Issue |
A&A
Volume 420, Number 3, June IV 2004
|
|
---|---|---|
Page(s) | 873 - 879 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20035697 | |
Published online | 04 June 2004 |
Properties of isolated disk galaxies*
1
Instituto de Astrofísica de Andalucía (C.S.I.C.) Apartado 3004, 18080 Granada, Spain e-mail: jesusv@imaff.cfmac.csic.es;isabel@iaa.es;pepa@iaa.es
2
Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: galletta@pd.astro.it
3
Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy e-mail: bettoni@pd.astro.it
Corresponding author: M. Moles, moles@iaa.es
Received:
17
November
2003
Accepted:
27
February
2004
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 for isolated galaxies. The candidates were chosen from the CfA catalog of galaxies within the volume defined by
km s-1, galactic latitude higher than
and declination
. 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
and
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 LFIR/LB and
Mmol/LB 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.
Key words: galaxies: interactions / galaxies: evolution / galaxies: spiral
© ESO, 2004
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