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Register a new userThe near-to-mid infrared spectrum of quasars
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Added by
Antonio Hern\\'an-Caballero
Publication date
2016
fields
Physics
and research's language is
English
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We analyse a sample of 85 luminous (log(nuLnu(3um)/erg s-1)>45.5) quasars with restframe ~2-11 um spectroscopy from AKARI and Spitzer. Their high luminosity allows a direct determination of the near-infrared quasar spectrum free from host galaxy emission. A semi-empirical model consisting of a single template for the accretion disk and two blackbodies for the dust emission successfully reproduces the 0.1-10 um spectral energy distributions (SEDs). Excess emission at 1-2 um over the best-fitting model suggests that hotter dust is necessary in addition to the ~1200 K blackbody and the disk to reproduce the entire near-infrared spectrum. Variation in the extinction affecting the disk and in the relative strength of the disk and dust components accounts for the diversity of individual SEDs. Quasars with higher dust-to-disk luminosity ratios show slightly redder infrared continua and less prominent silicate emission. We find no luminosity dependence in the shape of the average infrared quasar spectrum. We generate a new quasar template that covers the restframe range 0.1-11 um, and separate templates for the disk and dust components. Comparison with other infrared quasar composites suggests that previous ones are less reliable in the 2-4 um range. Our template is the first one to provide a detailed view of the infrared emission on both sides of the 4 um bump.
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We assemble a catalogue of 488 spectroscopically confirmed very high ($zgeq5.00$) redshift quasars and report their near- ($ZYJHK_{s}/K$) and mid- (WISE W1234) infrared properties. 97% of the VH$z$Q sample is detected in one or more NIR ($ZYJHK/K_{s}$) band, with lack of coverage rather than lack of depth being the reason for the non-detections. 389 (80%) of the very high redshift quasars are detected at 3.4$mu$m in the W1 band from the unWISE catalog and all of the $zgeq7$ quasars are detected in both unWISE W1 and W2. Using archival WFCAM/UKIRT and VIRCAM/VISTA data we check for photometric variability that might be expected from super-Eddington accretion. We find 28 of the quasars have sufficient NIR measurements and signal-to-noise ratio to look for variability. Weak variability was detected in multiple bands of SDSS J0959+0227, and very marginally in the $Y$-band of MMT J0215-0529. Only one quasar, SDSS J0349+0034, shows significant differences between WFCAM and VISTA magnitudes in one band. With supermassive black hole accretion likely to be redshift invariant up to very high-redshift, further monitoring of these sources is warranted. All the data, analysis codes and plots used and generated here can be found at: https://github.com/d80b2t/VHzQ}{tt github.com/d80b2t/VHzQ.
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