Seminar Abstracts: 2007-2008
Abstract:
Over the past four decades, submillimeter astronomy has evolved from a small group of experimentalists performing difficult, pioneering observations with crude equipment, to a much larger field with a central role in modern astrophysics. Indeed, major investments are now being made through projects such as Herschel, ALMA, and JCMT/SCUBA 2. The underlying scientific and technological developments that are driving this transformation will be discussed, along with their implications for future projects, such as the proposed 25m CCAT telescope.
Over the past four decades, submillimeter astronomy has evolved from a small group of experimentalists performing difficult, pioneering observations with crude equipment, to a much larger field with a central role in modern astrophysics. Indeed, major investments are now being made through projects such as Herschel, ALMA, and JCMT/SCUBA 2. The underlying scientific and technological developments that are driving this transformation will be discussed, along with their implications for future projects, such as the proposed 25m CCAT telescope.
Mark Swinbank
Durham University
Exploring superwinds in high redshift galaxies through integral field spectroscopy
Abstract:
The problem with galaxy formation models is not to understand how galaxies form (this is due to the condensing and cooling of gas), but to understand why such a small fraction of baryons are locked up in stars. Simple prescriptions for cooling predict that over 50% of baryons should be locked up in stars, yet a census of the baryonic content of galaxies suggests that the baryonic fraction is <10%. To solve this problem requires some form of feedback -- a method of expelling baryons from the galaxy and reheating the galaxy halo. As such, probing the energetics, mass out-flow rates and kinematics in high-redshift galaxies is a key observational goal in order to test exactly how this mechanism regulates galaxy formation. In this talk, I will show recent observations which use sensitive integral field spectrographs to spatially resolve the kinematics, energetics and mass outflow rates in high redshift galaxies. In particular I will show how gravitational lensing can be used to probe the relation between star-formation and gas dynamics in "normal" high-redshift galaxies which would otherwise be too faint to observe via conventional observations.
The problem with galaxy formation models is not to understand how galaxies form (this is due to the condensing and cooling of gas), but to understand why such a small fraction of baryons are locked up in stars. Simple prescriptions for cooling predict that over 50% of baryons should be locked up in stars, yet a census of the baryonic content of galaxies suggests that the baryonic fraction is <10%. To solve this problem requires some form of feedback -- a method of expelling baryons from the galaxy and reheating the galaxy halo. As such, probing the energetics, mass out-flow rates and kinematics in high-redshift galaxies is a key observational goal in order to test exactly how this mechanism regulates galaxy formation. In this talk, I will show recent observations which use sensitive integral field spectrographs to spatially resolve the kinematics, energetics and mass outflow rates in high redshift galaxies. In particular I will show how gravitational lensing can be used to probe the relation between star-formation and gas dynamics in "normal" high-redshift galaxies which would otherwise be too faint to observe via conventional observations.
Abstract:
Sometimes discovering the most precious gems requires novel efforts and a bit of polish to bring out their luster.
Nearby stellar gems will be discussed in the context of the solar neighborhood, with special emphasis on results from the SCR (SuperCOSMOS RECONS) survey. Bucketfuls of red dwarfs, white dwarfs, and subdwarfs have been found via concentrated digging. Discoveries include the 24th nearest star system, a late-type red dwarf with a brown dwarf companion.
An invitation extended by Nigel Hambly to Todd Henry to visit the ROE five years ago has led to a remarkable collaboration that has revealed numerous nearby stars, and is helping to revolutionize our understanding of the Sun's neighbors.
Sometimes discovering the most precious gems requires novel efforts and a bit of polish to bring out their luster.
Nearby stellar gems will be discussed in the context of the solar neighborhood, with special emphasis on results from the SCR (SuperCOSMOS RECONS) survey. Bucketfuls of red dwarfs, white dwarfs, and subdwarfs have been found via concentrated digging. Discoveries include the 24th nearest star system, a late-type red dwarf with a brown dwarf companion.
An invitation extended by Nigel Hambly to Todd Henry to visit the ROE five years ago has led to a remarkable collaboration that has revealed numerous nearby stars, and is helping to revolutionize our understanding of the Sun's neighbors.
Abstract:
The radio luminosity function (RLF) of extragalactic radio sources arises from a combination of the luminosity evolution of individual radio-loud AGN and their population as a whole. I will show how analytical models of radio galaxy evolution can be used to construct the RLF. At the same time we can use the same models to make predictions for other observable parameters like the size of the radio lobes. By comparison with complete, flux-limited samples of radio-loud AGN it is possible to infer the properties of the source environments. We can constrain which radio-loud AGN are evolving in which type of environment as a function of cosmological redshift. Finally we can derive a history of cosmic heating by AGN only based on radio observations.
The radio luminosity function (RLF) of extragalactic radio sources arises from a combination of the luminosity evolution of individual radio-loud AGN and their population as a whole. I will show how analytical models of radio galaxy evolution can be used to construct the RLF. At the same time we can use the same models to make predictions for other observable parameters like the size of the radio lobes. By comparison with complete, flux-limited samples of radio-loud AGN it is possible to infer the properties of the source environments. We can constrain which radio-loud AGN are evolving in which type of environment as a function of cosmological redshift. Finally we can derive a history of cosmic heating by AGN only based on radio observations.
Abstract:
I will focus on the bending of light by mass in the Universe, cosmic shear, as a probe of dark energy. I will discuss how intrinsic alignments of galaxies can contaminate the signal and show how galaxy-galaxy lensing can produce an intrinsic alignment signal. I will present results for how the dark energy constraints can be degraded by intrinsic alignments, in particular in the presence of realistic photometric redshifts. Finally I will discuss whether or not galaxy cluster counts and cosmic shear double count information on dark energy.
I will focus on the bending of light by mass in the Universe, cosmic shear, as a probe of dark energy. I will discuss how intrinsic alignments of galaxies can contaminate the signal and show how galaxy-galaxy lensing can produce an intrinsic alignment signal. I will present results for how the dark energy constraints can be degraded by intrinsic alignments, in particular in the presence of realistic photometric redshifts. Finally I will discuss whether or not galaxy cluster counts and cosmic shear double count information on dark energy.
Abstract:
I will discuss how joint analysis of the physical properties of galaxies together with their clustering are yielding insights into the processes repsonsible for triggering both starburst and AGN phenomena in nearby galaxies.
I will discuss how joint analysis of the physical properties of galaxies together with their clustering are yielding insights into the processes repsonsible for triggering both starburst and AGN phenomena in nearby galaxies.
