Search

We compare the distribution of optically and Halpha (Ha) selected galaxies in the Southern half of the nearby Abell 85 (A85) cluster with the recently discovered X-ray filament (XRF). We search for galaxies where star formation (SF) may have been triggered by interactions with intracluster gas or tidal pressure due to the cluster potential when entering the cluster. Our analysis is based on images obtained with CFHT MegaPrime/MegaCam (1x1 deg2 field) in four bands (ugri) and ESO 2.2mWFI (38'x36' field) in a narrow band filter corresponding to the redshifted Halpha (Ha) line and in a broad R-band filter. The LFs are estimated by statistically subtracting a reference field. Background contamination is minimized by cutting out galaxies redder than the observed red sequence in the g-i vs. i colour-magnitude diagram. The galaxy distribution shows a significantly flattened cluster, whose principal axis is slightly offset from the XRF. The analysis of the broad band LFs shows that the filament region is well populated. The filament is also independently detected as a gravitationally bound structure by the Serna & Gerbal hierarchical method. 101 galaxies are detected in Ha, among which 23 have spectroscopic redshifts in the cluster, 2 have spectroscopic redshifts higher than the cluster and 58 have photometric redshifts that tend to indicate that they are background objects.The 23 galaxies with spectroscopic redshifts in the cluster are mostly concentrated in the South part of the cluster and along the filament. We find a number of galaxies showing evidence for SF in the XRF, and all our results are consistent with the previous hypothesis that the XRF in A85 is a gravitationally bound structure made of groups falling on to the main cluster., Comment: Accepted in A&A. 39 pages, 107 figures. Full resolution images available at ftp://ftp.iap.fr/pub/from_users/gam/A85/

We investigate the LF in the very relaxed cluster Abell 496. Our analysis is based on deep images obtained at CFHT with MegaPrime/MegaCam in four bands (ugri) covering a 1x1 deg2 region, which is centered on the cluster Abell 496 and extends to near its virial radius. The LFs are estimated by statistically subtracting a reference field taken as the mean of the 4 Deep fields of the CFHTLS survey. Background contamination is minimized by cutting out galaxies redder than the observed Red Sequence in the g-i versus i colour-magnitude diagram. In Abell 496, the global LFs show a faint-end slope alpha=-1.55+/-0.06 and vary little with observing band. Without colour cuts, the LFs are much noisier but not significantly steeper. The faint-end slopes show a statistically significant steepening from alpha=-1.4+/-0.1 in the central region (extending to half a virial radius) to -1.8+/-0.1 in the Southern envelope of the cluster. Cosmic variance and uncertain star-galaxy separation are our main limiting factors in measuring the faint-end of the LFs. The large-scale environment of Abell 496, probed with the fairly complete 6dFGS catalogue, shows a statistically significant 36 Mpc long filament at PA=137 deg, but we do not find an enhanced LF along this axis. Our LFs do not display the large number of dwarf galaxies (alpha ~ -2) inferred by several authors, whose analyses may suffer from field contamination caused by inexistent or inadequate colour cuts. Alternatively, different clusters may have different faint-end slopes, but this is hard to reconcile with the wide range of slopes found for given clusters and for wide sets of clusters., Comment: Accepted in A&A. 13 pages, 11 figures

The highly obscured radio-bright galaxy PKS1343-601 (l=309.7, b=+1.8) has been suspected to mark the centre of a hitherto unknown cluster in the Great Attractor region. As such it presents an ideal region for a search of galaxies in the near-infrared (NIR) and an in-depth study of their colours as a function of extinction. A visual search of a ~30 square-degree area centered on this radio galaxy on images of the NIR DENIS survey (IJK) revealed 83 galaxies (including two AGNs) and 39 possible candidates. Of these, 49 are also listed in the 2MASS Extended Source Catalog 2MASX. Taking the IRAS/DIRBE extinction values (Schlegel et al. 1998) at face value, the absorption in the optical (A_B) ranges from ~2m to over 100m across the Galactic Plane. Comparing the detections with other systematic surveys, we conclude that this search is highly complete up to the detection limits of the DENIS survey and certainly surpasses any automatic galaxy finding algorithm applied to crowded areas. The NIR galaxy colours from the 7" aperture were used as a probe to measure total Galactic extinction. A comparison with the IRAS/DIRBE Galactic reddening maps suggests that the IRAS/DIRBE values result in a slight overestimate of the true extinction at such low Galactic latitudes; the inferred extinction from the galaxy colours corresponds to about 87% of the IRAS/DIRBE extinctions. Although this determination still shows some scatter, it proves the usefulness of NIR surveys for calibrating the IRAS/DIRBE maps in the extinction range of 2m < A_B < 12m., Comment: 28 pages, 15 figures, submitted to A&A

