Veron Catalog Research Articles

Search for extragalactic sources of ultrahigh-energy cosmic rays

Possible extragalactic sources of cosmic rays at energies above 4*10^{19} eV detected with the Yakutsk array are sought. Correlation of the shower arrival directions with objects from Veron's catalog that are located closer than 100 Mpc from the Earth confirms the observations at the Pierre Auger observatory, as well as the Greisen-Zatsepin-Kuzmin effect on ultrahigh-energy cosmic rays. The detailed analysis of the data reveals the classes of objects belonging to the active galactic nuclei that are probable sources of ultrahigh-energy cosmic rays.

Nearby AGN and their hosts in the near infrared

We present near infrared ISAAC VLT observations of nine nearby (0.01 ≤ z ≤ 0.06) Active Galactic Nuclei selected from the Hamburg/ESO Survey and the Veron-Cetty & Veron catalog. Hydrogen recombination lines Paα and Brγ are observed in seven of the nine sources of which five show a broad component. In three sources, extended 1-0S(1) rotational-vibrational molecular hydrogen emission is detected. Stellar CO absorption is seen in four sources. In one of these objects, an upper limit of the central mass can be determined from the stellar velocity field. H -a ndKs-band imaging allow us to determine the morphology class of the host galaxies. Colors (with supplementary J-band 2MASS images) show that the four galaxies with detected CO absorption are characterized by an overall strong stellar contribution. One galaxy shows an increased extinction towards the nucleus. After removal of the nuclear point source, the host galaxies show colors typical for non-active spiral galaxies.

Search for Cross‐Correlations of Ultrahigh‐Energy Cosmic Rays with BL Lacertae Objects

Data taken in stereo mode by the High Resolution Fly's Eye (HiRes) air fluorescence experiment are analyzed to search for correlations between the arrival directions of ultrahigh-energy cosmic rays with the positions of BL Lacertae objects. Several previous claims of significant correlations between BL Lac objects and cosmic rays observed by other experiments are tested. These claims are not supported by the HiRes data. However, we verify a recent analysis of correlations between HiRes events and a subset of confirmed BL Lac objects from the 10th Veron Catalog, and we study this correlation in detail. Due to the a posteriori nature of the search, the significance level cannot be reliably estimated and the correlation must be tested independently before any claim can be made. We identify the precise hypotheses that will be tested with statistically independent data.

Star formation in quasar and active galaxy environments

We use the 2dF public 100 K data release of galaxies and samples of quasars and active galaxies taken from the Veron-Cetty and Veron catalogue to study the nature of galaxies in the surroundings of active objects withredshifts in the range 0.1 3.5, in the vicinity of quasars and active galaxies compared to that in the neighbourhood of typical galaxies, bright early types and groups. This effect extends up to projected distance rp ∼ 1 h - 1 Mpc for active galaxies and r p ∼ 3 h - 1 Mpc for quasars. We also find a tendency for companion galaxies of quasars to be brighter than the neighbours of active galaxies within r p ∼ 3 h - 1 Mpc. We estimate average star-formation rates for objects at different distances from quasars, active galaxies, galaxies and groups. We find a significantly higher star-formation activity within ∼2.0 h - 1 Mpc from quasars with respect to typical galaxies, which reinforces the idea that star formation is enhanced in the neighbourhood of quasars. Our tests with the group environment provide evidence against quasars being associated with groups. Also, our analysis of the neighbours of bright early types shows that although these galaxies are typical hosts of quasars, their companion galaxies are significantly different in terms of the star-formation activity.

Quasars in the 2MASS Second Incremental Data Release

Using the 2MASS Second Incremental Data Release, we have searched for near-infrared counterparts to 13214 quasars from the Veron-Cetty & Veron catalog. We have detected counterparts within 4'' for 2277 of the approximately 6320 quasars within the area covered by the 2MASS Second Incremental Data Release. Only 1.6% of these are expected to be chance coincidences. Though this sample is heterogeneous, we find that known radio-loud quasars are more likely to have large near-infrared-to-optical luminosity ratios than radio-quiet quasars are, at a statistically significant level. This is consistent with dust-reddened quasars being more common in radio-selected samples than in optically selected samples, due to stronger selection effects against dust-reddened quasars in the latter. We also find a statistically significant dearth of optically luminous quasars with large near-infrared-to-optical luminosity ratios. This can be explained in a dust obscuration model but not in a model where synchrotron emission extends from the radio into the near-infrared and creates such large ratios. We also find that selection of quasar candidates from the B-J/J-K color-color diagram, modeled on the V-J/J-K selection method of Warren, Hewett, & Foltz, is likely to be more sensitive to dust-obscured quasars than selection using only infrared-infrared colors.

