17 research outputs found
Investigating the [C]-to-H conversion factor and the H gas budget of galaxies at with hydrodynamical simulations
One of the most fundamental baryonic matter components of galaxies is the
neutral atomic hydrogen (H). At low redshifts, this
component can be traced directly through the 21-cm transition, but to infer
H gas content of the most distant galaxies, a viable
tracer is needed. We here investigate the fidelity of the fine structure
transition of the () transition of singly-ionized carbon
[C] at m as a proxy for H in a set simulated galaxies at , following the work by Heintz
et al. (2021). We select 11,125 star-forming galaxies from the SIMBA
simulations, with far-infrared line emissions post-processed and modeled within
the SIGAME framework. We find a strong connection between [C] and H, with the relation between this [C]-to-H relation () being anti-correlated with the gas-phase metallicity of the
simulated galaxies. We further use these simulations to make predictions for
the total baryonic matter content of galaxies at , and specifically
the HI gas mass fraction. We find mean values of ,
and . These results provide strong evidence
for H being the dominant baryonic matter component by
mass in galaxies at .Comment: 7 pages, 3 figures. Accepted for publication by ApJ
Multiwavelength Vertical Structure in the AU Mic Debris Disk: Characterizing the Collisional Cascade
Debris disks are scaled-up analogs of the Kuiper Belt in which dust is generated by collisions between planetesimals. In the âcollisional cascadeâ model of debris disks, dust lost to radiation pressure and winds is constantly replenished by grinding collisions between planetesimals. The model assumes that collisions are destructive and involve large velocities; this assumption has not been tested beyond our Solar System. We present 0. 0025 (â2.4 au) resolution observations of the λ = 450 ”m dust continuum emission from the debris disk around the nearby M dwarf AU Microscopii with the Atacama Large Millimeter/submillimeter Array. We use parametric models to describe the disk structure, and an MCMC algorithm to explore the posterior distributions of the model parameters; we fit the structure of the disk to both our data and archival λ = 1.3 mm data (Daley et al. 2019), from which we obtain two aspect ratio measurements at 1.3 mm (h1300 = 0.025+0.008 â0.002) and at 450 ”m (h450 = 0.019+0.006 â0.001), as well as the grain size distribution index q = 3.03 ± 0.02. Contextualizing our aspect ratio measurements within the modeling framework laid out in Pan & Schlichting (2012), we derive a power law index of velocity dispersion as a function of grain size p = 0.28 ± 0.06 for the AU Mic debris disk. This result implies that smaller bodies are more easily disrupted than larger bodies by collisions, which is inconsistent with the strength regime usually assumed for such small bodies. Possible explanations for this discrepancy are discussed
sĂgame v3: Gas Fragmentation in Postprocessing of Cosmological Simulations for More Accurate Infrared Line Emission Modeling
We present an update to the framework called Simulator of Galaxy Millimeter/submillimeter Emission (SĂGAME). SĂGAME derives line emission in the far-infrared (FIR) for galaxies in particle-based cosmological hydrodynamics simulations by applying radiative transfer and physics recipes via a postprocessing step after completion of the simulation. In this version, a new technique is developed to model higher gas densities by parameterizing the probability distribution function (PDF) of the gas density in higher-resolution simulations run with the pseudoLagrangian, Voronoi mesh code AREPO. The parameterized PDFs are used as a look-up table, and reach higher densities than in previous work. SĂGAME v3 is tested on redshift z = 0 galaxies drawn from the SIMBA cosmological simulation for eight FIR emission lines tracing vastly different phases of the interstellar medium. This version of SĂGAME includes dust radiative transfer with SKIRT and high-resolution photoionization models with CLOUDY, the latter sampled according to the density PDF of the AREPO simulations to augment the densities in the cosmological simulation. The quartile distributions of the predicted line luminosities overlap with the observed range for nearby galaxies of similar star formation rate (SFR) for all but two emission lines: [O I]63 and CO(3â2), which are overestimated by median factors of 1.3 and 1.0 dex, respectively, compared to the observed lineâSFR relation of mixed-type galaxies. We attribute the remaining disagreement with observations to the lack of precise attenuation of the interstellar light on sub-grid scales (200 pc) and differences in sample selection