Elements of kinematical and dynamical modeling of elliptical galaxies (Es) are presented. In projection, NFW models resemble Sersic models, but with a very narrow range of shapes (m=3+/-1). The total density profile of Es cannot be NFW-like because the predicted local M/L and aperture velocity dispersion within an effective radius (Re) are much lower than observed. Stars must then dominate Es out to a few Re. Fitting an NFW model to the total density profile of Sersic+NFW (stars+dark matter [DM]) Es results in very high concentration parameters, as found by X-ray observers. Kinematical modeling of Es assuming an isotropic NFW DM model underestimates M/L at the virial radius by a factor of 1.6 to 2.4, because dissipationless LCDM halos have slightly different density profiles and slightly radial velocity anisotropy. In N-body+gas simulations of Es as merger remnants of spirals embedded in DM halos, the slope of the DM density profile is steeper when the initial spiral galaxies are gas-rich. The Hansen & Moore (2006) relation between anisotropy and the slope of the density profile breaks down for gas and DM, but the stars follow an analogous relation with slightly less radial anisotropies for a given density slope. Using kurtosis (h_4) to infer anisotropy in Es is dangerous, as h_4 is also sensitive to small levels of rotation. The stationary Jeans equation provides accurate masses out to 8 Re. The discrepancy between the modeling of Romanowsky et al. (2003), indicating a dearth of DM in Es, and the simulations analyzed by Dekel et al. (2005), which match the spectroscopic observations of Es, is partly due to radial anisotropy and to observing oblate Es face-on. However, one of the 15 solutions to the orbit modeling of Romanowsky et al. is found to have an amount and concentration of DM consistent with LCDM predictions., Comment: Invited talk, 21st IAP meeting, Mass Profiles and Shapes of Cosmological Structures, ed. G. A. Mamon, F. Combes, C. Deffayet & B. Fort (Paris: EDP). 10 pages, 7 figures (8 plots)

High-resolution N-body re-simulations of 15 massive (10^{14}-10^{15} Msun) dark matter haloes have been combined with the hybrid galaxy formation model GalICS (Hatton et al. 2003), to study the formation and evolution of galaxies in clusters, within the framework of the hierarchical merging scenario. New features in GalICS include a better description of galaxy positioning within dark matter haloes, a more reliable computation of the temperature of the inter-galactic medium as a function of redshift, and a description of the ram pressure stripping process. We focus on the luminosity functions, morphological fractions and colour distributions of galaxies in clusters and in cluster outskirts, at z=0. No systematic dependency on cluster richness is found either for the galaxy luminosity functions, morphological mixes, or colour distributions. Moving from higher density (cluster cores), to lower density environments (cluster outskirts), we detect a progressive flattening of the luminosity functions, an increase of the fraction of spirals and a decrease of that of ellipticals and S0s, and the progressive emergence of a bluer tail in the distributions of galaxy colours, especially for spirals. As compared to cluster spirals, early-type galaxies show a flatter luminosity function, and more homogeneous and redder colours. An overall good agreement is found between our results and the observations, particularly in terms of the cluster luminosity functions and morphological mixes. However, some discrepancies are also apparent, with too faint magnitudes of the brightest cluster members, especially in the B band, and galaxy colours tendentially too red (or not blue enough) in the model, with respect to the observations. Finally, ram pressure stripping appears to affect very little our results., Comment: Accepted for publication in MNRAS. 17 pages, 11 figures. High-resolution Figure 1 available in the on-line version of the paper

