Search

Primordial Black Holes (PBHs) could explain some fraction of dark matter andshed light on many areas of early-universe physics. Despite over half a centuryof research interest, a PBH population has so far eluded detection. The mostcompetitive constraints on the fraction of dark matter comprised of PBHs($f_{\rm DM}$) in the $(10^{-9}-10)M_{\odot}$ mass-ranges come from photometricmicrolensing and bound $f_{\rm DM}\lesssim10^{-2}-10^{-1}$. With the advent ofthe Roman Space Telescope with its sub-milliarcsecond (mas) astrometriccapabilities and its planned Galactic Bulge Time Domain Survey (GBTDS),detecting astrometric microlensing signatures will become routine. Comparedwith photometric microlensing, astrometric microlensing signals are sensitiveto different lens masses-distance configurations and contains differentinformation, making it a complimentary lensing probe. At sub-mas astrometricprecision, astrometric microlensing signals are typically detectable at largerlens-source separations than photometric signals, suggesting a microlensingdetection channel of pure astrometric events. We use a Galactic simulation topredict the number of detectable microlensing events during the GBTDS via thispure astrometric microlensing channel. We find that the number of detectableevents peaks at $\approx 10^{3} f_{\rm DM}$ for a population of $ 1 M_{\odot}$PBHs and tapers to $\approx 10f_{\rm DM}$ and $\approx 100f_{\rm DM}$ at$10^{-4}M_{\odot}$ and $10^{3}M_{\odot}$, respectively. Accounting for thedistinguishability of PBHs from Stellar lenses, we conclude the GBTDS will besensitive and PBH population at $f_{\rm DM}$ down to $\approx10^{-1}-10^{-3}$for $(10^{-1}-10^{2})M_{\odot}$ likely yielding novel PBH constraints.

We present the kinematic anaylsis of $246$ stars within $4^\prime$ from thecenter of Orion Nebula Cluster (ONC), the closest massive star cluster withactive star formation across the full mass range, which provides valuableinsights in the the formation and evolution of star cluster on anindividual-star basis. High-precision radial velocities and surfacetemperatures are retrieved from spectra acquired by the NIRSPEC instrument usedwith adaptive optics (NIRSPAO) on the Keck II 10-m telescope. Athree-dimensional kinematic map is then constructed by combining with theproper motions previously measured by the Hubble Space Telescope (HST)ACS/WFPC2/WFC3IR and Keck II NIRC2. The measured root-mean-squared velocitydispersion is $2.26\pm0.08~\mathrm{km}\,\mathrm{s}^{-1}$, significantly higherthan the virial equilibrium's requirement of$1.73~\mathrm{km}\,\mathrm{s}^{-1}$, suggesting that the ONC core issupervirial, consistent with previous findings. Energy equipartition is notdetected in the cluster. Most notably, the velocity of each star relative toits neighbors is found to be negatively correlated with stellar mass. Low-massstars moving faster than their surrounding stars in a supervirial clustersuggests that the initial masses of forming stars may be related to theirinitial kinematic states. Additionally, a clockwise rotation preference isdetected. A weak sign of inverse mass segregation is also identified amongstars excluding the Trapezium stars, though it could be a sample bias. Finally,this study reports the discovery of four new candidate spectroscopic binarysystems.

We report the discovery of a large-scale structure at z=3.44 revealed by JWSTdata in the Extended Groth Strip (EGS) field. This structure, called the CosmicVine, consists of 20 galaxies with spectroscopic redshifts at 3.4370\%$).Comparisons with simulations suggest that the Cosmic Vine would form a clusterwith halo mass $M_{\rm halo}>10^{14}M_\odot$ at z=0, and the two massivegalaxies are likely forming the brightest cluster galaxies (BCGs). The resultsunambiguously reveal that massive quiescent galaxies can form in growinglarge-scale structures at z>3, thus disfavoring the environmental quenchingmechanisms that require a virialized cluster core. Instead, as suggested by theinteracting and bulge-dominated morphologies, the two galaxies are likelyquenched by merger-triggered starburst or active galactic nucleus (AGN)feedback before falling into a cluster core. Moreover, we found that theobserved specific star formation rates of massive quiescent galaxies in z>3dense environments are one to two orders of magnitude lower than that of theBCGs in the TNG300 simulation. This discrepancy potentially poses a challengeto the models of massive cluster galaxy formation. Future studies comparing alarge sample with dedicated cluster simulations are required to solve theproblem.

We study the cross-correlation of damped Lyα systems (DLAs) and their background quasars, using the most updated DLA catalog and the Planck 2018 CMB lensing convergence field. Our measurement suggests that the DLA bias bDLA is smaller than 3.1, corresponding to at a confidence of 90%. These constraints are broadly consistent with Alonso et al. and previous measurements by cross-correlation between DLAs and the Lyα forest (e.g., Font-Ribera et al.; Prez-Rfols et al.). Further, our results demonstrate the potential of obtaining a more precise measurement of the halo mass of the high-redshift sources using next generation CMB experiments with a higher angular resolution. The python-based codes and data products of our analysis are available at https://github.com/LittleLin1999/CMB-lensingxDLA.

ABSTRACT We examine the thermodynamic state and cooling of the low-z circumgalactic medium (CGM) in five FIRE-2 galaxy formation simulations of Milky Way-mass galaxies. We find that the CGM in these simulations is generally multiphase and dynamic, with a wide spectrum of largely non-linear density perturbations sourced by the accretion of gas from the intergalactic medium (IGM) and outflows from both the central and satellite galaxies. We investigate the origin of the multiphase structure of the CGM with a particle-tracking analysis and find that most of the low-entropy gas has cooled from the hot halo as a result of thermal instability triggered by these perturbations. The ratio of cooling to free-fall time-scales tcool/tff in the hot component of the CGM spans a wide range of ∼1−100 at a given radius but exhibits approximately constant median values of ∼5−20 at all radii 0.1Rvir < r < Rvir. These are similar to the ≈10−20 value typically adopted as the thermal instability threshold in ‘precipitation’ models of the ICM. Consequently, a one-dimensional model based on the assumption of a constant tcool/tff and hydrostatic equilibrium approximately reproduces the number density and entropy profiles of each simulation but only if it assumes the metallicity profile and temperature boundary condition taken directly from the simulation. We explicitly show that the tcool/tff value of a gas parcel in the hot component of the CGM does not predict its probability of subsequently accreting on to the central galaxy. This suggests that the value of tcool/tff is a poor predictor of thermal stability in gaseous haloes in which large-amplitude density perturbations are prevalent.

We use FIRE-2 simulations to examine 3D variations of gas-phase elemental abundances of [O/H], [Fe/H], and [N/H] in 11 MW and M31-mass galaxies across their formation histories at z ≤ 1.5 (tlookback ≤ 9.4 Gyr), motivated by characterizing the initial conditions of stars for chemical tagging. Gas within 1 kpc of the disc mid-plane is vertically homogeneous to ≲ 0.008 dex at all z ≤ 1.5. We find negative radial gradients (metallicity decreases with galactocentric radius) at all times, which steepen over time from -0.01 dex kpc-1 at z = 1 (tlookback} = 7.8 Gyr) to -0.03 dex kpc-1 at z = 0, and which broadly agree with observations of the MW, M31, and nearby MW/M31-mass galaxies. Azimuthal variations at fixed radius are typically 0.14 dex at z = 1, reducing to 0.05 dex at z = 0. Thus, over time radial gradients become steeper while azimuthal variations become weaker (more homogeneous). As a result, azimuthal variations were larger than radial variations at z ≥ 0.8 (tlookback ≳ 6.9 Gyr). Furthermore, elemental abundances are measurably homogeneous (to ≤0.05 dex) across a radial range of Δ R ≈ 3.5 kpc at z ≥ 1 and Δ R ≈ 1.7 kpc at z = 0. We also measure full distributions of elemental abundances, finding typically negatively skewed normal distributions at z ≥ 1 that evolve to typically Gaussian distributions by z = 0. Our results on gas abundances inform the initial conditions for stars, including the spatial and temporal scales for applying chemical tagging to understand stellar birth in the MW.