Abstract:
A popular model for the coevolution of bulges and supermassive black holes is one in which a galaxy merger leads to the inflow of gas which fuels a strong starburst, followed by an AGN phase in which the black hole grows significantly. I will present and discuss recent results from the SDSS spectroscopic galaxy catalogue, which use a new, high signal-to-noise ratio spectral diagnostic of recent star formation history, to show that the majority of low redshift black hole accretion in Type II AGN occurs under less spectacular circumstances. However, a small number of galaxies (<10% of our sample of ~34000) which are undergoing, or have recently undergone, a major star formation episode, have the highest average black hole growth rates and show evidence for recent strong interactions and mergers in their light distributions. A significant fraction of this black hole growth occurs in AGN with high amounts of dust extinction, often coinciding with an old, post-starburst stellar population.
A popular model for the coevolution of bulges and supermassive black holes is one in which a galaxy merger leads to the inflow of gas which fuels a strong starburst, followed by an AGN phase in which the black hole grows significantly. I will present and discuss recent results from the SDSS spectroscopic galaxy catalogue, which use a new, high signal-to-noise ratio spectral diagnostic of recent star formation history, to show that the majority of low redshift black hole accretion in Type II AGN occurs under less spectacular circumstances. However, a small number of galaxies (<10% of our sample of ~34000) which are undergoing, or have recently undergone, a major star formation episode, have the highest average black hole growth rates and show evidence for recent strong interactions and mergers in their light distributions. A significant fraction of this black hole growth occurs in AGN with high amounts of dust extinction, often coinciding with an old, post-starburst stellar population.
Abstract:
The enrichment of the intergalactic medium (IGM) with heavy elements provides us with a fossil record of past star formation and a unique laboratory to study galactic feedback processes. I will present measurements of the distribution and relative abundances of intergalactic carbon, silicon, and oxygen as obtained from high-redshift quasar absorption spectra. I will also present evidence for the existence of a very large population of compact, highly enriched gas clouds which has important implications for the small-scale mixing of the heavy elements. Finally, I will explore the connection between the IGM and starburst galaxies using a large Lyman-break galaxy redshift survey in the fields of background quasars.
The enrichment of the intergalactic medium (IGM) with heavy elements provides us with a fossil record of past star formation and a unique laboratory to study galactic feedback processes. I will present measurements of the distribution and relative abundances of intergalactic carbon, silicon, and oxygen as obtained from high-redshift quasar absorption spectra. I will also present evidence for the existence of a very large population of compact, highly enriched gas clouds which has important implications for the small-scale mixing of the heavy elements. Finally, I will explore the connection between the IGM and starburst galaxies using a large Lyman-break galaxy redshift survey in the fields of background quasars.
Abstract:
Most astrophysically relevant accretion discs might be twisted or warped. The reaction of the disc to a warp disturbance can have major effects on the evolution of the system. For example, the process of alignment between the spin of a black hole and the angular momentum of the disc due to the so-called Bardeen-Petterson effect strongly depends on the effectiveness of warp propagation, with major consequenses on the spin history of the black hole. Here I discuss these issues in the light of a series of high resolution numerical simulations that I have performed to investigate the complex hydrodynamics which is responsible for these phenomena. Detailed hydrodynamical models predict (perhaps counter-intuitively) that as the disc viscosity decreases, the rate of warp propagation increases. Here we demonstrate numerically that this is indeed the case, as long as viscosity is high enough. For low viscosities, on the other hand, the analytic theory breaks down and the rate of warp propagation becomes progressively much slower than expected.
Most astrophysically relevant accretion discs might be twisted or warped. The reaction of the disc to a warp disturbance can have major effects on the evolution of the system. For example, the process of alignment between the spin of a black hole and the angular momentum of the disc due to the so-called Bardeen-Petterson effect strongly depends on the effectiveness of warp propagation, with major consequenses on the spin history of the black hole. Here I discuss these issues in the light of a series of high resolution numerical simulations that I have performed to investigate the complex hydrodynamics which is responsible for these phenomena. Detailed hydrodynamical models predict (perhaps counter-intuitively) that as the disc viscosity decreases, the rate of warp propagation increases. Here we demonstrate numerically that this is indeed the case, as long as viscosity is high enough. For low viscosities, on the other hand, the analytic theory breaks down and the rate of warp propagation becomes progressively much slower than expected.
Lance Miller
University of Oxford
Active galaxy evolution and the growth of supermassive black holes
Abstract:
These days you see a lot of talks discussing the link between supermassive black hole growth and galaxy formation. This talk will discuss the extent to which we understand, in this context, the luminous phase of black hole growth - the cosmic evolution of active galaxies - and will look at what we know about AGN cosmic downsizing - which black holes are most active at low and moderate redshifts, and what shapes the active galaxy populations that we see in the local universe?
These days you see a lot of talks discussing the link between supermassive black hole growth and galaxy formation. This talk will discuss the extent to which we understand, in this context, the luminous phase of black hole growth - the cosmic evolution of active galaxies - and will look at what we know about AGN cosmic downsizing - which black holes are most active at low and moderate redshifts, and what shapes the active galaxy populations that we see in the local universe?
Mike Lockwood
Rutherford Appleton Laboratory
Quantifying the solar contribution to recent global climate change
Abstract:
Paleoclimate evidence suggests that solar variations had a persistent influence on Earth's climate throughout the Holocene (the warm interglacial since the last ice age). Two mechanisms have been proposed, associated with variations in the total solar irradiance (TSI) and with heliospheric modulation of galactic cosmic rays (GCRs) and their postulated effect on clouds. The variations both will be reviewed, as will the evidence for a link between GCRs and the formation of clouds. A key question is how much of this pre-industrial solar effect on climate is relevant to the rapid climate change we have seen in recent years. This is analysed allowing for ocean energy storage and release (principally via El Nino and La Nina events in the equatorial Pacific), along with volcanic anthropogenic and solar climate forcings. The analysis also allows for the response time of the climate system to each forcing individually. The results will be compared to the IPCC's conclusions and the implications discussed (including those for the detection of Earth-like extra-solar planets).
Paleoclimate evidence suggests that solar variations had a persistent influence on Earth's climate throughout the Holocene (the warm interglacial since the last ice age). Two mechanisms have been proposed, associated with variations in the total solar irradiance (TSI) and with heliospheric modulation of galactic cosmic rays (GCRs) and their postulated effect on clouds. The variations both will be reviewed, as will the evidence for a link between GCRs and the formation of clouds. A key question is how much of this pre-industrial solar effect on climate is relevant to the rapid climate change we have seen in recent years. This is analysed allowing for ocean energy storage and release (principally via El Nino and La Nina events in the equatorial Pacific), along with volcanic anthropogenic and solar climate forcings. The analysis also allows for the response time of the climate system to each forcing individually. The results will be compared to the IPCC's conclusions and the implications discussed (including those for the detection of Earth-like extra-solar planets).
