Roger Ball

The mid-infrared radio correlation at high angular resolution : NGC 253

We present high angular resolution (1″.2), narrow-band (Δλ/λ=0.1) images of the nucleus of NGC 253 at three wavelengths in the mid-infrared (8.5, 10.0, and 12.5 μm). We find that most of the mid-IR flux in the nucleus of NGC 253 derives from a very small region ≤120 pc in diameter. Within this small region there are three spatially and spectrally distinct IR components: two bright compact sources, and a surrounding envelope of low-level, diffuse emission. The mid-IR and 6 cm radio are loosely correlated in position but not in brightness. The implication is that the mid-IR-radio correlation may begin to break down on small spatial scales relevant to individual star-forming regions and large individual sources

The environments of young stars : mid-infrared and molecular line imaging

Young late-type stars in massive-star-forming regions, though much fainter than their early-type neighbors, are detectable in brightened molecular line emission, IR continuum, and H 2 O maser emission. The stars are found deeply embedded in high-temperature, high-density gas and near newly formed massive stars. Because the time scales in massive-star-forming regions are so short, these lower mass stars must be in very early evolutionary stages relative to their much longer lifetimes

Subarcsecond mid-infrared imaging of the nuclei of the infrared bright galaxies NGC 1614 and NGC 7469

The first subarcsecond resolution mid-IR images of the nuclei of two galaxies from the IRAS bright sample, NGC 1614 and NGC 7469, are reported. These results show that the starburst galaxy NGC 1614 contains a double structure in the nuclear region. Most of the flux, 78% of 650 ± 50 mJy, is emitted in two unresolved regions of 0.6″ FWHM (190 pc at 64 Mpc) of nearly equal strength separated by 0.6″ (200 pc). Most of the remaining flux is derived from a small arm 1″ in length (310 pc). The Seyfert I galaxy NGC 7469 shows an elongated structure, 1.4″ × 0.7″ (450 × 220 pc at 66 Mpc)

A dynamical analysis of the barred spiral galaxy NGC 3359

The dynamics of gas in the disk of the SBc galaxy NGC 3359 are studied by means of hydrodynamical simulations. These models are compared to the observed structure and kinematics of neutral hydrogen in the galaxy, as mapped with a resolution of 1 kpc at the VLA. Near-infrared surface photometric observations of the stellar bar are used to constrain models further. The most successful models reproduce the essentials of the observed gaseous spiral structure in both its distribution and kinematics. However, this success is achieved only by arbitrarily imposing an oval distortion potential which does not correspond to the shape of the observed stellar bar

Thermal dust imaging - The onset of asymmetry in the ultracompact H II region G5.89 - 0.39

We have obtained images of the compact radio and infrared nebula G5.89-0.39 with the Berkeley/IGPP mid-infrared array camera. The images have a resolution of 1″.1 and cover five wavelength bands between 8 and 13 μm. On the basis of the structure and spectral energy distribution, we concur with previously published assertions that G5.89-0.39 is an ultracompact H II region. The infrared emission is extended over 6″×4″.5, very similar to the objects size in published high-resolution radio continuum maps

Mid-infrared imaging of Markarian 231 and Arp 220

High angular resolution observations of Arp 220 and Mrk 231 provide images of the nuclei and show that the source of the strong mid-IR emission is confined to regions less than about 0.5 arcsec or 400 pc in diameter in Mrk 231 and less than 1.5 arcsec x 0.9 arcsec or 320 x 530 pc in Arp 220. If much of the far-IR emission also derives from such a small region, the implied radiation densities are quite high, equivalent to one O star per cu pc. Although in normal galaxies the near-IR traces an older population of evolved, cool stars, such high radiation densities in the IR bright galaxies suggest the possibility that the spatial correlation observed between the near-IR, mid-IR, and radio may hold because emission in all three bands is associated with hot interstellar gas and dust. 23 refs.

CHARACTERIZATION OF SOLID STATE ARRAY CAMERAS FOR THE MID-IR

We present a characterization of some processes affecting the performance of solid state array cameras designed for ground based astronomical imaging in the 8–13μm atmospheric window. Our discussion includes a novel model for electron-hole generationrecombination noise based on the probable pathlength of an electron in a photoconductor. We use the Berkeley mid-IR Array Camera as an example. For this camera, the results show that the total optical system composed of the camera, a 3m telescope, and the atmosphere has an efficiency of about 3%, a 1σ noise equivalent flux density of 25 mJy min−1/2arcsec−2 measured over a Δλ/λ=10% band width, and a noise equivalent expressed as the ambient temperature thermal black body noise of 23%.

High angular resolution broad-band imaging in the mid-infrared : the infrared bright galaxy NGC 34

A high angular resolution (1″) mid-IR image of the IR-bright galaxy NGC 34 is reported. The observation shows the mid-IR emission to be very compact, ≤ 2.3″ × 1.7″. This and previous observations indicate sizes smaller than predicted by starburst models for the emission. The achieved sensitivity, 15 mJy minutes −1/2 arcsec −2 , is the highest sensitivity ever obtained for any observation with a mid-IR array camera

The mid-IR radio correlation at high angular resolution: NGC253

We present high angular resolution (1.2″), narrow band (Δλ/λ = 0.1) images of the nucleus of NGC253 at three wavelengths in the mid-IR (8.5, 10.0, and 12.5µm). We find that most of the mid-IR flux in the nucleus of NGC253 derives from a very small region ≤ 120 pc in diameter. Within this small region there are three spatially and spectrally distinct IR components: two bright compact sources, and a surrounding envelope of low level, diffuse emission. The mid-IR and 6cm radio are loosely correlated in position but not in brightness. The implication is that the mid-IR — radio correlation may begin to break down on small spatial scales relevant to individual star forming regions and large individual sources. These variations in the mid-IR spectra and in the radio-IR correlation imply that the nuclear emission is excited by more than one mechanism and source type.