North Galactic Cap Research Articles

An Updated Multi-Wavelength Radio and Optical Catalog of Quasars and Radio Galaxies

AbstractWe present a catalog of millions of radio sources, created by consolidating large-area radio and optical surveys GB6 (6cm), FIRST (20cm), NVSS (20cm), WENSS (92cm), VLSS (4m), and SDSS DR9 (optical). The region where all surveys overlap covers 3269 deg2 in the North Galactic Cap, and contains >160,000 20-cm sources, with about 12,000 detected in all five radio surveys and over one-third detected optically. Combining parameters from the sky surveys allows easy and efficient classification by radio and optical morphology and radio spectral index. The catalog is available at http://www.atnf.csiro.au/people/Amy.Kimball/radiocat.shtml.

A SPATIAL CHARACTERIZATION OF THE SAGITTARIUS DWARF GALAXY TIDAL TAILS

We measure the spatial density of F turnoff stars in the Sagittarius dwarf tidal stream, from Sloan Digital Sky Survey (SDSS) data, using statistical photometric parallax. We find a set of continuous, consistent parameters that describe the leading Sgr stream's position, direction, and width for 15 stripes in the North Galactic Cap, and 3 stripes in the South Galactic Cap. We produce a catalog of stars that has the density characteristics of the dominant leading Sgr tidal stream that can be compared with simulations. We find that the width of the leading (North) tidal tail is consistent with recent triaxial and axisymmetric halo model simulations. The density along the stream is roughly consistent common disruption models in the North, but possibly not in the South. We explore the possibility that one or more of the dominant Sgr streams has been mis-identified, and that one or more of the `bifurcated' pieces is the real Sgr tidal tail, but we do not reach definite conclusions. If two dwarf progenitors are assumed, fits to the planes of the dominant and `bifurcated' tidal tails favor an association of the Sgr dwarf spheroidal galaxy with the dominant Southern stream and the `bifurcated' stream in the North. In the North Galactic Cap, the best fit Hernquist density profile for the smooth component of the stellar halo is oblate, with a flattening parameter q = 0.53, and a scale length of r_0 = 6.73. The Southern data for both the tidal debris and the smooth component of the stellar halo do not match the model fits to the North, although the stellar halo is still overwhelmingly oblate. Finally, we verify that we can reproduce the parameter fits on the asynchronous Milkyway@home volunteer computing platform.

The LEGUE high latitude bright survey design for the LAMOST pilot survey

We describe the footprint and input catalog for bright nights in the LAMOST Pilot Survey, which began in October 2011. Targets are selected from two stripes in the north and south Galactic Cap regions, centered at δ = 29°, with 10° width in declination, covering right ascensions of 135° to 290° and −30° to 30° respectively. We selected spectroscopic targets from a combination of the SDSS and 2MASS point source catalogs. The catalog of stars defining the field centers (as required by the Shack-Hartmann wavefront sensor at the center of the LAMOST field) consists of all V < 8m stars from the Hipparcos catalog. We employ a statistical selection algorithm that assigns priorities to targets based on their positions in multidimensional color/magnitude space. This scheme overemphasizes rare objects and de-emphasizes more populated regions of magnitude and color phase space, while ensuring a smooth, well-understood selection function. A demonstration of plate design is presented based on the Shack-Hartmann star catalog and an input catalog that was generated by our target selection routines.

A TWO MICRON ALL SKY SURVEY VIEW OF THE SAGITTARIUS DWARF GALAXY. VI.s-PROCESS AND TITANIUM ABUNDANCE VARIATIONS ALONG THE SAGITTARIUS STREAM

We present high-resolution spectroscopic measurements of the abundances of titanium (Ti), yttrium (Y) and lanthanum (La) for M giant candidates of the Sagittarius (Sgr) dwarf spheroidal (dSph) + tidal tail system pre-selected on the basis of position and radial velocity. The majority of these stars show peculiar abundance patterns compared to those of nominal Milky Way (MW) stars. The overall [Ti/Fe], [Y/Fe], [La/Fe] and [La/Y] patterns with [Fe/H] of the Sgr stream plus Sgr core do resemble those seen in the Large Magellanic Cloud (LMC) and other dSphs, only shifted [Fe/H] by ~+0.4 from the LMC and by ~+1 dex from the other dSphs; these relative shifts reflect the faster and/or more efficient chemical evolution of Sgr compared to the other satellites, and show that Sgr has had an enrichment history more like the LMC than the other dSphs. By tracking the evolution of the abundance patterns along the Sgr stream we can follow the time variation of the chemical make-up of dSph stars donated to the MW halo by Sgr. This evolution demonstrates that while the bulk of the stars currently in the Sgr dSph are quite unlike those of the MW halo, an increasing number of stars farther along the Sgr stream have abundances like MW halo stars, a trend that shows clearly how the MW halo could have been contributed by present day satellite galaxies even if the present chemistry of those satellites is now different from typical halo field stars. Finally, we analyze the chemical abundances of a moving group of M giants among the Sgr leading arm stars at the North Galactic Cap, but having radial velocities unlike the infalling Sgr leading arm debris there. Through use of "chemical fingerprinting", we conclude that these northern hemisphere M giants also are Sgr stars, likely trailing arm debris overlapping the leading arm in the north.

