arXiv subjects

David Vizgan

Publications and source records attributed to David Vizgan.

At least 19 recordsLinked to original sources

arXiv2026

An extreme ram-pressure stripping event in a protocluster at redshift 4.3

In the nearby Universe, the environment plays a crucial role in suppressing star formation in dense regions. In particular, ram-pressure stripping (RPS) is a major mechanism for removing gas from galaxies in clusters, occurring when galaxies travel through a dense hot atmosphere and leave trailing gaseous wakes. By depleting the cold gas reservoir, RPS can drive outside-in quenching and is therefore thought to be an important route for transforming cluster galaxies. At earlier times, however, protoclusters are dynamically young and their hot atmospheres are expected to be immature, so environmental effects are commonly assumed to be dominated by gravitational interactions rather than hydrodynamic stripping. Recent observations have begun to show that RPS can already operate before mature cluster assembly, including extended gas tails in a forming cluster at $z=2.51$ and in a galaxy group at $z=3.06$. These studies demonstrate that hydrodynamic stripping is possible at earlier times, but whether RPS can become sufficient enough to quench massive galaxies at $z>2$ remains unclear. Here we report ALMA and JWST observations of SPT2349$-$56-C26, a massive galaxy experiencing an extreme RPS event in the SPT2349$-$56 protocluster at $z=4.30$. C26 appears to exhibit a particularly severe active-stripping phase: the displaced gas contains more than half of the observed cold-gas reservoir, with the gas-emission peak showing a large 6-kpc offset from the stellar body. These observations show that RPS can remove most of the cold gas from massive galaxies in dense protocluster cores as early as $z=4.3$, providing a direct hydrodynamic pathway for environmental quenching at $z>4$.

astro-ph.GA↗

arXiv2026

JWST's PEARLS: A clumpy ring galaxy at $z = 4.0148$

Ring galaxies are an uncommon class of galaxies whose morphology is closely related to dynamical processes that govern galaxy evolution. Some ring galaxies, known as "collisional ring galaxies", are thought to form as a consequence of head-on collisions between galaxies, and a number of high-redshift collisional ring galaxies have been discovered and/or studied in the era of the James Webb Space Telescope (JWST). In this paper, we present HST/ACS, JWST/NIRCam, and JWST/NIRSpec observations of a candidate ring galaxy at $z_{\rm spec} = 4.0148$, previously identified as a potential gravitational lens. The galaxy exhibits a complex morphology, including three bright clumps along an apparent ring with radius $\approx 0.25$" $\simeq 1.8$ kpc. It has a total SFR $= 140^{+20}_{-30}$ ${\rm M}_{\rm \odot}$ yr$^{-1}$ and $\log(M_\ast/{\rm M}_\odot) = 10.41^{+0.11}_{-0.13}$, making it similar to other high-redshift collisional ring galaxies. Although we argue strongly in favor of the collisional ring explanation, we cannot entirely rule out a galaxy-galaxy strong lensing explanation for the system's morphology, in which a foreground galaxy at $z \simeq 1.7$ lenses a galaxy at $z \simeq 4.0$ into an Einstein ring-like configuration; to confirm the nature of this source, we require kinematic information via high spectral resolution observations. We suggest that current and future gravitational lens surveys should consider high-redshift ring galaxies as possible but significant contaminants.

astro-ph.GA↗

arXiv2026

A census of star-formation and gas mass tracers in two lensed $z \sim 4$ dusty star-forming galaxies

We present new and archival Atacama Large Millimeter/submillimeter Array (ALMA) observations of two strongly lensed dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope survey, SPT0418-47 $(z = 4.225)$ and SPT2147-50 $(z = 3.760)$. We study the [C II], CO(7-6), [C I](2-1), and, in SPT0418-47, $p$-H$_2$O emission, which along with the underlying continuum (rest-frame 160 $\mu$m and 380 $\mu$m) are routinely used as tracers of gas mass and/or star-formation rate (SFR). We perform a pixel-by-pixel analysis of both sources in the image plane to study the resolved Kennicutt-Schmidt relation, finding generally good agreement between the slopes of the SFR versus gas mass surface density using the different tracers. Using lens modeling methods, we find that the dust emission is more compact than the line emission in both sources, with CO(7-6) and [C I](2-1) similar in extent and [C II] the most extended, reminiscent of recent findings of extended [C II] spatial distributions in galaxies at similar cosmic epochs. We develop the [C I](2-1) / CO(7-6) flux density ratio as an observable proxy for gas depletion timescale ($\tau_{\rm dep}$), which can be applied to large samples of DSFGs, in lieu of more detailed inferences of this timescale which require analysis of observations at multiple wavelengths. Furthermore, the extended [C II] emission in both sources, compared to the total continuum and line emission, suggests that [C II], used in recent years as a molecular gas mass and SFR tracer in high-$z$ galaxies, may not always be a suitable tracer of these physical quantities.

