arXiv subjects

Norman Murray

Publications and source records attributed to Norman Murray.

At least 19 recordsLinked to original sources

arXiv2026

Dynamical formation of high-eccentricity compact binaries through BH--BH*/TZO collisions

The rapidly accumulating discoveries of binary stellar-mass black-hole (sBH) coalescences, detected by LIGO, have opened a new window into the formation and evolution of compact binaries. In particular, residual orbital eccentricity may provide a distinctive signature of their formation channels. Here, we investigate a scenario in which high-eccentricity compact binaries form through the sequential capture of multiple sBHs by massive main-sequence stars, using a combination of hydrodynamical and semianalytic few-body simulations. We find that sBHs with $M_\bullet\lesssim 0.2\,M_{\star}$ can be captured by massive stars and settle into a quasi-hydrostatic black-hole star (BH*) through gas dynamical friction. A subsequent encounter with a second sBH can then produce a compact binary embedded within the stellar envelope. Our hydrodynamical simulations show that through captures with small impact parameter, some binaries are born with high eccentricity ($e\gtrsim 0.5$), with its orbital frequency already entering the LISA band. Our semianalytic models further demonstrate that gas dynamical friction can pump the eccentricity to $e_{\rm 10\,Hz}>0.9$ before gravitational-wave emission eventually circularizes the binary during the final stage of coalescence. Once formed, the binary can merge quickly in $\sim 10$ hours. This channel may operate in dense stellar environments, such as star clusters and active galactic nucleus (AGN) disks. The same mechanism can also be applied to Thorne-\.Zytkow objects. A high-eccentricity binary in the LIGO band could therefore provide a distinctive signature of this formation scenario.

astro-ph.HE↗

arXiv2026

Formation of black hole stars via star--black hole collisions

In dense stellar environments such as globular clusters and active galactic nucleus (AGN) disks, stellar-mass black holes (sBHs) may frequently collide with massive stars. We investigate this process using semi-analytic models, three-dimensional hydrodynamical simulations, and one-dimensional stellar evolution calculations, focusing on collisions between sBHs and a $100\,M_\odot$ main-sequence star. We find that gas drag retains the BH within the stellar envelope unless the impact velocity exceeds $\sim2\sqrt{G(M_\star+M_\bullet)/R_\star}$. The post-collision outcome depends primarily on the BH-to-star mass ratio. For $M_\bullet\gtrsim30\,M_\odot$, the retained envelope is either quasi-spherical or disc-like, but remains dynamically unstable because of shock heating. In contrast, for $M_\bullet\lesssim10\,M_\odot$, the collision forms a ``black hole star'' (BH*): a quasi-hydrostatic, extended stellar envelope surrounding the embedded BH. These results agree with our analytic prediction that BH* formation necessarily requires $M_\bullet\lesssim0.2\,M_\star$. Follow-up \texttt{MESA} calculations further show that, for these low-mass BHs, the shock-heated remnant thermally relaxes without triggering runaway expansion. We discuss several astrophysical implications of BH*s, including their evolution, the possibility of gravitational-wave events from BH binaries assembled within a stellar envelope, and repeated star--sBH collisions as a pathway for rapid BH growth in dense stellar systems. This mechanism may contribute to the formation of massive BHs in high-redshift nuclear star clusters and may be relevant to the origin of the ``little red dots'' discovered by JWST.

astro-ph.HE↗

arXiv2026

Stellar mergers and chemical element mixing: implications for the metamorphic stellar evolution in AGN disks

