The deaths of massive stars seed our universe with black holes and neutron stars - the most exotic objects of the stellar graveyard. The births of these stellar remnants, as well as their mergers when paired in binaries, power explosions that can launch the most relativistic jets we know of in the universe (gamma-ray bursts) and shake the very fabric of space-time via ripples called gravitational waves. GW170817, the merger of two neutron stars witnessed through both its gravitational wave siren and its glow at all wavelengths of light, represents the first multi-messenger detection of one such extreme cosmic bang. Starting from the example of GW170817, in this talk I will discuss how radio light in particular, and gravitational waves, can be used in tandem to unveil the physics of relativistic transients. I will also highlight opportunities and challenges that lie in front of us, as improvements in detectors’ sensitivities will transform a trickle of multi-messenger discoveries into a flood.
Elements condensing into dust grains is an important physical process that occurs in the ISM. Through studies on extinction, scattering, heating and depletion of elements out of gas-phase, it has long been known that grains have a major effect on observed spectra of galaxies. Despite the large amount of observations available on extinction, scatter and heating, details of depletions onto grains and their effect on observed emission-line spectra are rarely studied. We explore the effects of grain depletions on strong spectral lines, and find non-trivial results. Our results suggest that the level of depletion, not only affects the emission line strength of corresponding ions, but also changes the abundance of coolants in the ISM gas, hence affecting its temperature. In addition, we include new code into Cloudy, allowing a user to alter the degree of grain depletions in a given model.
Elements condensing into dust grains is an important physical process that occurs in the ISM. Through studies on extinction, scattering, heating and depletion of elements out of gas-phase, it has long been known that grains have a major effect on observed spectra of galaxies. Despite the large amount of observations available on extinction, scatter and heating, details of depletions onto grains and their effect on observed emission-line spectra are rarely studied. We explore the effects of grain depletions on strong spectral lines, and find non-trivial results. Our results suggest that the level of depletion, not only affects the emission line strength of corresponding ions, but also changes the abundance of coolants in the ISM gas, hence affecting its temperature. In addition, we include new code into Cloudy, allowing a user to alter the degree of grain depletions in a given model.
WEAVE is the next-generation wide-field survey facility for the William Herschel Telescope (WHT). WEAVE will provide the instrument required for full scientific exploitation of the Gaia, LOFAR, and APERTIF surveys in the Northern Hemisphere. WEAVE is a multi-object and multi-integral-field-unit (IFU) facility utilizing a large, new 2-degree-diameter prime focus corrector at the WHT with a pick-and-place fibre positioner system hosting nearly 1000 multi-object fibres or 20 mini-IFUs for each observation, or a single wide-field IFU. The fibres are fed into a dual-beam spectrograph located in the GHRIL enclosure on the WHT's Nasmyth platform. The spectrograph records nearly 1000 spectra simultaneously at a resolution of R~5000 over an instantaneous wavelength range of 366-959 nm or at a resolution of R~20000 over two more-limited wavelength ranges. WEAVE has been delivered to the WHT and will be on sky in the summer of 2021 to provide complete phase-space coordinates of roughly 3 million stars in the northern sky selected with ESO’s Gaia satellite, chemical analysis of more than 1 million stars from Gaia, half a million massive stars in the Galactic Plane, distances and properties of galaxies selected from the low-frequency radio-wave surveys being conducted with LOFAR, “three-dimensional" spectroscopy of galaxies selected from surveys using the new Apertif focal plane array at WSRT, and deep surveys of galaxy clusters and moderate-redshift galaxies. I will discuss the design of WEAVE, its current status, and the eight surveys that comprise the 5- to 7-year WEAVE Survey.
WEAVE is the next-generation wide-field survey facility for the William Herschel Telescope (WHT). WEAVE will provide the instrument required for full scientific exploitation of the Gaia, LOFAR, and APERTIF surveys in the Northern Hemisphere. WEAVE is a multi-object and multi-integral-field-unit (IFU) facility utilizing a large, new 2-degree-diameter prime focus corrector at the WHT with a pick-and-place fibre positioner system hosting nearly 1000 multi-object fibres or 20 mini-IFUs for each observation, or a single wide-field IFU. The fibres are fed into a dual-beam spectrograph located in the GHRIL enclosure on the WHT's Nasmyth platform. The spectrograph records nearly 1000 spectra simultaneously at a resolution of R~5000 over an instantaneous wavelength range of 366-959 nm or at a resolution of R~20000 over two more-limited wavelength ranges. WEAVE has been delivered to the WHT and will be on sky in the summer of 2021 to provide complete phase-space coordinates of roughly 3 million stars in the northern sky selected with ESO’s Gaia satellite, chemical analysis of more than 1 million stars from Gaia, half a million massive stars in the Galactic Plane, distances and properties of galaxies selected from the low-frequency radio-wave surveys being conducted with LOFAR, “three-dimensional" spectroscopy of galaxies selected from surveys using the new Apertif focal plane array at WSRT, and deep surveys of galaxy clusters and moderate-redshift galaxies. I will discuss the design of WEAVE, its current status, and the eight surveys that comprise the 5- to 7-year WEAVE Survey.