TEMPLATES: A Robust Outlier Rejection Method for JWST/NIRSpec Integral Field Spectroscopy
We describe a custom outlier rejection algorithm for JWST/NIRSpec integral
field spectroscopy. This method uses a layered sigma clipping approach that
adapts clipping thresholds based upon the spatial profile of the science
target. We find that this algorithm produces a robust outlier rejection while
simultaneously preserving the signal of the science target. Originally
developed as a response to unsatisfactory initial performance of the jwst
pipeline outlier detection step, this method works either as a standalone
solution, or as a supplement to the current pipeline software. Comparing
leftover (i.e., not flagged) artifacts with the current pipeline's outlier
detection step, we find that our method results in one fifth as many residual
artifacts as the jwst pipeline. However, we find a combination of both methods
removes nearly all artifacts -- an approach that takes advantage of both our
algorithm's robust outlier rejection and the pipeline's use of individual
dithers. This combined approach is what the TEMPLATES Early Release Science
team has converged upon for our NIRSpec observations. Finally, we publicly
release the code and Jupyter notebooks for the custom outlier rejection
algorithm.Comment: 10 pages, including 5 figures. Submitted to the Publications of the
Astronomical Society of the Pacific (PASP). Code associated with paper
released at https://github.com/aibhleog/baryon-swee
TEMPLATES: Direct Abundance Constraints for Two Lensed Lyman-Break Galaxies
Using integrated spectra for two gravitationally lensed galaxies from the
JWST TEMPLATES Early Release Science program, we analyze faint auroral lines,
which provide direct measurements of the gas-phase chemical abundance. For the
brighter galaxy, SGAS172334 (), we detect the
[OIII], [SIII], and [OII]7320,7330
auroral emission lines, and set an upper limit for the [NII] line.
For the second galaxy, SGAS122621 (), we do not detect any
auroral lines, and report upper limits. With these measurements and upper
limits, we constrain the electron temperatures in different ionization zones
within both of these galaxies. For SGAS172334, where auroral lines are
detected, we calculate direct oxygen and nitrogen abundances, finding an N/O
ratio consistent with observations of nearby () galaxies. These
observations highlight the potent combination of JWST and gravitational lensing
to measure faint emission lines in individual distant galaxies and to directly
study the chemical abundance patterns in those galaxies.Comment: Submitted to the Astrophysical Journal's Focus Issue on the TEMPLATES
JWST Early Release Science Program. 15 pages, 6 figures. Comments welcom
Chaotic and Clumpy Galaxy Formation in an Extremely Massive Reionization-era Halo
© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/by/4.0/Abstract: The SPT 0311â58 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 ÎŒm emission in the central pair of galaxies and reach physical resolutions of âŒ100â350 pc, among the most detailed views of any reionization-era system to date. The observations resolve the source into at least a dozen kiloparsec-size clumps. The global kinematics and high turbulent velocity dispersion within the galaxies present a striking contrast to recent claims of dynamically cold thin-disk kinematics in some dusty galaxies just 800 Myr later at z ⌠4. We speculate that both gravitational interactions and fragmentation from massive parent disks have likely played a role in the overall dynamics and formation of clumps in the system. Each clump individually is comparable in mass to other 6 < z < 8 galaxies identified in rest-UV/optical deep field surveys, but with star formation rates elevated by a factor of ~3-5. Internally, the clumps themselves bear close resemblance to greatly scaled-up versions of virialized cloud-scale structures identified in low-redshift galaxies. Our observations are qualitatively similar to the chaotic and clumpy assembly within massive halos seen in simulations of high-redshift galaxies.Peer reviewe
JWST's TEMPLATES for Star Formation: The First Resolved Gas-Phase Metallicity Maps of Dust-Obscured Star-Forming Galaxies at 4
We present the first spatially resolved maps of gas-phase metallicity for