astro-ph.GA↗

arXiv2025

An Overabundance of Radio-AGN in the SPT2349-56 Protocluster: Preheating the Intra-Cluster Medium

Following the detection of a radio-loud Active Galactic Nucleus (AGN) in the z=4.3 protocluster SPT2349-56, we have obtained additional observations with MeerKAT in S-band (2.4 GHz) with the aim of further characterizing radio emission from amongst the ~30 submillimeter (submm) galaxies (SMGs) identified in the structure. We newly identify three of the protocluster SMGs individually at 2.4GHz as having a radio-excess, two of which are now known to be X-ray luminous AGN. Two additional members are also detected with radio emission consistent with their star formation rate (SFR). Archival MeerKAT UHF (816 MHz) observations further constrain luminosities and radio spectral indices of these five galaxies. The Australia Telescope Compact Array (ATCA) is used to detect and resolve the central two sources at 5.5 and 9.0 GHz finding elongated, jet-like morphologies. The excess radio luminosities range from L1.4,rest = (1-20)x10^25 W/Hz, ~10-100x higher than expected from the SFRs, assuming the usual far-infrared-radio correlation. Of the known cluster members, only the SMG `N1' shows signs of AGN in any other diagnostics, namely a large and compact excess in CO(11-10) line emission. We compare these results to field samples of radio sources and SMGs. The overdensity of radio-loud AGN in the compact core region of the cluster may be providing significant heating to the recently discovered nascent intra-cluster medium (ICM) in SPT2349-56.

astro-ph.GA↗

arXiv2025

Testing Lens Models of PLCK G165.7+67.0 Using Lensed SN H0pe

Supernova H0pe is a multiply-imaged Type Ia supernova (SN~Ia) and the second lensed SN to yield a measurement of the Hubble constant by the time-delay cosmography method, finding $H_0 = 75.4^{+8.1}_{-5.5} \text{km s}^{-1} \text{Mpc}^{-1}$ (Pascale et. al 2025). We investigate the seven lens modeling approaches used to derive $H_0$, assessing their agreement with $\Lambda \text{CDM}$ constraints from SN~Ia surveys through a purely observational comparison. \textbf{We test each lens model by combining its predicted magnifications with the observed time delays to reconstruct the intrinsic SN~Ia luminosity and corresponding distance modulus.} While photometrically derived magnifications yield distance moduli in line with $\Lambda \text{CDM}$ expectations, our comparison reveals that lens model predictions, even the most precise ones, \textbf{consistently overestimate the magnification, with an offset $> 1$~mag}. This known bias, already appreciated by modeling teams, is independently confirmed through our analysis and highlights the value of lensed SNe as a tool to test model accuracy. If unaccounted for, such magnification biases can propagate into uncertainties in derived cosmological parameters, including $H_0$, a critical challenge for precision cosmology using strongly lensed transients.

astro-ph.CO↗

arXiv2025

Discovery of a $z \sim 0.8$ Ultra Steep Spectrum Radio Halo in the MeerKAT-South Pole Telescope Survey

Radio halos are diffuse synchrotron sources that trace the turbulent intracluster medium (ICM) of galaxy clusters. However, their origin remains unknown. Two main formation models have been proposed: the hadronic model, in which relativistic electrons are continuously injected by cosmic-ray protons; and the leptonic turbulent re-acceleration model, where cluster mergers re-energise electrons in situ. A key discriminant between the two models would be the existence of ultra-steep spectrum radio halos (USSRHs), which can only be produced through turbulent re-acceleration. Here we report the discovery of an USSRH in the galaxy cluster SPT-CLJ2337$-$5942 at redshift $z = 0.78$ in the MeerKAT-South Pole Telescope 100 deg$^2$ survey. This discovery is noteworthy for two primary reasons: it is the highest redshift USSRH system to date; and the close correspondence of the radio emission with the thermal ICM as traced by $\mathit{Chandra}$ X-ray observations, further supporting the leptonic re-acceleration model. The halo is under-luminous for its mass, consistent with a minor merger origin, which produces steep-spectrum, lower luminosity halos. This result demonstrates the power of wide-field, high-fidelity, $\lesssim1$ GHz surveys like the MeerKAT-SPT 100 deg$^2$ programme to probe the origin and evolution of radio halos over cosmic time, ahead of the Square Kilometre Array.