There is strong evidence that the mass in the Universe is dominated by dark matter, which exerts gravitational attraction but whose exact nature is unknown. In particular, all galaxies are believed to be embedded in massive haloes of dark matter. This view has recently been challenged by surprisingly low random stellar velocities in the outskirts of ordinary elliptical galaxies, which were interpreted as indicating a lack of dark matter (Mendez et al. 2001; Romanowsky et al. 2003). Here we show that the low velocities are in fact compatible with galaxy formation in dark-matter haloes. Using numerical simulations of disc-galaxy mergers, we find that the stellar orbits in the outer regions of the resulting ellipticals are very elongated. These stars were torn by tidal forces from their original galaxies during the first close passage and put on outgoing trajectories. The elongated orbits, combined with the steeply falling density profile of the observed tracers, explain the observed low velocities even in the presence of large amounts of dark matter. Projection effects when viewing a triaxial elliptical can lead to even lower observed velocities along certain lines of sight., Comment: Letter to Nature, 13+15 pages, 2+11 figures, improved text, extended Supplementary Information added

The origin of the deficiency in neutral Hydrogen of 13 spiral galaxies lying in the outskirts of the Virgo cluster is reassessed. If these galaxies have passed through the core of the cluster, their interstellar gas should have been lost through ram pressure stripping by the hot X-ray emitting gas of the cluster. We analyze the positions of these HI-deficient and other spiral galaxies in velocity-distance plots, in which we include our compilation of velocity-distance data on 61 elliptical galaxies, and compare with simulated velocity-distance diagrams obtained from cosmological N-body simulations. We find that ~20% relative Tully-Fisher distance errors are consistent with the great majority of the spirals, except for a small number of objects, whose positions in the velocity-distance diagram suggest grossly incorrect distances, which implies that the Tully-Fisher error distribution function has non-gaussian wings. Moreover, we find that the distance errors may lead to an incorrect fitting of the Tolman-Bondi solution that can generate significant errors in the distance and especially the mass estimates of the cluster. We suggest 4 possibilities for the outlying HI-deficient spirals (in decreasing frequency): 1) they have large relative distance errors and are in fact close enough (at distances between 12.7 and 20.9 Mpc from us) to the cluster to have passed through its core and seen their gas removed by ram pressure stripping; 2) their gas is converted to stars by tidal interactions with other galaxies; 3) their gas is heated during recent mergers with smaller galaxies; and 4) they are in reality not HI-deficient (e.g. S0/a's misclassified as Sa's)., Comment: 22 pages, 6 figures. Accepted for publication in A&A

Spiral galaxies that are deficient in neutral Hydrogen are observed on the outskirts of the Virgo cluster. If their orbits have crossed the inner parts of the cluster, their interstellar gas may have been lost through ram pressure stripping by the hot X-ray emitting gas of the cluster. We estimate the maximum radius out to which galaxies can bounce out of a virialized system using analytical arguments and cosmological N-body simulations. In particular, we derive an expression for the turnaround radius in a flat cosmology with a cosmological constant that is simpler than previously derived expressions. We find that the maximum radius reached by infalling galaxies as they bounce out of their cluster is roughly between 1 and 2.5 virial radii. Comparing to the virial radius of the Virgo cluster, which we estimate from X-ray observations, these HI-deficient galaxies appear to lie significantly further away from the cluster center. Therefore, if their distances to the cluster core are correct, the HI-deficient spiral galaxies found outside of the Virgo cluster cannot have lost their gas by ram pressure from the hot intracluster gas., Comment: A&A, in press. 8 pages LaTeX2e with 1 figure

Where's the matter? The answer seems to be: ``distributed according to a power spectrum with at least one feature (local maximum) near 120-130h^-1Mpc''. Analyses of the Iovino, Clowes & Shaver quasar candidate catalogue at z~2 and the 2dF Quasar Survey 10K Release (2QZ-10K) support this claim, which has previously been made both for low redshift survey analyses and for high z~3) redshift surveys will be presented. This feature (i) offers a comoving standard ruler which can lift the matter density-cosmological constant (Omega_m-Omega_Lambda) degeneracy and (ii) might be due either to baryonic acoustic oscillations or to Planck epoch physics which survives through inflation. (i) The 95% confidence constraint from the 2QZ-10K is Omega_m= 0.25\pm0.15, Omega_Lambda=0.60{\pm0.35}. This constraint is independent of cosmic microwave background constraints and type Ia supernovae constraints. The only assumptions required are (a) that the Universe satisfies a perturbed Friedmann-Lema\^{\i}tre-Robertson-Walker model with a possibly non-zero cosmological constant, (b) that the density perturbations in this model on large scales (>> 10h^-1Mpc) remain small (``linear'') and approximately spatially fixed in comoving coordinates, (c) that the statistics (power spectrum or correlation function) of the perturbations are redshift independent, and (d) that quasar redshifts are cosmological., Comment: 2 pages, 1 figure, proceedings of Marseille conference 25-29 June 2001, "Where's the Matter? Tracing Dark and Bright Matter with the New Generation of Large Scale Surveys", June 2001, eds Treyer & Tresse, Frontier Group

