High-z Galaxies

Using ZEUS on the CSO I have made the first detections of two far-infrared fine-structures lines, [OIII] 88 micron line and the [NII] 122 micron line, from high redshift galaxies (Figure 1; Ferkinhoff et al. 2010, Ferkinhoff et al. 2011). The line strengths indicate that the source galaxies contain significantly more ionized gas than nearby galaxies. From one source, SMMJ02399 at z ~ 2.8, I detect both lines. Using the [OIII] to [NII] line ratio, which is very sensitive to ionization source, I am able to conclude that the line emission either arises due to massive O9.5 stars or from an AGN. These observations successful demonstrated the utility of the [NII] and [OIII] lines in constraining properties of the galaxies in the early universe.

ZEUS-1 spectra as reported in Ferkinhoff et al. 2010 and 2011. (top) [NII] and [OIII] spectra from SMMJ02399.
(bottom left) [NII] spectrum from the Cloverleaf QSO. (bottom right) [OIII] spectrum from APM08279.

Also using ZEUS, the submillimeter group at Cornell University, led by my university advisor Prof. Gordon Stacey, has made ~ 25 detections of the [CII] 158 micron line from z > 1 galaxies (Stacey et al 2010). This is the first survey of this line from galaxies in the early universe. The [CII] 158 micron line is an important spectral probe because it dominates the cooling in photo-dissociation regions (PDRs; regions between ionized and molecular gas) and atomic clouds. The line is also an important coolant of the warm ionized medium. The ratio of [CII] line luminosity to the total far-infrared luminosity of a galaxy is sensitive to the strength of the interstellar UV radiation field. Measurement of this ratio can constrain both the source of the ultraviolet photons as well as the size of the emitting region. Our observations indicate that early star-forming galaxies have similar [CII] to far-IR ratios to that of local normal galaxies (~0.1%), but unlike local systems they are undergoing star formation on galaxy wide scales and forming thousands of stars per year.

Figure from Ferkinhoff et al. 2013 showing the ratio of the [CII] luminosity to FIR versus FIR luminosity for ZEUS-1 sources,
the ZEUS-2 detection from SDP11 and a selection of sources from literature.