Research Highlights and News

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Quantifying the cosmic variance in low-z galaxy distribution

Our Universe is not so homogeneous even at scales larger than hundreds of millions of light years . The properties of cosmic objects, which form and co-evolve with their environments, are also expected to be fluctuated in space. Limited by the sizes of telescopes, the astronomical observations are always constrained in restricted volume, and are not guaranteed to give an un-biased representation of the whole Universe. This inspires studies of such an effect known as cosmic variance (CV). Previous works have found that CV could have un-negligible effect for small surveys (e.g. pencil beam surveys [3], high-resolution shallow surveys [4], etc). Corresponding corrections have been made either in a statistical manner, or by a lowest-order assumption that the spatial distribution of bright and faint galaxies are much similar. However, these are far from enough to give a sample-to-sample quantifying of CV, and give a precise estimates of the statistics of galaxy distribution.


The Dark Ages and the Dawn of the Universe

On the night of May 11th, 2018, the 22nd session of the "New Worlds, New Horizons" Public Astronomy Lecture series-The Dark Ages and the Dawn of the Universe was held in the Back Hall Auditorium in the Main Building of Tsinghua University. The lecturer, Dr. Xuelei Chen is a leading researcher from the National Astronomical Observatory of China. The lecture attracted an audience of over 500, including students, teachers and the general public.


Low-Luminosity AGNs: Fed More, Spit Up More

In the center of almost every major galaxy there exists a supermassive black hole. When matters fall onto the black hole, the gravitational potential energy can be released and radiated away via some physical processes that are still not well understood. This makes them bright sources called the active galactic nuclei (AGNs). However, it remains unclear how such processes work when the mass feeding rate (the accretion rate) is extremely low. THCA student Rui She led a project to study these AGNs in nearby galaxies and found that, in the low-luminosity regime, the more the AGNs are fed, the more they reject the in-fall materials in the form of outflow. The observed results are in good agreement with numerical simulations. The paper was accepted for publication in the Astrophysical Journal.


Understanding neutral hydrogen clustering during re-ionization

Upcoming observations of cosmic radio signals will mark the beginning of a new era in cosmology as they will provide a first glance on the neutral hydrogen distribution in the early universe. These observations will give us insights into a key process in the evolution of the universe – the reionization of the neutral hydrogen by the first stars and galaxies. The neutral hydrogen distribution can be observed via photons, which are emitted by neutral hydrogen atoms at the wavelength of 21cm and are redshifted to radio signals during their journey through the expanding universe before being observed on earth.


Neutron Stars, viewed through Photons, Gravitational Waves and Neutrinos

On the night of March 30th, 2018, the 21st session of the "New Worlds, New Horizons" Public Lecture series was held in the Auditorium of Tsinghua University. The lecture was delivered by Prof. Peter Mascaros, Abelli Chair Professor of Astronomy and Astrophysics of Pennsylvania State University. Nearly 300 people from Tsinghua University and elsewhere attended the lecture.


A MaNGA view of how galaxies distribute in the mass-size plane

The universe houses hundreds of billions of galaxies with different color, sizes and morphologies. As seen in the Hubble Ultra-Deep Field (Figure 1): some galaxies appear to be red, nearly featureless and elliptical, while some have beautiful and blue spiral arms (spiral galaxies). Surprisingly these diverse galaxies follow simple global scaling relations. Recent work led by an PhD student, Hongyu Li (NAOC), Profs. Shude Mao (Tsinghua) and Michele Cappellari (Oxford) extended such scaling relations using spatially-resolved integral field unit data from MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), one of the world-leading SDSS surveys. This study provides further constraints on how galaxies form and evolve.