astronomy

Bangs, fizzles, and whistles - the physics of AGN feedback in galaxy clusters

Date: 
Wednesday, March 31, 2021 - 3:00pm to 4:00pm
Location: 
Online by Zoom
Type of Event (for grouping events):

The need for AGN feedback in the cores of galaxy clusters has been long established- without the energy injection by jetted AGN in the central galaxy, we believe that the intracluster medium (ICM) would undergo a cooling catastrophe, leading to prodigious star formation and galaxy building in contravention with observations.  However, the actual physical mechanisms that govern the AGN feedback cycle remain elusive.  In this talk, I will discuss the possible physical process by which the central AGN can heat the ICM.  I will present a series of studies that, step-by-step, move us away from a simple hydrodynamic picture and force us to treat the ICM as a weakly collisional plasma with important properties governed by non-trivial kinetic physics.

 

Zoom Recording: https://uky.zoom.us/rec/share/KJ27-i3LbcWzxliPLFwhB2tPE-xMj43IbtwwGZkRP7IuIjzXhGwsk4wcHuNH0sde.byF_p5cyNdvVl9EG

Unveiling the origin of filamentary structure in central cluster and group galaxies

Date: 
Wednesday, January 27, 2021 - 3:00pm to 4:00pm
Location: 
Zoom
Type of Event (for grouping events):

The classical cooling-flow model of galaxy clusters fails in the absence of a non-gravitational heating mechanism needed to compensate for radiative cooling in the hot intra-cluster medium (ICM). Feedback from an active galactic nucleus (AGN) offset the cooling via the energy released from the bubbles inflated by radio jets launched from supermassive black holes (SMBH). However, it cannot completely offset the cooling as central cluster galaxies (BCGs) harbor a complex multiphase medium of extended warm and cold gas reservoirs, whose physical origin remains unknown. In the first part of this talk, I will present Atacama Large Millimeter Array (ALMA) and new Multi-Unit Spectroscopic Explorer (MUSE) observations of 15 central cluster galaxies to unveil the origin and life-cycle of these filamentary networks. In the second part of this talk, by extending the sample, including new MUSE observations of 15 central group galaxies (BGGs), I will explore the origin of the gas and the effect of AGN-feedback in the intermediate-mass range between individual galaxies and massive clusters.

 

Zoom Recording: https://uky.zoom.us/rec/share/dajH7CuefLj_6dRqFEzD7_mWq2TFff7m5JIfWEdY3B9yBR_pnVcG2csgG2-veIin.C2Vqlat9ui9roNhJ

X-ray Variability Spectra of Black Holes

Date: 
Thursday, October 8, 2020 - 4:00pm to 5:00pm
Location: 
Online by Zoom
Type of Event (for grouping events):

Both stellar mass and supermassive black holes can vary in brightness extremely rapidly, changing by orders of magnitude within hours. This variability gives us a powerful tool to understand the accretion disks around black holes, and the relativistic winds that they can launch. Because the X-ray spectra are made up of multiple complex variable components, the observed variability can be strongly energy dependent. By calculating the variance of X-ray lightcurves as a function of energy, we can build a variance spectrum. These spectra have been used to qualitatively study black hole variability for many years, but are rarely used quantitatively. I will present recent results from an ongoing research program to model variance spectra of compact objects, including a new method for detecting ultra-fast outflows, implications for accretion disk physics and new constraints on AGN feedback.

Zoom recording:  https://uky.zoom.us/rec/share/z8MTXvJhSmbuS3lYhUsiczW67IPyTDUGMYHrCWXbESp8kCbnmy53RMeJyPfQ66oL.H0J1IJ9f7C5H-iS2

What can the Occult Do for You?

Date: 
Thursday, September 24, 2020 - 4:00pm to 5:00pm
Location: 
Zoom
Type of Event (for grouping events):

Interstellar dust is still a dominant uncertainty in Astronomy, limiting precision in e.g., cosmological distance estimates and models of how light is re-processed within a galaxy. When a foreground galaxy serendipitously overlaps a more distant one, the latter backlights the dusty structures in the nearer foreground galaxy. Such an overlapping or occulting galaxy pair can be used to measure the distribution of dust in the closest galaxy with great accuracy. The STARSMOG program uses Hubble to map the distribution of dust in foreground galaxies in fine (<100 pc) detail. Integral Field Unit (IFU) observations will map the effective extinction curve, disentangling the role of fine-scale geometry and grain composition on the path of light through a galaxy. The overlapping galaxy technique promises to deliver a clear understanding of the dust in galaxies: geometry, a probability function of dimming as a function of galaxy mass and radius, and its dependence on wavelength.

