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Welcome and opening remarks on the status of the Chandra X-ray Observatory.
Studies of galaxy clusters have proved crucial in helping to establish the standard model of cosmology, and X-ray observations have been central to this work. I will summarize the latest results on cosmology from cluster studies, highlighting Chandra's key role in providing precise, relative mass calibration. The prospects for progress over the next decade and beyond are outstanding with new cluster catalogs, hundreds of times larger and with far greater redshift reach, being constructed across a variety of wavelengths. X-ray follow-up observations will be vital to the full exploitation of these catalogs. I will discuss ways in which to make these contributions as efficient and impactful as possible.
The intracluster medium (ICM) of clusters of galaxies is the largest example of a space plasma. The high angular resolution of the Chandra X-ray Observatory has revealed a wealth of complex structure in the ICM, which in principle can be used to probe its plasma physics and kinematics. The microphysical properties of the plasma, such as its viscosity and thermal conduction, are still poorly constrained. It is known from radio observations that the ICM is magnetized, but no evidence has yet been seen of dynamical effects of the weak magnetic field on the gas, despite the fact that simulations predict that the magnetic field should grow strong enough in some cases to have an effect. Observations of surface brightness fluctuations and cold fronts with Chandra have also provided indirect evidence of complex gas motions, including bulk flows and turbulence. The first direct measurements of such gas motions in the Perseus cluster were made by Hitomi with its microcalorimeter, but its low angular resolution severely limits the conclusions that can be drawn about the nature of these motions. In order to provide answers to these questions, a mission with comparable angular resolution to Chandra but higher effective area and higher spectral resolution is needed. I will present results from mock observations of MHD simulations of the ICM to show how Lynx will constrain the detailed physical and kinematical properties of the cluster plasma. In particular, Lynx will have the capability to detect the effects of strong magnetic fields on the cluster plasma, definitively resolve hydrodynamical instabilities to place limits on the ICM viscosity, and map the velocity structure of the gas down to small scales.
In recent years, the outskirts of galaxy clusters have emerged as a frontier to study the evolution of galaxy clusters and the intergalactic medium. In this talk, we will present results from a mass-limited sample of 65 galaxy clusters from the Omega500 cosmological hydrodynamical simulations and corresponding mock Chandra/Lynx X-ray observations. With these results, we will discuss the prospects of probing physical processes in cluster outskirts (such as gas motions, gas clumping, and ion equilibration) with recent deep Chandra XVP observations of A133, large samples of SZ-selected clusters, and the proposed Lynx mission.
As the deepest X-ray surveys ever performed, the Chandra Deep Fields have provided fundamental insights about active galactic nuclei (AGNs) and starburst/normal galaxies in the distant universe. Together they have detected more than 1800 faint X-ray sources that can be characterized in detail using the unmatched deep multiwavelength coverage in these sky regions; e.g., about 98% of the sources have multiwavelength counterparts and spectroscopic/photometric redshifts. I will briefly summarize some of the main recent results from the Chandra Deep Fields, focusing on the most-distant AGNs at z∼3-5 and available constraints upon the seeds of the first supermassive black holes (SMBHs) in the Universe. I will then describe how these studies can be advanced in the relatively near-term, combining Chandra and XMM-Newton data with observations by, e.g., ALMA, JWST, LSST, and new instruments on large ground-based telescopes. I will end by highlighting the advances expected from Athena and the unique, critical role that Lynx surveys will play by detecting large numbers of SMBH seeds down to ∼30,000 solar masses at z∼10.
Despite remarkable recent progress, connecting the growth of black holes to the evolution of their host galaxies and dark matter halos has remained challenging. AGN exhibit complex variability in luminosity, accretion processes, and obscuration over a wide range of timescales, so we require large X-ray and multiwavelength surveys to obtain a complete picture via statistical studies of AGN host galaxies and spatial clustering. I will present recent studies by our group and colleagues that use extragalactic surveys (particularly with Chandra, NuSTAR, and WISE) to uncover as much as possible of the complete population of AGN and study their hosts and large-scale structures. These results suggest that AGN accretion is a surprisingly universal, yet highly stochastic process, and uncover an underlying connection between the gas supply that fuels star formation and the accretion rates and obscuration of the growing black holes. I will outline the exciting science in this area that will be enabled by the upcoming Chandra Deep Wide Field Survey, as well as forecasts for the future with NASA's Lynx concept X-ray mission. This work is supported in part by NASA through grant numbers NNX15AP24G and NNX15AU32H, and the National Science Foundation through grant number 1554584.
