The IRAS bright galaxy sample. V. Multibeam photometry of galaxies with L(IR) ⩾ 10^(11) L_☉

Forty-seven galaxies from the IRAS Bright Galaxy Sample with infrared luminosities L_(IR)⩾ 10^(11) L_☉ have been measured at 1.3, 1.65, and 2.2 µm with beam diameters of 17", 33", and 55". These measurements, combined with 5" and 10" observations presented in an earlier paper, provide an opportunity to study the spatial distribution of the near-infrared emission in luminous IRAS galaxies. It is found that the unusually red near-infrared colors known previously for many of these galaxies are confined to the nuclear regions, whereas the outer disk regions have near-infrared colors essentially appropriate for a normal stellar population. Since dust reddening and emission are required to explain the unusual nuclear colors, it follows that the observed effects of dust in these galaxies are also confined primarily to the nuclei. Thus, it is probable that the far-infrared emission, the bulk of the entire luminosity in infrared luminous galaxies, is highly concentrated about the nuclei, and that the physical processes responsible for the unusual properties of infrared luminous galaxies tend to occur within the central regions, with diameters ≾1-3 kpc. The nuclei are found to have considerably higher 2.2 µm luminosities than are found in classical “starburst” nuclei, implying that infrared luminous galaxies are characterized by extremely high radiation densities in their central regions, presumably due to intense star formation activity and/or the presence of a dust-enshrouded quasar. However, the nuclei of the galaxies studied are typically not as luminous at 2.2 µm as classical Seyfert nuclei, which may be partly attributable to extinction from dust at near-infrared wavelengths, particularly for those sources in the sample that have been identified in the literature as having Seyfert nuclei. Finally, the large diameter beam measurements are used to obtain estimates of the total near-infrared emission. It is found that, since most of the infrared luminosity is coming from the nuclei, the global near-infrared properties of infrared luminous galaxies are not good tracers of infrared activity. Also, the contribution from the observed stellar emission to the total observed luminosity is found to be ≾25% for most of the galaxies in the sample, considerably smaller than the value for typical low-luminosity spiral galaxies

The near-infrared morphology of ultraluminous infrared galaxies

Near-infrared images at 1.25 μm, 1.65 μm, and 2.2 μm have been obtained of nine galaxies from the IRAS Bright Galaxy Sample with infrared luminosities L_(IR) ≥ 10^(12) L_☉. Two of the 2.2 μm images reveal previously undetected double nuclei, increasing the number of close double nuclei known for this sample from two to four. For three of these four sources, the colors of both nuclei are substantially different from those of normal spiral galaxies, indicating that the high activity state in high-luminosity mergers tends to occur in both nuclei. Three sources show 2.2 μm emission that is more centrally concentrated than the emission at 1.3 μm, a result that can be explained as the effects of dust emission and/or extinction or, alternatively, as the result of direct emission at 2.2 μm from the accretion disk of a central active galactic nucleus. Implications of these results for the model that galaxy collisions lead to quasar formation are briefly discussed. Finally, from the frequency and separation of the double nucleus sources, the lifetime of the ultraluminous phase of galaxies is estimated to be ~ 4 x 10^8 yr

The IRAS Bright Galaxy Sample. III. 1-10 µm observations and coadded IRAS data for galaxies with L_(IR) ⩾ 10^(11) L⊙

Galaxies from the IRAS Bright Galaxy Sample with infrared luminosities L_(IR) ⩾ 10^(11) L⊙ have been measured at 1.3, 1.6, 2.2, 3.7, and 10 µm. In addition, coadded IRAS measurements at all four IRAS bands have been obtained. It is found that an increase in the total infrared luminosity above L_(IR) ⩾ 10^(11) L⊙ is correlated with increased emission from hot dust with characteristic temperatures ~800 K contributing a substantial fraction of the 2.2 and 3.7 µm emission. This hot dust emission appears to “turn on” at luminosities of roughly 10^(11) L⊙. The far-infrared emission cannot be modeled with a single dust temperature, but requires a cold (T~30-50 K) component coupled with a warmer (T≳70 K) component. Although the relative contribution from the cold component decreases with increasing luminosity, the temperature of the warmer component is independent of luminosity. The f_v (12 µm)/f_v (25 µm) ratios for the galaxies in this sample are small compared with other extragalactic objects, indicating that the radiation at 12 and 25 µm is dominated by emission from large dust grains radiating at high temperatures, rather than PAHs. The spatial distribution of the 10 µm emission indicates a substantial extended component for most of the galaxies in this sample, implying that star-formation processes contribute significantly to the luminosities. However, one-third of the galaxies have exponential scale sizes characteristic of compact sources, and half of the galaxies have 10 µm emission consistent with a contribution of 50% or more from a central point source