astro-ph.CO↗

arXiv2025

Bright [CII]158$\mu$m Streamers as a Beacon for Giant Galaxy Formation in SPT2349$-$56 at $z=4.3$

Observations of extreme starbursts, often located in the cores of protoclusters, challenge the classical bottom-up galaxy formation paradigm. Giant elliptical galaxies at $z=0$ must have assembled rapidly, possibly within few 100 Myr through an extreme growth phase at high-redshift, characterized by elevated star-formation rates of several thousand solar masses per year distributed over concurrent, gas-rich mergers. We present a novel view of the $z=4.3$ protocluster core SPT2349$-$56 from sensitive multi-cycle ALMA dust continuum and [CII]158$\mu$m line observations. Distributed across 60 kpc, a highly structured gas reservoir with a line luminosity of $L_\mathrm{[CII]}=3.0\pm0.2\times10^9$ $L_\odot$ and an inferred cold gas mass of $M_{gas}= 8.9\pm0.7\times10^{9}$ $M_\odot$ is found surrounding the central massive galaxy triplet. Like ``beads on a string'', the newly-discovered [CII] streamers fragment into a few kpc-spaced and turbulent clumps that have a similar column density as local Universe spiral galaxy arms at $\Sigma_{gas}=20$--$60$ $M_\odot$ pc$^{-2}$. For a dust temperature of 30 K, the [CII] emission from the ejected clumps carry $\gtrsim$3% of the FIR luminosity, translating into an exceptionally low mass-to-light ratio of $\alpha_\mathrm{[CII]}=2.95\pm0.3$ $M_\odot$ $L_\odot^{-1}$, indicative of shock-heated molecular gas. In phase space, about half of the galaxies in the protocluster core populate the same caustic as the [CII] streamers ($r/r_{vir}\times|\Delta v|/\sigma_{vir}\approx0.1$), suggesting angular momentum dissipation via tidal ejection while the brightest cluster galaxy (BCG) is assembling. Our findings provide new evidence for the importance of tidal ejections of [CII]-bright, shocked material following multiple major mergers that might represent a landmark phase in the $z\gtrsim4$ co-evolution of BCGs with their hot, metal enriched atmospheres.

astro-ph.GA↗

arXiv2025

A large thermal energy reservoir in the nascent intracluster medium at a redshift of 4.3

Most baryons in present-day galaxy clusters exist as hot gas ($\boldsymbol{\gtrsim10^7\,\rm}\mathrm{K}$), forming the intracluster medium (ICM). Cosmological simulations predict that the mass and temperature of the ICM rapidly decrease with increasing cosmological redshift, as intracluster gas in younger clusters is still accumulating and being heated. The thermal Sunyaev-Zeldovich (tSZ) effect arises when cosmic microwave background (CMB) photons are scattered to higher energies through interactions with energetic electrons in hot ICM, leaving a localized decrement in the CMB at a long wavelength. The depth of this decrement is a measure of the thermal energy and pressure of the gas. To date, the effect has been detected in only three systems at or above $z\sim2$, when the Universe was 4 billion years old, making the time and mechanism of ICM assembly uncertain. Here, we report observations of this effect in the protocluster SPT2349$-$56 with Atacama Large Millimeter/submillimeter Array (ALMA). SPT2349$-$56 contains a large molecular gas reservoir, with at least 30 dusty star-forming galaxies (DSFGs) and three radio-loud active galactic nuclei (AGN) in a 100-kpc region at $z=4.3$, corresponding to 1.4 billion years after the Big Bang. The observed tSZ signal implies a thermal energy of $\mathbf{\sim 10^{61}\,\mathrm{erg}}$, exceeding the possible energy of a virialized ICM by an order of magnitude. Contrary to current theoretical expectations, the strong tSZ decrement in SPT2349$-$56 demonstrates that substantial heating can occur and deposit a large amount of thermal energy within growing galaxy clusters, overheating the nascent ICM in unrelaxed structures, two billion years before the first mature clusters emerged at $\mathbf{z \sim 2}$.