I will discuss the feasibility of a few per cent level measurement of the local black hole occupation fraction through Lynx imaging observations of local volume galaxies. I will provide quantitative estimates of how the occupation fraction accuracy and observational strategy vary as a function of a series of parameters, including the HDXI angular resolution, exposure time, distance, and host galaxy stellar mass. Most notably, I will show that 0.1 arcsec resolution will yield a 1-5 per cent accuracy in the occupation fraction below stellar masses of 1e+10 Msun with observations of about 3,500 galaxies within 100 Mpc. This measurement can be efficiently carried out by combining dedicated, snapshot observations of low mass galaxies with a commensal survey approach. It will constitute a long-lasting legacy for the mission by establishing a benchmark for any model which aims to reproduce the assembly of galaxies and their nuclear black holes. Concurrently, it will yield an independent constraint to black hole seed formation models, complementing orthogonal efforts which will be carried out at high red-shifts.
Detection of X-ray emission from the first population of sources could constrain formation of super-massive black holes and properties of the first population of X-ray binaries. However, direct observations of high redshift populations require large integration times and are highly biased because only the brightest objects at high redshifts can be detected. A useful measurement is of the unresolved cosmic X-ray background (CXB) which constrains both the luminosity of the most common objects and clustering of these sources. An alternative way to probe the first population of X-ray sources is via its effect on the environment. These sources had a dramatic effect on the Universe heating and mildly ionizing the intergalactic medium. One of the most efficient tools to probe the thermal state of the IGM at high redshifts is the radio signal of neutral hydrogen with the rest-frame wavelength of 21 cm. In my talk I will discuss how cross-correlation between cosmic X-ray background and the 21 cm signal can be used to constrain the first population of X-ray sources.
Today, we know that most of the metals (70-90%) and nearly half of the baryons are unaccounted for, predicted to be in a hot phase (0.5-10E6 K) that is accessible to X-ray observations. X-ray absorption lines, mainly O VII, are detected in sight lines through the Milky Way halo, helping to define the density and mass of the gas at the virial temperature of about 2E6 K. No extragalactic sight lines show absorption, consistent with theoretical predictions. After Athena, there will be more high-quality sight lines through the Milky Way hot halo and the first extragalactic absorption systems should have been detected, through galaxy halos at impact parameters less than 100 kpc. Lynx will usher in a new age in that it will be able to detect absorption from galaxy halos out to the virial radius, and in the surrounding large-scale structures, the Cosmic Web; absorption should be detectable to z∼1, if not beyond. It will also measure the dynamics of the Milky Way hot halo — rotation, turbulence, and accretion/outflow, thereby providing powerful constraints on galaxy formation and evolution.
Galactic nuclei are believed to play a central role in galaxy formation and evolution. The lifecyle of their activity, however, remains greatly uncertain. I'll demonstrate how high-resolution X-ray imaging and spectroscopy of hot gas in galactic bulge regions can be used to probe AGN activity in the recent past (within one million year or so). We have developed an AGN relic model, which accounts for both photo-ionization and non-equilibrium evolution of distributed hot gas and allows for comparison with spatially resolved X-ray spectroscopic data. As an example, I'll describe the application of this model to the analysis of the Chandra and XMM-Newton X-ray data of the M31 central region, which is quiescent in both AGN and star formation, but shows strong indications for recent AGN activity. The diffuse X-ray emission from the high spatial resolution Chandra observations reveals interesting substructures with radio counterparts, as well as an overall negative temperature gradient in the diffuse hot gas distrbution. The X-ray grating spectra from the XMM-Newton observations show enhanced forbidden lines of He-like Oxygen, Neon, and Nitrogen Kalpha triplets, as well as signatures for multi-temperature hot gas. We find that these results can be well interpreted by the AGN-relic model, suggesting that galaxy is a bright AGN about 0.4 Myrs ago. In addition, we have also found evidence for resonance scattering effects, which broaden the spatial distribution of the relevant line emission and provide a sensitive probe of the hot gas turbulent motion. This application demonstrates the power of the spatially-resolved X-ray spectroscopy, as will be provided more effectively by Lynx, in our understanding of the recurrence history or frequency of AGN and galaxy feedback in general.
We present preliminary results from the whole 1.6 Ms XMM-Newton observation of the z∼0.5 Blazar 1ES 1553+113. The final 1.6 Ms spectrum of 1ES 1553+113 has reached a 90% sensitivity to 4 mA absorption line equivalent width. In the XMM-Newton and Chandra grating archives such sensitivities are reached only in the spectra of the brightest blazar in the Universe, Mkn421, which however explores a line-of-sight pathlength >10 times shorter than that seen against 1ES 1553+113. According to theoretical predictions between 3.1-6.2 WHIM OVII Ka absorbers should have been detected down to these sensitivities and up to such pathlengths along the line of sight to 1ES 1553+113. However, the RGS spectrum of 1ES 1553+113, which clearly detects several of the expected Galactic absorption lines down to such sensitivities and hints to a bunch of even weaker Galactic transitions, shows only two >3-sigma absorption lines potentially identifiable with intervening OVII Ka WHIM (and two more identifiable with NVII at the same redshift of one of the two OVII Ka, and NeX Ka at a different redshift). This invalidates the most optimistic predictions at >4-sigma confidence level and questions the most conservative ones, opening a number of questions that desperately need to be properly investigated and possibly addressed, both theoretically and observationally, before the advent of the next generation of high-resolution X-ray spectrometers, like Athena and/or Linx.
