Principal Component Analysis of Multiwavelength Properties of Seyfert Galaxies

Symp. - Int. Astron. Union

et al. 1999

The first statistical study of the environment of Seyfert galaxies (of both types 1 and 2) was done by Petrosian (1982), who found that Sy2 galaxies had an excess of nearby companion galaxies with respect to field galaxies. Dahari (1985) made a similar study, and obtained that both types of Seyfert galaxies are found five times more often in interacting systems that “normal” galaxies. Fuentes-Williams & Stocke (1988) obtained the opposite result: that Seyfert galaxies have no significative excess of nearby companions, and MacKenty (1989) obtained the same result as Petrosian. The last papers appeared in 1995: Rafanelli, Violato & B.aruffolo (1995) obtained a similar result as Dahari. Laurikainen & Salo (1995) made a careful attempt to understand the discrepancies; they concluded that the incompatibilities in the results were mainly due to control sample selection, and problems in background galaxy determination. Their work confirmed the result of the first study. However, in order to explain the discrepancies between previous results, they also used incorrectly defined control samples. Objections can be made against all of these works for this only reason. We have repeated the study using, for the first time, the digitized Palomar Sky Survey plates (paSS), an automated selection procedure, and correctly defined control samples (Osterbrock 1993).

Section: Interpretation Of the Resultssupporting

confidence: 58%

Unified Scheme for Seyferts or the Influence of Interactions?

Dultzin‐Hacyan¹,

Guridi

Symp. - Int. Astron. Union

et al. 1999

“…Intermediate types can be obviously explained due to intermediate proportions of these contributions. Statistical studies of the multifrequency emission of Seyferts (Mas-Hesse et al 1995;Dultzin-Hacyan & Ruano 1996), independently support this scheme. It is also strongly supported by direct observations which show that Sy2 galaxies have more circumnuclear star-forming regions than Sy1, both in the optical (Gonzalez-Delgado & Perez 1993), and in the IR (Maiolino & Rieke 1995;Maiolino et al 1997).…”

Section: Discussionmentioning

confidence: 96%

The Close Environment of Seyfert Galaxies and Its Implication for Unification Models

Dultzin‐Hacyan

The Astrophysical Journal

Fuentes-Guridi

et al. 1999

This paper presents a statistical analysis of the circumgalactic environment of nearby Seyfert galaxies based on a computer-aided search of companion galaxies on the Digitized Sky Survey (DSS). We defined a sample of 72 nearby Seyfert 1 (redshift 0.007 ≤ z ≤ 0.034) and a sample of 60 Seyfert 2 galaxies (0.007 ≤ z≤ 0.020), which include only high galactic latitude objects. In addition, we built two control samples of non-active galaxies matching the number of sample members, the redshift, morphological type, and diameter distribution of the Seyfert 1 and Seyfert 2 samples separately. We stress how our sample selection introduces important methodological improvements that avoid several sources of strong bias. An intrinsic difference between the environment of Seyfert 1 and Seyfert 2 galaxies, suggested by previous work, is confirmed as statistically significant. For Seyfert 2 galaxies we find a significant excess of large companions (D C > ∼ 10 Kpc) within a search radius < ∼ 100 Kpc of projected linear distance, as well as within a search radius equal to three times the diameter D S of each Seyfert galaxy. For Seyfert 1 galaxies there is no clear evidence of any excess of companion galaxies neither within 100 Kpc, nor within 3D S . For all samples the number of companions actually counted within a search radius of 3 D S is a factor ≈ 2 above the expectation values derived from the number density of galaxies over one square degree fields centered on the sample galaxies, suggesting a markedly non-Poissonian distribution for galaxies on scales < ∼ 100 Kpc. This difference in environment is not compatible with the simplest formulation of the Unification Model (UM) for Seyferts: both types 1 and 2 should be intrinsicaly alike, the only difference being due to orientation of an obscuring torus. We propose an alternative formulation.

“…where the brace indicates that Sy1 and Sy2 may be actually the same kind of objects seen in different orientations. There are several lines of (admittedly circumstantial) evidence that also support this simple evolutionary path: first, the contribution of thermal emission to the bolometric luminosity appears to decrease along the sequence (Dultzin-Hacyan & Ruano (1996)). Sy1 nuclei have been revealed in several evolved mergers (for instance, see Rafanelli, Marziani, Birkle, & Thiele (1993)).…”

Section: Star Forming and Seyfert Galaxies: An Evolutionary Sequence?mentioning

confidence: 93%

The Circumgalactic Environment of BrightIRASGalaxies

Dultzin‐Hacyan

Marziani

2002

ApJ

This paper studies systematically, for the first time, the circumgalactic environment of bright IRAS galaxies as defined by Soifer, et al. (1989). While the role of gravitational interaction for luminous and ultraluminous IRAS galaxies has been well established by various studies, the situation is by far more obscure in the IR luminosity range of the bright IRAS sample, 10 10 L < ∼ L FIR < ∼ 10 11 L. To easily identify nearby companion galaxies, the bright IRAS sample was restricted to 87 objects with redshift range 0.008 ≤ z ≤ 0.018 and galactic latitude δ | 30 o |. A control sample, selected from the Center for Astrophysics redshift survey catalogue, includes 90 objects matching the Bright IRAS sample for distribution of isophotal diameter, redshift, and morphological type. From a search of nearby companion galaxies within 250 Kpc on the second-generation Digitized Sky Survey (DSS-II), we found that the circumgalactic environment of the Bright IRAS galaxies contains more large companions than the galaxies in the optically selected control sample, and is similar to that of Seyfert 2 galaxies. We found a weak correlation over a wide range of far IR luminosity (10 9 L < ∼ L FIR < ∼ 10 12.5 L) between projected separation and L FIR which confirms a very close relationship between star formation rate of a galaxy and the strength of gravitational perturbations. We also find that the far IR colors depend on whether a source is isolated or interacting. Finally, we discuss the intrinsic difference and evolution expectations for the bright IRAS galaxies and the control sample, as well as the relationship between starbursting and active galaxies.