| 1. |
- Doughty, Caitlin, et al.
(författare)
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Aligned metal absorbers and the ultraviolet background at the end of reionization
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 475:4, s. 4717-4727
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Tidskriftsartikel (refereegranskat)abstract
- We 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 similar to 6. We accomplish this by comparing observations with predictions from a cosmological hydrodynamic simulation using three trial UVBs applied in post-processing: a spectrally soft, fluctuating UVB calculated using multifrequency radiative transfer; a soft, spatially uniform UVB; and a hard, spatially uniform 'quasars-only' model. When considering our paired high-ionization absorbers (C IV/Si IV), the observed statistics strongly prefer the hard, spatially uniform UVB. This echoes recent findings that cosmological simulations 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, whereas 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 constraints on the UVB.
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| 2. |
- Finlator, Kristian, et al.
(författare)
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Reionization in Technicolor
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 480:2, s. 2628-2649
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Tidskriftsartikel (refereegranskat)abstract
- We present the Technicolor Dawn simulations, a suite of cosmological radiation hydrodynamic simulations of the first 1.2 billion yr. By modelling a spatially inhomogeneous ultraviolet background (UVB) on the fly with 24 frequencies and resolving dark matter haloes down to 10(8) M-circle dot within 12 h(-1) Mpc volumes, our simulations unify observations of the intergalactic and circumgalactic media, galaxies, and reionization into a common framework. The only empirically tuned parameter, the fraction f(esc,gal)(z) of ionizing photons that escape the interstellar medium, is adjusted to match observations of the Lyman-alpha forest and the cosmic microwave background. With this single calibration, our simulations reproduce the history of reionization; the stellar mass and star formation rate relation of galaxies; the number density and metallicity of damped Lyman-alpha absorbers (DLAs) at z similar to 5; the abundance of weak metal absorbers; the ultraviolet background amplitude; and the Lyman-a flux power spectrum at z = 5.4. The galaxy stellar mass and ultraviolet luminosity functions are underproduced by <= 2 x, suggesting an overly vigorous feedback model. The mean transmission in the Lyman-alpha forest is underproduced at z < 6, indicating tension between measurements of the UVB amplitude and Lyman-alpha transmission. The observed Si IV column density distribution is reasonably well reproduced (similar to 1 sigma low). By contrast, C IV remains significantly underproduced despite being boosted by an intense >4 Ryd UVB. Solving this problem by increasing metal yields would overproduce both weak absorbers and DLA metallicities. Instead, the observed strength of high-ionization emission from high-redshift galaxies and absorption from their environments suggest that the ionizing flux from conventional stellar population models is too soft.
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| 3. |
- Finlator, Kristian, et al.
(författare)
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The minimum halo mass for star formation at z=6-8
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 464:2, s. 1633-1639
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Tidskriftsartikel (refereegranskat)abstract
- Recent analysis of strongly lensed sources in the Hubble Frontier Fields indicates that the rest-frame UV luminosity function of galaxies at z=6-8 rises as a power law down to M-UV=-15, and possibly as faint as-12.5. We use predictions from a cosmological radiation hydrodynamic simulation to map these luminosities on to physical space, constraining the minimum dark matter halo mass and stellar mass that the Frontier Fields probe. While previously published theoretical studies have suggested or assumed that early star formation was suppressed in haloes less massive than 10(9)-10(11) M-circle dot, we find that recent observations demand vigorous star formation in haloes at least as massive as (3.1, 5.6, 10.5) x10(9) M-circle dot at z =(6, 7, 8). Likewise, we find that Frontier Fields observations probe down to stellar masses of (8.1, 18, 32) x10(6) M-circle dot: that is, they are observing the likely progenitors of analogues to Local Group dwarfs such as Pegasus and M32. Our simulations yield somewhat different constraints than two complementary models that have been invoked in similar analyses, emphasizing the need for further observational constraints on the galaxy-halo connection.
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| 4. |
- Finlator, Kristian, et al.
