J/AJ/144/11 IR imaging, nuclear SEDs, Spitzer spectra of 22 AGNs (Mason+, 2012)
The nuclear infrared emission of low-luminosity active galactic nuclei.
Mason R.E., Lopez-Rodriguez E., Packham C., Alonso-Herrero A.,
Levenson N.A., Radomski J., Ramos Almeida C., Colina L., Elitzur M.,
Aretxaga I., Roche P.F., Oi N.
<Astron. J., 144, 11 (2012)>
=2012AJ....144...11M 2012AJ....144...11M
ADC_Keywords: Active gal. nuclei ; Galaxies, spectra ; Photometry, infrared ;
Energy distributions ; X-ray sources
Keywords: galaxies: active - galaxies: nuclei - galaxies: photometry -
galaxies: Seyfert - infrared: galaxies
Abstract:
We present high-resolution mid-infrared (MIR) imaging, nuclear
spectral energy distributions (SEDs), and archival Spitzer spectra for
22 low-luminosity active galactic nuclei (LLAGNs; Lbol≲1042erg/s).
Infrared (IR) observations may advance our understanding of the
accretion flows in LLAGNs, the fate of the obscuring torus at low
accretion rates, and, perhaps, the star formation histories of these
objects. However, while comprehensively studied in higher-luminosity
Seyferts and quasars, the nuclear IR properties of LLAGNs have not yet
been well determined. We separate the present LLAGN sample into three
categories depending on their Eddington ratio and radio emission,
finding different IR characteristics for each class. (1) At the
low-luminosity, low-Eddington-ratio (log Lbol/LEdd< -4.6) end of
the sample, we identify "host-dominated" galaxies with strong
polycyclic aromatic hydrocarbon bands that may indicate active
(circum-)nuclear star formation. (2) Some very radio-loud objects are
also present at these low Eddington ratios. The IR emission in these
nuclei is dominated by synchrotron radiation, and some are likely to
be unobscured type 2 AGNs that genuinely lack a broad-line region. (3)
At higher Eddington ratios, strong, compact nuclear sources are
visible in the MIR images. The nuclear SEDs of these galaxies are
diverse; some resemble typical Seyfert nuclei, while others lack a
well-defined MIR "dust bump." Strong silicate emission is present in
many of these objects. We speculate that this, together with high
ratios of silicate strength to hydrogen column density, could suggest
optically thin dust and low dust-to-gas ratios, in accordance with
model predictions that LLAGNs do not host a Seyfert-like obscuring
torus. We anticipate that detailed modeling of the new data and SEDs
in terms of accretion disk, jet, radiatively inefficient accretion
flow, and torus components will provide further insights into the
nuclear structures and processes of LLAGNs.
Description:
We have acquired new MIR imaging of 20 IR-faint nuclei with Michelle
and T-ReCS on the Gemini telescopes (the angular resolution of the
observations is ∼0.35" at λ∼10µm). We have also obtained
seeing limited images at 3-5µm of 5 objects. To the new data, we
add published, high-resolution IR photometry of these and a further
2 nuclei. We combine these data with published measurements at other
wavelengths to produce nuclear spectral energy distributions (SEDs)
for these objects. Finally, we also present archival Spitzer
low-resolution spectroscopy for the 18/22 galaxies with available
data.
