Interferometric CO observations of the ultraluminous IRAS galaxies ARP 220, IC 694/NGC 3690, NGC 6420 and NGC 7469

High resolution CO observations of the IRAS galaxies Arp 220, IC 694/NGC 3690, NGC 6240 and NGC 7469 were made with the Millimeter Wave Interferometer of the Owen Valley Radio Observatory. These yield spatial information on scales of 1 to 5 kpc and allow the separation of compact condensations from the more extended emission in the galaxies. In the case of the obviously interacting system IC 694/NGC 3690 the contributions of each component can be discerned. For that galaxy, and also for Arp 220, the unusually high lumonisities may be produced by nonthermal processes rather than by intense bursts of star formation

Near-threshold high-order harmonic spectroscopy with aligned molecules

We study high-order harmonic generation in aligned molecules close to the ionization threshold. Two distinct contributions to the harmonic signal are observed, which show very different responses to molecular alignment and ellipticity of the driving field. We perform a classical electron trajectory analysis, taking into account the significant influence of the Coulomb potential on the strong-field-driven electron dynamics. The two contributions are related to primary ionization and excitation processes, offering a deeper understanding of the origin of high harmonics near the ionization threshold. This work shows that high harmonic spectroscopy can be extended to the near-threshold spectral range, which is in general spectroscopically rich.Comment: 4 pages, 4 figure

Studying the universality of field induced tunnel ionization times via high-order harmonic spectroscopy

High-harmonics generation spectroscopy is a promising tool for resolving electron dynamics and structure in atomic and molecular systems. This scheme, commonly described by the strong field approximation, requires a deep insight into the basic mechanism that leads to the harmonics generation. Recently, we have demonstrated the ability to resolve the first stage of the process -- field induced tunnel ionization -- by adding a weak perturbation to the strong fundamental field. Here we generalize this approach and show that the assumptions behind the strong field approximation are valid over a wide range of tunnel ionization conditions. Performing a systematic study -- modifying the fundamental wavelength, intensity and atomic system -- we observed a good agreement with quantum path analysis over a range of Keldysh parameters. The generality of this scheme opens new perspectives in high harmonics spectroscopy, holding the potential of probing large, complex molecular systems.Comment: 11 pages, 5 figure

Black hole in the West Nucleus of Arp 220

We present new observations with the IRAM Interferometer, in its longest-baseline configuration, of the CO(2-1) line and the 1.3mm dust radiation from the Arp 220 nuclear region. The dust source in the West nucleus has a size of 0.19 x 0.13 arcsec and a 1.3mm brightness temperature of 90K. This implies that the dust ring in the West nucleus has a high opacity, with tau = 1 at 1.1mm. Not only is the dust ring itself optically thick in the submm and far-IR, but it is surrounded by the previously-known, rapidly rotating molecular disk of size 0.5 arcsec that is also optically thick in the mid-IR. The molecular ring is cooler than the hot dust disk because the CO(2-1) line is seen in absorption against the dust disk. The dust ring is massive (1E9 solar masses), compact (radius 35pc), and hot (true dust temperature 170K). It resembles rather strikingly the dust ring detected around the quasar APM 08279+52, and is most unlike the warm, extended dust sources in starburst galaxies. Because there is a strong temperature gradient from the hot dust ring to the cooler molecular disk, the heating must come from a concentrated source, an AGN accretion disk that is completely invisible at optical wavelengths, and heavily obscured in hard X-rays.Comment: Reference list updated for 2007 publications; estimated position errors increase

Millimeter Observations of Optically Selected Quasars

We have observed a group of optically selected quasars at a wavelength of 1.25mm with the Caltech Submillimeter Observatory in 1988 May. Except for Mrk 231, they were chosen from the PG sample of quasars (Schmidt and Green 1983) and are thus UV bright objects. All of them, except for PG 2209+184, were also detected at 60μm by IRAS

Near Infrared Observations of IRAS 09104+4109

Near infrared imaging and grism spectroscopy of the high luminosity infrared bright galaxy IRAS 09104+4109 have been obtained with the W. M. Keck Telescope. The imaging shows 6 “knots” of emission projected against the extended stellar envelope of the cD galaxy thought to be the source of the large far infrared luminosity. The luminosities of the knots are consistent with the bulges of galaxies accreting onto the central galaxy. In addition, there are 11 companion galaxies seen at radii of 40-150 kpc from the cD nucleus. These objects have colors in the range R—K~ 3.5±0.5 mag, J-H~0.9±0.2 mag H-K ~0.7±0.2 mag, which are consistent with galaxies at a redshift of 0.4. The companion galaxies have luminosities comparable to or less than the characteristic luminosity (L^*) of field galaxies. While the central cD galaxy is identified with the luminous infrared source, it appears to be a quiescent, radio-quiet galaxy, showing no evidence from its near infrared colors for a highly reddened nucleus as seen in other infrared luminous galaxies. The grism spectroscopy shows forbidden lines of low ionization stages of sulfer, iron, and oxygen, as well as hydrogen recombination lines and a strong line of neutral helium. A visual extinction of Av—2 mag is derived to the narrow line region surrounding the galaxy nucleus, based on the line ratios [S II]1.03 µm/0.407 µm and Pδ/Hβ. The near infrared spectrum is consistent with the optical classification of this system being a Seyfert 2 nucleus

The IRAS Revised Bright Galaxy Sample (RBGS)