(författare)
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The reionization of carbon
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 447:3, s. 2526-2539
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Tidskriftsartikel (refereegranskat)abstract
- Observations suggest that CII was more abundant than CIV in the intergalactic medium towards the end of the hydrogen reionization epoch (z similar to 6). This transition provides a unique opportunity to study the enrichment history of intergalactic gas and the growth of the ionizing ultraviolet background (UVB) at early times. We study how carbon absorption evolves from z = 10 to 5 using a cosmological hydrodynamic simulation that includes a self-consistent multifrequency UVB as well as a well-constrained model for galactic outflows to disperse metals. Our predicted UVB is within similar to 2-4 times of that from Haardt & Madau, which is fair agreement given the uncertainties. Nonetheless, we use a calibration in post-processing to account for Lyman a forest measurements while preserving the predicted spectral slope and inhomogeneity. The UVB fluctuates spatially in such a way that it always exceeds the volume average in regions where metals are found. This implies both that a spatially uniform UVB is a poor approximation and that metal absorption is not sensitive to the epoch when HII regions overlap globally even at column densities of 10(12) cm(-2). We find, consistent with observations, that the CII mass fraction drops to low redshift while CIV rises owing the combined effects of a growing UVB and continued addition of carbon in low-density regions. This is mimicked in absorption statistics, which broadly agree with observations at z = 6-3 while predicting that the absorber column density distributions rise steeply to the lowest observable columns. Our model reproduces the large observed scatter in the number of low-ionization absorbers per sightline, implying that the scatter does not indicate a partially neutral Universe at z similar to 6.
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| 5. |
- Finlator, Kristian, et al.
(författare)
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The soft, fluctuating UVB at z similar to 6 as traced by C IV, Si IV, and C II
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 459:3, s. 2299-2310
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Tidskriftsartikel (refereegranskat)abstract
- The sources that drove cosmological reionization left clues regarding their identity in the slope and inhomogeneity of the ultraviolet ionizing background (UVB): bright quasars (QSOs) generate a hardUVBwith predominantly large-scale fluctuations while Population II stars generate a softer one with smaller scale fluctuations. Metal absorbers probe the UVB's slope because different ions are sensitive to different energies. Likewise, they probe spatial fluctuations because they originate in regions where a galaxy-driven UVB is harder and more intense. We take a first step towards studying the reionization-epoch UVB's slope and inhomogeneity by comparing observations of 12 metal absorbers at z similar to 6 versus predictions from a cosmological hydrodynamic simulation using three different UVBs: a soft, spatially inhomogeneous ' galaxies+QSOs' UVB; a homogeneous 'galaxies+QSOs' UVB, and a 'QSOs-only' model. All UVBs reproduce the observed column density distributions of CII, Si IV, and CIV reasonably well although high-column, high-ionization absorbers are underproduced, reflecting numerical limitations. With upper limits treated as detections, only a soft, fluctuating UVB reproduces both the observed Si IV/CIV and CII/CIV distributions. The QSOs-only UVB overpredicts both CIV/CII and CIV/Si IV, indicating that it is too hard. The Haardt & Madau (2012) UVB underpredicts CIV/Si IV, suggesting that it lacks amplifications near galaxies. Hence current observations prefer a soft, fluctuating UVB as expected from a predominantly Population II background although they cannot rule out a harder one. Future observations probing a factor of 2 deeper in metal column density will distinguish between the soft, fluctuating and QSOs-only UVBs.
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| 6. |
- Kuschel, Maxwell, et al.
(författare)
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Investigating the Dominant Environmental Quenching Process in UVCANDELS/COSMOS Groups
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 947:1
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Tidskriftsartikel (refereegranskat)abstract
- We explore how the fraction of quenched galaxies changes in groups of galaxies with respect to the distance to the center of the group, redshift, and stellar mass to determine the dominant process of environmental quenching in 0.2 < z < 0.8 groups. We use new UV data from the UVCANDELS project in addition to existing multiband photometry to derive new galaxy physical properties of the group galaxies from the zCOSMOS 20 k group catalog. Limiting our analysis to a complete sample of log (M*/M⊙) > 10.56 group galaxies, we find that the probability of being quenched increases slowly with decreasing redshift, diverging from the stagnant field galaxy population. A corresponding analysis on how the probability of being quenched increases with time within groups suggests that the dominant environmental quenching process is characterized by slow (∼Gyr) timescales. We find a quenching time of approximately Gyr, consistent with the slow processes of strangulation and delayed-then-rapid quenching although more data are needed to confirm this result.
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