J/A+A/489/217 CO maps of diffuse Galactic gas towards NRAO 150 (Pety+, 2008)
Imaging galactic diffuse gas: Bright, turbulent CO surrounding the line of
sight to NRAO 150.
Pety J., Lucas R., Liszt H.S.
<Astron. Astrophys. 489, 217 (2008)>
=2008A&A...489..217P 2008A&A...489..217P
ADC_Keywords: Radio sources ; Interstellar medium
Keywords: ISM: clouds - ISM: structure - ISM: molecules -
ISM: kinematics and dynamics - radio lines: ISM -
techniques: interferometric
Abstract:
To understand the environment and extended structure of the host
galactic gas whose molecular absorption line chemistry, we previously
observed along the microscopic line of sight to the
blazar/radio-continuum source NRAO 150 (aka B0355+508).
We used the IRAM 30m Telescope and Plateau de Bure Interferometer to
make two series of images of the host gas: i) 22.5" resolution
single-dish maps of 12CO J=1-0 and 2-1 emission over a 220" by
220" field; ii) a hybrid (interferometer+singledish) aperture
synthesis mosaic of 12CO J=1-0 emission at 5.8" resolution over
a 90"-diameter region.
At 22.5" resolution, the CO J=1-0 emission toward NRAO 150 is
30-100% brighter at some velocities than seen previously with 1'
resolution, and there are some modest systematic velocity gradients
over the 220" field. Of the five CO components seen in the
absorption spectra, the weakest ones are absent in emission toward
NRAO 150 but appear more strongly at the edges of the region mapped in
emission. The overall spatial variations in the strongly emitting gas
have Poisson statistics with rms fluctuations about equal to the mean
emission level in the line wings and much of the line cores. The
J=2-1/J=1-0 line ratios calculated pixel-by-pixel cluster around 0.7.
At 6" resolution, disparity between the absorption and emission
profiles of the stronger components has been largely ameliorated. The
12CO J=1-0 emission exhibits i) remarkably bright peaks, Tmb=12-13K,
even as 4" from NRAO 150; ii) smaller relative levels of spatial
fluctuation in the line cores, but a very broad range of possible
intensities at every velocity; and iii) striking kinematics whereby
the monotonic velocity shifts and supersonically broadened lines in
22.5" spectra are decomposed into much stronger velocity
gradients and abrupt velocity reversals of intense but narrow,
probably subsonic, line cores.
CO components that are observed in absorption at a moderate optical
depth (0.5) and are undetected in emission at 1' resolution
toward NRAO 150 remain undetected at 6" resolution. This implies
that they are not a previously-hidden large-scale molecular component
revealed in absorption, but they do highlight the robustness of the
chemistry into regions where the density and column density are too
low to produce much rotational excitation, even in CO. Bright CO lines
around NRAO 150 most probably reflect the variation of a chemical
process, i.e. the C±CO conversion. However, the ultimate cause of the
variations of this chemical process in such a limited field of view
remains uncertain.
Description:
The three spectra cubes (RA,Dec,Velocity) of the diffuse Galactic gas
around the line of sight towards NRAO 150: 1) Two 22.5" resolution
single-dish maps of 12CO J=1-0 and 2-1 emission over a 220" by
220" field; the noise is uniformly distributed on those cubes. 2)
A hybrid (interferometer+singledish) aperture synthesis mosaic of
12CO J=1-0 emission at 5.8" resolution over a 90"-diameter region.
Due to the observational technique, the noise increases sharply at the
edges of the imaged field of view. The data cubes are available in
FITS format.
Objects:
----------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------
03 59 29.7 +50 57 50 NRAO 150 = QSO B0355+508
----------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
maps.dat 84 3 List of the maps
fits/* . 3 FITS files (velocity resolution 0.2km/s)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: maps.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- FITSfile Name of the FITS map, in subdirectory fits (1)
26- 84 A59 --- Title Title of the file
--------------------------------------------------------------------------------
Note (1): File headers as given by the GILDAS
(http://www.iram.fr/IRAMFR/GILDAS/) HEADER command are listed
below in the "GILDAS headers" section below.