Abstract:
Brown dwarfs are intermediate in mass between stars and planets, and there is roughly one brown dwarf per five stars. But we do not know how brown dwarfs form. I will explain why we think brown dwarfs form more like stars than planets, and discuss the two main theories of brown dwarf formation - cores and ejection - and a new theory that they form as companions to M-dwarfs. I hope to convince you that they most often form in binary systems, and in fact almost every star forms in a multiple system.
Brown dwarfs are intermediate in mass between stars and planets, and there is roughly one brown dwarf per five stars. But we do not know how brown dwarfs form. I will explain why we think brown dwarfs form more like stars than planets, and discuss the two main theories of brown dwarf formation - cores and ejection - and a new theory that they form as companions to M-dwarfs. I hope to convince you that they most often form in binary systems, and in fact almost every star forms in a multiple system.
Abstract:
Understanding star formation in a galaxies involves how they organise their interstellar gas to produce giant molecular clouds where star formation occurs, the formation of stars inside the clouds as well as the feedback from young stars on the ISM. I will present numerical simulations of these processes including the spiral triggering of star formation which can produce GMCs and their internal properties relate to the overall efficiency of star formation. The collapse and fragmentation of these clouds plus continued accretion can generate the full range of stellar properties. Feedback processes can also be modeled to explore the physical affects of stellar winds, ionising radiation and supernova explosions on the galactic ISM and any subsequent star formation.
Understanding star formation in a galaxies involves how they organise their interstellar gas to produce giant molecular clouds where star formation occurs, the formation of stars inside the clouds as well as the feedback from young stars on the ISM. I will present numerical simulations of these processes including the spiral triggering of star formation which can produce GMCs and their internal properties relate to the overall efficiency of star formation. The collapse and fragmentation of these clouds plus continued accretion can generate the full range of stellar properties. Feedback processes can also be modeled to explore the physical affects of stellar winds, ionising radiation and supernova explosions on the galactic ISM and any subsequent star formation.
Abstract:
I plan to discuss various steps involved in extracting the power spectrum (PS) from a third generation all sky CMB survey namely Planck, which will map the entire sky in exquisite detail in nine different frequency channels starting next year. Paying particular attention to various PS estimation techniques for Temperature and Polarization maps I plan to compare diverse methods which are typically used to deal with such cosmological data sets: from brute force likelihood techniques to Monte-Carlo based approaches and their recent incarnations in a hybrid paradigm. Results of applying these techniques along with KL Generalized-Eigenmode analysis to realistic simulations will be presented in some detail. Issues related to interfacing map-making and components separation algorithms with PS estimation techniques will be addressed. Bias, scatter and associated error covariances of pseudo-Cl approaches and their relation to exact likelihood based schemes are surveyed. Extensions of such methods to analyze cross-correlation with external data sets such as NVSS, HEAO or APM surveys are discussed briefly. Possibility of generalization of these techniques to extract information on non-Gaussianity are explored. I also plan to discuss inherent adaptability of such generalized techniques in analyzing other cosmological data sets which include various projected surveys as well as surveys with redshift or tomographical information. Results realted to lensing of CMB and its possible recovery from realistic Planck simulations are also discussed.
I plan to discuss various steps involved in extracting the power spectrum (PS) from a third generation all sky CMB survey namely Planck, which will map the entire sky in exquisite detail in nine different frequency channels starting next year. Paying particular attention to various PS estimation techniques for Temperature and Polarization maps I plan to compare diverse methods which are typically used to deal with such cosmological data sets: from brute force likelihood techniques to Monte-Carlo based approaches and their recent incarnations in a hybrid paradigm. Results of applying these techniques along with KL Generalized-Eigenmode analysis to realistic simulations will be presented in some detail. Issues related to interfacing map-making and components separation algorithms with PS estimation techniques will be addressed. Bias, scatter and associated error covariances of pseudo-Cl approaches and their relation to exact likelihood based schemes are surveyed. Extensions of such methods to analyze cross-correlation with external data sets such as NVSS, HEAO or APM surveys are discussed briefly. Possibility of generalization of these techniques to extract information on non-Gaussianity are explored. I also plan to discuss inherent adaptability of such generalized techniques in analyzing other cosmological data sets which include various projected surveys as well as surveys with redshift or tomographical information. Results realted to lensing of CMB and its possible recovery from realistic Planck simulations are also discussed.
Dimitris Stamatellos
Cardiff University
Brown dwarf formation by gravitational fragmentation of massive discs
Abstract:
We suggest that stars like the Sun should sometimes form with massive extended discs, and we show by means of radiative hydrodynamic simulations that the outer parts of such discs (R >100 AU) are likely to fragment on a dynamical time-scale (a few thousand years), forming low-mass companions: principally brown dwarfs, but also very low-mass hydrogen-burning stars and planetary-mass objects. We will compare the properties of the objects produced by this mechanism with the observed properties of low-mass objects, and show that this formation theory appears to avoid some of the problems associated with the `embryo ejection' scenario, and to answer some of the questions not yet answered by the `turbulent fragmentation' scenario.
We suggest that stars like the Sun should sometimes form with massive extended discs, and we show by means of radiative hydrodynamic simulations that the outer parts of such discs (R >100 AU) are likely to fragment on a dynamical time-scale (a few thousand years), forming low-mass companions: principally brown dwarfs, but also very low-mass hydrogen-burning stars and planetary-mass objects. We will compare the properties of the objects produced by this mechanism with the observed properties of low-mass objects, and show that this formation theory appears to avoid some of the problems associated with the `embryo ejection' scenario, and to answer some of the questions not yet answered by the `turbulent fragmentation' scenario.
Abstract:
Planets are believed to form in the gas and dust discs observed around young stars. As a forming planet grows in mass, it interacts gravitationally with the protoplanetary disc, leading to angular momentum exchange and migration. A cursory glance at the architecture of extrasolar planetary systems suggests that migration is common during planetary formation. I will review the current theory of disc-planet interactions, and present the results of recent simulations that examine: (i) planet migration in turbulent discs; (ii) planetesimal accretion in turbulent discs; (iii) terrestrial planet formation in the prescence of migrating giant planets.
Planets are believed to form in the gas and dust discs observed around young stars. As a forming planet grows in mass, it interacts gravitationally with the protoplanetary disc, leading to angular momentum exchange and migration. A cursory glance at the architecture of extrasolar planetary systems suggests that migration is common during planetary formation. I will review the current theory of disc-planet interactions, and present the results of recent simulations that examine: (i) planet migration in turbulent discs; (ii) planetesimal accretion in turbulent discs; (iii) terrestrial planet formation in the prescence of migrating giant planets.
