arXiv subjects

F. Durret

Publications and source records attributed to F. Durret.

106 records · Page 6Linked to original sources

arXiv1999

Near-infrared photometry of isolated spirals with and without an AGN. I: The Data

We present infrared imaging data in the J and K' bands obtained for 18 active spiral galaxies, together with 11 non active galaxies taken as a control sample. All of them were chosen to satisfy well defined isolation criteria so that the observed properties are not related to gravitational interaction. For each object we give: the image in the K' band, the sharp-divided image (obtained by dividing the observed image by a filtered one), the difference image (obtained by subtracting a model to the observed one), the color J-K' image, the ellipticity and position angle profiles, the surface brightness profiles in J and K', their fits by bulge+disk models and the color gradient. We have found that four (one) active (control) galaxies previously classified as non-barred turn out to have bars when observed in the near-infrared. One of these four galaxies (UGC 1395) also harbours a secondary bar. For 15 (9 active, 6 control) out of 24 (14 active, 10 control) of the optically classified barred galaxies (SB or SX) we find that a secondary bar (or a disk, a lense or an elongated ring) is present. The work presented here is part of a large program (DEGAS) aimed at finding whether there are differences between active and non active galaxies in the properties of their central regions that could be connected with the onset of nuclear activity.

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arXiv1998

The rich cluster of galaxies ABCG~85. IV. Emission line galaxies, luminosity function and dynamical properties

This paper is the fourth of a series dealing with the cluster of galaxies ABCG 85. Using our two extensive photometric and spectroscopic catalogues (with 4232 and 551 galaxies respectively), we discuss here three topics derived from optical data. First, we present the properties of emission line versus non-emission line galaxies, showing that their spatial distributions somewhat differ; emission line galaxies tend to be more concentrated in the south region where groups appear to be falling onto the main cluster, in agreement with the hypothesis (presented in our previous paper) that this infall may create a shock which can heat the X-ray emitting gas and also enhance star formation in galaxies. Then, we analyze the luminosity function in the R band, which shows the presence of a dip similar to that observed in other clusters at comparable absolute magnitudes; this result is interpreted as due to comparable distributions of spirals, ellipticals and dwarfs in these various clusters. Finally, we present the dynamical analysis of the cluster using parametric and non-parametric methods and compare the dynamical mass profiles obtained from the X-ray and optical data.

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arXiv1998

Near infrared observations of quasars with extended ionized envelopes

We have observed a sample of 15 and 8 quasars with redshifts between 0.11 and 0.87 (mean value 0.38) in the J and K' bands respectively. Eleven of the quasars were previously known to be associated with extended emission line regions. After deconvolution of the image, substraction of the PSF when possible, and identification of companions with the help of HST archive images when available, extensions are seen for at least eleven quasars. However, average profiles are different from that of the PSF in only four objects, for which a good fit is obtained with an $r^{1/4}$ law, suggesting that the underlying galaxies are ellipticals. Redshifts were available in the literature for surrounding objects in five quasar fields. For these objects, one to five companion galaxies were found. One quasar even belongs to a richness class 1 cluster. Most other quasars in our sample have nearby galaxies in projection which may also be companions. Environmental effects are therefore probably important to account for the properties of these objects.

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arXiv1998

Deep probing of the Coma cluster

As a continuation of our study of the faint galaxy luminosity function in the Coma cluster of galaxies, we report here on the first spectroscopic observations of very faint galaxies (R $\le$ 21.5) in the direction of the core of this cluster. Out of these 34 galaxies, only one may have a redshift consistent with Coma, all others are background objects. The predicted number of Coma galaxies is 6.7 $\pm$ 6.0, according to Bernstein et al. (1995, B95). If we add the 17 galaxies observed by Secker (1997), we end up with 5 galaxies belonging to Coma, while the expected number is 16.0 $\pm$ 11.0 according to B95. Notice that these two independent surveys lead to the same results. Although the observations and predicted values agree within the error, such results raise into question the validity of statistical subtraction of background objects commonly used to derive cluster luminosity functions (e.g. B95). More spectroscopic observations in this cluster and others are therefore urgently needed. As a by-product, we report on the discovery of a physical structure at a redshift z$\simeq$0.5.