Detections of local maxima in the density perturbation spectrum at characteristic comoving scales L~100-200h^{-1}Mpc have previously been claimed. Here, this cosmic standard ruler is sought in the ``10K'' release of the 2dF QSO Redshift Survey (2QZ-10K), by estimating the comoving, spatial correlation functions \xi(r) of the three-dimensional distribution of the N=2378 quasars in the most completely observed and ``covered'' sky regions, over the three redshift ranges 0.6 < z < 1.1, 1.1 < z < 1.6 and 1.6 < z < 2.2. Because of the selection method of the survey and sparsity of the data, the analysis was done conservatively to avoid non-cosmological artefacts. (i) Avoiding 'a priori' estimates of the length scales of features, local maxima in \xi(r) are found in all three redshift ranges. The requirement that a local maximum be present in all three redshift ranges at a fixed comoving length scale implies strong, purely geometric constraints on the local cosmological parameters. The length scale of the local maximum common to the three redshift ranges is 2L= (244\pm17)h^{-1}Mpc. (ii) For a standard FLRW model, the matter density \Omm and cosmological constant \Omega_\Lambda are constrained to \Omm= 0.25\pm0.10, \Omega_\Lambda=0.65\pm0.25 (68% confidence), \Omm= 0.25\pm0.15, \Omega_\Lambda=0.60\pm0.35 (95%), respectively, *from the 2QZ-10K alone*. Independently of the SNe Ia data, the zero cosmological constant model (\Omega_\Lambda=0) is rejected at the 99.7% confidence level. (iii) For an effective quintessence (w_Q) model and zero curvature, w_Q<-0.5 (68%), w_Q<-0.35 (95%) are found, again *from the 2QZ-10K alone*., Comment: 16 pages, 15 figures, accepted, Astronomy & Astrophysics, minor changes in revised version

Bottom-up hierarchical formation of dark matter haloes is not as monotonic as implicitly assumed in the Press-Schechter formalism: matter can be ejected into tidal tails, shells or low density `atmospheres'. The implications that the possible truncation of star formation in these tidal `debris' may have for observational galaxy statistics are examined here using the ArFus N-body plus semi-analytical galaxy modelling software. Upper and lower bounds on stellar losses implied by a given set of N-body simulation output data can be investigated by choice of the merging/identity criterion of haloes between successive N-body simulation output times. A median merging/identity criterion is defined and used to deduce an upper estimate of possible star formation and stellar population losses. A largest successor merging/identity criterion is defined to deduce an estimate which minimises stellar losses. In the N-body simulations studied, the debris losses are short range in length and temporary; maximum loss is around 16%. The induced losses for star formation and luminosity functions are strongest (losses of 10%-30%) for low luminosity galaxies and at intermediate redshifts (1 < z < 3). This upper bound on likely losses is smaller than present observational uncertainties. Hence, Press-Schechter based galaxy formation models are approximately valid despite ignoring loss of debris, provided that dwarf galaxy statistics are not under study., Comment: 17 pages, 14 figures, accepted for Astronomy & Astrophysics

We discuss the possibilities of extragalactic large-scale studies behind the Zone of Avoidance (ZOA) using complementary multi-wavelength data from optical, systematic blind HI, and near-infrared (NIR) surveys. Applying these data to the NIR Tully-Fisher relation permits the mapping of the peculiar velocity field across the ZOA. Here, we present results of a comparison of galaxies identified in the rich low-latitude cluster Abell 3627 in the B-band with NIR (DENIS) data, and cross-identifications of galaxies detected with the blind Parkes HI Multibeam survey with NIR data - many of which are optically invisible., Comment: 9 pages, 5 figures, Latex using newpasp.sty; to appear in Mapping the Hidden Univese, ASP Conf. Ser., eds. R.C. Kraan-Korteweg, P.A. Henning, H. Andernach

