Southern Galactic Hemisphere Research Articles

Loose groups of galaxies in the Perseus–Pisces survey

We present a large catalog 1 of loose groups of galaxies in the Southern Galactic Hemisphere, selected from the Perseus{Pisces redshift Survey (PPS). Particular care is taken in order to obtain group samples as ho- mogeneous as possible to previously published catalogs. All our catalogs contain about 200 groups, signicantly more than in most previous studies where group samples were obtained from galaxy data sets of comparable qual- ity to (but smaller extent than) PPS. Groups are iden- tied with the adaptive Friends{Of{Friends (FOF) algo- rithm of Huchra & Geller (1982), with suitable normal- izations D0 =0 :231 h 1 Mpc and V0 = 350 km s 1 at cz0 = 1000 km s 1 . The luminosity function (LF) normal- ization =0 :02 h 3 Mpc 3 appropriate for PPS yields a number density threshold n=n 180 for the adopted D0, instead of n=n 80 used in previous studies of other samples. However, the customary choice of D0 obtained (through the LF) from a xed mass overdensity= = 80, well motivated in theory, suers from important observa- tional uncertainties and sample{to{sample variations of the LF normalization, and from major uncertainties in the relation between galaxy densityn and mass density .W e discuss how to self{consistently match FOF parameters among dierent galaxy samples. We then separately vary several FOF and sample parameters, and discuss their ef- fect on group properties. Loose groups in PPS nicely trace the large scale structure (LSS) in the parent galaxy sam- ple. The group properties vary little with dierent redshift corrections, redshift cut{o, and galaxy LF, but are rather sensitive to the adopted links D0 and V0. More precisely, the typical group size (velocity dispersion) is linearly re-

A Survey of High‐Latitude Molecular Gas in the Northern Galactic Hemisphere

We surveyed the northern Galactic hemisphere (NGH) at b ≥ 30° in the CO (1-0) emission line to determine the surface filling factor of molecular gas at high Galactic latitudes and to search for heretofore unknown molecular clouds. The NGH was sampled on a locally Cartesian grid with 1° (true-angle) spacing in Galactic longitude and latitude. Of the 11,478 points in our grid, we observed all 10,562 positions that rise to an elevation above 30° in Cambridge, MA, the site of the 1.2 m millimeter-wave telescope that was used for the survey. Only 26 lines of sight showed CO emission. Monte Carlo simulations based on our sampling grid and with cloud sizes, in a uniform distribution, ranging from 0 to 2 deg2 suggest that the survey is ~70% complete. Power-law distributions yield fractional completenesses that are typically a factor of 2 lower. The surface filling factor, corrected for the incompleteness of our sampling grid, is 0.004-0.008, depending on which cloud size distribution is used. These values are substantially lower than what is found in the southern Galactic hemisphere at b ≤ -30°. Adopting as the CO to H2 conversion ratio NH2/WCO = 2.5 × 1020 cm-2 (K km s-1)-1, the mass surface density of molecular gas in the north ranges from 0.015 ± 0.009 to 0.035 ± 0.020 M☉ pc-2. With the exception of four fairly significant aggregations of clouds (the complexes associated with the Polaris flare, Ursa Major, Draco, and L134), and a handful of isolated cloudlets, the northern Galactic hemisphere at b ≥ 30° is found to be largely free of molecular gas.

On the completeness of the lists of Compact Galaxy Groups

AbstractIt is shown that the lists of Shakhbazian Compact Galaxy Groups (SCGGs) are not complete. The number of the detected groups in the strip between b = ±30° and b = ±20° is by four to five times smaller than expected. The most probable reason is that during the search for SCGGs it was hard to distinguish images of compact galaxies from that of stars on the POSS prints in dense areas of the sky at lower galactic latitudes. There is some deficit of the detected groups between 60° and 40° of the north galactic latitudes. The surface density of SCGGs in the southern galactic hemisphere between b = −50° and b = −30° is by about three times less than it is expected. Obviously, the southern sky has not been searched properly. The list of Hickson's groups is complete down to galactic latitude ±30°. However, some excess of HCGs is found in the southern hemisphere, where the surface density of the found groups is by about two times higher than that of in the northern hemisphere.

The supercluster-void network - II. An oscillating cluster correlation function

We use rich clusters of galaxies in the Northern and Southern Galactic hemispheres up to a redshift z=0.12 to determine the cluster correlation function. We show that superclusters of galaxies and voids between them form a moderately regular network. As a result the correlation function determined for clusters located in rich superclusters oscillates: it has a series of regularly spaced secondary maxima and minima. The scale of the supercluster-void network, determined from the period of oscillations, is P=115 Mpc. The amplitude of oscillations is about 3 times larger than the estimated error. We compare the observed cluster correlation function with similar functions derived for popular models of structure formation. We find that the production of the observed cluster correlation function in any model with a smooth transition of the power spectrum from a Harrison-Zeldovich regime with positive spectral index on long wavelengths to a negative spectral index on short wavelengths is highly unlikely. The power spectrum must have an extra peak located at the wavelength equal to the period of oscillations of the correlation function.