astro-ph.GA↗

arXiv2025

An Image-Plane Approach to Gravitational Lens Modeling of Interferometric Data

Strong gravitational lensing acts as a cosmic telescope, enabling the study of the high-redshift universe. Astronomical interferometers, such as the Atacama Large Millimeter/submillimeter Array (ALMA), have provided high-resolution images of strongly lensed sources at millimeter and submillimeter wavelengths. To model the mass and light distributions of lensing and source galaxies from strongly lensed images, strong lens modeling for interferometric observations is conventionally performed in the visibility space, which is computationally expensive. In this paper, we implement an image-plane lens modeling methodology for interferometric dirty images by accounting for noise correlations. We show that the image-plane likelihood function produces accurate model values when tested on simulated ALMA observations with an ensemble of noise realizations. We also apply our technique to ALMA observations of two sources selected from the South Pole Telescope survey, comparing our results with previous visibility-based models. Our model results are consistent with previous models for both parametric and pixelated source-plane reconstructions. We implement this methodology for interferometric lens modeling in the open-source software package lenstronomy.

astro-ph.GA↗

arXiv2024

A Large Molecular Gas Reservoir in the Protocluster SPT2349$-$56 at $z\,{=}\,4.3$

We present Atacama Compact Array (ACA) Band-3 observations of the protocluster SPT2349$-$56, an extreme system hosting ${\gtrsim}\,12$ submillimeter galaxies (SMGs) at $z\,{=}\,4.3$, to study its integrated molecular gas content via CO(4-3) and long-wavelength dust continuum. The $\sim$30-hour integration represents one of the longest exposures yet taken on a single pointing with the ACA 7-m. The low-resolution ACA data ($21.0''\,{\times}\,12.2''$) reveal a 75% excess CO(4-3) flux compared to the sum of individual sources detected in higher-resolution Atacama Large Millimeter Array (ALMA) data ($1.0''\,{\times}\,0.8''$). Our work also reveals a similar result by tapering the ALMA data to $10''$. In contrast, the 3.2mm dust continuum shows little discrepancy between ACA and ALMA. A single-dish [CII] spectrum obtained by APEX/FLASH supports the ACA CO(4-3) result, revealing a large excess in [CII] emission relative to ALMA. The missing flux is unlikely due to undetected faint sources but instead suggests that high-resolution ALMA observations might miss extended and low-surface-brightness gas. Such emission could originate from the circum-galactic medium (CGM) or the pre-heated proto-intracluster medium (proto-ICM). If this molecular gas reservoir replenishes the star formation fuel, the overall depletion timescale will exceed 400Myr, reducing the requirement for the simultaneous SMG activity in SPT2349$-$56. Our results highlight the role of an extended gas reservoir in sustaining a high star formation rate (SFR) in SPT2349$-$56, and potentially establishing the ICM during the transition phase to a mature cluster.

astro-ph.GA↗

arXiv2024

Evidence for environmental effects in the $z\,{=}\,4.3$ protocluster core SPT2349$-$56

We present ALMA observations of the [CI] 492 and 806$\,$GHz fine-structure lines in 25 dusty star-forming galaxies (DSFGs) at $z\,{=}\,4.3$ in the core of the SPT2349$-$56 protocluster. The protocluster galaxies exhibit a median $L^\prime_{[\text{CI}](2-1)}/L^\prime_{[\text{CI}](1-0)}$ ratio of 0.94 with an interquartile range of 0.81-1.24. These ratios are markedly different to those observed in DSFGs in the field (across a comparable redshift and 850$\,\mu$m flux density range), where the median is 0.55 with an interquartile range of 0.50-0.76, and we show that this difference is driven by an excess of [CI](2-1) in the protocluster galaxies for a given 850$\,\mu$m flux density. Assuming local thermal equilibrium, we estimate gas excitation temperatures of $T_{\rm ex}\,{=}\,59.1^{+8.1}_{-6.8}\,$K for our protocluster sample and $T_{\rm ex}\,{=}\,33.9^{+2.4}_{-2.2}\,$K for the field sample. Our main interpretation of this result is that the protocluster galaxies have had their cold gas driven to their cores via close-by interactions within the dense environment, leading to an overall increase in the average gas density and excitation temperature, and an elevated [CI](2-1) luminosity-to-far-infrared luminosity ratio.

