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Title: Probing the active massive black hole candidate in the center of NGC 404 with VLBI

Recently, Nyland et al. argued that the radio emission observed in the center of the dwarf galaxy NGC 404 originates in a low-luminosity active galactic nucleus powered by a massive black hole (MBH, M ≲ 10{sup 6} M{sub ☉}). High-resolution radio detections of MBHs are rare. Here we present sensitive, contemporaneous Chandra X-ray, and very long baseline interferometry (VLBI) radio observations with the European VLBI Network. The source is detected in the X-rays, and shows no long-term variability. If the hard X-ray source is powered by accretion, the apparent low accretion efficiency would be consistent with a black hole (BH) in the hard state. Hard state BHs are known to show radio emission compact on the milliarcsecond scales. However, the central region of NGC 404 is resolved out on 10 mas (0.15-1.5 pc) scales. Our VLBI non-detection of a compact, partially self-absorbed radio core in NGC 404 implies that either the BH mass is smaller than 3{sub −2}{sup +5}×10{sup 5} M{sub ☉}, or the source does not follow the fundamental plane of BH activity relation. An alternative explanation is that the central BH is not in the hard state. The radio emission observed on arcsecond (tens of parsecs) scales maymore » originate in nuclear star formation or extended emission due to AGN activity, although the latter would not be typical considering the structural properties of low-ionization nuclear emission-line region galaxies with confirmed nuclear activity.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo (Netherlands)
  2. FÖMI Satellite Geodetic Observatory, P.O. Box 585, H-1592 Budapest (Hungary)
  3. Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242 (United States)
  4. Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, NL-6500 GL Nijmegen (Netherlands)
  5. Observatório Nacional, Rua José Cristino, 77. CEP 20921-400, Rio de Janeiro (Brazil)
  6. Indian Institute of Astrophysics, II Block, Koramangala, Bangalore 560034 (India)
Publication Date:
OSTI Identifier:
22365439
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 791; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; COMPACTS; DETECTION; EFFICIENCY; EMISSION; GALAXY NUCLEI; HARD X RADIATION; INTERFEROMETRY; LUMINOSITY; MASS; RESOLUTION; STARS; X-RAY GALAXIES