We have compiled the near infrared Point Source Catalogue (PSC) towards the Magellanic Clouds (MCs) extracted from the data obtained with the Deep Near Infrared Survey of the Southern Sky - DENIS (Epchtein et al. 1997). The catalogue covers an area of of 19.87* 16 square degrees centered on (RA, DEC)=(5h27m20s, -69o00'00'') for the Large Magellanic Cloud (LMC) and 14.7* 10 square degrees centered on (RA, DEC)=(h02m40s, -73o00'00'' for the Small Magellanic Cloud (SMC) at the epoch J2000. It contains about 1300000 sources towards the LMC and 300000 sources towards the SMC each detected in at least 2 of the 3 photometric bands involved in the survey (I, J, Ks). 70% of the detected sources are true members of the Magellanic Clouds, respectively and consist mainly of red giants, asymptotic giant branch stars and super-giants. The observations have all been made with the same instrument and the data have been calibrated and reduced uniformly. The catalogue provides a homogeneous set of photometric data., Comment: 1 figure changed, published

A galaxy system must have a minimum velocity dispersion for its mass to be greater than the sum of the masses of its galaxies. Nearly half of the nearby Hickson compact groups (HCGs) have too low a velocity dispersion in comparison with the rotational velocities of their spiral galaxies and internal velocity dispersions of their early types. A detailed study of the low velocity dispersion group, HCG 16 -- the only known group of late-type galaxies with diffuse intergalactic X-ray emitting hot gas -- reveals that half of the diffuse X rays are associated with foreground/background sources and the remaining gas is clumpy and mostly associated with the bright galaxies of the group. The large-scale environment of the group suggests that HCG 16 lies where a cosmological filament falls perpendicularly onto a large-scale sheet. The observed frequency of compact groups is lower than predicted from the extended Press-Schechter formalism, which also predicts that most 10^13 Msun objects in the Universe must be fairly old and hence have already coalesced into single objects, reminiscent of elliptical galaxies over-luminous in X-rays that are now being discovered. Thus, the low survival time of dense groups against the merging instability is no longer a worry for compact groups, as they form in large enough numbers. I show why other arguments against the reality of HCGs no longer hold, partly because of the biases of Hickson's sample., Comment: To appear in IAU Colloq. 174, Small Galaxy Groups (meeting held in Turku, Finland, June 1999), ed. M. Valtonen & Chris Flynn (San Francisco: ASP). 8 pages LaTeX2e, uses graphics.sty and journals.sty (included), 5 encapsulated PS figures. Full resolution paper available at ftp://ftp.iap.fr/pub/from_users/gam/PAPERS/iau174.ps.gz (1261967 bytes)

The completeness and reliability of the DENIS IJK survey and the EDSGC (derived from the COSMOS scans of USKT plates) are obtained by detailed cross-identifications and systematic visual inspections of conflictual classifications. The DENIS galaxy extraction turns out to be over 95% complete and reliable out to I < 16, while the COSMOS/EDSGC galaxy catalogue is less than 80% complete and reliable at B_J = 17.5, and even less than 10% complete at B_J < 14.5. Spectroscopic followups of DENIS and the similar Near-IR 2MASS survey are described: 1) a redshift survey of 120,000 galaxies using the 6dF robotic multi-fiber spectrograph, currently under construction at the UKST, and for which a total of 300 nights are guaranteed for 2001-2003, 2) a peculiar velocity survey of 12,000 early-type galaxies with the 6dF, and 3) the DENIS-HI peculiar velocity survey of 5000 inclined spirals visible from Nancay (delta > -38 deg), which has just begun. The DENIS-HI and 6dF peculiar velocity samples will have the strong advantage of covering entire regions of the southern sky, and combined, will multiply by 10 and 4 respectively the projected and space number densities of objects in the Southern sky. These two surveys should thus provide considerably more accurate estimates of the bulk flow, Omega_matter^{0.6}/bias, Omega_matter itself, and the primordial density fluctuation spectrum., Comment: Workshop on Cosmic Flows, held in Victoria, BC, Canada, July 13-17, 1999, ed. S. Courteau, M. Strauss & J. Willick, ASP series. 4 pages, LaTeX2e, 2 figures (encapsulated using `graphics'). Uses paspconf.sty (included)

