George Helou

The remarkable infrared galaxy Arp 220 = IC 4553

IRAS observations of the peculiar galaxy Arp 220 = IC 4553 show that it is extremely luminous in the far-infrared with a total luminosity of - 2 X 10^(12) L_☉. The infrared-to-blue luminosity ratio of this galaxy is - 80, which is the largest value of the ratio for galaxies in the UGC catalog, and places it in the range of the nunidentified infrared sources recently reported by Houck et al. in the IRAS all-sky survey. Other observations of Arp 220, combined with the luminosity in the infrared, allow either a Seyfert-like or starburst origin for this luminosity.

Emission Features and Source Counts of Galaxies in Mid-Infrared

In this work we incorporate the newest Infrared Space Observatory (ISO) results on the mid-infrared spectral energy distributions (MIR SEDs) of galaxies into models for the number counts and redshift distributions of MIR surveys. A three-component model, with empirically determined MIR SED templates of (1) a cirrus/photodissociation region component, (2) a starburst component, and (3) an active galactic nucleus (AGN) component, is developed for infrared (3-120 μm) SEDs of galaxies. The model includes a complete IRAS 25 μm selected sample of 1406 local galaxies (z ≤ 0.1). Results based on these 1406 spectra show that the MIR emission features cause significant effects on the redshift dependence of the K-corrections for fluxes in the WIRE 25 μm band and ISOCAM 15 μm band. This in turn will affect deep counts and redshift distributions in these two bands, as shown by the predictions of two evolution models [a luminosity evolution model with L ∝ (1 + z)3 and a density evolution model with ρ ∝ (1 + z)4]. The dips and bumps on curves of MIR number counts, caused by the emission features, should be useful indicators of the evolution mode. The strong emission features at ~6-8 μm will help the detections of relatively high redshift (z ~ 2) galaxies in MIR surveys. On the other hand, determinations of the evolutionary rate based on the slope of source counts and studies on the large-scale structures using the redshift distribution of MIR sources will have to treat the effects of the MIR emission features carefully. We have also estimated a 15 μm local luminosity function from the predicted 15 μm fluxes of the 1406 galaxies using the bivariate (15 μm vs. 25 μm luminosities) method. This luminosity function will improve our understanding of the ISOCAM 15 μm surveys.

Discovery of an infrared-loud quasar

The IRAS source 13349 + 2438 is a quasar with a redshift of z = 0.107, broad (15,000 km/s) emission lines and a luminosity of 2.7 x 10 to the 12th solar luminosity, emitted mostly between 4.8 and 12 microns. The object, a weak radio source, is the first previously unidentified quasar selected through its infrared emission and is the prototype radio-quiet, infrared-bright quasar. A dusty interstellar medium may be responsible for the infrared emission as well as for quenching the visual emission and attenuating the radio emission from the central energy source.

NED and SIMBAD Conventions for Bibliographic Reference Coding

The uniform 19—digit code used for bibliographic references within NED and SIMBAD was developed by both teams in consultation with Dr. H. Abt, editor of the Astrophysical Journal. The primary purpose of the “REF_CODE” is to provide a unique and traceable representation of a bibliographic reference within the structure of each database. However, in many cases, the code has sufficient information to be quickly deciphered by eye, and it is used frequently in the interfaces as a succinct abbreviation of a full bibliographic reference. Since its inception, it has become a standard code not only for NED and SIMBAD, but — with minor variations — for ADS and other bibliographic services. In addition, the acronyms for journals used as part of the code have become standards for some of the main astronomical journals in their own bibliographies.

The brightest high-latitude 12-micron IRAS sources

The Infrared Astronomical Satellite (IRAS) Point Source catalog was searched for sources brighter than 28 Jy (0 mag) at 12 μm with absolute galactic latitude greater than 30° excluding the Large Magellanic Cloud. The search resulted in 269 sources, two of which are the galaxies NGC 1068 and M82. The remaining 267 sources are identified with, or have infrared color indices consistent with late-type stars some of which show evidence of circumstellar dust shells. Seven sources are previously uncataloged stars. K and M stars without circumstellar dust shells, M stars with circumstellar dust shells, and carbon stars occupy well-defined regions of infrared color-color diagrams.

Capabilities of the NASA/IPAC extragalactic database in the era of a global virtual observatory

