J/A+A/592/A94 Radio continuum and gas reservoir in NGC 3998 (Frank+, 2016)
A rare example of low surface-brightness radio lobes in a gas-rich early-type
galaxy: the story of NGC 3998.
Frank B.S., Morganti R., Oosterloo T., Nyland K., Serra P.
<Astron. Astrophys. 592, A94 (2016)>
=2016A&A...592A..94F 2016A&A...592A..94F (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Radio sources ; H I data
Keywords: galaxies: active - galaxies: individual: NGC 3998 -
ISM: jets and outflow - radio continuum: galaxies -
radio lines: galaxies - history and philosophy of astronomy
Abstract:
We study the nearby lenticular galaxy NGC 3998. This galaxy is known
to host a low-power radio AGN with a kpc-size one-sided jet and a
large, nearly polar HI disc. It is therefore a good system to study
to understand the relation between the availability of cold-gas and
the triggering of AGNs in galaxies. Our new WSRT data reveal two
faint, S-shaped radio lobes extending out to ∼10 kpc from the galaxy
centre. Remarkably, we find that the inner HI disc warps back
towards the stellar mid-plane in a way that mirrors the warping of the
radio lobes. We suggest that the polar HI disc was accreted through
a minor merger, and that the torques causing it to warp in the inner
regions are also responsible for feeding the AGN. The "S" shape of
the radio lobes would then be due to the radio jets adapting to the
changing angular momentum of the accreted gas. The extended radio jets
are likely poorly collimated, which would explain their quick fading
and, therefore, their rarity in galaxies similar to NGC 3998. The
fuelling of the central super-massive black hole is likely occurring
via "discrete events", suggested by the observed variability of
the radio core and the extremely high core dominance, which we
attribute to the formation and ejection of a new jet resulting from a
recent fuelling event.
Description:
The study of the radio continuum and HI emission of NGC 3998 was done
with deep radio observations at L-band using the WSRT telescope. Here
we provide the radio continuum image and spectral line cube as
presented in the paper. The radio continuum was imaged using uniform
(robust=-2) weighting, and is at a resolution of roughly 15". The HI
data cube was imaged using a robustness of 0.4, with a taper of 30".
Objects:
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RA (2000) DE Designation(s)
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11 57 56.13 +55 27 12.9 NGC 3998 = RX J1157.9+5527
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 136 2 List of fits files
fits/* . 2 Individual fits files
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx [1050] Number of pixels along X-axis
25- 28 I4 --- Ny [1050] Number of pixels along Y-axis
30- 32 I3 --- Nz [150]? Number of slices
34- 54 A21 --- Obs.Date Observation date (YYYY-MM-DDThh:mm:ss.ss)
56- 66 E11.6 Hz Freq Frequency or lower value of frequency interval
68- 77 E10.6 Hz BFreq ? Upper value of frequency interval
79- 85 F7.2 Hz dFreq ? Frequency resolution
87- 92 I6 Kibyte size Size of FITS file
94-105 A12 --- FileName Name of FITS file, in subdirectory fits
107-136 A30 --- Title Title of the FITS file
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Acknowledgements:
Bradley S. Frank, bradley(at)ast.uct.ac.za
(End) Bradley S. Frank [Univ. of Cape Town], Patricia Vannier [CDS] 03-Jun-2016