Christopher Lovell

Christopher Lovell
University of Hertfordshire | UH · Centre for Astrophysics Research (CAR)

Doctor of Philosophy
Cosmological simulations and machine learning applications

About

46
Publications
1,707
Reads
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470
Citations
Introduction
Postdoc at the University of Hertfordshire working on cosmological simulations and machine learning applications
Education
September 2015 - May 2019
University of Sussex
Field of study
  • Astrophysics
September 2009 - July 2013
Cardiff University
Field of study

Publications

Publications (46)
Article
Full-text available
We study the characteristics of galaxy protoclusters using the latest L-galaxies semi-analytic model. Searching for protoclusters on a scale of $\sim 10 \, \mathrm{cMpc}$ gives an excellent compromise between the completeness and purity of their galaxy populations, leads to high distinction from the field in overdensity space, and allows accurate d...
Article
Full-text available
We introduce the First Light And Reionisation Epoch Simulations (Flares), a suite of zoom simulations using the Eagle model. We resimulate a range of overdensities during the Epoch of Reionisation (EoR) in order to build composite distribution functions, as well as explore the environmental dependence of galaxy formation and evolution during this c...
Article
Full-text available
Matching the number counts of high-z sub-millimetre-selected galaxies (SMGs) has been a long standing problem for galaxy formation models. In this paper, we use 3D dust radiative transfer to model the sub-mm emission from galaxies in the Simba cosmological hydrodynamic simulations, and compare predictions to the latest single-dish observational con...
Article
Full-text available
High-resolution cosmological hydrodynamic simulations are currently limited to relatively small volumes due to their computational expense. However, much larger volumes are required to probe rare, overdense environments, and measure clustering statistics of the large scale structure. Typically, zoom simulations of individual regions are used to stu...
Preprint
Full-text available
The distribution of dark matter halo masses can be accurately predicted in the $\Lambda$CDM cosmology. The presence of a single massive halo or galaxy at a particular redshift, assuming some baryon and stellar fraction for the latter, can therefore be used to test the underlying cosmological model. A number of recent measurements of very large gala...
Article
With its exquisite sensitivity, wavelength coverage, and spatial and spectral resolution, the James Webb Space Telescope (JWST) is poised to revolutionise our view of the distant, high-redshift (z > 5) Universe. While Webb’s spectroscopic observations will be transformative for the field, photometric observations play a key role in identifying dist...
Preprint
Full-text available
We use two independent, cosmological galaxy formation simulations, FLARES, a hydrodynamical simulation, and SHARK, a semi-analytic model, to explore how well the James Webb Space Telescope (JWST) will be able to uncover the existence and parameters of the star-forming main sequence (SFS) at $z=5\to10$, i.e. shape, scatter, normalisation. Using two...
Preprint
The star formation and metal enrichment histories of galaxies - at any epoch - constitute one of the key properties of galaxies, and their measurement is a core aim of observational extragalactic astronomy. The lack of deep rest-frame optical coverage at high-redshift has made robust constraints elusive, but this is now changing thanks to the \emph...
Preprint
Full-text available
We analyse the photometric and spectroscopic properties of four galaxies in the epoch of reionisation (EoR) within the SMACS 0723 JWST Early Release Observations field. Given the known spectroscopic redshifts of these sources, we investigated the accuracy with which photometric redshifts can be derived using NIRCam photometry alone, finding that F1...
Article
Recent high-resolution interferometric images of submillimetre galaxies (SMGs) reveal fascinatingly complex morphologies. This raises a number of questions: how does the relative orientation of a galaxy affect its observed submillimetre emission, and does this result in an ‘orientation bias’ in the selection and analysis of such galaxies in flux-li...
Preprint
Full-text available
With its exquisite sensitivity, wavelength coverage, and spatial and spectral resolution, the James Webb Space Telescope is poised to revolutionise our view of the distant, high-redshift ($z>5$) Universe. While Webb's spectroscopic observations will be transformative for the field, photometric observations play a key role in identifying distant obj...
Article
We present the intrinsic and observed sizes of galaxies at z ≥ 5 in the First Light And Reionisation Epoch Simulations (FLARES). We employ the large effective volume of FLARES to produce a sizeable sample of high redshift galaxies with intrinsic and observed luminosities and half light radii in a range of rest frame UV and visual photometric bands....
Preprint
Full-text available
The James Webb Space Telescope (JWST) is set to transform many areas of astronomy, one of the most exciting is the expansion of the redshift frontier to $z>10$. In its first year alone JWST should discover hundreds of galaxies, dwarfing the handful currently known. To prepare for these powerful observational constraints, we use the First Light And...
Article
Full-text available
The SPT 0311–58 system at z = 6.900 is an extremely massive structure within the reionization epoch and offers a chance to understand the formation of galaxies at an extreme peak in the primordial density field. We present 70 mas Atacama Large Millimeter/submillimeter Array observations of the dust continuum and [C ii ] 158 μ m emission in the cent...
Preprint
Full-text available
The SPT0311-58 system at z=6.900 is an extremely massive structure within the reionization epoch, and offers a chance to understand the formation of galaxies in an extreme peak in the primordial density field. We present 70mas Atacama Large Millimeter/submillimeter Array observations of the dust continuum and CII 158um emission in the central pair...
