arXiv subjects

Joel N. Bregman

Publications and source records attributed to Joel N. Bregman.

At least 19 recordsLinked to original sources

arXiv2026

A Possible Hidden Hot Halo Component Revealed by Joint X-ray and Sunyaev--Zel'dovich Observations

Massive galaxies are expected to host extended halos of hot gas that contain a substantial fraction of their baryons and feedback energy. X-ray observations probe the dense, X-ray-bright component of this circumgalactic medium (CGM), while the thermal Sunyaev-Zel'dovich (SZ) effect is also sensitive to lower-density gas through its integrated thermal pressure. We present the first spatially resolved joint X-ray and SZ analysis of a massive isolated disk galaxy, using deep XMM-Newton observations of NGC 4594 from the X-raying the Accretion Reservoir Transferred to the ATmosphere Orbiting a Massive Spiral (XART-ATOMS) program, together with multiple independent Planck-based SZ reconstructions. The measured SZ signal in the inner halo appears to exceed the value predicted from the X-ray-derived gas properties, even after accounting for major systematic uncertainties. Our preferred interpretation is that an additional lower-density CGM component contributes little to the observed soft X-ray emission but carries substantial thermal pressure. Under a simple two-phase model in approximate pressure equilibrium, the most probable X-ray-to-SZ ratio implies that the detected X-ray-emitting gas occupies only a small fraction of the halo volume, with a characteristic filling factor of f_X ~ (4-6)x10^-3 near r~50 kpc. Such a small filling factor implies that single-phase X-ray analyses can underestimate the baryon mass contained in the hot CGM by a factor of ~2.5, while the thermal energy content of the CGM is underestimated by about one order of magnitude. The non-detection of the additional component in the X-ray spectra requires it to be very hot and/or spatially extended, so weak in the soft X-ray emissions. These results favor the presence of a "hidden" X-ray-faint hotter halo component, while alternative interpretations, including a nonthermal contribution, are not excluded.

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arXiv2026

X-ray grating spectroscopy as a mission enhancement

We propose to add instruments to any potential future X-ray mission with focussing optics that is considered in NASA's ASTRA framework. Such an instrument is a necessity to study AGN wind outflows and feedback, find the missing baryons, study the intergalactic medium, and analyze abundances and chemical bonds in dust grains throughout the Milky Way. We conclude that those science goals can be achieved with a spectral resolving power > 3000 in the soft X-ray band (about 10-40 Ang) and an effective area a few times larger than current instruments. We describe a possible mission implementation for a soft X-ray grating spectrometer that can be folded in and out or be mounted permanently in the beam. Such an instrument can reach the requirements for a wide variety of host mission properties. A small UV imager and a UV spectrograph can be mounted on the same platform with independent optics. These added instruments vastly enhance the science capabilities of the host mission for a modest cost (100-200 million $) and with weight and power needs that can be easily accommodated in any major mission.

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arXiv2026

Lynx2030 Science Analysis Group: Final Report

The Lynx2030 Science Analysis Group (SAG) was convened to reassess the scientific goals and technical drivers of the Lynx mission concept amid a rapidly evolving astrophysics landscape. Building on the original Lynx Concept Study, the SAG examined how recent discoveries, emerging facilities, and advances in instrumentation influence the scientific opportunities for a next-generation flagship X-ray observatory. Through focused working groups, the SAG investigated the scientific impact of enhanced capabilities: (i) improved angular resolution, (ii) broader bandpass coverage, (iii) an enhanced microcalorimeter, (iv) new capabilities and observing modes, and (v) larger fields of view. Across a broad range of topics, from the formation of the first black holes and the evolution of galaxies to the baryon cycle, compact objects, stellar explosions, multi-messenger astrophysics, and the dynamic high-energy Universe, the SAG finds that the scientific motivation for a Lynx-class observatory remains compelling and, in many areas, has significantly strengthened over the past decade, prominently through JWST's discovery of the "Little Red Dots", likely massive accreting black holes in infant galaxies whose nature is fundamentally an X-ray question. This report shows that modest extensions beyond the original Lynx design reference mission can unlock transformative science while preserving the observatory's core architecture. Powerful current and future facilities such as Roman, Rubin, JWST, SKA, ngVLA, LISA, and NewAthena highlight the unique role a high-angular-resolution, high-throughput X-ray observatory would play in the multi-wavelength and multi-messenger ecosystem of the 2030s and beyond. The findings of the Lynx2030 SAG confirm Lynx's central vision: an unprecedented view of the hot and energetic Universe, enabling discoveries that will define high-energy astrophysics in the coming decades.