Compared to the currently funded X-ray missions, Lynx offers two distinct advantages: high resolution imaging and high resolution gratings spectroscopy. High resolution imaging is necessary for studying stellar populations and diffuse plasma structures within crowded star forming regions, supernova remnants, and the Galactic Center. However, gratings spectroscopy is an often overlooked advantage of the Lynx mission. X-ray observations have a unique capability for studying metals in all phases, whether in cold neutral gas or hot ionized plasmas. In particular, carbon and oxygen — the two most abundant metals — have spectral features in the soft X-ray, where micro-calorimeters lose both sensitivity and resolving power. I will review the primary instrumentation limitations, avenues for solving them with Lynx, and the science outcomes to be expected, from supermassive black holes to the interstellar medium.
Since its emergence, high resolution X-ray spectroscopy has greatly impacted studies of properties of the gas phases in the interstellar medium (ISM). Resolving the O K, Fe L, and Ne K edge structures revealed how X-ray spectra are affected by absorption and exposed the physics of the cold, warm, ionized and hot phases of the ISM. Some studies identified signatures related to dust and molecular components but their true existence remained unclear. Studies of higher Z edges such as Mg K, Si K and S K in contrast indicate dominant dust signatures in the edge structure. In a recent survey of the Si K edge in X-ray binaries located in the Galactic Bulge of the Milky Way we describe the edge using several components which include multiple edge functions, near edge absorption excesses from silicates in dust form, contributions from X-ray scattering optical depths as well a the presence of a variable warm absorber from atomic silicon. Some of the details require spectral resolutions of better than 3 eV, which even with the high energy gratings (HEG) onboard Chandra is already challenging. LYNX will provide us with ultra-resolved and high signal K edge structures from Mg, Si, S, Ar, Ca, Fe, and Ni allowing for the first time to effciently survey the Galactic plane and bulge in terms of identifying various dust species and their ratio to the gas phase. We present current results with Chandra on this topic and discuss them in the context of ISM physics and how this will be impacted by the power of LYNX.
One of the most striking phenomena in the Galactic center are the numerous radio filamentary structures extending up to tens of parsecs. The radio polarization detection from the filaments point to a synchrotron origin with constant feeding of GeV electrons. In the X-ray band, about 20 elongated filaments have been discovered so far. They used to be interpreted as pulsar wind nebulae (PWNe). However, recent X-ray and radio observations have revealed a diverse origin of the X-ray filaments. In this talk, I am going to discuss the source nature of the three brightest X-ray filaments, as candidates for a PWN, a supernova remnant and cloud interaction, or a magnetic flux tube. Future deeper X-ray observation will hold the key to discover fainter X-ray filaments and to reveal their source nature.
Just above the detection limits of the unprecedented 7 Ms Chandra Deep Field-South, X-ray detected normal galaxies, powered primarily by X-ray binary (XRB) populations, now outnumber active galactic nuclei (AGN). As such, when we move into an era of even deeper X-ray surveys with Lynx, populations of distant (z>1.5) normal galaxies will be detected in large abundance, ready for exciting new studies of these populations and their cosmic evolution. In this talk, I will discuss recent results that show scaling relations between X-ray emission from low-mass XRBs (LMXBs) with stellar mass (LX/M) and high-mass XRBs (HMXBs) with star-formation rate (LX/SFR) evolve significantly out to z∼2.5, such that LX(LMXB)/M∼(1+z)2-3 and LX(HMXB)/SFR∼(1+z). I will put these findings into the context of theoretical population synthesis models, which indicate that the evolution XRBs can be attributed to global changes in the stellar ages and metallicities of galaxies in the Universe. Extending these models to higher redshifts suggest that the XRB emissivity of the Universe is expected to overpower AGN at z>5-8 and could play an important role in heating the intergalactic medium of the early Universe. I will conclude by discussing how future Lynx and multiwavelength observatories will extend constraints on XRB population evolution and how ground-based 21-cm experiment results could be paired with high-z X-ray galaxy studies to learn about these populations in the z∼10-15 Universe.
