Research

 

I am an observational astronomer. On my Album page, you can see pretty pictures from Hawaii and Chile where I carry out most of my observations.

My research interests cover a wide range of subjects from Galactic ultra-cool dwarfs to high-redshift quasars and star forming galaxies. I am particularly interested in the metal poor galaxies and galaxies at high-redshift to better understand the galaxy formation and chemical enrichment history.

 My Main Research Projects

 I     Strong emission-line, extremely metal-poor galaxies 
 II    Wide-field optical survey for high-redshift Quasars (z > 5)
 III   Metallicity and kinematics studies of star-forming galaxies at 3 < z < 5



  1. I.Strong emission-line, extremely metal-poor galaxies
    Ultra-Strong Emission Line Galaxies (USELs)
       
      (Refs:
    Kakazu, Cowie, Hu 2007Hu, Cowie, Kakazu, Barger 2009 )


  We have shown that narrowband filters, traditionally used to search for high-z Lyα emitting galaxies,
       are also very powerful in finding extremely metal poor galaxies at intermediate redshift (z < 1.5).

    


  
“Green Pea” galaxies and XMPGs (Extremely Metal Poor Galaxies)

    










     

       Until a few years ago, extremely metal poor galaxies (XMPG: Z < Zsun/12) were extremely rare.
    
       For example,  only a dozen XMPGs were found from an analysis of 250,000 spectra over
       ~3,000 deg^2 for the SDSS (Kniazev et al. 2003).  It was the help from volunteers in the
      
Galaxy Zoo project that led to the discovery of several dozen XMPGs in the SDSS. 
       These galaxies were named “Green Peas” because of their appearances
       (e.g. Cardamon et al. 2009).

       Kakazu et al. (2007) have shown that the narrowband method is a powerful way to find these
       extremely metal deficient populations. Furthermore, we found that they contribute to a significant
       amount of star formation at 0 < z < 1.

       The large EW (out to 1,000 Å) and low metallicity suggest that they have just undergone major
       starbursts within a few million years.  Thus, they serve as an ideal laboratory to probe the early
       phase of galaxy formation, galaxy interactions, and the pre-enrichment of intergalactic gas in
       formation regions.











 

 



   

      I have been studying these strong emission line, metal poor galaxies using various survey data;
      Hawaii deep survey (PI: E. Hu), COSMOS survey (PI: N. Scoville), and Dark Energy Survey
      (PI: J. Frieman).
      



  1. II.Wide-Field Optical Survey for High-Redshift Quasars (z > 5)
    Hawaii Quasar and T-dwarf Survey (HQT)
      

   (Ref:  Kakazu, Y., Hu, E. M., Liu. M. C. et al. 2010)


    
As part of my Ph.D. thesis, I conducted a wide-field survey for high-redshift Quasars under the
      supervision of Profs. Esther M. Hu and Lennox L. Cowie at the University of Hawaii.
      My survey specifically targeted low-luminosity quasars (M(1450) < -22.5), which are considered to
      form the bulk of the quasar population at high-redshift. Our other goal was to probe rare, distan
      T-type dwarfs that have similarly red optical colors as QSOs.


     
Method --- A New color technique
     










        
       
      
     
       
High-redshift QSOs are traditionally selected as I-band dropouts (or red I-z colors) owing to the
          strong neutral HI absorption below Lyα as light travels through the intergalactic medium.

          The major difficulty in identifying z >> 5 quasars is that cool dwarfs (mainly late M and L types)
          possess similarly red
I-z colors as high-z galaxies.

      

          Hence, in Kakazu et al. (2010) we introduced a new color selection technique using a narrowband
          filter NB816 to separate out quasars from these foreground red objects.

          Our technique is unique and efficient since it does not require time expensive near-IR data,

          which had commonly been used to remove contaminants.





  1. III. Metallicity and kinematics studies of star-forming galaxies at 3 < z < 5.

          

           Coming soon!



 

HST/ACS B,V,i composite image of a metal poor galaxy (Z ~ 0.1 Zsun) at z=0.644  (Kakazu et al. 2007)

The Keck/DEIMOS spectrum of narrowband selected USEL at z=0.398 from Kakazu et al. 2007., overlaid with filter response (V, R, I, NB912). The spectrum is characterized by strong emission lines, but little continuum. The [OIII]4363, a hallmark of metal deficient system, is clearly detected.

Mauna Kea, Hawaii  (©Wei-Hao Wang)

Green Pea galaxy at z= 0.212 found in SDSS. (Amorin et al.)