ABSTRACT: The 21-cm signal from the Cosmic Dawn (CD) is likely to contain large fluctuations, with the most extreme astrophysical models on the verge of being ruled out by observations from radio interferometers. It is therefore vital that we understand not only the astrophysical processes governing this signal, but also other inherent processes impacting the signal itself, and in particular line-of-sight effects. Using our suite of fully numerical radiative transfer simulations, we investigate the impact on the redshifted 21-cm from the CD from one of these processes, namely the redshift-space distortions (RSDs). When RSDs are added, the resulting boost to the power spectra makes the signal more or equally detectable for our models for all redshifts, further strengthening hopes that a power spectra measurement of the CD will be possible. RSDs lead to anisotropy in the signal at the beginning and end of the CD, but not while X-ray heating is underway. The inclusion of RSDs, however, decreases detectability of the non-Gaussianity of fluctuations from inhomogeneous X-ray heating as measured by the skewness and kurtosis. On the other hand, mock observations created from all our simulations that include telescope noise corresponding to 1000 h of observation with the Square Kilometre Array telescope show that we may be able to image the CD for all heating models considered and suggest RSDs dramatically boost fluctuations coming from the inhomogeneous Ly α background.

ABSTRACT Star-forming galaxies are rich reservoirs of dust, both warm and cold. But the cold dust emission is faint alongside the relatively bright and ubiquitous warm dust emission. Recently, evidence for a very cold dust (VCD) component has also been revealed via millimetre/submillimetre (mm/sub-mm) photometry of some galaxies. This component, despite being the most massive of the three dust components in star-forming galaxies, is by virtue of its very low temperature, faint and hard to detect together with the relatively bright emission from warmer dust. Here, we analyse the dust content of a carefully selected sample of four galaxies detected by IRAS, WISE, and South Pole Telescope (SPT), whose spectral energy distributions (SEDs) were modelled to constrain their potential cold dust content. Low-frequency radio observations using the Giant Metrewave Radio Telescope (GMRT) were carried out to segregate cold dust emission from non-thermal emission in mm/sub-mm wavebands. We also carried out AstroSat/Ultraviolet Imaging Telescope (UVIT) observations for some galaxies to constrain their SED at shorter wavelengths so as to enforce energy balance for the SED modelling. We constructed their SEDs across a vast wavelength range (extending from UV to radio frequencies) by assembling global photometry from GALEX FUV + NUV, UVIT, Johnson BRI, 2MASS, WISE, IRAC, IRAS, AKARI, ISO PHOT, Planck HFI, SPT, and GMRT. The SEDs were modelled with cigale to estimate their basic properties, in particular to constrain the masses of their total and VCD components. Although the galaxies’ dust masses are dominated by warmer dust, there are hints of VCD in two of the targets, NGC 7496 and NGC 7590.

We investigate thin and thick stellar disc formation in Milky Way-mass galaxies using 12 FIRE-2 cosmological zoom-in simulations. All simulated galaxies experience an early period of bursty star formation that transitions to a late-time steady phase of near-constant star formation. Stars formed during the late-time steady phase have more circular orbits and thin-disc-like morphology at z = 0, while stars born during the bursty phase have more radial orbits and thick-disc structure. The median age of thick-disc stars at z = 0 correlates strongly with this transition time. We also find that galaxies with an earlier transition from bursty to steady star formation have a higher thin-disc fractions at z = 0. Three of our systems have minor mergers with Large Magellanic Cloud-size satellites during the thin-disc phase. These mergers trigger short starbursts but do not destroy the thin disc nor alter broad trends between the star formation transition time and thin/thick-disc properties. If our simulations are representative of the Universe, then stellar archaeological studies of the Milky Way (or M31) provide a window into past star formation modes in the Galaxy. Current age estimates of the Galactic thick disc would suggest that the Milky Way transitioned from bursty to steady phase ~6.5 Gyr ago; prior to that time the Milky Way likely lacked a recognizable thin disc.

In hierarchical structure formation, metal-poor stars in and around the Milky Way (MW) originate primarily from mergers of lower mass galaxies. A common expectation is therefore that metal-poor stars should have isotropic, dispersion-dominated orbits that do not correlate strongly with the MW disc. However, recent observations of stars in the MW show that metal-poor ([Fe/H] ≲ -2) stars are preferentially on prograde orbits with respect to the disc. Using the Feedback In Realistic Environments 2 (FIRE-2) suite of cosmological zoom-in simulations of MW/M31-mass galaxies, we investigate the prevalence and origin of prograde metal-poor stars. Almost all (11 of 12) of our simulations have metal-poor stars on preferentially prograde orbits today and throughout most of their history: we thus predict that this is a generic feature of MW/M31-mass galaxies. The typical prograde-to-retrograde ratio is ~2:1, which depends weakly on stellar metallicity at [Fe/H] ~ -1. These trends predicted by our simulations agree well with MW observations. Prograde metal-poor stars originate largely from a single Large/Small Magellanic Cloud (LMC/SMC)-mass gas-rich merger 7-12.5 Gyr ago, which deposited existing metal-poor stars and significant gas on an orbital vector that sparked the formation of and/or shaped the orientation of a long-lived stellar disc, giving rise to a prograde bias for all low-metallicity stars. We find subdominant contributions from in situ stars formed in the host galaxy before this merger, and in some cases, additional massive mergers. We find few clear correlations between any properties of our MW/M31-mass galaxies at z = 0 and the degree of this prograde bias as a result of diverse merger scenarios.

We study the projected spatial offset between the ultraviolet continuum and Ly α emission for 65 lensed and unlensed galaxies in the Epoch of Reionization (5 ≤ z ≤ 7), the first such study at these redshifts, in order to understand the potential for these offsets to confuse estimates of the Ly α properties of galaxies observed in slit spectroscopy. While we find that ∼40 per cent of galaxies in our sample show significant projected spatial offsets ($|\Delta {\rm {Ly}\alpha -\rm {UV}}|$), we find a relatively modest average projected offset of $|\widetilde{\Delta }{\rm {Ly}\alpha -\rm {UV}}|$ = 0.61 ± 0.08 proper kpc for the entire sample. A small fraction of our sample, ∼10 per cent, exhibit offsets in excess of 2 proper kpc, with offsets seen up to ∼4 proper kpc, sizes that are considerably larger than the effective radii of typical galaxies at these redshifts. An internal comparison and a comparison to studies at lower redshift yielded no significant evidence of evolution of $|\Delta {\rm {Ly}\alpha -\rm {UV}}|$ with redshift. In our sample, ultraviolet (UV)-bright galaxies ($\widetilde{L{\mathrm{ UV}}}/L{\ast }{\mathrm{ UV}}=0.67$) showed offsets a factor of three greater than their fainter counterparts ($\widetilde{L{\mathrm{ UV}}}/L{\ast }{\mathrm{ UV}}=0.10$), 0.89 ± 0.18 versus 0.27 ± 0.05 proper kpc, respectively. The presence of companion galaxies and early stage merging activity appeared to be unlikely causes of these offsets. Rather, these offsets appear consistent with a scenario in which internal anisotropic processes resulting from stellar feedback, which is stronger in UV-brighter galaxies, facilitate Ly α fluorescence and/or backscattering from nearby or outflowing gas. The reduction in the Ly α flux due to offsets was quantified. It was found that the differential loss of Ly α photons for galaxies with average offsets is not, if corrected for, a limiting factor for all but the narrowest slit widths (