X-ray binaries are our main tool for studying compact object populations and addressing key areas of Astrophysics, including the mass spectrum of compacts objects, the progenitors of gravitational waves and short gamma-ray bursts, and the preheating of the intergalactic medium in the epoch of reionization. Chandra and XMM-Newton have revolutionized our understanding of the X-ray binary populations and their dependence on the current and past star-forming activity of their host galaxy. They have even allowed us to set limits on parameters related to the formation and evolution of X-ray binaries. The unprecedented capabilities of Lynx and its synergy with the excellent suite of multi-wavelength observatories that are planned for the 2030s will enable the next quantum leap in studies of the X-ray binary populations in the nearby as well as the more distant Universe. We will discuss the prospects for studies of X-ray binary populations using a suite of end-to-end simulations of nearby as well as distant galaxies for different assumptions in X-ray binary population synthesis models. This way we will explore how Lynx will be able to constrain key parameters that determine the formation and evolution of X-ray binaries in the local Universe, by means of (a) resolved population studies in nearby galaxies, and (b) studies of ULXs and integrated X-ray emission of galaxies in wide area and deep surveys. Such constraints will have important implications for estimating the contribution of the host galaxy in studies of the gaseous component and the supermassive black-holes in high-z galaxies. In addition we will discuss how these results depend on key mission design parameters such as energy range and spatial resolution.
Lynx promises to make remarkable progress in high-energy astrophysics instrumentation, with attendant improvements in data quality. As we learned during the development of Chandra, improvements in data quality require considerable thought on how to analyze the data. For instance, Chandra data has forced the migration of data analysis away from chi-square minimization, to the explicit use of Poisson likelihoods, and the common use of MCMC. It is illustrative to realize that wavdetect was developed just to apply to Chandra images. These techniques were developed and used mainly to obtain better and more robust astrophysical results. We anticipate a similar revolutionary advance with Lynx. We describe several examples of how Lynx data analysis will benefit from advanced techniques that are being currently developed or are anticipated. We consider issues like image deconvolution/segmentation/reconstruction, non-parametric flux estimation from calorimeter spectra, robust photometry in crowded fields, combining datasets, etc. We invite people to join us in an informal Working Group whose goal is to anticipate and game out upcoming data and analysis issues.
X-ray observations of supernova remnants (SNRs) are a crucial means to investigate the mechanisms of SN explosions and the acceleration of particles to TeV energies by SN shocks. Since Chandra's first-light image of Cassiopeia A, modern X-ray facilities have revealed that SNRs have complex morphological and spectral characteristics that give important insights to the nature of explosions, progenitor stars, and their effects on their surroundings. In this presentation, I will review some of the major advances in SNR science in the past 18 years, focusing principally on results and discoveries from Chandra data. I will also discuss the open questions in the field and Lynx's role in addressing these outstanding issues.
There is extensive evidence that the progenitors of some core collapse supernovae undergo extensive mass loss in the years leading up to core collapse. The imprint of the mass loss episodes may be seen in the spectra and dynamics of the expanding remnant, on timescales of years to centuries after the supernovae. In this talk, I will discuss how Lynx observations of young supernovae in the local Universe will allow us to understand mass loss mechanisms in massive stars. I will discuss how high resolution spectra will allow us to reconstruct the progenitor mass loss history and infer properties of massive stars in the late stages of their evolution.
Extensive Chandra surveys have revealed that globular clusters are veritable treasure troves of X-ray faint compact binaries. Among them are the class of X-ray binaries with thermally-emitting "quiescent" neutron stars. Sensitive spectroscopic observations of such systems can provide limits on the mass-radius relation of neutron stars, thereby producing constraints on the pressure-density relation of matter at extreme densities. Effective studies of globular cluster sources require sub-arcsecond resolution, which among the future generation of X-ray missions only Lynx would provide. I will describe the prospects of dense matter equation of state measurements with Lynx as well as the wealth of secondary science that would be enabled by the same observations.
Powerful radio jets launched by a central supermassive black hole pump a substantial amount of energy into their host galaxies and cluster environment. This feedback from the central AGN is thought to suppress gas cooling and star formation at late times to regulate the growth of massive galaxies and their hot atmospheres. The most massive galaxies, located at the centres of rich clusters, often host substantial reserves of molecular gas, which are likely fuelling star formation and the black hole activity. I will review ALMA Early Science observations that resolve the structure of these molecular reservoirs and reveal massive filaments extending 5-15 kpc, which likely formed from gas cooling out of the surrounding hot atmosphere. I will present recent ALMA observations of extended molecular filaments in the Phoenix, PKS0745-191 and Abell 1795 central cluster galaxies, which are drawn up around giant radio bubbles. Smooth velocity gradients along these filaments are consistent with ordered molecular gas flows around the bubbles and show that radio jets interact with cold, dense molecular gas as well as the hot, diffuse intracluster medium. I will also discuss the exciting possibilities of combining ALMA and Lynx observations.
The search for life around stars other than the Sun requires detailed knowledge of the host stars themselves. The star interacts with an exoplanet's environment through X-ray and extreme ultraviolet radiation and high energy particle fluxes, manifestations of the star's magnetic activity. Stellar winds can exhibit high particle enhancements during coronal mass ejections associated with energetic stellar flares. Deleterious effects on habitability by the star's magnetic activity are easy to imagine; at the same time, some level of activity may also be necessary to catalyze life.
