Juan E. Cabanela

The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later

We have used the Very Large Array (VLA) FIRST survey and the Automated Plate Measuring Facility (APM) catalog of the Palomar Observatory Sky Survey I (POSS-I) plates as the basis for constructing a new radio-selected sample of optically bright quasars. This is the first radio-selected sample that is competitive in size with current optically selected quasar surveys. Using only two basic criteria, radio-optical positional coincidence and optical morphology, quasars and BL Lac objects can be identified with 60% selection efficiency; the efficiency increases to 70% for objects fainter than 17 mag. We show that a more sophisticated selection scheme can predict with better than 85% reliability which candidates will turn out to be quasars. This paper presents the second installment of the FIRST Bright Quasar Survey (FBQS), with a catalog of 636 quasars distributed over 2682 deg2. The quasar sample is characterized and all spectra are displayed. The FBQS detects both radio-loud and radio-quiet quasars out to redshift z > 3. We find a large population of objects of intermediate radio loudness; there is no evidence in our sample for a bimodal distribution of radio characteristics. The sample includes ~29 broad absorption line quasars, both high and low ionization, and a number of new objects with remarkable optical spectra.

The Automated Plate Scanner Catalog of the Palomar Observatory Sky Survey. II. The Archived Database

The Minnesota Automated Plate Scanner Catalog of the POSS I has been available on-line since 1994. We are now archiving it for distribution to the national and international data centers. In this brief paper, we describe the calibration of the digitized data and the characteristics of the archived database.

Mapping the Asymmetric Thick Disk. III. The Kinematics and Interaction with the Galactic Bar

In the first two papers of this series, Larsen et?al. describe our faint CCD survey in the inner Galaxy and map the overdensity of thick disk stars in Quadrant 1 (Q1) to 5?kpc or more along the line of sight. The regions showing the strongest excess are above the density contours of the bar in the Galactic disk. In this third paper on the asymmetric thick disk, we report on radial velocities and derived metallicity parameters for over 4000 stars in Q1, above and below the plane, and in Quadrant 4 (Q4) above the plane. We confirm the corresponding kinematic asymmetry first reported by Parker et?al., extended to greater distances and with more spatial coverage. The thick disk stars in Q1 have a rotational lag of 60-70?km?s?1 relative to circular rotation, and the metal-weak thick disk stars have an even greater lag of 100?km?s?1. Both lag their corresponding populations in Q4 by 30?km?s?1. Interestingly, the disk stars in Q1 also appear to participate in the rotational lag by about 30?km?s?1. The enhanced rotational lag for the thick disk in Q1 extends to 4?kpc or more from the Sun. At 3-4?kpc, our sight lines extend above the density contours on the near side of the bar, and as our lines of sight pass directly over the bar the rotational lag appears to decrease. This is consistent with a gravitational wake induced by the rotating bar in the disk which would trap and pile up stars behind it. We conclude that a dynamical interaction with the stellar bar is the most probable explanation for the observed kinematic and spatial asymmetries.

Mapping the Asymmetric Thick Disk: The Hercules Thick-Disk Cloud

The stellar asymmetry of faint thick-disk/inner-halo stars in the first quadrant (l = 20°-45°) that was first reported by Larsen & Humphreys and investigated further by Parker et al. has recently been confirmed by the Sloan Digital Sky Survey (SDSS). Their interpretation of the excess in the star counts as a ringlike structure, however, is not supported by critical complementary data in the fourth quadrant, which is not covered by the SDSS. We present stellar density maps from the Minnesota Automated Plate Scanner Catalog of the POSS I showing that the overdensity does not extend into the fourth quadrant. The overdensity is most probably not a ring. It could be due to interaction with the disk bar, or it could be evidence of a triaxial thick disk or a merger remnant/stream. We call this feature the Hercules Thick-Disk Cloud.

Mapping the Asymmetric Thick Disk. I. A Search for Triaxiality

A significant asymmetry in the distribution of faint blue stars in the inner Galaxy, Quadrant 1 (l = 20°-45°) compared to Quadrant 4 was first reported by Larsen & Humphreys in 1996. Parker et al. greatly expanded the survey to determine its spatial extent and shape and the kinematics of the affected stars. This excess in the star counts was subsequently confirmed by Juric et al. using Sloan Digital Sky Survey data. Possible explanations for the asymmetry include a merger remnant, a triaxial thick disk, and a possible interaction with the bar in the disk. In this paper, we describe our program of wide field photometry to map the asymmetry to fainter magnitudes and therefore larger distances. To search for the signature of triaxiality, we extended our survey to higher Galactic longitudes. We find no evidence for an excess of faint blue stars at l ≥55° including the faintest magnitude interval. The asymmetry and star count excess in Quadrant 1 is thus not due to a triaxial thick disk.

Mining Astronomical Databases

The development of software tools and techniques for the efficient ac- cess and analysis of large astronomical databases poses some unique challenges. We briefly describe some of the problems astronomical data and datasets present and give an example from our own efforts to auto- mate the classification of galaxies, and then discuss where “clustering” algorithms may be applicable.

A WWW Database of APS Poss Images

We have used the Automated Plate Scanner (APS) at the University of Minnesota to digitize glass copies of the blue and red plates of the original Palomar Observatory Sky Survey (POSS I) with |b| > 20°. The APS Image Database is a database of all digitized images larger than the photographic noise threshold. It includes all of the matched images in the object catalog, as well as those unmatched images above the noise threshold. The matched image data of the catalog has the advantage of confirming the reality of the image. This is especially important for small images near the plate limit. But these are not all of the detected real images; very blue or very red faint objects may be excluded by this matching requirement. The image database allows information on them to be retrieved, and is therefore a valuable complement to the object catalog. The operation of the APS and the scanning procedures are described in detail in Pennington et al. (1993). We are now processing plate data into the image database. A set of query forms, a tutorial and documentation can be found at http://isis.spa.umn.edu/IDB/homepage.idb.html.