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arXiv2026

The XMM-Newton Line Emission Analysis Program (X-LEAP) III: Earth's Magnetospheric X-ray Emission Revealed by 22-Year XMM-Newton Observations

The magnetosphere, protecting the Earth from intense solar activity, is also shaped by the solar wind, while its structure is still uncertain in observation. In this study, we map the X-ray emission in the magnetosphere, which is induced by the charge exchange between the highly-ionized solar wind and the neutral gas around the Earth, known as the magnetospheric solar wind charge exchange (SWCX). In particular, we extract the magnetospheric SWCX in the O VII line emission data adopted from the XMM Line Emission Analysis Program (X-LEAP). The observed magnetospheric SWCX shows an enhanced emission of approximately $I_{\rm OVII}^{\rm mag}\approx 2$ photons $\rm cm^{-2}~ s^{-1}~sr^{-1}$ toward the Sun, showing a consistent shape predicted by numerical simulations. Furthermore, this magnetospheric SWCX exhibits a dependence on the XMM pointing direction, which traces the path length of SWCX emission in the Earth's magnetosphere. Building on this directional dependence, we model the 3D magnetosheath structure using soft X-ray observations for the first time, constraining the averaged boundary geometry and SWCX emissivity distribution over 22 years. Finally, utilizing the XMM data, we derive an empirical O VII emission efficiency of $α_{\rm OVII}=(2.1\pm0.4) \times 10^{-16}\ {\rm eV\,cm^{2}}$.

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arXiv2025

An XMM-Newton View of the ANdromeda Galaxy as Explored in a Legacy Survey (New-ANGELS) II: Luminosity Function of X-ray Sources

As part of the New-ANGELS program, we systematically investigate the X-ray luminosity functions (XLFs) of 4506 X-ray sources projected within a radius of 2.5 deg centering on M31. We construct XLFs for different regions in the disk and halo of M31, accounting for the incompleteness with an effective sensitivity map. Assuming that the halo regions contain (mostly) foreground stars and background active galactic nuclei, they are taken as "background" for deriving the XLFs of the sources in the disk. Through modeling XLFs, we decompose the X-ray sources into distinct populations for each region. We find that low-mass X-ray binaries are the dominant X-ray population throughout the disk of M31. The XLFs of M31 reveal a consistently lower integrated LMXB luminosity per stellar mass ($α_\mathrm{LMXB}$) compared to other galaxies, likely due to M31's prolonged period of quiescent star formation. Variations in the XLF shape and $α_\mathrm{LMXB}$ across different regions of M31 suggest that the relationship between integrated luminosity and stellar mass may vary within the galaxy. Additionally, the relatively low integrated luminosity observed in the inner-arm region provides crucial evidence for a rapid fading of M31's LMXBs around 1 Gyr, a finding consistent with recent observations of other nearby galaxies.

