Oral Presentation
Search for Broad Hα Emitters in the nearby universe (z < 1) with Subaru PFS
Presenter: Yuki Taki (NAOJ/SOKENDAI)
One of the most interesting discoveries revealed by the JWST is the large number of broad (FWHM>1000 km/s) Hα emitters (bHAEs) in the high-redshift universe (z~5). Detection of the broad Hα emission line is characteristic of AGN, but bHAEs do not exhibit other features typical of AGN. Thus, whether bHAEs are truly AGN remains unclear.
The discovery of bHAEs was completely unexpected, because no objects like bHAEs have been found at such high number densities in the nearby universe (z<1).
In this study, we conducted wide wavelength coverage and high spectral resolution Subaru PFS spectroscopy of ~15,000 nearby galaxies (z<1) within the COSMOS field. We fitted spectra to confirm the presence or absence of broad Hα emission line components, and identified ~10 galaxies with statistically significant broad Hα emission components (i.e., bHAEs).
All these bHAEs are faint in deep Chandra X-ray data, and show no evidence for mid-infrared (3-10 μm) excess emission from an AGN dust torus. These characteristics resemble those of bHAEs discovered at high redshift (z~5) by JWST.
Based on the luminosity function derived from our bHAEs sample, the number density of bHAEs at z<1 is ~1/100 of that of bHAEs at z~5, and ~1/1000 of the total galaxy population at z<1. Our study reveals that bHAEs also exist in the nearby universe (z<1) and are rare compared to the high-redshift universe (z~5).
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