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Activity > Colloquium

Colloquiums and Seminars(2021)

ASIAA Colloquium is usually held on Wednesdays at 2:20-3:20 pm in Room 1203 of the Astronomy-Mathematics Building, NTU. All scientists are welcome to attend. Seminars on more specialized topics are also held on a regular basis.

The ASIAA-NTU joint colloquium series aims to bring to the physics/astronomy/cosmology community in ASIAA/NTU world renown researchers who will talk about the forefront development of physical sciences.

Contact: Colloquium Committee (talks_replace2@_asiaa.sinica.edu.tw)

NEXT Colloquium: 2021-01-27 Wed 14:20~15:20 [R1203]
Speaker:Tony Mroczkowski
Topic:The Atacama Large Aperture Submillimeter Telescope Project
Abstract:Astrophysical observations at (sub-)mm wavelengths (λ from ~300 μm to ~3mm) allow us to study the cold and dense material in the Universe, hence probing the formation of stars and planets, and the interstellar and circumgalactic medium within galaxies across cosmic time. The current generation of 10-meter-class single dish telescopes has delivered some of the first surveys at (sub-)mm wavelengths, allowing us to go far beyond the previously optical-biased view of the Universe. Follow-up observations with interferometers then revealed in exquisite detail the morphology and kinematics of such (sub-)mm sources, enabling tests and revisions of theoretical models for the formation and evolution of planets, stars, and galaxies. However, it is now clear that without a transformative change in the capabilities of single-dish facilities in the 2030s, interferometers (like the ALMA observatory) will soon become source-starved. The current generation of 10-m class single dish telescopes, with their limited fields of view, spatial resolutions, and sensitivities, can only reveal the ‘tip of the iceberg’ of the (sub-)mm source population, both for Galactic and extragalactic studies. These limitations cannot be fully mitigated by interferometers, which are all intrinsically affected by a low mapping speed and by the loss of diffuse extended signals. The Atacama Large Aperture Submillimeter telescope (AtLAST; http://atlast-telescope.org/;https://ui.adsabs.harvard.edu/abs/2020arXiv201107974K/abstract) project is a concept for a 50-meter diameter single dish observatory to be built near the ALMA site. With its extremely large field of view (the goal is ~ 2 degrees), spatial resolution (up to ~1.5” at 350 μm), and sensitivity to both point sources and large-scale structures, AtLAST will be transformational for all fields of Astronomy in the 2030s. Here we will describe the recently approved EU Horizon2020 project to deliver a comprehensive design study for such a next-generation single-single dish facility. Beyond the EU, AtLAST would welcome an international consortium, and is beginning to garner broad support, with support from the Japanese 50-meter Large Submm Telescope community as well as many US Astro2020 decadal and Canadian Long Range Plan 2020 science case submissions.
No. Time/Place Speaker Topic / Abstract
download PDF: download talk PDF file
12021-03-17 Wed
14:20~15:20
R1203
Yong Tian
[NCU]
Colloquium
Mass-Velocity Dispersion Relation in HIFLUGCS Galaxy Clusters
Abstract

We investigate the mass-velocity dispersion relation (MVDR) in 29 galaxy clusters in the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS). We measure the spatially resolved, line-of-sight velocity dispersion profiles of these clusters, which we find to be mostly flat at large radii, reminiscent of the rotation curves of galaxies. We discover a tight empirical relation between the baryonic mass Mbar and the flat velocity dispersion of the member galaxies. The residuals of the MVDR are uncorrelated with other cluster properties. These characteristics are reminiscent of the MVDR for individual galaxies, albeit about ten times larger characteristic acceleration scale. The cluster baryon fraction falls short of the cosmic value, exposing a problem: the discrepancy increases systematically for clusters of lower mass and lower baryonic acceleration.

