J/A+A/645/A36 NGC 3269 CO spectra (Haikala+, 2021)
ALMA detection of the dusty object silhouetted against the S0 galaxy NGC 3269
in the Antlia cluster.
Haikala L.K., Salinas R., Richtler T., Gomez M., Gahm G.F., Mattila K.
<Astron. Astrophys. 645, A36 (2021)>
=2021A&A...645A..36H 2021A&A...645A..36H (SIMBAD/NED BibCode)
ADC_Keywords: Carbon monoxide ; Galaxies, spectra ; Interferometry;
Interstellar medium ; Spectra, millimetric/submm
Keywords: galaxies: individual: NGC 3269 - galaxies: ISM - ISM: dust, extinction
Abstract:
An intriguing silhouette of a small dust patch can be seen against the
disk of the S0 galaxy NGC 3269 in the Antlia cluster in optical
images. The images do not provide any clue as to whether the patch is
a local Jupiter mass-scale cloudlet or a large extragalactic dust
complex.
We aim to resolve the nature of this object: is it a small Galactic
cloudlet or an extragalactic dust complex?
ALMA and APEX spectroscopy and Gemini GMOS long-slit spectroscopy were
used to measure the velocity of the patch and the NGC 3269 disk radial
velocity curve.
A weak 16±2.5km/s wide 12CO (2-1) TMB 19±2.5mK line in a 2.2"
by 2.12" beam associated with the object was detected with ALMA. The
observed heliocentric velocity, Vr,hel=3878±5.0km/s, immediately
establishes the extragalactic nature of the object. The patch velocity
is consistent with the velocity of the nucleus of NGC 3269, but not
with the radial velocity of the NGC 3269 disk of the galaxy at its
position. The ∼4" angular size of the patch corresponds to a linear
size of ∼1kpc at the galaxy's Hubble distance of 50.7Mpc. The mass
estimated from the 12CO (2-1) emission is
∼1.4x106(d/50.7Mpc)2M☉, while the attenuation derived from
the optical spectrum implies a dust mass of
∼2.6x104(d/50.7Mpc)2M☉. The derived attenuation ratio
A'B/(A'B-A'R) of 1.6±0.11 is substantially lower than the
corresponding value for the mean Milky Way extinction curve for point
sources (2.3).
We established the extragalactic nature of the patch, but its origin
remains elusive. One possibility is that the dust patch is left over
from the removal of interstellar matter in NGC 3269 through the
interaction with its neighbour, NGC 3268.
Description:
We present 625 12CO (2-1) spectral lines (spacing 0.42") in a 10' by
10' area centered on a small dust patch seen silhouetted against the
disk of the S0 galaxy NGC 3269 in the Antlia cluster in optical
images. The centre coordinate of the spectra, extracted from ALMA
(Project 2017.1.00066.S) image convolved to a 2.2" by 2.12" beam, is
10 29 55.8, -35 13 58.0 (J2000). The observations were conducted with
44 12m antennas in configuration C43-2 (baselines 15m to 500m,
maximum resolvable scale 7.8"). The spectrum channel width is
0.9767MHz (1.270km/s) and intensity scale is Jy/beam. The spectra are
in the LSR velocity scale. Header values for integration time and
system temperature in each spectrum has been artificially set to 1s
and 100K. No baseline has been subtracted. The spectra are presented
in one binary table FITS file.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
10 29 57.07 -35 13 27.8 NGC 3269 = LEDA 30945
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 33 625 List of spectra
spectra.fit 2880 1672 Fits spectra
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Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Scan [34/58] Scan
4- 5 I2 --- SubScan [34/58] Subscan
8- 19 E12.6 --- oRA [] Centre of the spectrum right ascension offset
22- 33 E12.6 --- oDE Centre of the spectrum declination offset
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Acknowledgements:
Lauri Haikala, lkhaikala(at)gmail.com
(End) Patricia Vannier [CDS] 20-Nov-2020