Browsing by Author "Finlator, Kristian"
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Item Aligned metal absorbers and the ultraviolet background at the end of reionization(Oxford University Press, 2018) Doughty, Caitlin; Finlator, Kristian; Oppenheimer, Benjamin D.; Dave, Romeel; Zackrisson, ErikWe use observations of spatially-aligned C ii, C iv, Si ii, Si iv, and O i absorbers to probe the slope and intensity of the ultraviolet background (UVB) at z ∼ 6. We accom- plish this by comparing observations with predictions from a cosmological hydrody- namic simulation using three trial UVBs applied in post-processing: a spectrally soft, fluctuating UVB calculated using multi-frequency radiative transfer; a soft, spatially- uniform UVB; and a hard, spatially-uniform “quasars-only” model. When considering our paired high-ionization absorbers (Civ/Siiv), the observed statistics strongly prefer the hard, spatially-uniform UVB. This echoes recent findings that cosmological sim- ulations generically underproduce strong C iv absorbers at z > 5. A single low/high ionization pair (Si ii/Si iv), by contrast, shows a preference for the HM12 UVB, while two more (C ii/C iv and O i/C iv) show no preference for any of the three UVBs. Despite this, future observations of specific absorbers, particularly Si iv/C iv, with next-generation telescopes probing to lower column densities should yield tighter con- ts on the UVB.Item The host haloes of O I absorbers in the reionization epoch(Oxford University Press, 2013) Finlator, Kristian; Muñoz, Joseph A.; Dave, Romeel; Oppenheimer, B. D.; Peng Oh, S.; Özel, FeryalWe use a radiation hydrodynamic simulation of the hydrogen reionization epoch to study OI absorbers at z ∼ 6. The intergalactic medium (IGM) is reionized before it is enriched; hence, OI absorption originates within dark matter haloes. The predicted abundance of OI absorbers is in reasonable agreement with observations. At z = 10, ≈70 per cent of sightlines through atomically cooled haloes encounter a visible (NOI > 1014cm−2) column. Reionization ionizes and removes gas from haloes less massive than 108.4M , but 20 per cent of sightlines through more massive haloes encounter visible columns even at z = 5. The mass scale of absorber host haloes is 10–100 times smaller than the haloes of Lyman-break galaxies and Lyman α emitters, hence absorption probes the dominant ionizing sources more directly. OI absorbers have neutral hydrogen columns of 1019–1021 cm−2, suggesting a close resemblance between objects selected in OI and HI absorption. Finally, the absorption in the foreground of the z = 7.085 quasar ULAS J1120+0641 cannot originate in a dark matter halo because halo gas at the observed HI column density is enriched enough to violate the upper limits on the OI column. By contrast, gas at less than one-third the cosmic mean density satisfies the constraints. Hence, the foreground absorption likely originates in the IGM.Item Physical properties of spectroscopically confirmed galaxies at Z ≥ 6. I. Basic characteristics of the rest-frame UV continuum and lyman-alpha emission(American Astronomical Society, 2013) Jiang, Linhua; Egami, Eiichi; Mechtley, Matthew; Fan, Xiaohui; Cohen, Seth H.; Windhorst, Rogier A.; Dave, Romeel; Finlator, Kristian; Kashikawa, Nobunari; Ouchi, Masami; Shimasaku, KazuhiroWe present deep HST near-IR and Spitzer mid-IR observations of a large sample of spectroscopically- confirmed galaxies at z ≥ 6. The sample consists of 51 Ly-alpha emitters (LAEs) at z ≃ 5.7, 6.5, and 7.0, and 16 Lyman-break galaxies (LBGs) at 5.9 ≤ z ≤ 6.5. The near-IR images were mostly obtained with WFC3 in the F125W and F160W bands, and the mid-IR images were obtained with IRAC in the 3.6μm and 4.5μm bands. Our galaxies also have deep optical imaging data from Subaru Suprime- Cam. We utilize the multi-band data and secure redshifts to derive their rest-frame UV properties. These galaxies have steep UV continuum slopes roughly between ≃ −1.5 and –3.5, with an average value of ≃ −2.3, slightly steeper than the slopes of LBGs in previous studies. The slope shows little dependence on UV continuum luminosity except for a few of the brightest galaxies. We find a statistically significant excess of galaxies with slopes around ≃ −3, suggesting the existence of very young stellar populations with extremely low metallicity and dust content. Our galaxies have moderately strong rest-frame Ly equivalent width (EW) in a range of ∼10 to ∼200 °A. The star- formation rates are also moderate, from a few to a few tens solar masses per year. The LAEs and LBGs in this sample share many common properties, implying that LAEs represent a subset of LBGs with strong Ly-alpha emission. Finally, the comparison of the UV luminosity functions between LAEs and LBGs suggests that there exists a substantial population of faint galaxies with weak Ly-alpha emission (EW < 20 °A) that could be the dominant contribution to the total ionizing flux at z ≥ 6.Item Testing galaxy formation simulations with damped Lyman-α abundance and metallicity evolution(Oxford University Press, 2020) Hassan, Sultan; Finlator, Kristian; Dave, RomeelWe examine the properties of damped Lyman-α absorbers (DLAs) emerging from a single set of cosmological initial conditions in two state-of-the-art cosmological hydrodynamic simulations: SIMBA and TECHNICOLOR DAWN. The former includes star formation and black hole feedback treatments that yield a good match with low-redshift galaxy properties, while the latter uses multifrequency radiative transfer to model an inhomogeneous ultraviolet background (UVB) self-consistently and is calibrated to match the Thomson scattering optical depth, UVB amplitude, and Ly α forest mean transmission at z > 5. Both simulations are in reasonable agreement with the measured stellar mass and star formation rate functions at z ≥ 3, and both reproduce the observed neutral hydrogen cosmological mass density, ΩHI(z).