arXiv subjects

Luke Davies

Publications and source records attributed to Luke Davies.

7 recordsLinked to original sources

arXiv2026

Exploring biases in derived stellar parameters and the ionizing photon production efficiency

Constraining the timescale and manner in which the Epoch of Reionization (EoR) occurred is a major JWST science goal. However, any constraints on the stellar or ionizing parameters (xi ion) of galaxies in the EoR must contend with biases introduced by both the data and the models used. We explore three techniques that use spectroscopic and photometric data as well as three different spectral energy distribution (SED) fitting codes, each comprised of multiple star formation history, stellar population synthesis, dust, and photoionization prescriptions to determine their relative influence on stellar parameters and xi ion. We use z=3 EoR analog galaxies due to their reliable photometric coverage (improved physical constraints) in comparison to direct EoR sources and potential for direct Lyman Continuum escape research. For this population the median stellar mass can vary by over 0.6 dex and the SFR by more than 0.9 dex. Further, the xi ion can vary by over 1.1 dex for individual sources when comparing spectroscopic and photometric derivations, or by more than 0.5 dex when fitting SEDs with different models. As such, the choice of methodology can have significant consequences for the derived xi ion and the subsequent sources of reionization. We find that the presence of a redshift evolution for xi ion is dependent on the method adopted for its derivation, where a consistent method yields an evolutionary trend with redshift in extreme emitters while an indiscriminant selection of studies does not. The model, method and data dependence of the xi ion parameter is undeniable even for a homogeneous population.

astro-ph.GA↗

arXiv2026

DINGO/GAMA /WAVES: HI-halo mass relation

We investigate the relation between neutral atomic hydrogen (HI) and dark matter halo mass (HIHM) using observations from the Deep Investigation of Neutral Gas Origins (DINGO) pilot survey 100h data, combined with spectroscopic data from the Galaxy and Mass Assembly (GAMA) survey and photometric data from the Wide Area VISTA Extragalactic Survey (WAVES) photometric catalog. We employ a combination of direct detections and spectral stacking to probe the HI content of halos across a wide mass range ($10^{10.5} \lesssim M_\mathrm{h}/M_\odot \lesssim 10^{14.5}$). By incorporating WAVES photometric members on top of the existing GAMA group catalog, we present a novel approach of extending stacking analyses beyond spectroscopic completeness limits, enabling recovery of satellite HI content otherwise missed. We find that the HIHM relation exhibits a double power-law form, with a turnover near $M_\mathrm{h} \sim 10^{11.2} \text{ M}_\odot$. Central galaxies dominate the halo HI budget below $M_\mathrm{h} \sim 6 \times 10^{12} \text{ M}_\odot$, while satellites dominate at higher halo masses. Including photometric members increases the measured HI content in halos above $10^{13} \text{ M}_\odot$ by a factor of 1.5-3, highlighting the importance of gas-rich satellites in the group and cluster regime. Comparison with previous group-stacking studies shows that low-surface brightness galaxies, and intra-group HI structures contribute only a minor fraction to the total HI mass in group and cluster halos, as the summed galaxy HI masses are consistent with the total halo HI content.

astro-ph.GA↗

arXiv2026

Mapping dark matter and the emergence of large-scale structure

We discuss a potential survey to map dark matter and the emergence of large-scale structure to redshift z ~ 1.5 (baseline) or z~3.5 (with near-IR extension) using a massively multiplexed spectrograph on a 10m-class telescope, such as the proposed Widefield Spectroscopic Telescope.

astro-ph.CO↗

arXiv2025

Archaeological investigation of galaxies' evolutionary history in the cosmic middle ages

The cosmic Middle Ages, spanning the last 8-10 Gyr of the Universe, is a critical period in which massive early-formed systems coexist with global star formation quenching in less massive galaxies, yet galaxies experience further dynamical, morphological and chemical evolution. Understanding the relative role of internal drivers and of interaction with the evolving large-scale structures remains a highly complex and unsettled issue. To make transformative progress on these questions we must characterize the physical and kinematic properties (integrated and spatially resolved) of stellar populations in galaxies, fossil record of their past star formation and assembly histories, together with gas properties, across a wide range of masses and environmental scales, over this critical cosmic epoch. Volume-representative samples of 10^6 galaxies down to 10^9 solar masses are essential to fully trace the complex interplay between physical processes and to physically connect progenitor and descendant galaxy populations. This demands a deep and extensive survey with high signal-to-noise, medium-resolution, rest-frame optical spectroscopy. Current and planned facilities in the 2020-2030s cannot simultaneously achieve the required sample size, spectral quality, mass limit, and spatial coverage. A dedicated large-aperture spectroscopic facility with wide-area high-multiplex MOS and large field-of-view IFU is needed to provide transformative insights into the physical mechanisms regulating star formation and galaxy evolution.

