Bibcode
Ramos Almeida, C.; Martínez González, M. J.; Asensio Ramos, A.; Acosta-Pulido, J. A.; Hönig, S. F.; Alonso-Herrero, A.; Tadhunter, C. N.; González-Martín, O.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 461, Issue 2, p.1387-1403
Fecha de publicación:
9
2016
Número de citas
32
Número de citas referidas
29
Descripción
The origin of the unification model for active galactic nuclei (AGN) was
the detection of broad hydrogen recombination lines in the optical
polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a
search for the hidden broad-line region (HBLR) of nearby Sy2s started,
but polarized broad lines have only been detected in ˜30-40 per
cent of the nearby Sy2s observed to date. Here we present new VLT/FORS2
optical spectropolarimetry of a sample of 15 Sy2s, including
Compton-thin and Compton-thick sources. The sample includes six galaxies
without previously published spectropolarimetry, some of them normally
treated as non-hidden BLR (NHBLR) objects in the literature, four
classified as NHBLR, and five as HBLR based on previous data. We report
≥4σ detections of a HBLR in 11 of these galaxies (73 per cent
of the sample) and a tentative detection in NGC 5793, which is
Compton-thick according to the analysis of X-ray data performed here.
Our results confirm that at least some NHBLRs are misclassified,
bringing previous publications reporting differences between HBLR and
NHBLR objects into question. We detect broad Hα and Hβ
components in polarized light for 10 targets, and just broad Hα
for NGC 5793 and NGC 6300, with line widths ranging between 2100 and
9600 km s-1. High bolometric luminosities and low column
densities are associated with higher polarization degrees, but not
necessarily with the detection of the scattered broad components.