arXiv subjects

Christopher C. Hayward

Publications and source records attributed to Christopher C. Hayward.

At least 73 records · Page 4Linked to original sources

arXiv2023

Two massive, compact, and dust-obscured candidate $z\sim 8$ galaxies discovered by JWST

We present a search for extremely red, dust-obscured, $z>7$ galaxies with $\textit{JWST}$/NIRCam+MIRI imaging over the first 20 arcmin$^2$ of publicly-available Cycle 1 data from the COSMOS-Web, CEERS, and PRIMER surveys. Based on their red color in F277W$-$F444W ($\sim 2.5$ mag) and detection in MIRI/F770W ($\sim 25$ mag), we identify two galaxies$\unicode{x2014}$COS-z8M1 and CEERS-z7M1$\unicode{x2014}$which have best-fit photometric redshifts of $z=8.5^{+0.3}_{-0.4}$ and $z=7.6^{+0.1}_{-0.1}$, respectively. We perform SED fitting with a variety of codes (including BAGPIPES, PROSPECTOR, BEAGLE, and CIGALE), and find a $>95\%$ probability that these indeed lie at $z>7$. Both sources are compact ($R_{\rm eff} \lesssim 200$ pc), highly obscured ($A_V \sim 1.5$$\unicode{x2013}$$2.5$), and, at our best-fit redshift estimates, likely have strong [OIII]+H$β$ emission contributing to their $4.4\,μ$m photometry. We estimate stellar masses of $\sim 10^{10}~M_\odot$ for both sources; by virtue of detection in MIRI at $7.7\,μ$m, these measurements are robust to the inclusion of bright emission lines, for example, from an AGN. We identify a marginal (2.9$σ$) ALMA detection at 2 mm within $0.5''$ of COS-z8M1, which if real, would suggest a remarkably high IR luminosity of $\sim 10^{12} L_\odot$. These two galaxies, if confirmed at $z\sim 8$, would be extreme in their stellar and dust masses, and may be representative of a substantial population of modestly dust-obscured galaxies at cosmic dawn.

astro-ph.GA↗

arXiv2023

A Near-Infrared Faint, Far-Infrared-Luminous Dusty Galaxy at z~5 in COSMOS-Web

A growing number of far-infrared bright sources completely invisible in deep extragalactic optical surveys hint at an elusive population of z>4 dusty, star-forming galaxies. Cycle 1 JWST surveys are now detecting their rest-frame optical light, which provides key insight into their stellar properties and statistical constraints on the population as a whole. This work presents the JWST/NIRCam counterpart from the COSMOS-Web survey to a far-infrared SCUBA-2 and ALMA source, AzTECC71, which was previously undetected at wavelengths shorter than 850 microns. AzTECC71, amongst the reddest galaxies in COSMOS-Web with F277W - F444W~0.9, is undetected in NIRCam/F150W and F115W and fainter in F444W than other sub-millimeter galaxies identified in COSMOS-Web by 2-4 magnitudes. This is consistent with the system having both a lower stellar mass and higher redshift than the median dusty, star-forming galaxy. With deep ground- and space-based upper limits combined with detections in F277W, F444W and the far-IR including ALMA Band 6, we find a high probability (99%) that AzTECC71 is at z>4 with z_phot=5.7(+0.8,-0.7). This galaxy is massive (logM*/Msun~10.7) and IR-luminous (logLIR/Lsun~12.7), comparable to other optically-undetected but far-IR bright dusty, star-forming galaxies at z>4. This population of luminous, infrared galaxies at z>4 is largely unconstrained but comprises an important bridge between the most extreme dust-obscured galaxies and more typical high-redshift star-forming galaxies. If further far-IR-selected galaxies that drop out of the F150W filter in COSMOS-Web have redshifts z>4 like AzTECC71, then the volume density of such sources may be ~3-10x greater than previously estimated.

