns, and increasing radiation field hardness on N2-BPT diagrams. We find that either decreasing the ionization parameter or increasing the N/O ratio of galaxies at fixed O/H can move galaxies along a self-similar arc in N2-BPT space that is occupied by high-redshift galaxies.
U2 - 10.3847/1538-4357/ac43b8
DO - 10.3847/1538-4357/ac43b8
M3 - Journal article
AN - SCOPUS:85125835884
VL - 926
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 80
ER -
ID: 307292221