astro-ph.GA↗

arXiv2022

The eROSITA Final Equatorial Depth Survey (eFEDS): X-ray emission around star-forming and quiescent galaxies at $0.05<z<0.3$

We aim at characterizing the hot phase of the Circum-Galactic Medium in a large sample of galaxies. We stack X-ray events from the SRG/eROSITA eFEDS survey around central galaxies in the GAMA 9hr field to construct radially projected soft X-ray luminosity profiles as a function of their stellar mass and specific star formation rate. We consider samples of quiescent (star-forming) galaxies in the stellar mass range $2\times 10^{10}$ -- $10^{12}$ M$_\odot$ ($3\times 10^9$ -- $6\times10^{11}$ M$_\odot$). For quiescent galaxies, the X-ray profiles are clearly extended throughout the available mass range; however, the measured profile is likely biased high due to projection effects, as these galaxies tend to live in dense and hot environments. For the most massive star forming samples ($\geq10^{11}$ M$_\odot$), there is a hint of detection of extended emission. For star-forming galaxies with $< 10^{11}$ M$_\odot$ the X-ray stacked profiles are compatible with unresolved sources and consistent with the expected emission from faint Active Galactic Nuclei and X-ray binaries. We measure for the first time the mean relation between average X-ray luminosity and stellar mass separately for quiescent and star-forming galaxies. High-mass ($\geq 10^{11}$ M$_\odot$) star-forming or quiescent galaxies follow the expected scaling of virialized hot haloes, while lower mass star-forming galaxies show a less prominent luminosity and a weaker dependence on stellar mass, consistent with empirical models of the weak AGN population. When comparing our results with state-of-the art numerical simulations, we find an overall consistency on large ($>80$ kpc) scales at masses $\geq 10^{11}$ M$_\odot$, but disagreement on the small scales, where brighter than observed compact cores are predicted. Simulations also do not predict the clear differentiation that we observe between quiescent and star-forming galaxies.

astro-ph.GA↗

arXiv2018

Investigating a population of infrared-bright gamma-ray burst host galaxies

We identify and explore the properties of an infrared-bright gamma-ray burst (GRB) host population. Candidate hosts are selected by coincidence with sources in WISE, with matching to random coordinates and a false alarm probability analysis showing that the contamination fraction is approx 0.5. This methodology has already identified the host galaxy of GRB 080517. We combine survey photometry from Pan-STARRS, SDSS, APASS, 2MASS, GALEX and WISE with our own WHT/ACAM and VLT/X- shooter observations to classify the candidates and identify interlopers. Galaxy SED fitting is performed using MAGPHYS, in addition to stellar template fitting, yielding 13 possible IR-bright hosts. A further 7 candidates are identified from previously published work. We report a candidate host for GRB 061002, previously unidentified as such. The remainder of the galaxies have already been noted as potential hosts. Comparing the IR-bright population properties including redshift z, stellar mass M*, star formation rate SFR and V-band attenuation Av to GRB host catalogues in the literature, we find that the infrared-bright population is biased toward low z, high M* and high Av. This naturally arises from their initial selection - local and dusty galaxies are more likely to have the required IR flux to be detected in WISE. We conclude that while IR-bright GRB hosts are not a physically distinct class, they are useful for constraining existing GRB host populations, particularly for long GRBs.

astro-ph.GA↗

arXiv2016

The Detailed Science Case for the Maunakea Spectroscopic Explorer: the Composition and Dynamics of the Faint Universe

MSE is an 11.25m aperture observatory with a 1.5 square degree field of view that will be fully dedicated to multi-object spectroscopy. More than 3200 fibres will feed spectrographs operating at low (R ~ 2000 - 3500) and moderate (R ~ 6000) spectral resolution, and approximately 1000 fibers will feed spectrographs operating at high (R ~ 40000) resolution. MSE is designed to enable transformational science in areas as diverse as tomographic mapping of the interstellar and intergalactic media; the in-situ chemical tagging of thick disk and halo stars; connecting galaxies to their large scale structure; measuring the mass functions of cold dark matter sub-halos in galaxy and cluster-scale hosts; reverberation mapping of supermassive black holes in quasars; next generation cosmological surveys using redshift space distortions and peculiar velocities. MSE is an essential follow-up facility to current and next generations of multi-wavelength imaging surveys, including LSST, Gaia, Euclid, WFIRST, PLATO, and the SKA, and is designed to complement and go beyond the science goals of other planned and current spectroscopic capabilities like VISTA/4MOST, WHT/WEAVE, AAT/HERMES and Subaru/PFS. It is an ideal feeder facility for E-ELT, TMT and GMT, and provides the missing link between wide field imaging and small field precision astronomy. MSE is optimized for high throughput, high signal-to-noise observations of the faintest sources in the Universe with high quality calibration and stability being ensured through the dedicated operational mode of the observatory. (abridged)

astro-ph.IM↗