Focus Meeting 2 - Abstracts
Missing metals and baryons in galaxies: Clues from our Milky Way
Mathur, Smita
It is well-known that most galaxies are missing most of their metals and their baryonic mass. I will present Chandra observations probing our Milky Way halo in absorption. Together with XMM and Suzaku data on emission, our results show that the Milky Way halo contains a huge reservoir of warm-hot gas that may account for a large fraction of missing baryons and metals. I'll review current status of this field, discuss implications of our results to models of galaxy formation and evolution and outline paths for future progress.
Cosmic Ultraviolet Baryon Survey
Chen, Hsiao-Wen
I will summarize the scope, scientific objectives, and initial results from the COS Ultraviolet Baryon Survey (CUBS), a new HST Cycle 25 program designed to map `dark' baryonic structures in the crucial but unconstrained epoch between z=0.4 and z~2,
XARM ability for the distant warm hot plasmas
Tashiro, Makoto
In this paper, we demonstrate the JAXA-NASA joint mission X-ray Astronomy Recovery Mission (XARM) ability to measure the chemical evolution in the early universe utilizing the X-ray afterglows of gamma-ray bursts (GRBs) and distant blazars at redshift of z > 2 as background light sources and to constrain the physics of jetted emission from these sources. XARM carries an X-ray micro-calorimeter with an X-ray Mirror Assembly named Resolve. As shown in the ASTRO-H whitepaper (Tashiro et al. 2015), the combination of the X-ray Mirror and the X-ray micro-calorimeter has a capability to search for redshifted emission and absorption features from heavy elements in the ejecta of GRB explosions, circumstellar material in the host galaxies and perhaps from the inter-galactic medium (IGM) in the soft-X-ray spectra of GRB afterglows and distant blazars, because of its combination of high spectral resolution, broad band pass, large collecting area and low background. In addition to the purpose above, the combination of the Resolve and Xtend (X-ray CCD camera system) will measure the temporal behavior of the spectral continuum of GRB afterglows and blazars. The ability to obtain these data from GRB afterglows will depend critically on the availability of GRB triggers and the capability of XARM to respond rapidly to targets of opportunity. At the present time it seems as if Swift will still be functioning normally during the first two years of XARM operations providing the needed triggering capability.
HUBS: Hot Universe Baryon Surveyor
Cui, Wei
HUBS is being conceptualized in China as a major X-ray mission for the next decade. It is designed to be highly focused scientifically, with the primary driver being to look for "missing baryons", the bulk of which are hypothesized to exist in the low-density, hot gas that lies in intergalactic and circumgalactic space. The gas is thus expected to produce weak emission in soft X-rays, which is technically difficult to detect. On the other hand, the spectrum of the emission would be rich in spectral lines, so it may be quite effective to detect the gas in selected emission or absorption lines. An instrument combining a high spectral resolution, large effective area and large field of view would be required for such a purpose. HUBS will couple a TES-based X-ray imaging spectrometer to a focusing X-ray optical system to satisfy these requirements. Various observational strategies will be employed to significantly enhance its scientific output. A preliminary design of HUBS will be presented.
Understanding diffuse baryons in galaxy clusters with simulations
Borgani, Stefano
In my talk I will review the state-of-the-art in the description of the thermo- and chemo-dynamical properties of the intra-cluster medium (ICM) using cosmological hydrodynamic simulations. I will hyghlight how the inclusion of different sources of stellar and AGN feedbaack allow modern simulation codes to produce populations of synthetic clusters that reproduce several observational properties, such as the mass of the brightest cluster galaxies, the cool-coreness and the pattern of metal enrichment of the ICM. In particular I will highlight how the combined study of the metal enrichment in the external regions of the ICM and future observations of proto-clusters at redshift z~2 would provide unique information about the history of feedback and of the cosmic cycle of baryons in the cluster environment.
The Multiphase Circumgalactic Medium
Peeples, Molly
The circumgalactic medium (CGM) is a dynamic, multiphase reservoir of gas regulating the flow of gas between galaxies and intergalactic medium. I will review the current observational landscape of the multiphase CGM, with a focus on its mass, content, partitioning by phase, and coevolution with galaxies. I will also review the successes and failures of hydrodynamic simulations at reproducing these observations and giving insight to interpreting them. Finally, I will present new results from the FOGGIE (Figuring Out Gas & Galaxies In Enzo) simulation suite, wherein we achieve unprecedented circumgalactic resolution in a cosmological context. I will show that resolving the small-scale structure of the simulated CGM has important ramifications for interpreting and predicting observable circumgalactic gas.
