J/MNRAS/462/3376 Radial velocities of NGC 6822 carbon stars (Thompson+, 2016)
The rotation of the halo of NGC 6822 from the radial velocities of carbon stars.
Thompson G.P., Ryan S.G., Sibbons L.F.
<Mon. Not. R. Astron. Soc., 462, 3376-3385 (2016)>
=2016MNRAS.462.3376T 2016MNRAS.462.3376T (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, carbon ; Stars, giant ;
Radial velocities
Keywords: techniques: radial velocities - stars: AGB and post-AGB -
galaxies: individual: NGC 6822 - galaxies: kinematics and dynamics -
Local Group - infrared: stars
Abstract:
Using spectra taken with the AAOmega spectrograph, we measure the
radial velocities of over 100 stars, many of which are intermediate
age carbon stars, in the direction of the dwarf irregular galaxy
NGC 6822. Kinematic analysis suggests that the carbon stars in the
sample are associated with NGC 6822, and estimates of its radial
velocity and galactic rotation are made from a star-by-star analysis
of its carbon star population. We calculate a heliocentric radial
velocity for NGC 6822 of -51±3km/s and show that the population
rotates with a mean rotation speed of 11.2±2.1km/s at a mean
distance of 1.1kpc from the galactic centre, about a rotation axis
with a position angle of 26°±13°, as projected on the sky.
This is close to the rotation axis of the HI gas disc and suggests
that NGC 6822 is not a polar ring galaxy, but is dynamically closer to
a late-type galaxy. However, the rotation axis is not aligned with the
minor axis of the AGB isodensity profiles and this remains a mystery.
Description:
Wide band, low-resolution spectra for 323 target objects, out to ∼8kpc
from the galactic centre, were obtained using the AAOmega multifibre
spectrograph on 2011 August 30 and 31 (Sibbons et al., 2015, Cat.
J/A+A/574/A102). An optical fibre was placed over each target object
position on the field plate of the spectrograph and throughout this
paper, objects are referred to by their fibre number. Wide band
gratings 385R and 580V were used in the spectroscopy but this study
uses only the spectra from grating 385R, which has a bandpass from
5687 to 8856Å, covering the CaII triplet, dispersed at 1.6Å/pix.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 83 282 Individual results for objects meeting the
criteria (hght≥0.2, -200km/s≤HV≤+200km/s)
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See also:
J/AJ/123/832 : C star population in NGC 6822 (Letarte+, 2002)
J/A+A/540/A135 : AGB population of NGC 6822 (Sibbons+, 2012)
J/A+A/574/A102 : AGB candidates in NGC 6822 (Sibbons+, 2015)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Fibre Fibre number (1)
5- 10 I6 --- ID Target identifier (1)
12- 17 F6.2 deg RAdeg Right ascension (J2000) (1)
19- 24 F6.2 deg DEdeg Declination (J2000) (1)
26- 29 F4.1 mag Imag ? I-band magnitude of C-type AGBs in the inner
region from the catalogue of
Letarte et al. (2002, Cat. J/AJ/123/832)
31- 34 F4.2 kpc Dist Distance of the object from the putative
galactic centre (2)
36- 40 A5 --- PClass Photometric classification (3)
42- 45 A4 ---- SClass Spectroscopic classification (1)
47- 48 I2 --- SNR1 ? SNR in the band 8560-8650Å for the night
of 2011 August 30
51- 54 F4.2 --- hght1 [0.2/0.84]? Strength of the cross-correlation
function for the night of 2011 August 30
56- 59 I4 km/s HV1 ? Heliocentric radial velocity returned from
fxcor for the night of 2011 August 30
61- 63 I3 km/s e_HV1 ? rms uncertainty on HV1
66- 67 I2 --- SNR2 ? NR in the band 8560-8650Å for the night
of 2011 August 31
69- 72 F4.2 --- hght2 [0.21/0.89]? Strength of the cross-correlation
function for the night of 2011 August 31
74- 77 I4 km/s HV2 ? Heliocentric radial velocity returned from
fxcor for the night of 2011 August 31
79- 81 I3 km/s e_HV2 ? rms uncertainty on HV2
83 A1 --- Flag [CM] flag showing which objects were used in
the composite templates (4)
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Note (1): from Sibbons et al. (2015, Cat. J/A+A/574/A102)
Note (2): Distance of the object from the putative galactic centre
(RA=19:44:56 (296.2333°), DE=-14:48:0.6 (-14.8017°), J2000, centred on
the optical co-ordinates of NGC 6822 adopted by Sibbons et al.
(2012, Cat. J/A+A/540/A135 and 2015, Cat. J/A+A/574/A102)
and a galactic distance of 490kpc (Mateo, 1998ARA&A..36..435M 1998ARA&A..36..435M).
Note (3): from Sibbons et al. (2012, Cat. J/A+A/540/A135)
Note (4): Flag as follows:
C = C-type composite
M = M-type composite
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 23-Mar-2018