Abstract
We present low-resolution, near-IR JHK spectra of the weak z = 2.39 radio galaxy 53W002, obtained with the OH-airglow Suppressor spectrograph (OHS) and Cooled Infrared Spectrograph and Camera for OHS (CISCO) on the Subaru Telescope. They cover rest-frame wavelengths of 3400-7200 Å, and the emission lines of [O II] λ 3727, Hβ, [O III] λλ 4959, 5007, Hα, [N II] λλ 6548, 6583 and [S II] λλ 6716, 6731 were detected. Using the Hα/Hβ line ratio, we find an extinction of E (B - V) = 0.14. The emission-line ratios are reproduced by a cloud of electron density ne = 1 × 103-4cm-3 with solar metallicity, ionized by an α = -0.7 power-law continuum with ionizing parameter U = 1 × 10-3. In addition to these emission lines, we make the first spectroscopic confirmation of the Balmer discontinuity in a high-z radio galaxy. Together with rest-frame UV photometry from the literature, we show that at least 1/3 of the present stellar mass was formed in the current starburst. The stellar mass was estimated to be (1-1.4) × 1011 M⊙ by one-component model fitting, which is smaller than that of typical z ∼ 1 B2/6C radio galaxies. We suggest that 53W002 is currently assembling a large part of its stellar mass through merger events with the surrounding sub-galactic clumps, some of which can be identified with the Lα emitters detected in narrow-band imaging. After a few such events over the next few Gyr, 53W002 will evolve into a massive elliptical galaxy.
Original language | English |
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Pages (from-to) | 459-467 |
Number of pages | 9 |
Journal | Publications of the Astronomical Society of Japan |
Volume | 53 |
Issue number | 3 |
DOIs | |
Publication status | Published - 2001 Jun 25 |
Externally published | Yes |
Keywords
- Galaxies: active
- Galaxies: individual (53W002)
- Galaxies: spectroscopy
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science