Preprint
Full-text available
We present the intrinsic and observed sizes of galaxies at $z\geq5$ in the First Light And Reionisation Epoch Simulations (FLARES). We employ the large effective volume of FLARES to produce a sizeable sample of high redshift galaxies with intrinsic and observed luminosities and half light radii in a range of rest frame UV and visual photometric ban...
Article
Full-text available
Using the First Light And Reionisation Epoch Simulations (Flares) we explore the dust driven properties of massive high-redshift galaxies at z ∈ [5, 10]. By post-processing the galaxy sample using the radiative transfer code skirt we obtain the full spectral energy distribution. We explore the resultant luminosity functions, IRX-β relations as well...
Article
The Baldwin, Philips, & Terlevich diagram of [O iii ]/H β versus [N ii ]/H α (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 seri...
Preprint
Full-text available
The Baldwin, Philips, & Terlevich diagram of [O III]/H$\beta$ vs. [N II]/H$\alpha$ (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 $z\sim2$ reside offset from local galaxies in the N2-BPT space. In this paper, we condu...
Preprint
Full-text available
Using the First Light And Reionisation Epoch Simulations (\textsc{Flares}) we explore the dust driven properties of massive high-redshift galaxies at $z\in[5,10]$. By post-processing the galaxy sample using the radiative transfer code \textsc{skirt} we obtain the full spectral energy distribution. We explore the resultant luminosity functions, IRX-...
Preprint
Full-text available
Recent high-resolution interferometric images of submillimetre galaxies (SMGs) reveal fascinatingly complex morphologies. This raises a number of questions: how does the relative orientation of a galaxy affect its observed submillimetre emission, and does this result in an 'orientation bias' in the selection and analysis of such galaxies in flux-li...
Preprint
Full-text available
High-resolution cosmological hydrodynamic simulations are currently limited to relatively small volumes due to their computational expense. However, much larger volumes are required to probe rare, overdense environments, and measure clustering statistics of the large scale structure. Typically, zoom simulations of individual regions are used to stu...
Article
The emergence of passive galaxies in the early Universe results from the delicate interplay among the different physical processes responsible for their rapid assembly and the abrupt shut-down of their star formation activity. Investigating the individual properties and demographics of early passive galaxies improves our understanding of these mech...
Article
We present new empirical constraints on the evolution of ρ H2, the cosmological mass density of molecular hydrogen, back to z ≈ 2.5. We employ a statistical approach measuring the average observed 850 μm flux density of near-infrared selected galaxies as a function of redshift. The redshift range considered corresponds to a span where the 850 μm ba...
Preprint
Full-text available
We present new empirical constraints on the evolution of $\rho_{\rm H_2}$, the cosmological mass density of molecular hydrogen, back to $z\approx2.5$. We employ a statistical approach measuring the average observed $850\mu{\rm m}$ flux density of near-infrared selected galaxies as a function of redshift. The redshift range considered corresponds to...
Article
We present powderday (available at https://github.com/dnarayanan/powderday), a flexible, fast, open-source dust radiative transfer package designed to interface with both idealized and cosmological galaxy formation simulations. powderday builds on fsps stellar population synthesis models, and hyperion dust radiative transfer, and employs yt to inte...
Article
Full-text available
We present Sengi, (https://christopherlovell.github.io/sengi), an online tool for viewing the spectral outputs of stellar population synthesis (SPS) codes. Typical SPS codes require significant disk space or computing resources to produce spectra for simple stellar populations with arbitrary parameters. This makes it difficult to present their resu...
Preprint
Full-text available
We aim to determine some physical properties of distant galaxies (for example, stellar mass, star formation history, or chemical enrichment history) from their observed spectra, using supervised machine learning methods. We know that different astrophysical processes leave their imprint in various regions of the spectra with characteristic signatur...
Article
Full-text available
We present the photometric properties of galaxies in the First Light and Reionisation Epoch Simulations (Flares). The simulations trace the evolution of galaxies in a range of overdensities through the Epoch of Reionistion (EoR). With a novel weighting scheme we combine these overdensities, extending significantly the dynamic range of observed comp...
Preprint
Full-text available
The emergence of passive galaxies in the early Universe results from the interplay among the physical processes responsible for their rapid assembly and for the abrupt shut-down of their SF. Investigating the individual properties and demographics of early passive galaxies will improve our understanding of these mechanisms. In this work we present...
Preprint
Full-text available
We present the photometric properties of galaxies in the First Light and Reionisation Epoch Simulations (FLARES). The simulations trace the evolution of galaxies in a range of overdensities through the Epoch of Reionistion (EoR). With a novel weighting scheme we combine these overdensities, extending significantly the dynamic range of observed comp...
Preprint
Full-text available
Matching the number counts of high-$z$ sub-millimetre-selected galaxies (SMGs) has been a long standing problem for galaxy formation models. In this paper, we use 3D dust radiative transfer to model the sub-mm emission from galaxies in the SIMBA cosmological hydrodynamic simulations, and compare predictions to the latest single-dish observational c...
