Stellar velocity dispersion is found to be worse than stellar mass for linking galaxies to their dark matter halos

Posted on 4/12/2012

A recent work done by Cheng Li and Lixin Wang from our group, in collaboration with Yipeng Jing from CAA at Shanghai Jiao Tong University, has revealed that, when compared to its stellar mass, the stellar velocity dispersion of a galaxy is correlated less tightly with the dark matter mass of the host halo. The figure on the left summarizes the result of this work by plotting the central galaxies in SDSS groups as small dots on the plane of stellar mass vs. stellar velocity dispersion. Subsamples selected on the plane are enclosed by the boxes, while the median of the stellar mass and stellar velocity dispersion in each subsample is marked by a cross. For each subsample, the estimated halo mass is indicated by the size of the red circle, with bigger circules for larger halo masses. As can be seen, halo mass increases with stellar mass when stellar velocity dispersion is fixed, while showing almost no dependence on stellar velocity dispersion if stellar mass is fixed. The paper is accepted for publication in ApJ Letters, and is available at arXiv:1210.5700.

Measuring the velocity dispersion of satellites in galaxy groups by modeling the redshift distortions in group-galaxy cross-correlations

Posted on 4/12/2012

A collaboration led by Cheng Li from our group has recently measured the velocity dispersion profile (VDP) for galaxy groups in the final data release of the Sloan Digital Sky Survey (SDSS/DR7). For this they have estimated the redshift-space cross-correlation function (CCF) between central galaxies of given mass (or luminosity) and a reference galaxy sample. The VDP is then measured by modeling the redshift distortion in the CCF. It is found that, within rivial radius, the VDP shows a roughly flat profile, while the average velocity dispersion (VD) is a strongly increasing function of central galaxy mass. By applying the same method to N-body cosmological simulations, the authors showed that the velocity dispersion vs. stellar mass relation can be used to constrain both the density fluctuation parameter (sigma_8), and the dispersion in stellar mass at fixed halo mass for central galaxies. Since the velocity dispersion is caused by the local gravitational field, the VDP measurements also provided a direct measure of the dark matter halo mass for central galaxies of different masses and luminosities. The work is published in ApJ (2012, vol 758, id 50), and is available at arXiv:1206.3566.

Dr. Ting Xiao joined our group as a postdoc

Posted on 24/3/2012

Dr. Ting Xiao joined our group as a postdoc in early February, 2012, just after she got a Ph.D in astrophysics from Department of Astronomy at University of Science and Technology of China. Ting has been working on connections between black holes and galaxies, as well as correlations of the dust and gas contents with galaxy properties.

Dr. Bernardo Cervantes-Sodi joined our group as a postdoc

Posted on 9/9/2011

Dr. Bernardo Cervantes-Sodi joined us today. Bernardo got his Ph.D from the National University of Mexico in 2009. After that he moved to Korea Astronomy and Space Science Institute as a postdoc. Bernardo has been working on the spin parameter of galaxies as a function of physical properties and local environment.

The 9-th Sino-German Workshop was held in Hangzhou

Posted on 27/5/2011

The 9-th Sino-German Workshop on Galaxy Formation and Cosmology was held in Hangzhou, April, from 26th till 29th inclusive. More than 110 participants from 26 institutions in 7 countries attended the workshop, 66 of which gave a talk on their work on the theme of the workshp, that is, understanding star formation and gas accretion in galaxies from high to low redshifts.

Establishment ceremony of the MPPG is held today

Posted on 25/4/2011

The ceremony for establishment of two new Max Planck Institute (MPI) partner groups is held today at the Shanghai Branch of Chinese Acamedy of Sciences (CAS). The first group is the one between the Max-Planck-Institute for Astrophysics (MPA) and the Shanghai Astronomical Observatory (SHAO), with Dr. Cheng Li at SHAO and Dr. Guinevere Kauffmann at MPA as the two leaders of the group. The group has officially started since the January 1st this year. The other group is constructed between the MPA and National Astronomical Observatories (NAOC), with Dr. Liang Gao at NAOC and Prof. Simon White at MPA as group leaders. The group started runing on 1st April.

The 9-th Sino-German Workshop to be held in Hangzhou, April, 2011

Posted on 24/2/2011

Shanghai Astronomical Observatory (SHAO) and Max-Planck Institute for Astrophysics (MPA) are organizing the 9-th Sino-German workshop on galaxy formation and cosmology, which will be held in Hangzhou during April 26-29, 2011. The theme of this workshop is “Understanding gas accretion and star formation in galaxies from high to low redshifts”. The following topics will be covered:

  • Star formation and gas properties in nearby galaxies;

  • Star formation and gas properties in high-z galaxies;

  • Galaxy clusters and their gaseous content;

  • Theoretical studies of galaxy formation and evolution;

  • Supermassive black holes, active galactic nuclei and high energy astrophysics;

  • Galaxy environment from small to large scales and from high to low redshifts;

For more information, please consult the workshop website or contact us.

Official start of the 3rd Max-Planck-Institute Partner Group (MPPG) at Shanghai Astronomical Observatory

Posted on 1/1/2011

The Max Planck Society (MPG) and the Chinese Academy of Sciences (CAS) have agreed to set up a new partner group (MPPG) between the Max-Planck-Institute for Astrophysics (MPA) and the Shanghai Astronomical Observatory (SHAO), with Dr. Cheng Li at SHAO and Dr. Guinevere Kauffmann at MPA as the two leaders of the group. The partner group will run the end of 2015. The research theme of the group is "understanding star formation, gas accretion and the clustering properties of galaxies from high to low redshifts".

The new partner group is the third in a series of scientific exchanges between MPA and SHAO. The first such group was founded in 2000 between Prof. Dr. Yipeng Jing at SHAO and Prof. Dr. Gerhard Boerner at MPA. The second group was set up in 2006 between Dr. Xiaohu Yang at SHAO and Dr. Volker Springel at MPA. Both partner groups have led to many successful collaborations, which are still ongoing today.

Currently there are 44 Max-Plank-Institute Partner Groups worldwide, of which about 20 are associated with institutes in mainland China.