TY - JOUR
T1 - HST unveils a compact mildly relativistic broad-line region in the candidate true type 2 NGC 3147
AU - Bianchi, Stefano
AU - Antonucci, Robert
AU - Capetti, Alessandro
AU - Chiaberge, Marco
AU - Laor, Ari
AU - Bassani, Loredana
AU - Carrera, Francisco J.
AU - La Franca, Fabio
AU - Marinucci, Andrea
AU - Matt, Giorgio
AU - Middei, Riccardo
AU - Panessa, Francesca
N1 - Publisher Copyright: © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2019/9/1
Y1 - 2019/9/1
N2 - NGC 3147 has been considered the best case of a true type 2 AGN: an unobscured AGN, based on the unabsorbed compact X-ray continuum, which lacks a broad-line region (BLR). However, the very low luminosity of NGC 3147 implies a compact BLR, which produces very broad lines, hard to detect against the dominant background host galaxy. Narrow (0.1 arcsec × 0.1 arcsec) slit HST spectroscopy allowed us to exclude most of the host galaxy light, and revealed an H α line with an extremely broad base (FWZI${\sim }27\, 000$ km s-1). The line profile shows a steep cut-off blue wing and an extended red wing, which match the signature of a mildly relativistic thin accretion disc line profile. It is indeed well fit with a nearly face on thin disc, at i ∼23°, with an inner radius at 77 ± 15 rg, which matches the prediction of $62^{+18}_{-14}$rg from the RBLR-L1/2 relation. This result questions the very existence of true type 2 AGN. Moreover, the detection of a thin disc, which extends below 100 rg in an L/LEdd ∼10-4 system, contradicts the current view of the accretion flow configuration at extremely low accretion rates.
AB - NGC 3147 has been considered the best case of a true type 2 AGN: an unobscured AGN, based on the unabsorbed compact X-ray continuum, which lacks a broad-line region (BLR). However, the very low luminosity of NGC 3147 implies a compact BLR, which produces very broad lines, hard to detect against the dominant background host galaxy. Narrow (0.1 arcsec × 0.1 arcsec) slit HST spectroscopy allowed us to exclude most of the host galaxy light, and revealed an H α line with an extremely broad base (FWZI${\sim }27\, 000$ km s-1). The line profile shows a steep cut-off blue wing and an extended red wing, which match the signature of a mildly relativistic thin accretion disc line profile. It is indeed well fit with a nearly face on thin disc, at i ∼23°, with an inner radius at 77 ± 15 rg, which matches the prediction of $62^{+18}_{-14}$rg from the RBLR-L1/2 relation. This result questions the very existence of true type 2 AGN. Moreover, the detection of a thin disc, which extends below 100 rg in an L/LEdd ∼10-4 system, contradicts the current view of the accretion flow configuration at extremely low accretion rates.
KW - galaxies: Seyfert
KW - galaxies: active
KW - galaxies: individual: NGC3147
UR - http://www.scopus.com/inward/record.url?scp=85073048981&partnerID=8YFLogxK
U2 - https://doi.org/10.1093/mnrasl/slz080
DO - https://doi.org/10.1093/mnrasl/slz080
M3 - مقالة
SN - 1745-3925
VL - 488
SP - L1-L15
JO - Monthly Notices of the Royal Astronomical Society: Letters
JF - Monthly Notices of the Royal Astronomical Society: Letters
IS - 1
ER -