The Si2 (8.7µm) filter in T-ReCS was used for the majority of
the T-ReCS observations. NGC 1052 was also observed with T-ReCS's Qa
(18.3µm) filter. Most of the Michelle observations were taken using
the sensitive semibroad N' filter (11.2µm). Some of the brighter
galaxies were also observed with Michelle in one or more of the Si2
(8.8µm), Si4 (10.3µm), Si6 (12.5µm), and Qa (18.1µm) filters.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 130 22 Source properties
table3.dat 46 34 MIR photometric results
table4.dat 46 9 NIR photometric results
table5.dat 52 22 IR and X-Ray properties of the low-luminosity
active galactic nuclei (LLAGNs)
table6.dat 23 6 Intrinsic X-Ray luminosity estimates for
suspected Compton-thick low-luminosity active
galactic nuclei (LLAGNs)
table7.dat 63 446 Spectral energy distribution data
refs.dat 184 110 References
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See also:
J/ApJ/730/19 : IR spectra and SEDs for starbursts and AGNs (Sargsyan+, 2011)
J/ApJS/187/135 : SEDs of weak AGNs associated with LINERs (Eracleous+, 2010)
J/ApJS/187/64 : The simultaneous optical-to-X-ray SED of AGNs (Grupe+, 2010)
J/ApJ/725/2270 : Mid-IR emission lines in AGNs (Pereira-Santaella+, 2010)
J/ApJ/683/114 : IRS spectra of faint IRAS sources (Sargsyan+, 2008)
J/ApJ/642/673 : IR-selected obscured AGN candidates (Polletta+, 2006)
J/A+A/357/839 : AGN 2.5-11um spectroscopy (Clavel+, 2000)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC NGC galaxy number
10- 20 A11 --- OName Other galaxy name
22- 33 A12 --- MType Morphological type
35- 43 A9 --- AGNt AGN type (LL=low-luminosity, S=Seyfert)
45- 48 F4.1 Mpc Dist ? Distance
50- 52 F3.1 [Msun] logMBH [7.1/9]? log of black hole mass
54- 57 F4.1 --- logER ? log of the Eddington ratio Lbol/LEdd
59- 62 F4.1 [-] Rx [-5.3/-1.1]? Radio to X emission ratio RX (1)
64- 66 A3 --- Cat Category depending on the Eddington ratio and
radio emission (3)
68-130 A63 --- SMBH Evidence that the galaxy hosts an actively
accreting supermassive black hole (SMBH), with
reference. See Section 2 for more details (2)
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Note (1): RX=log(νLν(5GHz)/LX).
Note (2): This is not intended to be an exhaustive list for each object:
X-ray = hard X-ray point source(s);
Hα = broad Hα line;
Pol Hα = broad Hα detected in polarized light;
Radio = high brightness-temperature radio nucleus and/or radio jet;
UV = UV variability;
[Ne V] = [Ne V]24µm line;
NLR = ionization cone(s) in the narrow-line region.
Note (3): Category as follows:
I = Host-dominated, low-Eddington-ratio galaxy (log Lbol/LEdd< -4.6).
See Section 2 for details;
II = Radio-loud, low-Eddington-ratio galaxy (log Lbol/LEdd< -4.6,
log νLν(5GHz)/LX>-2.7). See Section 2 for details;
III = High-Eddington-ratio galaxy (log(Lbol/LEdd)>-4.6).
See Section 2 for details.
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Byte-by-byte Description of file: table[34].dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC NGC galaxy number
10 A1 --- f_NGC Flag on NGC (1)
12- 14 A3 --- Flt Filter used (4)
16 A1 --- l_F2 Upper limit on F2
18- 20 I3 mJy F2 [3/257] Photometric flux in 2" diameter
aperture
22- 23 I2 mJy e_F2 ? Error in F2
25- 27 I3 mJy Fpsf [2/197]? PSF-scaling photometry (2)
29 A1 --- f_Fpsf [e] Questionable Fpsf (3)
31- 32 I2 mJy e_Fpsf ? Error in Fpsf
34- 37 F4.2 arcsec FWHMg ? FWHM (Moffat) of galactic nucleus
39 A1 --- f_FWHMg [f] Gaussian FWHMg (3)
41- 44 F4.2 arcsec FWHMs FWHM (Moffat) of standard star
46 A1 --- f_FWHMs [f] Gaussian FWHMs (3)
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Note (1): Flag on NGC as follows:
g = Re-analysis of data originally published by
Perlmann et al. (2001ApJ...561L..51P 2001ApJ...561L..51P), Mason et al. (2007ApJ...659..241M 2007ApJ...659..241M);
h = The M' images of NGC 4579 showed a strong background gradient that made
reliable photometry impossible.
Note (2): The standard star was scaled to the centroid of the galaxy emission
and then the flux measured in a 2" aperture around the scaled star.
Note (3): Remarks:
e = For NGC 1052 only, the standard star image in the Qa filter contains
a prominent diffraction ring. This means that the Moffat function
used to model the PSF for the PSF-scaling photometry does not provide
a good representation of the flux profile in this case.
f = Gaussian FWHM; Moffat function did not converge for this source.