Zoom recording: https://uky.zoom.us/rec/share/ApA_YxbNmZhyvRh6jOJV2-1oZh-8L1zw9O_kKivxWqPvTl1eiVTbv07if7cFx0bO.v9GsO7V4klwdB90p

A Good Hard Look at Cosmic Supermassive Black Hole Growth

Date: 
Thursday, August 27, 2020 - 4:00pm to 5:00pm
Location: 
Zoom
Type of Event (for grouping events):
The 7 Ms Chandra X-ray Observatory exposure on the Chandra
Deep Field-South (CDF-S) has provided the most sensitive
extragalactic X-ray survey by a wide margin. About 1050
X-ray sources have been detected, primarily distant active
galactic nuclei (AGNs) and starburst/normal galaxies. The
unmatched deep multiwavelength coverage for these sources
allows superb follow-up investigations, revealing the
details of supermassive black hole growth over most of
cosmic time. I will briefly describe the sources in the
7 Ms CDF-S and highlight some exciting science results.
The latter will include (1) evidence for black-hole vs.
bulge co-evolution in the distant universe; (2) constraints
on supermassive black hole growth in the first galaxies as
revealed by direct detection and stacking; and (3) the
discovery of representatives of a new population of faint,
fast X-ray transient sources. Finally, I will discuss some
future prospects for X-ray surveys of AGNs in the distant
universe, including the ongoing 5 Ms XMM-SERVS survey of
the LSST Deep Drilling Fields and new X-ray missions.

SimBAL: Spectral Synthesis Analysis of Broad Absorption Line Quasars

Date: 
Thursday, November 12, 2020 - 4:00pm to 5:00pm
Location: 
Zoom
Type of Event (for grouping events):
A significant fraction of quasars exhibit blueshifted broad
absorption lines (BALs) in their rest-UV spectra, indicating powerful
outflows emerging from the central engine. Despite more than 50 years
of study, the physical conditions of the outflowing gas are poorly
understood.  Our group has developed SimBAL, a novel spectral
synthesis fitting method for BAL quasar spectra that uses Bayesian
model calibration to compare synthetic to observed spectra. I will
describe the construction of SimBAL, and illustrate its unique
strengths by discussing the results from several projects.

Bridging the Gap Between Galaxy and Star Formation with Star Clusters

Date: 
Thursday, September 17, 2020 - 4:00pm to 5:00pm
Location: 
Zoom
Type of Event (for grouping events):

Over the past decades, the discovery of a large number of young massive clusters (YMCs) in the local Universe and giant clumps in high-z galaxies suggests that clustered star formation is the dominant star formation mode across cosmic time. Mass and energy feedback from these enormous clusters is inevitably responsible for shaping their host galaxies. In this talk, I will discuss the tight relationship between giant molecular clouds on small scales and galaxies on large scales and provide the first attempts to bring star formation and galaxy formation community together. On the one hand, the properties of YMCs and GMCs populations can be used to calibrate and help improve the current cosmological simulations. On the other hand, galaxy formation simulations provide the perfect initial conditions for the modeling GMCs in realistic environments. Finally, bringing together the collective wisdom from both galaxy and star formation, I will highlight some of my recent works on solving the mystery of the origin of globular cluster populations in the Universe.

Zoom Recording: https://uky.zoom.us/rec/share/gU3PD8lWcY7ckp8yX1hzar4ehA2fRStP3in6YZPpUFYvsIVbmRrsxNpoHvP3qCOw.8tPxhtnTxMA4vByE

Probing Magnetic Field Morphology in Galaxy Clusters with the Gradient Technique

Date: 
Thursday, September 10, 2020 - 4:00pm to 5:00pm
Location: 
Zoom
Type of Event (for grouping events):

