17 New Strong Gravitational Lenses Discovered by NAOC Researchers Using HST Data

Various experiments have been carried out to further determine the nature of dark matter, one of which is to constrain the properties of dark-matter subhalos with the aid of strong gravitational lensing. Dark-matter subhalos are small satellites around galaxies that primarily consist of dark matter. Their abundance and mass distribution provide direct evidence of the nature of dark matter. “In this experiment, the capability of detecting low-mass dark-matter subhalos is crucial because predictions by different dark-matter models are only different for low-mass subhalos,” adds Kochanek. Previous studies have shown that the smaller the background source is, the lower the mass limit can be achieved. “However, background source sizes in previous strong-lens samples are still larger than required for a decisive conclusion on the nature of dark matter,” comments Oguri.

In order to push the detection limit downward, Shu and collaborators specifically selected 21 strong-lens candidates involving redshift 2-3 Lyα emittersas the background sources from approximately one million galaxies. Lyα emitters are young galaxies that emit strong Lyα emission due to the transition of the electron of a hydrogen atom from the first excited state to the ground state. “Compared to previous samples, Lyα emitters are intrinsically smaller by a factor of 3 to 5, and therefore can push the detection limit down by roughly an order of magnitude,” comments Shu.

 

Follow-up HST imaging observations confirmed that 17 of the 21 candidates are definite strong lenses (see Figure 1). “This is also the very first discovery of galaxy-scale strong lenses made by Chinese astronomers using the HST data,” adds Mao.

Credit: National Astronomical Observatories, Chinese Academy of Sciences

By analyzing the HST data, Shu and collaborators found that the background Lyα emitters are generally irregular and clumpy. “With the aid of lensing magnification, we can resolve the Lyα emitters in exceptional detail with sizes from a hundred to several thousand light years,” comments Perez-Fournon. “Future follow-up observations of the Lyα emitters will expand our understanding of how galaxies form and evolve,” adds Zheng. This specially designed, new strong-lens sample promises to be an invaluable resource for studying high-redshift Lyα emitters and the nature of dark matter.

Contacts and sources:
National Astronomical Observatories, Chinese Academy of Sciences

This work has been recently published in The Astrophysical Journal (Shu et al., 2016, ApJ, 833, 264). This work is also supported by the National Science Foundation of China. Other members of the team are Prof. Adam Bolton (National Optical Astronomy Observatory), Prof. Christopher Kochanek (Ohio State University), Dr. Ismael Perez-Fournon (Instituto de Astrofisica de Canarias), Prof. Masamune Oguri (University of Tokyo), Dr. Antonio D. Montero-Dorta (University of Utah), Matthew A. Cornachione (University of Utah), Dr. Rui Marques-Chaves (Instituto de Astrofisica de Canarias), Prof. Zheng Zheng (University of Utah), Dr. Joel Brownstein (University of Utah), and Prof. Brice Menard (Johns Hopkins University).