Properties of isolated disk galaxies

Abstract

Abstract. We present a new sample of northern isolated galaxies, which are defined by the physical criterion that they were not affected by other galaxies in their evolution during the last few Gyr. To find them we used the logarithmic ratio, f , between inner and tidal forces acting upon the candidate galaxy by a possible perturber. The analysis of the distribution of the f -values for the galaxies in the Coma cluster lead us to adopt the criterion f ≤ −4.5 for isolated galaxies. The candidates were chosen from the CfA catalog of galaxies within the volume defined by cz ≤ 5000 km s −1 , galactic latitude higher than 40 • and declination ≥−2.5 • . The selection of the sample, based on redshift values (when available), magnitudes and sizes of the candidate galaxies and possible perturbers present in the same field is discussed. The final list of selected isolated galaxies includes 203 objects from the initial 1706. The list contains only truly isolated galaxies in the sense defined, but it is by no means complete, since all the galaxies with possible companions under the f -criterion but with unknown redshift were discarded. We also selected a sample of perturbed galaxies comprised of all the disk galaxies from the initial list with companions (with known redshift) satisfying f ≥ −2 and ∆(cz) ≤ 500 km s −1 ; a total of 130 objects. The statistical comparison of both samples shows significant differences in morphology, sizes, masses, luminosities and color indices. Confirming previous results, we found that late spiral, Sc-type galaxies are, in particular, more frequent among isolated galaxies, whereas Lenticular galaxies are more abundant among perturbed galaxies. Isolated systems appear to be smaller, less luminous and bluer than interacting objects. We also found that bars are twice as frequent among perturbed galaxies compared to isolated galaxies, in particular for early Spirals and Lenticulars. The perturbed galaxies have higher L FIR /L B and M mol /L B ratios, but the atomic gas content is similar for the two samples. The analysis of the luminosity-size and mass-luminosity relations shows similar trends for both families, the main difference being the almost total absence of big, bright and massive galaxies among the family of isolated systems, together with the almost total absence of small, faint and low mass galaxies among the perturbed systems. All these aspects indicate that the evolution induced by interactions with neighbors would proceed from late, small, faint and low mass Spirals to earlier, bigger, more luminous and more massive spiral and lenticular galaxies, producing at the same time a larger fraction of barred galaxies but preserving the same relations between global parameters. The properties we found for our sample of isolated galaxies appear similar to those of high redshift galaxies, suggesting that the present-day isolated galaxies could be quietly evolved, unused building blocks surviving in low density environments.

Frequency and properties of bars in cluster and field galaxies at intermediate redshifts

“…This was confirmed by Elmegreen et al (1990) and Giuricin et al (1993), who both found that galaxies in binary systems are preferentially early type and barred. A similar result was reported by Varela et al (2004). Interestingly, while the fraction of barred disks in clusters or groups is not higher than in the field (Kumai et al 1986;van den Bergh 2002van den Bergh , 2007Marinova et al 2009), Thompson (1981) and Andersen (1996) presented evidence that barred galaxies in the Coma and Virgo clusters are more concentrated toward the cluster centers than unbarred disks.…”

“…This finding indicates that bar formation, in general, is independent of environment, which was also found by van den Bergh (2002). On the other hand, Varela et al (2004) found twice as many bars in perturbed as in isolated galaxies. We investigate these results further in Sect.…”

“…The large relative velocities of the galaxies in cluster centers prevent galaxy mergers, but galaxy flybys and the corresponding interactions are frequent. There is theoretical (Gerin et al 1990;Mihos & Hernquist 1994;Noguchi 1996) and observational (Elmegreen et al 1990;Giuricin et al 1993;Varela et al 2004) evidence that galaxy-galaxy interactions trigger bar formation. The triggered formation of bars in the cluster center could also be responsible for the size distribution of bars.…”

The properties of early-type galaxies in the Ursa Major cluster

“…In order to compare interaction probabilities, we calculate the perturbation parameter f for the galaxies in the Ursa Major cluster and the Virgo cluster. The f value is defined by Varela et al (2004) as f = log Fext Fint = 3log R Dp + 0.4(mG − mp),…”

Bars, Spiral Structure, and Secular Evolution in Disk Galaxies

“…Even binary companions promote bar formation and may shift the galaxy to an earlier Hubble type because of torqued inflow (Elmegreen, Elmegreen, & Bellin 1990). Bars are also more common in perturbed galaxies (Varela et al 2004). Major mergers form ellipticals (Toomre & Toomre 1972;Schweizer 1998), and in the process, they form at least the youngest halo globular clusters (Ashman & Zepf 1992), and may produce counter-rotating cores (Kannappan & Fabricant 2001).…”