Browsing by Author "Appleby, Sarah"
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Item The impact of quenching on galaxy profiles in the SIMBA simulation(Oxford University Press, 2020) Dave, Romeel; Appleby, Sarah; Kraljic, KatarinaWe study specific star formation rate (sSFR) and gas profiles of star-forming (SF) and green valley (GV) galaxies in the SIMBA cosmological hydrodynamic simulation. SF galaxy half-light radii (Rhalf) at z = 0 and their evolution (∝(1 + z)−0.78) agree with observations. Passive galaxy Rhalf agree with observations at high redshift, but by z = 0 are too large, owing to numerical heating. We compare SIMBAz = 0 sSFR radial profiles for SF and GV galaxies to observations. SIMBA shows strong central depressions in star formation rate (SFR), sSFR, and gas fraction in GV galaxies and massive SF systems, qualitatively as observed, owing to black hole X-ray feedback, which pushes central gas outwards.Item The low-redshift circumgalactic medium in SIMBA(Oxford University Press, 2021-08) Appleby, Sarah; Dave´, Romeel; Sorini, Daniele; Storey-Fisher, Kate; Smith, BrittonWe examine the properties of the low-redshift circumgalactic medium (CGM) around star-forming and quenched galaxies in the SIMBA cosmological hydrodynamic simulations, focusing on comparing H I and metal line absorption to observations from the Cosmic Origins Spectrograph (COS)-Halos and COS-Dwarfs surveys. Halo baryon fractions are generally 50 per cent of the cosmic fraction due to stellar feedback at low masses, and jet-mode AGN feedback at high masses. Baryons and metals in the CGM of quenched galaxies are 90 per cent hot gas, while the CGM of star-forming galaxies is more multiphase. Hot CGM gas has low metallicity, while warm and cool CGM gas have metallicity close to that of galactic gas. Equivalent widths, covering fractions and total path absorption of H I and selected metal lines (Mg II, Si III, C IV, and O VI) around a matched sample of SIMBA star-forming galaxies are mostly consistent with COS-Halos and COS-Dwarfs observations to 0.4 dex, depending on ion and assumed ionizing background. Around matched quenched galaxies, absorption in all ions is lower, with H I absorption significantly underpredicted. Metal-line absorption is sensitive to choice of photoionizing background; assuming recent backgrounds, SIMBA matches O VI but underpredicts low ions, while an older background matches low ions but underpredicts O VI. SIMBA reproduces the observed dichotomy of O VI absorption around star-forming and quenched galaxies. CGM metals primarily come from stellar feedback, while jet-mode AGN feedback reduces absorption particularly for lower ions.Item The physical nature of circumgalactic medium absorbers in SIMBA(Oxford University Press, 2023) Appleby, Sarah; Dave, Romeel; Sorini, DanieleWe study the nature of the low-redshift circumgalactic medium (CGM) in the SIMBA cosmological simulations as traced by ultraviolet absorption lines around galaxies in bins of stellar mass (M > 1010M) for star-forming, green valley and quenched galaxies at impact parameters r⊥ ≤ 1.25r200. We generate synthetic spectra for H I , Mg II , C II , Si III , C IV , and O VI , fit Voigt profiles to obtain line properties, and estimate the density, temperature, and metallicity of the absorbing gas. We find that CGM absorbers are most abundant around star-forming galaxies with M < 1011 M, while the abundance of green valley galaxies show similar behaviour to those of quenched galaxies, suggesting that the CGM ‘quenches’ before star formation ceases. H I absorbing gas exists across a broad range of cosmic phases [condensed gas, diffuse gas, hot halo gas, and Warm-Hot Intergalactic Medium (WHIM)], while essentially all low ionization metal absorption arises from condensed gas. O VI absorbers are split between hot halo gas and the WHIM. The fraction of collisionally ionized CGM absorbers is ∼ 25–55 per cent for C IV and ∼ 80–95 per cent for O VI , depending on stellar mass and impact parameter. In general, the highest column density absorption features for each ion arise from dense gas. Satellite gas, defined as that within 10r1/2,, contributes ∼ 3 per cent of overall H I absorption but∼ 30 per cent of Mg II absorption, with the fraction fromsatellites decreasing with increasing ion excitation energy.