IRAS flux densities, redshifts, and infrared luminosities are reported for all sources identified in the IRAS Revised Bright Galaxy Sample (RBGS), a complete flux-limited survey of all extragalactic objects with total 60 micron flux density greater than 5.24 Jy, covering the entire sky surveyed by IRAS at Galactic latitude |b| > 5 degrees. The RBGS includes 629 objects, with a median (mean) sample redshift of 0.0082 (0.0126) and a maximum redshift of 0.0876. The RBGS supersedes the previous two-part IRAS Bright Galaxy Samples, which were compiled before the final ("Pass 3") calibration of the IRAS Level 1 Archive in May 1990. The RBGS also makes use of more accurate and consistent automated methods to measure the flux of objects with extended emission. Basic properties of the RBGS sources are summarized, including estimated total infrared luminosities, as well as updates to cross-identifications with sources from optical galaxy catalogs established using the NASA/IPAC Extragalactic Database (NED). In addition, an atlas of images from the Digitized Sky Survey with overlays of the IRAS position uncertainty ellipse and annotated scale bars is provided for ease in visualizing the optical morphology in context with the angular and metric size of each object. The revised bolometric infrared luminosity function, phi(L_ir), for infrared bright galaxies in the local Universe remains best fit by a double power law, phi(L_ir) ~ L_ir^alpha, with alpha = -0.6 (+/- 0.1), and alpha = -2.2 (+/- 0.1) below and above the "characteristic" infrared luminosity L_ir ~ 10^{10.5} L_solar, respectively. (Abridged)Comment: Accepted for publication in the Astronomical Journal. Contains 50 pages, 7 tables, 16 figures. Due to astro-ph space limits, only 1 of 26 pages of Figure 1, and 1 of 11 pages of Table 7, are included; full resolution Postscript files are available at http://nedwww.ipac.caltech.edu/level5/March03/IRAS_RBGS/Figures/ . Replacement: Corrected insertion of Fig. 15 (MethodCodes.ps) in LaTe

K band Spectroscopy of Ultraluminous Infrared Galaxies: The 2 Jy Sample

We present near-infrared spectroscopy for a complete sample of 33 ultraluminous infrared galaxies at a resolution of R\approx 1000. Most of the wavelength range from 1.80-2.20 microns in the rest frame is covered, including the Pa-alpha and Br-gamma hydrogen recombination lines, and the molecular hydrogen vibration-rotation 1-0 S(1) and S(3) lines. Other species, such as He I, [Fe II], and [Si VI] appear in the spectra as well, in addition to a number of weaker molecular hydrogen lines. Nuclear extractions for each of the individual galaxies are presented here, along with spectra of secondary nuclei, where available. The Pa-alpha emission is seen to be highly concentrated on the nuclei, typically with very little emision extending beyond a radius of 1 kpc. Signatures of active nuclei are rare in the present sample, occurring in only two of the 33 galaxies. It is found that visual extinctions to the nuclei via the Pa-alpha/Br-gamma line ratio in excess of 10 magnitudes are relatively common among ULIRGs, and that visual extinctions greater than 25 mag are necessary to conceal a QSO emitting half the total bolometric luminosity. The vibration-rotation lines of molecular hydrogen appear to be predominantly thermal in origin, with effective temperatures generally around 2200 K. The relative nuclear velocities between double nucleus ULIRGs are investigated, through which it is inferred that the maximum deprojected velocity difference is about 200 km/s. This figure is lower than the velocities predicted by physical models of strong interactions/mergers of large, gas-rich galaxies.Comment: 52 pages (19 with just figures), 9 figures, accepted for publication in the Astronomical Journal; Table 3 not formatted properly on astro-ph: get source and print Murphy.tab3.p

Mid-infrared spectral evidence for a luminous dust enshrouded source in Arp220

We have re-analyzed the 6-12 micron ISO spectrum of the ultra-luminous infrared galaxy Arp220 with the conclusion that it is not consistent with that of a scaled up version of a typical starburst. Instead, both template fitting with spectra of the galaxies NGC4418 and M83 and with dust models suggest that it is best represented by combinations of a typical starburst component, exhibiting PAH emission features, and a heavily absorbed dust continuum which contributes ~40% of the 6-12 micron flux and likely dominates the luminosity. Of particular significance relative to previous studies of Arp220 is the fact that the emission feature at 7.7 micron comprises both PAH emission and a broader component resulting from ice and silicate absorption against a heavily absorbed continuum. Extinction to the PAH emitting source, however, appears to be relatively low. We tentatively associate the PAH emitting and heavily dust/ice absorbed components with the diffuse emission region and the two compact nuclei respectively identified by Soifer et al. (2002) in their higher spatial resolution 10 micron study. Both the similarity of the absorbed continuum with that of the embedded Galactic protostars and results of the dust models imply that the embedded source(s) in Arp220 could be powered by, albeit extremely dense, starburst activity. Due to the high extinction, it is not possible with the available data to exclude that AGN(s) also contribute some or all of the observed luminosity. In this case, however, the upper limit measured for its hard X-ray emission would require Arp220 to be the most highly obscured AGN known.Comment: 11 pages, 9 figures. Accepted for publication in A&A. Also available at http://www.astro.rug.nl/~spoon/publications.htm

One Millimeter Continuum Observations of High Redshift Quasars

Upper limits to the one-millimeter continuum flux densities of the high redshift quasars 82 1225 + 31, Ton 490, and PHL 957 are presented. The upper limit to the power observed from these quasars at I mm is, on average, ½ the observed power in the continuum at Lɑ. These observations are used to constrain the temperature of a hypothètical dust shell which reddens the quasar line and continuum emission by an extinction optical depth sufficient to account for the anomalously low Lɑ/Hɑ emission line ratio observed in each of these quasars. For the quasars studied, dust shell temperatures between 25 K and 50 to 95 K are prohibited by the present data. A dust shell at a temperature within this span reradiating all the power absorbed from the quasar ultraviolet continuum would produce a one-millimeter flux density greater than the measured upper limit. The average radius of the model dust shell cannot be between 70 kpc and 1 Mpc