High Frequency Peakers: The faint sample

AbstractWe present a sample of sources with convex radio spectra peaking at frequencies above a few GHz, known as “High Frequency Peakers” (HFPs). A “bright” sample with a flux density limit of 300 mJy at 5 GHz has been presented by Dallacasa et al. (2000). Here we present the “faint” sample with flux density between 50 and 300 mJy at 5 GHz, restricted to the area around the North Galactic Cap, where the FIRST catalogue is available. The candidates have been observed with the VLA at several frequencies ranging from 1.4 to 22 GHz, in order to derive a simultaneous radio spectrum. The final list of confirmed HFP sources consists of 61 objects (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A 2MASS All‐Sky View of the Sagittarius Dwarf Galaxy. V. Variation of the Metallicity Distribution Function along the Sagittarius Stream

We present reliable measurements of the metallicity distribution function (MDF) at different points along the tidal stream of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy, based on high-resolution, echelle spectroscopy of candidate M giant members of the Sgr system. The Sgr MDF is found to evolve significantly from a median [Fe/H] ~ -0.4 in the core to ~-1.1 dex over a Sgr leading arm length representing ~2.5-3.0 Gyr of dynamical (i.e., tidal stripping) age. This is direct evidence that there can be significant chemical differences between current dSph satellites and the bulk of the stars they have contributed to the halo. Our results suggest that Sgr experienced a significant change in binding energy over the past several gigayears, which has substantially decreased its tidal boundary across a radial range over which there must have been a significant metallicity gradient in the progenitor galaxy. By accounting for MDF variation along the debris arms, we approximate the MDF Sgr would have had several gigayears ago. We also analyze the MDF of a moving group of M giants we previously discovered toward the north Galactic cap. These objects have the opposite radial velocities to the infalling Sgr leading arm stars there, and we propose that most of them represent Sgr trailing arm stars overlapping the Sgr leading arm in this part of the sky. If so, these trailing arm stars further demonstrate the strong MDF evolution within the Sgr stream.

An Orphan in the “Field of Streams”

We use Sloan Digital Sky Survey Data Release 5 photometry and spectroscopy to study a tidal stream that extends over ~50° in the north Galactic cap. From the analysis of the path of the stream and the colors and magnitudes of its stars, the stream is ~20 kpc away at its nearest detection (the celestial equator). We detect a distance gradient: the stream is farther away from us at higher declination. The contents of the stream are made up from a predominantly old and metal-poor population that is similar to the globular clusters M13 and M92. The integrated absolute magnitude of the stream stars is estimated to be Mr ~ -7.5. There is tentative evidence for a velocity signature, with the stream moving at ~-40 km s-1 at low declinations and ~+100 km s-1 at high declinations. The stream lies on the same great circle as Complex A, a roughly linear association of H I high-velocity clouds stretching over ~30° on the sky, and as Ursa Major II, a recently discovered dwarf spheroidal galaxy. Lying close to the same great circle are a number of anomalous, young, and metal-poor globular clusters, including Palomar 1 and Ruprecht 106.

The Milky Way's stellar halo - lumpy or triaxial?

We present minimum chi-squared fits of power law and Hernquist density profiles to F-turnoff stars in eight 2.5° wide stripes of SDSS data: five in the North Galactic Cap and three in the South Galactic cap. Portions of the stellar Galactic halo that are known to contain large streams of tidal debris or other lumpy structure, or that may include significant contamination from the thick disk, are avoided. The data strongly favor a model that is not symmetric about the Galaxy's axis of rotation. If included as a free parameter, the best fit to the center of the spheroid is surprisingly ≈ 3kpc from the Galactic center in the direction of the Sun's motion. The model fits favor a low value of the density of halo stars at the solar position. The alternative to a non-axisymmetric stellar distribution is that our fits are contaminated by previously unidentified lumpy substructure.