Host Galaxies and Circumgalactic Environment of “Narrow Line” Seyfert 1 Nuclei

This paper presents a statistical study of the host galaxies and environment for a sample of 27 narrow line Seyfert 1 (NLSy1) nuclei, based on a computer-aided search of companions in the Digitized Sky Survey. The sample includes all objects listed as NLSy1 in the Veron-Cetty & Veron catalog (8th edition) with redshift in the range 0.010 ≤ z ≤ 0.061 and Galactic latitude |b| ≥ 30°. We compared the environments of NLSy1's with those of Seyfert 1 and Seyfert 2 galaxies using the method and the Seyfert samples employed in 1999 by Dultzin-Hacyan et al. The frequency of physical companions was measured within a search radius equal to 3 times the diameter DS of each NLSy1 and up to a projected linear distance of ≈100 kpc. No statistical difference was found between the environments of NLSy1's and those of Seyfert 1 galaxies. Our results further suggest that NLSy1 hosts may show fewer companions and may be preferentially farther away from bright companion galaxies than normal galaxies with similar morphological type, diameter, and redshift distribution. The results for host galaxies and environments help to disprove the hypothesis that NLSy1 objects have characteristics similar to those of Seyfert 2 galaxies: whereas Seyfert 2 galaxies show a highly significant excess of bright companions, Seyfert 1's and NLSy1's do not. The morphological distribution of NLSy1's and Seyfert 1 objects is similar, but NLSy1 nuclei are hosted in galaxies smaller than Seyfert 1 and nonactive galaxies, to a statistical confidence level of 95%. These results support the interpretation of NLSy1 nuclei (suggested by X-ray observations) as Seyfert 1 nuclei with higher Eddington ratio, since smaller diameter galaxies may host central black holes of lower mass.

Quasar‐Galaxy and AGN‐Galaxy Cross‐Correlations

We compute quasar-galaxy and AGN-galaxy cross-correlation functions for samples taken from the Veron-Cetty & Veron catalog of quasars and active galaxies, using tracer galaxies taken from the Edinburgh/Durham Southern Catalog. The sample of active galaxy targets shows positive correlation at projected separations rp<6 h−1 Mpc consistent with the usual power law. On the other hand, we do not find a statistically significant positive quasar-galaxy correlation signal except in the range 3 h−1 Mpc<rp<6 h−1 Mpc, where we find similar AGN-galaxy and quasar-galaxy correlation amplitudes. At separations rp<3 h−1 Mpc, a strong decline of quasar-galaxy correlations is observed, suggesting a significant local influence of quasars in galaxy formation. In an attempt to reproduce the observed cross-correlation between quasars and galaxies, we have performed cold dark matter cosmological hydrodynamic simulations and tested the viability of a scenario based on the model developed by Silk & Rees. In this scheme a fraction of the energy released by quasars is considered to be transferred into the baryonic component of the intergalactic medium in the form of winds. The results of the simulations suggest that the shape of the observed quasar-galaxy cross-correlation function could be understood in a scenario where a substantial amount of energy is transferred to the medium at the redshift of maximum quasar activity.

Distribution and evolution of quasars

In this paper we investigate: a) The evolution of quasars on the basis of gravitational contraction model of proto-galaxies. This is done by studying the number density of quasars given by Veron catalogue [1] in different luminosity classes. The order of classes increase with increasing the luminosity of corresponding quasars. It is shown that the decay of quasars is more sensible to their luminosities as expected by assuming that they are evolved from the contraction of slowly rotating proto-galaxies. The role of the angular momentum in the evolution of galaxies is emphasized by the results obtained from the size-luminosity relation of about 40,000 normal galaxies given by LEDA database [2]. In the model mentioned above the normal galaxies are assumed to be evolved from the contraction of relatively fast rotating proto-galaxies. b) The filamentary structures and voids of the large scale universe by plotting the entire sky map of quasars in the galactic coordinate. This is done by assuming that these objects are at cosmological distances. The result which is plotted in the following figure, seems to show some spatial correlations of quasars distribution. The region of missing quasars is due to the dust clouds in our galaxy which block our view of other quasars. Note the voids and clumpy distribution of quasars looking like filaments.

