Nikole M. Nielsen's research while affiliated with Swinburne University of Technology and other places

... Ultraviolet (UV) absorption lines (e.g., Si-IV, C-IV, N-V) can trace gas in the warm CGM ( ∼ 10 5.5 K) if collisionally ionized or the cool CGM ( ∼ 10 4 K) if photoionized. Fixing the radiation field to a redshift-dependent uniform metagalactic background field (e.g., Haardt & Madau 1996;Faucher-Giguère et al. 2009;Haardt & Madau 2012; Faucher-Giguère 2020) is a common assumption when performing photoionization modeling to interpret absorption-line spectra (e.g., Savage & Wakker 2009;Werk et al. 2014Werk et al. , 2016Lehner et al. 2019Lehner et al. , 2020Lehner et al. , 2022Qu et al. 2023Qu et al. , 2024Sameer et al. 2024, but see Fumagalli et al. 2016 for a notable exception). The same assumption is employed when generating synthetic absorption-line spectra from simulations (e.g. ...

... These measures are evaluated as the respective outflowing quantity (e.g., mass or energy) normalized by the star formation rate, resulting in a dimensionless quantity that describes an efficiency relative to star formation. Loading factors have been frequently used in simulations to investigate and quantify galactic outflows and galaxy evolution (Muratov et al. 2015;Kim et al. 2020b;Mitchell et al. 2020;Pandya et al. 2021;Steinwandel et al. 2024), and while loading factors are more difficult to ascertain in observations, there still exists a sample to compare against theory (Martin 1999;Heckman et al. 2015;Chisholm et al. 2017;McQuinn et al. 2019;Reichardt Chu et al. 2022;McPherson et al. 2023). However, measurements can vary across several orders of magnitude based on galaxy properties and dynamics. ...

... These measures are evaluated as the respective outflowing quantity (e.g., mass or energy) normalized by the star formation rate, resulting in a dimensionless quantity that describes an efficiency relative to star formation. Loading factors have been frequently used in simulations to investigate and quantify galactic outflows and galaxy evolution (Muratov et al. 2015;Kim et al. 2020b;Mitchell et al. 2020;Pandya et al. 2021;Steinwandel et al. 2024), and while loading factors are more difficult to ascertain in observations, there still exists a sample to compare against theory (Martin 1999;Heckman et al. 2015;Chisholm et al. 2017;McQuinn et al. 2019;Reichardt Chu et al. 2022;McPherson et al. 2023). However, measurements can vary across several orders of magnitude based on galaxy properties and dynamics. ...

... One of the largest uncertainties is the structure of the absorbing gas -the simplest assumption is that the absorbing gas is a single cloud with uniform temperature, density, and metallicity, but many absorption spectra are best fit by assuming multiple clouds spanning a range of properties (e.g. Boksenberg, Carswell & Sargent 1979 ;Muzahid et al. 2015 ;Liang & Kravtsov 2017 ;Wotta et al. 2019 ;Lehner et al. 2019b ;Haislmaier et al. 2021 ;Marra et al. 2021 ;Narayanan et al. 2021 ;Sameer et al. 2021 ;Zahedy et al. 2021a ;Nielsen et al. 2022 ), with possible o v erlapping spectra from MNRAS 528, 39-60 (2024) physically separated clouds (e.g. Marra et al. 2022 ). ...

... Therefore, it is possible that some fraction of our RR galaxies also show similarly irregular H I distributions. Although its physical origin is still under debate, such H I-dominated rings are likely expelled gas from H I-rich ETGs caused by a collision with an intruder galaxy (e.g., Michel-Dansac et al. 2010;Bait et al. 2020) or tidal tripping by the group potential (e.g., Bekki et al. 2005;Serra et al. 2013;Corbelli et al. 2021), or falling back of the tidal tail of gas-rich major mergers (e.g., Morganti et al. 2003;Sameer et al. 2022). Considering the extreme paucity of such observational cases in the literature as well as the fact that the majority of our RR galaxies have no close companions, we would expect such an irregular or off-galaxy H I distribution to be not a common feature in the RR galaxies. ...

... One of the largest uncertainties is the structure of the absorbing gas-the simplest assumption is that the absorbing gas is a single cloud with uniform temperature, density, and metallicity, but many absorption spectra are best fit by assuming multiple clouds spanning a range of properties (e.g. Boksenberg et al. 1979;Muzahid et al. 2015;Liang & Kravtsov 2017;Lehner et al. 2019b;Wotta et al. 2019;Haislmaier et al. 2021;Sameer et al. 2021;Zahedy et al. 2021a;Marra et al. 2021;Narayanan et al. 2021;Nielsen et al. 2022), with possible overlapping spectra from physically-separated clouds (e.g. Marra et al. 2022). ...

... Assuming that half of this mass fraction is recycled as gas we obtain a ratio of gas mass to the mass of old stars of 0.06, which is a factor of 2 higher than the observed average mass ratio of the young to the old population (see Figure 9, bottom). A starburst of very high star formation efficiency (Fisher et al. 2022) could, thus, explain the observations within the framework of our model. Figure 14. ...

... It may also be possible to perform a similar exercise for gas in multiphase galactic outflows (e.g., Strickland & Heckman 2009;Reichardt Chu et al. 2022). ...

... For instance, assuming that C IV absorbers with equi v alent width (EW) > 0.06 Å arise in the CGM of Lyman break galaxies (LBGs), Cooksey et al. ( 2013 ) estimated that the observed incidence can be modelled by filling the inner ≈ 50 kpc of LBGs haloes with ionized carbon with time. More recently, Hasan et al. ( 2022 ) expanded this argument both in mass and redshift, combining C IV absorption statistics with dark matter haloes to constrain the link between gas and galaxies. ...

... Rupke, Veilleux & Sanders 2005 ;Martin & Bouch é 2009 ;Rubin et al. 2011 ;Martin et al. 2013 ) can reco v er outflow properties and loading factors. We also plan to use our simulations to assess potential biases in reco v ering spatially resolved outflow metallicities from emission line maps (Cameron et al. 2021 ). ...