Matthew Lehnert
Observatoire de
Paris
Direct Observations of (some of) the Physical Drivers
of Galaxy Evolution
Abstract:
I discuss several on-going programs to understand observationally the physical processes important for driving galaxy evolution. I present integral field spectroscopic and imaging observations of galaxies from z=0.6 to 5 to demonstrate the wide range of phenomenology exhibited by high redshift galaxies. I then turn to how these properties may translate into a deeper understanding of how galaxies form and evolve, touching on the physical characteristics of galaxies such as their dynamical masses, metallicities, angular momenta, etc., the importance of feedback of massive stars and supermassive black holes, and the possible relative roles of mergers and gas accretion in influencing galaxies at different redshifts.
I discuss several on-going programs to understand observationally the physical processes important for driving galaxy evolution. I present integral field spectroscopic and imaging observations of galaxies from z=0.6 to 5 to demonstrate the wide range of phenomenology exhibited by high redshift galaxies. I then turn to how these properties may translate into a deeper understanding of how galaxies form and evolve, touching on the physical characteristics of galaxies such as their dynamical masses, metallicities, angular momenta, etc., the importance of feedback of massive stars and supermassive black holes, and the possible relative roles of mergers and gas accretion in influencing galaxies at different redshifts.
Martin Bureau
University of Oxford
Star Formation in Local Early-Type Galaxies: Insights from UV, Optical, and mm
Abstract:
The incidence, location, and origin of young stars and star formation in nearby early-type galaxies are constrained from multi-wavelength observations. From two-dimensional maps of the ionised-gas and stellar absorption linestrengths from SAURON, I will briefly discuss the distributions of age, metallicity and alpha elements in local early-types and review the evidence for recent star formation. The apparent relationship between young stars and kinematically decoupled components such as central disks suggests recent accretion or merging events. Complementary evidence for both internal and external star formation drivers arises from our parallel GALEX UV imaging survey, as well as entirely new constraints on the origin of the so-called UV-upturn phenomenon. I will further discuss a new survey of the molecular gas in SAURON galaxies, and targeted mm synthesis observations of many galaxies in CO, on the same spatial scales as the integral-field data. Those indicate a surprisingly high star formation efficiency in early-types and show stunning correlations between molecular gas structures and young dynamically decoupled components. In particular, many objects in the process of forming regular kpc-size disks are revealed. Our observations thus offer a fairly complete picture of residual star formation in early-types and reveal disk formation in real time, in a setting probably not unlike that of disk formation in dark halos at high redshifts.
The incidence, location, and origin of young stars and star formation in nearby early-type galaxies are constrained from multi-wavelength observations. From two-dimensional maps of the ionised-gas and stellar absorption linestrengths from SAURON, I will briefly discuss the distributions of age, metallicity and alpha elements in local early-types and review the evidence for recent star formation. The apparent relationship between young stars and kinematically decoupled components such as central disks suggests recent accretion or merging events. Complementary evidence for both internal and external star formation drivers arises from our parallel GALEX UV imaging survey, as well as entirely new constraints on the origin of the so-called UV-upturn phenomenon. I will further discuss a new survey of the molecular gas in SAURON galaxies, and targeted mm synthesis observations of many galaxies in CO, on the same spatial scales as the integral-field data. Those indicate a surprisingly high star formation efficiency in early-types and show stunning correlations between molecular gas structures and young dynamically decoupled components. In particular, many objects in the process of forming regular kpc-size disks are revealed. Our observations thus offer a fairly complete picture of residual star formation in early-types and reveal disk formation in real time, in a setting probably not unlike that of disk formation in dark halos at high redshifts.
Abstract:
Diverse astronomical observations (on scales ranging from individual galaxies to the entire Universe) indicate that most of the matter in the Universe is dark and non-baryonic, and particle physics provides us with several well motivated dark matter candidates, including WIMPs (Weakly Interacting Massive Particles). Numerous experiments/observations are underway attempting to detect WIMPs either directly, in the lab, or indirectly, via the productions of their annihilation. The signals expected in these experiments depend on the dark matter distribution on sub-galactic scales. I will explain how WIMP micro-physics in the early Universe sets the properties of the first, earth mass, microhalos to form and discuss ongoing work attempting to understand their dynamical evolution and the resulting small scale dark matter distribution.
Diverse astronomical observations (on scales ranging from individual galaxies to the entire Universe) indicate that most of the matter in the Universe is dark and non-baryonic, and particle physics provides us with several well motivated dark matter candidates, including WIMPs (Weakly Interacting Massive Particles). Numerous experiments/observations are underway attempting to detect WIMPs either directly, in the lab, or indirectly, via the productions of their annihilation. The signals expected in these experiments depend on the dark matter distribution on sub-galactic scales. I will explain how WIMP micro-physics in the early Universe sets the properties of the first, earth mass, microhalos to form and discuss ongoing work attempting to understand their dynamical evolution and the resulting small scale dark matter distribution.
Abstract:
The formation and evolution of disk galaxies continues to be a very active field of research. I will start by describing simulations exploring the formation and evolution of disk outskirts, in particular the observed 'truncations' in the stellar density. These simulations lead to the realization that stars may migrate extensively across the disks over their lives while retaining near-circular orbits. I will discuss the consequences of such migration. I will then discuss the formation 'pseudo-bulges' as seen in simulations and present a diagnostic for recognizing such systems. Recent observational data have successfully applied this diagnostic. Future applications with these observational methods will allow us to obtain a detailed census of 'classical' versus 'pseudo' bulges. Finally I briefly touch upon the evolution of nuclear star clusters and their morphologies. This talk therefore covers a range of scales from the parsec scale up to the 10s of kiloparsec scales.
The formation and evolution of disk galaxies continues to be a very active field of research. I will start by describing simulations exploring the formation and evolution of disk outskirts, in particular the observed 'truncations' in the stellar density. These simulations lead to the realization that stars may migrate extensively across the disks over their lives while retaining near-circular orbits. I will discuss the consequences of such migration. I will then discuss the formation 'pseudo-bulges' as seen in simulations and present a diagnostic for recognizing such systems. Recent observational data have successfully applied this diagnostic. Future applications with these observational methods will allow us to obtain a detailed census of 'classical' versus 'pseudo' bulges. Finally I briefly touch upon the evolution of nuclear star clusters and their morphologies. This talk therefore covers a range of scales from the parsec scale up to the 10s of kiloparsec scales.
Abstract:
Accreting black holes are found in two families of objects: AGN and X-ray binaries. Distant quasars that shaped the early Universe are powered by supermassive black holes. They are, however, difficult to study, as they are usually very faint. X-ray binaries are much brighter and they evolve on much shorter timescales, providing us with perfect laboratories for studying black hole accretion flows. Yet the properties of the accretion flow should be fairly scale invariant, so what we learn about accretion flows from stellar mass systems should also be applicable to the supermassive black holes. I will review recent progress in understanding Galactic binary systems, in particular how the bewildering variety of spectral, timing and jet properties - the so called 'spectral states' - can be explained by changing the nature (and hence geometry) of the accretion flow.
