17728532
The Off-Nuclear Starbursts in NGC 4038/4039 (The Antennae Galaxies)
Imaging of the Antennae galaxies (NGC 4038/4039) with the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope reveals large concentrations of star-forming activity away from both nuclei of the two merging galaxies. These images confirm earlier findings based on Infrared Space Observatory (ISO) data with lower angular resolution. The short-wavelength emission shows numerous compact sources identified as stellar clusters. At the longer wavelengths, bright, more amorphous and filamentary features correlate well with the known distributions of denser gas, warm dust, and H II regions. There are also fainter, more diffuse components at all wavelengths that permeate the entire region and extend into the two tidal tails. Nonstellar dust emission dominates the 5.8 and 8.0 μm images, accounting for as much as 79% of the light at 5.8 μm and 95% at 8 μm, averaged over the entire galaxy. Assuming that the nonstellar emission traces star formation, the IRAC data provide a view into the total underlying star-forming activities unaffected by obscuration. Using the flux ratio of nonstellar to stellar emission as a guide, we map the local star formation rate in the Antennae and compare that to similar measurements in both normal and infrared-luminous galaxies. This rate in the active regions is found to be as high as those seen in starburst and some ultraluminous infrared galaxies on a "per unit mass" basis. The two galactic centers actually have lower star-forming rates than the off-nuclear regions despite the presence of abundant dense gas and dust, suggesting that the latter is a necessary but not sufficient condition for ongoing star formation.
18719624
Warm Molecular Gas in Galaxy-Galaxy Merger NGC 6090
We present Submillimeter Array observations of the CO (2-1) and (3-2) transitions toward the merging galaxies of NGC 6090. The high-resolution CO data reveal three gas concentrations. The main component is peaking in the overlap region between the two galaxies, where the near-IR and radio continuum emission are weak. The CO (2-1) emission from the face-on galaxy NGC 6090E is somewhat stronger than that from the edge-on galaxy NGC 6090W. The CO (3-2) emission peaks in the overlap region, similar to the CO (2-1) emission. More than 50% of the CO (3-2) emission arises from the 2'' (1.2 kpc) area of the overlap region. There appears to be CO (3-2) emission toward the nuclear region and the northwest arm of NGC 6090E, while no CO (3-2) emission is detected toward NGC 6090W. Unlike the CO gas, most of the radio continuum emission comes from NGC 6090E. The strong CO emission, together with the weak radio continuum emission, suggests that star formation in the overlap region has not proceeded long enough to produce significant numbers of supernovae that would be detectable from their radio continuum emission.
119548246
Subarcsecond Resolution Mid-Infrared Observations of Super Star Clusters in the Antennae (NGC 4038/4039)*
We present ground-based subarcsecond mid-infrared imaging and spectroscopy of young super star clusters in the overlap region of the merging galaxies NGC 4038/4039 (the Antennae) obtained with the VLT Imager and Spectrometer for mid-InfraRed (VISIR). With its unprecedented spatial resolution, VISIR begins for the first time to resolve the H II/photodissociation region complexes around the star-forming regions. In the N-band spectra of two young star clusters, unexpectedly low polycyclic aromatic hydrocarbon (PAH) emission is observed, compared to what is seen with the Infrared Space Observatory and with the Spitzer Space Telescope. We conclude that a large fraction of the PAH emission cannot be directly associated with the super star clusters but originates from an extended region of at least 215 pc radius around the clusters. In the distribution of [Ne II] 12.81 μm emission, a highly obscured cluster is discovered that does not have an optical or near-infrared counterpart.
119282064
Topological field theory and thermal responses of interacting topological superconductors
We investigate the three-dimensional, time-reversal invariant topological superconductors with generic interaction by their response to external fields. The first description is a gravitational topological field theory, which gives a $Z_2$ classification of topological superconductors, and predicts a half-quantized thermal Hall effect on the surface. The second description introduces an s-wave proximity pairing field on the surface, and the associated topological defects give an integer $Z$ classification of the topological superconductors.
119180657
THE STRUCTURE OF ACTIVE MERGER REMNANT NGC 6240 FROM IRAC OBSERVATIONS
NGC 6240 is a rare object in the local universe: an active merger remnant viewed at the point of merging where two active galactic nuclei are visible. We present IRAC data of this object, providing high-sensitivity maps of the stellar and PAH distribution in this complicated system. We use photometry to analyze the variation in these distributions with radius and provide an SED in the four IRAC bands: 3.6, 4.5, 5.8, and 8 μm. We fit the radial profiles of the 3.6 μm band to r1/4 and exponential profiles to evaluate the structure of the remnant. Finally, we compare the IRAC images with multiwavelength data and examine how outflows in the X-ray, Hα, and CO correlate with 8 μm emission. The results support the general picture of NGC 6240 as a system experiencing a major merger and transitioning from a disk galaxy to a spheroid. The sensitivity of IRAC to low surface brightness mid-infrared features provides detailed information on the extended distributions of stars and dust in this rare system.
