Direct Physical Diagnostics of Triggered Star Formation

Rachel Friesen

NRAO Postdoctoral FellowNorth American ALMA Science Center

C. Brogan, R. Indebetouw, C. Cyganowski, E. Churchwell, M. Wolfire, B. Whitney, C. Watson, W. Dirienzo

triggered star formation in HII regions

this work

- analyse tracers of low-density, high-density and ionized gas in a set of HII regions

- e.g. NH3 observations reveal the temperature and kinematics of the cold molecular gas in shell

- compare with predictions of collect-and-collapse, radiation driven implosion models of triggered star formation

- the expansion of HII regions can trigger star formation- ~20 % of HII region bubbles (sufficiently resolved at 870 μm) show evidence for massive star formation (Deharveng et al. 2010)

targets

- set of 4 HII regions- D ~ 4 – 5 kpc- associated 13CO (GRS)- evidence for triggered SF (IRAC/MIPS, masers)

- GBT NH3 (1,1) – (4,4) inversion transitions - Spitzer IRS – 6.9 μm – 36 μm

+ GLIMPSE, MIPSGAL (Spitzer IRAC, MIPS), GRS (13CO), MAGPIS (20 cm), BGPS (1.1 mm)

3.5μm, 8.0 μm, 24μm

G41.9+0.0G41.1+0.2

G44.3-0.8

G44.3+0.1

census of YSOs

Protostar properties:

Class 1 Class II

based on SED fitting of IRAC/MIPS data (Dirienzo et al. in prep, SED models by Robitaille et al. 2006, 2007) ¾ detections

Class II protostarM = 7 MSun

3.5μm, 8.0 μm, 24μm

G41.1+0.2 G41.9+0.0

Class I protostarM = 0.3 Msun

GBT NH3 results & analysis

- NH3 emission follows infrared-dark areas

3.5μm, 8.0 μm, 24μm

NH3 (1,1), (2,2), map extents

G41.1+0.2 G44.3+0.1 G44.3-0.8

3

2

1

0

40 60 80

NH3 (1,1)

NH3 (2,2)

NH3 (3,3) x 3

Self-consistent fitting of the (1,1) and (2,2) line profiles:

- vlsr consistent with shell 13CO (GRS) – dense gas associated with HII regions

- evidence of local heating near embedded protostars, but TK ~ 15 - 25 K

- supersonic line widths ~ 1.3 – 2.3 km s-1, some asymmetric line wings

NH3 (1,1) emission correlates with 1.1 mm

(Bolocam GPS; Aguirre et al. 2010)

3D clump analysis finds 4 distinct clumps

- R ~ 0.9 – 1.5 pc, elongated along shell

- M ~ 1000 – 3000 Mo

- TK ~ 14 – 25 K

- N(H2) ~ 6 x 1022 cm-2

- M/Mvir ~ 1 ~ 3

G41.10: molecular gas

NH3 (1,1), 1.1 mm

H2 emission shows shocked molecular gas

Bottom RGB: [H2] + [SIII] + [8 μm]

- H2 emission, ionized gas surrounds one clump

- warmer with no internal heat source

Top RB: [SIII] (33.5 μm)+ [SIII] (18.7 μm)

- can determine ne from ratio of [SIII] lines (Dudik et al. 2007) - Pe

Spitzer IRS maps:

- fine structure lines reveal the physical conditions in the ionized gas

- photoionization modeling to determine ionized gas and PDR properties

G41.10: ionized gas

NH3 TK

TK = 25 K

TK = 19 K

TK = 14 K

NH3 (1,1) contours

.. ongoing summary

- existing and new datasets allows characterization of - low density gas- high density gas- ionized gas - current YSO population

towards 4 HII regions with ongoing, active star formation in their shells

- compare directly measurements with predictions of triggering scenarios

stay tuned…