Accreting black holes are found in two families of objects: AGN and X-ray binaries. Distant quasars that shaped the early Universe are powered by supermassive black holes. They are, however, difficult to study, as they are usually very faint. X-ray binaries are much brighter and they evolve on much shorter timescales, providing us with perfect laboratories for studying black hole accretion flows. Yet the properties of the accretion flow should be fairly scale invariant, so what we learn about accretion flows from stellar mass systems should also be applicable to the supermassive black holes. I will review recent progress in understanding Galactic binary systems, in particular how the bewildering variety of spectral, timing and jet properties - the so called 'spectral states' - can be explained by changing the nature (and hence geometry) of the accretion flow.
Steve Torchinsky
Observatoire de Paris
The Square Kilometre Array: Science Goals and Technology Development in Europe
Abstract:
The Square Kilometre Array will be an enormous radio astronomy facility with first-light of the completed array expected by 2020, and initial operations beginning in 2015. The SKA will be a massive array of many receiving elements, and it will thus have both exquisite sensitivity and angular resolution, as well as an ultra wide field of view. The fully sampled field-of-view, of the order of 200 square degrees, makes the SKA effectively a 10-gigapixel ultra wide field spectroscopic radio camera. Survey science will especially benefit from this instrument. For example, a billion galaxy redshift survey out to z=2 can be completed within a year, and will be used to detect Baryonic Acoustic Oscillations in the galaxy distribution, leading directly to a measure of the Dark Energy equation of state parameter. I will review the key science projects of the SKA, and give an overview of the planned implementation, in particular with a focus on the technology developments currently underway in Europe as part of the FP6 funded project SKADS (Square Kilometre Array Design Studies).
The Square Kilometre Array will be an enormous radio astronomy facility with first-light of the completed array expected by 2020, and initial operations beginning in 2015. The SKA will be a massive array of many receiving elements, and it will thus have both exquisite sensitivity and angular resolution, as well as an ultra wide field of view. The fully sampled field-of-view, of the order of 200 square degrees, makes the SKA effectively a 10-gigapixel ultra wide field spectroscopic radio camera. Survey science will especially benefit from this instrument. For example, a billion galaxy redshift survey out to z=2 can be completed within a year, and will be used to detect Baryonic Acoustic Oscillations in the galaxy distribution, leading directly to a measure of the Dark Energy equation of state parameter. I will review the key science projects of the SKA, and give an overview of the planned implementation, in particular with a focus on the technology developments currently underway in Europe as part of the FP6 funded project SKADS (Square Kilometre Array Design Studies).
Abstract:
Most of the so far acquainted knowledge about protoplanetary disks originates from the dust component (SEDs, images in scattered light, etc.) whereas the gas in the disks is more difficult to observe and more difficult to model. Yet, it is the gas component that sets the initial conditions for planet formation and drives - by it's dispersal - the evolution toward debris disks. With the launch of the HERSCHEL observatory, we will have the opportunity to study faint gas emission lines from the disks in the far infrared. In our GASPS open time key proposal, we are planning to observe CII, OI fine-structure and H2O, CO rotational lines that probe the surface, the volume and the midplane of the disks, respectively. These complementary observations will allows us to determine the disk gas mass, the chemical composition and the gas temperature structure. For a qualified interpretation of these observational data, we need accurate models. In this colloquium, I will summarise first results of new models for protoplanetary disks that solve the kinetic chemical equilibrium and the balance between non-LTE heating and cooling consistently with the vertical hydrostatic stratification. Current results suggest that the disk is vertically much more extended than expected close to the star. This "bulge" contains mainly atomic hydrogen with copious amounts of warm molecules like H2O.
Most of the so far acquainted knowledge about protoplanetary disks originates from the dust component (SEDs, images in scattered light, etc.) whereas the gas in the disks is more difficult to observe and more difficult to model. Yet, it is the gas component that sets the initial conditions for planet formation and drives - by it's dispersal - the evolution toward debris disks. With the launch of the HERSCHEL observatory, we will have the opportunity to study faint gas emission lines from the disks in the far infrared. In our GASPS open time key proposal, we are planning to observe CII, OI fine-structure and H2O, CO rotational lines that probe the surface, the volume and the midplane of the disks, respectively. These complementary observations will allows us to determine the disk gas mass, the chemical composition and the gas temperature structure. For a qualified interpretation of these observational data, we need accurate models. In this colloquium, I will summarise first results of new models for protoplanetary disks that solve the kinetic chemical equilibrium and the balance between non-LTE heating and cooling consistently with the vertical hydrostatic stratification. Current results suggest that the disk is vertically much more extended than expected close to the star. This "bulge" contains mainly atomic hydrogen with copious amounts of warm molecules like H2O.
Abstract:
As the only late-type spiral in the Local Group, M33 is an important laboratory for studying disk galaxy evolution. The fossil record of disk evolution is encoded in the ages, chemical compositions, kinematics, and spatial distributions of stellar populations. I will describe recent work to characterize this record in M33's outer disk using HST/ACS photometry reaching ~2.5 magnitudes below the horizontal branch of core helium burning stars. These observations reveal a composite stellar population whose youngest constituents have ages no greater than 100 Myr and whose oldest members have ages of several Gyr or more. The star formation and chemical enrichment histories, as revealed by the detailed color-magnitude distribution of stars, paint a picture in which M33's outer disk formed from the protracted inflow of gas, with at least half of the inflow occuring since z ~ 1. I will also briefly discuss the possible consequences our observations have for the issues of star formation thresholds and stellar migration in galactic disks.
As the only late-type spiral in the Local Group, M33 is an important laboratory for studying disk galaxy evolution. The fossil record of disk evolution is encoded in the ages, chemical compositions, kinematics, and spatial distributions of stellar populations. I will describe recent work to characterize this record in M33's outer disk using HST/ACS photometry reaching ~2.5 magnitudes below the horizontal branch of core helium burning stars. These observations reveal a composite stellar population whose youngest constituents have ages no greater than 100 Myr and whose oldest members have ages of several Gyr or more. The star formation and chemical enrichment histories, as revealed by the detailed color-magnitude distribution of stars, paint a picture in which M33's outer disk formed from the protracted inflow of gas, with at least half of the inflow occuring since z ~ 1. I will also briefly discuss the possible consequences our observations have for the issues of star formation thresholds and stellar migration in galactic disks.
HongShen Zhao
University of St-Andrews
Coincidences of Dark Energy with Dark Matter: Clues for a Simple
Alternative?
