Transcript Dynamical Properties of Infrared Dark Clouds

Galactic 1Distribution
of 2Southern
Infrared
Dark Clouds
1
3
1
J. M. Jackson , S. Finn , J. Rathborne , R. Simon , E. Chambers
1Institute
for Astrophysical Research, Boston University, 2Harvard-Smithsonian Center for Astrophysics, 3I.Physikal. Institut, Universitat
zu Koln, Germany
Abstract
Infrared Dark Clouds (IRDCs) are a new class of interstellar clouds seen as dark extinction features against the bright Galactic background at mid-infrared
(mid-IR) wavelengths. Studies thus far have shown these IRDCs to be dense (>105 cm-3), cold (<25 K), and to have very high column densities (>10231025 cm-2; e.g., Egan et al. 1998; Carey et al. 1998, 2000). The characteristic high column densities and low temperatures of IRDCs suggest that they host
the earliest stages of star formation (e.g., Rathborne et al. 2006). Mapping the Galactic distribution of IRDCs will enhance knowledge of Galactic
structure and the global distribution of star formation in the Milky Way.
GOAL: To measure the distances to IRDCs in order to understand their
Galactic distribution.
TECHNIQUE: We measure the radial velocities of IRDC molecular lines
and convert these to kinematic distances. Because the rotation of the Milky
Way is approximately known (e.g., Clemens 1985), each longitude-velocity
pair corresponds to a unique Galactocentric radius. The distribution of
Southern IRDCs can then be compared to Northern IRDCs.
OBSERVATIONS: We observed the CS 2-1 line toward a large sample of
IRDCs with the Mopra 22-m Telescope near Coonabarabran, Australia.
Because CS requires high densities for excitation, it uniquely traces the
dense gas found in IRDCs (Figs 1 and 2).
13CO
CS
Figure 1: A CS 2-1 map of a typical IRDC. CS 2-1 integrated intensity contours are
overlaid on a Spitzer/GLIMPSE three-color image (3.6 µm in blue, 4.5 µm in green, and
8.0 µm in red). The CS emission corresponds very well with the mid-IR extinction.
Figure 2: (Left) 13CO 1-0 and (right) CS 2-1 spectra toward an IRDC. Although the 13CO
typically shows multiple velocity components, the CS shows only one. Thus, CS uniquely
traces IRDCs, and a single CS spectrum can be used to find their velocities and kinematic
distances.
RESULTS: CS velocity (and therefore kinematic distance) measurements were made for
210 southern IRDCs (identified by Simon et al. 2006a). The Galactocentric radial
distribution differs in the northern and southern Milky Way (Figs. 3 and 4). In the
north, the IRDC distribution peaks at a Galactocentric radius of 5 kpc, and in the south
at 6 kpc.
Northern
Southern
Figure 3: Histograms comparing the Galactocentric radial distributions of
the northern IRDCs (top; Simon et al. 2006b) with the southern IRDCs
(bottom, this work). A peak in the north can be seen at 5 kpc (the peak at
R=8 kpc is an artifact). Surprisingly, the southern distribution shows a
peak at a different radius of 6 kpc.
Southern
Northern
Figure 4: (Left) A face on plot of the Galactic IRDCs [Northern: 13CO Simon et al. 2006b; Southern, this work].
The positions of the Sun and Galactic Center are marked. Comparing this to a two-armed model of the Milky
Way’s spiral arms (right, courtesy of B. Benjamin), it can be seen that the IRDC distribution matches the
location of the Scutum-Centaurus spiral arm, which comes closer to the sun in the southern Milky Way.
CONCLUSIONS
IRDCs are confined to a distinct, non-axisymmetric Galactic feature that matches the so-called “Scutum-Centarus
arm” in two-armed models of the Milky Way.
Since they are found primarily in spiral arms, IRDCs probably form during compression caused by the passage of a
spiral density wave.