astro-ph.GA↗

arXiv2024

The RAdio Galaxy Environment Reference Survey (RAGERS): Evidence of an anisotropic distribution of submillimeter galaxies in the 4C 23.56 protocluster at z=2.48

High-redshift radio(-loud) galaxies (H$z$RGs) are massive galaxies with powerful radio-loud active galactic nuclei (AGNs) and serve as beacons for protocluster identification. However, the interplay between H$z$RGs and the large-scale environment remains unclear. To understand the connection between H$z$RGs and the surrounding obscured star formation, we investigated the overdensity and spatial distribution of submillimeter-bright galaxies (SMGs) in the field of 4C\,23.56, a well-known H$z$RG at $z=2.48$. We used SCUBA-2 data ($σ\,{\sim}\,0.6$\,mJy) to estimate the $850\,{\rm μm}$ source number counts and examine the radial and azimuthal overdensities of the $850\,{\rm μm}$ sources in the vicinity of the H$z$RG. The angular distribution of SMGs is inhomogeneous around the H$z$RG 4C\,23.56, with fewer sources oriented along the radio jet. We also find a significant overdensity of bright SMGs (${\rm S}_{850\rm\,μm}\geq5\,$mJy). Faint and bright SMGs exhibit different spatial distributions. The former are concentrated in the core region, while the latter prefer the outskirts of the H$z$RG field. High-resolution observations show that the seven brightest SMGs in our sample are intrinsically bright, suggesting that the overdensity of bright SMGs is less likely due to the source multiplicity.

astro-ph.GA↗

arXiv2024

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, SGAS1723$+$34 ($z = 1.3293$), we detect the [OIII]$\lambda4363$, [SIII]$\lambda6312$, and [OII]$\lambda\lambda$7320,7330 auroral emission lines, and set an upper limit for the [NII]$\lambda5755$ line. For the second galaxy, SGAS1226$+$21 ($z = 2.925$), we do not detect any auroral lines, and report upper limits. With these measurements and upper limits, we constrain the electron temperatures in different ionization zones within both of these galaxies. For SGAS1723$+$34, where auroral lines are detected, we calculate direct oxygen and nitrogen abundances, finding an N/O ratio consistent with observations of nearby ($z\sim 0$) 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.

astro-ph.GA↗

arXiv2023

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.

astro-ph.IM↗

arXiv2023

JWST Early Release Science Program TEMPLATES: Targeting Extremely Magnified Panchromatic Lensed Arcs and their Extended Star formation

This paper gives an overview of TEMPLATES, a JWST Early Release Science program that targeted four extremely bright, gravitationally lensed galaxies: two extremely dusty, two with low attenuation, as templates for galaxy evolution studies with JWST. TEMPLATES obtains a common set of spectral diagnostics for these 1.3 < z < 4.2 galaxies, in particular H alpha, Paschen alpha, and the rest-frame optical and near-infrared continua. In addition, two of the four targets have JWST coverage of [O III] 5007 Angstrom and H beta; the other two targets have have JWST coverage of PAH 3.3 micron and complementary ALMA data covering the [C II] 158 micron emission line. The science goals of TEMPLATES are to demonstrate attenuation-robust diagnostics of star formation, map the distribution of star formation, compare the young and old stellar populations, and measure the physical conditions of star formation and their spatial variation across the galaxies. In addition, TEMPLATES has technical goals to establish best practices for the Integral Field Units (IFU) within the NIRSpec and MIRI instruments, both in terms of observing strategy and in terms of data reduction. The paper describes TEMPLATES's observing program, scientific and technical goals, data reduction methods, and deliverables, including high-level data products and data reduction cookbooks.

astro-ph.GA↗

arXiv2023

JWST's TEMPLATES for Star Formation: The First Resolved Gas-Phase Metallicity Maps of Dust-Obscured Star-Forming Galaxies at $z$ $\sim$ 4