Dust and gas in luminous infrared galaxies - results from SCUBA observations

We present new data taken at 850 $\mu$m with SCUBA at the JCMT for a sample of 19 luminous infrared galaxies. Fourteen galaxies were detected. We have used these data, together with fluxes at 25, 60 and 100 $\mu$m from IRAS, to model the dust emission. We find that the emission from most galaxies can be described by an optically thin, single temperature dust model with an exponent of the dust extinction coefficient ($k_\lambda \propto \lambda^{-\beta}$) of $\beta \simeq 1.5 - 2$. A lower $\beta\simeq 1$ is required to model the dust emission from two of the galaxies, Arp 220 and NGC 4418. We discuss various possibilities for this difference and conclude that the most likely is a high dust opacity. In addition, we compare the molecular gas mass derived from the dust emission, $M_{dust}$, with the molecular gas mass derived from the CO emission, $M_{CO}$, and find that $M_{CO}$ is on average a factor 3 higher than $M_{dust}$.Comment: 10 pages, 6 figures, latex, with MN-macros, accepted by MNRAS - revised version (changed flux values for some galaxies

The double nucleus of ARP 220 unveiled

IR imaging at the f/415 focus of the Palomar 200 inch telescope with 0."39 x 0."49 resolution is used to determine that the ultraluminous IRAS galaxy Arp 220 has a double nucleus with separation 0."95. The presence of two closely separated nuclei (330 pc) confirms the circumstantial evidence that Arp 220 is an evolved merger remnant; and the degree of correlation between the IR and cm wavelength radio emission shows that it is an ongoing merger containing two active nuclei accompanied by circumnuclear starbursts of moderate intensity. The extent of the 2.2 µm radiation is evidence that the flux is most probably dominated by starlight. It is pointed out that if the nuclear activity is powered by accretion onto black holes, then a black hole binary will be formed. Such a binary may be an essential ingredient of many quasars, and therefore Arp 220 may suggest another connection between mergers, ultraluminous IRAS galaxies, and quasars

Anomalous Features of EMT during Keratinocyte Transformation

During the evolution of epithelial cancers, cells often lose their characteristic features and acquire a mesenchymal phenotype, in a process known as epithelial-mesenchymal transition (EMT). In the present study we followed early stages of keratinocyte transformation by HPV16, and observed diverse cellular changes, associated with EMT. We compared primary keratinocytes with early and late passages of HF1 cells, a cell line of HPV16-transformed keratinocytes. We have previously shown that during the progression from the normal cells to early HF1 cells, immortalization is acquired, while in the progression to late HF1, cells become anchorage independent. We show here that during the transition from the normal state to late HF1 cells, there is a progressive reduction in cytokeratin expression, desmosome formation, adherens junctions and focal adhesions, ultimately leading to poorly adhesive phenotype, which is associated with anchorage-independence. Surprisingly, unlike “conventional EMT”, these changes are associated with reduced Rac1-dependent cell migration. We monitored reduced Rac1-dependent migration also in the cervical cancer cell line SiHa. Therefore we can conclude that up to the stage of tumor formation migratory activity is eliminated

Millimeter Observations of Luminous IRAS Galaxies

We have observed a group of luminous IRAS galaxies in the continuum at 1.25mm with the Caltech Submillimeter Observatory in 1988 May and September. Table I lists the galaxies and their measured flux densities in a 30 beam. The observing conditions for these observations were excellent and stable. Uranus was the fundamental flux density calibrator, it was assumed to have a brightness temperature of 100 K at 1.25 mm (Hildebrand et al. 1985; Ulich 1974). Integration times were typically a half hour per night, repeated for a total of two or three nights. The bolometer NEFD is 0.5 Jy Hz^(-1/2) giving statistical errors of 8 to 12 mJy. Systematic uncertainties have not been included in the error estimates, but we believe that they are small, at most 20%