astro-ph.GA↗

arXiv2023

Molecular gas and star formation in nearby starburst galaxy mergers

We employ the Feedback In Realistic Environments (FIRE-2) physics model to study how the properties of giant molecular clouds (GMCs) evolve during galaxy mergers. We conduct a pixel-by-pixel analysis of molecular gas properties in both the simulated control galaxies and galaxy major mergers. The simulated GMC-pixels in the control galaxies follow a similar trend in a diagram of velocity dispersion ($σ_v$) versus gas surface density ($Σ_{\mathrm{mol}}$) to the one observed in local spiral galaxies in the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey. For GMC-pixels in simulated mergers, we see a significant increase of factor of 5 - 10 in both $Σ_{\mathrm{mol}}$ and $σ_v$, which puts these pixels above the trend of PHANGS galaxies in the $σ_v$ vs $Σ_{\mathrm{mol}}$ diagram. This deviation may indicate that GMCs in the simulated mergers are much less gravitationally bound compared with simulated control galaxies with virial parameter ($α_{\mathrm{vir}}$) reaching 10 - 100. Furthermore, we find that the increase in $α_{\mathrm{vir}}$ happens at the same time as the increase in global star formation rate (SFR), which suggests stellar feedback is responsible for dispersing the gas. We also find that the gas depletion time is significantly lower for high $α_{\mathrm{vir}}$ GMCs during a starburst event. This is in contrast to the simple physical picture that low $α_{\mathrm{vir}}$ GMCs are easier to collapse and form stars on shorter depletion times. This might suggest that some other physical mechanisms besides self-gravity are helping the GMCs in starbursting mergers collapse and form stars.

astro-ph.GA↗

arXiv2023

Public data release of the FIRE-2 cosmological zoom-in simulations of galaxy formation

We describe a public data release of the FIRE-2 cosmological zoom-in simulations of galaxy formation, available at http://flathub.flatironinstitute.org/fire, from the Feedback In Realistic Environments (FIRE) project. FIRE-2 simulations achieve parsec-scale resolution to explicitly model the multi-phase interstellar medium while implementing direct models for stellar evolution and feedback, including stellar winds, core-collapse and Ia supernovae, radiation pressure, photoionization, and photoelectric heating. We release complete snapshots from 3 suites of simulations. The first comprises 20 simulations that zoom in on 14 Milky Way-mass galaxies, 5 SMC/LMC-mass galaxies, and 4 lower-mass galaxies including 1 ultra-faint; we release 39 snapshots across z = 0 - 10. The second comprises 4 massive galaxies, with 19 snapshots across z = 1 - 10. Finally, a high-redshift suite comprises 22 simulations, with 11 snapshots across z = 5 - 10. Each simulation also includes dozens of resolved lower-mass (satellite) galaxies in its zoom-in region. Snapshots include all stored properties for all dark matter, gas, and star particles, including 11 elemental abundances for stars and gas, and formation times (ages) of star particles. We also release accompanying (sub)halo catalogs, which include galaxy properties and member star particles. For the simulations to z = 0, including all Milky Way-mass galaxies, we release the formation coordinates and an "ex-situ" flag for all star particles, pointers to track particles across snapshots, catalogs of stellar streams, and multipole basis expansions for the halo mass distributions. We describe publicly available python packages for reading and analyzing these simulations.

astro-ph.GA↗

arXiv2023

COSMOS-Web: An Overview of the JWST Cosmic Origins Survey

We present the survey design, implementation, and outlook for COSMOS-Web, a 255 hour treasury program conducted by the James Webb Space Telescope in its first cycle of observations. COSMOS-Web is a contiguous 0.54 deg$^2$ NIRCam imaging survey in four filters (F115W, F150W, F277W, and F444W) that will reach 5$σ$ point source depths ranging $\sim$27.5-28.2 magnitudes. In parallel, we will obtain 0.19 deg$^2$ of MIRI imaging in one filter (F770W) reaching 5$σ$ point source depths of $\sim$25.3-26.0 magnitudes. COSMOS-Web will build on the rich heritage of multiwavelength observations and data products available in the COSMOS field. The design of COSMOS-Web is motivated by three primary science goals: (1) to discover thousands of galaxies in the Epoch of Reionization ($6 4$ and place constraints on the formation of the Universe's most massive galaxies ($M_\star>10^{10}$\,M$_\odot$), and (3) directly measure the evolution of the stellar mass to halo mass relation using weak gravitational lensing out to $z\sim2.5$ and measure its variance with galaxies' star formation histories and morphologies. In addition, we anticipate COSMOS-Web's legacy value to reach far beyond these scientific goals, touching many other areas of astrophysics, such as the identification of the first direct collapse black hole candidates, ultracool sub-dwarf stars in the Galactic halo, and possibly the identification of $z>10$ pair-instability supernovae. In this paper we provide an overview of the survey's key measurements, specifications, goals, and prospects for new discovery.