Abstract:
A rare coincidence of scales in standard particle physics is needed to explain why \Lambda or the negative pressure of cosmological dark energy (DE) coincides with the positive pressure P0 of random motion of dark matter (DM) in bright galaxies. Recently Zlosnik and coworkers proposed to modify the Einstein curvature by adding nonlinear pressure from a medium flowing with a four-velocity vector field U\mu. We propose to check whether a smooth extension of general relativity with a simple kinetic Lagrangian of U\mu can be constructed, and whether the pressure can bend spacetime sufficiently to replace the roles of DE, cold DM, and heavy neutrinos in explaining anomalous accelerations at all scales. As a specific proof of concept we find a vector-for-\Lambda model (V\Lambda model) and its variants. With essentially no free parameters, these appear broadly consistent with the solar system, gravitational potentials in dwarf spiral galaxies and the Bullet Cluster of galaxies, the early universe with inflation, structure formation, and big bang nucleosynthesis, and late acceleration with a 1:3 ratio of DM:DE.
A rare coincidence of scales in standard particle physics is needed to explain why \Lambda or the negative pressure of cosmological dark energy (DE) coincides with the positive pressure P0 of random motion of dark matter (DM) in bright galaxies. Recently Zlosnik and coworkers proposed to modify the Einstein curvature by adding nonlinear pressure from a medium flowing with a four-velocity vector field U\mu. We propose to check whether a smooth extension of general relativity with a simple kinetic Lagrangian of U\mu can be constructed, and whether the pressure can bend spacetime sufficiently to replace the roles of DE, cold DM, and heavy neutrinos in explaining anomalous accelerations at all scales. As a specific proof of concept we find a vector-for-\Lambda model (V\Lambda model) and its variants. With essentially no free parameters, these appear broadly consistent with the solar system, gravitational potentials in dwarf spiral galaxies and the Bullet Cluster of galaxies, the early universe with inflation, structure formation, and big bang nucleosynthesis, and late acceleration with a 1:3 ratio of DM:DE.
Abstract:
Ordinary baryonic particles (such as protons and neutrons) account for only one-sixth of the total matter in the Universe. The remainder is a mysterious "dark matter" component, which does not interact via the electromagnetic force and thus neither emits nor reflects light. However, evidence for its gravitational influence is mounting. The past few years have seen dramatic progress in measurements of weak gravitational lensing, the slight deflection of light from distant galaxies due to the curvature of intervening space. Recent observations from the Hubble Space Telescope have provided direct proof for, and large-scale maps of dark matter in the Universe. I review the current state of the art, then prospects and challenges for future measurements of gravitational lensing from space.
Ordinary baryonic particles (such as protons and neutrons) account for only one-sixth of the total matter in the Universe. The remainder is a mysterious "dark matter" component, which does not interact via the electromagnetic force and thus neither emits nor reflects light. However, evidence for its gravitational influence is mounting. The past few years have seen dramatic progress in measurements of weak gravitational lensing, the slight deflection of light from distant galaxies due to the curvature of intervening space. Recent observations from the Hubble Space Telescope have provided direct proof for, and large-scale maps of dark matter in the Universe. I review the current state of the art, then prospects and challenges for future measurements of gravitational lensing from space.
Abstract:
Clusters of galaxies are important probes both for cosmology and galaxy evolution. With the recent advent of wide-field infrared cameras, optical/infrared detection of clusters has been pushed to much higher-redshift limits. UKIDSS is the UK's dedicated deep and wide-field infrared survey program. In this talk I will present new results using combined optical and infrared data using our specifically designed cluster-detection algorithm. Spectroscopic follow-up of a subsample of high redshift (z~1) clusters allowed a detailed investigation of the complexity of such structures. To conclude I will discuss the shortcomings of using photometric optical cluster detection alone in the investigation of the fundamental cosmological paradigm.
Clusters of galaxies are important probes both for cosmology and galaxy evolution. With the recent advent of wide-field infrared cameras, optical/infrared detection of clusters has been pushed to much higher-redshift limits. UKIDSS is the UK's dedicated deep and wide-field infrared survey program. In this talk I will present new results using combined optical and infrared data using our specifically designed cluster-detection algorithm. Spectroscopic follow-up of a subsample of high redshift (z~1) clusters allowed a detailed investigation of the complexity of such structures. To conclude I will discuss the shortcomings of using photometric optical cluster detection alone in the investigation of the fundamental cosmological paradigm.
Abstract:
Low-frequency radio observations of neutral hydrogen during and before the epoch of cosmic reionisation will provide ~ 1000 quasi-independent source planes, each of precisely known redshift, if a resolution of ~ 1 arcminutes or better can be attained. These planes can be used to reconstruct the projected mass distribution of foreground material through the effects of gravitational lensing. Both resolution and signal-to-noise could exceed those of even the most optimistic idealized mass maps from galaxy lensing by more than an order of magnitude. A wide-area survey of 21 cm lensing would provide very sensitive constraints on cosmological parameters, in particular on dark energy. These are up to 20 times tighter than the constraints obtainable from comparably sized, very deep surveys of galaxy lensing, although the best constraints come from combining data of the two types.
Low-frequency radio observations of neutral hydrogen during and before the epoch of cosmic reionisation will provide ~ 1000 quasi-independent source planes, each of precisely known redshift, if a resolution of ~ 1 arcminutes or better can be attained. These planes can be used to reconstruct the projected mass distribution of foreground material through the effects of gravitational lensing. Both resolution and signal-to-noise could exceed those of even the most optimistic idealized mass maps from galaxy lensing by more than an order of magnitude. A wide-area survey of 21 cm lensing would provide very sensitive constraints on cosmological parameters, in particular on dark energy. These are up to 20 times tighter than the constraints obtainable from comparably sized, very deep surveys of galaxy lensing, although the best constraints come from combining data of the two types.
Abstract:
Planets form in circumstellar discs of gas and dust that are commonly found around young stars. Gravitational interaction between the planet and the disc may result in drastic changes in the orbital elements of the planet, which has consequences for the distribution of planets as observed today. Hot Jupiters, massive planets with orbital periods of a few days, are thought to have formed far out in the disc and migrated inward due to tidal interaction with the disc. The same migration mechanism, however, predicts that Earth-like analogs will all fall into the central star before the disc disappears and migration stops. I will discuss recent insights that indicate that the situation may be that bad, and that there is a powerful way of stopping or slowing down low-mass planet migration.
Planets form in circumstellar discs of gas and dust that are commonly found around young stars. Gravitational interaction between the planet and the disc may result in drastic changes in the orbital elements of the planet, which has consequences for the distribution of planets as observed today. Hot Jupiters, massive planets with orbital periods of a few days, are thought to have formed far out in the disc and migrated inward due to tidal interaction with the disc. The same migration mechanism, however, predicts that Earth-like analogs will all fall into the central star before the disc disappears and migration stops. I will discuss recent insights that indicate that the situation may be that bad, and that there is a powerful way of stopping or slowing down low-mass planet migration.
