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Circumnuclear star-forming activities along the Hubble sequence
In order to study circumnuclear star-forming activity along the Hubblesequence, we cross-correlated the Sloan Digital Sky Survey Data Release2 (SDSS DR2) with the Third Reference Catalog of Bright Galaxies (RC3)to derive a large sample of 1015 galaxies with both morphological andspectral information. Among these, 385 sources are classified asstar-forming galaxies, and the SDSS fibre covered the circumnuclearregions (0.2-2.0 kpc). By using the spectral synthesis method to removethe contribution from the underlying old stellar population, we measuredthe emission lines fluxes accurately, which are then used to estimatethe star-formation rates(SFRs). Our main findings are: (1) early-typespirals show much higher Hα luminosities, and hence higher SFRs,and also suffer more extinctions than late-type ones. The equivalentwidths (EWs) of Hα emission lines show a similar trend; however,the very late types (Sdm ~ Irr) do have large fractions of high EWs; (2)we confirm that D_n(4000) shows a strong correlation with the strengthsof metallic absorption lines (such as CN band, G band, and Mg Ib). Boththese lines and the Balmer absorption lines show interesting variationsbetween Sbc and Sd type galaxies; (3) the bar structure tightly relatesto the enhanced star formation activity, an effect that is even moresignificant in the early-type spirals. But we should note that the barstructure is not a necessary or sufficient condition for galaxies toharbor circumnuclear star formations.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| An extended galaxy redshift survey. I - The catalogue
Redshifts and blue magnitudes are presented for a sample of 264 'field'galaxies virtually complete to a limiting magnitude of 16.80 mag. Thegalaxies were selected by sampling one galaxy in every three in order ofapparent magnitude on each of nine high-latitude UK Schmidt (UKST)fields. The spectral data came from observations with the 1.9-mtelescope at the South African Astronomical Observatory (SAAO), and theresulting radial velocities have a precision of 130 + or - km/s. Thissurvey augments substantially the Durham/AAT redshift survey. Theobservational techniques and reduction procedures are discussed.
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