L1495-B218 Filaments in Taurus
seen in NH3 and CCS
Youngmin Seo
University of Arizona/Steward Observatory
Collaborators: Yancy L. Shirley, Paul Goldsmith, Derek-Ward Thompson,
Jason M. Kirk, Markus Schmalzl, Jeong-Eun Lee, Rachel Friesen,
Glen Langston, Joe Masters Robert W. Garwood
1. Filaments
Filaments are universal structures in molecular clouds
Why dense molecular filaments?
→ 75% of starless cores are within filaments [Aquila-Rift, Andre
et al. 2010]
1. Low Mass Star Formation
Want to know about main mode of low mass star forming
processes?
→ filaments and dense cores
What do I do?
→ Study formation and evolution of dense cores
within filaments
2. L1495-B218 Filaments in the Taurus Cloud
1.1 Why the Taurus Cloud?
→ It is close. Only 140 pc far from us.
→ Multiple observations in different tracers
Goldsmith et al. 2008
12CO 1-0 & 13CO 1-0
Schmalzl et al. 2010
Hershel 250, 350, 500 um
FCRAO
Av map
Hacar et al. 2013
C18O, SO, N2H+
2. Mapping of filaments and
complete population of dense cores
We use NH3 to see dense cores
NH3
→ A good intermediate & dense gas tracer [Aikawa et al 2005]
→ A measure of kinetic temperature [e.g. Rosolowsky et al. 2008]
3. The Green Bank Telescope
GBT KFPA
3-degree long map in 60 hours
Median rms of 0.1 K and the lowest rms of 0.06 K @ 0.08 km/s
Galactic latitude
500µ m & NH3
NH3 Map and YSOs
More Evolved
Less
evolved
Less Evolved
Less
evolved
More Evolved
More Evolved
Kinetic Temperature from NH3
Less
evolved
Less
evolved
Less
evolved
1. Dense Cores Identification
Intensity
1.1 Dense core identification : CSAR [Kirk et al 2013]
A
B
C
D
CSAR vs Clumpfind
• Hybrid algorithm of seeded-watershed and dendrogram
 Identify hierarchical dense structures
• Red: leaf containing single intensity peak
Blue: branches containing multiple leaves
ID
1. Dense Cores Identification
1.2 NH3 CSAR leaves
39 leaves & 16 branches
2. Physical Properties
• Observed properties
Mass : 0.05 – 9.5 Msun
Size : 0.01 - 0.1 pc
Median Tk : 9.5 K
• Observed mass is estimated from
500 µm dust continuum
• Virial mass
Estimated from velocity dispersion
of NH3 (1,1)
Geometry is assumed as spheroid
with density following ρ~r-2
•
•
•
•
Inactive
Active
Virial
observed
2. Physical Properties
Only 9 out of 39 are gravitationally bound
7 out of 9 gravitationally bound leaves are active
Pressure-confined structure → gravitationally bound structure → Star formation
Agrees with theoretical studies of dense core formation
by turbulent converging flows[e.g. Chen & Ostriker 2015]
Why CCS?
→ Traces younger stages of dense cores compared to NH3 [Suzuki et al. 1992]
Bright in CCS but also bright in NH3
L1495A
B213A
L1495A
B213A
Bright in NH3 : dense core
Bright in CCS + Inv. P-cygni HCN, HCO+
Multiple YSOs
Formation of stellar association
Large scale flows seen in
12CO and 13CO
[Goldsmith et al. 2008
Narayanan et al. 2008
Palmeirim et al. 2013]
STAR FORMING PROCESSES: FROM FILAMENTS
TO DENSE CORES
Dynamics filaments to dense cores and from dense cores to protostars
in HCN, HCO+, and N2H+ (W-band array : ARGUS)
7” resolution (0.005 pc or 1000 AU)
ARGUS : 10 Hours per core
ALMA+ACA : more than a day
• L1495-B218 filaments
Found 39 CSAR leaves and 16 branches
Mass: 0.05 – 9.5 Msun, Size : 0.01 – 0.1 pc, Tk ~ 9.5 K
• Some of CSAR leaves are pressure-confined (13 out of 39).
Most of gravitationally bound CSAR leaves are active leaves (7 out of 9)
↓
Dense core : pressure-confined → gravitationally bound → Star formation
• Bright in both NH3 and CCS : Accretion to dense cores and
possible stellar association formation
↓
Good targets for ARGUS