118849324
NGC 4102: High-Resolution Infrared Observations Of A Nuclear Starburst Ring
The composite galaxy NGC 4102 hosts a LINER nucleus and a starburst. We mapped NGC 4102 in the 12.8 μm line of [Ne II], using the echelon spectrometer TEXES on the NASA IRTF, to obtain a data cube with 15 spatial, and 25 km s–1 spectral, resolution. Combining near-infrared, radio, and the [Ne II] data shows that the extinction to the starburst is substantial, more than 2 mag at the K band, and that the neon abundance is less than half solar. We find that the star formation in the nuclear region is confined to a rotating ring or disk of 43 (~300 pc) diameter, inside the inner Lindblad resonance. This region is an intense concentration of mass, with a dynamical mass ~3 × 109 M ☉, and of star formation. The young stars in the ring produce the [Ne II] flux reported by Spitzer for the entire galaxy. The mysterious blue component of line emission detected in the near-infrared is also seen in [Ne II]; it is not a normal active galactic nucleus outflow.
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.
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.
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.
8334493
MOLECULAR GAS AND THE YOUNG STARBURST IN NGC 5253 REVISITED
We report the detection of CO(2–1) and 3.1 and 1.3 mm continuum emission toward the extremely young starburst in NGC 5253, with data taken from the Owens Valley Millimeter Array. Faint CO emission originates in five molecular clouds distributed along the prominent dust lane seen in visual images. With the gas, the morphology of NGC 5253 looks much like a dwarf elliptical version of the ‘‘ dust-lane ellipticals ’’ or ‘‘ polar-ring ’’ class of galaxies. The molecular gas resides in GMCs well away from the radio-IR super–star cluster/supernebula seen in the radio and infrared. The millimeter continuum data confirm that the 2 cm flux from the supernebula is optically thick; the Lyman continuum rate derived from the 1.3 mm continuum is NLyc � 6 � 10 52 s � 1 for the central � 20 00 . CO may underestimate the true molecular column density, as expected for a low-metallicity system, although there are regions along the dust lane that appear to have near-Galactic conversion factors. We estimate a total molecular gas mass of MH2 d10 7 M� . The molecular gas in the dust lane is falling into the galaxy, supporting an accretion hypothesis. The dust lane gas cannot therefore be causally associated with the current burst of star formation. A relatively small amount, MH2 d5 � 10 5 M� , of molecular gas is associated with the current starburst. We estimate a star formation efficiency of at least 25% and more likely � 75%, consistent with the formation of a bound cluster. Despite the extreme youth of the starburst, the specific trigger of the starburst remains elusive, although the infall of gas in the dust lane suggests that there is more star formation to come in NGC 5253.
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.