22021-03-10 Wed
14:20~15:20
R1203
Hsien Shang
[ASIAA]
Colloquium
TBD
Abstract

TBD

32021-02-03 Wed
14:20~15:20
R1203
Chih-Fan Chen
[UCLA]
Colloquium
[Remote talk] H0 measurement from time-delay cosmography
Abstract

The Hubble constant is one of the most important parameters in cosmology. Its value directly sets the age, the size, and the critical density of the Universe. Despite the success of the flat LCDM model, the derived Hubble constant from Planck data under the assumption of a flat LCDM model has 4.4-sigma tension with the direct measurements. If this tension is not due to the systematics, it may indicate the new physics beyond the standard cosmological model. H_0 from time-delay lensing is a powerful independent tool for addressing the H_0 tension since it is independent of both Planck and the distance ladder. One way to do this is to increase the number of high-quality lens systems since this allows us to look for correlations and other effects due to systematics, and to do hierarchical approaches to assess known systematic effects. Keck AO data is not only the key component to increase the precision of H0 measurement but also provides systematic checks with the H_0 results based on HST imaging. In this talk, I will present the current H_0 measurement, the systematic checks, and the future prospective of TDCOSMO collaboration.

42021-01-27 Wed
14:20~15:20
R1203
Tony Mroczkowski
[ESO]
Colloquium
The Atacama Large Aperture Submillimeter Telescope Project
Abstract

Astrophysical observations at (sub-)mm wavelengths (λ from ~300 μm to ~3mm) allow us to study the cold and dense material in the Universe, hence probing the formation of stars and planets, and the interstellar and circumgalactic medium within galaxies across cosmic time. The current generation of 10-meter-class single dish telescopes has delivered some of the first surveys at (sub-)mm wavelengths, allowing us to go far beyond the previously optical-biased view of the Universe. Follow-up observations with interferometers then revealed in exquisite detail the morphology and kinematics of such (sub-)mm sources, enabling tests and revisions of theoretical models for the formation and evolution of planets, stars, and galaxies. However, it is now clear that without a transformative change in the capabilities of single-dish facilities in the 2030s, interferometers (like the ALMA observatory) will soon become source-starved. The current generation of 10-m class single dish telescopes, with their limited fields of view, spatial resolutions, and sensitivities, can only reveal the ‘tip of the iceberg’ of the (sub-)mm source population, both for Galactic and extragalactic studies. These limitations cannot be fully mitigated by interferometers, which are all intrinsically affected by a low mapping speed and by the loss of diffuse extended signals. The Atacama Large Aperture Submillimeter telescope (AtLAST; http://atlast-telescope.org/;https://ui.adsabs.harvard.edu/abs/2020arXiv201107974K/abstract) project is a concept for a 50-meter diameter single dish observatory to be built near the ALMA site. With its extremely large field of view (the goal is ~ 2 degrees), spatial resolution (up to ~1.5” at 350 μm), and sensitivity to both point sources and large-scale structures, AtLAST will be transformational for all fields of Astronomy in the 2030s. Here we will describe the recently approved EU Horizon2020 project to deliver a comprehensive design study for such a next-generation single-single dish facility. Beyond the EU, AtLAST would welcome an international consortium, and is beginning to garner broad support, with support from the Japanese 50-meter Large Submm Telescope community as well as many US Astro2020 decadal and Canadian Long Range Plan 2020 science case submissions.

52021-01-26 Tue
10:30~11:30
R1203
Alex Tetarenko
[EAO]
Seminar
Unraveling the complex nature of black holes and how they power explosive outflows with time-domain observations
Abstract

Time-domain observations now offer a promising new way to study accretion and jet physics in X-ray binaries. Through detecting and characterizing rapid flux variability in these systems across a wide range of wavelength/energy bands (probing emission from different regions of the accretion flow and jet), we can measure properties that are difficult, if not impossible, to measure by traditional spectral and imaging methods (e.g., size scales, geometry, jet speeds, the sequence of events leading to jet launching). While variability studies in the X-ray bands are a staple in the X-ray binary community, there are many challenges that accompany such studies at longer wavelengths. However, with recent advances to observing techniques/instrumentation, the availability of new computational tools, and today's improved coordination capabilities, we are no longer limited by these challenges. In this talk, I will discuss new results from multi-wavelength fast timing observations of Cygnus X-1 and MAXI J1820+070, highlighting how we can directly connect variability properties to internal jet physics. Additionally, I will discuss future prospects for obtaining more of these invaluable data sets, and the key role that next-generation instruments will play in driving new discoveries through this science.