astro-ph.GA↗

arXiv2023

GOALS-JWST: Revealing the Buried Star Clusters in the Luminous Infrared Galaxy VV 114

We present the results of a {\it James Webb Space Telescope} NIRCam investigation into the young massive star cluster (YMC) population in the luminous infrared galaxy VV 114. We identify 374 compact YMC candidates with a $S/N \geq 3$, 5, and 5 at F150W, F200W, and F356W respectively. A direct comparison with our {\it HST} cluster catalog reveals that $\sim 20\%$ of these sources are undetected at optical wavelengths. Based on {\it yggdrasil} stellar population models, we identify 17 YMC candidates in our {\it JWST} imaging alone with F150W-F200W and F200W-F356W colors suggesting they are all very young, dusty ($A_{V} = 5 - 15$), and massive ($10^{5.8} < M_{\odot} < 10^{6.1}$). The discovery of these `hidden' sources, many of which are found in the `overlap' region between the two nuclei, quadruples the number of $t < 3$ Myr clusters, and nearly doubles the number of $t < 6$ Myr clusters detected in VV 114. Now extending the cluster age distribution ($dN/dτ\propto τ^γ$) to the youngest ages, we find a slope of $γ= -1.30 \pm 0.39$ for $10^{6} < τ(\mathrm{yr}) < 10^{7}$, which is consistent with the previously determined value from $10^{7} < τ(\mathrm{yr}) < 10^{8.5}$, and confirms that VV 114 has a steep age distribution slope for all massive star clusters across the entire range of cluster ages observed. Finally, the consistency between our {\it JWST}- and {\it HST}-derived age distribution slopes indicates that the balance between cluster formation and destruction has not been significantly altered in VV 114 over the last 0.5 Gyr.

astro-ph.GA↗

arXiv2023

Brightest Cluster Galaxy Formation in the z=4.3 Protocluster SPT2349-56: Discovery of a Radio-Loud AGN

We have observed the z=4.3 protocluster SPT2349-56 with ATCA with the aim of detecting radio-loud active galactic nuclei (AGN) amongst the ~30 submillimeter galaxies identified in the structure. We detect the central complex of SMGs at 2.2\,GHz with a luminosity of L_2.2=(4.42pm0.56)x10^{25} W/Hz. The ASKAP also detects the source at 888 MHz, constraining the radio spectral index to alpha=-1.6pm0.3, consistent with ATCA non-detections at 5.5 and 9GHz, and implying L_1.4(rest)=(2.4pm0.3)x10^{26}W/Hz. This radio luminosity is about 100 times higher than expected from star formation, assuming the usual FIR-radio correlation, which is a clear indication of an AGN driven by a forming brightest cluster galaxy (BCG). None of the SMGs in SPT2349-56 show signs of AGN in any other diagnostics available to us (notably 12CO out to J=16, OH163um, CII/IR, and optical spectra), highlighting the radio continuum as a powerful probe of obscured AGN in high-z protoclusters. No other significant radio detections are found amongst the cluster members, consistent with the FIR-radio correlation. We compare these results to field samples of radio sources and SMGs, along with the 22 SPT-SMG gravitational lenses also observed in the ATCA program, as well as powerful radio galaxies at high redshifts. Our results allow us to better understand the effects of this gas-rich, overdense environment on early supermassive black hole (SMBH) growth and cluster feedback. We estimate that (3.3pm0.7)x10^{38} W of power are injected into the growing ICM by the radio-loud AGN, whose energy over 100Myr is comparable to the binding energy of the gas mass of the central halo. The AGN power is also comparable to the instantaneous energy injection from supernova feedback from the 23 catalogued SMGs in the core region of 120kpc projected radius. The SPT2349-56 radio-loud AGN may be providing strong feedback on a nascent ICM.

astro-ph.GA↗

arXiv2022

GOALS-JWST: NIRCam and MIRI Imaging of the Circumnuclear Starburst Ring in NGC 7469