Magnetic fields in the intracluster medium (ICM) affect the structure and the evolution of galaxy
clusters. However, their properties are largely unknown, and measuring magnetic fields in galaxy
clusters is challenging, especially on large-scales outside of individual radio sources. Here we
probe the plane-of-the-sky orientation of magnetic fields in clusters using the intensity gradients.
The technique is a branch of the Gradient Technique (GT) that employs emission intensity maps
from turbulent gas. We utilize the Chandra X-ray images of the Perseus, M 87, Coma, and
A2597 galaxy clusters, and the VLA radio observations of the synchrotron emission from
Perseus. We find that the fields predominantly follow the sloshing arms in Perseus, which is in
agreement with numerical simulations. The GT-predicted magnetic field shows signatures of
magnetic draping around rising bubbles driven by supermassive black hole (SMBH) feedback in
the centers of cool-core clusters, as well as draping around substructures merging with the Coma
cluster.

Zoom Recording: https://uky.zoom.us/rec/share/mkGB72TcxVuohGMJ5EVwN282koaKcMinbki7FuSKX3UvAwcl4j22df-zG5VZJnS_.gnvslk37Wx91DbZZ

The Javalambre-Physics of the Accelerated Universe Astrophysical Survey, current status and preliminary results from the miniJPAS survey

Date: 
Thursday, October 1, 2020 - 4:00pm to 5:00pm
Location: 
Zoom
Type of Event (for grouping events):

The Javalambre-Physics of the Accelerated Universe Astrophysical Survey (J-PAS) is a narrow band, very wide field cosmological and astrophysical survey to be carried out from the Javalambre Astrophysical Observatory in Spain with a purpose-built, dedicated 2.5m telescope and a 5 sq.deg. 1.2Gpix camera. With first light obtained in June 2020, J-PAS plans to observe >8000sq.deg. of Northern Sky and measure sigma_z~0.003(1+z) photo-z for up to 9E7 LRG and ELG galaxies plus several million QSOs, sampling an effective volume of ~ 14 Gpc^3 up to z~1.3 reaching Stage IV radial BAO experiment. J-PAS is expected to detect ~7E5 galaxy clusters and groups, setting constraints on Dark Energy which rival those obtained from its BAO measurements. 

Thanks to the superb characteristics of the site (seeing ~0.7 arcsec), J-PAS is expected to obtain a deep, sub-arcsec multi-band image of the Northern sky, which combined with its unique photo-z precision will have an immense legacy value for almost all astrophysical areas. The key to the J-PAS potential is its innovative approach: a contiguous system of 54+2 filters with 145A width, placed 100A apart over a multi-degree FoV is a powerful "redshift machine", with the survey speed of a 4000 multiplexing low resolution spectrograph. Its commissioning camera, the PathFinder, has collected data since 2018 with all J-PAS filters of a variety of targets and fields, in particular of the AEGIS field (miniJPAS) as a proof of concept for photo-z depth and others. 

Here I will present the status of J-PAS, the main results of miniJPAS and how it impacts the expectations for J-PAS.

 

Zoom recording: https://uky.zoom.us/rec/share/F9E1ic1VTD7A1b0uY0c6sWNlWtCvII8N1eESjj8WC4UNIHGTzMJzxRa_mj3iIdnL.ay0DT-aSZ6MRRBTU

Modeling Dispersal of Giant Molecular Clouds by UV Radiation Feedback

Date: 
Thursday, October 29, 2020 - 4:00pm to 5:00pm
Location: 
Zoom
Type of Event (for grouping events):

Giant molecular clouds (GMCs) are the primary reservoir of cold molecular gas in the interstellar medium and sites of ongoing star formation. It has been known for decades that star formation efficiency (SFE) of GMCs is very low. While UV radiation feedback from massive stars are expected to play a crucial role in controlling the GMC lifetime and SFE, our theoretical understanding of how it actually works in turbulent, magnetized clouds remains incomplete. In this talk, I will report recent progress we made in modeling GMC destruction by UV radiation feedback. I will first briefly review the predictions made by 1D models about SFE, cloud lifetime, and importance of photoionization and radiation pressure in different star-forming environments. I will then present the results of radiation (magneto)hydrodynamic simulations of star-forming GMCs and discuss how turbulence and magnetic fields can change the picture. If time allows, I will also talk about ongoing efforts in modeling GMC evolution with all major forms of feedback processes (radiation/winds/SNe).

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