References
Carey et al. 1998, ApJ, 508,72
Carey et al. 2000, ApJ, 543, L157
Clemens 1985, ApJ, 295, 422
Egan et al. 1998, ApJ, 494, L199
Rathborne et al. 2006, 641, 389
Simon et al. 2006a, ApJ, 639, 227
We gratefully acknowledge funding support from grants NSF AST-0507657
Simon et al. 2006b, ApJ, 653, 1325
and NASA NNG04GGC92G.
Extinction Mapping of
Infrared Dark Clouds
Michael J. Butler, Jonathan C. Tan, Audra K. Hernandez
IRDC Sample
 Map (g cm-2)
Dynamical Properties of
Infrared Dark Clouds
Audra K. Hernandez, Jonathan C. Tan, Michael J. Butler
Dept. of Astronomy, University of Florida
Virial Masses:
The GRS Survey and Kinematic Distances:
 R  Vrms 2
M v  466M sun


0.5 pc 2.0km/s 
A
B
C
D
E
F
G
H
I

2
4
5
7
8
3
Log Mv/Mext
Log Mext/Msun
Log Mext/Msun
6
b
l
2.35

Table1
1
 FW HM
9
Log Mv,p/Mext
E
Vrms  3
Log Mv/Mext
F
A CD
Log Mv,p/Mext
B GIH
1
  FWHM 4   
M v,p  220M sun
 

2.0km/s  0.05g/cm 2 
Log Mext/Msun
Log Mext/Msun
Initial conditions of IRDC fragmentation
Clump mass function
Spitzer IRAC 8m
3
Number with Mobs > m
2
10
8
7
6
5
4
3
N (M > m) m-0.42±0.03
2
1
8
7
6
2
4
6 8
100
2
4
6 8
1000
2
4
Mass, m (Solar Mass)
Clump Mass function in IRDCs
•consistent with CO clump surveys of local clouds
•inconsistent with dust emission studies
S. Ragan
6
J. Greissl
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
The Properties of Clumps and Cores in
Molecular Clouds
Sami Dib
Collaborators:Jongsoo Kim, Andreas Burkert, Roland Jesseit, Thomas Henning, Enrique
Vazquez-Semadeni, Mohsen Shadmehri
molecular cloud models: Isothermal, magnetized, self-gravitating and turbulent
Barnard 59: Inside The Dark Spot
Carlos Román-Zúñiga, Charles Lada, Joao Alves, August Muench & Jill Rathborne
Harvard Smithsonian Center for Astrophysics
FLAMINGOS Near-IR Survey of Serpens Molecular Cloud:
understanding protostellar zoo
and a starformation
history
in the cloud
Nadya Gorlova, E. Lada ,
C. Roman-Zuniga ,
A. Stolte,A. Steinhauer,
J. Levine, B. Ferreira,
C. Gomez, N. Rashkind
FLAMINGOS SPECTROSCOPY OF LOW MASS STARS AND BROWN DWARFS IN NG
Noah H. Rashkind1, Joanna L. Levine1, August A. Muench2, Elizabeth A. Lada1
1Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
2Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
OBJECTIVE
● Collect NGC 1977 spectra, FLAMINGOS & KPNO 4-m telescope
● Classify spectra sample to determine effective temperatures
● Combine J, H, and K-band photometry to determine b
luminosities
09
● Place objects on H-R diagram, compare to evolutionary models
● Estimate an age and brown dwarf fraction for NGC 1977
● Investigate dependence of brown dwarf fraction on environment
RESULTS
COME SEE OUR POSTER FOR THE ANSWERS!
A Multi-wavelength Study of NGC1333: Brown Dwarfs & Low-Mass Stars
Gómez Martín, C.1, Lada, E.A.1, Levine, J.L.1,
Bayo Arán, A.2, Barrado y Navascués, D.2, Morales Calderón, M.2
1 University
of Florida, 2 Laboratorio de Astrofísica Espacial y Física Fundamental
OBJECTIVE
* Collect NGC 1333 spectra, FLAMINGOS & KPNO 4-m telescope
* Classify spectra sample to determine effective temperatures
* Combine J, H, and K-band photometry to determine bolometric
luminosities
* Place objects on H-R diagram, compare to evolutionary models
* Estimate an age NGC 1333
* Investigate dependence of brown dwarf fraction on environment
* Combine FLAMINGOS data with archival data (USNOB, 2MASS,
NOMAD & SPITZER) to produce SEDs.
RESULTS
COME SEE OUR POSTER FOR THE ANSWERS!