David S. Meier

Spatially Resolved Chemistry in Nearby Galaxies. I. The Center of IC 342

We have imaged emission from the millimeter lines of eight molecules—C2H, C 34 S, N2H + ,C H3OH, HNCO, HNC, HC3N, and SO—in the central half-kiloparsec of the nearby spiral galaxy IC 342. The 5 00 (� 50 pc) resolution images were made with the Owens Valley Millimeter Array. Using these and previously published CO and HCN images, we obtain a picture of the chemistry within the nuclear region on the size scales of individual giant molecular clouds. Bright emission is detected from all but SO. There are marked differences in morphology for the different molecules. A principal-component analysis is performed to quantify similarities and differences among the images. This analysis reveals that while all molecules are to zeroth order correlated, that is, that they are all found in dense molecular clouds, there are three distinct groups of molecules distinguished by the location of their emission within the nuclear region. N2H + ,C 18 O, HNC, and HCN are widespread and bright, good overall tracers of dense molecular gas. C2 Ha nd C 34 S, tracers of photodissociation region chemistry, originate exclusively from the central 50–100 pc region, where radiation fields are high. The third group of molecules, CH3OH and HNCO, correlates well with the expected locations of bar-induced orbital shocks. The good correlation of HNCO with the established shock tracer molecule CH3OH is evidence that this molecule, whose chemistry has been uncertain, is indeed produced by the processing of grain mantles. HC3N is observed to correlate tightly with 3 mm continuum emission, demonstrating that the young starbursts are the sites of the warmest and densest molecular gas. We compare our HNC images with the HCN images of Downes and coworkers to produce the first highresolution, extragalactic HCN/HNC map: the HNC/HCN ratio is near unity across the nucleus, and the correlation of both of these gas tracers with star formation is excellent. The ratio exhibits no obvious correlation with gas temperature or star formation strength. Subject headings: astrochemistry — galaxies: individual (IC 342) — galaxies: ISM — galaxies: starburst — radio lines: galaxies

ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst

We use ALMA to derive the mass, length, and time scales associated with the nuclear starburst in NGC 253. This region forms ~2 M_sun/yr of stars and resembles other starbursts in scaling relations, with star formation consuming the gas reservoir 10 times faster than in galaxy disks. We present observations of CO, the high effective density transitions HCN(1-0), HCO+(1-0), CS(2-1), and their isotopologues. We identify ten clouds that appear as peaks in line emission and enhancements in the HCN-to-CO ratio. These clouds are massive (~10^7 M_sun) structures with sizes (~30 pc) similar to GMCs in other systems. Compared to disk galaxy GMCs, they show high line widths (~20-40 km/s) given their size, with implied Mach numbers ~90. The clouds also show high surface (~6,000 M_sun/pc^2) and volume densities (n_H2~2,000 cm^-3). Given these, self-gravity can explain the line widths. This short free fall time (~0.7 Myr) helps explain the more efficient star formation in NGC 253. We also consider the starburst region as a whole. The geometry is confused by the high inclination, but simple models support a non-axisymmetric, bar-like geometry with a compact, clumpy region of high gas density embedded in an extended CO distribution. Even for the whole region, the surface density still exceeds that of a disk galaxy GMC. The orbital time (~10 Myr), disk free fall time (<~ 3 Myr), and disk crossing time (<~ 3 Myr) are each much shorter than in a normal spiral galaxy disk. Some but not all aspects of the structure correspond to predictions from assuming vertical dynamical equilibrium or a marginally stable rotating disk. Finally, the CO-to-H2 conversion factor implied by our cloud calculations is approximately Galactic, contrasting with results showing a low value for the whole starburst region. The contrast provides resolved support for the idea of mixed molecular ISM phases in starburst galaxies.

Suppression of Star Formation in NGC 1266

NGC1266 is a nearby lenticular galaxy that harbors a massive outflow of molecular gas powered by the mechanical energy of an active galactic nucleus (AGN). It has been speculated that such outflows hinder star formation (SF) in their host galaxies, providing a form of feedback to the process of galaxy formation. Previous studies, however, indicated that only jets from extremely rare, high power quasars or radio galaxies could impart significant feedback on their hosts. Here we present detailed observations of the gas and dust continuum of NGC1266 at millimeter wavelengths. Our observations show that molecular gas is being driven out of the nuclear region at

A Survey of Large Molecules of Biological Interest toward Selected High Mass Star Forming Regions

\dot{M}_{\rm out} \approx 110 M_\odot

Molecular Gas and Star Formation in the Nucleus of IC 342: C18O and Millimeter Continuum Imaging

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ALMA MULTI-LINE IMAGING OF THE NEARBY STARBURST NGC 253

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An extragalactic supernebula confined by gravity.

, of which the vast majority cannot escape the nucleus. Only 2

Submillimeter ALMA Observations of the Dense Gas in the Low-Luminosity Type-1 Active Nucleus of NGC1097

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MOLECULAR GAS PROPERTIES OF THE STARBURST NUCLEUS OF IC 342: HIGH-RESOLUTION 13CO (2¨1) IMAGING

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RADIO-INFRARED SUPERNEBULAE IN II Zw 40

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