Abstract:
The SUPA Astrobiology initiative was planned to exploit our leading work in planet detection. As well as our latest exciting results in transit and microlensing observations, new areas have developed in the broader context of international astrobiology. I will discuss new SUPA programmes in studying planet formation (by theory, observation and experiment); pinpointing where to look for nearby (habitable) exo-Earths; and a novel project looking for life-signs in the outer Solar System.
The SUPA Astrobiology initiative was planned to exploit our leading work in planet detection. As well as our latest exciting results in transit and microlensing observations, new areas have developed in the broader context of international astrobiology. I will discuss new SUPA programmes in studying planet formation (by theory, observation and experiment); pinpointing where to look for nearby (habitable) exo-Earths; and a novel project looking for life-signs in the outer Solar System.
Abstract:
Following a series of prototypes over the last three years, AstroGrid is now releasing a full working product : the AstroGrid Desktop Suite. This is a set of client applications that run on your own computer, but connect through the internet to data services worldwide. The suite includes VODesktop, which allows you to browse and bookmark resources, and run queries against catalogues and so on; Topcat, for manipulating and plotting tables and doing cross matches; and AstroGrid Python, a way to write your own scripts to automate sequences of VO jobs. We also provide access to other VO tools worldwide, such as Aladin for analysing images, VOSpec and SPLAT-VO for analysing spectra, and AstroWeka and Astroneural for data mining. All these tools interoperate, i.e. they can pass data and messages to each other. In the talk, I will some brief background to the Virtual Observatory and how the technical stuff in the background works, and then will demonstrate the software.
Following a series of prototypes over the last three years, AstroGrid is now releasing a full working product : the AstroGrid Desktop Suite. This is a set of client applications that run on your own computer, but connect through the internet to data services worldwide. The suite includes VODesktop, which allows you to browse and bookmark resources, and run queries against catalogues and so on; Topcat, for manipulating and plotting tables and doing cross matches; and AstroGrid Python, a way to write your own scripts to automate sequences of VO jobs. We also provide access to other VO tools worldwide, such as Aladin for analysing images, VOSpec and SPLAT-VO for analysing spectra, and AstroWeka and Astroneural for data mining. All these tools interoperate, i.e. they can pass data and messages to each other. In the talk, I will some brief background to the Virtual Observatory and how the technical stuff in the background works, and then will demonstrate the software.
Mike Hobson
Cavendish Laboratory, University of Cambridge
Fast Bayesian inference in cosmology: neural networks and nested sampling
Abstract:
Methods for vastly accelerating the process of cosmological parameter estimation and model selection will be presented, focussing in two areas. First, a neural network approach will be discussed for the fast calculation of CMB and matter power spectra and experimental likelihood functions from a set of cosmological parameter values. Such networks can be easily trained to `learn' the observable properties of a wide class of cosmological models, and thereafter be used to replace costly calculations using CMBfast/CMB and the WMAP likelihood code with rapid model evaluations typically requiring only microseconds. Second, a multimodal nested sampling algorithm will be described, which, unlike standard MCMC, is capable of efficiently obtaining posterior samples and evidence values from high-dimensional distributions that may be multimodal and/or exhibit pronounced (curving) degeneracies. The method is around 2-3 orders of magnitude faster than standard MCMC on typical cosmological (and particle physics) problems. The combination of these methods means that cosmological (and other) Bayesian analyses that previously required weeks of supercomputing time can now be performed in minutes on a standard desktop computer.
Methods for vastly accelerating the process of cosmological parameter estimation and model selection will be presented, focussing in two areas. First, a neural network approach will be discussed for the fast calculation of CMB and matter power spectra and experimental likelihood functions from a set of cosmological parameter values. Such networks can be easily trained to `learn' the observable properties of a wide class of cosmological models, and thereafter be used to replace costly calculations using CMBfast/CMB and the WMAP likelihood code with rapid model evaluations typically requiring only microseconds. Second, a multimodal nested sampling algorithm will be described, which, unlike standard MCMC, is capable of efficiently obtaining posterior samples and evidence values from high-dimensional distributions that may be multimodal and/or exhibit pronounced (curving) degeneracies. The method is around 2-3 orders of magnitude faster than standard MCMC on typical cosmological (and particle physics) problems. The combination of these methods means that cosmological (and other) Bayesian analyses that previously required weeks of supercomputing time can now be performed in minutes on a standard desktop computer.
Abstract:
Dark energy, the mysterious energy component which is responsible for the observed accelerated expansion of the universe, has yet to be explained within theories of particle physics. A scalar field has been proposed as a possible candidate for dark energy. It is usually assumed that the dark energy scalar field interacts only via gravity with the rest of the world and is decoupled otherwise. However, this is very unlikely when one studies the problem from the particle physics point of view. In this talk I will describe the implications of new interactions between a dark energy scalar field with matter in the universe (such as neutrinos and dark matter). I will discuss how cosmological observations and laboratory experiments can search for new interactions mediated by dark energy.
Dark energy, the mysterious energy component which is responsible for the observed accelerated expansion of the universe, has yet to be explained within theories of particle physics. A scalar field has been proposed as a possible candidate for dark energy. It is usually assumed that the dark energy scalar field interacts only via gravity with the rest of the world and is decoupled otherwise. However, this is very unlikely when one studies the problem from the particle physics point of view. In this talk I will describe the implications of new interactions between a dark energy scalar field with matter in the universe (such as neutrinos and dark matter). I will discuss how cosmological observations and laboratory experiments can search for new interactions mediated by dark energy.
Abstract:
I present the recent discoveries of two Galactic massive young clusters, which together contain 40 Red Supergiants ~V 20% of all those known in the Galaxy, and as many in the entire Large Magellanic Cloud. From observations and evolutionary synthesis models, we argue that the cluster masses are comparable to the other Galactic "Super Star Clusters" such as Westerlund 1 and the Arches Cluster. The two clusters are located at the base of the Scutum-Crux spiral arm, and appear to lie at the tip of the Galactic Bar. Therefore, these objects can be used as a probe to study the star-formation history and evolution of the Galaxy. Further, the distinctly different ages of the clusters, uniform metallicity, and large number of RSGs, mean that these objects now offer an unprecedented opportunity to study the pre-supernova evolution of massive stars.
I present the recent discoveries of two Galactic massive young clusters, which together contain 40 Red Supergiants ~V 20% of all those known in the Galaxy, and as many in the entire Large Magellanic Cloud. From observations and evolutionary synthesis models, we argue that the cluster masses are comparable to the other Galactic "Super Star Clusters" such as Westerlund 1 and the Arches Cluster. The two clusters are located at the base of the Scutum-Crux spiral arm, and appear to lie at the tip of the Galactic Bar. Therefore, these objects can be used as a probe to study the star-formation history and evolution of the Galaxy. Further, the distinctly different ages of the clusters, uniform metallicity, and large number of RSGs, mean that these objects now offer an unprecedented opportunity to study the pre-supernova evolution of massive stars.