(some parameters are lost in the FITS conversion):
--------------------------------------------------------------------------------
GILDAS headers:
File : nrao150-12co21-30m.lmv REAL*4
-----------------------------
Size Reference Pixel Value Increment
31 15.93260924562524 0.000000000000000 -3.3936958061531186E-05
31 16.09596206043402 0.000000000000000 3.3936958061531186E-05
201 106.1865539550781 -10.00000000000000 0.2031841874122620
1 1.000000000000000 1.000000000000000 1.000000000000000
Blanking value and tolerance -1000.0000 0.0000000
Source name B0355+508
Map unit K (Ta*)
Axis type RA DEC VELOCITY Unknown
Coordinate system EQUATORIAL
Right Ascension 03:59:29.748 Declination 50:57:50.16
Lii 150.3773478985418 Bii -1.603677543105950
Epoch 2000.0000
Projection type RADIO Angle 0.000000000000000
Axis 1 A0 03:59:29.748 Axis 2 D0 50:57:50.16
Minimum -0.69813681 at 1 11 126 1
Maximum 6.9673486 at 23 5 107 1
Axis 3 Line Name 12CO(2-1) Rest Frequency 230538.0000000000
Resolution in Velocity 0.20318419 in Frequency -0.1562470197677612
Offset in Velocity -10.000000 Image Frequency 239053.7159368165
File : nrao150-12co10-30m.lmv REAL*4
-----------------------------
Size Reference Pixel Value Increment
31 15.93260924562524 0.000000000000000 -3.3936958061531186E-05
31 16.09596206043402 0.000000000000000 3.3936958061531186E-05
201 106.1865539550781 -10.00000000000000 0.2031841874122620
1 1.000000000000000 1.000000000000000 1.000000000000000
Blanking value and tolerance -1000.0000 0.0000000
Source name B0355+508
Map unit K
Axis type RA DEC VELOCITY Unknown
Coordinate system EQUATORIAL
Right Ascension 03:59:29.748 Declination 50:57:50.16
Lii 150.3773478985418 Bii -1.603677543105950
Epoch 2000.0000
Projection type RADIO Angle 0.000000000000000
Axis 1 A0 03:59:29.748 Axis 2 D0 50:57:50.16
Minimum -1.2228174 at 30 31 32 1
Maximum 9.2075863 at 24 6 109 1
Axis 3 Line Name 12CO(1-0) Rest Frequency 115271.2020000000
Resolution in Velocity 0.20318419 in Frequency -7.8125000000000000E-02
Offset in Velocity -10.000000 Image Frequency 118267.1060641971
File : nrao150-12co10-pdbi.lmv REAL*4
-----------------------------
Size Reference Pixel Value Increment
67 34.00000000000000 0.000000000000000 -7.2722054937912617E-06
67 34.00000000000000 0.000000000000000 7.2722054937912617E-06
151 78.18661499023438 -10.00000000000000 0.2031842023134232
1 0.000000000000000 0.000000000000000 0.000000000000000
Blanking value and tolerance 1.23455997E+34 0.0000000
Source name B0355+508
Map unit K
Axis type RA DEC VELOCITY Unknown
Coordinate system EQUATORIAL
Right Ascension 03:59:29.747 Declination 50:57:50.16
Lii 150.3773464825498 Bii -1.603680434246657
Epoch 2000.0000
Projection type AZIMUTHAL Angle 0.000000000000000
Axis 1 A0 03:59:29.747 Axis 2 D0 50:57:50.16
Minimum -3.8927937 at 46 61 149 1
Maximum 13.259477 at 52 16 44 1
Axis 3 Line Name 12CO(1-0) Rest Frequency 115271.2020000000
Resolution in Velocity 0.20318420 in Frequency -7.8125004826103628E-02
Offset in Velocity -10.000000 Image Frequency 0.000000000000000
Beam 6.04 5.49 82.42
Acknowledgements:
Jerome Pety, pety(at)iram.fr
(End) Jerome Pety [IRAM, France], Patricia Vannier [CDS] 25-Jul-2008