Roughly 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various surveys are presently being employed to uncover the galaxy distribution in the Zone of Avoidance (ZOA) but all suffer from (different) limitations and selection effects. We illustrate the promise of using a multi-wavelength approach for extragalactic large-scale studies behind the ZOA, i.e. a combination of three surveys -- optical, systematic blind HI and near-infrared (NIR), which will allow the mapping of the peculiar velocity field in the ZOA through the NIR Tully-Fisher relation. In particular, we present here the results of cross-identifying HI-detected galaxies with the DENIS NIR survey, and the use of NIR colours to determine foreground extinctions., Comment: Accepted for publication in PASA. Proceedings of workshop "HI in the Local Universe, II", held in Melbourne, Sept. 1998. 9 pages, LaTeX2e, 2 encapsulated PS figures, 3 JPEG figures, Full resolution figures 2, 3 and 4 and full resolution paper are at ftp://ftp.iap.fr/pub/from_users/gam/PAPERS/HICONF/

We reanalyze the ROSAT PSPC X-ray spectro-photometric observations of HCG 16. Its X-ray morphology resembles its morphology at 20 cm, seen by the NVSS. We detect diffuse emission in 8 regions filling half of the 200/h50 kpc (8.7") radius circle around the optical center of the group: one encompassing galaxies a&b, two surrounding galaxies c&d, a clumpy region roughly 140/h50 kpc from the group galaxies, which may be gas ejected from one of the galaxies, plus regions associated with background galaxies, radio-sources or groups, and foreground stars. Excluding the background / foreground sources, we get L_X^bol = 2.3 10^41 / h50^2 erg/s, i.e. half the luminosity found by Ponman et al. The diffuse emission is cool (T < 0.55 keV [90% confidence] with a best fit T = 0.27 keV). The correction for photoelectric absorption in L_X^bol is a factor 3.5 and varies rapidly with temperature. The clumpy distribution of hot diffuse gas in HCG 16 is illustrated by the low mean X-ray surface brightness and hot gas density of the regions of undetected emission within 8' (at most 1/4 and 1/6 of those of the detected gas, assuming both have same temperature, metallicity and clumpiness). The irregular X-ray morphology of the diffuse emission rules out a (nearly) virialized nature for HCG 16, unless intergalactic gas had sufficiently high specific entropy to be unable to collapse with the group. Most of the diffuse gas originates from galaxies, either through tidal stripping or through galactic winds driven by supernova remnants. Our results show the need for a careful 2D spatial analysis and multi-wavelength study of the diffuse X-ray emission from groups, suggesting that other compact groups could be significantly contaminated by superimposed X-ray sources.(abridged), Comment: Accepted in A&A. Major revisions, including title change. Abridged abstract. Full resolution figures available at ftp://ftp.iap.fr/pub/from_users/gam/PAPERS/H16

The numerous extragalactic and cosmological motivations of the DENIS and 2MASS near infrared surveys are outlined. The performance of the DENIS survey is estimated from 50 deg^2 of high galactic latitude data (20 deg < |b| < 60 deg). Simple star/galaxy separation methods are presented and comparison with 300 visually classified objects as well as COSMOS and APM classifications. We find that the peak intensity over isophotal area is an excellent star/galaxy separation algorithm, fairly robust to variations of the PSF within the frames, achieving 98.5% completeness and 92.5% reliability for I < 16.5, in comparison with visual classification. A new estimate of the photometric accuracy for galaxies is presented. The limiting factors for homogeneous galaxy extraction at high galactic latitudes are completeness and photometric accuracy in K, photometric accuracy in J and star/galaxy separation in I (also used for classification in J and K). Galaxy counts are presented on 50 deg^2. The I counts are in excellent agreement with a Euclidean extrapolation of the published counts around I=16-17 (more so than in all previous studies), and thus point to a high normalization at the bright end, in contrast with the counts published from the APM and COSMOS plate scans. The J-band differential galaxy counts follow the relation N(J) = 12 \pm 1 dex (0.6 [J-14]) deg^{-2} mag^{-1}. Extrapolation of these high latitude counts suggest that DENIS will produce highly homogeneous catalogs of roughly 6000 (K < 11), 700,000 (J < 14.8) and, 1,000,000 (I < 16.5) galaxies, respectively with photometric accuracy of 0.08^m in I and 0.20^m in J and K. Larger highly homogeneous samples are expected with improvements to the camera and the algorithms., Comment: Invited review to appear in ``The Impact of Near-Infrared Surveys on Galactic and Extragalactic Astronomy'', meeting held in Meudon, France, June 1997, ed. N. Epchtein (Dordrecht: Kluwer). LaTeX2e, using psfig and supplied other macro. 16 pages. 7 PostScript figures inserted