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arXiv2025

Supervised Extraction of the Thermal Sunyaev$-$Zel'dovich Effect with a Three-Dimensional Convolutional Neural Network

The thermal Sunyaev$-$Zel'dovich (SZ) effect offers a unique probe of the hot and diffuse universe that could help close the missing baryon problem. Traditional extractions of the SZ effect, however, exhibit systematic noise that may lead to unreliable results. In this work, we provide an alternative solution using a three-dimensional Attention Nested U-Net trained end-to-end with supervised learning. Our labeled data consists of simulated SZ signals injected into $\textit{Planck}$ frequency maps, allowing our model to learn how to extract SZ signals in the presence of realistic noise. We implement a curriculum learning scheme that gradually exposed the model to weaker SZ signals. The absence/presence of curriculum learning significantly impacted the amount of bias and variance present in the reconstructed SZ signal. The results from our method were comparable to those from the popular $\textit{needlet internal linear combination}$ (NILC) method when evaluated on simulated data as well as real-world SZ signals. We conclude by discussing future avenues for advancing machine learning extractions of SZ signals.

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arXiv2025

Modeling the cool gas clumps in the circumgalactic medium

A major challenge in CGM studies is determining the three-dimensional (3D) properties from the observed projected observations. Here, we decompose the 3D gas density and spatial distribution of cool clouds by fitting a cool CGM model with the absorption observations, including the cool gas density, Ly$α$, and Mg II equivalent widths. The clumpiness in the cool CGM is considered by modeling individual clouds. This model has four major components: the radial profile of the cool gas density; the number density of clouds; the absorption properties within individual clouds; and the velocity dispersion in the CGM. The observed cool gas density exhibits a large dispersion of $\approx2-3$ dex within the virial radius ($r_{vir}$). This dispersion can be reproduced with a combination of the projection effect (i.e., distant low-density clouds projected at small radii) and the intrinsic variation in the gas density. By modeling the probability density functions of gas density at different radii, the cool gas density is modeled as a $β$-model with a characteristic gas density of $\log n_{H,0}/{\rm cm^{-3}}=-2.57_{-0.25}^{+0.43}$ at $r_{vir}$ and a slope of $β_c=0.63_{-0.20}^{+0.16}$, and the intrinsic dispersion is $σ_{n_{H}}\approx 0.56_{-0.20}^{+0.19}$ dex. Assuming a cloud mass of $10^4M_\odot$, we further constrain the number density of cool clouds by jointly reproducing Ly$α$ and Mg II equivalent width samples, resulting into a number density of $\log n_{\mathcal{N}_{cl},0}/ r_{vir}^{-3}=4.76^{+0.27}_{-0.21}$ at $r_{vir}$ and a slope of $β_N=0.65^{+0.06}_{-0.07}$. This spatial distribution of the cool CGM leads to a total cool gas mass of $\log M_{cool}/M_\odot=10.01^{+0.06}_{-0.06}$ for $L^*$ galaxies, while varying the cloud mass from $10^3M_\odot$ to $10^6M_\odot$ leads to the total cool CGM mass of $9.62_{-0.07}^{+0.05}$ to $10.46_{-0.05}^{+0.05}$.

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arXiv2024

CO-CHANGES II: spatially resolved IRAM 30M CO line observations of 23 nearby edge-on spiral galaxies

Molecular gas, as the fuel for star formation, and its relationship with atomic gas are crucial for understanding how galaxies regulate their star forming (SF) activities. We conducted IRAM 30m observations of 23 nearby spiral galaxies from the CHANG-ES project to investigatet the distribution of molecular gas and the Kennicutt-Schmidt law. Combining these results with atomic gas masses from previous studies, we aim to investigate the scaling relations that connect the molecular and atomic gas masses with stellar masses and the baryonic Tully-Fisher relation. Based on spatially resolved observations of the three CO lines, we calculated the total molecular gas masses, the ratios between different CO lines, and derived physical parameters such as temperature and optical depth. The median line ratios for nuclear/disk regions are 8.6/6.1 (^{12}\mathrm{CO}/^{13}\mathrm{CO}\ J=1{-}0) and 0.53/0.39 (^{12}\mathrm{CO}\ J=2{-}1/J=1{-}0). Molecular gas mass derived from ^{13}\mathrm{CO} is correlated but systematically lower than that from ^{12}\mathrm{CO}. Most galaxies follow the spatially resolved SF scaling relation with a median gas depletion timescale of approximately 1 Gyr, while a few exhibit shorter timescales of approximately 0.1 Gyr. The molecular-to-atomic gas mass ratio correlates strongly with stellar mass, consistent with previous studies. Galaxies with lower stellar masses show an excess of atomic gas, indicating less efficient conversion to molecular gas. Most galaxies tightly follow the baryonic Tully-Fisher relation, but NGC 2992 and NGC 4594 deviate from the relation due to different physical factors. We find that the ratio of the cold gas (comprising molecular and atomic gas) to the total baryon mass decreases with the gravitational potential of the galaxy, as traced by rotation velocity, which could be due to gas consumption in SF or being heated to the hot phase.

