The He ii reionization epoch is expected to take place at z ∼ 3–5. In this stage, the helium and metals in the intergalactic medium are further ionized with additional contributions from harder nonstellar 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 ≈ 3.9–5.2 to investigate Ly α , C iv , and other metal absorption lines during this epoch. Additionally, we employ narrowband imaging to search for Ly α emitters associated with C iv absorbers, alongside multiwavelength 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 multiwavelength observations that may significantly impact the related science.

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 ∼ 10), relics of which we posit exist today as dwarf galaxies. Previous work has argued 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 distributions (DTDs), and the luminosity functions (LFs) 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 ± 0.24 for 0.07 < M / M _⊙ < 1.75 and α _hi = 0.53 ± 0.01 for 1.75 < M / M _⊙ < 150; and (2) α _lo = 1.06 ± 0.11 for 0.07 < M / M _⊙ < 6 and α _hi = 0.53 ± 0.01 for 6 < M / M _⊙ < 150. We compare these with sl-5 from M. Loewenstein (2013), with α = 0.5 for 0.07 < M / M _⊙ < 8 and α = 0.3 for 8 < M / M _⊙ < 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.

Arcus is a high-resolution soft X-ray and far-ultraviolet spectroscopy mission submitted to the National Aeronautics and Space Administration's inaugural Astrophysics Probe solicitation. Arcus makes simultaneous observations in these two critical wavelength regimes to address a broad range of science questions highlighted by the 2020 Astronomy and Astrophysics Decadal Survey, from the temperature and composition of the missing baryons in the intergalactic medium to the evolution of stars and their influence on orbiting planets. We present the science motivation for and performance of the Arcus ultraviolet spectrograph (UVS). UVS comprises a 60-cm, off-axis Cassegrain telescope feeding an imaging spectrograph operating over the 970- to 1580-angstrom bandpass. The instrument employs two interchangeable diffraction gratings to provide medium-resolution spectroscopy (R>20,000 in two grating modes centered at similar to 1110 and 1390 angstrom). The spectra are recorded on an open-face, photon-counting microchannel plate detector. The instrument design achieves an end-to-end sensitivity >10 times that of the Far-Ultraviolet Spectroscopic Explorer over the key 1020- to 1150-angstrom range and offers arcsecond-level angular resolution spectral imaging over a 6-arcminute-long slit for observations of extended sources. We describe the example science investigations for far-ultraviolet spectroscopy on Arcus, the resultant instrument design and predicted performance, and simulated data from potential General Observer programs with Arcus.

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 3D attention nested U-Net trained end to end with supervised learning. Our labeled data consist of simulated SZ signals injected into 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 needlet internal linear combination 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.

We develop and present the Descriptive Parametric Model (DPM), a tool for generating profiles of gaseous haloes (pressure, electron density, and metallicity) as functions of radius, halo mass, and redshift. The model assumes single-phase, spherically symmetric, volume-filling warm/hot gas. The DPM framework enables mock observations of the circumgalactic medium (CGM), group haloes, and clusters across a number of wavebands including X-ray, sub-millimetre/millimetre, radio, and ultraviolet (UV). We introduce three model families calibrated to reproduce cluster profiles while having different extrapolations to the CGM-(i) self-similar haloes, (ii) a reduced gas model for lower halo masses, and (iii) a model with shallower radial slopes at lower masses. We demonstrate how our z = 0 . 0-0 . 6 models perform when applied to stacked and individual X-ray emission profiles, measurements of the thermal and kinetic Sunyaev-Zel'dovich effect, electron dispersion measures from fast radio bursts, O VI absorption, and UV-derived pressures. Our investigation supports models that remove baryons from haloes more effectively and have shallower profiles at lower halo mass. We discuss biases and systematics when modelling observables using consistent hot gaseous halo models for all wavebands explored. We release the DPMHALO code to encourage the use of our framework and new formulations in future investigations. Included with the DPMHALO distribution is a set of recent observations that allow the reproduction of most plots in this paper.

