Mathematics – Logic
Scientific paper
Jun 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991apj...374...72s&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 374, June 10, 1991, p. 72-82.
Mathematics
Logic
37
H I Regions, Interacting Galaxies, Quasars, Ultraviolet Spectra, Absorption Spectra, Astronomical Spectroscopy, Charge Coupled Devices, Iue, Galaxies: Individual (Ngc 3067), Galaxies: Interactions, Interstellar: Matter, Quasars, Ultraviolet: Spectra
Scientific paper
We present new optical Na I and Ca II spectra, new Hα images, and archival IUE ultraviolet spectra of the quasar-galaxy pair 3C 232/NGC 3067, to study the H I gas cloud seen in 21 cm emission between the eastern edge of NGC 3067 and 3C 232. High-resolution optical spectra show two, and possibly three, absorption systems in Ca II and Na I, with a large velocity spread (Δυ ≍ 160 km s-1); IUE spectra show Fe II and Mg II absorption. The strongest system is coincident with narrow 21 cm absorption at cz = 1420 km s-1 and has Na I/Ca II ≍ 0.7-2, suggesting that the Ca-bearing grains have not been strongly disturbed. The H I absorption is most likely produced by cold (T ≤ 300 K) gas comprising 1%-2% of the 3 × 1021 cm-2 of warm H I (T ≍ 8000 K) seen in 21 cm emission. At a distance of (14.7 Mpc)h-1, this cloud has mass ˜(108 Msun)h-2, linear extent ˜(2.5 kpc)h-1, and mean hydrogen density nH = (0.42 cm-3)h.
We detect no Hα, to a limit of 27.5 mag arcsec-2, coincident with the H I cloud in broad-band R images or in narrow-band redshifted CCD images. The absence of Hα sets a limit of Φion < 8.35 × 104 photons s 1 on the ionizing photon flux, corresponding to I0 ≡ Iv(13.6 eV) < 1.8 × 10-22 ergs cm-2 s-1 Hz-1 sr-1 on the diffuse extragalactic ionizing flux. The ionization balance of Na I and Ca II can provide even lower limits, I0 [(1-6) × 10-23 ergs cm-2 s-1 Hz-1 sr-1]h, assuming depletion factors dNa = 0.25 and dCa = 0.1 for Na and Ca. From the flux of ionizing photons inferred from IUE spectra of 3C 232, the Hα limit implies that the quasar must lie at least (25 kpc)h-1 behind the H I cloud, and the Na-Ca limits imply a distance of at least (25-66 kpc)h-3/2. While this does not rule out the noncosmological redshift interpretation for the quasar, 3C 232 is unlikely to be the perturber that stripped the H I finger from NGC 3067. The H I is most likely a chance projection at the quasar position and offers no additional support for the association of the pair.
Case James
Donahue Megan
Shull Michael J.
Snow Theodore P.
Stocke John T.
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