Chemical mixing during stellar mergers can significantly influence the subsequent evolution of the merger remnant. We perform a suite of three-dimensional hydrodynamical simulations of stellar mergers, each evolved for $\sim100$ stellar dynamical times until the remnant reaches a quasi-hydrostatic equilibrium. The simulations incorporate subgrid-scale diffusion models to capture the turbulent mixing of chemical elements. Starting with an idealized polytropic equation of state (EOS), we first identify the dominant mixing mechanisms and investigate how the merger outcome depends on the mass ratio, relative velocity, impact parameter, and stellar structure. We then extend our simulations to the context of stars embedded in active galactic nucleus (AGN) disks, using a realistic, composition-dependent EOS and AGN stellar models generated with the stellar evolution code MESA. We find that mergers with both younger metamorphic stars and H-rich accreting AGN stars can substantially rejuvenate old metamorphic stars through efficient core mixing after thermal relaxation. The merger remnants are nitrogen-enriched, with ${\rm N/O}\sim1$--3 and ${\rm N/C}\gtrsim5$, comparable to the abundances observed in the nebula surrounding SN 1987A. During subsequent stellar evolution, the remnants may converge onto the main sequence of isolated metamorphic AGN stars once they reach accretion--wind equilibrium. They may also deposit a significant amount of chemically enriched material into the AGN disk. This work provides a physical framework for connecting hydrodynamical stellar mergers with the long-term evolution of AGN stars and their observational and chemical signatures.

astro-ph.GA↗

arXiv2026

Strongest constraints on dark acoustic oscillations from the Lyman-alpha forest

We set the first constraints on a small-scale dark acoustic oscillation (DAO) in the linear matter power spectrum arising from dark sector interactions, with a full forward model of the Ly-$\alpha$ forest. No more than 30\% of dark matter can form DAOs if they peak at wavenumbers $< 50\,h\,\mathrm{Mpc}^{-1}$ (95\% c.l.), probing scales $25 \times$ smaller than the cosmic microwave background (CMB). Given the complex covariance of DAO and nuisance parameters, we use a deep kernel learning emulator of hydrodynamical simulations to capture imprints of linear oscillations in the Ly-$\alpha$ forest.

astro-ph.CO↗

arXiv2026

The Two Component Circumgalactic Medium Emission around z~2 Radio-loud Quasars

We present Ly$\alpha$, He II and C IV observations of 7 redshift ~ 2 radio-loud quasars observed using the Keck Cosmic Web Imager (KCWI) and compare it to observed radio jet emission using archival VLA and ALMA radio observations. We detect 80-120 kpc diameter Ly$\alpha$ and 10-40 kpc He II and C IV emission around the targets. We find the Ly$\alpha$ emission to be brighter in the inner 30 kpc by factors of 2-10 compared to other literature samples. We reproduce the trend for increased total luminosity for a larger area on sky, but find our targets tend to be brighter for a given area when compared to literature observations, even when adjusting for the observational sensitivity. We infer that the He II and C IV is likely powered by quasar photoionization, with the ionizing radiation likely escaping along the radio jet axis which is aligned with the He II and C IV emission. The observations agree with a two component model of the CGM where the inner CGM (< 30 kpc) is directly influenced by the host galaxies, whereas the gas motion in the outer CGM (> 30 kpc) is influenced by gas turbulence and the larger environment around the host galaxies.

astro-ph.GA↗

arXiv2026

The In Situ Growth of Stellar-mass "Light" Seed Black Holes in Nuclear Star Clusters

Remnant black holes (BHs) of massive stars (``light seeds'') are a potential origin for supermassive black holes (SMBHs). We use magnetohydrodynamic simulations to study the formation and growth of light seeds in star-forming giant molecular clouds (GMCs) with masses $10^5$--$10^9\,M_\odot$, which evolve for $\sim 10$--$30\,\rm Myr$ and form compact star clusters, akin to high-redshift nuclear star clusters. In particular, the simulations resolve very massive stars (VMSs, 100--$300\,M_\odot$), including their radiative and mechanical feedback, and model feedback-regulated accretion onto remnant BHs. We find that, even in compact GMCs capable of forming deep potential wells, the gas reservoir is expelled by sustained stellar feedback and rapidly dispersed after supernova explosions. Remnant BH populations emerge $\sim 3\,\rm Myr$ after the starburst and concentrate at the cluster center (where $\rho_{\rm BH}\sim 10^4$--$10^6\,M_\odot\,{\rm pc}^{-3}$). With our fiducial sub-grid BH accretion/feedback model, in-situ BH accretion is inefficient for forming heavy seeds: some direct-collapse BHs briefly accrete at $\sim$(1--10)$\times$ the Eddington rate, but they reach only $\sim 400$--$500\,M_\odot$. A top-heavy initial mass function or natal kicks do not change this conclusion. Runaway accretion is only possible if the sub-grid BH model allows a high fraction of Bondi inflow to reach the BH, in which case a few seeds can grow to $\sim 10^6\,M_\odot$. We also discuss multiple-generation star formation that may be intrinsically correlated with remnant BH accretion.