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arXiv1998

The rich cluster of galaxies ABCG 85. III. Analyzing the ABCG 85/87/89 complex

We present a combined X-ray and optical analysis of the ABCG 85/87/89 complex of clusters of galaxies, based on the ROSAT PSPC image, optical photometric catalogues (Slezak et al. 1998), and an optical redshift catalogue (Durret et al. 1998). From this combined data set, we find striking alignments at all scales at PA$\simeq$160°. At small scales, the cD galaxy in ABCG 85 and the brightest galaxies in the cluster are aligned along this PA. At a larger scale, X-ray emission defines a comparable PA south-southeast of ABCG 85 towards ABCG 87, with a patchy X-ray structure very different from the regular shape of the optical galaxy distribution in ABCG 87. The galaxy velocities in the ABCG 87 region show the existence of subgroups, which all have an X-ray counterpart, and seem to be falling onto ABCG 85 along a filament almost perpendicular to the plane of the sky. To the west of ABCG 85, ABCG 89 appears as a significant galaxy density enhancement, but is barely detected at X-ray wavelengths. The galaxy velocities reveal that in fact this is not a cluster but two groups with very different velocities superimposed along the line of sight. These two groups appear to be located in intersecting sheets on opposite sides of a large bubble. These data and their interpretation reinforce the cosmological scenario in which matter, including galaxies, groups and gas, falls onto the cluster along a filament.

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arXiv1998

A kinematical analysis of NGC 2992

We present long slit spectroscopy for the [OIII] and H$α$ wavelength ranges along nine different position angles for the Sa Seyfert 1.9 galaxy NGC 2992. Double profiles are present in several regions, suggesting that the gas is not simply following galaxy rotation. A simple kinematical model, which takes into account circular rotation together with a constant radial outflow, seems to be a good approximation to account for the observed kinematics.

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arXiv1997

A photometric catalogue of galaxies in the cluster Abell 85

We present two catalogues of galaxies in the direction of the rich cluster \a85. The first one includes 4,232 galaxies located in a region $\pm 1^\circ$ from the cluster centre. It has been obtained from a list of more than 25,000 galaxy candidates detected by scanning a Schmidt photographic plate taken in the \bj band. Positions are very accurate in this catalogue but magnitudes are not. This led us to perform CCD imaging observations in the V and R bands to calibrate these photographic magnitudes. A second catalogue (805 galaxies) gives a list of galaxies with CCD magnitudes in the V and R bands for a much smaller region in the centre of the cluster. These two catalogues will be combined with a redshift catalogue of 509 galaxies (Durret et al. 1997; astro-ph/9709298) to investigate the cluster properties at optical wavelengths (Durret et al. in preparation), as a complement to our previous X-ray studies (Pislar et al. 1997, Lima-Neto et al. 1997).

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arXiv1997

A catalogue of velocities in the cluster of galaxies Abell 85

We present a catalogue of velocities for 551 galaxies (and give the coordinates of 39 stars misclassified as galaxies in our photometric plate catalogue) in a region covering about 100'$\times$100' (0.94$\times$0.94 Mpc for an average redshift of 0.0555, assuming H$_\circ$=50 km s$^{-1}$ Mpc$^{-1}$) in the direction of the rich cluster Abell 85. This catalogue includes previously published redshifts by Beers et al. (1991) and Malumuth et al. (1992), together with our 367 new measurements. A total of 305 galaxies have velocities in the interval 13350-20000 km s$^{-1}$, and will be considered as members of the cluster. Abell 85 therefore becomes one of the clusters with the highest number of measured redshifts; its optical properties are being investigated in a companion paper.

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arXiv1997

A Deep Probing of the Coma cluster

We present here results from a deep spectroscopic survey of the Coma cluster of galaxies (29 galaxies between 18.98<m_R<21.5). Only 1 of these galaxies is within Coma compared to an expected 6.7 galaxies computed from nearby control fields. This discrepancy potentially indicates that Coma's faint end luminosity function has been grossly overestimated and raises concerns about the validity of using 2D statistical subtraction to correct for the background galaxy population when constructing cluster luminosity functions.

