Galactic Rotation Curves with Dark Matter Self-Interactions

Dr. Ayuki Kamada (UC Riverside)
2015-08-31 

ISAS seminar

Abstract: 
It has been shown that the LambdaCDM model can successfully explain large-scale structure of the universe. But it is not clear that it can accommodate observations on (sub-)galactic scales. In fact, the LambdaCDM model predicts dark matter halos, which are systematically denser than inferred from astrophysical observations. One interesting alternative assumes that dark matter particles are strongly interacting with each other. Dark matter self-interactions will lead to heat transfer from the hotter outer region to the cold inner region, reducing the central dark matter density. In this talk, I will show that the observed rotation curves of spiral galaxies are consistent with predicted in the SIDM model. I will also emphasize the importance of the baryonic disk in determining the SIDM halo profile.

Luminous Supermassive Black Holes in the Brightest Cluster Galaxies

2015-08-06 ISAS astro seminar

Shutaro Ueda (ISAS/JAXA)

Title: 
Abstract:
Supermassive black holes (SMBHs) in the central galaxies of clusters of galaxies (i.e.,
in the brightest cluster galaxies; BCGs) are the most massive BH in the Universe. Their
masses are estimated to be up to 1011 M. The SMBHs in nearby BCGs have a slight gas
accretion rate, which is typically less than 1 % of the Eddington limit. This indicates
that their mass growth may be performed at the early stage of evolution of their hosted
cluster. However its mechanism is still under debate. We therefore search for quasar
hosted BCGs (i.e., with high accretion rate) systematically by referring both the Planck
SZ cluster catalogue and the Swift hard X-ray catalogue. We find two sources out of 1203
clusters, which are the Phoenix cluster and H1821+643 cluster. We also investigate their
surrounding environment by using X-ray observations with Chandra and Suzaku. We find the
neutral iron K-shell line (Fe I) from both quasars and heavily absorption component from
the quasar of the Phoenix cluster. We discuss the environments of both quasars and the
origin of neutral medium surrounding quasars.

A Multiwavelength View of the HST Frontier Fields Clusters

2015-05-28 @ ISAS

Speaker : Dr. Georgiana Ogrean ( CfA, Harvard)
http://hea-www.cfa.harvard.edu/~gogrean/

Title:
A Multiwavelength View of the HST Frontier Fields Clusters

Abstract:
Structure growth in the universe is one of the fundamental astrophysical problems. Merging galaxy clusters are the perfect laboratories to study the effects of structure growth on the thermal and the non-thermal particle populations in the ICM. I will present results from recent deep Chandra observations of the merging HST Frontier Clusters MACS J0416.1-2403 and MACS J0717.5+3745. I will talk about multiwavelength evidence for shocks and turbulence in the ICM, and discuss the constraints set on the merger geometries by optical, X-ray, and radio data.

The Planck Catalogue of Galactic Cold Clumps

Title:
The Planck Catalogue of Galactic Cold Clumps

Speaker:
Dr. Ludovic Montier (CNRS, IRAP, Toulouse, France)
Abstract: We have combined the Planck-HFI and IRAS maps to perform an all-sky detection of the cold submillimetre Galactic sources over the whole sky, to build the The Planck Catalogue of Galactic Cold Clumps, counting 13188 sources. I will describe how we proceed to build this catalogue using an original multi-frequency detection method, and how we characterized this population of objects using new distance estimates for one third of them. I will finally discuss the results provided by the Herschel Galactic Cold Core follow-up Key Programme of about 350 PGCC sources, yieldings important clues about the early phases of the star-formation.

Cosmology and Astrophysics with Galaxy Clusters

ISAS astro seminar

Prof. Daisuke Nagai (Yale)
Thursday December 25, 11:00 am
1134 : Bldg-A 1F Nyusatsu room

Title:  Cosmology and Astrophysics with Galaxy Clusters

Abstract: 
Galaxy clusters are the most recently formed cosmological objects in
the universe, making them ideal for studying the interplay between
cosmology and baryonic physics in structure formation. Understanding
their formation and growth requires not only an understanding of the
baryonic physics behind gas cooling, star and black hole formation,
and feedback processes, but also the detailed dynamics of how gas
accretes from the cosmic filaments onto the virialization regions in
the outskirts of galaxy clusters throughout their lifetime. Recent
X-ray and microwave observations have revealed detailed thermodynamic
structure of the hot X-ray emitting plasma from their cores to the
virial radii, making comparisons of baryonic component in simulations
to observations a strong cosmological probe. In this talk, I will
review recent advances in our understanding of cluster astrophysics
and discuss future prospects, opportunities and challenges (including
upcoming measurement of turbulent gas motions with ASTRO-H) a for
the use of galaxy clusters as a precision cosmological probe.

http://physics.yale.edu/people/daisuke-nagai