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arXiv2024

Early Enrichment Population Theory at High Redshift

An Early Enrichment Population (EEP) has been theorized to produce the observed intracluster medium (ICM) metallicity of galaxy clusters. This population likely existed at high redshifts (z$\sim$10), relics of which we posit exist today as dwarf galaxies. Previous work argues that the initial mass function (IMF) of the EEP must be flatter than those found at lower redshifts, but with considerable uncertainties. In this work, we present a more quantitative model for the EEP and demonstrate how observational constraints can be applied to the IMF using supernova Type Ia (SN Ia) rates, delay time distribution (DTD), and the luminosity function (LF) of galaxy clusters. We determine best-fit values for the slope and mass break of the IMF by comparing IMFs from literature with observed DTDs, and the low-luminosity component ($M(R)> -12$) of the Coma LF. We derive two best-fit IMFs, flatter than standard IMFs: (1) $α_{lo} = -0.13 \pm 0.24$ for $0.07 < M/M_\odot < 1.75$ and $α_{hi} = 0.53 \pm 0.01$ for $1.75 < M/M_\odot < 150$, and (2) $α_{lo} = 1.06 \pm 0.11$ for $0.07 < M/M_\odot < 6$ and $α_{hi} = 0.53 \pm 0.01$ for $6 < M/M_\odot < 150$. We compare these with \textit{sl-5} from \cite{Loew2013}, with $α=0.5$ for $0.07 < M/M_\odot < 8$, and $α=0.3$ for $8 < M/M_\odot < 150$. This EEP model, along with stars formed at later times, can produce the observed ICM metallicity, is consistent with observations, and predicts a significant rise in the SN Ia rate at increasing redshift.

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arXiv2024

Probing the He II re-Ionization ERa via Absorbing C IV Historical Yield (HIERACHY) II: Project Design, Current Status, and Examples of Initial Data Products

The He II reionization epoch is expected to take place at $z\sim3-5$. In this stage, the helium and metals in the inter-galactic medium (IGM) are further ionized with additional contributions from harder non-stellar sources, and some large-scale gravitationally bound systems approach virialization. The "Probing the He II re-Ionization ERa via Absorbing C IV Historical Yield (HIERACHY)" program utilizes high- and medium-resolution spectra of bright background quasars at $z\approx3.9-5.2$ to investigate Ly$α$, C IV, and other metal absorption lines during this epoch. Additionally, we employ narrow-band imaging to search for Ly$α$ emitters associated with C IV absorbers, alongside multi-wavelength observations to identify and study particularly intriguing cases. In this paper, we present the design of the HIERACHY program, its current status, major scientific goals, and examples of initial data products from completed Magellan/MIKE, MagE spectroscopy, and MDM imaging observations. We also provide a brief outlook on future multi-wavelength observations that may significantly impact the related science.