The DENIS survey is currently imaging 21334 deg^2 of the mainly southern sky in the IJK and the observations are expected to go on until mid 2000. The expectations for extragalactic and cosmological research are outlined, including a quantitative assessment of the effects of recent star formation on the measured fluxes of galaxies. The galaxy extraction is much improved with the modeling of the PSF across the 12'x12' frames and the reliability of star/galaxy separation (currently based upon a combination of classical and neural-network based methods) is measured from visual inspection to be >90% at I = 16. The I band counts follow the high bright-end normalization and the J differential counts follow N(J) \simeq 11 \times dex [0.6 (J-14)] deg^{-2} mag^{-1} and are expected to be complete, reliable and photometrically accurate (\Delta m < 0.1) for J \leq 14., Comment: Invited review, XVIIth Moriond Astrophysics Meeting, Les Arcs, France, March 1997, eds. G.A. Mamon, T.X. Thuan & J. Tran Van Thanh (Paris: Frontieres) 12 pages, LaTeX2e, uses psfig, 5 PS and 3 gif figures

About 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various approaches are presently being employed to uncover the galaxy distribution in the Zone of Avoidance (ZOA) but all suffer from (different) limitations and selection effects. We investigated the potential of using the DENIS NIR survey for studies of galaxies behind the obscuration layer of our Milky Way and for mapping the Galactic extinction. As a pilot study, we recovered DENIS I, J and K band images of heavily obscured but optically still visible galaxies. We determined the I, J and K band luminosity functions of galaxies on three DENIS strips that cross the center of the nearby, low-latitude, rich cluster Abell 3627. The extinction-corrected I-J and J-K colours of these cluster galaxies compare well with that of an unobscured cluster. We searched for and identified galaxies at latitudes where the Milky Way remains fully opaque (|b| < 5deg and A_B > 4-5mag) - in a systematic search as well as around positions of galaxies detected with the blind HI survey of the ZOA currently conducted with the Multibeam Receiver of the Parkes Radiotelescope., Comment: 12 pages, including 5 PS figures, LaTeX, uses crckapb.sty and epsf.tex. Better resolved figures available upon request. To appear in proceedings of the 3rd Euroconference (Meudon, France, June 1997) on ``The Impact of Near IR Surveys'', Kluwer 1998

We investigated the potential of using DENIS for studies of galaxies behind the obscuration layer of our Milky Way, and mapping the Galactic extinction. As a pilot study, we examined DENIS I-, J-, and K-band images of heavily obscured galaxies from a deep optical (B_J-band) galaxy survey in the Zone of Avoidance. We tried to uncover additional galaxies at latitudes where the Milky Way remains fully opaque, i.e. we conducted a `blind' search at |b| < 5deg and A_B > 4-5 mag. Furthermore, we determined the I, J and K magnitudes of galaxies in the low-latitude, nearby, rich cluster Abell 3627 and compared the resulting colour-colour diagram with that of an unobscured cluster., Comment: Contributed talk, XXXIInd Moriond Meeting (les Arcs, France, March 1997) on "Extragalactic Astronomy in the Infrared". 6 pages, LateX, format file plus 5 ps-figures included. Fig 1 & 3 also available as better resolved gif-files

A statistical method is developed to infer the typical density profiles of poor galaxy systems without resort to binning of data or assuming a given center to each system. The method is applied to the accordant redshift quartets in Hickson's compact groups (HCGs). The distribution of separations in these groups is consistent with a unique generalized modified Hubble surface density profile, with best-fit asymptotic slope beta = 1.4 and core radius R_c = 18 h^{-1} kpc, although a King profile (beta = 1) is also consistent with the data (with R_c = 6 h^{-1} kpc). These distributions are more concentrated than what has been previously determined for these groups. HCGs are unlikely to act as strong gravitational lenses, but analogous systems 5 to 10 times more distant should produce a non-negligible fraction of giant arcs., Comment: ApJL in press. 12 pages, incl. 1 table and 2 figures. LaTeX, uses aaspp4

