Download VLA HI Zeeman Observations of the Cygnus X Region: Abstract

VLA HI Zeeman Observations of the Cygnus X Region:
DR 22 and ON 2
E.A. Mayo (South Carolina State University) and T.H. Troland (University of Kentucky)
Abstract
The Natures of DR 22 and ON 2
OBSERVATIONAL PARAMETERS FOR VLA OBSERVATIONS
Parameter
Date………………………………...
The Very Large Array in Socorro, New Mexico has been used to study the Zeeman
Effect in the 21cm HI line seen in absorption against radio sources in the Cygnus X
region. Cygnus X is geometrically favorable for Zeeman effect observations as the
region lies along the mean field direction of the diffuse interstellar medium (ISM) of the
galaxy. We present observations of two compact H+ regions within Cygnus X, DR 22
and ON 2. The data show magnetic field strengths of the order -80 μG toward DR 22
alone with no significant detections toward ON 2. This information is used to estimate
the magnetic energy of the DR 22 star-forming cloud, and allows for a complete analysis
of the energetics of the region revealing the role of the magnetic field.
Configuration…………………........
R.A. of field center (J2000)……….
Decl. of field center (J2000)……...
Total Bandwidth (MHz)…………...
Number of Channels………………
Hanning smoothing………………..
Channel Spacing (km/s)………….
Approximate time on source (hr)
DR 22.......................................
ON 2.........................................
Rest Frequency (MHz)……………
FWHM of synthesized beam……..
DR 22………………………......
ON 2…………………………….
RMS noise (mJy/beam)…………..
Line channels…………………..
Continuum……………………...
HI
May 2nd, 2003 and
May 5th, 2003
D
20h39m26s
41o20’00.0”
0.78
256
No
0.64
6
6
1420.406
DR 22 is a compact H+ region that lies at the edge of a molecular cloud. The H+ region/molecular
cloud are associated with a star cluster visible in the infrared (see figures below.)
The ON 2 star–forming region contains several compact H+ regions. The 21 cm continuum maps of
the region (see figure below) show two strong unresolved sources labeled ON 2N and S respectively
and a weaker northern source labeled ON 2NE. Low intensity continuum emission stretches
between ON 2N and S.
59”x52”
56”x53”
13
14
21cm continuum map of ON 2 at 1420 MHz. Contour intervals are at 0.03, 0.1,
0.3, 0.5, 0.7, 0.9 of the peak continuum flux of 3.1 Jy/beam.
ON 2
The beam is
56"x53".
HI 1420 MHz optical depth profile
toward
(a) ON 2N α=20h21m38s.3,
δ=37º31'08";
(b) ON 2NE at α=20h21m49s.7,
δ=37º30'08";
(c) ON 2S α=20h21m40s.3,
δ=37º26'12".
21cm continuum map of DR 22 at 1420 MHz. Contour intervals are at 0.075, 0.1,
Plot of N(HI)/Tex toward DR 22. The optical depths were integrated over the
0.3, 0.5, 0.7, 0.9 of the peak continuum flux of 2.1 Jy/beam.
velocity range –19.8 km/s to –5.0 km/s. The contours represent the 21cm
The beam is
continuum. Contour intervals are at 0.0725, 0.1, 0.3, 0.5, 0.7, 0.9 of the peak
59"x52".
continuum flux of 2.1 Jy/beam. The beam is 59"x52". The + indicates the position
of the magnetic field detection.
21cm continuum map of ON 2 at 1420 MHz. Contour intervals are at 0.01, 0.03,
0.05, 0.07, 0.09 of the peak continuum flux 3.1 Jy/beam. The beam is 56"x53".
DR 22
Stokes I (top) and V (bottom)
profiles in the HI 1420 MHz line
toward DR 22 at the position
α=20h39m24s.8, δ=41º20‘08". The
solid line superimposed on the V
spectrum is the derivative of I scaled
by the derived value of
Blos=-84±11μG.
HI 1420 MHz optical depth profile
toward the core of DR 22 at
α=20h39m26s.5, δ=41º20'01".
Results and Conclusions
ON 2
DR 22
DR22: DERIVED VALUES AND
VIRIAL ESTIMATES
Parameter
mA………………...
ms………………...
βρ…………………
[M/ΦB]obs/crit………
W…………………
T/W……………...
M/W……………...
Value
0.60
8.0
0.01
2.0
7.8x1047 ergs
0.18
0.22
NOTE.---mA is the magnetic Mach number,
mS is the turbulent Mach number, M/ΦB is
the mass to magnetic flux ratio, W is the
virial gravitational energy, T is the virial
kinetic energy, and M is the virial
magnetic energy; all terms are defined in
Crutcher (1999).
DR 22 PARAMETERS
DERIVED EXCITING STARS FOR ON 2 REGION
Parameter
Radius (r)............
Mass (M)………..
N(H)…………….
np………………...
Tk…………………
Δυ………………..
Blos……………….
Value
1.3 pc
4200 Msun
3.4x1022 cm-2
1.5x104 cm-3
15K
2.5 km/s
84 μG
POSITION
EXCITING STAR
SOURCE
ON 2 N
R.A.
(J2000)
20 21 38.0
Decl.
(J2000)
37 31 13
Radio Flux
4.03
1 kpc
B0
5.5 kpc
06
ON 2 S
20 21 41.6
37 30 53
3.09
B0
06-06.5
ON 2 NE 20 21 49.7
37 30 13
0.15
B0.5
B0
NOTE. ---Units of right ascension are hours, minutes, and seconds, and
units of declination are degrees, arcminutes, and arcseconds. Radio
flux is in Jy.
Estimated required ionizing sources
for ON2 N, S, and NE at both 5.5 and
1 kpc based on the 1420 MHz radio
continuum emission.
λ=2 indicating the molecular cloud is magnetically supercritical.
CO 2→1 line toward DR 22. The contours represent the 21cm
K Band image of DR 22 from 2MASS (Skrutskie et al., AJ, 131, 1163 2006). The
continuum. Contour intervals are at 0.05, 0.1, 0.3, 0.5, 0.7, 0.9 of the peak
contours represent the 21cm continuum. Contour intervals are at 0.0725, 0.1,
Integrated
13
continuum flux of 2.1 Jy/beam. The beam is 59"x52".
0.3, 0.5, 0.7, 0.9 of the peak continuum flux of 2.1 Jy/beam. The beam is
59"x52".
Thermal energy is insignificant compared to the turbulent energy
density in the molecular core.
Magnetic energy density is comparable to the turbulent energy
density.
Acknowledgments:
CO line data for DR 22 (see figure above) were graciously provided in advance of publication by Nicola Schneider-Bontemps.
Support for this work was provided by the NSF PAARE program to South Carolina State University under award AST-0750814.
Support was also provided by NSF awards 0307642 and 0908841 to the University of Kentucky.
Magnetic field fitting toward ON 2 revealed average magnetic field strengths
of –20±8 μG toward ON 2N and +13±12 μG toward ON 2S.
These results are below the 3σ level and are not considered significant.
Weak line strengths toward ON 2NE limited the fitting process in this region.