In this talk, I will review the status of some of the big questions in coronal physics: the coronal heating problem, unsolved since its identification in 1941; stellar dynamo theory, recently highlighted by Chandra studies of fully convective M dwarfs; and the relationship between stellar winds and the confinement of plasma in coronal loops.
X-ray grating spectra obtained with Chandra and XMM-Newton reveal high electron densities and sharply peaked emission measure distributions in the coronae of active stars, unlike features observed in the solar corona. These spectra typically have long exposure times, and thus are limited to nearby, highly active stars, with poor sampling of accreting systems, lower mass dwarfs and older, slow rotators like the Sun. Even at the highest spectral resolution of the Chandra gratings, many diagnostic line ratios are blended, velocity measurements are rare, and equilibrium tests are not possible. Lynx offers large improvements in spectral resolution and throughput. I will discuss new types of measurements that Lynx will enable, including velocities and tests of thermal equilibration, and how these will inform our understanding of stellar coronae.
The solar corona shows us a range of magnetic and plasma phenomena that are also going to be present on other stars. Stars allow us to study what happens to these phenomena when driven to extremes of magnetic activity, or when displayed by stars of different underlying fundamental parameters. We look at these phenomena, from wave process to reconnection, from thermal instabilities and oscillations to flares and CMEs, and highlight the physical processes that a next generation X-ray mission such as Lynx can hope to observe and help understand.
We are examining in a numerical study the relation between CMEs and flares in different stellar activity regimes. The computational tools used to achieve this task are BATS-R-US on the magnetohydrodynamic end and (implicit) iPIC on the kinetic end. A bidirectional coupling between the two codes has been implemented in order to examine the heating, acceleration and emission mechanisms linked to stellar CMEs and flares. In particular, magnetic reconnection, that is a kinetic process, takes place at the coronal loop apex. As a result of the reconnection, electrons get accelerated and as they descend with high velocities from the sparse corona they collide with the denser chromospheric material and emit in hard X-rays creating two flaring sites at the footpoints of the loop. Three distinct X-ray bright regions are the observational signatures of the whole process, namely, the loop apex (soft X-rays) and its footpoints (hard X-rays). We examine how numerical modelling of these processes coupled with observations of stars with Lynx might be used to provide new physical insights into stellar flares and CMEs.
In this presentation I discuss what we have learned from Chandra observations of nearby young stellar clusters such as NGC 1333, IC 348, The Orion Nebular Cluster and more distant Clusters such as Eta Carina and NGC3603. Then I examine what the additional capabilities of Lynx would imply for similar observations. The net result is that Lynx should be able to make complete samples of Young stellar clusters out to 2 kpc. This is similar to the grasp of Gaia and JWST. I close with a discussion of problems which will exist in the 2030's which Lynx may be able to address.
We present Chandra High Energy Transmission Grating (HETG) observations of the ∼3 Myr old pre-main sequence (pre-MS) stellar cluster IC 348. With 300-400 cluster members at a distance of ∼300 pc, IC 348 is an ideal target to observe a large number of X-ray sources in a single pointing and is thus an extremely efficient use of Chandra-HETG. High resolution X-ray spectroscopy offers a means to investigate detailed spectral characteristic of X-ray emitting plasmas and their surrounding environments. We present our initial findings where we compare X-ray spectral signatures (e.g., luminosity, temperature, column density, abundance) of the X-ray brightest pre-MS stars in IC 348 with spectral type, multiwavelength signatures of accretion, and the presence of circumstellar disks at multiple stages of pre-MS stellar evolution. Assuming all IC 348 members formed from the same primordial molecular cloud, any disparity between coronal abundances of individual members, as constrained by the identification and strength of emission lines, will constrain the source(s) of coronal chemical evolution at a stage of pre-MS evolution vital to the formation of planets. Chandra-HETG observations of pre-MS stellar clusters like those presented here for IC 348 are essential motivation for the inclusion of gratings on Lynx, the next generation X-ray telescope. For HETG observations of nearby pre-MS stellar clusters, Chandra's sensitivity is capable of producing high signal-to-noise ratio spectra for only the X-ray brightest cluster members in a reasonable exposure time. With the significant increase in sensitivity of Lynx, observations of crowded star-forming regions can produce more high resolution spectra at a fraction of the exposure time resulting in an unprecedented view of pre-MS stellar evolution.
With 10,000 resolution, 0.5 arcsec angular resolution, and high throughput, the proposed Lynx XUV observatory could provide valuable insights into major issues in astrophysics. In this talk, I will describe the many ways in which observations with Lynx are needed to understand the evolution of exoplanet atmospheres. I will also mention some important discoveries that Lynx could make concerning coronal physics and the interstellar medium.