A Faint New Milky Way Satellite in Bootes

In this Letter, we announce the discovery of a new satellite of the Milky Way in the constellation of Bootes at a distance of 60 kpc. It was found in a systematic search for stellar overdensities in the North Galactic Cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The color-magnitude diagram shows a well-defined turn-off, red giant branch, and extended horizontal branch. Its absolute magnitude is -5.8, which makes it one of the faintest galaxies known. The half-light radius is 220 pc. The isodensity contours are elongated and have an irregular shape, suggesting that Boo may be a disrupted dwarf spheroidal galaxy.

A New Milky Way Dwarf Satellite in Canes Venatici

In this Letter, we announce the discovery of a new dwarf satellite of the Milky Way, located in the constellation Canes Venatici. It was found as a stellar overdensity in the North Galactic Cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The satellite's color-magnitude diagram shows a well-defined red giant branch, as well as a horizontal branch. As judged from the tip of the red giant branch, it lies at a distance of ~220 kpc. Based on the SDSS data, we estimate an absolute magnitude of Mv ~ -7.9, a central surface brightness of mu_0,V ~ 28 mag arcsecond^-2, and a half-light radius of \~ 8.5' (~ 550 pc at the measured distance). The outer regions of Canes Venatici appear extended and distorted. The discovery of such a faint galaxy in proximity to the Milky Way strongly suggests that more such objects remain to be found.

The Field of Streams: Sagittarius and Its Siblings

We use Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) u,g,r,i,z photometry to study Milky Way halo substructure in the area around the North Galactic Cap. A simple color cut (g-r < 0.4) reveals the tidal stream of the Sagittarius dwarf spheroidal, as well as a number of other stellar structures in the field. Two branches (A and B) of the Sagittarius stream are clearly visible in an RGB-composite image created from 3 magnitude slices, and there is also evidence for a still more distant wrap behind the A branch. A comparison of these data with numerical models suggests that the shape of the Galactic dark halo is close to spherical.

A Two Micron All Sky Survey View of the Sagittarius Dwarf Galaxy. I. Morphology of the Sagittarius Core and Tidal Arms

We present the first all-sky view of the Sagittarius (Sgr) dwarf galaxy mapped by M-giant star tracers detected in the complete Two Micron All Sky Survey (2MASS). Near-infrared photometry of Sgr's prominent M-giant population permits an unprecedentedly clear view of the center of Sgr. The main body is fitted with a King profile of limiting major-axis radius 30°—substantially larger than previously found or assumed—beyond which is a prominent break in the density profile from stars in the Sgr tidal tails; thus the Sgr radial profile resembles that of Galactic dwarf speroidal (dSph) satellites. Adopting traditional methods for analyzing dSph light profiles, we determine the brightness of the main body of Sgr to be MV = -13.27 (the brightest of the known Galactic dSph galaxies) and the total Sgr mass-to-light ratio to be 25 in solar units. However, we regard the latter result with suspicion and argue that much of the observed structure beyond the King-fit core radius (224') may be outside the actual Sgr tidal radius as the former dwarf spiral/irregular satellite undergoes catastrophic disruption during its last orbits. The M-giant distribution of Sgr exhibits a central density cusp at the same location as, but not due to, the old stars constituting the globular cluster M54. A striking trailing tidal tail is found to extend from the Sgr center and arc across the south Galactic hemisphere with approximately constant density and mean distance varying from ~20 to 40 kpc. A prominent leading debris arm extends from the Sgr center northward of the Galactic plane to an apogalacticon ~45 kpc from the Sun and then turns toward the north Galactic cap (NGC), from where it descends back toward the Galactic plane, becomes foreshortened, and, at brighter magnitudes, covers the NGC. The leading and trailing Sgr tails lie along a well-defined orbital plane about the Galactic center. The Sun lies within a kiloparsec of that plane and near the path of leading Sgr debris; thus, it is possible that former Sgr stars are near or in the solar neighborhood. We discuss the implications of this new view of the Sgr galaxy and its entrails for the character of the Sgr orbit, mass, mass-loss rate, and contribution of stars to the Milky Way halo. The minimal precession displayed by the Sgr tidal debris along its inclined orbit supports the notion of a nearly spherical Galactic potential. The number of M giants in the Sgr tails is at least 15% that contained within the King limiting radius of the main Sgr body. The fact that M giants, presumably formed within the past few gigayears in the Sgr nucleus, are nevertheless so widespread along the Sgr tidal arms not only places limits on the dynamical age of these arms but also poses a timing problem that bears on the recent binding energy of the Sgr core and that is most naturally explained by recent and catastrophic mass loss. Sgr appears to contribute more than 75% of the high-latitude, halo M giants, despite substantial reservoirs of M giants in the Magellanic Clouds. No evidence of extended M-giant tidal debris from the Magellanic Clouds is found. Generally good correspondence is found between the M-giant, all-sky map of the Sgr system and all previously published detections of potential Sgr debris, with the exception of Sgr carbon stars, which must be subluminous compared with counterparts in other Galactic satellites in order to resolve the discrepancy.