A Catalog of Molecular Gas at High Galactic Latitudes

view Abstract Citations (82) References (108) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Catalog of Molecular Gas at High Galactic Latitudes Magnani, Loris ; Hartmann, Dap ; Speck, Bryan G. Abstract The global distribution and physical properties of the high-latitude molecular clouds are tabulated and discussed. As of this writing, more than 100 objects have been identified at Galactic latitudes |b| > 25°. Positions are listed for all the known clouds and LSR velocity, angular extent, mass, and internal velocity dispersion are listed when such data are available from the literature. The high-latitude molecular clouds consist primarily of translucent clouds, so that this catalog is the largest, most complete compendium of these objects at high Galactic latitudes. The velocity dispersion of the ensemble of clouds is 5.8 km s-1 if seven intermediate velocity objects are excluded and 9.9 km s-1 otherwise. The former dispersion implies a scale height for the clouds of 124 pc and a mean distance of 150 pc; the latter dispersion yields 210 pc and 260 pc, respectively. Thus, the majority of high-latitude clouds are local objects that may be situated at the nearer edges of the Local Bubble. As a group, they are the nearest molecular clouds to the Sun. The average velocity of the ensemble of clouds is -0.3 km s-1 without the intermediate velocity objects and -2.4 km s-1 including these clouds. From the catalog of clouds, we determine values for the filling fraction and mass surface density of the high-latitude molecular clouds (and thus of translucent gas) of 0.005 and 0.1-0.2 M0 pc -2, respectively, at |b| > 25°. Including the lower latitude contribution, we estimate the total local mass surface density of translucent clouds to be 0.2-0.3 Msun pc-2 In the local interstellar medium, these objects represent from 10% to 20% of the molecular gas inventory. Individual clouds range in size from less than 10-1 to 101 pc and in mass from 10-1 to 103 Msun. An asymmetry between the northern and southern Galactic hemisphere distribution of the clouds can be interpreted as a displacement of the Sun from the Galactic midplane of 18 pc, a value consistent with determinations based on other tracers. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1996 DOI: 10.1086/192344 Bibcode: 1996ApJS..106..447M Keywords: CATALOGS; GALAXY: STRUCTURE; ISM: CLOUDS; ISM: KINEMATICS AND DYNAMICS; ISM: MOLECULES full text sources ADS | data products SIMBAD (121)

Large-scale mass distribution behind the Galactic plane

We map the smoothed mass-density distribution in the Galactic zone of avoidance (zoa), within $6000\kms$ of the Local Group, using potent reconstruction from peculiar velocities of galaxies. The interpolation into the zoa is based on the assumed gravitational nature of the velocity field implying a potential flow. The main dynamical features at a distance r=4000 km/s are (a) the peak of the Great Attractor connecting Centaurus and Pavo at l=330, (b) a moderate bridge connecting Perseus-Pisces and Cepheus at l= 140, and (c) an extension of a large void from the southern Galactic hemisphere into the zoa near the direction of Puppis, l=220-270. We find a strong correlation between the mass density and the IRAS and optical galaxy density at $b=+-20, which indicates that the main dynamical features in the zoa should also be seen in galaxy surveys through the Galactic plane. The gravitational acceleration at the Local Group, based on the mass distribution out to 6000 km/s, is strongly affected by the mass distribution in the zoa: its direction changes by 31 when the |b| < 20 zoa is included, bringing it to within 4 +- 19 of the CMB dipole.

Power spectrum of the matter distribution in the Universe on large scales

The power spectrum of the distribution of clusters of galaxies in the northern and southern galactic hemispheres has been evaluated. Corrections have been applied for the smoothing effect, and for the Poisson noise. The effects of incompleteness of data and observational errors have been investigated. The cluster spectrum has been transformed to galaxy and matter power spectra. Data suggest that the power spectrum has an index − 2 ≤ n ≤ − 1 on intermediate scales; on very large scales the spectrum is consistent with the Harrison-Zeldovich index n = 1. The transition from the Harrison-Zeldovich index to a lower index occurs at the scale λ t ≃ 150 ± 50 h −1 Mpc