Context. Molecular gas, which serves as the fuel for star formation, and its relationship with atomic gas are essential for understanding how galaxies regulate their star forming activities. Aims. We conducted IRAM 30 m observations of 23 nearby spiral galaxies as part of the CHANG-ES project to investigate the distribution of molecular gas and the Kennicutt-Schmidt star formation law in these galaxies. By combining these results with atomic gas masses studied in previous work, we aim to investigate the scaling relations that connect the molecular and atomic gas masses with stellar masses and the baryonic Tully-Fisher relation. Methods. Based on spatially resolved observations of the 12CO J = 1 - 0, 13CO J = 1 - 0, and 12CO J = 2 - 1 molecular lines, we calculated the total molecular gas masses, obtained the ratios between different CO lines, and derived some key physical parameters, such as the temperature and optical depth of the molecular gas. Results. For the nuclear and disc regions, the median values of the 12CO/13CO J = 1 - 0 line ratio are 8.6 and 6.1, respectively, while those of the 12CO J = 2 - 1/J = 1 - 0 line ratio are 0.53 and 0.39. The molecular gas mass derived from 13CO J = 1 - 0 is strongly correlated with but systematically lower than that derived from 12CO J = 1 - 0. Most of the galaxies in our sample follow the spatially resolved star forming scaling relation between the star formation rate surface density and molecular gas mass surface density, with a median gas depletion time scale of similar to 1 Gyr. A few galaxies exhibit enhanced star formation efficiency, with shorter time scales of similar to 0.1 Gyr. Our sample shows a weak correlation between molecular and atomic gas but a strong correlation between the molecular-to-atomic gas mass ratio (MH2/MHI) and stellar mass, consistent with previous studies. Galaxies with lower stellar masses in our sample exhibit an excess of atomic gas by one magnitude compared to molecular gas, suggesting that the transformation of atomic gas into molecular gas is less efficient. 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 star formation or being heated to the hot phase.

The AXIS Community Science Book represents the collective effort of 592 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with 1.5” imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles 138 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks.

A major challenge in circumgalactic medium (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 alpha, and Mg ii equivalent widths. The clumpiness in the cool CGM is considered by modelling 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 approximate to 2-3 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 modelling the probability density functions of gas density at different radii, the cool gas density is modelled as a beta-model with a characteristic gas density of log n(H,0)/cm(-3) = -2.57(-0.25)(+0.43) at r(vir) and a slope of beta(c) = 0.63(-0.20)(+0.16), and the intrinsic dispersion is sigma(nH) approximate to 0.56(-0.20)(+0.19) dex. Assuming a cloud mass of 10(4) M-circle dot, we further constrain the number density of cool clouds by jointly reproducing Ly alpha and Mg ii equivalent width samples, resulting into a number density of log n(Ncl,0)/r(vir)(-3) = 4.76(-0.21)(+0.27) at r(vir) and a slope of beta(Ncl) = 0.65(-0.07)(+0.06). This spatial distribution of the cool CGM leads to a total cool gas mass of log M-cool/M-circle dot = 10.01(-0.06)(+0.06) for L* galaxies, while varying the cloud mass from 10(3) to 10(6) M-circle dot leads to the total cool CGM mass of 9.62(-0.07)(+0.05) to 10.46(-0.05)(+0.05).

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 presents 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 ≈2–18 photons cm ^−2 s ^−1 sr ^−1 (line unit (LU)), ≈0–8 LU, and ≈0–9 LU, respectively. We report long-term variations in O vii and O viii intensities over 22 yr, closely correlating with the solar cycle and attributed to SWCX emissions. These variations contribute ∼30% and ∼20% to the observed intensities on average and peak at ≈4 and ≈1 LU 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.

The Arcus Probe mission addresses a wide range of Astro2020 Decadal and NASA Science Mission Directorate Priority science areas, and is designed to explore astrophysical feedback across all mass scales. Arcus' three baseline science goals include: (i) Characterizing the drivers of accretion-powered feedback in supermassive black holes, (ii) Quantifying how feedback at all scales drives galaxy evolution and large-scale structure, including the tenuous cosmic web, and (iii) Analyzing stellar feedback from exoplanetary to galactic scales, including its effects on exoplanet environments targeted by current and future NASA missions. These science goals, along with a robust General Observer program, will be achieved using a mission that provides a high-sensitivity soft (10-60 angstrom) X-ray spectrometer (XRS), working simultaneously with a co-aligned UV spectrometer (UVS; 970-1580 angstrom). Arcus enables compelling baseline science and provides the broader astronomy community a revolutionary tool to characterize the full ionization range of warm and hot plasmas - including hydrogen, helium, and all abundant metals - in the Universe, from the halos of galaxies and clusters to the coronae of stars.

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.

Context. The kinematic information of the extraplanar diffuse ionized gas (eDIG) around galaxies provides clues to the origin of the gas. Aims. The eDIG-CHANGES project studies the physical and kinematic properties of the eDIG around the CHANG-ES sample of nearby edge-on disk galaxies. Methods. We use a novel multi-slit narrow-band spectroscopy technique to obtain the spatial distribution of the spectral properties of the ionized gas around NGC 891, which is often regarded as an analogue of the Milky Way. We developed specific data reduction procedures for the multi-slit narrow-band spectroscopy data taken with the MDM 2.4 m telescope. The data presented in this paper cover the H alpha and [N II]lambda lambda 6548, 6583 & Aring; emission lines. Results. The eDIG traced by the H alpha and [N II] lines shows an obvious asymmetric morphology, being brighter in the northeastern part of the galactic disk and extending a few kiloparsecs above and below the disk. Global variations in the [N II]/H alpha 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. Modelling 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. Conclusions. Our measured vertical gradients of the rotation curve parameters suggest significant differential rotation of the ionized gas in the halo, often referred to as the lagging eDIG. Systematic study of the lagging eDIG, using the multi-slit narrow-band spectroscopy technique developed in our eDIG-CHANGES project, will help us to better understand the dynamics of the ionized gas in the halo.

