49 research outputs found
The Declined Activity in the Nucleus of NGC 1316
NGC 1316 (Fornax A) is a radio galaxy with prototypical double lobes, where
the magnetic field intensity is accurately measured via the inverse-Compton
technique. The radio-emitting electrons in the lobes are inferred to have a
synchrotron life time of 0.1 Gyr. Considering the lobe energetics, we estimate
the past nuclear X-ray luminosity of NGC 1316 to be at least 4 times 10^{34} W
(4 times 10^{41} erg s^{-1}). Thus, the nucleus was rather active at least 0.1
Gyr ago. In contrast, we confirmed with ASCA and ROSAT that the nucleus of NGC
1316 is very faint in X-rays at present, with the 2--10 keV luminosity of any
AGN-like hard component being < 2 times 10^{33} W (2 times 10^{40} erg s^{-1})
even assuming a nuclear obscuration up to 10^{28} m^{-2} (10^{24} cm^{-2}).
This is at least an order of magnitude lower than the estimated past activity,
indicating that the nucleus is presently very inactive. From these two results,
we conclude that the nucleus of NGC 1316 has become dormant during the last 0.1
Gyr. This suggests the possible abundance of ``dormant'' quasars in nearby
galaxies.Comment: 7 pages, 2 figures, to be published in the Astrophysical Journal
Letter
Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XIV. A Candidate Type-II Quasar at z=6.1292
We present deep Keck/MOSFIRE near-infrared spectroscopy of a strong Lyman
alpha emitting source at z=6.1292, HSC J142331.71-001809.1, which was
discovered by the SHELLQS program from imaging data of the Subaru Hyper
Suprime-Cam (HSC) survey. This source is one of five objects that show
unresolved (10^44 erg s-1) Lyman alpha emission
lines at absolute 1450 angstrom continuum magnitudes of M1450~-22 mag. Its
rest-frame Lyman alpha equivalent width (EW) is 370+/-30 angstrom. In the 2
hour Keck/MOSFIRE spectrum in Y band, the high-ionization CIV 1548,1550 doublet
emission line was clearly detected with FWHM =120+/-20 km s-1 and a total
rest-frame EW of 37-5+6 angstrom. We also report the detection of weak
continuum emission, and the tentative detection of OIII] 1661,1666 in the 4
hour J band spectrum. Judging from the UV magnitude, line widths, luminosities,
and EWs of Lyman alpha and CIV, we suggest that this source is a
reionization-era analog of classical type-II AGNs, although there is a
possibility that it represents a new population of AGN/galaxy composite objects
in the early universe. We compare the properties of J1423-0018 to
intermediate-redshift type-II AGNs and CIV emitters seen in z=6-7 galaxy
samples. Further observations of other metal emission lines in the rest-frame
UV or optical, and X-ray follow-up observations of the z=6-7 narrow-line
quasars are needed for more robust diagnostics and to determine their nature.Comment: 15 pages, 8 figures, accepted for publication in the Astrophysical
Journa
Subaru high-z exploration of low-luminosity quasars (SHELLQs). I. Discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9
We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9.