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arXiv2024

eDIG-CHANGES III: the lagging eDIG revealed by multi-slit spectroscopy of NGC 891

The kinematic information of the extraplanar diffuse ionized gas (eDIG) around galaxies provides clues to the origin of the gas. The eDIG-CHANGES project studies the physical and kinematic properties of the eDIG around the CHANG-ES sample of nearby edge-on disk galaxies. We use a novel multi-slit narrow-band spectroscopy technique to obtain the spatial distribution of spectral properties of the ionized gas around NGC 891, which is often regarded as an analog of the Milky Way. We developed specific data reduction procedures for the multi-slit narrow-band spectroscopy data taken with the MDM 2.4m telescope. The data presented in this paper covers the H$α$ and [N II]$λλ$6548,6583Åemission lines. The eDIG traced by the H$α$ and [N II] lines shows an obvious asymmetric morphology, being brighter in the northeastern part of the galactic disk and extending a few kpc above and below the disk. Global variations in the [N II]/H$α$ line ratio suggest additional heating mechanisms for the eDIG at large heights beyond photoionization. We also construct position-velocity (PV) diagrams of the eDIG based on our optical multi-slit spectroscopy data and compare them to similar PV diagrams constructed with the H I data. The dynamics of the two gas phases are generally consistent with each other. Modeling the rotation curves at different heights from the galactic mid-plane suggests a vertical negative gradient in turnover radius and maximum rotation velocity, with magnitudes of approximately $3$ kpc kpc$^{-1}$ and $22-25$ km s$^{-1}$ kpc$^{-1}$, respectively. Measured vertical gradients of the rotation curve parameters suggest significant differential rotation of the ionized gas in the halo, or often referred to as the lagging eDIG. Systematic study of the lagging eDIG in our eDIG-CHANGES project, will help us to better understand the dynamics of the ionized gas in the halo.

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arXiv2024

A SN Ia Near a Globular Cluster in the Early-Type Galaxy NGC 5353

No progenitor of a Type Ia supernova is known, but in old population early-type galaxies, one may find SN Ia associated with globular clusters, yielding a population age and metallicity. It also provides insight into the formation path and the SN enhancement rate in globular clusters. We sought to find such associations and identified SN 2019ein to be within the ground-based optical positional uncertainty of a globular cluster candidate within the early-type galaxy NGC 5353 at about 30 Mpc distance. We reduced the positional uncertainties by obtaining Hubble Space Telescope images with the Advanced Camera for Surveys, using filters F475W and F814W and obtained in June 2020. We find that the globular cluster candidate has a magnitude, color, and angular extent that are consistent with it being a typical globular cluster. The separation between the globular cluster and SN 2019ein is 0.43'', or 59 pc in projection. The chance occurrence with a random globular cluster is about 3%, favoring but not proving an association. If the SN progenitor originated in the globular cluster, one scenario is that SN 2019ein was previously a double degenerate white dwarf binary that was dynamically ejected from the globular cluster and exploded within 10 Myr; models do not predict this to be common. Another, but less likely scenario is where the progenitor remained bound to the globular cluster, allowing the double degenerate binary to inspiral on a much longer timescale before producing a SN.

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arXiv2024

eDIG-CHANGES II: Project Design and Initial Results on NGC 3556

The extraplanar diffuse ionized gas (eDIG) represents ionized gases traced by optical/UV lines beyond the stellar extent of galaxies. We herein introduce a novel multi-slit narrow-band spectroscopy method to conduct spatially resolved spectroscopy of the eDIG around a sample of nearby edge-on disk galaxies (eDIG-CHANGES). In this paper, we introduce the project design and major scientific goals, as well as a pilot study of NGC 3556 (M108). The eDIG is detected to a vertical extent of a few kpc above the disk, comparable to the X-ray and radio images. We do not see significant vertical variation of the [N II]/H$α$ line ratio. A rough examination of the pressure balance between different circum-galactic medium (CGM) phases indicates the magnetic field is in a rough pressure balance with the X-ray emitting hot gas, and may play an important role in the global motion of both the eDIG and the hot gas in the lower halo. At the location of an HST/COS observed UV bright background AGN $\sim29\rm~kpc$ from the center of NGC 3556, the magnetic pressure is much lower than that of the hot gas and the ionized gas traced by UV absorption lines, although the extrapolation of the pressure profiles may cause some biases in this comparison. By comparing the position-velocity diagrams of the optical and CO lines, we also find the dynamics of the two gas phases are consistent with each other, with no evidence of a global inflow/outflow and a maximum rotation velocity of $\sim150\rm~km~s^{-1}$.