A search for stars of very low metal abundance. II

view Abstract Citations (522) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Search for Stars of Very Low Metal Abundance. II Beers, Timothy C. ; Preston, George W. ; Shectman, Stephen A. Abstract Spectroscopic observations for 1044 stars located primarily in the southern Galactic hemisphere are reported; the stars were chosen from a list of candidate metal-deficient stars discovered in the HK objective-prism survey. Radial velocities and line indices based on the equivalent widths of Ca II, K, H-gamma and H-delta, and the CH G band are reported. Estimates of metallicity for 874 stars with derived abundances less than -0.5 are presented. The number of extremely metal-poor stars (Fe/H is not greater than -2.0) reported in the present sample is roughly quadruple the same size of nonkinematically selected stars of similar metal abundance reported in previous work, and is on the order of the total previous samples of stars in this abundance regime when all sources are included. The number of stars with Fe/H not greater than -3.0 in the present sample is seven times the number of previously identified stars with spectroscopically determined abundances which are this low. Publication: The Astronomical Journal Pub Date: June 1992 DOI: 10.1086/116207 Bibcode: 1992AJ....103.1987B Keywords: Metallicity; Stellar Composition; Stellar Spectrophotometry; Abundance; Color-Color Diagram; Spectral Line Width; Star Formation; Stellar Magnitude; Ubv Spectra; Astrophysics; STARS: ABUNDANCES full text sources ADS | data products SIMBAD (1024) GCPD (1) CDS (1) Related Materials (5) Part 1: 1985AJ.....90.2089B Part 3: 1999ApJS..123..639N Part 4: 2000AJ....119.2882A Part 5: 2000AJ....120.2065B Part 6: 2014AJ....147..136R

Distribution of galaxies in the Southern Galactic CAP

Observations in the southern galactic hemisphere in the declination range between -17.5 and 2.5 degrees are combined with other available observation. The data set is used to study the spatial distribution of galaxies of a contiguous area of 3.13 sr of the Southern Galactic Cap. An approximately homogeneous magnitude-limited sample of galaxies in the Southern Galactic Cap is constructed from different catalogs. The resulting large scale structure is similar to that of previous surveys in which bright galaxies are distributed on surfaces which intersect at sharp corners and nearly surround voids that are almost empty of galaxies.

Evidence for clustering of field horizontal-branch stars in the Galactic halo

view Abstract Citations (49) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evidence for Clustering of Field Horizontal-Branch Stars in the Galactic Halo Doinidis, Steve P. ; Beers, Timothy C. Abstract An investigation of the clustering of field horizontal-branch stars in the Galactic halo is reported which examines this question using a catalog of over 4400 candidate field horizontal-branch stars distributed over roughly 2300 sq deg of sky, primarily in the southern Galactic hemisphere. A two-point correlation analysis indicates that the catalog contains an excess of stellar pairs with angular separations of less than 10 arcsec; at the approximate distances of these stars (5-8 kpc from the Sun) the corresponding linear separations are r of less than 25 pc. The possible connection with loose groups of halo field horizontal-branch stars noted previously by Sommer-Larsen and Christensen (1987) and by Beers and Doinidis (1988) is discussed. Publication: The Astrophysical Journal Pub Date: May 1989 DOI: 10.1086/185438 Bibcode: 1989ApJ...340L..57D Keywords: Horizontal Branch Stars; Milky Way Galaxy; Stellar Spectrophotometry; Distance; Monte Carlo Method; Spectral Line Width; Astrophysics; CLUSTERS: ASSOCIATIONS; STARS: HORIZONTAL-BRANCH full text sources ADS |

A catalog of candidate field horizontal-branch stars.

Coordinates and brightness estimates are presented for 4408 candidate field horizontal-branch stars selected using an objective-prism, interference-filter survey technique. The candidates lie primarily in the southern Galactic hemisphere, and are distributed in color over the range B-V from -0.2 to 0.40. Previous spectroscopic observation of a subset of these candidates indicates that roughly 85 percent of the catalog objects are bona fide members of the field blue horizontal branch. The remaining candidates include, in order of frequency, stars with main-sequence gravity which are likely to be a mix of metal-deficient turnoff stars and field blue stragglers, metallic line (Am) stars, A stars of near-solar metallicity, and high-luminosity or binary stars. 16 references.

Alignments of brightest cluster galaxies with large-scale structures

Using an independent sample of brightest galaxies in rich clusters in the southern galactic hemisphere, the Argyres et al. (1986) result that galaxy counts on scales to at least 15/h Mpc are systematically higher in the direction of the major axes of brightest cluster galaxies is confirmed.