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arXiv1997

The rich cluster of galaxies ABCG 85. II. X-ray analysis using the ROSAT HRI

We present a new X-ray analysis mainly based on ROSAT HRI data. The HRI spatial resolution combined with an improved wavelet analysis method and with complementary radio and optical data provides new results compared to a previous paper based on ROSAT PSPC data (Pislar et al. 1997). We use also redshift data in order to identify galaxies dynamically belonging to the main body of the cluster and/or to superimposed substructures. Various kinds of emission are superimposed on a mean thermal X-ray emission due to the intra-cluster gas: a) an X-ray flux excess in the centre; b) a south blob, partially generated by individual galaxies. The mean velocity and velocity dispersion of the galaxies located in this region are the same as those of the cluster as a whole: it therefore does not seem to be a bound subgroup; c) West emission due to a foreground group with self-emission from a Seyfert galaxy located at the north-west; d) emission in the south-west due to inverse Compton emission associated to a very steep radio source (the remnant of an active galactic nucleus). We have examined the possibility for the central peak to be an "unusual" galaxy, as assumed for the central galaxy of J2310-43 (Tananbaum et al. 1997). We conclude on the existence of a cooling flow region, in which the presence of at least three small features certainly related to cooler blobs is revealed by the wavelet analysis. We have performed a pixel-to-pixel modelling of the double X-ray emission. The large scale emission component is comparable to those derived from by the PSPC data and the small scale one is interpreted as a cooling-flow. A multiphase gas model analysis leads to a mass deposit of 50-150 M_\odot/yr.

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arXiv1997

The rich cluster of galaxies ABCG 85.I. X-ray analysis

We present an X-ray analysis of the rich cluster ABCG 85 based on ROSAT PSPC data. By applying an improved wavelet analysis, we show that our view of this cluster is notably changed from what was previously believed (a main region and a south blob). The main emission comes from the central part of the main body of the cluster on which is superimposed that of a foreground group of galaxies. The foreground group and the main cluster are separated (if redshifts are cosmological) by 46 1/h_50 Mpc. The southern blob is clearly not a group: it is resolved into X-ray emitting galaxies (in particular the second more luminous galaxy of the main cluster). Several X-ray features are identified with bright galaxies. We performed a spectral analysis and derived the temperature (T), metallicity (Z) and hydrogen column density NH. The global quantities are: T=4keV (in agreement with the velocity dispersion of 760km/s) and $Z=0.2Z_\odot$. We cannot derive accurate gradients for these quantities with our data, but there is strong evidence that the temperature is lower ($\sim 2.8 keV$) and the metallicity much higher (Z $\sim 0.8 Z_\odot$) in the very centre (within about 50 1/h_50 kpc). We present a pixel by pixel method to model the physical properties of the X-ray gas and derive its density distribution. We apply classical methods to estimate the dynamical, gas and stellar masses, as well as the cooling time and cooling flow characteristics. At the limiting radius of the image (1.4 1/h_50 Mpc), we find $M_{\rm Dyn}\sim (2.1-2.9)10^{14} 1/h_50 M$_{\odot}$, $M_{gas}/M_{Dyn}\sim 0.18 h_{50}^{-1.5}$. The stellar mass is $6.7\ 10^{12}M_{\odot}$, giving a mass to light ratio of $M/L_{V}\sim 300$. The cooling time is estimated for different models, leading to a cooling radius of 30-80 kpc depending on the

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arXiv1996

A photometric catalogue of the Coma cluster core

We have obtained a mosaic of CCD images of the Coma cluster in the V-band covering a region of approximately 0.4 degrees$^2$ around both central cluster galaxies NGC 4889 and NGC 4874. An additional frame of $\sim$ 90 arcmin$^2$ was taken of the south-west region around NGC 4839. We derived a catalogue of 7023 galaxies and 4096 stars containing positions, central surface brightnesses and isophotal V$_{26.5}$ magnitudes. We estimate that data is complete up to V $_{26.5}\sim$ 22.5 and the surface brightness limiting detection value is $μ$ $\sim$ 24 mag/arcsec$^2$. In this paper we present the catalogue (available in electronic form alone), along with a detailed description of the steps concerning the data reduction and quality of the computed parameters.