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arXiv2024

The XMM-Newton Line Emission Analysis Program (X-LEAP) II: The Multi-scale Temperature Structures in the Milky Way Hot Gas

This paper presents the multi-scale temperature structures in the Milky Way (MW) hot gas, as part of the XMM-Newton Line Emission Analysis Program (X-LEAP), surveying the O VII, O VIII, and Fe-L band emission features in the XMM-Newton archive. In particular, we define two temperature tracers, $I_{\rm OVIII}/I_{\rm OVII}$ (O87) and $I_{\rm FeL}/(I_{\rm OVII}+I_{\rm OVIII})$ (FeO). These two ratios cannot be explained simultaneously using single-temperature collisional ionization models, which indicates the need for multi-temperature structures in hot gas. In addition, we show three large-scale features in the hot gas: the eROSITA bubbles around the Galactic center (GC); the disk; and the halo. In the eROSITA bubbles, the observed line ratios can be explained by a log-normal temperature distribution with a median of $\log T/{\rm K} \approx 6.4$ and a scatter of $σ_T \approx 0.2$ dex. Beyond the bubbles, the line ratio dependence on the Galactic latitude suggests higher temperatures around the midplane of the MW disk. The scale height of the temperature variation is estimated to be $\approx$2 kpc assuming an average distance of $5$ kpc for the hot gas. The halo component is characterized by the dependence on the distance to the GC, showing a temperature decline from $\log\,T/{\rm K}\,\approx\, 6.3$ to $5.8$. Furthermore, we extract the auto-correlation and cross-correlation functions to investigate the small-scale structures. O87 and FeO ratios show a consistent auto-correlation scale of $\approx$$ 5^\circ$ (i.e., $\approx$$ 400$ pc at 5 kpc), which is consistent with expected physical sizes of X-ray bubbles associated with star-forming regions or supernova remnants. Finally, we examine the cross-correlation between the hot and UV-detected warm gas, and show an intriguing anti-correlation.

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arXiv2024

The XMM-Newton Line Emission Analysis Program (X-LEAP) I: Emission Line Survey of O VII, O VIII, and Fe L-Shell Transitions

The XMM-Newton Line Emission Analysis Program (X-LEAP) is designed to study diffuse X-ray emissions from the Milky Way (MW) hot gas, as well as emissions from the foreground solar wind charge exchange (SWCX). This paper reports an all-sky survey of spectral feature intensities corresponding to the O VII, O VIII, and iron L-shell (Fe-L) emissions. These intensities are derived from 5418 selected XMM-Newton observations with long exposure times and minimal contamination from point or extended sources. For 90% of the measured intensities, the values are within $\approx$ 2-18 photons cm$^{-2}$ s$^{-1}$ sr$^{-1}$ (line unit; L.U.), $\approx$ 0-8 L.U., and $\approx$ 0-9 L.U., respectively. We report long-term variations in O VII and O VIII intensities over 22 years, closely correlating with the solar cycle and attributed to SWCX emissions. These variations contribute $\sim30\%$ and $\sim20\%$ to the observed intensities on average and peak at $\approx$ 4 L.U. and $\approx$ 1 L.U. during solar maxima. We also find evidence of short-term and spatial variations in SWCX, indicating the need for a more refined SWCX model in future studies. In addition, we present SWCX- and absorption-corrected all-sky maps for a better view of the MW hot gas emission. These maps show a gradual decrease in oxygen intensity moving away from the Galactic center and a concentration of Fe-L intensity in the Galactic bubbles and disk.

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arXiv2024

Optimizing NILC Extractions of the Thermal Sunyaev-Zeldovich Effect with Deep Learning

All-sky maps of the thermal Sunyaev-Zel'dovich effect (SZ) tend to suffer from systematic features arising from the component separation techniques used to extract the signal. In this work, we investigate one of these methods known as needlet internal linear combination (NILC) and test its performance on simulated data. We show that NILC estimates are strongly affected by the choice of the spatial localization parameter ($Γ$), which controls a bias-variance trade-off. Typically, NILC extractions assume a fixed value of $Γ$ over the entire sky, but we show there exists an optimal $Γ$ that depends on the SZ signal strength and local contamination properties. Then we calculate the NILC solutions for multiple values of $Γ$ and feed the results into a neural network to predict the SZ signal. This extraction method, which we call Deep-NILC, is tested against a set of validation data, including recovered radial profiles of resolved systems. Our main result is that Deep-NILC offers significant improvements over choosing fixed values of $Γ$.

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arXiv2023

Exploring chemical enrichment of the intracluster medium with the Line Emission Mapper

Synthesized in the cores of stars and supernovae, most metals disperse over cosmic scales and are ultimately deposited well outside the gravitational potential of their host galaxies. Since their presence is well visible through their X-ray emission lines in the hot gas pervading galaxy clusters, measuring metal abundances in the intracluster medium (ICM) offers us a unique view of chemical enrichment of the Universe as a whole. Despite extraordinary progress in the field thanks to four decades of X-ray spectroscopy using CCD (and gratings) instruments, understanding the precise stellar origins of the bulk of metals, and when the latter were mixed on Mpc scales, requires an X-ray mission capable of spatial, non-dispersive high resolution spectroscopy covering at least the soft X-ray band over a large field of view. In this White Paper, we demonstrate how the Line Emission Mapper (LEM) probe mission concept will revolutionize our current picture of the ICM enrichment. Specifically, we show that LEM will be able to (i) spatially map the distribution of ten key chemical elements out to the virial radius of a nearby relaxed cluster and (ii) measure metal abundances in serendipitously discovered high-redshift protoclusters. Altogether, these key observables will allow us to constrain the chemical history of the largest gravitationally bound structures of the Universe. They will also solve key questions such as the universality of the initial mass function (IMF) and the initial metallicity of the stellar populations producing these metals, as well as the relative contribution of asymptotic giant branch (AGB) stars, core-collapse, and Type Ia supernovae to enrich the cosmic web over Mpc scales. Concrete observing strategies are also briefly discussed.

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arXiv2023

CO-CHANGES I: IRAM 30m CO Observations of Molecular Gas in the Sombrero Galaxy

Molecular gas plays a critical role in explaining the quiescence of star formation (SF) in massive isolated spiral galaxies, which could be a result of either the low molecular gas content and/or the low SF efficiency. We present IRAM 30m observations of the CO lines in the Sombrero galaxy (NGC~4594), the most massive spiral at $d\lesssim30\rm~Mpc$. We detect at least one of the three CO lines covered by our observations in all 13 observed positions located at the galactic nucleus and along a $\sim25\rm~kpc$-diameter dusty ring. The total extrapolated molecular gas mass of the galaxy is $M_{\rm H_2}\approx4\times10^{8}\rm~M_\odot$. The measured maximum CO gas rotation velocity of $\approx379\rm~km~s^{-1}$ suggests that NGC~4594 locates in a dark matter halo with a mass $M_{\rm200}\gtrsim10^{13}\rm~M_\odot$. Comparing to other galaxy samples, NGC~4594 is extremely gas poor and SF inactive, but the SF efficiency is apparently not inconsistent with that predicted by the Kennicutt-Schmidt law, so there is no evidence of enhanced SF quenching in this extremely massive spiral with a huge bulge. We also calculate the predicted gas supply rate from various sources to replenish the cold gas consumed in SF, and find that the galaxy must experienced a starburst stage at high redshift, then the leftover or recycled gas provides SF fuels to maintain the gradual growth of the galactic disk at a gentle rate.

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