We review the capabilities of the NASA/IPAC Extragalactic Database (NED, http://ned.ipac.caltech.edu) for information retrieval and knowledge discovery in the context of a globally distributed virtual observatory. Since its inception in 1990, NED has provided astronomers world-wide with the results of a systematic cross-correlation of catalogs covering all wavelengths, along with thousands of extragalactic observations culled from published journal articles. NED is continuously being expanded and revised to include new catalogs and published observations, each undergoing a process of cross-identification to capture the current state of knowledge about extragalactic sources in a panchromatic fashion. In addition to assimilating data from the literature, the team in incrementally folding in millions of observations from new large-scale sky surveys such as 2MASS, NVSS, APM, and SDSS. At the time of writing the system contains over 3.3 million unique objects with 4.2 million cross-identifications. We summarize the recent evolution of NED from its initial emphasis on object name-, position-, and literature-based queries into a research environment that also assists statistical data exploration and discovery using large samples of objects. Newer capabilities enable intelligent Web mining of entries in geographically distributed astronomical archives that are indexed by object names and positions in NED, sample building using constraints on redshifts, object types and other parameters, as well as image and spectral archives for targeted or serendipitous discoveries. A pilot study demonstrates how NED is being used in conjunction with linked survey archives to characterize the properties of galaxy classes to form a training set for machine learning algorithms; an initial goal is production of statistical likelihoods that newly discovered sources belong to known classes, represent statistical outliers, or candidates for fundamentally new types of objects. Challenges and opportunities for tighter integration of NED capabilities into data mining tools for astronomy archives are also discussed.

Revised sizes and positions for the Mailyan dwarf galaxy catalog

New positions (good to ± 15 arcsec), revised sizes, and sample cross-identifications are presented for dwarf galaxies and published by Mailyan (1973). Of the 104 originally catalogued galaxies we were able to recover only 100, despite an extensive search of the red and blue POSS prints. Over half of the recovered objects were found to correspond to previously catalogued galaxies; few if any of these are dwarf spheroidal galaxies, but rather mostly dwarf irregulars of low surface brightness.

Analysis and Visualization of Multiwavelength Spectral Energy Distributions in the NASA/IPAC Extragalactic Database (NED)

The NASA/IPAC Extragalactic Database (NED,http://ned.ipac.caltech.edu/) currently contains over 4.5 million photometric measurements covering the electromagnetic spectrum from gamma rays through radio wavelengths for objects that are being cross-correlated among major sky surveys (e.g., SDSS, 2MASS, IRAS, NVSS, FIRST) and thousands of smaller, but unique and important, catalogs and journal articles. The ability to retrieve photometric data (including uncertainties, aperture information, and references) and display spectral energy distributions (SEDs) for individual objects has been available in NED for six years. In this paper we summarize recent enhancements that enable construction of large panchromatic data sets to facilitate multi-dimensional photometric analysis. The database can now be queried for samples of objects that meet flux constraints at any wavelength(e.g., objects with any available 20cm flux, or objects with fν10μm] > 5.0Jy). The ability to utilize criteria involving flux ratios (e.g., objects with fν[20cm]/fν[60μm] > 0.5) is under development. Such queries can be jointly combined with additional constraints on sky area, redshifts, object types, or sample membership, and the data are output with consistent physical units required for comparative analysis. Some results derived from fused photometric data in NED are presented to highlight the large number and diversity of available SEDs.

ATLAS probe for the study of galaxy evolution with 300,000,000 galaxy spectra

ATLAS (Astrophysics Telescope for Large Area Spectroscopy) Probe is a mission concept for a NASA probe-class space mission with primary science goal the definitive study of galaxy evolution through the capture of 300,000,000 galaxy spectra up to z=7. It is made of a 1.5-m Ritchey-Chretien telescope with a field of view of solid angle 0.4 deg2. The wavelength range is at least 1 μm to 4 μm with a goal of 0.9 μm to 5 μm. Average resolution is 600 but with a possible trade-off to get 1000 at the longer wavelengths. The ATLAS Probe instrument is made of 4 identical spectrographs each using a Digital Micro-mirror Device (DMD) as a multi-object mask. It builds on the work done for the ESA SPACE and Phase-A EUCLID projects. Three-mirror fore-optics re-image each sub-field on its DMD which has 2048 x 1080 mirrors 13.6 μm wide with 2 possible tilts, one sending light to the spectrograph, the other to a light dump. The ATLAS Probe spectrographs use prisms as dispersive elements because of their higher and more uniform transmission, their larger bandwidth, and the ability to control the resolution slope with the choice of glasses. Each spectrograph has 2 cameras. While the collimator is made of 4 mirrors, each camera is made of only one mirror which reduces the total number of optics. All mirrors are aspheric but with a relatively small P-V with respect to their best fit sphere making them easily manufacturable. For imaging, a simple mirror to replace the prism is not an option because the aberrations are globally corrected by the collimator and camera together which gives large aberrations when the mirror is inserted. An achromatic grism is used instead. There are many variations of the design that permit very different packaging of the optics. ATLAS Probe will enable ground-breaking science in all areas of astrophysics. It will (1) revolutionize galaxy evolution studies by tracing the relation between galaxies and dark matter from the local group to cosmic voids and filaments, from the epoch of reionization through the peak era of galaxy assembly; (2) open a new window into the dark universe by mapping the dark matter filaments to unveil the nature of the dark Universe using 3D weak lensing with spectroscopic redshifts, and obtaining definitive measurements of dark energy and modification of gravity using cosmic large-scale structure; (3) probe the Milky Ways dust-shrouded regions, reaching the far side of our Galaxy; and (4) characterize asteroids and other objects in the outer solar systems.