We present James Webb Space Telescope (JWST) imaging of NGC 7469 with the Near-Infrared Camera (NIRCam) and the Mid-InfraRed Instrument (MIRI). NGC 7469 is a nearby, $z=0.01627$, luminous infrared galaxy (LIRG) that hosts both a Seyfert Type-1.5 nucleus and a circumnuclear starburst ring with a radius of $\sim$0.5 kpc. The new near-infrared (NIR) JWST imaging reveals 66 star-forming regions, 37 of which were not detected by HST observations. Twenty-eight of the 37 sources have very red NIR colors that indicate obscurations up to A$_{\rm{v}}\sim7$ and a contribution of at least 25$\%$ from hot dust emission to the 4.4$μ$m band. Their NIR colors are also consistent with young ($<$5 Myr) stellar populations and more than half of them are coincident with the MIR emission peaks. These younger, dusty star-forming regions account for $\sim$6$\%$ and $\sim$17$\%$ of the total 1.5$μ$m and 4.4$μ$m luminosity of the starburst ring, respectively. Thanks to JWST, we find a significant number of young dusty sources that were previously unseen due to dust extinction. The newly identified 28 young sources are a significant increase compared to the number of HST-detected young sources (4-5). This makes the total percentage of the young population rise from $\sim$15$\%$ to 48$\%$. These results illustrate the effectiveness of JWST in identifying and characterizing previously hidden star formation in the densest star-forming environments around AGN.

astro-ph.GA↗

arXiv2022

GOALS-JWST: Resolving the Circumnuclear Gas Dynamics in NGC 7469 in the Mid-Infrared

The nearby, luminous infrared galaxy (LIRG) NGC 7469 hosts a Seyfert nucleus with a circumnuclear star-forming ring and is thus the ideal local laboratory for investigating the starburst--AGN connection in detail. We present integral-field observations of the central 1.3 kpc region in NGC 7469 obtained with the JWST Mid-InfraRed Instrument. Molecular and ionized gas distributions and kinematics at a resolution of {\sim}100 pc over the 4.9 - 7.6μm region are examined to study gas dynamics influenced by the central AGN. The low-ionization [Fe II] λ5.34μm and [Ar II] λ6.99μm lines are bright on the nucleus and in the starburst ring, as opposed to H2 S(5) λ6.91μm which is strongly peaked at the center and surrounding ISM. The high-ionization [Mg V] line is resolved and shows a broad, blueshifted component associated with the outflow. It has a nearly face-on geometry that is strongly peaked on the nucleus, where it reaches a maximum velocity of -650 km/s, and extends about 400 pc to the East. Regions of enhanced velocity dispersion in H2 and [Fe II] {\sim}180 pc from the AGN that also show high L(H2)/L(PAH) and L([Fe II])/L(Pfα) ratios to the W and N of the nucleus pinpoint regions where the ionized outflow is depositing energy, via shocks, into the dense interstellar medium between the nucleus and the starburst ring. These resolved mid-infrared observations of the nuclear gas dynamics demonstrate the power of JWST and its high-sensitivity integral-field spectroscopic capability to resolve feedback processes around supermassive black holes in the dusty cores of nearby LIRGs.

astro-ph.GA↗

arXiv2022

Spiral Arms are Metal Freeways: Azimuthal Gas-Phase Metallicity Variations in Simulated Cosmological Zoom-in Flocculent Disks

We examine the azimuthal variations in gas-phase metallicity profiles in simulated Milky Way mass disk galaxies from the Feedback in Realistic Environments (FIRE-2) cosmological zoom-in simulation suite, which includes a sub-grid turbulent metal mixing model. We produce spatially resolved maps of the disks at $z \approx 0$ with pixel sizes ranging from 250 to 750~pc, analogous to modern integral field unit (IFU) galaxy surveys, mapping the gas-phase metallicities in both the cold & dense gas and the ionized gas correlated with HII regions. We report that the spiral arms alternate in a pattern of metal rich and metal poor relative to the median metallicity on the order of $\lesssim 0.1$~dex, appearing generally in this sample of flocculent spirals. The pattern persists even in a simulation with different strengths of metal mixing, indicating that the pattern emerges from physics above the sub-grid scale. Local enrichment does not appear to be the dominant source of the azimuthal metallicity variations at $z \approx 0$: there is no correlation with local star formation on these spatial scales. Rather, the arms are moving inwards and outwards relative to each other, carrying their local metallicity gradients with them radially before mixing into the larger-scale interstellar medium. We propose that the arms act as freeways channeling relatively metal poor gas radially inwards, and relatively enriched gas radially outwards.

