18820148
First Views of a Nearby LIRG: Star Formation and Molecular Gas in IRAS 04296+2923
We present a first look at the local luminous infrared galaxy (LIRG) IRAS 04296+2923. This barred spiral galaxy, overlooked because of its location behind the Taurus molecular cloud, is among the half dozen closest (D = 29 Mpc) LIRGs. More IR-luminous than either M82 or the Antennae, it may be the best local example of a nuclear starburst caused by bar-mediated secular evolution. We present Palomar J and Pa β images, Very Large Array continuum maps from λ= 20-1.3 cm, a subarcsecond Keck Long Wavelength Spectrometer image at 11.7 μm and Owens Valley Millimeter Array CO(1-0), ^(13)CO(1-0), and 2.7 mm continuum images. The J-band image reveals a symmetric barred spiral galaxy. Two bright, compact mid-infrared and radio sources in the nucleus mark a starburst that is energetically equivalent to ~10^5 O7 stars, separated by ≲50 pc. This is probably a pair of young super star clusters, with estimated stellar masses of ~10^7 M_☉ each. The nuclear starburst is forming stars at the rate of ~12 ± 6 M_☉ yr^(–1), or about half of the total star formation rate for the galaxy of ~25 ± 10 M_☉ yr^(–1). IRAS 04296+2923 is very bright in CO, and among the most gas-rich galaxies in the local universe. The ^(12)CO luminosity of the inner half kpc is equivalent to that of the entire Milky Way. While the most intense CO emission is extended over a 15" (2 kpc) diameter region, the nuclear starburst is confined to within 1"-2" (150-250 pc) of the dynamical center. Based on masses obtained with ^(13)CO, we find that the CO conversion factor in the nucleus is lower than the Galactic value, X^(Gal)_(CO) by a factor of three to four, typical of gas-rich spiral nuclei. The nuclear star formation efficiency (SFE) is ^(nuc)M_(gas)/SFR^(nuc) = 2.7 × 10^(–8)yr^(–1), corresponding to a gas consumption timescale, τ^(nuc)_(SF) ~ 4 × 10^7 yr. The SFE is 10 times lower in the disk, with τ^(disk)_(SF) ~ 3.3 × 10^8 yr. The low absolute SFE in the disk implies that the molecular gas is not completely consumed before it drifts into the nucleus, and is capable of fueling a sustained nuclear starburst. IRAS 04296+2923 appears to be beginning a 100 Myr period as an LIRG, during which it will turn much of its 6 × 10^9 M_☉ of molecular gas into a nuclear cluster of stars.
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.
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.
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.
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.
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.
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.