Restarting radio activity and dust emission in radio-loud broad
  absorption line quasars
  Broad absorption line quasars (BAL QSOs) are objects showing absorption from
relativistic outflows, with velocities up to 0.2c. These manifest, in about 15%
of quasars, as absorption troughs on the blue side of UV emission lines, such
as C iv and Mg ii. In this work, we complement the information collected in the
cm band for our previously presented sample of radio loud BAL QSOs with new
observations at m and mm bands. Our aim is to verify the presence of old,
extended radio components in the MHz range, and probe the emission of dust
(linked to star formation) in the mm domain. We observed 5 sources from our
sample, already presenting hints of low-frequency emission, with the GMRT at
235 and 610 MHz. Other 17 sources (more than half the sample) were observed
with bolometer cameras at IRAM-30m and APEX. All sources observed with the GMRT
present extended emission at a scale of tens of kpc. In some cases these
measurements allow us to identify a second component in the SED, at frequencies
below 1.4 GHz, beyond the one already studied in the GHz domain. In the
mm-band, only one source shows emission clearly ascribable to dust. Upper
limits were obtained for the remaining targets. These findings confirm that BAL
QSOs can also be present in old radio sources, or even in restarting ones,
where favourable conditions for the outflow launching/acceleration are present.
A suggestion that these outflows could be precursors of the jet comes from the
fact that ~70% of our sample can be considered in a GigaHertz Peaked Spectrum
(GPS) or Compact Steep Spectrum (CSS)+GPS phase. This would confirm the idea
proposed by other authors that these outflows could be recollimated to form the
jet. Comparing with previous works in the literature, dust emission seems to be
weaker than the what expected in 'normal' QSOs, suggesting that a feedback
mechanism could inhibit star formation in radio-loud BAL QSOs.