astro-ph.GA↗

arXiv2025

Very Massive Stars and High N/O: A Tale of the Nitrogen-enriched Super Star Cluster in the Sunburst Arc

The lensed Sunburst Arc ($z = 2.369$) hosts a young ($\sim2$--$4\,\rm Myr$), massive ($M_\star \sim 10^7\,M_\odot$), compact ($R_{\rm eff} \sim 8\,\rm pc$) Lyman-continuum (LyC) leaking super star cluster, which powers a compact ($< 10\,\rm pc$), high-pressure nebula at sub-solar metallicity $\sim0.2\,Z_\odot$ and with an anomalously elevated nitrogen-to-oxygen ratio $\log({\rm N/O}) \sim -0.2$. We present semi-analytic models and 3D magnetohydrodynamic simulations with radiative feedback in an attempt to reproduce this system. The results indicate that the progenitor giant molecular cloud (GMC) may have $M_{\rm cloud} \gtrsim 3 \times 10^7\,M_\odot$ and $R_{\rm cloud} \sim 70\,\rm pc$, corresponding to a surface density $\sim10^3$--$10^4\,M_\odot\,{\rm pc}^{-2}$. Incorporating feedback from individual Very Massive Stars (VMSs; $\ge 100\,M_\odot$) sampled from the Kroupa initial mass function, we find that their winds rapidly enrich $\sim 10^4\,M_\odot$ of nearby gas with nitrogen ($\sim 1\,$dex) and helium ($\sim 0.1$--$0.2\,$dex). In the first $1$--$3\,$Myr, some cold gas falls to the system center where a central cluster builds up from sub-cluster mergers. There, the gas is photoionized, pressurized, and chemically enriched by the newly formed VMSs, before being radiatively expelled in the next $\sim1\,\rm Myr$. We find that both VMS feedback and a high-surface-density progenitor GMC are necessary to reproduce the observed nebular properties, such as high N/O, high pressure, and stellar proximity. Low metallicity ($Z \le 0.004$) may be essential to avoid overproduction of carbon from WC stars. Such enrichment processes localized to compact starburst events may have caused strong nitrogen emission from dense ionized gas as observed in high-redshift galaxies such as GN-z11 and GS_3073.

astro-ph.GA↗

arXiv2025

Zooming In On The Multi-Phase Structure of Magnetically-Dominated Quasar Disks: Radiation From Torus to ISCO Across Accretion Rates