The development of organic chemistry in protoplanetary disks likely begins with the host star's XUV emission photoionizing hydrogen to produce H2+ and H3+. The photoionization is primarily at EUV wavelengths which are mostly unobservable through the interstellar medium. With its high spectral resolution, Lynx could separate X-ray emission lines from continua leading to more accurate emission measure distributions from which the unobservable EUV emission can be calculated. As protoplanets evolve, the X-ray and EUV emission of host stars photoionize and heat their outer atmospheres, leading to hydrodynamic mass loss, which may remove the entire atmosphere. EUV and UV photons also photodissociate important molecules in exoplanet atmospheres. With a resolution of 30 km/s, Lynx could measure the accretion flow of protoplanetary disk gas onto the host star and search for coronal mass ejections (CMEs) that can destroy ozone in planetary atmospheres, thereby sterilizing the planetary surface. CMEs may be detected by their transient X-ray absorption during flares.
Lynx should search for Doppler shifts in coronal emission lines to study upflows and downflows during stellar flares and outflowing hot gas emission from protostellar disks and perhaps even quiescent stellar coronae. Lynx spectra will be useful for measuring coronal electron densities from the He-like triplet lines, including the blended Ne IX lines, and lines of Fe XXI and Fe XXII. Lynx spectra may be able to study departures from collisional ionization equilibrium at quiescent times and during flares. Measuring fluxes of weak emission lines will be needed to study a wide range of ionization stages. Spectra of transition region lines such as He II 30.4 nm can test for theimportance of ambipolar diffusion. Finally, high-resolution spectra of the He II 30.4 nm resonance line and the ionization edge of He II at 22.8 nm could measure the abundance of ionized helium in the local interstellar medium.
In stellar evolution one of the shortest evolutionary phases is the planetary nebula (PN) phase. The phase exists for tens of thousands of years after the mass lost during the asymptotic giant branch phase is sculpted into a nebular shell and the emerging hot stellar core, which ionizes the shell, fades towards the white dwarf cooling track. The Chandra Planetary Nebulae Survey (ChanPlaNS) identified an even shorter phase that pertains to the period when the nebula is filled with a X-ray emitting plasma called a hot bubble. This hot bubble phase exists early in the lifetime of the PN and is the result of the initial violent collision of stellar winds that shapes the nebula. A surprising result made by Chandra are the homogeneous and unexpectedly cool plasma temperatures of these hot bubbles. It is believed that heat conduction across the nebular-hot bubble interface leads to mixing of these two plasmas and cooling of the hot bubble to the observed range of 1-3 MK. The heat conduction process is uncertain because these hot bubbles are chemically enriched and difficult to detect. Their cool temperatures (1-3 MK) require sensitivity to soft X-ray photons (E<1 keV) and only one PN has a high enough flux to obtain the high quality grating spectrum required to study its chemistry. Future gratings observations by Athena+ and/or Hitomi 2 will help establish the chemical distribution amongst hot bubbles in PNe, but high sensitivity and high spatial resolution imaging, like that proposed for Lynx, is essential in our study of these hot bubbles. Lynx will allow us to map the spatial distribution of the hot bubble plasma properties. This spatial information provides a key test of the heat conduction process. Ultimately, Lynx will allow us to realize the full potential of these wonderful astrophysical plasma laboratories.
The X-ray line profiles from the winds of massive stars are determined by the wind structure and dynamics. Stellar winds, however, are not necessarily uniform or constant, as is seen in features migrating through UV and optical lines, interpreted as co-rotating interaction regions (CIR). We have searched for line variability in the O-star, zeta Puppis (among others), with suggestive but unconvincing results. With greater sensitivity and high spectral resolution, we would be able to determine if there are X-ray counterparts to CIR and refine our understanding of plasma heating in winds and the use of X-ray emission lines as diagnostics of mass loss.
Lynx promises to make critical, and potentially game-changing, improvements to our understanding of supernova-driven feedback in starburst galaxies by resolving down to the arcsecond scales of structure seen in deep Chandra observations and at other wavelengths. A first step at assessing this would be to produce diffuse X-ray flux maps for nearby galaxies to derive the temperature and abundance distribution based on Chandra observations. Here we describe our analysis of the Chandra data for nearby starburst galaxies and the use of these data to simulate future Lynx and Athena observations. Our main goals will be to determine how well Lynx will be able to constrain stellar feedback in nearby galaxies and to assess design requirements for Lynx to constrain the energetics of stellar feedback, map the dispersion of metals into the ISM and IGM and to resolve the interaction of the superwind fluid with swept-up ISM on the scales of filaments and shocks. Additionally Lynx holds the promise of resolving extranuclear diffuse emission at distances ∼10× further than Athena, and have the sensitivity to detect the hot superwind fluid directly in some systems, e.g., by detecting H-like Fe-K emission.
