Roger Coziol

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

Using a sample of 91 galaxies distributed over 27 compact groups (CGs) of galaxies, we define an index that allows us to quantify their level of activity due to an active galactic nucleus (AGN) or star formation. By combining the mean activity index with the mean morphological type of the galaxies in a group, we are able to quantify the evolutionary state of the groups. We find that they span an evolutionary sequence that correlates with the spatial configuration of the galaxies in the CG. We distinguish three main configuration types: A, B, and C. Type A CGs show predominantly low velocity dispersions and are rich in late-type spirals that show active star formation or harbor an AGN. Type B groups have intermediate velocity dispersions and contain a large fraction of interacting or merging galaxies. Type C comprises CGs with high velocity dispersions, which are dominated by elliptical galaxies that show no activity. We suggest that evolution proceeds A B C. Mapping the groups with different evolution levels in a diagram of radius versus velocity dispersion does not reveal the pattern expected based on the conventional fast merger model for CGs, which predicts a direct relation between these two parameters. Instead, we observe a trend contrary to expectation: the evolutionary state of a group increases with velocity dispersion. This trend seems to be related to the masses of the structures in which CGs are embedded. In general, the evolutionary state of a group increases with the mass of the structure. This suggests either that galaxies evolve more rapidly in massive structures or that the formation of CGs embedded in massive structures predated the formation of CGs associated with lower mass systems. Our observations are consistent with the structure formation predicted by the CDM model (or ΛCDM), only if the formation of galaxies is a biased process.

HCG 16 Revisited: Clues about Galaxy Evolution in Groups

We present new spectroscopic observations of five galaxies, members of the unusually active compact group HCG 16, observed using the Palomar 5 m telescope. The high signal-to-noise ratios (S/N ~ 70) of the spectra allow us to study the variation of the emission-line characteristics and the stellar populations in the nucleus and the circumnuclear regions of the galaxies. The emission-line characteristics of these galaxies are complex, varying between Seyfert 2s and LINERs or between LINERs and starbursts. All of the galaxies show traces of intermediate-age stellar populations, which supports our previous result that poststarburst galaxies are common in compact groups. The galaxies HCG 16-4 and HCG 16-5 show double nuclei and therefore could be two cases of recent merger. Our observations support a scenario in which HCG 16 was formed by the successive merger of metal-poor, low-mass galaxies. The galaxies HCG 16-1 and HCG 16-2, which are more evolved, form the old core of the group. Galaxies HCG 16-4 and HCG 16-5 are two more recent additions that are still in a merging phase. Galaxy HCG 16-5 is a starburst galaxy that is just beginning to fall into the core. If HCG 16 is representative of compact groups in their early stage, the whole set of observations implies that the formation of compact groups is the result of hierarchical galaxy formation. HCG 16 could be one example of this process operating in the local universe.

The Montreal blue galaxy survey. I: first list of ultraviolet-bright candidates

We describe and present the first results of a UV-bright galaxy survey using the Montreal-Cambridge-Tololo (MCT) plate collection. Visual inspection of 57 CTIO Curtis Schmidt plates, covering more than 1300 deg 2 , has resulted in the identification of 95 UV-bright galaxies brighter than B=15.5. Even though 80% of these objects are IRAS sources, barely 20% have their nature already established. The initial result of our survey shows that the bulk of our UV-bright candidates are narrow emission-line galaxies commonly known as starburst or H II galaxies

Mass of the black hole in the Seyfert 1.5 galaxy H 0507+164 from reverberation mapping

We present the results of our optical monitoring campaign of the X-ray source H 0507+164, a low luminosity Seyfert 1.5 galaxy at a redshift, z = 0.018. Spectroscopic observations were carried out during 22 nights in 2007, from the 21 of November to the 26 of December. Photometric observations in the R-band for 13 nights were also obtained during the same period. The continuum and broad line fluxes of the galaxy were found to vary during our monitoring period. The R-band differential light curve with respect to a companion star also shows a similar variability. Using cross correlation analysis, we estimated a time delay of τcen = 3.01 +0.42 −1.84 days (in the rest frame), (

The PDS versus Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12 and 25 μm in the nearby Universe

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 (vh < 7500 km s 1 ) and absolute B magnitude (MB < 18). An important difference is found: the Markarian galaxies are generally undetected at 12µm and 25µm in 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 12µm and 25µm in IRAS in the nearby universe. The Markarian and PDS starburst galaxies are shown to share the same environment. This rules out an explanation of the differences observed in terms of external parameters. These differences may be explained by assuming two different levels of evolution, the Markarian being less evolved than the PDS galaxies. This interpretation is fully consistent with the disk formation hypothesis proposed in Coziol et al. (2000) to explain the special properties of the Markarian SBNG.

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 a sample of 92 galaxies found in different density environments: galaxies in compact groups (CGs; HCGs in the Hickson Catalog of Compact Groups of Galaxies), isolated pairs of galaxies (KPGs in Karachentsevs list of isolated pairs of galaxies), and isolated galaxies (KIGs in Karachentsevas Catalog of Isolated Galaxies). 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; the interaction between galaxies in 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. Cosmologically speaking, the difference in formation time between pairs of galaxies and CGs may be relatively small. The two phenomena are typical of the formation of structures in low-density environments. Their formation represents relatively recent events.

What sparks the radio-loud phase of nearby quasars?

To better constrain the hypotheses proposed to explain why only a few quasars are radio loud (RL), we compare the characteristics of 1958 nearby

The Association of Compact Groups of Galaxies with Large-scale Structures

(z\le 0.3)

Narrow-Line AGNs: confirming the relationship between metallicity and accretion rate

SDSS quasars, covered by the FIRST and NVSS radio surveys. Only 22\% are RL with

Dynamics and Shape of Brightest Cluster Galaxies

\log(L_{1.4{\rm GHz}}) \ge 22.5