62021-01-20 Wed
14:20~15:20
R1203
Ting-Yun Cheng (Sunny)
[Durham University]
Colloquium
What a machine sees? - Galaxy morphological classification told through machine learning
Abstract

Along with the significant development of astronomical data in 4V aspects (Volume, Velocity, Variety, and Value/Veracity), machine learning techniques, as an analysis tool, are applied in a broad range of astronomical studies. In my PhD, I studied galaxy morphology with supervised and unsupervised machine learning techniques for two types of tasks - classification and exploration. In this talk, I will give an overview about how I think machine learning techniques can be used in astronomical studies, in particular, galaxy morphological classification, with four projects I accomplished during my PhD using a broad range of data (DES, SDSS, simulated data for Euclid). Additionally, I would like to bring up a discussion about a possibility of a new astronomical approach may be carried out through machine’s perspective.

72021-01-19 Tue
13:30~14:30
R1203
Haifeng Yang
[THU]
Seminar
Dichroic thermal emission from aligned dust grains in protoplanetary disks
Abstract

(Sub)millimeter dust thermal emission is a traditional and successful method to study the magnetic fields on scales larger than disks. Thanks to the recent development of interferometric polarimetry, especially ALMA, we have been able to study resolved polarization image on disk scales. The results, however, have been surprising. Instead of dichroic thermal emission from grains aligned with magnetic fields, disks show mostly scattering-induced polarization pattern, especially at shorter wavelengths. In this talk, I will first discuss the feasibility of the alignment of dust grains with magnetic fields in PPDs, with the so-called superparamagnetic inclusions taken into account. I will show that large millimeter-sized dust grains can hardly be aligned with magnetic fields, due to the dense environment and frequent gas bombardment. With similar grain alignment analysis, we perform synthetic polarimetric observation using a disk formation simulation. Our results show a transition from magnetically aligned polarization to scattering-induced polarization going from the envelope scale to the disk scale. This is in agreement with a recent polarization survey in the Perseus molecular cloud. At last, I will present some preliminary results on the explanation of a non-detection of polarization from a debris disk system and discuss its implication on grain alignment theory.

82021-01-13 Wed
14:20~15:20
R1203
Yu-Ching (Tony) Chen
[UIUC]
Colloquium
Searching binary supermassive black holes in astronomical surveys
Abstract

Binary Supermassive Black Holes (BSBHs) are important objects for studying galaxy evolution, gravitational wave, and cosmology. However, searching close BSBHs at high redshift (z>1) is difficult due to the angular resolution of the telescopes. For the first half of the talk, I will present our new discovery of candidate periodic quasars as possible BSBHs at milli-pc scale. The search is based on 20-yr light curves by combining DES and SDSS. I will also discuss the implications of those candidates. For the second half of the talk, I will show a new astrometric technique to find the unresolved dual/lensed quasars at (sub)kpc scale using Gaia. The follow-up HST observations returned handful dual/lensed quasar candidates proving the feasibility of the technique. Those candidates if confirmed could form a pilot sample for studying close dual AGNs at high redshift.

92021-01-06 Wed
14:20~15:20
R1203
Chun-Hao To
[Stanford University]
Colloquium
Cosmological constraints from a joint analysis of cluster abundances, galaxy correlations, and weak gravitational lensing in the Dark Energy Survey
Abstract

Three cosmic tracer fields are measured from imaging surveys: galaxy density, weak gravitation lensing shear, and cluster density. The joint analysis of the auto and cross correlations of the first two fields, often referred to as the 3x2pt analysis, has become a popular and competitive cosmological test of the standard cosmological model. The abundances and spatial distributions of galaxy clusters, which are associated with the highest peaks in the matter density field, provide another powerful probe of cosmic structure formation and evolution; thus, the combination of cluster abundances and 3x2pt analysis is expected to yield precise cosmological constraints. In the first part of the talk, I will present a novel multi-probe cluster cosmology analysis, which focuses exclusively on large scales. This new cluster cosmology analysis yields competitive cosmological constraints while being robust against several systematics. I will describe the extensive validation of the measurements, modeling, and inferences using N-body simulations populated with galaxies. In the second part of the talk, I will present cosmological constraints from the first joint analysis of cluster abundances and auto/cross correlations of all three cosmic tracer fields measured from the first year of the Dark Energy Survey (DES-Y1). The talk will be concluded by a discussion on the implication of the result, potential improvements, and expected constraining powers in the up-coming DES-Y3 analysis and future wide imaging surveys.

TEL: 886-2-3365-2200 FAX: 886-2-2367-7849
General: asiaa_replace2@_asiaa.sinica.edu.tw Media Request: epo_replace2@_asiaa.sinica.edu.tw
11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, R.O.C.