Recent radiation-thermochemical-magnetohydrodynamic simulations resolved formation of quasar accretion disks from cosmological scales down to ~300 gravitational radii $R_{g}$, arguing they were 'hyper-magnetized' (plasma $\beta\ll1$ supported by toroidal magnetic fields) and distinct from traditional $\alpha$-disks. We extend these, refining to $\approx 3\,R_{g}$ around a $10^{7}\,{\rm M_{\odot}}$ BH with multi-channel radiation and thermochemistry, and exploring a factor of 1000 range of accretion rates ($\dot{m}\sim0.01-20$). At smaller scales, we see the disks maintain steady accretion, thermalize and self-ionize, and radiation pressure grows in importance, but large deviations from local thermodynamic equilibrium and single-phase equations of state are always present. Trans-Alfvenic and highly-supersonic turbulence persists in all cases, and leads to efficient vertical mixing, so radiation pressure saturates at levels comparable to fluctuating magnetic and turbulent pressures even for $\dot{m}\gg1$. The disks also become radiatively inefficient in the inner regions at high $\dot{m}$. The midplane magnetic field remains primarily toroidal at large radii, but at super-Eddington $\dot{m}$ we see occasional transitions to a poloidal-field dominated state associated with outflows and flares. Large-scale magnetocentrifugal and continuum radiation-pressure-driven outflows are weak at $\dot{m}<1$, but can be strong at $\dot{m}\gtrsim1$. In all cases there is a scattering photosphere above the disk extending to $\gtrsim 1000\,R_{g}$ at large $\dot{m}$, and the disk is thick and flared owing to magnetic support (with $H/R$ nearly independent of $\dot{m}$), so the outer disk is strongly illuminated by the inner disk and most of the inner disk continuum scatters or is reprocessed at larger scales, giving apparent emission region sizes as large as $\gtrsim 10^{16}\,{\rm cm}$.

astro-ph.GA↗

arXiv2024

The Effect of Galaxy Interactions on Starbursts in Milky Way-Mass Galaxies in FIRE Simulations

Simulations and observations suggest that galaxy interactions may enhance the star formation rate (SFR) in merging galaxies. One proposed mechanism is the torque exerted on the gas and stars in the larger galaxy by the smaller galaxy. We analyze the interaction torques and star formation activity on six galaxies from the FIRE-2 simulation suite with masses comparable to the Milky Way galaxy at redshift $z=0$. We trace the halos from $z = 3.6$ to $z=0$, calculating the torque exerted by the nearby galaxies on the gas in the central galaxy. We calculate the correlation between the torque and the SFR across the simulations for various mass ratios. For near-equal-stellar-mass-ratio interactions in the galaxy sample, occurring between $z=1.2-3.6$, there is a positive and statistically significant correlation between the torque from nearby galaxies on the gas of the central galaxies and the SFR. For all other samples, no statistically significant correlation is found between the torque and the SFR. Our analysis shows that some, but not all, major interactions cause starbursts in the simulated Milky Way-mass galaxies, and that most starbursts are not caused by galaxy interactions. The transition from `bursty' at high redshift ($z\gtrsim1$) to `steady' star-formation state at later times is independent of the interaction history of the galaxies, and most of the interactions do not leave significant imprints on the overall trend of the star formation history of the galaxies.

astro-ph.GA↗

arXiv2024

SF-R You Sure? The Conflicting Role of Star Formation Rates in Constraining the Evolution of Milky Way Analogues in Cosmological Simulations

Milky Way analogues (MWAs) have long been studied by astronomers to place our Galaxy within an extragalactic context. With the power of cosmological simulations, we are now able to not only characterize MWAs today, but also watch as they evolve through cosmic time. We use the EAGLE and IllustrisTNG simulations to study a group of MWAs defined by their stellar mass (SM) and star formation rate (SFR). We trace these galaxies back along their evolution to investigate the star forming and mass assembly tracks taken by a galaxy to become a MWA today in light of these chosen parameters. We also take mock-observations of "MWAs" at $z>0$ and trace them forwards in time to determine if galaxies that looked similar to the Milky Way earlier in their evolution still look like the Milky Way today, thus quantifying a selection efficiency which could inform future observational studies of MWAs. We find that most galaxies with Milky Way-SM follow a similar evolution regardless of present-day SFR, although MWAs in IllustrisTNG generally have not quenched, leading to star formation histories that produce "too-blue" galaxies today. Additionally, we find contamination by MWA-"imposters" in our mock-observations, with low selection efficiency at high redshift due to the tight constraint requiring convergence to the Milky Way's present-day SFR. Our work suggests present-day SM may suffice as a stand-alone selection parameter and helps to clarify how MWAs should be selected, and thus will be an important reference for future studies of both simulated and observed MWAs.