astro-ph.GA↗

arXiv2022

GOALS-JWST: Unveiling Dusty Compact Sources in the Merging Galaxy IIZw096

We have used the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST) to obtain the first spatially resolved, mid-infrared (mid-IR) images of IIZw096, a merging luminous infrared galaxy (LIRG) at $z = 0.036$. Previous observations with the Spitzer Space Telescope suggested that the vast majority of the total IR luminosity (LIR) of the system originated from a small region outside of the two merging nuclei. New observations with JWST/MIRI now allow an accurate measurement of the location and luminosity density of the source that is responsible for the bulk of the IR emission. We estimate that 40-70% of the IR bolometric luminosity, or $3-5 \times 10^{11}\,{\rm{L_{\odot}}}$, arises from a source no larger than 175pc in radius, suggesting a luminosity density of at least $3-5 \times 10^{12} \, {\rm{L_{\odot} \, kpc^{-2}}}$. In addition, we detect 11 other star forming sources, five of which were previously unknown. The MIRI F1500W/F560W colors of most of these sources, including the source responsible for the bulk of the far-IR emission, are much redder than the nuclei of local LIRGs. These observations reveal the power of JWST to disentangle the complex regions at the hearts of merging, dusty galaxies.

astro-ph.GA↗

arXiv2022

GOALS-JWST: Tracing AGN Feedback on the Star-Forming ISM in NGC 7469

We present James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) integral-field spectroscopy of the nearby merging, luminous infrared galaxy, NGC 7469. This galaxy hosts a Seyfert type-1.5 nucleus, a highly ionized outflow, and a bright, circumnuclear star-forming ring, making it an ideal target to study AGN feedback in the local Universe. We take advantage of the high spatial/spectral resolution of JWST/MIRI to isolate the star-forming regions surrounding the central active nucleus and study the properties of the dust and warm molecular gas on ~100 pc scales. The starburst ring exhibits prominent Polycyclic Aromatic Hydrocarbon (PAH) emission, with grain sizes and ionization states varying by only ~30%, and a total star formation rate of $\rm 10 - 30 \ M_\odot$/yr derived from fine structure and recombination emission lines. Using pure rotational lines of H2, we detect 1.2$\times$10$^{7} \rm \ M_\odot$ of warm molecular gas at a temperature higher than 200 K in the ring. All PAH bands get significantly weaker towards the central source, where larger and possibly more ionized grains dominate the emission. However, the bulk of the dust and molecular gas in the ring appears unaffected by the ionizing radiation or the outflowing wind from the AGN. These observations highlight the power of JWST to probe the inner regions of dusty, rapidly evolving galaxies for signatures of feedback and inform models that seek to explain the co-evolution of supermassive black holes and their hosts.

astro-ph.GA↗

arXiv2022

The effects of local stellar radiation and dust depletion on non-equilibrium interstellar chemistry

Interstellar chemistry is important for galaxy formation, as it determines the rate at which gas can cool, and enables us to make predictions for observable spectroscopic lines from ions and molecules. We explore two central aspects of modelling the chemistry of the interstellar medium (ISM): (1) the effects of local stellar radiation, which ionises and heats the gas, and (2) the depletion of metals onto dust grains, which reduces the abundance of metals in the gas phase. We run high-resolution (400 M$_\odot$ per baryonic particle) simulations of isolated disc galaxies, from dwarfs to Milky Way-mass, using the FIRE galaxy formation models together with the CHIMES non-equilibrium chemistry and cooling module. In our fiducial model, we couple the chemistry to the stellar fluxes calculated from star particles using an approximate radiative transfer scheme, and we implement an empirical density-dependent prescription for metal depletion. For comparison, we also run simulations with a spatially uniform radiation field, and without metal depletion. Our fiducial model broadly reproduces observed trends in HI and H2 mass with stellar mass, and in line luminosity versus star formation rate for [CII] 158$μ$m, [OI] 63$μ$m, [OIII] 88$μ$m, [NII] 122$μ$m and H$α$ 6563A. Our simulations with a uniform radiation field predict fainter luminosities, by up to an order of magnitude for [OIII] 88$μ$m and H$α$ 6563A, while ignoring metal depletion increases the luminosity of carbon and oxygen lines by a factor $\approx$2. However, the overall evolution of the galaxy is not strongly affected by local stellar fluxes or metal depletion, except in dwarf galaxies where the inclusion of local fluxes leads to weaker outflows and hence higher gas fractions.

