19 research outputs found
Molecular Cloud Structure in the Magellanic Clouds: Effect of Metallicity
The chemical structure of neutral clouds in low metallicity environments is
examined with particular emphasis on the H to H_2 and C+ to CO transitions. We
observed near-IR H_2 lines and the CO J=1-0 line from 30 Doradus and N159/N160
in the Large Magellanic Cloud and from DEM S 16, DEM S 37, and LI-SMC 36 in the
Small Magellanic Cloud. We find that the H_2 emission is UV-excited and that
(weak) CO emission always exists (in our surveyed regions) toward positions
where H_2 and [CII] emission have been detected. Using a PDR code and a
radiative transfer code, we simulate the emission of line radiation from
spherical clouds and from large planar clouds. Because the [CII] emission and
H_2 emission arise on the surface of the cloud and the lines are optically
thin, these lines are not affected by changes in the relative sizes of the
neutral cloud and the CO bearing core, while the optically thick CO emission
can be strongly affected. The sizes of clouds are estimated by measuring the
deviation of CO emission strength from that predicted by a planar cloud model
of a given size. The average cloud column density and therefore size increases
as the metallicity decreases. Our result agrees with the photoionization
regulated star formation theory by Mc Kee (1989).Comment: 45 Pages including 15 figures. To be published in the ApJ May 10,
1998 issue, Vol. 49
The effects of star formation on the low-metallicity ISM: NGC4214 mapped with Herschel/PACS spectroscopy
We present Herschel/PACS spectroscopic maps of the dwarf galaxy NC4214
observed in 6 far infrared fine-structure lines: [C II] 158mu, [O III] 88mu, [O
I] 63mu, [O I] 146mu, [N II] 122mu, and [N II] 205mu. The maps are sampled to
the full telescope spatial resolution and reveal unprecedented detail on ~ 150
pc size scales. We detect [C II] emission over the whole mapped area, [O III]
being the most luminous FIR line. The ratio of [O III]/[C II] peaks at about 2
toward the sites of massive star formation, higher than ratios seen in dusty
starburst galaxies. The [C II]/CO ratios are 20 000 to 70 000 toward the 2
massive clusters, which are at least an order of magnitude larger than spiral
or dusty starbursts, and cannot be reconciled with single-slab PDR models.
Toward the 2 massive star-forming regions, we find that L[CII] is 0.5 to 0.8%
of the LTIR . All of the lines together contribute up to 2% of LTIR . These
extreme findings are a consequence of the lower metallicity and young,
massive-star formation commonly found in dwarf galaxies. These conditions
promote large-scale photodissociation into the molecular reservoir, which is
evident in the FIR line ratios. This illustrates the necessity to move to
multiphase models applicable to star-forming clusters or galaxies as a whole.Comment: Accepted for publication in the A&A Herschel Special Issu
High spatial resolution isotopic CO and CS observation of M17 SW: The clumpy structure of the molecular cloud core
SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
The Orion molecular cloud and star forming region
SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
A multi-line study of the molecular interstellar medium in M82's starburst nucleus
SIGLEAvailable from TIB Hannover: RN 9303(213) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Photodissociation regions Proceedings
SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
First observations of the CO J=6-5 transition in starburst galaxies
SIGLEAvailable from TIB Hannover: RN 9303(209) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Detection of an isotopic short submillimeter CO line: Column densities of warm gas in molecular clouds
SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
First detection of SO_2 and CH_3OH emission and one unidentified line near 800 GHz
SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman