New Observations of the Gas Cloud Associated with the Quasar-Galaxy Pair 3C 232/NGC 3067

Abstract

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 (δv ~ 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 x 10^21^ 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 ~ (10^8^ M_sun_ )h^-2^, linear extent ~ (2.5 kpc)h^-1^, and mean hydrogen density n_H_ = (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 {PHI}_ion_ < 8.35 x 10^4^ photons s^-1^ on the ionizing photon flux, corresponding to O_0_ =I_v_(13.6 eV) < 1.8 x 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 Il can provide even lower limits, I_0_ ~ [(1-6) x 10^-23^ ergs cm^-2^ s^-1^ Hz^-1^ sr^-1^]h, assuming depletion factors d_Na_ = 0.25 and d_Ca_ = 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.