Preprint
Full-text available
We present Powderday, a flexible, fast, open-source dust radiative transfer package designed to interface with galaxy formation simulations. Powderday builds on FSPS population synthesis models, Hyperion dust radiative transfer, and employs yt to interface between different software packages. We include our stellar population synthesis modeling on...
Preprint
Full-text available
We introduce the First Light And Reionisation Epoch Simulations (FLARES), a suite of zoom simulations using the EAGLE model. We resimulate a range of overdensities during the Epoch of Reionisation (EoR) in order to build composite distribution functions, as well as explore the environmental dependence of galaxy formation and evolution during this c...
Article
Full-text available
Nebular emission lines associated with galactic H ii regions carry information about both physical properties of the ionized gas and the source of ionizing photons as well as providing the opportunity of measuring accurate redshifts and thus distances once a cosmological model is assumed. While nebular-line emission has been extensively studied at...
Article
Full-text available
The calibrations linking observed luminosities to the star formation rate (SFR) depend on the assumed stellar population synthesis model, initial mass function, star formation and metal enrichment history, and whether reprocessing by dust and gas is included. Consequently the shape and normalization of the inferred cosmic star formation history is...
Preprint
Full-text available
We present Sengi ( christopherlovell.github.io/sengi, https://christopherlovell.github.io/sengi ), an online tool for viewing the spectral outputs of stellar population synthesis (SPS) codes. Typical SPS codes require significant disk space or computing resources to produce spectra for simple stellar populations with arbitrary parameters. This make...
Article
Full-text available
We present a new method for inferring galaxy star formation histories (SFH) using machine learning methods coupled with two cosmological hydrodynamic simulations. We train convolutional neural networks to learn the relationship between synthetic galaxy spectra and high-resolution SFHs from the eagle and Illustris models. To evaluate our SFH reconst...
Preprint
Full-text available
The calibrations linking observed luminosities to the star formation rate depend on the assumed stellar population synthesis model, initial mass function, star formation and metal enrichment history, and whether reprocessing by dust and gas is included. Consequently the shape and normalisation of the inferred cosmic star formation history is sensit...
Preprint
Full-text available
Nebular emission lines associated with galactic HII regions carry information about both physical properties of the ionised gas and the source of ionising photons as well as providing the opportunity of measuring accurate redshifts and thus distances once a cosmological model is assumed. While nebular line emission has been extensively studied at l...
Preprint
Full-text available
We present a new method for inferring galaxy star formation histories (SFH) using machine learning methods coupled with two cosmological hydrodynamic simulations, EAGLE and Illustris. We train Convolutional Neural Networks to learn the relationship between synthetic galaxy spectra and high resolution SFHs. To evaluate our SFH reconstruction we use...
Article
Exoplanet discoveries now number in the thousands, but the search for life beyond Earth remains fruitless. What does this tell us about the probability of extraterrestrial intelligence? Christopher Lovell investigates
Article
Motivated by recent observational constraints on dust reprocessed emission in star forming galaxies at $z\sim 6$ and above we use the very-large cosmological hydrodynamical simulation \bluetides\ to explore predictions for the amount of dust obscured star formation in the early Universe ($z>8$). \bluetides\ matches current observational constraints...
Article
We employ the very large cosmological hydrodynamical simulation BLUETIDES to investigate the predicted properties of the galaxy population during the epoch of reionisation ($z>8$). BLUETIDES has a resolution and volume ($(400/h\approx 577)^{3}\,{\rm cMpc^3}$) providing a population of galaxies which is well matched to depth and area of current obse...
Article
We use the large cosmological hydro-dynamic simulation BlueTides to predict the photometric properties of galaxies during the epoch of reionisation (z = 8 − 15). These properties include the rest-frame UV to near-IR broadband spectral energy distributions, the Lyman continuum photon production, the UV star formation rate calibration, and intrinsic...
Technical Report
http://bankunderground.co.uk/2015/08/18/tweets-runs-and-the-minnesota-vikings/

Questions

Questions (3)
Question
The Sheth & van de Weygaert 2004 paper (http://arxiv.org/abs/astro-ph/0311260) shows a plot of number density of voids of a given radius (figure 8, bottom left), but does not give details on its derivation. I am struggling to arrive at the correct formula from the one given on the previous page in the paper (equation 6). If anyone has done this before, or is feeling particularly bored this week, I would really appreciate some help with the derivation.
Question
I'm running simulations using the Enzo code over a large volume (256 Mpc/h) but I'm not sure which values to provide to the Tinker fit when calculating the hmf fit. I'm pretty sure that the delta=200 values given in the enzo code are sufficient but I'd like to be sure, and I don't know what values to pass to the equation given in the tinker et al. 08 paper on page 4 to find my own value for delta.
Question
Anybody familiar with creating initial conditions for the ENZO simulation code? I'm looking to run low resolution simulations to study high mass clusters; these would be without baryons. I'm mostly hung up on the comoving box size that I would need, and the resolution for such a box to produce realistic conditions.