J/ApJ/755/90 [NeII] emission line observations from SgrA West (Irons+, 2012)
Ionized gas in the Galactic Center: new observations and interpretation.
Irons W.T., Lacy J.H., Richter M.J.
<Astrophys. J., 755, 90 (2012)>
=2012ApJ...755...90I 2012ApJ...755...90I
ADC_Keywords: Spectra, infrared ; H II regions
Keywords: Galaxy: center; Galaxy: kinematics and dynamics; H II regions;
ISM: kinematics and dynamics
Abstract:
We present new observations of the [NeII] emission from the ionized
gas in Sgr A West with improved resolution and sensitivity. About half
of the emission comes from gas with kinematics indicating it is
orbiting in a plane tipped about 25° from the Galactic plane. This
plane is consistent with that derived previously for the circumnuclear
molecular disk and the northern arm and western arc ionized features.
However, unlike most previous studies, we conclude that the ionized
gas is not moving along the ionized features, but on more nearly
circular paths. The observed speeds are close to, but probably
somewhat less than expected for orbital motions in the potential of
the central black hole and stars and have a small inward component.
The spatial distribution of the emission is well fitted by a spiral
pattern. We discuss possible physical explanations for the spatial
distribution and kinematics of the ionized gas, and conclude that both
may be best explained by a one-armed spiral density wave, which also
accounts for both the observed low velocities and the inward velocity
component. We suggest that a density wave may result from the
precession of elliptical orbits in the potential of the black hole and
stellar mass distribution.
Description:
[NeII] line emission from Sgr A West was observed in 2003 June with
TEXES on the NASA IRTF. TEXES, the Texas Echelon Cross Echelle
Spectrograph, is a high-resolution spectrograph for wavelengths of
5-25um. At the 12.8um (780.42cm-1) wavelength of the [NeII]
fine-structure line, it has a spectral resolution of ∼0.01/cm, or
4km/s, and a spatial resolution along the entrance slit of ∼1.3".
Spectral and spatial sampling is 4 pixels per resolution element.
To map Sgr A West, the spectrograph slit was oriented N-S and stepped
in 0.7" steps to the east, covering 76". As the slit length is only
10", multiple scans were made, separated by 5" in declination, to
cover a region of 76"x78" centered near Sgr A* (17:45:40.04
-29:00:28.11 (J2000)). At 12.8um, the echelon spectral orders are
about 10% longer than the detector width, leaving gaps between orders,
with ∼230km/s of each 255km/s order covered. To fill in these gaps, we
made two sets of observations: one with the spectrum offset to center
the red side of each echelon order on the detector array and one with
the blue side centered. The spectral coverage of the combined data
cube is -1300-800km/s.
Objects:
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RA (2000) DE Designation(s)
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17 45 39.4 -29 00 24 Sgr A West = NAME SGR A WEST
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fits.dat 97 1 List of the 3-D data cube parameters of Sgr A West
(from erratum 2013, ApJ, 771, 75)
fits/* . 1 [NeII] data cube of Sgr A West in FITS format
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See also:
J/A+A/534/A117 : NIR polarimetry of sources near SgrA* (Buchholz+, 2011)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/ApJ/737/73 : Infrared extinction toward the Galactic Centre (Fritz+, 2011)
J/ApJ/699/186 : VLA observations of the Galactic center (Zhao+, 2009)
J/ApJ/703/1323 : Spectro. of stars in the Galaxy's nuclear cluster (Do+ 2009)
J/A+A/499/483 : NIR obs. of sources in galactic center (Buchholz+, 2009)
J/ApJ/642/861 : N-band imaging of the Galactic Center (Viehmann+, 2006)
J/A+A/426/81 : Kinematic analysis of the Minispiral (Paumard+, 2004)
Byte-by-byte Description of file: fits.dat
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Bytes Format Units Label Explanations
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1- 7 F7.3 deg RAdeg [266.418] Right Ascension of center (J2000)
10- 16 F7.3 deg DEdeg [-29.009] Declination of center (J2000)
19- 29 F11.9 arcsec/pix Scale Scale of the image
32- 34 I3 --- Nx [194] Number of pixels along X-axis (RA)
35 A1 --- --- [x]
36- 38 I3 --- Ny [216] Number of pixels along Y-axis (DEC)
39 A1 --- --- [x]
40- 42 I3 --- Nz [384] Number of pixels along Z-axis
(VELO-LSR)
45- 52 F8.3 km/s bVLSR [-416.044] Lower limit of LSR velocity
55- 60 F6.2 km/s BVLSR [345.36] Upper limit of LSR velocity
63- 67 F5.3 km/s dVLSR [1.988] Increment in the LSR velocity (1)
70- 76 A7 --- Line Spectral feature ([Ne II])
79- 83 I5 Kibyte size [62871/62871] Size of the FITS file
86- 97 A12 --- FileName Name of the FITS file in subdirectory fits
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Note (1): The channels of the data cube are evenly spaced in frequency, not
wavelength, so the velocity scale is strictly correct only at the
center of the cube.
The first channel of the data cube has been replaced with the 12.8um
continuum, taken from channels between -430 and -490km/s. The second
channel is the [NeII] line intensity, with continuum subtracted,
integrated over channels between +344 and -416km/s [in units of
erg(s.cm2.sr)-1=mW.m-2.sr-1]. The other maps have units of
erg(s cm2.sr.cm-1)-1=mW(m2.sr.cm-1)-1. The continuum has
also been subtracted from the channel maps.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 11-Mar-2014