Note (4): the filters
L" = λ=3.9um, Δλ=0.9um (Gemini)
M" = λ=4.8um, Δλ=0.1um (Gemini)
Si2 = λ=8.7um, Δλ=0.8um
Si4 = λ=10.3mu, Δλ=0.8um
N' = λ=11.2um, Δλ=2.4um
Si6 = λ=12.5mu, Δλ=1.2um
Qa = λ=18.1um, Δλ=1.9um
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC NGC galaxy number
10- 13 F4.2 --- Fpsf/F2 ? Ratio of mid-IR PSF-scaling flux to that
obtained in a 2" aperture (see Section 3.1
for details) (4)
15- 19 F5.2 --- S ? Strength of the ∼10µm silicate feature
S10 (see Section 4.2 for details) (5)
21- 23 F3.1 --- alpha ? Near- to mid-IR spectral index αIR,
F(ν)∝ν-α, for
objects possessing at least one mid-IR and
one H-band photometric point.
See Section 4.3 (4)
25 A1 --- l_logLMIR Upper limit on log(LMIR)
27- 30 F4.1 [10-7W] logLMIR [39.8/42.7] log of mid-infrared luminosity (4)
32- 35 F4.1 [10-7W] logLX [38.8/41.4] absorption-corrected 2-10keV X-ray
luminosity (erg/s); see Section 4.3
37 A1 --- l_NH Upper limit on NH
39- 44 F6.3 10+22cm-2 NH ? HI column density
46- 47 I2 --- r_logLX Reference for logLX (X-ray luminosity) and for
NH (HI column density), in refs. dat file
49 A1 --- CT Indicates whether the galaxy is suspected
to be Compton-thick (Y, N or ?) (6)
51- 52 I2 --- r_CT ? Reference for CT, in refs.dat file
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Note (4): Based on photometry in the Si2 (8.8µm) filter where available,
otherwise N'(11.2µm), Si5(NGC 1097; 11.7µm), or N (NGC 4486;
10.8µm). See Table 2 and Section 3 for more details.
Note (5): Positive values indicate emission. Typical errors on S10 are
estimated to be about 0.05.
Note (6): Combination of X-ray and optical indicators suggests that the galaxy
may be Compton-thick. The values of columns logLX and NH in this table
have not been modified to account for possible Compton-thickness.
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC NGC galaxy number
10- 13 F4.1 10-7W logLX [39/41.1] Intrinsic luminosity estimates as
given in Table 5 (Column logLX), from
spectral fitting of high-resolution X-ray
data (1)
15- 18 F4.1 10-7W logLX([OIII]) [40.6/42.9] Intrinsic "corrected" luminosity
from Gonzalez-Martin et al.
(2009A&A...506.1107G 2009A&A...506.1107G) and Panessa et al.
(2006A&A...455..173P 2006A&A...455..173P) (2)
20- 23 F4.1 10-7W logLX([OIV]) [39.3/41.6]? Intrinsic luminosity estimates
based on Lbol,AGN-L[OIV] relation of
Goulding et al. (2010MNRAS.406..597G 2010MNRAS.406..597G) (3)
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Note (1): Corrected for absorption, but will nonetheless underestimate the
intrinsic X-ray luminosity of a truly Compton-thick AGN.
Note (2): Based on FX(2-10keV)/F([OIII]) ratios.
Note (3): Using published [OIV] fluxes (Dudik et al., 2009ApJ...691.1501D 2009ApJ...691.1501D;
Pereira-Santaella et al., 2010, Cat. J/ApJ/725/2270;
Panuzzo et al., 2011A&A...528A..10P 2011A&A...528A..10P) and assuming Lbol/LX=16
(Ho, 2009ApJ...699..626H 2009ApJ...699..626H, Section 2).
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC NGC galaxy number
10- 16 E7.3 Hz nu Frequency of observation ν
18 A1 --- l_Lum Limit flag on Lum
19- 26 E8.3 10-7W Lum The νLν luminosity; in erg/s
28- 34 A7 arcsec Aper Aperture/resolution (1)
36- 50 A15 --- Facility Telescope/instrument
52- 63 A12 --- Ref Reference(s), in refs.dat file
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Note (1): Aperture diameter, resolution or beam size, as described in or
inferred from the original paper.
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Byte-by-byte Description of file: refs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Ref [1/110] Reference number
5- 23 A19 --- BibCode Bibliographic code
25- 57 A33 --- Aut Author's name
59-184 A126 --- Com Comments
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History:
* 04-Sep-2013: From electronic version of the journal
* 04-Oct-2013: Reformatted table1, to keep 1 galaxy per line
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 04-Sep-2013