This is the initial result from the Subaru High-z Exploration of Low-Luminosity
Quasars (SHELLQs) project, which exploits the exquisite multiband imaging data
produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The
candidate selection is performed by combining several photometric approaches
including a Bayesian probabilistic algorithm to reject stars and dwarfs. The
spectroscopic identification was carried out with the Gran Telescopio Canarias
and the Subaru Telescope for the first 80 deg2 of the survey footprint. The
success rate of our photometric selection is quite high, approaching 100 % at
the brighter magnitudes (zAB < 23.5 mag). Our selection also recovered all the
known high-z quasars on the HSC images. Among the 15 discovered objects, six
are likely quasars, while the other six with interstellar absorption lines and
in some cases narrow emission lines are likely bright Lyman-break galaxies. The
remaining three objects have weak continua and very strong and narrow Ly alpha
lines, which may be excited by ultraviolet light from both young stars and
quasars. These results indicate that we are starting to see the steep rise of
the luminosity function of z > 6 galaxies, compared with that of quasars, at
magnitudes fainter than M1450 ~ -22 mag or zAB ~24 mag. Follow-up studies of
the discovered objects as well as further survey observations are ongoing.Comment: Published in ApJ (828:26, 2016
Discovery of the First Low-Luminosity Quasar at z > 7
We report the discovery of a quasar at z = 7.07, which was selected from the
deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru
Strategic Program survey. This quasar, HSC J124353.93+010038.5, has an order of
magnitude lower luminosity than do the other known quasars at z > 7. The
rest-frame ultraviolet absolute magnitude is M1450 = -24.13 +/- 0.08 mag and
the bolometric luminosity is Lbol = (1.4 +/- 0.1) x 10^{46} erg/s. Its spectrum
in the optical to near-infrared shows strong emission lines, and shows evidence
for a fast gas outflow, as the C IV line is blueshifted and there is indication
of broad absorption lines. The Mg II-based black hole mass is Mbh = (3.3 +/-
2.0) x 10^8 Msun, thus indicating a moderate mass accretion rate with an
Eddington ratio 0.34 +/- 0.20. It is the first z > 7 quasar with sub-Eddington
accretion, besides being the third most distant quasar, known to date. The
luminosity and black hole mass are comparable to, or even lower than, those
measured for the majority of low-z quasars discovered by the Sloan Digital Sky
Survey, and thus this quasar likely represents a z > 7 counterpart to quasars
commonly observed in the low-z universe.Comment: Accepted for publication in ApJ Letter
Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). X. Discovery of 35 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 7.0
The American Astronomical Society, find out more The Institute of Physics, find out more THE FOLLOWING ARTICLE ISOPEN ACCESS Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). X. Discovery of 35 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 7.0 Yoshiki Matsuoka1, Kazushi Iwasawa2, Masafusa Onoue3, Nobunari Kashikawa4,5,6, Michael A. Strauss7, Chien-Hsiu Lee8, Masatoshi Imanishi5,6, Tohru Nagao1, Masayuki Akiyama9, Naoko Asami10Show full author list Published 2019 October 3 © 2019. The American Astronomical Society. The Astrophysical Journal, Volume 883, Number 2 DownloadArticle PDF DownloadArticle ePub Figures Tables References Download PDFDownload ePub 674 Total downloads 99 total citations on Dimensions. Turn on MathJax Share this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on Mendeley Article information Abstract We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high-z quasars, 31 high-z luminous galaxies, 16 [O iii] emitters at z ~ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg2, surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Lyα emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N v λ1240 emission and resembles that of lower-z narrow-line quasars, the small Lyα width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies
Discovery of the First Low-luminosity Quasar at z > 7
We report the discovery of a quasar at z = 7.07, which was selected from the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. This quasar, HSC J124353.93+010038.5, has an order of magnitude lower luminosity than do the other known quasars at z > 7. The rest-frame ultraviolet absolute magnitude is M1450 = −24.13 ± 0.08 mag and the bolometric luminosity is erg s−1. Its spectrum in the optical to near-infrared shows strong emission lines, and shows evidence for a fast gas outflow, as the C iv line is blueshifted and there is indication of broad absorption lines. The Mg ii-based black hole mass is , thus indicating a moderate mass accretion rate with an Eddington ratio . It is the first z > 7 quasar with sub-Eddington accretion, besides being the third most distant quasar known to date. The luminosity and black hole mass are comparable to, or even lower than, those measured for the majority of low-z quasars discovered by the Sloan Digital Sky Survey, and thus this quasar likely represents a z > 7 counterpart to quasars commonly observed in the low-z universe
Subaru High- z Exploration of Low-luminosity Quasars (SHELLQs). XVI. 69 New Quasars at 5.8 < z < 7.0
We present the spectroscopic discovery of 69 quasars at 5.8 0.1 in the HSC-SSP third public data release (PDR3). The sample reported here also includes three quasars with PQB 5.6. This demonstrates that the algorithm has very high efficiency, even though we are probing an unprecedentedly low luminosity population down to M 1450 ∼-21 mag.Y.M. was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI grant No. JP17H04830, No. 21H04494, and the Mitsubishi Foundation grant No. 30140. K.I. acknowledges support by the Spanish MCIN under grant PID2019-105510GB-C33/AEI/10.13039/501100011033 and "Unit of excellence María de Maeztu 2020-2023" awarded to ICCUB (CEX2019-000918-M)