Seyfert Galaxies and Their Environment

The role played by environment on nuclear activity in galaxies is not clear and largely debated (see e.g. Barnes &amp; Hernquist 1992, Kelm 1996). To overcome statistical uncertainties, environment properties of two large samples of Seyfert galaxies (Sy 1 and Sy 2 have been kept separated) have been computed and compared with equivalent size “normal galaxy” sample ones. Seyfert samples have been extracted from the Veron &amp; Veron catalogue (Veron &amp; Veron 1996), whilst “normal galaxies” have been randomly extracted from ZCAT (Huchra 1993). The samples are limited in cz ([1500–9500] km/sec) and contain 149 Sy 1, 173 Sy 2 and 160 “normal galaxies” (hundreds of random extractions from ZCAT). For each galaxy neighbors have been computed (from ZCAT) within two variables radii, R (isolation radius) and r (pair separation), which span [0.2 - 2] h100 Mpc. and [20–90]h100 kpc. respectively. Neighbors must lie also within 700 km/sec from the galaxy. In this way, for each value of R and r, environment of each galaxy has been “quantified”.

A Survey for H 2O Megamasers in Active Galactic Nuclei. I. Observations

We report an extensive search for 22 GHz H_2_O maser emission from nearby active galaxies. Our sample includes all Seyfert and LINER galaxies listed in the Huchra catalog or the Veron-Cetty &amp; Veron catalog with recessional velocities less than 7000 km s^-1^, and all Seyfert galaxies and LINERs in Huchra's catalog with m_b_ &lt;= 14. In addition to these distance- and magnitude-limited samples, we have also observed a number of active galaxies, including radio galaxies, at higher redshift; In all, some 354 galaxies have been surveyed. Ten new H_2_O megamaser sources have been detected, resulting in 16 galaxies that are currently known to contain H_2_O masers with isotropic luminosities greater than 20 L_sun_. Of the observed active galaxies with cz &lt; 7000 km s^-1^, 5.4% have detectable H_2_O megamaser emission. This fraction increases to 11% for those sources with cz &lt; 2000 km s^-1^. The newly discovered megamaser sources were monitored on subsequent observing runs. The strength of the maser features varies for these sources, as they do for Galactic masers. Three of the galaxies have sufficient data to test for velocity changes of narrow maser components comparable in magnitude to those of the well-studied systemic features in NGC 4258. The maser line in one of these galaxies-NGC 2639-is found to have a systematic redward velocity drift of 6.6 +/- 0.4 km s^-1^ yr^-1^. No systematic velocity drifts are found for the other two sources. We also report large apparent velocity changes in the unusual broad H_2_O emission feature in NGC 1052.

Galaxies clustering around QSOs with Z = 0.9-1.5 and the origin of blue field galaxies

Deep CCD images were obtained in Mould-Cousins R and I passbands of 16 radio quasars with z values between 0.9 and 1.5 and absolute values of b above 35 deg, chosen from the Veron-Cetty and Veron (1984) catalog. Results indicate that, in this population of radio quasars, there is a statistically significant excess of galaxies within 15 arcsec of the quasars and brighter than R = 23 and I = 22. However, contrary to the report of Tyson (1986), no excess was found of galaxies with R less than 21 lying within 30 arcsec of quasars in this redshift range. Data were also obtained for very blue galaxies seen among objects in the general field, all of which are bluer in R-I than Magellanic irregulars at any redshift less than 3. It is suggested that this population might be comprised of low-redshift low-luminosity (H II region) galaxies of the type studied by French (1980) and/or higher redshift galaxies with strong cooling flows and forbidden O II lines.

A Search for Companions to High Redshift (z ≥ 3.0) Quasars

Following the discovery by Djorgovski et al. (1985) of a companion to the high redshift quasar PKS 1614+051, we initiated a systematic search for such objects with the Danish 1.5 meter telescope at La Silla. The observing technique is CCD exposures in narrow filters (FWHM=100Å) centered on the redshifted Lyα. For an exposure time of 40 min. Our limiting magnitude is around 22.0 (where the r.m.s. error is approximately ±0.15), according to test runs with DAOPHOT. The aim of the search is to clarify the nature of such companions: are they “primordial” galaxies? Lyα clouds associated with the quasar? - and how frequent is such a phenomenon? Up to now we have covered 26 fields around quasars with redshift ≥3.0 (which is about 25% of all high redshift quasars in the Veron and Veron Catalogue). Furthermore 12 fields around z≈2.5 has also been observed (see Table 1). A quick visual inspection of all our frames has not revealed any companions except for the object found by Djorgovski et al. (which is easily picked up by our technique). However, a thorough photometric reduction (using DAOPHOT) might reveal fainter candidates. Taken together with the fields reported observed by Hu and Cowie (1987) and Djorgovski et al. (1987), a total of about 50 fields have so far been observed. The preliminary conclusion is therefore that such companions, whatever they might be, are very rare, and certainly much rarer than similar systems found around quasars of low redshift.

Quasar clustering in Sculptor and in the Veron catalog

Quasar clustering in Sculptor and in the Veron catalog