The Magellanic Stream and other hydrogen remnants of strong tidal disruption of the Magellanic Clouds

view Abstract Citations (32) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Magellanic Stream and other hydrogen remnants of strong tidal disruption of the Magellanic Clouds Mirabel, I. F. Abstract A review of results from recent surveys of neutral-hydrogen, high-velocity clouds reveals the connection of the Magellanic Stream with a widespread population of clouds with large infalling motions toward the Galaxy. The tidal disruption of the Magellanic Clouds during their last close encounter with the Milky Way produced, along with the Magellanic Stream, a population of high-velocity clouds scattered throughout the first and second quadrants of the southern galactic hemisphere. High angular resolution observations in the northern tip of the Magellanic Stream are presented. They show that the leading head of the Stream is disintegrating as it falls toward the Milky Way. The scattering material may be observed as a conglomerate of discrete clouds surrounding the tip of the Magellanic Stream. The need for new computer simulations of the remnants of strong tidal disruption of the Magellanic Clouds is discussed. Publication: The Astrophysical Journal Pub Date: November 1981 DOI: 10.1086/159399 Bibcode: 1981ApJ...250..528M Keywords: Hydrogen Clouds; Magellanic Clouds; Neutral Gases; Radio Sources (Astronomy); Tides; Centimeter Waves; Computerized Simulation; Gas Density; Milky Way Galaxy; Astrophysics full text sources ADS |

The soft X-ray diffuse background and the structure of the local interstellar medium

Data from five rocket flights of the Wisconsin soft X-ray sky survey, covering the southern galactic hemisphere with 6.5 deg spatial resolution between 0.1 and 2.0 keV, are presented as intensity maps. Analysis of the data in two energy bands below 0.3 keV is presented here. These low-energy X-rays appear to be emitted from a plasma of about one-million K, the bulk of which is closer to the sun than even the nearest 5 x 10 to the 19th/sq cm of neutral gas. No evidence is found for the presence of nearby small (radius of about 0.6 pc) clouds of cool neutral gas, as has been proposed by McKee and Ostriker (1977). The X-ray measurements are consistent with the small amounts of local neutral material inferred from Lyman-alpha absorption measurements.

Structure of superclusters and supercluster formation

The study of the spatial distribution of galaxies and clusters of galaxies in the southern galactic hemisphere is continued using Zwicky clusters as principal tracers of the large-scale structure. The densest condensations of matter, rich clusters, containing many radio sources and a high percentage of elliptical and S0 galaxies have been joined by slightly curved or straight chains of clusters of galaxies. Chains are moderately rich in E and S0 galaxies and contain radio sources. The planes joining neighbouring chains are also populated by galaxies. Galaxies form thin strata here, containing no radio galaxies and a very low percentage of elliptical and S0 galaxies. The whole picture resembles cells. One cell wall with surrounding cluster chains can be taken for a supercluster. All clusters of galaxies and most galaxies are located in superclusters. Neighbouring superclusters are in contact and contain common elements. The space inside the cell is void of clusters and almost void of galaxies. Arguments have been given suggesting that superclusters formed prior to the formation of galaxies or simultaneously with them.

Superclusters and galaxy formation

Most galaxies and rich clusters of galaxies1 are concentrated in superclusters, and there are great distances between superclusters2–6. In this paper we study the structure of superclusters using Zwicky clusters7 as principal tracers of the large-scale structure of the Universe. Our study is restricted to the southern galactic hemisphere.

Spatial distribution of galaxies and of clusters of galaxies in the southern galactic hemisphere

Spatial distribution of galaxies and of clusters of galaxies in the southern galactic hemisphere

Soft diffuse X-rays in the southern galactic hemisphere

A map is presented of the soft X-ray diffuse background flux in the C band (approximately 0.13-0.28 keV) covering almost all of the southern galactic hemisphere. A comparison at constant galactic latitude of both C band and B band (about 0.1-0.18 keV) soft X-ray data with neutral-hydrogen maps shows that the intensity does decrease with increasing neutral-hydrogen column density but in a manner that is inconsistent with photoelectric absorption. It is suggested that the inverse correlation is a displacement effect. X-ray emission regions appear to be where the cool gas is not. Further, the evidence against photoelectric absorption implies that the bulk of the cool gas is beyond the X-ray emitting regions. Fewer than 10 to the 20th power H atoms per sq cm can be between the sun and the X-ray emitting regions. The sun appears to be surrounded by a soft X-ray emission region consisting of gas at a temperature of about 1 million K.

Ultrasoft X-rays from the southern galactic hemisphere

Results are reported for sounding-rocket measurements of the X-ray background at ultrasoft energies (90 to 280 eV) in selected regions of the southern galactic hemisphere. The spectrum of the background is found to be extremely soft, being characterized by a kinetic temperature of less than 100 eV in thermal models. A lower limit of about 0.2 per cu pc is set on the space density of stellar sources in a discrete-source model for the background. The results show that the observed background radiation in the southern galactic hemisphere is about 50% less intense than that sampled at corresponding northern latitudes, the intensity at energies less than 150 eV varies along the scan path and is strongest south of -60 deg, there is no evidence for the existence of any ultrasoft pointlike sources, and the background is probably diffuse in origin. A temperature of about 600,000 K and an electron density of the order of 0.007 per cu cm are derived from a simple model where the radiation originates in a hot interstellar plasma interspersed with cold gas along the line of sight.