We study the escape fraction of ionizing photons (fesc) in two cosmological zoom-in simulations of galaxies in the reionization era with halo mass Mhalo ∼1010 and $10{11}\, \mathrm{ M}-{\odot }$ (stellar mass M∗ ∼107 and $109\, \mathrm{ M}-{\odot }$) at z = 5 from the Feedback in Realistic Environments project. These simulations explicitly resolve the formation of proto-globular clusters (GCs) self-consistently, where 17-39 per cent of stars form in bound clusters during starbursts. Using post-processing Monte Carlo radiative transfer calculations of ionizing radiation, we compute fesc from cluster stars and non-cluster stars formed during a starburst over ∼100 Myr in each galaxy. We find that the averaged fesc over the lifetime of a star particle follows a similar distribution for cluster stars and non-cluster stars. Clusters tend to have low fesc in the first few Myr, presumably because they form preferentially in more extreme environments with high optical depths; the fesc increases later as feedback starts to destroy the natal cloud. On the other hand, some non-cluster stars formed between cluster complexes or in the compressed shells at the front of a superbubble can also have high fesc. We find that cluster stars on average have comparable fesc to non-cluster stars. This result is robust across several star formation models in our simulations. Our results suggest that the fraction of ionizing photons from proto-GCs to cosmic reionization is comparable to the cluster formation efficiencies in high-redshift galaxies and thus proto-GCs likely contribute an appreciable fraction of photons but are not the dominant sources for reionization.

Characterizing the predicted environments of dwarf galaxies like the LargeMagellanic Cloud (LMC) is becoming increasingly important as next generationsurveys push sensitivity limits into this low-mass regime at cosmologicaldistances. We study the environmental effects of LMC-mass halos ($M_{200m} \sim10^{11}$ M$_\odot$) on their populations of satellites ($M_\star \geq 10^4$M$_\odot$) using a suite of zoom-in simulations from the Feedback In RealisticEnvironments (FIRE) project. Our simulations predict significant hot coronaswith $T\sim10^5$ K and $M_\text{gas}\sim10^{9.5}$ M$_\odot$. We identifysignatures of environmental quenching in dwarf satellite galaxies, particularlyfor satellites with intermediate mass ($M_\star = 10^{6-7}$ M$_\odot$). The gascontent of such objects indicates ram-pressure as the likely quenchingmechanism, sometimes aided by star formation feedback. Satellites of LMC-masshosts replicate the stellar mass dependence of the quiescent fraction found insatellites of MW mass hosts (i.e. that the quiescent fraction increases asstellar mass decreases). Satellites of LMC-mass hosts have a wider variety ofquenching times when compared to the strongly bi-modal distribution ofquenching times of nearby centrals. Finally, we identify significant tidalstellar structures around four of our six LMC-analogs, suggesting that stellarstreams may be common. These tidal features originated from satellites on closeorbits, extend to $\sim$80 kpc from the central galaxy, and contain$\sim10^{6-7}$ M$_\odot$~of stars.

AbstractThis Science White Paper, prepared in response to the ESA Voyage 2050 call for long-term mission planning, aims to describe the various science possibilities that can be realized with an L-class space observatory that is dedicated to the study of the interactions of cosmic microwave background (CMB) photons with the cosmic web. Our aim is specifically to use the CMB as a backlight – and survey the gas, total mass, and stellar content of the entire observable Universe by means of analyzing the spatial and spectral distortions imprinted on it. These distortions result from two major processes that impact on CMB photons: scattering by free electrons and atoms (Sunyaev-Zeldovich effect in diverse forms, Rayleigh scattering, resonant scattering) and deflection by gravitational potential (lensing effect). Even though the list of topics collected in this White Paper is not exhaustive, it helps to illustrate the exceptional diversity of major scientific questions that can be addressed by a space mission that will reach an angular resolution of 1.5 arcmin (goal 1 arcmin), have an average sensitivity better than 1 μK-arcmin, and span the microwave frequency range from roughly 50 GHz to 1 THz. The current paper also highlights the synergy of our Backlight mission concept with several upcoming and proposed ground-based CMB experiments.

We examine the prevalence, longevity, and causes of planes of satellite dwarf galaxies, as observed in the Local Group. We use 14 Milky Way/Andromeda-(MW/M31) mass host galaxies from the Feedback In Realistic Environments-2 simulations. We select the 14 most massive satellites by stellar mass within ≤ 300, kpc of each host and correct for incompleteness from the foreground galactic disc when comparing to the MW. We find that MW-like planes as spatially thin and/or kinematically coherent as observed are uncommon, but they do exist in our simulations. Spatially thin planes occur in 1-2 per cent of snapshots during z = 0-0.2, and kinematically coherent planes occur in 5 per cent of snapshots. These planes are generally transient, surviving for

Observations indicate that a continuous supply of gas is needed to maintainobserved star formation rates in large, disky galaxies. To fuel star formation,gas must reach the inner regions of such galaxies. Despite its crucialimportance for galaxy evolution, how and where gas joins galaxies is poorlyconstrained observationally and is rarely explored in fully cosmologicalsimulations. To investigate gas accretion in the vicinity of galaxies, weanalyze the FIRE-2 cosmological zoom-in simulations for 4 Milky Way massgalaxies (M_halo ~ 10E12 solar masses), focusing on simulations with cosmic rayphysics. We find that at z~0, gas approaches the disk with angular momentumsimilar to the gaseous disk edge and low radial velocities, piling-up near theedge and settling into full rotational support. Accreting gas movespredominantly parallel to the disk with small but nonzero vertical velocitycomponents, and joins the disk largely in the outskirts as opposed to "raining"down onto the disk. Once in the disk, gas trajectories are complex, beingdominated by spiral arm induced oscillations and feedback. However, time andazimuthal averages show clear but slow net radial infall with transport speedsof 1-3 km/s and net mass fluxes through the disk on the order of one solar massper year, comparable to the star formation rates of the galaxies and decreasingtowards galactic center as gas is sunk into star formation. These rates areslightly higher in simulations without cosmic rays (1-7 km/s, ~4-5 solar massesper year). We find overall consistency of our results with observationalconstraints and discuss prospects of future observations of gas flows in andaround galaxies.

Recent searches for the hosts of high-redshift ($z \sim 4$) damped Ly$\alpha$absorbers (DLAs) have detected bright galaxies at distances of tens of kpc fromthe DLA. Using the FIRE-2 cosmological zoom simulations, we argue that theserelatively large distances are due to a predominantly cool and neutral innercircumgalactic medium (CGM) surrounding high-redshift galaxies. The inner CGMis cool because of the short cooling time of hot gas in $\lesssim10^{12}$ Msunhalos, which implies that accretion and feedback energy are radiated quickly,while it is neutral due to the high volume densities and column densities athigh redshift which shield cool gas from photoionization. Our analysis predictslarge DLA covering factors ($\gtrsim50\%$) out to impact parameters $\sim0.3((1+ z)/5)^{3/2}\ R_{\rm vir}$ from the central galaxies at $z > 1$, equivalent toa physical distance of $\sim 21 M_{12}^{1/3} ((1 + z)/5)^{1/2}$ kpc ($R_{\rmvir}$ and $M_{12}$ are the halo virial radius and mass in units of $10^{12}$Msun, respectively). This implies that DLA covering factors at $z \sim 4$ maybe comparable to unity out to a distance $\sim 10$ times larger than stellarhalf-mass radii. A predominantly neutral inner CGM in the early universesuggests that its mass and metallicity can be directly constrained by CGMabsorption surveys, without resorting to large ionization corrections asrequired for ionized CGM.

