תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
The Nature of Nearby Counterparts to Intermediate-Redshift Luminous Compact Blue Galaxies. II. CO Observations
We present the results of a single-dish beam-matched survey of the threelowest rotational transitions of CO in a sample of 20 local (D<~70Mpc) luminous compact blue galaxies (LCBGs). These ~L*, blue, highsurface brightness, starbursting galaxies were selected on the samecriteria used to define LCBGs at higher redshifts. Our detection ratewas 70%, with those galaxies havingLB<7×109 Lsolar not detected.We find that the H2 masses of local LCBGs range from6.6×106 to 2.7×109 Msolar,assuming a Galactic CO-to-H2 conversion factor. Combiningthese results with our earlier H I survey of the same sample, we findthat the ratio of molecular to atomic gas mass is low, typically 5%-10%.Using a large velocity gradient model, we find that the average gasconditions of the entire interstellar medium in local LCBGs are similarto those found in the centers of star-forming regions in our Galaxy andin the nuclear regions of other galaxies. Star formation rates,determined from IRAS fluxes, are a few Msolaryr-1, much higher per unit dynamical mass than normal spiralgalaxies. If this rate remains constant, the molecular hydrogendepletion timescales are short, ~10-200 Myr.
| The Nature of Nearby Counterparts to Intermediate-Redshift Luminous Compact Blue Galaxies. I. Optical/H I Properties and Dynamical Masses
We present single-dish H I spectra obtained with the Green BankTelescope, along with optical photometric properties from the SloanDigital Sky Survey, of 20 nearby (D<~70 Mpc) luminous compact bluegalaxies (LCBGs). These ~L*, blue, high surface brightness, starburstinggalaxies were selected using the same criteria as were used to defineLCBGs at higher redshifts. We find that these galaxies are gas-rich,with MHI ranging from 5×108 to8×109 Msolar andMHIL-1B ranging from 0.2 to 2Msolar L-1solar, consistent with avariety of morphological types of galaxies. We find that the dynamicalmasses (measured within R25) span a wide range, from 1 to1×1011 Msolar. However, at least half havedynamical mass-to-light ratios smaller than those of nearby galaxies ofall Hubble types, as found for LCBGs at intermediate redshifts. Bycomparing line widths and effective radii with local galaxy populations,we find that LCBGs are consistent with the dynamical mass properties ofMagellanic (low luminosity) spiral galaxies and the more massiveirregular and dwarf elliptical galaxies, such as NGC 205.
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| A redshift survey toward a proposed void of galaxies suggested by the distribution of Abell clusters
A program of redshift measurements was carried out in a region of thesky in which a relative under-density of Abell clusters had been used toinfer the presence of a large (diameter about 40/h Mpc) void in thegeneral galaxy distribution. The purpose of this study was toinvestigate whether the large-scale distribution of galaxies is tracedby the distribution of rich clusters. Redshifts are presented for 308galaxies in the Zwicky Catalog in a 234 square degree region centered onR.A. about 2h, Decl. about 12 deg of which 229 have been newly measured.These data reveal a pattern of filamentary structure alternating withvoids of characteristic diameter about 25-30/h Mpc, throughout thevolume sampled. While the redshift data reveal an underdensity in thedistribution of galaxies in the general region suggested by the Abellcluster distribution, they do not support the existence there of a 40/hMpc diameter void.
| The ultraviolet continuum of quasars. I - The shape of the continuum, continuum reddening and intervening absorption. II - Continuum variability
UV data for a sample of 81 quasars covering a wide redshift andluminosity range are presented. The intrinsic optical and ultravioletcontinuum for quasars is found to steepen towards shorter wavelengths.The mean shape of the ultraviolet continuum is shown to be very similarfor the radio and nonradio selected quasars. No evidence is found forany intrinsic continuum reddening in the majority of know quasars. Anincrease of the observed continuum depression with increasing redshiftis found between the Ly-alpha and Ly-beta/O VI emission lines relativeto the continuum above Ly-alpha. This suggests evolution in the comovingnumber density of the intervening absorbing clouds. No variability isfound on the timescale of days, but variability is common on timescalesof weeks to months. No correlation between the two-folding timescale andluminosity and little evidence for variability in the shape of the UVcontinuum of quasars are observed.
| Investigation of the Galaxies from the Byurakan Classification at a Frequency of 102-MHZ
Not Available
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
קטלוגים וכינוים:
|
