Mn3335 31..33

Hawaii 167. Our observations confirm the hypothesis that Hawaii 167 contains a massive quantity of dust, the optical depth of which is sufficient to extinguish completely our ultraviolet view of a central, buried quasar. The submillimetre luminosity and associated dust mass of Hawaii 167 are similar to those of the ultraluminous class of infrared galaxies, supporting the existence of an evolutionary link between these and the active galaxy population. Hawaii 167 appears to be a young quasar that is emerging from its dusty cocoon. Key words: dust, extinction ± quasars: individual: Hawaii 167 ± infrared: galaxies. 1 I N T R O D U C T I O N Hawaii 167 was identified in the Hawaii K-band survey (Songalia et al. 1994). Displaying a rest-frame ultraviolet spectrum of a young stellar population at z ˆ 2:34; Hawaii 167 also possesses broad absorption troughs of both highand low-ionization species, consistent with the presence of bulk outflows (Cowie et al. 1994). While such features are characteristic of the broad absorption line (BAL) class of quasars, the broad emission lines indicative of an active galactic nucleus (AGN) core are not seen in the ultraviolet spectrum. Infrared spectroscopy, however, does reveal both broad Ha and Hb (Cowie et al. 1994; Egami et al. 1996), with a redshift of z ˆ 2:36: These observations indicate a substantial Balmer decrement (Hall et al. 1997), suggesting that Hawaii 167 is an example of a dust-enshrouded quasar; thought to represent an early evolutionary stage, such systems would appear as fully fledged quasars once all the dust has been removed. During the transition from one phase to another, as dust is blown from a central obscuring torus, the system will appear as a BAL-type quasar. It appears, therefore, that Hawaii 167 provides us with a view of an embryonic quasar. The limited data available on Hawaii 167, however, mean that an accurate determination of its dust mass, total luminosity and true evolutionary status is not currently possible. In this paper we present submillimetre observations of Hawaii 167, probing the emission from a dusty component. These were obtained as part of a survey of the dust properties of BAL quasars (Lewis & Chapman, in preparation). In Section 2 the details of the observations are presented, while Section 3 discusses the dust content and evolutionary status of Hawaii 167. The conclusions to this study are presented in Section 4. 2 O B S E RVAT I O N S We observed Hawaii 167 with the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT) on Mauna Kea, Hawaii. We used the PHOTOMETRY three-bolometer chopping mode described by Chapman et al. (2000) and Scott et al. (2000) to keep the source in a bolometer throughout the observation. This mode has the additional advantage of allowing a check on the apparent detection of a source over three independent bolometers. The observations were taken in 2000 May, using the 450and 850-mm arrays simultaneously. The alignment of the 450and 850-mm arrays is not perfect, and we did not include the 450-mm off-beams in our final flux estimate, except to check that the source had off-beam flux consistent with the detection in the primary bolometer. For our double-difference observations there are instantaneously N ˆ 3 beams, with the central beam having an efficiency of unity and the two off-beams having e ˆ 20:5 exp 2 d 2 2sb ; …1† where d is the angular distance of the off-beam centre from the source, and sb is the Gaussian half-width of the beam. For the secondary bolometer the beam efficiency is simply 0.5. However, distortion in the field results in our chosen third bolometer being slightly offset from the source position, resulting in a beam efficiency of 0.44. Our detection level increases from .3.0s to 3.7s , after folding in the negative flux density from the two offbeam pixels. The effective integration time on source was 1900 ks. The secondary was chopped at 7.8125 Hz with a chop throw at 53 arcsec to keep the source on-bolometer at all times. Pointing was checked before and after the observation on blazars, and a sky-dip was performed to measure the atmospheric opacity directly. The rms pointing errors were below 2 arcsec, while the q 2000 RAS w E-mail: [email protected] (GFL); [email protected] (SCC) at D alousie U niersity on M ay 1, 2016 hp://m nras.oxjournals.org/ D ow nladed from