Padeli Papadopoulos
University of Bonn
Molecular gas in galaxy-sized numerical simulations: another step towards realism
Abstract:
Stars form out of cool (~30-100K) H2 gas, not the 10^4 K WNM HI gas phase. I will describe the first attempt to incorporate this simple fact of Nature, using first principles, to galaxy-sized numerical models. Aside from making such models more amenable to comparison with current observations, the new physics now included contains a new feedback mechanism for H2-regulated star formation, which has been absent from galaxy-formation models until now. Implications regarding current approaches to feedback scenaria used in galaxy formation theories will be briefly discussed.
Stars form out of cool (~30-100K) H2 gas, not the 10^4 K WNM HI gas phase. I will describe the first attempt to incorporate this simple fact of Nature, using first principles, to galaxy-sized numerical models. Aside from making such models more amenable to comparison with current observations, the new physics now included contains a new feedback mechanism for H2-regulated star formation, which has been absent from galaxy-formation models until now. Implications regarding current approaches to feedback scenaria used in galaxy formation theories will be briefly discussed.
Abstract:
The next generation of surveys will enable the construction of large catalogues of galaxy clusters selected in different ways. With an eye to upcoming SZ and optical surveys, we use simple cluster finders on mock galaxy catalogues and SZ flux maps, at redshifts 0.5 and 0.9. The two catalogues at each redshift are then combined to measure how well they can improve each other, and compared to a catalogue made using SZ flux and galaxy information simultaneously. I will highlight some of the improvements which result, and issues which arise, in comparing and combining these two types of data sets.
The next generation of surveys will enable the construction of large catalogues of galaxy clusters selected in different ways. With an eye to upcoming SZ and optical surveys, we use simple cluster finders on mock galaxy catalogues and SZ flux maps, at redshifts 0.5 and 0.9. The two catalogues at each redshift are then combined to measure how well they can improve each other, and compared to a catalogue made using SZ flux and galaxy information simultaneously. I will highlight some of the improvements which result, and issues which arise, in comparing and combining these two types of data sets.
Abstract:
Accretion disks around Supermassive Black-Holes (SMBH's) in the centers of galaxies cause Active Galactic Nuclei (AGN), which are observable over the entire electromagnetic spectrum and out to the beginning of galaxy formation. The gradual assembly of galaxies is believed to have resulted in SMBH's today. The growth of SMBH's is largely hidden by dust, and possibly by large time-delays between galaxy mergers and the feeding of the central monster, so the connection between galaxy assembly and SMBH-growth is currently at best circumstantial. In this talk, we address to what extent the process of hierarchical galaxy assembly and supermassive black hole growth has gone hand-in-hand --- and with what kind of time delay --- from the epoch of reionization to the present. First, I summarize results from studies of early-stage mergers (using tadpole galaxies) and weak AGN (using variable objects) in the Hubble Ultra Deep Field (HUDF). The redshift distribution of both the tadpole galaxies and variable sources is similar to that of field galaxies, but there is very little overlap between the samples. This suggests that SMBH-growth did on average stay in pace with galaxy assembly, but with a time-delay of at least 1 Gyr since the last major merger, as recent hierarchical models predict. Using the panchromatic deep imaging data, ACS grism spectra, and ground-based spectroscopy in the GOODS and HUDF areas, I will next address this issue through the epoch dependent rate of major mergers in massive galaxies in the HUDF, and through SED-fitting of objects with and without (known) AGN in GOODS. On average, the field galaxy population at z=1--6 has an underlying star-forming SED with typical ages of 0.1--0.2 Gyr. AGN-dominated objects have an underlying stellar SED age of 1--2 Gyr on average. This suggests that AGN growth/supermassive black-hole feeding occurs about 1--2 Gyr AFTER the dynamical event which triggers the dominant starburst, that is visible in the average field galaxy at these redshifts. This is also reflected in the peak in the massive galaxy major merger-rate, compared to the peak in the redshift distribution of weak AGN. Finally, we discuss how the James Webb Space Telescope will expand on this topic in the next decade from the epoch of First Light to the present.
Accretion disks around Supermassive Black-Holes (SMBH's) in the centers of galaxies cause Active Galactic Nuclei (AGN), which are observable over the entire electromagnetic spectrum and out to the beginning of galaxy formation. The gradual assembly of galaxies is believed to have resulted in SMBH's today. The growth of SMBH's is largely hidden by dust, and possibly by large time-delays between galaxy mergers and the feeding of the central monster, so the connection between galaxy assembly and SMBH-growth is currently at best circumstantial. In this talk, we address to what extent the process of hierarchical galaxy assembly and supermassive black hole growth has gone hand-in-hand --- and with what kind of time delay --- from the epoch of reionization to the present. First, I summarize results from studies of early-stage mergers (using tadpole galaxies) and weak AGN (using variable objects) in the Hubble Ultra Deep Field (HUDF). The redshift distribution of both the tadpole galaxies and variable sources is similar to that of field galaxies, but there is very little overlap between the samples. This suggests that SMBH-growth did on average stay in pace with galaxy assembly, but with a time-delay of at least 1 Gyr since the last major merger, as recent hierarchical models predict. Using the panchromatic deep imaging data, ACS grism spectra, and ground-based spectroscopy in the GOODS and HUDF areas, I will next address this issue through the epoch dependent rate of major mergers in massive galaxies in the HUDF, and through SED-fitting of objects with and without (known) AGN in GOODS. On average, the field galaxy population at z=1--6 has an underlying star-forming SED with typical ages of 0.1--0.2 Gyr. AGN-dominated objects have an underlying stellar SED age of 1--2 Gyr on average. This suggests that AGN growth/supermassive black-hole feeding occurs about 1--2 Gyr AFTER the dynamical event which triggers the dominant starburst, that is visible in the average field galaxy at these redshifts. This is also reflected in the peak in the massive galaxy major merger-rate, compared to the peak in the redshift distribution of weak AGN. Finally, we discuss how the James Webb Space Telescope will expand on this topic in the next decade from the epoch of First Light to the present.
Francoise Combes
Observatoire de Paris
Some phenomena of galaxy dynamics:problems of the standard model and
comparison with MOND
Abstract:
I will review recent results on galaxy dynamics, bar evolution, destruction and re-formation, cold gas accretion, gas radial flows and AGN fueling, minor mergers. Some problems of galaxy evolution under the standard dark matter model will be emphasized, and alternative dynamics with modified gravity will be presented.
I will review recent results on galaxy dynamics, bar evolution, destruction and re-formation, cold gas accretion, gas radial flows and AGN fueling, minor mergers. Some problems of galaxy evolution under the standard dark matter model will be emphasized, and alternative dynamics with modified gravity will be presented.