Review of the Diffuse Soft X-ray Background
Shelton, Robin
Buried in the observed spectra of the diffuse Soft X-ray Background (SXRB) are spectral contributions from baryons in intergalactic space, the circumgalactic medium, our Galaxy's halo, hot bubbles in our Galaxy including the Local Bubble around us, the solar system, and even distant AGNs. In principle, if the various sources' contributions could be disentangled from each other, then the resulting measurements could then be used to determine the sources' physical properties. Many people, using a variety of clever observational techniques, have worked hard to do that. Meanwhile, others have created detailed simulations of many of these regions, pushing forward our understanding of how they behave and evolve. In this talk, I will review observations of the SXRB, efforts to dissect it and model it, and what we have learned about the material that makes the SXRB.
Observing the Warm and Hot Baryons at Low Redshift
Fang, Taotao
Theory suggests that a significant amount of the "missing baryons" at low redshift are distributed outside or at the vicinity of galaxies in the form of low-density, warm-hot gas. However, observing of this warm-hot gas, especially in the X-ray band, remains elusive, largely due to the faintness of the expected signals. In this talk, I will review recent progress in this field. I will also discuss the baryons in the vicinity of galaxies, the so-called "circum-galactic medium", and their implication of solving the "missing baryons" problem.
Detection of missing baryons with thermal and kinetic Sunyaev-Zeldovich effect
Ma, Yin-Zhe
Previous studies of galaxy formation have shown that only 10 per cent of the cosmic baryons are in stars and galaxies, while 90 per cent of them are missing. In this talk, I will present three observational studies that coherently find significant evidences of the missing baryons. The first is the cross-correlation between the kinetic Sunyaev-Zeldovich maps from Planck with the linear reconstructed velocity field. We find significance (4.6 sigma) detection of the peculiar motion of gas on Mpc scales, for which we can reconstruct the baryon fraction. The second study is the cross-correlation between the thermal Sunyaev- Zeldovich effect with gravitational lensing map and we detect the cross-correlation for 13 sigma with RCSLenS and Planck data. The third study is to stack the pairs of luminous red galaxies and subtract the halo contribution, which leads to the detection of gas within filaments. These studies directly show the evidence of missing baryons outside the virial radius of galaxy clusters.
The Hot Baryons Contained in the Circum-Galactic Medium Around Massive Isolated Spiral Galaxies
Li, Jiang-Tao
The baryon content around local galaxies is observed to be much less than is needed in Big Bang nucleosynthesis. Simulations indicate that a significant fraction of these “missing baryons” may be stored in a hot tenuous circum-galactic medium (CGM) around massive galaxies extending to or even beyond the virial radius of their dark matter halos. Previous observations in X-ray and Sunyaev-Zel'dovich (SZ) signal claimed that ~(1-50)% of the expected baryons are stored in a hot CGM within the virial radius. The large scatter is mainly caused by the very uncertain extrapolation of the hot gas density profile based on the detection in a small radial range (typically within (10-20)% of the virial radius). In this talk I will report results from stacking XMM-Newton observations of six local isolated massive spiral galaxies from the CGM-MASS sample. We find that the mean density profile can be characterized by a single power law out to a galactocentric radius of ~200kpc (or ~130kpc above the 1-σ background uncertainty), about half the virial radius of the dark matter halo. We can now estimate that the hot CGM within the virial radius accounts for (8+-4)% of the baryonic mass expected for the halos. Including the stars, the baryon fraction is (27+-16)%, or (39+-20)% by assuming a flattened density profile at r>130kpc. We conclude that the hot baryons within the virial radius of massive galaxy halos are insufficient to explain the “missing baryons”.
Large-scale mass distribution in the IllustrisTNG simulation
Artale, Maria Celeste
We explore the large-scale spatial distribution and physical properties of gas, metals, and ions in the cosmological hydrodynamical simulation IllustrisTNG. The aim of this work is to investigate the so-called missing baryon problem through the analysis of one of the state-of-the-art hydrodynamical cosmological simulations. IllustrisTNG includes an updated scheme for galactic winds, and a new kinetic black hole feedback model for the low accretion state. We compare our findings with those from Illustris simulation and observational data.