dust-obscured star-forming galaxies (DSFGs) at 4, from the JWST
TEMPLATES Early Release Science program, derived from NIRSpec integral field
unit spectroscopy of the H and [NII] emission lines. Empirically
derived literature optical line calibrations are used to determine that the
sources are highly metal rich, with both appearing to display regions of
supersolar metallicity, particularly in SPT2147-50. While we cannot rule out
shocks or AGN in these regions, we suggest that the two systems have already
undergone significant enrichment as a result of their extremely high
star-formation rates. Utilising ALMA rest-frame 380m continuum and
[CI](P-P) line maps we compare metallicity and gas-to-dust
ratio variations in the two galaxies, finding the two to be anticorrelated on
highly resolved spatial scales, consistent with various literature studies of
0 galaxies. The data are indicative of the enormous potential of
JWST to probe the enrichment of the interstellar medium on kpc scales in
extremely dust-obscured systems at 4 and beyond.Comment: 12 pages, 5 figures, submitted to Ap
JWST's TEMPLATES for Star Formation: The First Resolved Gas-phase Metallicity Maps of Dust-obscured Star-forming Galaxies at z ⌠4
We present the first spatially resolved maps of gas-phase metallicity for two dust-obscured star-forming galaxies at z ⌠4, from the JWST TEMPLATES Early Release Science program, derived from NIRSpec integral field unit spectroscopy of the Hα and [N ii] emission lines. Empirical optical line calibrations are used to determine that the sources are globally enriched to near-solar levels. While one source shows elevated [N ii]/Hα ratios and broad Hα emission consistent with the presence of an active galactic nucleus in a âł1 kpc region, we argue that both systems have already undergone significant metal enrichment as a result of their extremely high star formation rates. Utilizing Atacama Large Millimeter/submillimeter Array rest-frame 380 ÎŒm continuum and [Ci](3P2â3P1) line maps we compare the spatial variation of the metallicity and gas-to-dust ratio in the two galaxies, finding the two properties to be anticorrelated on highly resolved spatial scales, consistent with various literature studies of z ⌠0 galaxies. The data are indicative of the enormous potential of JWST to probe the enrichment of the interstellar medium on âŒkpc scales in extremely dust-obscured systems at z ⌠4 and beyond
A high-redshift calibration of the [O I]-to-H I conversion factor in star-forming galaxies
The assembly and build-up of neutral atomic hydrogen (H i) in galaxies is one of the most fundamental processes in galaxy formation and evolution. Studying this process directly in the early universe is hindered by the weakness of the hyperfine 21-cm H i line transition, impeding direct detections and measurements of the H i gas masses (MHI). Here we present a new method to infer MHI of high-redshift galaxies using neutral, atomic oxygen as a proxy. Specifically, we derive metallicity-dependent conversion factors relating the far-infrared [O i]-63 ”m and [O i]-145 ”m emission line luminosities and MHI in star-forming galaxies at z â 2â6 using gamma-ray bursts (GRBs) as probes. We calibrate the [O i]-to-H i conversion factor relying on a sample of local galaxies with direct measurements of MHI and [O i]-63 ”m and [O i]-145 ”m line luminosities in addition to the Sigame hydrodynamical simulation framework at similar epochs (z â 0). We find that the [O i]63 ”m-to-H i and [O i]145 ”m-to-H i conversion factors, here denoted ÎČ[OI]â63 ”m and ÎČ[OI]â145 ”m, respectively, universally appear to be anti-correlated with the gas-phase metallicity. The GRB measurements further predict a mean ratio of L[OI]â63 ”m/L[OI]â145 ”m = 1.55 ± 0.12 and reveal generally less excited [C ii] over [O i] compared to the local galaxy sample. The z â 0 galaxy sample also shows systematically higher ÎČ[OI]â63 ”m and ÎČ[OI]â145 ”m conversion factors than the GRB sample, indicating either suppressed [O i] emission in local galaxies likely due to their lower hydrogen densities or more extended, diffuse H i gas reservoirs traced by the H i 21-cm. Finally, we apply these empirical calibrations to the few detections of [O i]-63 ”m and [O i]-145 ”m line transitions at z â 2 from the literature and further discuss the applicability of these conversion factors to probe the H i gas content in the dense, star-forming interstellar medium (ISM) of galaxies well into the epoch of reionization.</p