Optical Counterparts for 70,000 Radio Sources: APM Identifications for the FIRST Radio Survey

We describe a program to identify optical counterparts to radio sources from the VLA FIRST survey using the Cambridge APM scans of the POSS-I plates. We use radio observations covering 4150 deg2 of the north Galactic cap to a 20 cm flux density threshold of 1.0 mJy; the 382,892 sources detected all have positional uncertainties of <1'' (radius of 90% confidence). Our description of the APM catalog, derived from the 148 POSS-I O and E plates covering this region, includes an assessment of its astrometric and photometric accuracy, a photometric recalibration using the Minnesota APS catalog, a discussion of the classification algorithm, and quantitative tests of the catalog's reliability and completeness. We go on to show how the use of FIRST sources as astrometric standards allows us to improve the absolute astrometry of the POSS plates by nearly an order of magnitude to ~015 rms. Matching the radio and optical catalogs yields counterparts for over 70,000 radio sources; we include detailed discussions of the reliability and completeness of these identifications as a function of optical and radio morphology, optical magnitude and color, and radio flux density. An analysis of the problem of radio sources with complex morphologies (e.g., double-lobed radio galaxies) is included. We conclude with a brief discussion of the source classes represented among the radio sources with identified counterparts.

Expectation for the X-ray Galactic Halo

We present an estimate of the strength and spectrum of the X-ray background from the warm gas associated with the Galactic halo. This investigation is motivated primarily by the recent detection of a spatially variable soft X-ray component towards the north Galactic polar cap by Kuntz et al. (2001), suggesting that the warm gas heated by gravitational shocks of the Galactic halo may produce a significant contribution to the soft X-ray sky. Another purpose of the study is to refine the recent theoretical prediction of the X-ray spectrum from the Galactic halo by Xue (2001) who adopted an ideal and simple isothermal model for the gas and dark matter distributions of the Galactic halo. We use the universal density profile for the dark matter distributions of the Galactic halo to evaluate the X-ray properties of the warm gas either in hydrostatic equilibrium with, or tracing the underlying gravitational potential of the Galaxy. It has been shown that our prediction is consistent with the measured soft X-ray component towards the north Galactic polar cap if the gas fraction is taken to be ∼0.005.

The X-ray Background from the Warm Gas of the Galactic Halo

Within the framework of the hierarchical scenario of galaxy formation, spiral galaxies like our own Galaxy are still growing at present. This opens a possi- bility that one might be able to see X-ray galactic halos from gravitationally heated gas with temperatures of 10 6 K as a result of bremsstrahlung. An interesting issue is whether the X-ray background produced by the warm gas in the halo of our Galaxy is detectable. We present a simple estimate of the strength and spectrum of the X-ray background from the Galactic halo and compare with the recent find- ings of a spatially variable soft X-ray component seen towards the north Galactic polar cap by Kuntz et al. (2001). It is shown that a good agreement, regardless of cosmological models, can be achieved if the gas fraction is as low as 0.01. This requirement seems to be consistent with the extrapolated result from a num- ber of independent observational and theoretical constraints established for groups and clusters of galaxies. In particular, the expected soft X-ray background from the warm gas of the Galactic halo is comparable to, or even exceeds that produced by the warm-hot gas in massive groups, and it may constitute the major source of contamination in the search for missing baryons through the detection of their soft X-ray emission, unless we can work out a way to properly remove the X-ray background (e.g., from anisotropy) from the halo of our Galaxy.

SiO maser survey of AGB stars in the North Galactic Cap

A SiO maser survey in the J =1 0, v = 1 and 2 transitions has been made for IRAS sources in the North Galactic Cap (b > 30) with the Nobeyama 45 m radio telescope. The sources were selected on the basis of their IRAS 12/25-m and 25/60-m flux ratios as likely oxygen-rich AGB candidates. SiO masers were detected from 24 out of the 97 selected sources, where 17 were new detections. The distances and heights above the Galactic plane are calculated. The Galactic distribution of detected and undetected stars indicates that metallicity is likely to govern the detection rate. The Galactocentric angular velocities of the subsampled stars are derived and their variation with the Galactic height is discussed.

The Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey of 104 deg2 in the North Galactic Cap, currently underway with the 2.5-m SDSS Telescope at the Apache Point Observatory in New Mexico. The data products will include u, g, r, i and z-band imaging of several 108 sources and R = 2000 spectra of 106 galaxies. The imaging will have 10-sigma limiting (AB) magnitudes of (u, g, r, i, z) = (21.4, 22.6, 22.3, 21.7, 20.1). The “Main” sample of 9 x 105 galaxies, selected to have r &lt; 17.7 mag, will have spectra with signal-to-noise ratio on the order of ~ 10 per resolution element, and median redshift z ~ 0.1. There will also be a sample of 105 luminous elliptical galaxies, selected on the basis of apparent color and magnitude, which will extend out to redshift z ~ 0.4. The data will be released steadily over the next five years.On the order of one percent of the eventual data volume has been assembled at the time of this meeting, with a few hundred square degrees of survey-quality 5-band imaging, and over 104 survey-quality spectra. In the refereed literature there are detailed descriptions of the survey design, goals and hardware (York et al 2000; Gunn et al. 1998) and first scientific results (e.g., Ivezic et al 2000; Fischer et al. 2000; Leggett et al. 2000; Yanny et al. 2000).Relevant to measures of the extragalactic background emission, the survey has found many z &gt; 4 quasars and has measured the evolution in their space density (e.g., Fan et al. 2000). Measures of bright galaxy counts, the local galaxy luminosity function, and the evolution of elliptical galaxies are in preparation.

The Sloan Digital Sky Survey

The Sloan Digital Sky Survey is an ambitious, multi-institutional project to create a huge digital imaging and spectroscopic data bank of 25% of the celestial sphere, approximately 10,000 deg^2 centred on the north galactic polar cap. The photometric atlas will be in 5 specially-chosen colours, covering the pi ster of the Survey area to a limiting magnitude of r~23.1, on 0.4 pixels, resulting in a 1 Tpixel map. This data base will be automatically analysed to catalog the photometric and astrometric properties of 10^8 stellar images, 10^8 galaxies, and 10^6 colour-selected QSO candidates; the galaxy data will in addition include detailed morphological data. The photometric data are used to autonomously and homogeneously select objects for the spectroscopic survey, which will include spectra of 10^6 galaxies, 10^5 QSOs, and 10^5 unusual stars. Although the project was originally motivated by the desire to study Large Scale Structure, we anticipate that these data will impact virtually every field of astronomy, from Earth-crossing asteroids to QSOs at z>6. In particular, the ~12 TByte multi-colour, precision calibrated imaging archive should be a world resource for many decades of the next century.

A Series of Faint Spectrophotometric Standard Stars at +33o Declination

We have obtained spectrophotometry in the wavelength range 350-920 nm for 21 15th magnitude stars. These stars have right ascension at 30 minute intervals in the range 8-18 hr and declination near +33°. Mean magnitudes are presented at 5 nm intervals, with calibration derived from Kitt Peak secondary spectrophotometric standards. Typical internal and absolute errors are estimated to be less than 0.02 and 0.05 mag, respectively. The sequence was established in order to provide calibration stars for drift-scan observations of a strip of sky centered at this declination. Because the stars are relatively faint and span the north Galactic cap, they should be well suited to the calibration of other data sets.

Kiss: A New Digital Survey for Emission-Line Objects

We have initiated a major new survey for emission-line galaxies (ELGs) which we call the KPNO International Spectroscopic Survey (KISS). Survey observations began in March 1994 with the 0.61-m Burrell Schmidt telescope. The technique we employ combines the benefits of a traditional photographic objective-prism survey with the advantages of using a CCD detector. The field of view of our CCD is 1.1° square, and the prism employed provides a dispersion of 19 Å/pixel at 5000 Å. The spectral range covered (4800-5500 Å) is restricted by a specially designed filter that transmits from rest-frame Hβ to just shortward of the strong night-sky line at 5577 Å; this greatly reduces the sky background. We expect KISS to be sensitive to galaxies with magnitudes as faint as B = 20m–21m, much deeper than existing photographic surveys. Our initial pilot project covers 100 square degrees (Salzer et al. 1994) and overlaps the CfA/Dartmouth Century Redshift Survey (α = 8h30m–16h45m and δ = 29°–30°) in the North Galactic cap.