ABSTRACT Star-forming galaxies are rich reservoirs of dust, both warm and cold. But the cold dust emission is faint alongside the relatively bright and ubiquitous warm dust emission. Recently, evidence for a very cold dust (VCD) component has also been revealed via millimetre/submillimetre (mm/sub-mm) photometry of some galaxies. This component, despite being the most massive of the three dust components in star-forming galaxies, is by virtue of its very low temperature, faint and hard to detect together with the relatively bright emission from warmer dust. Here, we analyse the dust content of a carefully selected sample of four galaxies detected by IRAS, WISE, and South Pole Telescope (SPT), whose spectral energy distributions (SEDs) were modelled to constrain their potential cold dust content. Low-frequency radio observations using the Giant Metrewave Radio Telescope (GMRT) were carried out to segregate cold dust emission from non-thermal emission in mm/sub-mm wavebands. We also carried out AstroSat/Ultraviolet Imaging Telescope (UVIT) observations for some galaxies to constrain their SED at shorter wavelengths so as to enforce energy balance for the SED modelling. We constructed their SEDs across a vast wavelength range (extending from UV to radio frequencies) by assembling global photometry from GALEX FUV + NUV, UVIT, Johnson BRI, 2MASS, WISE, IRAC, IRAS, AKARI, ISO PHOT, Planck HFI, SPT, and GMRT. The SEDs were modelled with cigale to estimate their basic properties, in particular to constrain the masses of their total and VCD components. Although the galaxies’ dust masses are dominated by warmer dust, there are hints of VCD in two of the targets, NGC 7496 and NGC 7590.

Line intensity mapping (LIM) proposes to efficiently observe distant faint galaxies and map the matter density field at high redshift. Building upon the formalism in a companion paper, we first highlight the degeneracies between cosmology and astrophysics in LIM. We discuss what can be constrained from measurements of the mean intensity and redshift-space power spectra. With a sufficient spectral resolution, the large-scale redshift-space distortions of the 2-halo term can be measured, helping to break the degeneracy between bias and mean intensity. With a higher spectral resolution, measuring the small-scale redshift-space distortions disentangles the 1-halo and shot noise terms. Cross-correlations with external galaxy catalogs or lensing surveys further break degeneracies. We derive requirements for experiments similar to SPHEREx, HETDEX, CDIM, COMAP and CONCERTO. We then revisit the question of the optimality of the LIM observables, compared to galaxy detection, for astrophysics and cosmology. We use a matched filter to compute the luminosity detection threshold for individual sources. We show that LIM contains information about galaxies too faint to detect, in the high-noise or high-confusion regimes. We quantify the sparsity and clustering bias of the detected sources and compare them to LIM, showing in which cases LIM is a better tracer of the matter density. We extend previous work by answering these questions as a function of Fourier scale, including for the first time the effect of cosmic variance, pixel-to-pixel correlations, luminosity-dependent clustering bias and redshift-space distortions.

Line intensity mapping (LIM) is a rapidly emerging technique for constraining cosmology and galaxy formation using multi-frequency, low angular resolution maps. Many LIM applications crucially rely on cross-correlations of two line intensity maps, or of intensity maps with galaxy surveys or galaxy/CMB lensing. We present a consistent halo model to predict all these cross-correlations and enable joint analyses, in 3D redshift-space and for 2D projected maps. We extend the conditional luminosity function formalism to the multi-line case, to consistently account for correlated scatter between multiple galaxy line luminosities. This allows us to model the scale-dependent decorrelation between two line intensity maps, a key input for foreground rejection and for approaches that estimate auto-spectra from cross-spectra. This also enables LIM cross-correlations to reveal astrophysical properties of the interstellar medium inacessible with LIM auto-spectra. We expose the different sources of luminosity scatter or "line noise"in LIM, and clarify their effects on the 1-halo and galaxy shot noise terms. In particular, we show that the effective number density of halos can in some cases exceed that of galaxies, counterintuitively. Using observational and simulation input, we implement this halo model for the Hα, [Oiii], Lyman-α, CO and [Cii] lines. We encourage observers and simulators to measure galaxy luminosity correlation coefficients for pairs of lines whenever possible. Our code is publicly available at https://github.com/EmmanuelSchaan/HaloGen/tree/LIM. In a companion paper, we use this halo model formalism and code to highlight the degeneracies between cosmology and astrophysics in LIM, and to compare the LIM observables to galaxy detection for a number of surveys.

Self-interacting dark matter (SIDM) models offer one way to reconcileinconsistencies between observations and predictions from collisionless colddark matter (CDM) models on dwarf-galaxy scales. In order to incorporate theeffects of both baryonic and SIDM interactions, we study a suite ofcosmological-baryonic simulations of Milky-Way (MW)-mass galaxies from theFeedback in Realistic Environments (FIRE-2) project where we vary the SIDMself-interaction cross-section $\sigma/m$. We compare the shape of the maindark matter (DM) halo at redshift $z=0$ predicted by SIDM simulations (at$\sigma/m=0.1$, $1$, and $10$ cm$^2$ g$^{-1}$) with CDM simulations using thesame initial conditions. In the presence of baryonic feedback effects, we findthat SIDM models do not produce the large differences in the inner structure ofMW-mass galaxies predicted by SIDM-only models. However, we do find that theradius where the shape of the total mass distribution begins to differ fromthat of the stellar mass distribution is dependent on $\sigma/m$. Thistransition could potentially be used to set limits on the SIDM cross-section inthe MW.

Abstract We use the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) project as a template to demonstrate how deep spectrophotometric surveys covering large cosmological volumes over extended fields (1– $15\, \rm{deg^2}$ ) with a mid-IR imaging spectrometer (17– $36\, \rm{\rm{\upmu m}}$ ) in conjunction with deep $70\, \rm{\rm{\upmu m}}$ photometry with a far-IR camera, at wavelengths which are not affected by dust extinction can answer the most crucial questions in current galaxy evolution studies. A SPICA-like mission will be able for the first time to provide an unobscured three-dimensional (3D, i.e. x, y, and redshift z) view of galaxy evolution back to an age of the universe of less than $\sim$ 2 Gyrs, in the mid-IR rest frame. This survey strategy will produce a full census of the Star Formation Rate (SFR) in the universe, using polycyclic aromatic hydrocarbons (PAH) bands and fine-structure ionic lines, reaching the characteristic knee of the galaxy luminosity function, where the bulk of the population is distributed, at any redshift up to $z \sim 3.5$ . Deep follow-up pointed spectroscopic observations with grating spectrometers onboard the satellite, across the full IR spectral range (17– $210\, \rm{\rm{\upmu m}}$ ), would simultaneously measure Black Hole Accretion Rate (BHAR), from high-ionisation fine-structure lines, and SFR, from PAH and low- to mid-ionisation lines in thousands of galaxies from solar to low metallicities, down to the knee of their luminosity functions. The analysis of the resulting atlas of IR spectra will reveal the physical processes at play in evolving galaxies across cosmic time, especially its heavily dust-embedded phase during the activity peak at the cosmic noon ( $z \sim 1$ –3), through IR emission lines and features that are insensitive to the dust obscuration.

We use the FIRE-2 cosmological simulations to study the formation of a quasi-static, virial-temperature gas phase in the circumgalactic medium (CGM) at redshifts 0 < z < 5 and how the formation of this virialized phase affects the evolution of galactic disks. We demonstrate that when the halo mass crosses ∼1012 Me, the cooling time of shocked gas in the inner CGM (∼0.1Rvir, where Rvir is the virial radius) exceeds the local free-fall time. The inner CGM then experiences a transition from on average subvirial temperatures (T = Tvir), large pressure fluctuations, and supersonic inflow/outflow velocities to virial temperatures (T ∼ Tvir), uniform pressures, and subsonic velocities. This transition occurs when the outer CGM (∼0.5Rvir) is already subsonic and has a temperature ∼Tvir, indicating that the longer cooling times at large radii allow the outer CGM to virialize at lower halo masses than the inner CGM. This outside-in CGM virialization scenario is in contrast with inside-out scenarios commonly envisioned based on more idealized simulations. We demonstrate that inner CGM virialization coincides with abrupt changes in the central galaxy and its stellar feedback: the galaxy settles into a stable rotating disk, star formation transitions from “bursty” to “steady,” and stellar-driven galaxy-scale outflows are suppressed. Our results thus suggest that CGM virialization is initially associated with the formation of rotation-dominated thin galactic disks, rather than with the quenching of star formation as often assumed.

