119373047
Infrared Emission from Clusters in the Starforming Disk of He2-10
We have made subarcsecond-resolution images of the central 10'' of the Wolf-Rayet dwarf galaxy He 2-10 at 11.7 μm, using the Long Wavelength Spectrometer on the Keck I Telescope. The spatial distribution of the infrared emission roughly agrees with that of the rising spectrum radio sources seen by Kobulnicky & Johnson and confirms that those sources are compact H II regions, rather than supernova remnants or other objects. The infrared sources are more extended than the subarcsecond rising spectrum radio sources, although the entire complex is still less than 5'' in extent. On size scales of 1'' the infrared and radio emission are in excellent agreement, with each source requiring several hundred to a thousand O stars for excitation. The nebulae lie in a flattened disklike distribution about 240 by 100 pc and provide all of the flux measured by IRAS for the entire galaxy in the 12 μm band; 30% of the total IRAS flux from the galaxy emanates from one 15–30 pc source. In this galaxy, intense star formation, probably triggered by an accretion event, is confined to a central disk, which breaks up into distinct nebulae presumably marking the sites of young super–star clusters.
15435454
RADIO-INFRARED SUPERNEBULAE IN II Zw 40
We report subarcsecond-resolution Very Large Array and Keck mid-infrared imaging of the dwarf starburst galaxy II Zw 40. II Zw 40 contains a bright compact thermal radio and infrared source with all the characteristics of a collection of dense H ii regions ionized by at least 14,000 O stars. The supernebula is revealed to consist of multiple sources within an envelope of weaker emission. The radio emission is dominated by free-free emission at 2 cm, and the spectrum of this emission appears to be rising. This suggests that the free-free emission is optically thick at 2 cm and that the individual H ii regions are � 1 pc in size. This complex of ‘‘ supernebulae ’’ dominates the total infrared luminosity of II Zw 40, although the radio source is less than � 150 pc in diameter. Multiple super–star clusters appear to be forming here, the much larger analogs of large Galactic H ii region complexes.
1155749
High Resolution Radio Maps of Four Nearby Spiral Galaxies
We report subarcsecond-resolution VLA imaging of the centers of four nearby spiral galaxies: IC 342, Maffei II, NGC 2903, and NGC 6946. In each galaxy, 7 - 12 compact radio continuum sources were identified within the central ∼ 15 ′′ × 15 ′′ . Slightly over half of the compact sources appear to be H ii regions with flat or positive spectral indices (�> ∼ −0.1). The H ii regions with rising spectra are optically thick at centimeter wavelengths, and thus dense (ni ∼ 10 4 cm −3 ) and young. The largest of these H ii regions require the excitation of 500 - 800 O stars, within regions of only few parsecs extent. These clusters approach the sizes expected for globular clusters.
7346529
WARM MOLECULAR GAS IN DWARF STARBURST GALAXIES: CO(3¨2) OBSERVATIONS
Eight dwarf starburst galaxies have been observed with the Caltech Submillimeter Observatory telescope in the CO J \ 3¨2 transition. The galaxies observed are He 2-10, NGC 5253, 1569, and 3077, Haro 2, Haro 3, II Zw 40, and Mrk 86; all but the last two are detected. The central regions of He 2-10 and NGC 5253 were mapped and a CO(2¨1) spectrum of NGC 5253 was obtained. The error-weighted mean CO(3¨2)/CO(1¨0) ratio of the detected galaxies is 0.60 ^ 0.06, which is virtually identical to that found for starbursts in the nuclei of nearby spirals and suggests that the molecular gas is optically thick, warm K), and moderately dense cm~3). The CO(3¨2)/CO(1¨0) ratio peaks at or (T k [ 20 (n H2 D 103¨104 close to the starburst in all cases. CO emission does not appear to be optically thin in these dwarfs, despite the low metallicity and intense radiation —elds, probably because for CO to exist in detectable amounts it must be self-shielding and hence optically thick. Physical properties of the molecular clouds in these dwarf starbursts appear to be essentially the same as those in nearby spiral nuclei, with the possible exception that CO is more con—ned to the cloud cores.
