Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
How large are the bars in barred galaxies?
I present a study of the sizes (semimajor axes) of bars in discgalaxies, combining a detailed R-band study of 65 S0-Sb galaxies withthe B-band measurements of 70 Sb-Sd galaxies from Martin (1995). As hasbeen noted before with smaller samples, bars in early-type (S0-Sb)galaxies are clearly larger than bars in late-type (Sc-Sd) galaxies;this is true both for relative sizes (bar length as fraction ofisophotal radius R25 or exponential disc scalelength h) andabsolute sizes (kpc). S0-Sab bars extend to ~1-10 kpc (mean ~ 3.3 kpc),~0.2-0.8R25 (mean ~ 0.38R25) and ~0.5-2.5h (mean ~1.4h). Late-type bars extend to only ~0.5-3.5 kpc,~0.05-0.35R25 and 0.2-1.5h their mean sizes are ~1.5 kpc, ~0.14R25 and ~0.6h. Sb galaxies resemble earlier-type galaxiesin terms of bar size relative to h; their smallerR25-relative sizes may be a side effect of higher starformation, which increases R25 but not h. Sbc galaxies form atransition between the early- and late-type regimes. For S0-Sbcgalaxies, bar size correlates well with disc size (both R25and h); these correlations are stronger than the known correlation withMB. All correlations appear to be weaker or absent forlate-type galaxies; in particular, there seems to be no correlationbetween bar size and either h or MB for Sc-Sd galaxies.Because bar size scales with disc size and galaxy magnitude for mostHubble types, studies of bar evolution with redshift should selectsamples with similar distributions of disc size or magnitude(extrapolated to present-day values); otherwise, bar frequencies andsizes could be mis-estimated. Because early-type galaxies tend to havelarger bars, resolution-limited studies will preferentially find bars inearly-type galaxies (assuming no significant differential evolution inbar sizes). I show that the bars detected in Hubble Space Telescope(HST) near-infrared(IR) images at z~ 1 by Sheth et al. have absolutesizes consistent with those in bright, nearby S0-Sb galaxies. I alsocompare the sizes of real bars with those produced in simulations anddiscuss some possible implications for scenarios of secular evolutionalong the Hubble sequence. Simulations often produce bars as large as(or larger than) those seen in S0-Sb galaxies, but rarely any as smallas those in Sc-Sd galaxies.
| A diagnosis of dust in active galactic nuclei through analysis of the infrared bump
We present model calculating results for the continuum spectra of activegalactic nuclei. The SUMA code has been updated and extended in order toinclude consistent calculations of grain temperature and grainsputtering inside the clouds of the narrow-line region (NLR). Silicategrains with a radius of 0.2 micron are adopted. The results arediscussed and compared with the observational data. The best fit to thecontinuum spectra is obtained for Seyfert 2 galaxies, indicating thatdust resides in the narrow-line region clouds.
| Galaxies with UV continuum having double and multiple nuclei. II
Based on examination of plates obtained with 0.5-m, 2.6-m, and 6.0-mtelescopes, it is found that 620 galaxies exhibiting a UV excess include59 objects with double or multiple nuclei. The encounter rate for theseobjects is shown to be significantly higher among galaxies with a UVexcess than among other galaxies, indicating that the former have moreactive nuclei than the latter. A list and photographs of the galaxieswith two or more nuclei are presented along with descriptions of theindividual galaxies and a discussion of their morphology. The dataindicate that on the average, the brightness of the galactic nucleiincreases and structural details (filaments, ejecta, and so forth)appear more frequently with increasing separation between thecomponents. It is noted that two of the galaxies with double nuclei areType 1 Seyferts.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
Cataloghi e designazioni:
|
NEWS@SKY (Science&Space News)