The role of AGN in the transition of galaxies from actively star forming to quiescence is still not fully understood, and is particularly challenging to study for AGN that are weak or hidden by obscuration or host dilution. The high spatial resolution of Chandra is critical in separating the AGN from the host emission in these complex systems. The Shocked Post-starburst Galaxy Survey (SPOGs) selects quenching galaxies still containing shocks and molecular gas based on their optical line diagnostics. SPOGs catches galaxies at an earlier stage of transition than classical post-starburst selection criteria, providing a crucial window into the role of AGN in this early phase of transformation. We recently obtained a deep Chandra observation of the proto-typical SPOG NGC1266 combined with a NuSTAR observation as well as Chandra observations of a set of SPOGs showing enhanced IR emission relative to their molecular content. I will discuss the insights obtained about the characteristics of AGN in SPOGs and the implications on the role of AGN in galaxy transitions.
The Athena X-ray observatory has been conceived to study the Hot and Energetic Universe. The principal areas of study will include studies of the physical and chemical evolution of the hot baryonic component in the Universe, the physics of galaxy clusters, phenomena generated around black holes and feedback on all mass scales. In this talk, I will detail the science objectives of Athena and provide an update on the mission's status in its present study phase, with the goal of being proposed for 'adoption' around 2019/20.
I will review a few of the key insights about how AGN feedback works to regulate itself in massive galaxies, yielded primarily through observations with the Chandra X-ray Observatory. I will present a framework that can be applied to lower-mass systems. I will show and provide a recipe for predicting the halo properties of the most luminous X-ray systems at range of galaxy mass scales.
Chandra observations have highlighted the role of radio outbursts from cluster central galaxies in limiting star formation in cool cores. In addition to being hosted by the central galaxy of a cool core cluster, the FRII radio galaxy Cygnus A is the archetype of powerful radio galaxies. I will present results from a detailed study of the cocoon shocks of Cygnus A using 2 Msec of Chandra observations. The AGN outburst has an age close to 20 Myr and a mean power of about 1046 erg/sec. Weak shock strengths are detected over the majority of the cocoon, implying a uniform pressure in the bulk of the radio lobes. Estimated hotspot pressures agree with synchrotron self-Compton models, while determined jet and lobe properties are broadly consistent with FRII models. These results required close to the deepest feasible Chandra observations, but similar results could be achieved routinely with the high throughput of Lynx. Furthermore, the high resolution X-ray spectroscopy of Lynx will enable us to examine issues currently inaccessible with Chandra, as I will demonstrate with simulations.
Compact Symmetric Objects (CSOs) are thought to be among the progenitors of large-scale radio galaxies. They show radio features typically observed in large-scale radio galaxies (jets, lobes, hot spots), but contained within the central 1 kpc region of the host galaxy. Because the CSOs are symmetric and not affected by beaming, their linear radio size can be translated into the source age if one measures the expansion velocity of the radio source. However, if the jet expansion is disturbed, e.g. by a dense interstellar medium (ISM), the ages derived this way may be biased. Until now we did not have means to discriminate between confined and non-confined radio sources. We present our X-ray studies of CSOs performed with Chandra and XMM-Newton. For the first time, the data reveal the evidence in favor of the idea that in a sub-population of CSOs the radio jets may be confined by a dense ISM. Thus, the CSO kinematic ages may be underestimated. We discuss the implications of our results on the high energy emission models of CSOs, the earliest stages of a radio source evolution, jet-galaxy co-evolution, and advances that are expected in the CSO field thanks to Lynx.
In recent years, the combination of SZ surveys and X-ray follow-up has led to rapid advances in our understanding of galaxy clusters and their evolution over the past ~10 billion years. I will summarize the progress we have made in a small amount of time, exploiting the synergy of the South Pole Telescope and Chandra X-ray Observatory. In the next decade, the number of known clusters at high redshift is poised to grow by several orders of magnitude, with X-ray surveys by eRosita, SZ surveys by SPT-3G, Advanced ACTPol, and CMB-S4, and OIR surveys by LSST, Euclid, and WFIRST. The most distant of these systems will be extremely faint and soft — we currently have no ability to follow these systems up in the X-ray. I will summarize several exciting programs that will be possible with Lynx in combination with these next-generation surveys, in particular highlighting the need for soft sensitivity and high angular resolution in any next generation X-ray mission.
The nature of SMBH-galaxy co-evolution remains one of the major outstanding problems in modern astronomy. A natural link exists between the fuelling of star formation in galaxies and SMBH growth, namely the availability of cold gas. The cluster environment influences gas reservoirs through processes such as ram-pressure stripping, evaporation, starvation, and tidal effects of the cluster potential. The relative importance of these processes depends on both the position within, the mass of, and the redshift of the host galaxy cluster. As such, comparisons of AGN populations between dense cluster environments and the field provides valuable additional constraints on fuelling processes, isolating the connection between SMBH and galaxy growth.