astro-ph.GA↗

arXiv2024

Oxygen Abundance Throughout the Dwarf Starburst IC 10

Measurements of oxygen abundance throughout galaxies provide insight to the formation histories and ongoing processes. Here we present a study of the gas phase oxygen abundance in the HII regions and diffuse gas of the nearby starburst dwarf galaxy, IC 10. Using the Keck Cosmic Web Imager (KCWI) at W.M. Keck Observatory, we map the central region of IC 10 from 3500-5500A. The auroral [OIII]4363A line is detected with high signal-to-noise in 12 of 46 HII regions observed, allowing for direct measurement of the oxygen abundance, yielding a median and standard deviation of $\rm12+log(O/H)=8.37\pm0.25$. We investigate trends between these directly measured oxygen abundances and other HII region properties, finding weak negative correlations with the radius, velocity dispersion, and luminosity. We also find weak negative correlations between oxygen abundance and the derived quantities of turbulent pressure and ionized gas mass, and a moderate correlation with the derived dynamical mass. Strong line, $\rm R_{23}$ abundance estimates are used in the remainder of the HII regions and on a resolved spaxel-by-spaxel basis. There is a large offset between the abundances measured with $\rm R_{23}$ and the auroral line method. We find that the $\rm R_{23}$ method is unable to capture the large range of abundances observed via the auroral line measurements. The extent of this variation in measured abundances further indicates a poorly mixed interstellar medium (ISM) in IC 10, which is not typical of dwarf galaxies and may be partly due to the ongoing starburst, accretion of pristine gas, or a late stage merger.

astro-ph.GA↗

arXiv2024

Aggressively-Dissipative Dark Dwarfs: The Effects of Atomic Dark Matter on the Inner Densities of Isolated Dwarf Galaxies

We present the first suite of cosmological hydrodynamical zoom-in simulations of isolated dwarf galaxies for a dark sector that consists of Cold Dark Matter and a strongly-dissipative sub-component. The simulations are implemented in GIZMO and include standard baryons following the FIRE-2 galaxy formation physics model. The dissipative dark matter is modeled as Atomic Dark Matter (aDM), which forms a dark hydrogen gas that cools in direct analogy to the Standard Model. Our suite includes seven different simulations of $\sim 10^{10} M_{\odot}$ systems that vary over the aDM microphysics and the dwarf's evolutionary history. We identify a region of aDM parameter space where the cooling rate is aggressive and the resulting halo density profile is universal. In this regime, the aDM gas cools rapidly at high redshifts and only a small fraction survives in the form of a central dark gas disk; the majority collapses centrally into collisionless dark "clumps", which are clusters of sub-resolution dark compact objects. These dark clumps rapidly equilibrate in the inner galaxy, resulting in an approximately isothermal distribution that can be modeled with a simple fitting function. Even when only a small fraction ($\sim 5\%$) of the total dark matter is strongly dissipative, the central densities of classical dwarf galaxies can be enhanced by over an order of magnitude, providing a sharp prediction for observations.

astro-ph.GA↗

arXiv2024

Accelerating Giant Impact Simulations with Machine Learning

Constraining planet formation models based on the observed exoplanet population requires generating large samples of synthetic planetary systems, which can be computationally prohibitive. A significant bottleneck is simulating the giant impact phase, during which planetary embryos evolve gravitationally and combine to form planets, which may themselves experience later collisions. To accelerate giant impact simulations, we present a machine learning (ML) approach to predicting collisional outcomes in multiplanet systems. Trained on more than 500,000 $N$-body simulations of three-planet systems, we develop an ML model that can accurately predict which two planets will experience a collision, along with the state of the post-collision planets, from a short integration of the system's initial conditions. Our model greatly improves on non-ML baselines that rely on metrics from dynamics theory, which struggle to accurately predict which pair of planets will experience a collision. By combining with a model for predicting long-term stability, we create an ML-based giant impact emulator, which can predict the outcomes of giant impact simulations with reasonable accuracy and a speedup of up to four orders of magnitude. We expect our model to enable analyses that would not otherwise be computationally feasible. As such, we release our training code, along with an easy-to-use API for our collision outcome model and giant impact emulator.

