J/MNRAS/489/1572 Spectroscopic dust reverberation in NGC 5548 (Landt+, 2019)
The first spectroscopic dust reverberation programme on active galactic nuclei:
the torus in NGC 5548.
Landt H., Ward M.J., Kynoch D., Packham C., Ferland G.J., Lawrence A.,
Pott J.-U., Esser J., Horne K., Starkey D.A., Malhotra D., Fausnaugh M.M.,
Peterson B.M., Wilman R.J., Riffel R.A., Storchi-Bergmann T., Barth A.J.,
Villforth C., Winkler H.
<Mon. Not. R. Astron. Soc., 489, 1572-1589 (2019)>
=2019MNRAS.489.1572L 2019MNRAS.489.1572L (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Galaxies, Seyfert ; Spectra, infrared ;
Accretion
Keywords: galaxies: Seyfert - quasars: emission lines -
quasars: individual: NGC 5548 - infrared: galaxies
Abstract:
We have recently initiated the first spectroscopic dust reverberation
programme on active galactic nuclei in the near-infrared. Spectroscopy
enables measurement of dust properties, such as flux, temperature, and
covering factor, with higher precision than photometry. In particular,
it enables measurement of both luminosity-based dust radii and dust
response times. Here we report results from a 1 yr campaign on
NGC5548. The hot dust responds to changes in the irradiating flux with
a lag time of ∼70 light-days, similar to what was previously found in
photometric reverberation campaigns. The mean and rms spectra are
similar, implying that the same dust component dominates both the
emission and the variations. The dust lag time is consistent with the
luminosity-based dust radius only if we assume a
wavelength-independent dust emissivity law, i.e. a blackbody, which is
appropriate for grains of large sizes (of a few µm). For such
grains the dust temperature is ∼1450K. Therefore, silicate grains have
most likely evaporated and carbon is the main chemical component. But
the hot dust is not close to its sublimation temperature, contrary to
popular belief. This is further supported by our observation of
temperature variations largely consistent with a heating/cooling
process. Therefore, the inner dust-free region is enlarged and the
dusty torus rather a 'dusty wall', whose inner radius is expected to
be luminosity-invariant. The dust-destruction mechanism that enlarges
the dust-free region seems to also partly affect the dusty region. We
observe a cyclical decrease in dust mass with implied dust reformation
times of ∼5-6 months.
Description:
We observed the source NGC 5548 between 2016 August and 2017 July
(semesters 2016B and 2017A) with the recently refurbished SpeX
spectrograph (Rayner et al. 2003PASP..115..362R 2003PASP..115..362R) at the NASA Infrared
Telescope Facility (IRTF), a 3m telescope on Maunakea, Hawaii. Our
approved proposal requested a cadence of about a week during the
period of a year starting 2016 August 1, excluding the 3.5-month
period (September to mid-December) when the source is unobservable. We
were scheduled 24 observing windows of 2-2.5h each between 2016 August
and 2017 July with an observing gap of about a month (mostly during
April) due to engineering time for the spectrograph. Of the scheduled
observing windows, we lost six due to weather and engineering issues,
resulting in a total of 18 near-IR spectra with an average cadence of
about 10d.
Objects:
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RA (ICRS) DE Designation(s)
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14 17 59.54 +25 08 12.6 NGC5548 = 1H 1415+255 = 1RXP J141759.3+250811
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ngc5548.dat 33 1 NGC 5548
tables4.dat 60 18 Near-IR spectral light curves corresponding to
the accretion disc
tables5.dat 80 18 Near-IR spectral light curves corresponding to
the hot dust
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Byte-by-byte Description of file: ngc5548.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name AGN name (NGC 5548)
10- 11 I2 h RAh Right ascension (J2000)
13- 14 I2 min RAm Right ascension (J2000)
16- 20 F5.2 s RAs Right ascension (J2000)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000)
26- 27 I2 arcmin DEm Declination (J2000)
29- 33 F5.2 arcsec DEs Declination (J2000)
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Byte-by-byte Description of file: tables4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 11 A11 "Y:M:D" Date Observation date
13- 20 F8.2 d HJD Heliocentric Julian Date; JD-2400000
22- 25 F4.2 10-17W/m2/nm f8700 Flux in the 8700-9000Å NIR band
27- 30 F4.2 10-17W/m2/nm e_f8700 Error on f8700
32- 35 F4.2 10-17W/m2/nm f8700corr Corrected flux in the 8700-9000Å
NIR band (1)
37- 40 F4.2 10-17W/m2/nm e_f8700corr Error on f8700corr
42- 45 F4.2 10-17W/m2/nm f9730 Flux in the 9730-9790Å NIR band
47- 50 F4.2 10-17W/m2/nm e_f9730 Error on f9730
52- 55 F4.2 10-17W/m2/nm f9730corr Corrected flux in the 9730-9790Å
NIR band (1)
57- 60 F4.2 10-17W/m2/nm e_f9730corr Error on f9730corr
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Note (1): Corrected using the multiplicative factors listed Table 1 of the
article, column 13
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Byte-by-byte Description of file: tables5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 11 A11 "Y:M:D" Date Observation date
13- 20 F8.2 d HJD Heliocentric Julian Date; JD-2400000
22- 25 F4.2 10-17W/m2/nm f1.55 Flux in the 1.55-1.60µm NIR band
27- 30 F4.2 10-17W/m2/nm e_f1.55 Error on f1.55
32- 35 F4.2 10-17W/m2/nm f1.55corr Corrected flux in the 1.55-1.60µm
NIR band (1)
37- 40 F4.2 10-17W/m2/nm e_f1.55corr Error on f1.55corr
42- 45 F4.2 10-17W/m2/nm f1.55subs Corrected and substracted flux in the
1.55-1.60µm NIR band (2)
47- 50 F4.2 10-17W/m2/nm e_f1.55subs Error on f1.55subs
52- 55 F4.2 10-17W/m2/nm f2.34 Flux in the 2.34-2.39µm NIR band
57- 60 F4.2 10-17W/m2/nm e_f2.34 Error on f2.34
62- 65 F4.2 10-17W/m2/nm f2.34corr Corrected flux in the 2.34-2.39µm
NIR band (1)
67- 70 F4.2 10-17W/m2/nm e_f2.34corr Error on f2.34corr
72- 75 F4.2 10-17W/m2/nm f2.34subs Corrected and substracted flux in the
2.34-2.39µm NIR band (2)
77- 80 F4.2 10-17W/m2/nm e_f2.34subs Error on f2.34subs
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Note (1): Corrected using the multiplicative factors listed Table 1 of the
article, column 13
Note (2): Corrected using the multiplicative factors listed Table 1 of the
article, column 13 and with the accretion disc spectrum subtracted.
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 05-Jan-2023