5667549
Large Misalignment between Stellar and Dust Bars in NGC 3488 Revealed by Spitzer and SDSS
A large position angle misalignment between the stellar and dust bars in the late-type barred spiral NGC 3488 was discovered, using mid-infrared images from the Spitzer Space Telescope and optical images from the Sloan Digital Sky Survey (SDSS). The angle between the two distinctive bar patterns was measured to be 25±2, larger than most of the misalignments found previously in barred systems based on Hα or H ii/CO observations. The stellar bar is bright at optical and 3.6μm, while the dust bar is more prominent in the 8μm band but also shows up in the SDSS u and g-band images, suggesting a rich interstellar medium environment harboring ongoing star formation. The angular misalignment between the two bars in NGC 3488 is unlikely to have been caused by spontaneous bar formation. We suggest that the two bars have different formation histories, and that the large misalignment was triggered by a tidal interaction with a small companion. A statistical analysis of a large sample of nearby galaxies with archival Spitzer data indicates that bar structure such as that seen in NGC 3488 is quite rare in the local Universe. Subject headings: galaxies: individual(NGC 3488) — galaxies: spiral — galaxies: structure — infrared: galaxies National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, P. R. China; caochen@bao.ac.cn, hwu@bao.ac.cn Graduate School, Chinese Academy of Sciences, Beijing 100039, China Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 College of Physical Sciences, Graduate School, Chinese Academy of Sciences, P.O. Box 3908, 100039 Beijing, China
283978
In-flight performance and calibration of the Infrared Array Camera (IRAC) for the Spitzer Space Telescope
The Infrared Array Camera (IRAC) is one of three focal plane instruments on board the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 μm in two nearly adjacent fields of view. We summarize here the in-flight scientific, technical, and operational performance of IRAC.
54803118
Analysis of the scalar doubly heavy tetraquark states with QCD sum rules
In this article, we perform a detailed study of the mass spectrum of the scalar doubly charmed and doubly bottom tetraquark states using the QCD sum rules.
121348798
Scaling theory of the Hall coefficient near the metal-insulator transition, a renormalization-group approach
Abstract We investigate the critical properties of the Hall conduxtivity in weak magetic fields near the disorder driven metal-insulator transition. We derive an effective lagrangian governing the interactions of the diffusive modes in the presence of time-reversal and particle-hole symmetry breaking and identify a new operator relevant to the scaling behavior of the weak-field Hall conductivity. A Wilson-Polyakov renormalization-group analysis is carried out and the flow equations are obtained near two dimensions. We show that the perturbative behavior of the Hall conductivity in the weakly localized regime, in two dimensions, is not simply related to the critical behavior of the Hall conductivity, due to the role played by a new scaling variable. Solving the renormalization-group equations close to the zero-field fixed point, our theory predicts that the Hall number vanishes at the mobility edge with an exponent g = 1 in agreement with several experimental observations. We clarify the connection between the field-theoretic approach and the conventional perturbative approach and elucidate why perturbation in the disorder, which is valid in the weak localization regime fails to predict the correct critical behavior.
117522082
First results on dilepton production at the Bevalac
We report on preliminary results of direct electron pair measurements in p+Be at 4.9 GeV and 2.1 GeV and Ca+Ca at 1.95 GeVA collisions at the Bevalac. The results are compared to existing data in p+Be at 12.1 GeV and ..pi../sup -/p at 15.9 and 16.9 GeV.
15362103
Spitzer Mid-Infrared Upper Limits on Anomalous X-Ray Pulsars 1E 1048.1-5937, 1RXS J170849.0-400910, and XTE J1810-197
We report on mid-infrared imaging observations of the anomalous X-ray pulsars (AXPs) 1E 1048.1-5937, 1RXS J170849.0-400910, and XTE J1810-197. The observations were carried out at 4.5 and 8.0 μm with the Infrared Array Camera and at 24 μm with the Multiband Imaging Photometer on the Spitzer Space Telescope. No mid-infrared counterparts were detected. As infrared emission from AXPs may be related to their X-ray emission either via the magnetosphere or via a dust disk, we compare the derived upper limits on the infrared/X-ray flux ratios of the AXPs to the same ratio for 4U 0142+61, an AXP previously detected in the mid-infrared range. The upper limits are above the flux ratio for 4U 0142+61, indicating that if AXPs have similar infrared/X-ray flux ratios, our observations were not sufficiently deep to detect our AXP targets. For XTE J1810-197, the upper limits set a constraint on its rising radio energy spectrum, suggesting a spectral break between 4.2 × 1010 and 6 × 1013 Hz.