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arXiv1996

Environmental effects on the Coma cluster luminosity function

Using our catalogue of V$_{26.5}$ isophotal magnitudes for 6756 galaxies in a region covering 60~$\times$~25~arcmin$^2$ in the center of the Coma cluster, plus 267 galaxies in a region of 9.7~$\times$~9.4~arcmin$^2$ around NGC~4839, we derive the luminosity function in the magnitude range 13.5$\leq V_{26.5} <$ 21.0 (corresponding to the absolute magnitude range $-22.24 < M_{V26.5} \leq -14.74$). The luminosity function for this region is well fitted by the combination of a gaussian in its bright part and of a steep Schechter function (of index $α=-1.8$) in its faint part. Luminosity functions derived for individual regions surrounding the brightest galaxies show less steep slopes, strongly suggesting the existence of environmental effects. The implications of such effects and galaxy formation scenarios are discussed.

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arXiv1995

Unveiling hidden structures in the Coma cluster

We have assembled a large data-set of 613 galaxy redshifts in the Coma cluster, the largest presently available for a cluster of galaxies. We have defined a sample of cluster members complete to b$_{26.5}=20.0$, using a membership criterion based on the galaxy velocity, when available, or on the galaxy magnitude and colour, otherwise. Such a data set allows us to define nearly complete samples within a region of 1~\Mpc\ radius, with a sufficient number of galaxies per sample to make statistical analyses possible. Using this sample and the {\em ROSAT} PSPC X--ray image of the cluster, we have re-analyzed the structure and kinematics of Coma, by applying the wavelet and adaptive kernel techniques. A striking coincidence of features is found in the distributions of galaxies and hot intracluster gas. The two central dominant galaxies, NGC4874 and NGC4889, are surrounded by two galaxy groups, mostly populated with galaxies brighter than b$_{26.5}=17$ and well separated in velocity space. On the contrary, the fainter galaxies tend to form a single smooth structure with a central peak coinciding in position with a secondary peak detected in X--rays, and located between the two dominant galaxies; we suggest to identify this structure with the main body of the Coma cluster. A continuous velocity gradient is found in the central distribution of these faint galaxies, a probable signature of tidal interactions rather than rotation. There is evidence for a bound population of bright galaxies around other brightest cluster members. Altogether, the Coma cluster structure seems to be better traced by the faint galaxy population, the bright galaxies being located in subclusters. We discuss this evidence in terms of an ongoing accretion of groups onto the cluster.

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arXiv1995

New Results on the Coma cluster: Revealing the Primary Component

Recent observations of the Coma cluster of galaxies in its central region have provided approximately 250 new redshifts - allowing a good membership criterion to be established for brighter galaxies - and magnitudes for 8000 objects in the same region derived from photometric data complete up to V$_{26.5}$=22.5. A thorough structural study of the galaxy distribution of the cluster galaxies, jointly with an X-ray wavelet analysis, and with a kinematical analysis of the velocity distribution allows us to uncover a primary body of the cluster, with evidence for a velocity gradient.

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arXiv1994

On the galaxy luminosity function in the central regions of the Coma cluster

We have obtained new redshifts for 265 objects in the central 48~$\times$~25~arcmin$^2$ region of the Coma cluster. When supplemented with literature data, our redshift sample is 95~\% complete up to a magnitude b$_{26.5}$=18.0 (the magnitudes are taken from the photometric sample of Godwin et al. 1983). Using redshift-confirmed membership for 205 galaxies, and the location in the colour-magnitude diagram for another 91 galaxies, we have built a sample of cluster members which is complete up to b$_{26.5}$=20.0. We show that the Coma cluster luminosity function cannot be adequately fitted by a single Schechter (1976) function, because of a dip in the magnitude distribution at b$_{26.5}$$\sim$17. The superposition of an Erlang (or a Gauss) and a Schechter function provides a significantly better fit. We compare the luminosity function of Coma to those of other clusters, and of the field. Luminosity functions for rich clusters look similar, with a maximum at $M_{b} \simeq -19.5 + 5 \times \log h_{50}$, while the Virgo and the field luminosity functions show a nearly monotonic behaviour. These differences may be produced by physical processes related to the environment which affect the luminosities of a certain class of cluster galaxies.

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