A search for warm-hot baryons in the cosmic web using Sunyaev-Zel'dovich effect
Cai, Yan-Chuan
In the context of the standard model, observations of galaxies and galaxy clusters in the local universe can not fully account for the baryon content inferred from measurements of the cosmic microwave background and from big bang nucleosynthesis. Locating the missing baryons has been one of the major challenges in cosmology. Cosmological simulations predict that they are spread throughout filamentary structures in the cosmic web, forming the warm-hot intergalactic medium (WHIM). I will present a recent detection of WHIM in filaments through the thermal Sunyaev-Zel'dovich effect by stacking pairs of galaxies from the SDSS CMASS sample. Part of the talk will be based on this paper: https://arxiv.org/abs/1709.10378.
Connecting the Dots: Stacking the Cosmic Web in Ly a emission with MUSE and EAGLE
Gallego, Sofia
Cosmological simulations suggest that most of the matter in the Universe is distributed along filaments connecting galaxies. Illuminated by the cosmic UV background (UVB), these structures are expected to glow in fluorescent Ly a emission with a surface brightness (SB) that is well below current limits for individual detections.We perform a stacking analysis of the deepest MUSE/VLT data using three-dimensional regions (subcubes) with orientations determined by the position of neighbouring Ly a galaxies at 3 < z < 4. Our method increase the probability of detecting filamentary Ly a emission, provided that these structures are Lyman-limit systems (LLSs). By stacking 390 oriented subcubes we reach a 2s sensitivity level of SB ˜ 0.44 × 10 -20 erg s -1 cm -2 arcsec -2 in an aperture of 1 arcsec 2 × 6.25 Å, three times below the expected fluorescent Ly a signal from the Haardt & Madau (HM) UVB at z ~ 3.5. No detectable emission is found on intergalactic scales, implying that at least two thirds of our subcubes do not contain oriented LLSs. On the other hand, significant emission is detected in the circumgalactic medium (CGM) in the direction of the neighbours. The signal is stronger for galaxies with a larger number of neighbours and appears to be independent of any other galaxy properties. We estimate that preferentially oriented satellite galaxies cannot contribute significantly to this signal, suggesting instead that gas densities in the CGM are typically larger in the direction of neighbouring galaxies on cosmological scales.In addition, we extend our stacking search for IGM filaments with constraints from the EAGLE simulation.
How Supernovae-driven Hot Outflows Regulate Circumgalactic Medium
Li, Miao
The circumgalactic medium (CGM), where cosmic inflows interact with feedback-driven outflows, provides critical clues for galaxy formation. The physics of feedback remains a bottleneck to theoretical modeling. In this talk I will introduce our numerical simulations of CGM impacted by supernovae (SNe)-driven hot outflows. Using outflow models that are directly obtained from our small-box high-resolution simulations, we study the large-scale evolution of the outflows in the CGM. The volume-filling hot outflows carry the majority of the energy and metals produced by SNe, and can travel to > 100 kpc from Milky Way-like galaxies. I will talk about how galaxy potentials, existing halo gas, and SF activity affects the impact of outflows. I will also discuss how the model can be compared against future X-ray observations and signals of the Sunyaev-Zel’dovich effect.
Missing baryons and the warm-hot circumgalactic medium of a late type galaxy NGC3221
Gupta, Anjali
Late-type galaxies are missing a large fraction of their baryonic mass, some of which is expected to be in the hot gaseous halo. However, searches of emission from such circumgalactic medium (CGM) have given mixed results. Theoretical models suggest that CGM properties depend on galaxy properties such as gravitational mass, stellar mass and specific star formation rate (sSFR). X-ray observations so far have focused on galaxies with high mass and low sSFR. NGC3221 has smaller stellar mass and higher sSFR, probing an unexplored parameter space. I will present our Suzaku and Chandra observations of NGC3221 and discuss our results on the detection and characterization of its warm-hot CGM.
Unbound warm/hot gas in filaments and superclusters
Tanimura, Hideki
We search for the Sunyaev-Zeldovich signal in unbound gas: in filaments and in superclusters. We focus on filaments between ~ 260,000 pairs of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey Data Relase 12 (SDSS DR12) tracing the large scale structure of the Universe. By stacking the LRG pairs, we estimate the SZ signal in the Planck data between them as y = (1.31 ± 0.25) × 10-8 at 5.3 s significance, marginally consistent with simulations. Assuming a simple model for all the filaments, the over-density of the electron gas in the filaments is found to be d = 3.2 ± 0.6.We also search for the SZ signal from the unbound gas outside clusters in 580 superclusters from the SDSS DR7. After stacking the superclusters, we estimate the SZ signal as y = (3.0 ± 1.4) × 10-8 at 2.2 s significance. Assuming a temperature of 106.5 K and simple model for unbound gas distribution, we find the over-density of the electron gas d = 2.3 ± 1.4.