We present the first spatially resolved maps of gas-phase metallicity for two dust-obscured star-forming galaxies (DSFGs) at $z\sim$ 4, from the JWST TEMPLATES Early Release Science program, derived from NIRSpec integral field unit spectroscopy of the H$α$ and [NII] 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 [NII]/H$α$ ratios and broad H$α$ emission consistent with the presence of an AGN in a $\gtrsim$1kpc region, we argue that both systems have already undergone significant metal enrichment as a result of their extremely high star formation rates. Utilizing ALMA rest-frame 380$μ$m continuum and [CI]($^3$P$_2$-$^3$P$_1$) 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 $z\sim$ 0 galaxies. The data are indicative of the enormous potential of JWST to probe the enrichment of the interstellar medium on $\sim$kpc scales in extremely dust-obscured systems at $z\sim$ 4 and beyond.

astro-ph.GA↗

arXiv2023

TEMPLATES: Characterization of a Merger in the Dusty Lensing SPT0418-47 System

We present JWST and ALMA results for the lensing system SPT0418-47, which includes a strongly-lensed, dusty star-forming galaxy at redshift z=4.225 and an associated multiply-imaged companion. JWST NIRCam and MIRI imaging observations presented in this paper were acquired as part of the Early Release Science program Targeting Extremely Magnified Panchromatic Lensed Arcs and Their Extended Star Formation (TEMPLATES). This data set provides robust, mutiwavelength detection of stellar light in both the main (SPT0418A) and companion (SPT0418B) galaxies, while the ALMA detection of [C II] emission confirms that SPT0418B lies at the same redshift as SPT0418A. From a source plane reconstruction, we infer that the projected physical separation of the two galaxies is $4.42\pm 0.05$ kpc. We derive total magnifications of $μ=29.5\pm1.2$ and $μ=4.2\pm 0.9$ for SPT0418A and SPT0418B, respectively. We use both CIGALE and PROSPECTOR to derive stellar masses. The stellar mass ratio of SPT0418A and SPT0418B is approximately 4 to 1 ($4.5\pm 1.0$ for CIGALE and $4.2^{+1.9}_{-1.6}$ for PROSPECTOR). We also see evidence of extended structure associated with SPT0418A in the lensing reconstruction that is suggestive of a tidal feature. Interestingly, the star formation rates and stellar masses of both galaxies are consistent with the main sequence of star-forming galaxies at this epoch, indicating that this ongoing interaction has not noticeably elevated the star formation levels.

astro-ph.GA↗

arXiv2023

A high-redshift calibration of the [OI]-to-HI conversion factor in star-forming galaxies

The assembly and build-up of neutral atomic hydrogen (HI) 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 HI line transition, impeding direct detections and measurements of the HI gas masses ($M_{\rm HI}$). Here we present a new method to infer $M_{\rm HI}$ of high-redshift galaxies using neutral, atomic oxygen as a proxy. Specifically, we derive metallicity-dependent conversion factors relating the far-infrared [OI]-$63μ$m and [OI]-$145μ$m emission line luminosities and $M_{\rm HI}$ in star-forming galaxies at $z\approx 2-6$ using gamma-ray bursts (GRBs) as probes. We substantiate these results by observations of galaxies at $z\approx 0$ with direct measurements of $M_{\rm HI}$ and [OI]-$63μ$m and [OI]-$145μ$m in addition to hydrodynamical simulations at similar epochs. We find that the [OI]$_{\rm 63μm}$-to-HI and [OI]$_{\rm 145μm}$-to-HI conversion factors universally appears to be anti-correlated with the gas-phase metallicity. The high-redshift GRB measurements further predict a mean ratio of $L_{\rm [OI]-63μm} / L_{\rm [OI]-145μm}=1.55\pm 0.12$ and reveal generally less excited [CII]. The $z \approx 0$ galaxy sample also shows systematically higher $β_{\rm [OI]-63μm}$ and $β_{\rm [OI]-145μm}$ conversion factors than the GRB sample, indicating either suppressed [OI] emission in local galaxies or more extended, diffuse HI gas reservoirs traced by the HI 21-cm. Finally, we apply these empirical calibrations to the few high-redshift detections of [OI]-$63μ$m and [OI]-$145μ$m line transitions from the literature and further discuss the applicability of these conversion factors to probe the HI gas content in the dense, star-forming ISM of galaxies at $z\gtrsim 6$, well into the epoch of reionization.

astro-ph.GA↗