Publications by Kearn Grisdale

Predicting the observability of population III stars with ELT-HARMONI via the helium 1640 Å emission line

Monthly Notices of the Royal Astronomical Society Oxford University Press 501 (2021) 5517-5537

K Grisdale, N Thatte, J Devriendt, M Pereira Santaella, A Slyz, T Kimm, Y Dubois, S Yi

Population III (Pop. III) stars, as of yet, have not been detected, however as we move into the era of extremely large telescopes this is likely to change. One likely tracer for Pop. III stars is the He IIλ1640 emission line, which will be detectable by the HARMONI spectrograph on the European Extremely Large Telescope (ELT) over a broad range of redshifts (2 ≤ z ≤ 14). By post-processing galaxies from the cosmological, AMR-hydrodynamical simulation NEWHORIZON with theoretical spectral energy distributions (SED) for Pop. III stars and radiative transfer (i.e. the Yggdrasil Models and CLOUDY look-up tables, respectively) we are able to compute the flux of He IIλ1640 for individual galaxies. From mock 10 h observations of these galaxies we show that HARMONI will be able to detect Pop. III stars in galaxies up to z ∼ 10 provided Pop. III stars have a top heavy initial mass function (IMF). Furthermore, we find that should Pop. III stars instead have an IMF similar to those of the Pop. I stars, the He IIλ1640 line would only be observable for galaxies with Pop. III stellar masses in excess of 107M⊙⁠, average stellar age <1Myr at z = 4. Finally, we are able to determine the minimal intrinsic flux required for HARMONI to detect Pop. III stars in a galaxy up to z = 10.

Physical properties and scaling relations of molecular clouds: the impact of star formation


K Grisdale

On the Observed Diversity of Star Formation Efficiencies in Giant Molecular Clouds

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 468 (2019) 5482-5491

K Grisdale, O Agertz, F Renaud, AB Romeo, J Devriendt, A Slyz

Observations find a median star formation efficiency per free-fall time in Milky Way Giant Molecular Clouds (GMCs) on the order of $\epsilon_{\rm ff}\sim 1\%$ with dispersions of $\sim0.5\,{\rm dex}$. The origin of this scatter in $\epsilon_{\rm ff}$ is still debated and difficult to reproduce with analytical models. We track the formation, evolution and destruction of GMCs in a hydrodynamical simulation of a Milky Way-like galaxy and by deriving cloud properties in an observationally motivated way, measure the distribution of star formation efficiencies which are in excellent agreement with observations. We find no significant link between $\epsilon_{\rm ff}$ and any measured global property of GMCs (e.g. gas mass, velocity dispersion). Instead, a wide range of efficiencies exist in the entire parameter space. From the cloud evolutionary tracks, we find that each cloud follow a \emph{unique} evolutionary path which gives rise to wide diversity in all properties. We argue that it is this diversity in cloud properties, above all else, that results in the dispersion of $\epsilon_{\rm ff}$.

Physical properties and scaling relations of molecular clouds: the effect of stellar feedback

Monthly Notices of the Royal Astronomical Society (2018)

K Grisdale, O Agertz, F Renaud, AB Romeo

The impact of stellar feedback on the density and velocity structure of the interstellar medium

Monthly Notices of the Royal Astronomical Society 466 (2017) 1093-1110

K Grisdale, O Agertz, AB Romeo, F Renaud, JI Read

© 2016 The Authors. We study the impact of stellar feedback in shaping the density and velocity structure of neutral hydrogen (H I) in disc galaxies. For our analysis, we carry out ~4.6 pc resolution N-body+adaptive mesh refinement hydrodynamic simulations of isolated galaxies, set up to mimic a Milky Way and a Large and Small Magellanic Cloud. We quantify the density and velocity structure of the interstellar medium using power spectra and compare the simulated galaxies to observedHI in local spiral galaxies from THINGS (TheHI Nearby Galaxy Survey). Our models with stellar feedback give an excellent match to the observed THINGS HI density power spectra. We find that kinetic energy power spectra in feedback-regulated galaxies, regardless of galaxy mass and size, show scalings in excellent agreement with supersonic turbulence (E(k) ∝ k -2 ) on scales below the thickness of the HI layer. We show that feedback influences the gas density field, and drives gas turbulence, up to large (kpc) scales. This is in stark contrast to density fields generated by large-scale gravity-only driven turbulence. We conclude that the neutral gas content of galaxies carries signatures of stellar feedback on all scales.

Characterizing gravitational instability in turbulent multicomponent galactic discs


O Agertz, AB Romeo, K Grisdale

Integral Field Spectroscopy of Luminous Infrared Main Sequence Galaxies at Cosmic Noon

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (0)

L Hogan, D Rigopoulou, GE Magdis, M Pereira-Santaella, I García-Bernete, N Thatte, K Grisdale, J-S Huang

<jats:title>Abstract</jats:title> <jats:p>We present the results of an integral field spectroscopy survey of a sample of dusty (ultra) luminous infrared galaxies (U/LIRGs) at 2 &amp;lt; z &amp;lt; 2.5 using KMOS on the Very Large Telescope. The sample has been drawn from Herschel deep field surveys and benefits from ancillary multi-wavelength data. Our goal is to investigate the physical characteristics, kinematics and the drivers of star formation in the galaxies whose contribution dominates the peak of the cosmic star formation density. Two thirds of the sample are main sequence galaxies in contrast to the starburst nature of local U/LIRGs. Our kinematic study, unique in its focus on z ∼ 2 dusty star forming galaxies, uses the Hα emission line to find that ∼ 40% appear to be isolated disks based on the ratio of rotational velocity to the velocity dispersion, suggesting steady state mechanisms are sufficient to power the large star formations rates (SFRs). The ratio of obscured to un-obscured star formation indicates the sample of galaxies experience less dust obscuration compared to intermediate and local counterparts, while also hosting cooler dust than local U/LIRGs. In addition to Hα we detect [NII] 6583 Å in our targets and show the gas phase metallicities do not exhibit the metal deficiency of local U/LIRGs. These results indicate that, despite their extreme IR luminosity, the underlying mechanisms driving the massive SFRs found at cosmic noon are due to scaled up disk galaxies as opposed to mergers.</jats:p>