Stellar streams record the accretion history of their host galaxy. We presenta set of simulated streams from disrupted dwarf galaxies in 13 cosmologicalsimulations of Milky Way (MW)-mass galaxies from the FIRE-2 suite at $z=0$,including 7 isolated Milky Way-mass systems and 6 hosts resembling the MW-M31pair (full dataset at: https://flathub.flatironinstitute.org/sapfire). Intotal, we identify 106 simulated stellar streams, with no significantdifferences in the number of streams and masses of their progenitors betweenthe isolated and paired environments. We resolve simulated streams with stellarmasses ranging from $\sim 5\times10^5$ up to $\sim 10^{9} M_\odot$, similar tothe mass range between the Orphan and Sagittarius streams in the MW. We confirmthat present-day simulated satellite galaxies are good proxies for stellarstream progenitors, with similar properties including their stellar massfunction, velocity dispersion, [Fe/H] and [$\alpha$/H] evolution tracks, andorbital distribution with respect to the galactic disk plane. Each progenitor'slifetime is marked by several important timescales: its infall, star-formationquenching, and stream-formation times. We show that the ordering of thesetimescales is different between progenitors with stellar masses higher andlower than $\sim 2\times10^6 M_\odot$. Finally, we show that the main factorcontrolling the rate of phase-mixing, and therefore fading, of tidal streamsfrom satellite galaxies in MW-mass hosts is non-adiabatic evolution of the hostpotential. Other factors commonly used to predict phase-mixing timescales, suchas progenitor mass and orbital circularity, show virtually no correlation withthe number of dynamical times required for a stream to become phase-mixed.

The standard picture of galaxy formation motivates the decomposition of theMilky Way into 3--4 stellar populations with distinct kinematic and elementalabundance distributions: the thin disk, thick disk, bulge, and stellar halo. Totest this idea, we construct a Gaussian mixture model (GMM) for both simulatedand observed stars in the Solar neighborhood, using measured velocities andiron abundances (i.e., an augmented Toomre diagram) as the distributions to bedecomposed. We compare results for the Gaia-APOGEE DR16 crossmatch catalog ofthe Solar neighborhood with those from a suite of synthetic Gaia-APOGEEcrossmatches constructed from FIRE-2 cosmological simulations of Milky Way-massgalaxies. We find that in both the synthetic and real data, the best-fit GMMuses five independent components, some of whose properties resemble thestandard populations predicted by galaxy formation theory. Two components canbe identified unambiguously as the thin disk and another as the halo. However,instead of a single counterpart to the thick disk, there are three intermediatecomponents with different age and alpha abundance distributions (although thesedata are not used to construct the model). We use decompositions of thesynthetic data to show that the classified components indeed correspond tostars with different origins. By analogy with the simulated data, we show thatour mixture model of the real Gaia-APOGEE crossmatch distinguishes thefollowing components: (1) a classic thin disk of young stars on circular orbits(46%), (2) thin disk stars heated by interactions with satellites (22%), (3, 4)two components representing the velocity asymmetry of the alpha-enhanced thickdisk (27%), and (5) a stellar halo consistent with early, massive accretion(4%).

In the currently favored cosmological paradigm galaxies form hierarchicallythrough the accretion of numerous satellite galaxies. Since the satellites aremuch less massive than the host halo, they occupy a small fraction of thevolume in action space defined by the potential of the host halo. Since actionsare conserved when the potential of the host halo changes adiabatically, starsfrom an accreted satellite are expected to remain clustered in action space asthe host halo evolves. In this paper, we identify accreted satellites in threeMilky Way like disk galaxies from the cosmological baryonic FIRE-2 simulationsby tracking satellite galaxies through simulation snapshots. We then try torecover these satellites by applying the cluster analysis algorithm Enlink tothe orbital actions of accreted star particles in the present-day snapshot. Wedefine several metrics to quantify the success of the clustering algorithm anduse these metrics to identify well-recovered and poorly-recovered satellites.We plot these satellites in the infall time-progenitor mass (or stellar mass)space, and determine the boundaries between the well-recovered andpoorly-recovered satellites in these two spaces with classification treemethod. The groups found by Enlink are more likely to correspond to a realsatellite if they have high significance, a quantity assigned by Enlink. Sincecosmological simulations predict that most stellar halos have a population ofinsitu stars, we test the ability of Enlink to recover satellites when thesample is contaminated by 10-50% of insitu star particles, and show that mostof the satellites well-recovered by Enlink in the absence of insitu stars, staywell-recovered even with 50% contamination. We thus expect that, in the future,cluster analysis in action space will be useful in upcoming data sets (e.g.Gaia) for identifying accreted satellites in the Milky Way.

The complex interplay of magnetohydrodynamics, gravity, and supersonic turbulence in the interstellar medium (ISM) introduces a non-Gaussian structure that can complicate a comparison between theory and observation. In this paper, we show that the wavelet scattering transform (WST), in combination with linear discriminant analysis (LDA), is sensitive to non-Gaussian structure in 2D ISM dust maps. WST-LDA classifies magnetohydrodynamic (MHD) turbulence simulations with up to a 97% true positive rate in our testbed of 8 simulations with varying sonic and Alfvénic Mach numbers. We present a side-by-side comparison with two other methods for non-Gaussian characterization, the reduced wavelet scattering transform (RWST) and the three-point correlation function (3PCF). We also demonstrate the 3D-WST-LDA, and apply it to the classification of density fields in position-position-velocity (PPV) space, where density correlations can be studied using velocity coherence as a proxy. WST-LDA is robust to common observational artifacts, such as striping and missing data, while also being sensitive enough to extract the net magnetic field direction for sub-Alfvénic turbulent density fields. We include a brief analysis of the effect of point-spread functions and image pixelization on 2D-WST-LDA applied to density fields, which informs the future goal of applying WST-LDA to 2D or 3D all-sky dust maps to extract hydrodynamic parameters of interest.

We present the steps taken to produce a reliable and complete input galaxy catalogue for the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) using the photometric Legacy Survey DR8 DECam. We analyse some of the main issues faced in the selection of targets for the DESI BGS, such as star-galaxy separation, contamination by fragmented stars and bright galaxies. Our pipeline utilizes a new way to select BGS galaxies using Gaia photometry and we implement geometrical and photometric masks that reduce the number of spurious objects. The resulting catalogue is cross-matched with the Galaxy And Mass Assembly (GAMA) survey to assess the completeness of the galaxy catalogue and the performance of the target selection. We also validate the clustering of the sources in our BGS catalogue by comparing with mock catalogues and the Sloan Digital Sky Survey (SDSS) data. Finally, the robustness of the BGS selection criteria is assessed by quantifying the dependence of the target galaxy density on imaging and other properties. The largest systematic correlation we find is a 7 per cent suppression of the target density in regions of high stellar density.

