Institute for Theory and Computation, P-256
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, MS-51
Cambridge, MA 02138, USA
Tel: (617) 495-5374
I am a postdoc at the Harvard-Smithsonian Center for Astrophysics. I got my PhD from the Department of Astrophysical Sciences at Princeton in 2009. Here is my CV (pdf). My email is yshen AT cfa.harvard.edu
you are looking for emission line properties of SDSS quasars, click here.
If you are looking for survey geometry information for SDSS statistical quasar samples, click here (DR5 only, DR7 coming up soon).
My main area is extragalactic astronomy, with an emphasis on active galactic nuclei (AGN) and supermassive black holes (SMBHs). I consider myself as a quasarologist for what I spend most of my time on. However, I am generally interested in topics in galaxy formation and observational cosmology, as well as in other branches of astronomy/astrophysics.
Quasars (and their low-luminosity counterparts AGNs) are accreting SMBHs. Because of their high luminosity, they can be witnessed up to very high redshift (and therefore the very early Universe). These cosmological beacons are by themselves fascinating objects, and beg for an understanding of their formation and evolution in the cosmic landscape. They are also "believed" to have influenced their host galaxy in many profound ways during their co-evolution with the host, via some feedback processes, the nature of which is still elusive at present.
I am working on an array of topics related to quasars and SMBHs, with the hope to better understand the phenomenology of SMBHs, how they evolve across cosmic time, and how they interact with their hosts. Below is a brief summary of what I have been working on in this field.
Just as galaxies, quasars (AGNs) as a cosmological luminous population can be used to trace the underlying large-scale structure (LSS) mapped by the unobservable dark matter. One statistical description of the LSS is the two-point correlation function (or clustering for short). I have been working on the measurements of quasar clustering using large, homogeneous quasar samples from the Sloan Digital Sky Survey (SDSS). The strength of quasar clustering tells us about what kind of dark matter halos quasars live in, and quasar clustering has become an important ingredient in cosmological quasar models.
Here is the link to the old DR5 high-z quasar clustering study (DR7 results coming up soon), and a press release on this.
Quasars are much more than just points on the sky! They have quite diverse properties derived from their multi-wavelength spectral energy distribution (SED). These spectral properties contain information about the properties of the BH, the accretion disk, as well as other emission regions. I am working on various statistical properties of quasars, with some emphases on determining the BH mass of quasars. Here is the link to the latest DR7 compilation of spectral measurements for SDSS quasars.
Currently our best method to measure the masses of quasars is the virial BH mass estimators, which are bootstrapped from studies on reverberation mapping AGNs. I am working on improving some of the frequently-used virial BH mass estimators for quasars/AGNs. Understanding the systematics with these BH mass estimates is crucial to many studies such as the active BH mass function, and the evolution of the BH-host correlations.
With increasingly larger data sets, it has become feasible and important to fit the SMBH population into its cosmological context, namely, how did the SMBH population evolve across cosmic time. My particular interest on this topic is to investigate how different observations of quasar statistics can be used to constrain certain evolutionary models, and how these models make predictions for future surveys. Here is my 2009 model on this subject, which is part of my PhD thesis.
Most (if not all) astronomers believe that binary SMBHs do exist (well, there have been reports of spatially-resolved binary SMBHs above pc scales), and, under certain circumstances will merge to form a single BH. This is currently a hot topic in the field, not only because the bearkthrough in numerical GR has led to predictions of many interesting phenomena during/after BH coalescence, but also because that the flood in astronomical data in recent years (owing to many surveys) has enabled systematic searches for these systems/events. Its relevance to gravitational wave detection is also a big boost factor to its popularity. The dynamics of binary SMBHs has always been an interesting topic ever since the idea of binary SMBHs was proposed a few decades ago.
I have been involved in several projects searching for binary AGNs/quasars from tens of kpc scales down to sub-pc scales. The goal is to increase the number of known binary SMBHs (below tens of kpc separations) by orders of magnitude, and to quantify the frequency of binary active SMBHs. The searches for binary SMBHs are very important in understanding BH fueling, feedback, and constraints on predictions for future low-frequency gravitational wave detection experiments.
Many quasars show absorption features imprinted on their spectra. These include broad absorption lines (BALs), high-velocity narrow absorption lines (NALs), and associated absorption lines (AALs). Many of the NALs are not physically connected to the quasar, and are simply absorption from cosmologically intervening systems. Intervening quasar absorbers have been a useful tool to study the intergalactic medium (IGM) and high-redshift foreground galaxies, using background quasars. But for me, I am interested in those absorbers that are physically associated with the quasar itself. This intrinsic absorber population is a great tool to probe the physical conditions and dynamical processes within the quasar hosts, and carries a key piece of information about the formation and evolution of quasars and massive galaxies. They are as useful as emission lines (even better than emission lines under many circumstances) in the studies of quasar evolution and feedback.
I have been working on the statistics of intrinsic quasar absorbers (BALs and "intrinsic" AALs -- the nomenclature is getting worse in astrophysics every day), as well as detalied follow-up studies of individual systems. Of particular interest here is what we can learn from these absorbers about the feedback processes that galaxy formation people have been desperately trying to understand.
Astrophysics is a diverse field. I generally find myself interested in other topics not in my main area. While I was in graduate school, I tried different things: I have worked on hydrodynamics/MHD, solar system dynamics and exoplanets, as well as dust aggregate models, under supervision of different advisors. I am definitely not an expert in these fields, but it's good to know something outside my main area. Maybe someday I will come back to these topics, when I am tired of quasars :-)
Last updated: May 2011 by Yue Shen