Origin and evolution of the X-ray luminous circumgalactic medium
Davies, Jonathan
Observations reveal that the baryon fraction of dark matter haloes is a strong function of their mass. This likely follows from a mass-dependent balance between gravitational accretion on one hand and, on the other, consumption by star formation and heating from the feedback that accompanies star formation and black hole growth. Authoritatively predicting the origin of the hot circumgalactic medium (CGM) and the fate of the missing baryons thus requires simulations that reproduce the observed properties of galaxies and their gaseous environments.The EAGLE simulations reproduce a range of galaxy properties, and by coupling them to plasma emission tables we show they also reproduce properties of the hot CGM, such as X-ray surface brightness profiles and the Lx-M* and Lx-M_500 scaling relations. Scatter in the scaling relations is driven by the state of the gas: more luminous haloes at fixed mass have a hot CGM whose centre is denser and more metal-rich, and we predict they also host bluer galaxies. Reproduction of these diagnostics requires efficient feedback, particularly at z ~ 1-3 when halo accretion rates peaked, to eject and/or redistribute gas from halo centres. We trace the fate of these missing baryons, and we find them in a diversity of present-day environments: the majority reside in the halo outskirts, but some cool onto neighbouring galaxies.EAGLE indicates that the hot CGM was mostly heated by gravitational accretion shocks. However, because feedback acts on the densest and most enriched gas in the CGM, X-ray emission can be dominated by feedback-heated gas. For Milky Way-like galaxies, we find that feedback-heated gas dominates the luminosity of the hot CGM until z~0.5, when the contribution from gravitationally-heated gas becomes similar. However, since the highest surface brightness gas in halo centres is mainly heated by feedback, we caution that X-ray observations can provide a highly unrepresentative view of the physical state of the hot CGM.
A survey of moclecular gas in HI-Absorption-Selected Systems
Klitsch, Anne
Studying the multiphase circum-galactic medium and its connection to the baryons in the host galaxies is an important step towards a better understanding of the evolution of galaxies over time. Large steps forward have been made in detecting the multiphase circum-galactic medium through absorption line studies. Today it is possible to connect the cold neutral gas in the halo to its host galaxy by combining absorption and emission selected samples. However, the link to the molecular gas phase from which the stars form is still missing. We have exploited ALMA calibrator observations to perform a novel (sub)mm survey, ALMACAL. We are searching for CO emission lines from the host galaxies of known Lyman alpha absorbers. The parent sample of 57 absorbers towards 26 quasars probes a redshift range of 0.05 < z < 3.0. We have detected CO emission more than a dozen galaxies coincident with the absorber redshift at 0.15 < z < 2.5 with impact parameters between 10 and 130 kpc. We derive molecular gas masses of around 10^10 M_sun and relate the molecular gas masses with the impact parameter or the quasar sight line. Furthermore, we can infer the conditions for star formation in those galaxies from the CO spectral line energy distribution and get first constraints of the temperature and density of the ISM. Preliminary modelling of the CO spectral line energy distribution suggests that some of these galaxies do not show Milky Way like star formation conditions.
CGM emission predictions from cosmological zoom-in simulations
Augustin, Ramona
Gas flows in and out of galaxies are poorly constrained and understanding these processes is crucial to studies of galaxy evolution.Observations of the Circum-Galactic Medium (CGM), where these processes take place, are therefore essential for making progress in understanding gas flows but remain challenging as this medium is intrinsically thin and very faint.To improve observing strategies, we have made CGM emission predictions from dedicated cosmological zoom-in simulations.We use hydrodynamical AMR RAMSES simulations down to z=0 with a maximum spatial resolution of 380 pc/h in the central region.Using CLOUDY emissivity models for different lines (e.g. Ly-alpha, CIV, OVI, OVIII), we post-process galaxy halos from the simulation with these models and compute the expected emission from the gas in the CGM.These post-processed simulated halos then give the flux for different lines at different redshifts and can be used as estimates for the observations in different wavelength regimes (X-Ray, UV, optical, IR).