The thermal and kinematic Sunyaev-Zel'dovich effects (tSZ, kSZ) probe the thermodynamic properties of the circumgalactic and intracluster medium (CGM and ICM) of galaxies, groups, and clusters, since they are proportional, respectively, to the integrated electron pressure and momentum along the line of sight. We present constraints on the gas thermodynamics of CMASS (constant stellar mass) galaxies in the Baryon Oscillation Spectroscopic Survey using new measurements of the kSZ and tSZ signals obtained in a companion paper [Schaan et al.]. Combining kSZ and tSZ measurements, we measure within our model the amplitude of energy injection ϵM⋆c2, where M⋆ is the stellar mass, to be ϵ=(40±9)×10-6, and the amplitude of the nonthermal pressure profile to be αNth

The scattering of cosmic microwave background (CMB) photons off the free-electron gas in galaxies and clusters leaves detectable imprints on high resolution CMB maps: the thermal and kinematic Sunyaev-Zel'dovich effects (tSZ and kSZ respectively). We use combined microwave maps from the Atacama Cosmology Telescope DR5 and Planck in combination with the CMASS (mean redshift ⟨z

We characterize mass, momentum, energy and metal outflow rates of multi-phasegalactic winds in a suite of FIRE-2 cosmological "zoom-in" simulations from theFeedback in Realistic Environments (FIRE) project. We analyze simulations oflow-mass dwarfs, intermediate-mass dwarfs, Milky Way-mass halos, andhigh-redshift massive halos. Consistent with previous work, we find that dwarfseject about 100 times more gas from their interstellar medium (ISM) than theyform in stars, while this mass "loading factor" drops below one in massivegalaxies. Most of the mass is carried by the hot phase ($>10^5$ K) in massivehalos and the warm phase ($10^3-10^5$ K) in dwarfs; cold outflows ($

The tightest and most robust cosmological results of the next decade will beachieved by bringing together multiple surveys of the Universe. This endeavorhas to happen across multiple layers of the data processing and analysis, e.g.,enhancements are expected from combining Euclid, Rubin, and Roman (as well asother surveys) not only at the level of joint processing and catalogcombination, but also during the post-catalog parts of the analysis such as thecosmological inference process. While every experiment builds their ownanalysis and inference framework and creates their own set of simulations,cross-survey work that homogenizes these efforts, exchanges information fromnumerical simulations, and coordinates details in the modeling of astrophysicaland observational systematics of the corresponding datasets is crucial.

As the signal-to-noise of Sunyaev-Zeldovich (SZ) cross-correlationmeasurements of galaxies improves our ability to infer properties about thecircumgalactic medium (CGM), we will transition from being limited bystatistical uncertainties to systematic uncertainties. Using thermodynamicprofiles of the CGM created from the IllustrisTNG (The Next Generation)simulations we investigate the importance of specific choices in modeling thegalaxy sample. These choices include different sample selections in thesimulation (stellar versus halo mass, color selections) and different fittingmodels (matching by the shape of the mass distribution, inclusion of a two-haloterm). We forward model a mock galaxy sample into projected SZ observableprofiles and fit these profiles to a generalized Navarro-Frenk-White profileusing forecasted errors of the upcoming Simons Observatory experiment. We testthe number of free parameters in the fits and show that this is anothermodeling choice that yields different results. Finally, we show how differentfitting models can reproduce parameters of a fiducial profile, and show thatthe addition of a two-halo term and matching by the mass distribution of thesample are extremely important modeling choices to consider.

We explore the impact of outer stellar companions on the occurrence rate of giant planets detected with radial velocities. We searched for stellar and planetary companions to a volume-limited sample of solar-type stars within 25 pc. Using adaptive optics imaging observations from the Lick 3 m and Palomar 200″ Telescopes, we characterized the multiplicity of our sample stars, down to the bottom of the main sequence. With these data, we confirm field star multiplicity statistics from previous surveys. We additionally combined three decades of radial velocity (RV) data from the California Planet Search with newly collected RV data from Keck/HIRES and the Automated Planet Finder/Levy Spectrometer to search for planetary companions in these same systems. Using an updated catalog of both stellar and planetary companions, as well as detailed injection/recovery tests to determine our sensitivity and completeness, we measured the occurrence rate of planets among the single- and multiple-star systems. We found that planets with masses in the range of 0.1–10 MJ and with semimajor axes of 0.1–10 au have an occurrence rate of 0.18-+0.030.04 planets per star when they orbit single stars and an occurrence rate of 0.12 ± 0.04 planets per star when they orbit a star in a binary system. Breaking the sample down by the binary separation, we found that only one planet-hosting binary system had a binary separation 100 au and 0.04-+0.020.04 planets per star for binaries with separation aB < 100 au. The similarity in the planet occurrence rate around single stars and wide primaries implies that wide binary systems should actually host more planets than single-star systems, since they have more potential host stars. We estimated a system-wide planet occurrence rate of 0.3 planets per wide binary system for binaries with separations aB > 100 au. Finally, we found evidence that giant planets in binary systems have a different semimajor-axis distribution than their counterparts in single-star systems. The planets in the single-star sample had a significantly higher occurrence rate outside of 1 au than inside 1 au by nearly 4σ, in line with expectations that giant planets are most common near the snow line. However, the planets in the wide binary systems did not follow this distribution, but rather had equivalent occurrence rates interior and exterior to 1 au. This may point to binary-mediated planet migration acting on our sample, even in binaries wider than 100 au.

Compact starburst galaxies are thought to include many or most of thegalaxies from which substantial Lyman continuum emission can escape into theintergalactic medium. Li and Malkan (2018) used SDSS photometry to find apopulation of such starburst galaxies at z~0.5. They were discovered by theirextremely strong [OIII]4959+5007 emission lines, which produce a clearlydetectable excess brightness in the i bandpass, compared with surroundingfilters. We therefore used the HST/COS spectrograph to observe two of the newlydiscovered i-band excess galaxies around their Lyman limits. One has stronglydetected continuum below its Lyman limit, corresponding to a relative escapefraction of ionizing photons of 20+/-2%. The other, which is less compact in UVimaging, has a 2-sigma upper limit to its Lyman escape fraction of

ABSTRACT To understand the cosmic accretion history of supermassive black holes, separating the radiation from active galactic nuclei (AGNs) and star-forming galaxies (SFGs) is critical. However, a reliable solution on photometrically recognizing AGNs still remains unsolved. In this work, we present a novel AGN recognition method based on Deep Neural Network (Neural Net; NN). The main goals of this work are (i) to test if the AGN recognition problem in the North Ecliptic Pole Wide (NEPW) field could be solved by NN; (ii) to show that NN exhibits an improvement in the performance compared with the traditional, standard spectral energy distribution (SED) fitting method in our testing samples; and (iii) to publicly release a reliable AGN/SFG catalogue to the astronomical community using the best available NEPW data, and propose a better method that helps future researchers plan an advanced NEPW data base. Finally, according to our experimental result, the NN recognition accuracy is around 80.29 per cent–85.15 per cent, with AGN completeness around 85.42 per cent–88.53 per cent and SFG completeness around 81.17 per cent–85.09 per cent.

Motivated by the discovery of the ultra-strong emission line starburstgalaxies (EELGs) known as "green pea galaxies", we consider here theircontribution to the intergalactic flux of ionizing UV at high redshifts. Mostgalaxies that have been observed show a precipitous drop in their flux bluewardof the Lyman limit. However, recent observations of EELGs have discovered thatmany more Lyman continuum photons escape from them into intergalactic spacethan was previously suspected. We calculate their contribution to theextragalactic background light (EBL). We also calculate the effect of thesephotons on the absorption of high energy $\gamma$-rays. For the more distant$\gamma$-ray sources, particularly at $z \ge 3$, the intergalactic opacityabove a few GeV is significantly higher than previous estimates which ignoredthe Lyman continuum photons. We calculate the results of this increased opacityon observed $\gamma$-ray spectra, which produces a high-energy turnoverstarting at lower energies than previously thought, and a gradual spectralsteepening that may also be observable.