astro-ph.EP↗

arXiv2024

Playing with FIRE: A Galactic Feedback-Halting Experiment Challenges Star Formation Rate Theories

Stellar feedback influences the star formation rate (SFR) and the interstellar medium of galaxies in ways that are difficult to quantify numerically, because feedback is an essential ingredient of realistic simulations. To overcome this, we conduct a feedback-halting experiment starting with a Milky Way-mass galaxy in the FIRE-2 simulation framework. Terminating feedback, and comparing to a simulation in which feedback is maintained, we monitor how the runs diverge. We find that without feedback, interstellar turbulent velocities decay. There is a marked increase of dense material, while the SFR increases by over an order of magnitude. Importantly, this SFR boost is a factor of $\sim$15-20 larger than is accounted for by the increased free fall rate caused by higher densities. This implies that feedback moderates the star formation efficiency per free-fall time more directly than simply through the density distribution. To probe changes at the scale of giant molecular clouds (GMCs), we identify GMCs using density and virial parameter thresholds, tracking clouds as the galaxy evolves. Halting feedback stimulates rapid changes, including a proliferation of new bound clouds, a decrease of turbulent support in loosely-bound clouds, an overall increase in cloud densities, and a surge of internal star formation. Computing the cloud-integrated SFR using several theories of turbulence regulation, we show that these theories underpredict the surge in SFR by at least a factor of three. We conclude that galactic star formation is essentially feedback-regulated on scales that include GMCs, and that stellar feedback affects GMCs in multiple ways.

astro-ph.GA↗

arXiv2024

Angular momentum transfer in cosmological simulations of Milky Way-mass discs

Fueling star formation in large, discy galaxies requires a continuous supply of gas accreting into star-forming regions. Previously, we characterized this accretion in 4 Milky Way mass galaxies ($M_{\rm halo}\sim10^{12}M_{\odot}$) in the FIRE-2 cosmological zoom-in simulations. At $z\sim0$, we found that gas within the inner circumgalactic medium (iCGM) approaches the disc with comparable angular momentum (AM) to the disc edge, joining in the outer half of the gaseous disc. Within the disc, gas moves inward at velocities of $\sim$1-5~km~s$^{-1}$ while fully rotationally supported. In this study, we analyze the torques that drive these flows. In all cases studied, we find that the torques in discs enable gas accreted near the disc edge to transport inwards and fuel star formation in the central few kpc. The primary sources of torque come from gravity, hydrodynamical forces, and the sub-grid $P dV$ work done by supernova (SNe) remnants interacting with gas on $\lesssim$10 pc scales. These SNe remnant interactions induce negative torques within the inner disc and positive torques in the outer disc. The gas-gas gravitational, hydro, and "feedback" torques transfer AM outward to where accreting gas joins the disc, playing an important role in driving inflows and regulating disc structure. Gravitational torques from stars and dark matter provide an AM sink within the innermost regions of the disc and iCGM, respectively. Feedback torques are dominant within the disc, while gravitational and hydrodynamical torques have similar significance depending on the system/region. Torques from viscous shearing, magnetic forces, stellar winds, and radiative transfer are less significant.