astro-ph.GA↗

arXiv2022

Magnetic Fields on FIRE: Comparing B-fields in the multiphase ISM and CGM of Simulated L$_*$ Galaxies to Observations

The physics of magnetic fields ($\textbf{B}$) and cosmic rays (CRs) have recently been included in simulations of galaxy formation. However, significant uncertainties remain in how these components affect galaxy evolution. To understand their common observational tracers, we analyze the magnetic fields in a set of high-resolution, magneto-hydrodynamic, cosmological simulations of Milky-Way-like galaxies from the FIRE-2 project. We compare mock observables of magnetic field tracers for simulations with and without CRs to observations of Zeeman splitting and rotation/dispersion measures. We find reasonable agreement between simulations and observations in both the neutral and the ionised interstellar medium (ISM). We find that the simulated galaxies with CRs show weaker ISM $|\textbf{B}|$ fields on average compared to their magnetic-field-only counterparts. This is a manifestation of the effects of CRs in the diffuse, low density inner circum-galactic medium (CGM). We find that equipartition between magnetic and cosmic ray energy densities may be valid at large ($>$ 1 kpc) scales for typical ISM densities of Milky-Way-like galaxies, but not in their halos. Within the ISM, the magnetic fields in our simulated galaxies follow a power-law scaling with gas density. The scaling extends down to hydrogen number densities $<$ 300 cm$^{-3}$, in contrast to observationally-derived models, but consistent with the observational measurements. Finally, we generate synthetic rotation measure (RM) profiles for projections of the simulated galaxies and compare to observational constraints in the CGM. While consistent with upper limits, improved data are needed to detect the predicted CGM RMs at 10-200 kpc and better constrain theoretical predictions.

astro-ph.GA↗

arXiv2022

Self-regulation of black hole accretion via jets in early protogalaxies

The early growth of black holes (BHs) in high-redshift galaxies is likely regulated by their feedback on the surrounding gas. While radiative feedback has been extensively studied, the role of mechanical feedback has received comparatively less scrutiny to date. Here we use high-resolution parsec-scale hydrodynamical simulations to study jet propagation and its effect on BH accretion onto 100 ${\rm M_\odot}$ BHs in the dense, low-metallicity gas expected in early protogalaxies. As the jet propagates, it shocks the surrounding gas and forms a jet cocoon. The cocoon consists of a rapidly-cooling cold phase at the interface with the background gas and an over-pressured subsonic phase of reverse shock-heated gas filling the cocoon interior. We systematically vary the background gas density and temperature, BH feedback efficiency, and the jet model. We found that the jet cocoon width roughly follows a scaling derived by assuming momentum conservation in the jet propagation direction, and energy conservation in the lateral directions. Depending on the assumed gas and jet properties, the cocoon either stays elongated out to a large radius or isotropizes before reaching the Bondi radius, forming a nearly spherical bubble. Lower jet velocities and higher background gas densities result in self-regulation to higher momentum fluxes and elongated cocoons. In all cases, the outward momentum flux of the cocoon balances the inward momentum flux of the inflowing gas near the Bondi radius, which ultimately regulates BH accretion. The larger the distance the jet cocoon reaches, the longer the variability timescale of the BH accretion rate. Overall, the average accretion rate always remains below the Bondi rate, and exceeds the Eddington rate only if the ambient medium is dense and cold, and/or the jet is weak. We derive the combination of jet and ambient gas parameters yielding super-Eddington growth.