Our goal is to investigate how these environmental processes influence the evolution of the cluster AGN population. To this end, we have launched a massive, multi-wavelength campaign anchored by Chandra data. Chandra's excellent spatial resolution is allowing us to explore the X-ray AGN population in more than 500 massive galaxy clusters from z=0 to z∼1.8. An X-ray AGN survey is crucial for such a study as it suffers little contamination, has low absorption bias, and provides direct access to most of the accretion power in the Universe. We expect to identify ∼40,000 X-ray AGN and will trace the evolution of the cluster AGN population across cosmic time and as a function of cluster mass. Using VLA FIRST data, we are performing a parallel analysis of the radio AGN population in a subset of these clusters, providing a complementary probe into the evolution of kinetic mode AGN activity. Furthermore, we have obtained deep VIMOS optical spectroscopy of 7 of these clusters, allowing us to extend our analysis to a background free investigation of the cluster AGN population as a function of stellar mass and star formation rates.
Looking to the future, Lynx's high spatial resolution, wide field of view, and large effective area at soft energies, uniquely enable an extension of this study out to both the highest redshift and lowest mass clusters. For the first time we will be able to investigate the complete story of AGN evolution in dense environments, from early-times, through the peaks of AGN and SF activity, to the present day.
A significant fraction of the mass of galaxy clusters is located in the outskirts of clusters, outside of their relatively well-studied central regions. Therefore, understanding the structure and ICM physics of clusters in this region, and how they depend on cluster dynamical state and local environment, is important for doing precision cosmology with clusters. Despite this fact, cluster outskirts remain relatively poorly understood. For example, entropy profiles of the ICM generally lie below what would be expected from simple gravitational collapse models of structure formation, possibly due to the presence of small unresolved gas clumps, although the clumping factors predicted by simulations are generally too small to explain observations. I will discuss what we know about the virialization region of clusters, with a focus on our recent work on merging clusters and the connection between cluster outskirts and large scale structure filaments. I will also discuss how upcoming and proposed X-ray missions such as Lynx can contribute to this important area of study.
The extragalactic surveys performed by Chandra over the past 18 years have shed light on AGN demographics and greatly shaped our current understanding of black hole and galaxy co-evolution. The combination of deep and large area X-ray studies, which probe a wide range of the luminosity-redshift space, and the associated multiwavelength data are the keys to the achieved progress.
In this talk, I will present the work performed primarily with the Chandra COSMOS Legacy survey as well as deeper and wider surveys, using both detected sources and stacking analysis of non-detections. I will focus on the relation between BH accretion and star formation, and SMBH growth in the high redshift Universe, including what we have learned about black hole seeds from nearby intermediate mass black holes. I will also present how archival X-ray and multiwavelength data allows us to derive cosmological parameters using AGN/QSO as standard candels. Finally, I will present what we will be able to learn on these subjects with Lynx and complementary multiwavelength data in the 2030s.
Active galactic nuclei (AGN) tend to ionize gas in their host galaxies via photoionization and kinematic outflows, creating extended X-ray signatures of feedback that Chandra can spatially resolve. Although the bulk of this emission occurs below 1 keV, in recent years deep Chandra observations of nearby AGN have shown extended harder emission both in lines and continuum, which has fundamentally challenged our conception of the nature of hard X-rays from AGN. We will discuss ways in which Chandra's ability to spatially resolve harder X-ray emission presents opportunities for deep observations in anticipation of Lynx's unprecedented sensitivity and energy resolution, in an era where the ACIS contaminant buildup makes this regime a natural focus.
High-resolution instruments like the VLA, HST, and Chandra have allowed us to map the structure and SED evolution of extragalactic jets on the kpc scale where they interact with the galactic and intergalactic environment, yet the physical description of these jets remains mysterious. Among things remaining to be settled are the particle makeup of these jets, their velocity profiles and total energy content, and in many cases even the radiation mechanism. One of the great discoveries by Chandra has been the 'anomalous' class of X-ray bright jets, for which the X-ray mechanism is still unsettled. I will describe some recent developments in the study of resolved X-ray detected AGN jets, and discuss how a successor to Chandra will be critical to finally solving the X-ray origin problem in large-scale jets.
I will discuss the current understanding of key physical properties of some of the first generation of growing supermassive black holes (SMBHs). This includes their accretion rates and history, their host galaxies, and the large-scale environments that enable their emergence about a billion years after the big-bang. The available multi-wavelength data is consistent with Eddington-limited, radiatively efficient accretion that had to proceed almost continuously since very early epochs. New ALMA data confirms high SFRs and gas content in the host galaxies, and moreover a high fraction of companion, interacting galaxies, separated by ~10-50 kpc. This clearly support the idea that the first generation of luminous SMBHs grew in overdense environments, and that major mergers are important drivers for rapid early SMBH and host galaxy growth, although other fueling processes and accretion modes may still be required. Current X-ray surveys cannot access the lower-mass counterparts of these rare massive quasars, which would elucidate the earliest stages of BH formation and growth. Such low-mass nuclear BHs will be the prime targets of the deepest surveys foreseen for Lynx, within the theme of "First Accretion Light".