The PDS vs. Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12μ\mum and 25μ\mum in the nearby universe

(Abridged) The characteristics of the starburst galaxies from the Pico dos Dias survey (PDS) are compared with those of the nearby UV-bright Markarian starburst galaxies, having the same limit in redshift ($v_h < 7500$ km s$^{-1}$) and absolute $B$ magnitude ($M_B < -18$). An important difference is found: the Markarian galaxies are generally undetected at 12$\mu$m and 25$\mu$m in \textit{IRAS}. This is consistent with the UV excess shown by these galaxies and suggests that the youngest star forming regions dominating these galaxies are relatively free of dust. The FIR selection criteria for the PDS is shown to introduce a strong bias towards massive (luminous) and large size late-type spiral galaxies. This is contrary to the Markarian galaxies, which are found to be remarkably rich in smaller size early-type galaxies. These results suggest that only late-type spirals with a large and massive disk are strong emitter at 12$\mu$m and 25$\mu$m in \textit{IRAS} in the nearby universe.Comment: Accepted for publication in MNRA

Comparative Study of Asymmetry Origin of Galaxies in Different Environments. II. Near-Infrared observations

In this second paper of two analyses, we present near-infrared (NIR) morphological and asymmetry studies performed in sample of 92 galaxies found in different density environments: galaxies in Compact Groups (HCGs), Isolated Pairs of Galaxies (KPGs), and Isolated Galaxies (KIGs). Both studies have proved useful for identifying the effect of interactions on galaxies. In the NIR, the properties of the galaxies in HCGs, KPGs, and KIGs are more similar than they are in the optical. This is because the NIR band traces the older stellar populations, which formed earlier and are more relaxed than the younger populations. However, we found asymmetries related to interactions in both KPG and HCG samples. In HCGs, the fraction of asymmetric galaxies is even higher than what we found in the optical. In the KPGs the interactions look like very recent events, while in the HCGs galaxies are more morphologically evolved and show properties suggesting they suffered more frequent interactions. The key difference seems to be the absence of star formation in the HCGs; while interactions produce intense star formation in the KPGs, we do not see this effect in the HCGs. This is consistent with the dry merger hypothesis (Coziol & Plauchu-Frayn 2007); the interaction between galaxies in compact groups, (CGs), is happening without the presence of gas. If the gas was spent in stellar formation (to build the bulge of the numerous early-type galaxies), then the HCGs possibly started interacting sometime before the KPGs. On the other hand, the dry interaction condition in CGs suggests that the galaxies are on merging orbits, and consequently such system cannot be that much older either. [abridge]Comment: 36 pages, 16 figures. Accepted for publication in AJ: corrected typos and reference

The Relation between Galaxy Activity and the Dynamics of Compact Groups of Galaxies

Peer reviewe

The Montreal Blue Galaxy Survey III. Third list of UV-bright candidates

We present and discuss the latest addition of the Montreal Blue Galaxy (MBG) survey. Inspection of 59 Curtis Schmidt plates resulted in the identification of 135 new UV-bright galaxies with B < 15.5. This brings the total number of MBGs to 469. New results of the $V/V_m$ test show that our survey is complete to B = 14.7. From our most recent spectroscopic follow-up, we confirm the discovery of one new Seyfert 1 galaxy and possibly one new Seyfert 2 galaxy. We confirm also the bias of the MBG survey towards the low-excitation and metal rich Starburst Nucleus Galaxies (SBNGs). The spectral characteristics of the MBGs are similar to those of the infrared luminous IRAS galaxies. As a common characteristic, they show a mean ratio Log([NII]/H$\alpha$) in excess of 0.2 dex as compared to normal disk HII regions. In general, the MBGs have lower far-infrared luminosities ($L_{IR} < 10^{11} L_{\odot}$) and are nearer (z < 0.05) than the luminous IRAS galaxies. The distribution of the morphologies of the MBGs indicates a high number of early-type spirals (Sb and earlier). Nearly half of these galaxies also possess a bar. In our sample, the fraction of galaxies with bars depends on the morphology and increases towards the late-type spirals. However, if we consider only isolated galaxies, the late-type spirals show a clear tendency to be barred. Signs of a recent interaction with neighbor galaxies are obvious only in 24% of our candidates. Although this number is only a lower limit, it is nevertheless sufficiently low to suggest that in a majority of massive galaxies the burst of star formation do not depends solely on dynamical processes.Comment: 24 pages, 6 Latex tables and 6 Postscript figures, uses aasms4.sty, accepted for publication in the Astronomical journa

Infrared Surface Brightness Analysis of Galaxies in Compact Groups

Images of 7 Compact groups of galaxies (CG) were obtained using the 2.1m telescope in San Pedro Martir (B.C. Mexico) equipped with the NIR camera CAMILA. The NIR images trace the mass of the galaxies, through the oldest and more evolved stellar populations. The goal of this project is to search for evidence of morphological perturbations correlated with the level of activity (AGN or star formation) of the galaxies. We find that the level of perturbation is well correlated with activity observed in optical spectrocopy (Coziol et al. 2004). Evidence for perturbations decreases from more active groups to less active groups, confirming the classification. Our analysis suggests that galaxies in more active groups are undergoing important transformations due to interaction and merging and that the whole groups is on a merger path. Galaxies in less active CG have gone through similar processes in the recent past and are either in a final merging phase or in equilibrium due to a more massive halo of dark matter.Comment: 2 pages, 1 figure, Proc. ESO Workshop "Groups of galaxies in the nearby Universe", Santiago, Chile, 5-9 Dec. 2005, ESO Astrophysics Symposia, eds. I. Saviane, V. Ivanov & J. Borissova, Springer-Verla