The environment in which a galaxy lives plays a key role in driving its evolution. As the most tenuously bound component of galaxies, neutral atomic hydrogen (HI) is a valuable tracer of both the interaction history of a galaxy with its environment and a measure of its future star formation potential. As galaxies move from the low-density field to high-density clusters, they lose their gas and star formation is quenched, but how exactly this happens is still poorly understood. In fact, perhaps most galaxies spend a large fraction of their life in the intermediate-density group environment where the signatures of galaxy evolution are more subtle and widely varied. In this talk I will present what my work on both wide-area HI surveys and individual observations have revealed about galaxy evolution, from the low mass group environment to the outskirts of massive galaxy clusters. Statistical studies of the HI provide insight on not only the gas processing and ongoing evolution within galaxy groups, but also the growth of large-scale structure. In addition, I'll present the first of the next generation of HI surveys, Apertif, which is observing 3500 square degrees at 14 times the spatial resolution of previous HI surveys and better HI mass sensitivity. Apertif will allows us to resolve and take the inventory, for the first time, of the physical mechanisms that remove gas from galaxies, across the full range of galaxy environments from poor groups to galaxy clusters.
The environment in which a galaxy lives plays a key role in driving its evolution. As the most tenuously bound component of galaxies, neutral atomic hydrogen (HI) is a valuable tracer of both the interaction history of a galaxy with its environment and a measure of its future star formation potential. As galaxies move from the low-density field to high-density clusters, they lose their gas and star formation is quenched, but how exactly this happens is still poorly understood. In fact, perhaps most galaxies spend a large fraction of their life in the intermediate-density group environment where the signatures of galaxy evolution are more subtle and widely varied. In this talk I will present what my work on both wide-area HI surveys and individual observations have revealed about galaxy evolution, from the low mass group environment to the outskirts of massive galaxy clusters. Statistical studies of the HI provide insight on not only the gas processing and ongoing evolution within galaxy groups, but also the growth of large-scale structure. In addition, I'll present the first of the next generation of HI surveys, Apertif, which is observing 3500 square degrees at 14 times the spatial resolution of previous HI surveys and better HI mass sensitivity. Apertif will allows us to resolve and take the inventory, for the first time, of the physical mechanisms that remove gas from galaxies, across the full range of galaxy environments from poor groups to galaxy clusters.
For the past 150 years, the local interstellar medium's prevailing view has been based on a peculiarity known as the Gould Belt, an expanding ring of young stars, gas and dust, tilted about 20 degrees to the Galactic plane. However, the physical relationship between local gas clouds has remained unknown because the accuracy in distance measurements to such clouds is of the same order as, or larger than, their sizes. With the advent of large photometric surveys and the astrometric survey, in particular ESA Gaia, this situation has changed. In this talk, I will present the three-dimensional structure of all local cloud complexes. We find a narrow and coherent 2.7-kiloparsec arrangement of dense gas in the solar neighborhood that contains many of the clouds thought to be associated with the Gould Belt. This finding is inconsistent with the notion that these clouds are part of a ring, bringing the Gould Belt model into question. The structure comprises the majority of nearby star-forming regions, has an aspect ratio of about 1:20, and contains about three million solar masses of gas. Remarkably, this structure appears to be undulating, and its three-dimensional shape is well described by a damped sinusoidal wave on the plane of the Milky Way. I will also present ongoing work on the gas's space motion in the closest massive star factory, the Orion complex, and the dispersal of young stars into the Galactic field.
For the past 150 years, the local interstellar medium's prevailing view has been based on a peculiarity known as the Gould Belt, an expanding ring of young stars, gas and dust, tilted about 20 degrees to the Galactic plane. However, the physical relationship between local gas clouds has remained unknown because the accuracy in distance measurements to such clouds is of the same order as, or larger than, their sizes. With the advent of large photometric surveys and the astrometric survey, in particular ESA Gaia, this situation has changed. In this talk, I will present the three-dimensional structure of all local cloud complexes. We find a narrow and coherent 2.7-kiloparsec arrangement of dense gas in the solar neighborhood that contains many of the clouds thought to be associated with the Gould Belt. This finding is inconsistent with the notion that these clouds are part of a ring, bringing the Gould Belt model into question. The structure comprises the majority of nearby star-forming regions, has an aspect ratio of about 1:20, and contains about three million solar masses of gas. Remarkably, this structure appears to be undulating, and its three-dimensional shape is well described by a damped sinusoidal wave on the plane of the Milky Way. I will also present ongoing work on the gas's space motion in the closest massive star factory, the Orion complex, and the dispersal of young stars into the Galactic field.
The cosmic downsizing of quasars is still a big puzzle in astronomy and it is commonly believed that the central active galactic nucleus (AGN) must have played a significant role in quenching itself, in a self-regulatory mechanism popularly termed “AGN feedback” . The AGN feedback also plays a crucial role in black hole and host galaxy co-evolution across cosmic time (the M-sigma relation). Here I will discuss the nature and impact of pc scale outflows from AGN, detected in X-rays. On the other hand, the feeding of the supermassive black hole (SMBH) at the center of AGNs is an equally interesting puzzle. We still do not know how matter from the host galaxy loses their angular momentum and falls into the accretion disk, finally feeding the SMBH. In an extensive X-ray spectral variability study of Compton-thin Type-II AGN, we found the presence of clumpy gas in the near vicinity (<pc) of the SMBH which are likely candidates of matter which fall into the black hole and feed them, creating the luminous AGN.
