1,844 research outputs found
Extreme Star Formation
Extreme star formation includes star formation in starbursts and regions
forming super star clusters. We survey the current problems in our
understanding of the star formation process in starbursts and super star
clusters - initial mass functions, cluster mass functions, star formation
efficiencies, and radiative feedback into molecular clouds - that are critical
to our understanding of the formation and survival of large star clusters,
topics that will be the drivers of the observations of the next decade.Comment: appeared in "Astrophysics in the Next Decade: JWST and Concurrent
Facilities", Astrophysics and Space Science Proceedings, 2009, ed. H. A.
Thronson, M. Stiavelli, and A. G. G. M. Tielens, proceedings of the
conference, Astrophysics in the Next Decade, 24-27 September 2007, Tucson, A
The Birth of a Super Star Cluster: NGC 5253
We present images of the 7mm free-free emission from the radio "supernebula"
in NGC 5253 made with the Very Large Array and the Pie Town link. The images
reveal structure in the nebula, which has a <~ 1 pc (~50 mas radius) core
requiring the excitation of 1200 O7 stars. The nebula is elongated, with an arc
of emission curving to the northeast and to the south. The total ionizing flux
within the central 1.2" (~20 pc) is 7 x 10^52 s^-1, corresponding to 7000 O7
stars. We propose that the radio source is coincident with a small, very red
near-infrared cluster and apparently linked to a larger, optical source some 10
pc away on the sky. We speculate on the causes of this structure and what it
might tell us about the birth of the embedded young super star cluster.Comment: Accepted, Astrophysical Journal Letters. 10 pages, including 2
figure
Cyanoacetylene in IC 342: An Evolving Dense Gas Component with Starburst Age
We present the first images of the J=5-4 and J=16-15 lines of the dense gas
tracer, cyanoacetylene, HC_3N, in an external galaxy. The central 200 pc of the
nearby star-forming spiral galaxy, IC 342, was mapped using the VLA and the
Plateau de Bure Interferometer. HC_3N(5-4) line emission is found across the
nuclear mini-spiral, but is very weak towards the starburst site, the location
of the strongest mid-IR and radio emission. The J=16-15 and 10-9 lines are also
faint near the large HII region complex, but are brighter relative to the 5-4
line, consistent with higher excitation. The brightest HC_3N emission is
located in the northern arm of the nuclear minispiral, 100 pc away from the
radio/IR source to the southwest of the nucleus. This location appears less
affected by ultraviolet radiation, and may represent a more embedded, earlier
stage of star formation. HC_3N excitation temperatures are consistent with
those determined from C^{18}O; the gas is dense, 10^{4-5}/cc, and cool, T_K ~<
40 K. So as to not violate limits on the total H_2 mass determined from
C^{18}O, at least two dense components are required to model IC 342's giant
molecular clouds. These observations suggest that HC_3N(5-4) is an excellent
probe of the dense, quiescent gas in galaxies. The high excitation combined
with faint emission towards the dense molecular gas at the starburst indicates
that it currently lacks large masses of very dense gas. We propose a scenario
where the starburst is being caught in the act of dispersing or destroying its
dense gas in the presence of the large HII region. This explains the high star
formation efficiency seen in the dense component. The little remaining dense
gas appears to be in pressure equilibrium with the starburst HII region.Comment: Accepted, AJ. 12 pages, 5 figure
Dense Molecular Filaments Feeding a Starburst: ALMA Maps of CO(3-2) in Henize 2-10
We present ALMA CO(3-2) observations at 0.3 arcsec resolution of He2-10, a
starburst dwarf galaxy and possible high-z galaxy analogue. The warm dense gas
traced by CO(3--2) is found in clumpy filaments that are kinematically and
spatially distinct. The filaments have no preferred orientation or direction;
this may indicate that the galaxy is not evolving into a disk galaxy. Filaments
appear to be feeding the active starburst; the velocity field in one filament
suggests acceleration onto an embedded star cluster. The relative strengths of
CO(3-2) and radio continuum vary strongly on decaparsec scales in the
starburst. There is no CO(3--2) clump coincident with the non-thermal radio
source that has been suggested to be an AGN, nor unusual kinematics.
The kinematics of the molecular gas show significant activity apparently
unrelated to the current starburst. The longest filament, east of the
starburst, has a pronounced shear of FWHM ~\kms\ across its 50~pc
width over its entire kpc length. The cause of the shear is not
clear. This filament is close in projection to a `dynamically distinct' CO
feature previously seen in CO(1--0). The most complex region and the most
highly disturbed gas velocities are in a region 200~pc south of the starburst.
The CO(3--2) emission there reveals a molecular outflow, of linewidth FWZI
120-140 \kms, requiring an energy . There is
at present {\it no} candidate for the driving source of this outflow.Comment: This was revised 31 October to correct some typos and to replace
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