Studying extra-planar, ionized gas with stacked MaNGA galaxies
Jones, Amy
Gas in the outskirts of galaxies can greatly influence the evolution of their host galaxies and additionally can help solve the missing baryons problem. Warm ionized gas is faint and diffuse and hence difficult to study. By stacking multiple similar SDSS IV MaNGA galaxies, we can clearly detect this extra-planar gas out to several kpc, between four and ten kpc depending on the sample. MaNGA is an IFU survey that covers the entire optical range, so we have detections of emission lines, including [OII], [OIII], H_beta, [OI], [NII] H_alpha, [SII], as a function of scale height. Currently there are over 4000 galaxies observed, and about 800 of those are edge-on systems that can be used in this study. This increases our previous sample by a factor of ten! We split this sample into many subsamples to see how the gas properties (e.g. temperature, density, ionization state) depend on the host galaxy properties (e.g. morphological type, star formation rate). Also, we determine the mass of metals and baryons in the outskirts for each subsample. We can compare our measurements for the extra-planar gas with what has been seen in other CGM studies with Quasars to form a complete picture of warm ionized gas in the outskirts of galaxies.
Hot X-ray halos as probes of galaxy formation
Bogdan, Akos
The existence of hot X-ray halos in the dark matter halos of galaxies is a fundamental prediction of galaxy formation models, and hence, observations of these halos can be used to probe the key physical processes that influence the evolution of galaxies. Although hot halos are well explored around elliptical galaxies, these halos remained unexplored around spiral galaxies for several decades. Our group played a key role in detecting several X-ray halos around massive spiral galaxies using Chandra and XMM-Newton observations. We have characterized the properties of these hot halos, and confronted the observed results with those predicted by state-of-the-art hydrodynamical galaxy formation models. This comparison pointed out that the properties of hot halos are extremely sensitive to the incorporated physics in the simulations, and hence observations of X-ray halos provide a powerful method to constrain the physical processes that play an essential role in the evolution of galaxies from the early Universe to the present epoch.
The signature of AGN feedback on CGM properties
Choi, Ena
Recently, theoretical work has begun to compare the simulated circumgalactic medium (CGM) to column densities and equivalent width measurements as a function of impact parameter from the center of the galaxy. The majority of the simulations underproduce the amount of metal-enriched gas at large impact parameters compared to observations and fail to match the large amount and high covering fraction of OVI measurements tracing the hottest gas phase, as well as less ionized cooler lines such as MgII, CIII and SiIV. However, none of these studies include mechanical AGN feedback, which may play an important role in driving winds and enriching CGM at large distance. To elucidate how the physical conditions and dynamical state of the CGM gas change by AGN feedback, we run a suite of hydrodynamical simulations incorporating a new treatment of AGN feedback which is implemented in a fully self-consistent way, launching high-velocity mass outflow. We post-process these sets of simulations with a synthetic spectrum generation code and compare covering fractions, equivalent widths, ion ratios, and kinematics to observations as a function of impact parameter and specific star formation rate. We show that the AGN feedback effectively enrich CGM ‘inside-out’ by spreading centrally enriched metals to the outskirts of galaxies along the AGN-driven outflow, as well as ‘outside-in’, where winds propagate further from galaxies at earlier epochs of high AGN activity and then ejected metals recollect into the CGM at later times.
Revealing the Invisible Drivers of Galaxy and Structure Formation with Lynx
Vikhlinin, Alexey
The assembly, growth, and state of visible matter in cosmic structures are largely driven by violent processes that produce and disperse large amounts of energy and metals into the surrounding medium. In galaxies at least as massive as the Milky Way, the relevant baryonic component is heated and ionized to X-ray temperatures. Lynx will be capable of mapping this hot gas around galaxies and in the Cosmic Web, as well as characterizing in detail all significant modes of energy feedback. Essential observations will require high-resolution spectroscopy (R ~5000) of background AGNs, the ability to detect low surface brightness continuum emission, and R~2000 spectroscopy of extended sources on arcsecond scales — all unique to Lynx.
Super DIOS mission
Ohashi, Takaya
We are studying an improved DIOS (Diffuse Intergalactic Oxygen Surveyor) program for a launch year after 2030. The aim of Super DIOS is an X-ray exploration of warm-hot intergalactic medium using emission and absorption lines, measured with TES microcalorimeters. This mission will perform wide field X-ray spectroscopy with FOV of about 30 arcmin and energy resolution of a few eV, but with much improved angular resolution, than the original DIOS, of about 10 arcseconds. Besides the WHIM science, gas dynamics, distribution of elements, and other physical properties of plasmas will be studied with very high sensitiviey for cluster outskirts, supernova remnants, normal and active galaxies, and Galactic interstellar medium. We will describe the Super DIOS mission and its expected science.