astro-ph.GA↗

arXiv2024

The instability mechanism of compact multiplanet systems

To improve our understanding of orbital instabilities in compact planetary systems, we compare suites of $N$-body simulations against numerical integrations of simplified dynamical models. We show that, surprisingly, dynamical models that account for small sets of resonant interactions between the planets can accurately recover $N$-body instability times. This points toward a simple physical picture in which a handful of three-body resonances, generated by interactions between nearby two-body mean motion resonances, overlap and drive chaotic diffusion, leading to instability. Motivated by this, we show that instability times are well described by a power law relating instability time to planet separations, measured in units of fractional semi-major axis difference divided by the planet-to-star mass ratio to the $1/4$ power, rather than the frequently adopted $1/3$ power implied by measuring separations in units of mutual Hill radii. For idealized systems, the parameters of this power-law relationship depend only on the ratio of the planets' orbital eccentricities to the orbit-crossing value, and we report an empirical fit to enable quick instability time predictions. This relationship predicts that observed systems comprised of three or more sub-Neptune-mass planets must be spaced with period ratios $P \gtrsim 1.35$ and that tightly spaced systems ($P \lesssim 1.5$) must possess very low eccentricities ($e \lesssim 0.05$) to be stable for more than $10^9$ orbits.

astro-ph.EP↗

arXiv2024

Probing $H_0$ and resolving AGN disks with ultrafast photon counters

Intensity interferometry is a technique developed many decades ago, that has recently enjoyed a renaissance thanks in part to advances in photodetector technology. We investigate the potential for long-baseline optical intensity interferometry to observe bright, active galactic nuclei (AGN) associated with rapidly accreting supermassive black holes. We argue that realistic telescope arrays similar in area to existing Cherenkov arrays, if equipped with modern high-precision single photon detectors, can achieve a sufficiently high signal to noise ratio not only to detect distant AGN, but also to study them in great detail. We explore the science potential of such observations by considering two examples. First, we find that intensity interferometric observations of bright nearby AGN can allow detailed studies of the central accretion disks powering the AGN, allowing reconstruction of many disk properties like the radial profile. Next, we argue that intensity interferometers can spatially resolve the broad-line regions of AGN at cosmological distances, and thereby provide a geometric determination of the angular diameter distances to those AGN when combined with reverberation mapping. Since this measurement can be performed for AGN at distances of hundreds of megaparsecs, this directly measures the Hubble expansion rate $H_0$, with a precision adequate to resolve the recent Hubble tension. Finally, we speculate on future applications that would be enabled by even larger intensity interferometer arrays.

astro-ph.CO↗

arXiv2024

COMAP Early Science: VIII. A Joint Stacking Analysis with eBOSS Quasars

We present a new upper limit on the cosmic molecular gas density at $z=2.4-3.4$ obtained using the first year of observations from the CO Mapping Array Project (COMAP). COMAP data cubes are stacked on the 3D positions of 243 quasars selected from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) catalog, yielding a 95% upper limit for flux from CO(1-0) line emission of 0.129 Jy km/s. Depending on the balance of the emission between the quasar host and its environment, this value can be interpreted as an average CO line luminosity $L'_\mathrm{CO}$ of eBOSS quasars of $\leq 1.26\times10^{11}$ K km pc$^2$ s$^{-1}$, or an average molecular gas density $ρ_\mathrm{H_2}$ in regions of the universe containing a quasar of $\leq 1.52\times10^8$ M$_\odot$ cMpc$^{-3}$. The $L'_\mathrm{CO}$ upper limit falls among CO line luminosities obtained from individually-targeted quasars in the COMAP redshift range, and the $ρ_\mathrm{H_2}$ value is comparable to upper limits obtained from other Line Intensity Mapping (LIM) surveys and their joint analyses. Further, we forecast the values obtainable with the COMAP/eBOSS stack after the full 5-year COMAP Pathfinder survey. We predict that a detection is probable with this method, depending on the CO properties of the quasar sample. Based on the achieved sensitivity, we believe that this technique of stacking LIM data on the positions of traditional galaxy or quasar catalogs is extremely promising, both as a technique for investigating large galaxy catalogs efficiently at high redshift and as a technique for bolstering the sensitivity of LIM experiments, even with a fraction of their total expected survey data.

astro-ph.GA↗