ABSTRACT The AKARI space infrared telescope has performed near-infrared to mid-infrared (MIR) observations on the North Ecliptic Pole Wide (NEPW) field (5.4 deg2) for about 1 yr. AKARI took advantage of its continuous nine photometric bands, compared with NASA's Spitzer and Wide-field Infrared Survey Explorer(WISE) space telescopes, which had only four filters with a wide gap in the MIR. The AKARI NEPW field lacked deep and homogeneous optical data, limiting the use of nearly half of the IR sources for extragalactic studies, because of the absence of photometric redshift (photo-z). To remedy this, we have recently obtained deep optical imaging over the NEPW field with five bands (g, r, i, z and Y) of the Hyper Suprime-Camera (HSC) on the Subaru 8-m telescope. We optically identify AKARI-IR sources along with supplementary Spitzer and WISE data as well as pre-existing optical data. In this work, we derive new photo-z using a χ2 template-fitting method code, PHotometric Analysis for Redshift Estimate (Le Phare) and reliable photometry from 26 selected filters including HSC, AKARI, Canada–France–Hawaii Telescope, Maidanak, Kitt Peak National Observatory, Spitzer and WISE data. We take 2026 spectroscopic redshifts (spec-z) from all available spectroscopic surveys over the NEPW field to calibrate and assess the accuracy of the photo-z. At z < 1.5, we achieve a weighted photo-z dispersion of σΔz/(1+z) = 0.053 with η = 11.3 per cent catastrophic errors.

Understanding the rate at which stars form is central to studies of galaxy formation. Observationally, the star formation rates (SFRs) of galaxies are measured using the luminosity in different frequency bands, often under the assumption of a time-steady SFR in the recent past. We use star formation histories (SFHs) extracted from cosmological simulations of star-forming galaxies from the FIRE project to analyse the time-scales to which the H α and far-ultraviolet (FUV) continuum SFR indicators are sensitive. In these simulations, the SFRs are highly time variable for all galaxies at high redshift, and continue to be bursty to z = 0 in dwarf galaxies. When FIRE SFHs are partitioned into their bursty and time-steady phases, the best-fitting FUV time-scale fluctuates from its ∼10 Myr value when the SFR is time-steady to ≥100 Myr immediately following particularly extreme bursts of star formation during the bursty phase. On the other hand, the best-fitting averaging time-scale for H α is generally insensitive to the SFR variability in the FIRE simulations and remains ∼5 Myr at all times. These time-scales are shorter than the 100 and 10 Myr time-scales sometimes assumed in the literature for FUV and H α, respectively, because while the FUV emission persists for stellar populations older than 100 Myr, the time-dependent luminosities are strongly dominated by younger stars. Our results confirm that the ratio of SFRs inferred using H α versus FUV can be used to probe the burstiness of star formation in galaxies.

We explore the origin of stellar metallicity gradients in simulated and observed dwarf galaxies. We use FIRE-2 cosmological baryonic zoom-in simulations of 26 isolated galaxies as well as existing observational data for 10 Local Group dwarf galaxies. Our simulated galaxies have stellar masses between 105.5 and 108.6 MO. Whilst gas-phase metallicty gradients are generally weak in our simulated galaxies, we find that stellar metallicity gradients are common, with central regions tending to be more metal-rich than the outer parts. The strength of the gradient is correlated with galaxy-wide median stellar age, such that galaxies with younger stellar populations have flatter gradients. Stellar metallicty gradients are set by two competing processes: (1) the steady 'puffing' of old, metal-poor stars by feedback-driven potential fluctuations and (2) the accretion of extended, metal-rich gas at late times, which fuels late-time metal-rich star formation. If recent star formation dominates, then extended, metal-rich star formation washes out pre-existing gradients from the 'puffing' process. We use published results from ten Local Group dwarf galaxies to show that a similar relationship between age and stellar metallicity-gradient strength exists among real dwarfs. This suggests that observed stellar metallicity gradients may be driven largely by the baryon/feedback cycle rather than by external environmental effects.

Radio sources at the highest redshifts can provide unique information on the first massive galaxies and black holes, the densest primordial environments, and the epoch of reionization. The number of astronomical objects identified at z > 6 has increased dramatically over the last few years, but previously only three radio-loud (R 2500 = f ν,5 GHz/f ν,2500 Å > 10) sources had been reported at z > 6, with the most distant being a quasar at z = 6.18. Here we present the discovery and characterization of PSO J172.3556+18.7734, a radio-loud quasar at z = 6.823. This source has an Mg ii-based black hole mass of ∼3 × 108 M o˙ and is one of the fastest accreting quasars, consistent with super-Eddington accretion. The ionized region around the quasar is among the largest measured at these redshifts, implying an active phase longer than the average lifetime of the z ⪆ 6 quasar population. From archival data, there is evidence that its 1.4 GHz emission has decreased by a factor of two over the last two decades. The quasar's radio spectrum between 1.4 and 3.0 GHz is steep (α = -1.31). Assuming the measured radio slope and extrapolating to rest-frame 5 GHz, the quasar has a radio-loudness parameter R 2500 ∼ 90. A second steep radio source (α = -0.83) of comparable brightness to the quasar is only 23.″1 away (∼120 kpc at z = 6.82; projection probability

We present a suite of baryonic cosmological zoom-in simulations ofself-interacting dark matter (SIDM) haloes within the ``Feedback In RealisticEnvironment'' (FIRE) project. The three simulated haloes have virial masses of$\sim 10^{12}\, \text{M}_\odot$ at $z=0$, and we study velocity-independentself-interaction cross sections of 1 and 10 ${\rm cm^2 \, g^{-1}}$. We studystar formation rates and the shape of dark matter density profiles of theparent haloes in both cold dark matter (CDM) and SIDM models. Galaxies formedin the SIDM haloes have higher star formation rates at $z\leq1$, resulting inmore massive galaxies compared to the CDM simulations. While both CDM and SIDMsimulations show diverse shape of the dark matter density profiles, the SIDMhaloes can reach higher and more steep central densities within few kpcscompared to the CDM haloes. We identify a correlation between the build-up ofthe stars within the half-mass radii of the galaxies and the growth in thecentral dark matter densities. The thermalization process in the SIDM haloes isenhanced in the presence of a dense stellar component. Hence, SIDM haloes withhighly concentrated baryonic profiles are predicted to have higher central darkmatter densities than the CDM haloes. Overall, the SIDM haloes are moreresponsive to the presence of a massive baryonic distribution than their CDMcounterparts.

We present an analysis of the R ≲ 1.5 kpc core regions of seven simulated Milky Way-mass galaxies, from the FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulation suite, for a finely sampled period (Δt = 2.2 Myr) of 22 Myr at z ≈ 0, and compare them with star formation rate (SFR) and gas surface density observations of the Milky Way's Central Molecular Zone (CMZ). Despite not being tuned to reproduce the detailed structure of the CMZ, we find that four of these galaxies are consistent with CMZ observations at some point during this 22 Myr period. The galaxies presented here are not homogeneous in their central structures, roughly dividing into two morphological classes; (a) several of the galaxies have very asymmetric gas and SFR distributions, with intense (compact) starbursts occurring over a period of roughly 10 Myr, and structures on highly eccentric orbits through the CMZ, whereas (b) others have smoother gas and SFR distributions, with only slowly varying SFRs over the period analyzed. In class (a) centers, the orbital motion of gas and star-forming complexes across small apertures (R ≲ 150 pc, analogously |l| < 1° in the CMZ observations) contributes as much to tracers of star formation/dense gas appearing in those apertures, as the internal evolution of those structures does. These asymmetric/bursty galactic centers can simultaneously match CMZ gas and SFR observations, demonstrating that time-varying star formation can explain the CMZ's low star formation efficiency.

We present the first set of cosmological baryonic zoom-in simulations ofgalaxies including dissipative self-interacting dark matter (dSIDM). Thesesimulations utilize the Feedback In Realistic Environments (FIRE-2) galaxyformation physics, but allow the dark matter to have dissipativeself-interactions analogous to Standard Model forces, parameterized by theself-interaction cross-section per unit mass, $(\sigma/m)$, and thedimensionless degree of dissipation, $0

We report the discovery of TOI-561, a multiplanet system in the galactic thick disk that contains a rocky, ultrashort- period planet. This bright (V = 10.2) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P = 0.44 days, Rp = 1.45 ± 0.11 R⊕), c (TOI-561.01, P = 10.8 days, Rp = 2.90 ± 0.13 R⊕), and d (TOI-561.03, P = 16.3 days, Rp = 2.32 ± 0.16 R⊕). The star is chemically ([Fe/ H] = -0.41 ± 0.05, [a/Fe]=+0.23 ± 0.05) and kinematically consistent with the galactic thick-disk population, making TOI-561 one of the oldest (10 ± 3 Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of 3.2 ± 0.8M⊕ and 5.5+2.0-1.6g cm-3, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is 7.0 ± 2.3M⊕ and 1.6 ± 0.6 g cm-3, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, groundbased photometric follow-up, and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies.