astro-ph.HE↗

arXiv2022

The observability of galaxy merger signatures in nearby gas-rich spirals

Galaxy mergers are crucial to understanding galaxy evolution, therefore we must determine their observational signatures to select them from large IFU galaxy samples such as MUSE and SAMI. We employ 24 high-resolution idealised hydrodynamical galaxy merger simulations based on the "Feedback In Realistic Environment" (FIRE-2) model to determine the observability of mergers to various configurations and stages using synthetic images and velocity maps. Our mergers cover a range of orbital configurations at fixed 1:2.5 stellar mass ratio for two gas rich spirals at low redshift. Morphological and kinematic asymmetries are computed for synthetic images and velocity maps spanning each interaction. We divide the interaction sequence into three: (1) the pair phase; (2) the merging phase; and (3) the post-coalescence phase. We correctly identify mergers between first pericentre passage and 500 Myr after coalescence using kinematic asymmetry with 66% completeness, depending upon merger phase and the field-of-view of the observation. We detect fewer mergers in the pair phase (40%) and many more in the merging and post-coalescence phases (97%). We find that merger detectability decreases with field-of-view, except in retrograde mergers, where centrally concentrated asymmetric kinematic features enhances their detectability. Using a cut-off derived from a combination of photometric and kinematic asymmetry, we increase these detections to 89% overall, 79% in pairs, and close to 100% in the merging and post-coalescent phases. By using this combined asymmetry cut-off we mitigate some of the effects caused by smaller fields-of-view subtended by massively multiplexed integral field spectroscopy programmes.

astro-ph.GA↗

arXiv2022

The Galactic Dust-Up: Modeling Dust Evolution in FIRE

Recent strides have been made developing dust evolution models for galaxy formation simulations but these approaches vary in their assumptions and degree of complexity. Here we introduce and compare two separate dust evolution models (labelled 'Elemental' and 'Species'), based on recent approaches, incorporated into the GIZMO code and coupled with FIRE-2 stellar feedback and ISM physics. Both models account for turbulent dust diffusion, stellar production of dust, dust growth via gas-dust accretion, and dust destruction from time-resolved supernovae, thermal sputtering in hot gas, and astration. The "Elemental" model tracks the evolution of generalized dust species and utilizes a simple, 'tunable' dust growth routine, while the "Species" model tracks the evolution of specific dust species with set chemical compositions and incorporates a physically motivated, two-phase dust growth routine. We test and compare these models in an idealized Milky Way-mass galaxy and find that while both produce reasonable galaxy-integrated dust-to-metals (D/Z) ratios and predict gas-dust accretion as the main dust growth mechanism, a chemically motivated model is needed to reproduce the observed scaling relation between individual element depletions and D/Z with column density and local gas density. We also find the inclusion of theoretical metallic iron and O-bearing dust species are needed in the case of specific dust species in order to match observations of O and Fe depletions, and the integration of a sub-resolution dense molecular gas/CO scheme is needed to both match observed C depletions and ensure carbonaceous dust is not overproduced in dense environments.

astro-ph.GA↗

arXiv2022

On the impact of runaway stars on dwarf galaxies with resolved interstellar medium

About ten to 20 percent of massive stars may be kicked out of their natal clusters before exploding as supernovae. These "runaway stars" might play a crucial role in driving galactic outflows and enriching the circumgalactic medium with metals. To study this effect, we carry out high resolution dwarf galaxy simulations that include velocity kicks to massive O/B stars above 8 M$_{\odot}$. We consider two scenarios, one that adopts a power law velocity distribution for kick velocities, resulting in more stars with high velocity kicks, and a more moderate scenario with a Maxwellian velocity distribution. We explicitly resolve the multi-phase interstellar medium (ISM), and include non-equilibrium cooling and chemistry channels. We adopt a resolved feedback scheme (\textsc{Griffin}) where we sample individual massive stars from an IMF. We follow the lifetime of these stars and add their photoionising radiation, their UV radiation field, and their photoelectric heating rate to the surrounding gas. At the end of their lifetime we explode the massive population as core collapse supernovae (CCSN). In the simulations with runaway massive stars, we add additional (natal) velocity kicks that mimic two and three body interactions that cannot be fully resolved in our simulations. We find that the inclusion of runaway or walkaway star scenarios has an impact on mass, metal, momentum and energy outflows as well as the respective loading factors. We find an increase in mass, metal and momentum loading by a factor of 2-3, whereas we find an increase in the mean energy loading by a factor of 5 in the runaway case and a factor of 3 in the walkaway case. However, we find that the peak values are increased by a factor of up to 10, independent of the adopted velocity kick model. We conclude that the inclusion of runaway stars could have a significant impact on the global outflow properties of dwarf galaxies.

astro-ph.GA↗