J/A+A/569/A68 Green Bank Telescope observations of NGC 2403 (de Blok+, 2014)
A low HI column density filament in NGC 2403:
signature of interaction or accretion.
de Blok W.J.G., Keating K.M., Pisano D.J., Fraternali F., Walter F.,
Oosterloo T., Brinks E., Bigiel F., Leroy A.
<Astron. Astrophys. 569, A68 (2014)>
=2014A&A...569A..68D 2014A&A...569A..68D
ADC_Keywords: Galaxies, radio ; Galaxies, nearby ; H I data
Keywords: galaxies: ISM - galaxies: kinematics and dynamics - galaxies: halos -
galaxies: individual: NGC 2403 - galaxies: structure
Abstract:
Observed HI accretion around nearby galaxies can only account for a
fraction of the gas supply needed to sustain the currently observed
star formation rates. It is possible that additional accretion happens
in the form of low column density cold flows, as predicted by
numerical simulations of galaxy formation. To contrain the presence
and properties of such flows, we present deep HI observations obtained
with the NRAO Green Bank Telescope of an area measuring 4 by 4 degrees
around NGC 2403. These observations, with a 5σ detection limit of
2.4x1018cm-2 over a 20km/s linewidth, reveal the presence of a
low-column density, extended cloud outside the main HI disk, about 17'
(∼16kpc or ∼2R25) to the NW of the center of the galaxy. The total
HI mass of the cloud is 6.3x106M☉, or 0.15% of the total HI
mass of NGC 2403. The cloud is associated with an 8kpc
anomalous-velocity HI filament in the inner disk, previously observed
in deep VLA observations by Fraternali et al. (2001ApJ...562L..47F 2001ApJ...562L..47F,
2002AJ....123.3124F 2002AJ....123.3124F). We discuss several scenarios for the origin of
the cloud, and conclude that it is either accreting from the
intergalactic medium, or is the result of a minor interaction with a
neigbouring dwarf galaxy.
Description:
We observed NGC 2403 with the Green Bank Telescopes in the 21-cm line
of neutral hydrogen, in 21 sessions between 29 May and 30 September
2009. The beam size of the observations is 8.7'. We include a FITS
file containing the data-cube (pos-pos-vel) of the HI emission line of
NGC 2403. We used equatorial coordinates for the spatial dimensions
and VLSR for the spectral dimension. The pixel size is 1.75' in
spatial dimension and the spectral resolution is 5.2km/s. All values
are in Jy/beam.
The data-cube spans an area of about 4x4 degrees (RAxDec) around the
center of the maps at 07:35:29.9 +65:35:48.5 (EQ=J2000) and the velocity
ranges from -895.6 to 1745.0km/s.
Objects:
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RA (2000) DE Designation(s)
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07 36 51.4 +65 36 09 NGC 2403 = UGC 3918
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 97 1 List of FITS datacube
n2403.fits 2880 20870 Individual FITS datacube
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See also:
J/A+AS/125/293 : NGC 2366, NGC 2403 + NGC 4236 HK' photometry (Pierini+ 1997)
J/AJ/139/1066 : X-ray view of NGC 2403 central region (Yukita+, 2010)
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- 22 I3 arcsec/pix Scale [105] Scale of the image
24- 30 F7.2 km/s lVlsr Lower value of LSR velocity (FELO-LSR)
32- 38 F7.2 km/s uVlsr Upper value of LSR velocity (FELO-LSR)
40- 44 F5.3 km/s dVlsr [5.167] LSR velocity resolution
48- 50 I3 pix Nx [177] Number of pixels along X-axis
51 A1 --- --- [x]
52- 54 I3 pix Ny [165] Number of pixels along Y-axis
55 A1 --- --- [x]
56- 58 I3 --- Nz [512] Number of slices (velocity)
60- 64 I5 Kibyte size [58700] Size of FITS file
66- 75 A10 --- FileName Name of FITS file
77- 97 A21 --- Title Title of the file
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Acknowledgements:
Erwin de Blok, blok (at) astron.nl
(End) Erwin de Blok [ASTRON, Netherlands], Patricia Vannier [CDS] 11-Aug-2014