ABSTRACT Extragalactic studies have demonstrated that there is a moderately tight (≈0.3 dex) relationship between galaxy stellar mass (M⋆) and star formation rate (SFR) that holds for star-forming galaxies at M⋆ ∼ 3 × 108–1011 M⊙, i.e. the ‘star formation main sequence’. However, it has yet to be determined whether such a relationship extends to even lower mass galaxies, particularly at intermediate or higher redshifts. We present new results using observations for 714 narrow-band H α-selected galaxies with stellar masses between 106 and 1010 M⊙ (average of 108.2 M⊙) at z ≈ 0.07–0.5. These galaxies have sensitive ultraviolet (UV) to near-infrared photometric measurements and optical spectroscopy. The latter allows us to correct our H α SFRs for dust attenuation using Balmer decrements. Our study reveals that: (1) for low-SFR galaxies, our H α SFRs systematically underpredict compared to far-UV measurements, consistent with other studies; (2) at a given stellar mass (≈108 M⊙), log (specific SFR) evolves as A log (1 + z) with A = 5.26 ± 0.75, and on average, specific SFR increases with decreasing stellar mass; (3) the SFR–M⋆ relation holds for galaxies down to ∼106 M⊙ (∼1.5 dex below previous studies), and over lookback times of up to 5 Gyr, follows a redshift-dependent relation of log (SFR) ∝ α log (M⋆/M⊙) + β z with α = 0.60 ± 0.01 and β = 1.86 ± 0.07; and (4) the observed dispersion in the SFR–M⋆ relation at low stellar masses is ≈0.3 dex. Accounting for survey selection effects using simulated galaxies, we estimate that the true dispersion is ≈0.5 dex.

We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 5 and Cycle 6 observations of CO (2 -1) and CO (3-2) emission at 0"2-0"3 resolution in two radio-bright, brightest group/cluster early-type galaxies, NGC 315 and NGC 4261. The data resolve CO emission that extends within their black hole (BH) spheres of influence (rg), tracing regular Keplerian rotation down to just tens of parsecs from the BHs. The projected molecular gas speeds in the highly inclined (i ≥ 60°) disks rise at least to 500 km s-1 near their galaxy centers. We fit dynamical models of thin-disk rotation directly to the ALMA data cubes and account for the extended stellar mass distributions by constructing galaxy surface brightness profiles corrected for a range of plausible dust extinction values. The best-fit models yield (MBH/109 M⊙)= 2.08 ± 0.01(stat)+0.32-0.14 (sys) for NGC315 and (MBH/109 M⊙) = 1.67 ± 0.10(stat)+0.39-0.24(sys) for NGC 4261, the latter of which is larger than previous estimates by a factor of ~3. The BH masses are broadly consistent with the relations between BH masses and host galaxy properties. These are among the first ALMA observations to map dynamically cold gas kinematics well within the BH-dominated regions of radio galaxies, resolving the respective rg by factors of ~5-10. The observations demonstrate ALMA's ability to precisely measure BH masses in active galaxies, which will enable more confident probes of accretion physics for the most massive galaxies.

In this contribution, we achieve the primary goal of the active galactic nucleus (AGN) STORM campaign by recovering velocity-delay maps for the prominent broad emission lines (Lyα, C iv, He ii, and Hβ) in the spectrum of NGC 5548. These are the most detailed velocity-delay maps ever obtained for an AGN, providing unprecedented information on the geometry, ionization structure, and kinematics of the broad-line region. Virial envelopes enclosing the emission-line responses show that the reverberating gas is bound to the black hole. A stratified ionization structure is evident. The He ii response inside 5-10 lt-day has a broad single-peaked velocity profile. The Lyα, C iv, and Hβ responses extend from inside 2 to outside 20 lt-day, with double peaks at ±2500 km s-1 in the 10-20 lt-day delay range. An incomplete ellipse in the velocity-delay plane is evident in Hβ. We interpret the maps in terms of a Keplerian disk with a well-defined outer rim at R = 20 lt-day. The far-side response is weaker than that from the near side. The line-center delay days gives the inclination i ≈ 45°. The inferred black hole mass is M BH ≈ 7 × 107 M o˙. In addition to reverberations, the fit residuals confirm that emission-line fluxes are depressed during the "BLR Holiday"identified in previous work. Moreover, a helical "Barber-Pole"pattern, with stripes moving from red to blue across the C iv and Lyα line profiles, suggests azimuthal structure rotating with a 2 yr period that may represent precession or orbital motion of inner-disk structures casting shadows on the emission-line region farther out.

The tight correlations between the mass of supermassive black holes ($M_{\rmBH}$) and their host-galaxy properties have been of great interest to theastrophysical community, but a clear understanding of their origin andfundamental drivers still eludes us. The local relations for active galaxiesare interesting in their own right and form the foundation for any evolutionarystudy over cosmic time. We present Hubble Space Telescope optical imaging of asample of 66 local active galactic nuclei (AGNs); for 14 objects, we alsoobtained Gemini near-infrared images. We use state of the art methods toperform surface photometry of the AGN host galaxies, decomposing them inspheroid, disk and bar (when present) and inferring the luminosity and stellarmass of the components. We combine this information with spatially-resolvedkinematics obtained at the Keck Telescopes to study the correlations between$M_{\rm BH}$ (determined from single-epoch virial estimators) and host galaxyproperties. The correlations are uniformly tight for our AGN sample, withintrinsic scatter 0.2-0.4 dex, smaller than or equal to that of quiescentgalaxies. We find no difference between pseudo and classical bulges or barredand non-barred galaxies. We show that all the tight correlations can besimultaneously satisfied by AGN hosts in the 10$^7$-10$^9$ $M_{\odot}$ regime,with data of sufficient quality. The MBH-$\sigma$ relation is also in agreementwith that of AGNs with $M_{\rm BH}$ obtained from reverberation mapping,providing an indirect validation of single-epoch virial estimators of $M_{\rmBH}$.

Understanding the rate at which stars form is central to studies of galaxy formation. Observationally, the star formation rates (SFRs) of galaxies are measured using the luminosity in different frequency bands, often under the assumption of a time-steady SFR in the recent past. We use star formation histories (SFHs) extracted from cosmological simulations of star-forming galaxies from the FIRE project to analyse the time-scales to which the H α and far-ultraviolet (FUV) continuum SFR indicators are sensitive. In these simulations, the SFRs are highly time variable for all galaxies at high redshift, and continue to be bursty to z = 0 in dwarf galaxies. When FIRE SFHs are partitioned into their bursty and time-steady phases, the best-fitting FUV time-scale fluctuates from its ∼10 Myr value when the SFR is time-steady to ≥100 Myr immediately following particularly extreme bursts of star formation during the bursty phase. On the other hand, the best-fitting averaging time-scale for H α is generally insensitive to the SFR variability in the FIRE simulations and remains ∼5 Myr at all times. These time-scales are shorter than the 100 and 10 Myr time-scales sometimes assumed in the literature for FUV and H α, respectively, because while the FUV emission persists for stellar populations older than 100 Myr, the time-dependent luminosities are strongly dominated by younger stars. Our results confirm that the ratio of SFRs inferred using H α versus FUV can be used to probe the burstiness of star formation in galaxies.