physics & astronomy

Festival del Espacio 2023 jgkl222 Mon, 05/15/2023 - 03:17 pm

Festival del Espacio 2023

The Arts & Sciences' Department of Physics and Astronomy invites local Hispanic and Latinx elementary school students from Cardinal Valley, Liberty and Maxwell elementary schools, to come explore outer space and learn about the amazing work that astronomers do! The celebration will include a fun-filled evening featuring activities, crafts, awesome speakers, and a chance to gaze into the beautiful night sky through our state-of-the-art space telescope housed inside UK's MacAdam Observatory. And to top it off, there will be free tacos, snacks and drinks! 

Date:
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Location:
Jacob's Science Building
Correlation Between the Gas-phase Metallicity and Ionization Parameter in Extra-galactic HII Regions super234 Wed, 10/06/2021 - 05:03 pm

The gas-phase metallicity and ionization parameter are two primary parameters that drive the variations of emission line spectra in HII regions. There is an increasing amount of evidence that these two parameters are correlated. Theoretical works on the dynamical evolution of HII regions predict an anti-correlation between metallicity and ionization parameter. However, observations of HII region spectra have yielded a variety of different correlations, including anti-correlations, positive correlations, and even no correlation. All these measurements of the correlation rely on photoionization modeling. Also, different combinations of emission lines are used for calibrating metallicity and ionization parameter in different works. To solve the above problem, we examine how the derived correlation between metallicity and ionization parameter depends on the choice of models and emission lines. In this talk, I will show that it is important to constrain the model parameters using observational data before making any measurement. With the MaNGA IFU data, we compute a best-fit photoionization model for general HII regions and use a Bayesian method to fit metallicities and ionization parameters simultaneously. Our result shows that a positive correlation exists between the gas-phase metallicity and ionization parameter, regardless of which combination of emission lines is used for the fitting. This result clearly contradicts the prediction by the dynamical model. I will discuss potential mechanisms that lead to this discrepancy, and how it might be solved with future IFU surveys on HII regions.

Date:
Location:
Blazer Dining 339 in person/on zoom
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An X-ray Perspective on the Evolution of Normal Galaxies

Studies of the extragalactic Universe, from ultraviolet to infrared wavelengths, have been extremely effective at piecing together a basic picture of how stars in galaxies evolved throughout cosmic history.  At X-ray wavelengths, galaxy emission is dominated by hot gas and populations of X-ray binaries, the latter of which consist of black holes and neutron stars accreting material from normal stellar companions.  Hot gas in star-forming galaxies traces energetics from young and massive stars and X-ray binaries provide unique and important information regarding the star-formation histories and chemical evolution (metallicities) of their host galaxies.  These energetic phenomena have been proposed to play roles in the ionization of nebulae and long-range heating of the intergalactic medium in the early Universe. Furthermore, some X-ray binaries are expected to be predecessors and tracers of the gravitational-wave source populations that are now being detected by LIGO/VIRGO.  Using X-ray and multiwavelength observations (e.g., from Chandra, GALEX, Hubble, NuSTAR, Spitzer, Herschel, and other telescopes) of nearby and distant galaxies, as well as large-scale theoretical modeling, we are developing a framework detailing how X-ray binary populations and their host galaxies evolved together over the last 12 billion years (~90%) of cosmic history.  In this talk, I will describe some of the exciting new insights from our work, and I will highlight how new data sets, future observational facilities, and improved theoretical modeling will continue to improve our understanding of X-ray binaries, compact objects, and galaxies.

 

Date:
Location:
Blazer Dining 339 (on zoom)
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Grain Depletions in the ISM rya225 Tue, 03/09/2021 - 10:32 am

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.

Date:
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Location:
Online by Zoom
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WEAVE: The next-generation spectroscopic survey facility for the Northern Sky

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.
 
Date:
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Location:
Online by Zoom
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From groups to clusters: gas processing and galaxy evolution

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.

Zoom Recording: https://uky.zoom.us/rec/share/HyMikMEOik6ZtjHliTbYeOx5-W5k-lH5hemITZcVBqec-w1Tu3rQOD6biC3qSb38.sPUbAc39PoZWKBwu

Date:
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Location:
Online by Zoom
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The Radcliffe Wave and the new Local Galactic Neighborhood

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.
Date:
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Location:
Online by Zoom
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Studying the central regions of Active Galactic Nuclei: Feeding and Feedback rya225 Tue, 02/23/2021 - 10:16 am

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.

 

Zoom Recording: https://uky.zoom.us/rec/share/2ffed6_OqD7gDmicFWJh_V2OHKSGO0Yqc8qctNtXi5iOnTwI9FQDlF8NZFGRsNa7.AXJT014OPTkA-TxI

Date:
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Location:
Online by Zoom
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The Southern Stellar Stream Spectroscopic Survey: Overview and Latest Science Results rya225 Sun, 01/31/2021 - 12:58 pm

The Southern Stellar Stream Spectroscopic Survey (S5) is an ongoing spectroscopic program that maps the newly discovered stellar streams with the fiber-fed AAOmega spectrograph on the Anglo-Australian Telescope (AAT). S5 is the first systematic program pursuing a complete census of known streams in the Southern Hemisphere, providing a uniquely powerful sample for understanding the building blocks of the Milky Way's stellar halo, the progenitors and formation of stellar streams, the mass and shape of the Milky Way's halo, and ultimately the nature of dark matter. The survey started in Summer 2018 and has mapped ~20 streams with over 50 nights on AAT. In this talk, I will give a brief overview of the current status of the program, highlighting the latest science results from the survey, and end the talk with the public data release plan.

Zoom Recording: https://uky.zoom.us/rec/share/paz-EUSX-RPTLxR_bh9fOpUkrdfRrijEg3vPg7cdyqpX6EQREvS9LPJ8_O_SjsI.Z-EES8dDkrCZJ0-6

Date:
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Location:
Online by Zoom
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Towards a better understanding of low mass galaxies beyond the Local Group

Low mass galaxies provide an essential testing ground for theoretical predictions of cosmology. Their number densities, structures, and internal dynamics can be extremely insightful for studying dark matter and galaxy formation on small scales. I will discuss recent results studying ultra-diffuse galaxies (UDGs). UDGs hold the promise of new constraints on low mass galaxies dynamics, as their spatial extent and often significant globular cluster populations provide probes on spatial scales where dark matter should dominate the kinematics. I will also discuss the dynamics of two UDGs that seem to lack most, if not all, of their dark matter and host an intriguing population of globular clusters. I will finish by presenting a new wide-field survey carried out with the 48-lens Dragonfly Telephoto Array. With an excellent photometric depth, the Dragonfly Wide Field Survey will provide an unprecedented view of the low surface brightness universe over a wide area of the sky (350 square degrees). The main goal of the survey is to provide information on the properties and statistics of the dwarf galaxy population beyond the Local Group but it will also provide a useful resource for other resolved, low surface brightness phenomena, such as stellar streams and tidal tails, stellar halos, intragroup light and the extent of massive galaxies.

Zoom Recording: https://uky.zoom.us/rec/share/enMKk_C1E4A0dIkX9Zhd5Ahkgr8FoOy-47Maqeu1dWM0X75nhZTPwWY8XkGV_uUm.isTz3MAuWX8Eo8q9

Date:
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Location:
Online by Zoom
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