6538411
LOCATING THE YOUNGEST H ii REGIONS IN M82 WITH 7 mm CONTINUUM MAPS
We present 7 mm Very Large Array continuum images of the starburst galaxy M82. On arcsecond scales, two-thirds of the 7 mm continuum consists of free-free emission from H?II regions. In the subarcsecond resolution map, we identify 14 compact sources, including 9 bright H?II regions with N lyc > 1051 s?1. Four of the H?II regions have rising spectra, implying emission measures >108 cm?6 pc. Except for one compact source with peculiar features, all other compact radio sources are found in dust lanes and do not have optical or near-infrared continuum counterparts. Four regions of extended, high brightness (EM >107 cm-6 pc) radio emission are found in our high-resolution map, including some as large as ~2'', or 30 pc, representing either associations of small H?II regions, or sheet-like structures of denser gas. The good correlation between 7 mm emission and Spitzer IRAC 8 ?m continuum-removed polycyclic aromatic hydrocarbon (PAH) feature suggests that PAH emission may track the recently formed OB stars. We find an excellent correlation between molecular gas and star formation, particularly dense gas traced by HCN, down to the ~45 pc scale in M82. We also find star formation efficiencies (SFEs) of 1%-10% on the same scale, based on CO maps. The highest SFE are found in regions with the highest dense gas fractions.
118400768
S IV In The NGC 5253 Supernebula: Ionized Gas Kinematics At High Resolution
The nearby dwarf starburst galaxy NGC 5253 hosts a deeply embedded radio-infrared supernebula excited by thousands of O stars. We have observed this source in the 10.5 {mu}m line of S{sup +3} at 3.8 km s{sup -1} spectral and 1.''4 spatial resolution, using the high-resolution spectrometer TEXES on the IRTF. The line profile cannot be fit well by a single Gaussian. The best simple fit describes the gas with two Gaussians, one near the galactic velocity with FWHM 33.6 km s{sup -1} and another of similar strength and FWHM 94 km s{sup -1} centered {approx}20 km s{sup -1} to the blue. This suggests a model for the supernebula in which gas flows toward us out of the molecular cloud, as in a 'blister' or 'champagne flow' or in the H II regions modelled by Zhu.
53662967
Supersymmetry of AdS and flat IIB backgrounds
A bstractWe present a systematic description of all warped AdSn ×wM10−n and ℝn−1,1×wM10−n$$ {\mathbb{R}}^{n-1,1}{\times}_w{M}^{10-n} $$ IIB backgrounds and identify the a priori number of supersymmetries N preserved by these solutions. In particular, we find that the AdSn backgrounds preserve N=2n2k$$ N={2}^{\left[\frac{n}{2}\right]}k $$ for n ≤ 4 and N=2n2+1k$$ N={2}^{\left[\frac{n}{2}\right]+1}k $$ for 4 < n ≤ 6 supersymmetries and for k∈ℕ+$$ k\in {\mathbb{N}}_{+} $$ suitably restricted. In addition under some assumptions required for the applicability of the maximum principle, we demonstrate that the Killing spinors of AdSn backgrounds can be identified with the zero modes of Dirac-like operators on M10−n establishing a new class of Lichnerowicz type theorems. Furthermore, we adapt some of these results to ℝn−1,1×wM10−n$$ {\mathbb{R}}^{n-1,1}{\times}_w{M}^{10-n} $$ backgrounds with fluxes by taking the AdS radius to infinity. We find that these backgrounds preserve N=2n2k$$ N={2}^{\left[\frac{n}{2}\right]}k $$ for 2 < n ≤ 4 and N=2n+12k$$ N={2}^{\left[\frac{n+1}{2}\right]}k $$ for 4 < n ≤ 7 supersymmetries. We also demonstrate that the Killing spinors of AdSn ×wM10−n do not factorize into Killing spinors on AdSn and Killing spinors on M10−n.