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An Investigation of Gravitational Lensing in the Southern BL Lac PKS 0537−441

“…Figure 1 presents the co-added spectrum (with the corresponding noise spectrum) in the 1 ′′ extracted band. The flux in the 6 ′′ extracted spectrum is a factor of ∼ 6 times lower than that presented by Stickel et al (1988), indicating that PKS 0537-441 was in a quiescent state. Our spectrum is also flatter, with a -6 -…”

“…Is there any indication of the presence of a galaxy in the PKS 0537-441 system? As discussed in Section 2, the existence of a galaxy component in this system has a checkered history, originally detected in the imaging work of Stickel et al (1988), with later studies failing to identify any extended emission (Falomo et al 1992;Kotilainen et al 1998 (Urry et al 1997;Urry et al 1999). Four exposures, of duration 14 sec, 80 sec, and 2 × 260 sec, all in the F702W filter (a 585Å wide passband centered on 6913Å), were obtained from the HST archive.…”

“…It was also suggested that C III] λ1909 was also seen in these early spectra, although this has not been confirmed in subsequent observations. Imaging by Stickel et al (1988) revealed that PKS 0537-441 lies superimposed within a system of low redshift galaxies. One of these, a spiral galaxy at z = 0.186, is seen 11 ′′ eastward, while PKS 0537-441 was inferred to lie at the core of a galaxy with an extended exponential disk profile.…”

“…One of these, a spiral galaxy at z = 0.186, is seen 11 ′′ eastward, while PKS 0537-441 was inferred to lie at the core of a galaxy with an extended exponential disk profile. However, deeper follow-up exposures in the optical and NIR with the NTT and ESO 2.2m telescope failed to detect any extended emission around PKS 0537-441 (Falomo et al 1992;Kotilainen et al 1998), suggesting that the findings of Stickel et al (1988) were erroneous.…”

“…Although problems exist with this microlensing hypothesis (Kayser 1988;Gear 1991;Lewis & Williams 1997), observationally a number of BL-Lac systems appear to be superimposed on extended nebulosities (Stickel et al 1988). While it is obvious that in several of these the nebulosity and the BL-Lac source are physically associated, in others the extended emission appears to be a foreground galaxy, distinct from the BL-Lac source (Stocke et al 1985), bolstering the case for the microlensing of BL-Lacs.…”