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 multislit 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 kiloparsecs 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 circumgalactic medium 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 Hubble Space Telescope/Cosmic Origins Spectrograph observed UV bright background active galactic nucleus ∼29 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 ∼150 km s −1 .

ABSTRACT 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 30-m observations of the CO lines in the Sombrero galaxy (NGC 4594), the most massive spiral at $d\lesssim 30\rm ~Mpc$. 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 an $\sim 25\rm ~kpc$-diameter dusty ring. The total extrapolated molecular gas mass of the galaxy is $M_{\rm H_2}\approx 4\times 10^{8}\rm ~M_\odot$. The measured maximum CO gas rotation velocity of $\approx 381\rm ~km~s^{-1}$ suggests that NGC 4594 locates in a dark matter halo with a mass $M_{\rm 200}\gtrsim 10^{13}\rm ~M_\odot$. 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 experience a starburst stage at high redshift, then the leftover or recycled gas provides SF fuels to maintain the gradual growth of the galactic disc at a gentle rate.

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.

This paper presents the multiscale temperature structures in the Milky Way (MW) hot gas, as part of the XMM-Newton Line Emission Analysis Program, 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 OVIII/I OVII (O87) and I FeL/(I OVII + I OVIII) (FeO). These two ratios cannot be explained simultaneously using single-temperature collisional ionization models, which indicates the need for multitemperature 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 / K approximate to 6.4 and a scatter of sigma T approximate to 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 approximate to 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 / K approximate to 6.3 to 5.8. Furthermore, we extract the autocorrelation and cross-correlation functions to investigate the small-scale structures. O87 and FeO ratios show a consistent autocorrelation scale of approximate to 5 degrees (i.e., approximate to 400 pc at 5 kpc), which is consistent with the 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 anticorrelation.

The extraplanar diffuse ionized gas (eDIG) represents the cool/warm ionized gas reservoir around galaxies. We present spatial analysis of the H alpha images of 22 nearby edge-on spiral galaxies taken with the Apache Point Observatory 3.5-m telescope (eDIG-CHANGES). We conduct an exponential fit to the vertical H alpha intensity profiles of the galaxies, of which 16 can be decomposed into thin + thick disk components. The median value of the H alpha scale height of the thick disk is (h(H alpha)) =1.13 +/- 0.14 kpc. We further examine the dependence of h(H alpha) on the stellar mass, SFR, and SFR surface density (SFRSD) of the galaxies. We find a tight sublinear correlation between h(H alpha) and SFR, expressed in h(H alpha) proportional to SFR alpha, where asymptotic to 0.29. Moreover, the offset of individual galaxies from the best-fit SFR-h(H alpha) relation, expressed in h(H alpha)/SFR alpha, shows significant anti-correlation with SFRSD. We further compare the vertical extension of the eDIG to multi-wavelength measurements of other CGM phases. We find the eDIG slightly more extended than the neutral gas. This indicates the existence of some extended ionizing sources, in addition to the leaking photons from the disk star formation regions. Most galaxies have an X-ray scale height smaller than H alpha, suggesting the majority of the X-ray photons are actually from the thick disk instead of the extended CGM. h(H alpha) is comparable to the L-band radio continuum scale height. This indicates that the thermal and non-thermal electrons have similar spatial distributions, a natural result if both are transported outwards by a galactic wind. This further indicates the thermal gas, cosmic rays, and magnetic field may be close to energy equipartition.

Arcus is a high-resolution soft X-ray and far-ultraviolet spectroscopy mission being developed for submission to NASA’s inaugural Astrophysics Probe solicitation. Arcus makes simultaneous observations in these two critical wavelength regimes to address a broad range of science questions highlighted by the 2020 Astronomy and Astrophysics Decadal Survey, from the temperature and composition of the missing baryons in the intergalactic medium to the evolution of stars and their influence on orbiting planets. This proceeding presents the science motivation for and performance of the Arcus UltraViolet spectrograph (UVS). UVS comprises a 60 cm, off-axis Cassegrain telescope feeding an imaging spectrograph operating over the 970 – 1580 ˚A bandpass. The instrument employs two interchangeable diffraction gratings to provide medium-resolution spectroscopy (R ⪆ 20,000 in two grating modes centered at approximately 1110 and 1390 ˚A, respectively). The spectra are recorded on an open-face, photon-counting microchannel plate detector. The instrument design achieves an end-to-end sensitivity ⪆ 10 times that of the Far-Ultraviolet Spectroscopic Explorer over the key 1020 – 1150 ˚A range and offers arcsecond-level angular resolution spectral imaging over a six arcminute long slit for observations of extended sources. We describe example science investigations for FUV spectroscopy on Arcus, the resultant instrument design and predicted performance, and simulated data from potential Guest Observer programs with Arcus.