The extragalactic applications of NIR surveys are summarized with a focus on the ability to map the interstellar extinction of our Galaxy. Very preliminary extraction of galaxies on a set of 180 consecutive images is presented, and the results illustrate some of the pitfalls in attempting an homogeneous extraction of galaxies from these wide-angle and shallow surveys., Comment: Invited talk at "The Impact of Large-Scale Near-IR Sky Surveys", meeting held in Tenerife, Spain, April 1996. 10 pages LaTeX with style file and 4 PS files included

We present $K'$-band surface photometry of a sample of 31 inclined Sa-Scd galaxies, together with additional $J$- and $H$-band data for four of them. In this first paper of a series, profiles are presented, together with global and isophotal parameters. Our profiles are compared to similar $B$, $R$ and $I$ data collected from other sources. Three galaxies exhibit previously unknown small bars in their center, while in five others, such bars may also be present. Four objects present a narrow elongated feature in their center aligned with their major axis, which could be an inward extension of the disk. A few galaxies display very thin spiral arms. Color-color diagrams indicate that the extinction inside the four galaxies for which we have $JHK'$ images is limited to $A_V < 2$., Comment: Accepted in Astronomy and Astrophysics (Supplements). 11 pages LaTeX with l-aa style file and 3 figures included. Figure 4 (35 pages of figures taking over 3.5 MB uuencoded gzipped tared) is available at ftp://ftp.iap.fr/pub/from_users/gam/PAPERS/hsm_fig4.uu

The production and destruction processes for molecules in very fast protostellar winds are analyzed and modeled with a one-dimensional chemical kinetics code. Radial density and temperature distributions suggested by protostellar theory are explored as are a range of mass-loss rates. The efficiency of in situ formation of heavy molecules is found to be high if the wind temperature falls sufficiently rapidly, as indicated by theory. The degree of molecular conversion is a strong function of the mass-loss rate and of density gradients associated with the acceleration and collimation of the wind. Even in cases where essentially all of the heavy atoms are processed into molecules, a significant fraction of atomic hydrogen remains so that hghly molecular, protostellar winds are able to emit the 21-cm line. Although CO has a substantial abundance in most models relevant to very young protostars, high abundances of other molecules such as SiO and H2O signify more complete association characteristic of winds containing regions of very high density. Although the models apply only to regions close to the protostar, they are in qualitative accord with recent observations at much larger distances of both atomic and molecular emission from extremely high-velocity flow.

Recent theoretical studies of circumstellar chemistry are discussed for both red-giant and protostellar winds. The generalized photochemical model is able to account for the recently discovered silicon-bearing molecules in the prototypical, C-rich, AGB star IRC + 10216. The surprising occurrence of CO in protostellar winds that are largely atomic is interpreted to be the result of the high density and the rapid decrease of the temperature with distance that is expected for such winds.

A time-dependent chemical model is used to analyze the processes generating and destroying molecules in very high velocity winds from low-mass protostars. CO and SiO are found to be generated in significant quantities despite the persistence of H in atomic form, consistently with recent protostellar wind detections of CO and H I at velocities in excess of 100 km/sec. A moderate mass-loss rate, in conjunction with a temperature distribution that decreases rather rapidly with distance from the protostar, are the conditions for substantial molecule formation.

The CO photodissociation rate for the unshielded ISM is calculated using recent laboratory results which confirm that photodissociation occurs by way of line absorption. A value of 2.0 x 10 to the -10th/s, an order of magnitude higher than the rate used in the past, is obtained. The new rate and a treatment of the radiative transfer and shielding are used to develop a theory for the CO abundance in the circumstellar envelopes of cool, evolved stars, and results are presented on the spatial variation of CO, C, and C(+). It is shown that these distributions play important roles in determining the observational properties of circumstellar envelopes.

A theory for the ionization of the circumstellar envelopes around O-rich red giants is developed from the photochemical model. The main source of ionization is photoionization of H2O, OH, and C by the interstellar UV radiation field, supplemented by cosmic-ray ionization of hydrogen. Significant amounts of H3O(+) and HCO(+) are produced, with peak abundances of about 10 to the -7th at intermediate distances from the star. Although H3O(+) may be difficult to detect with current instrumentation, HCO(+) is probably detectable in nearby O-rich envelopes with large millimeter-wave telescopes.

An earlier theory of ionization of C-rich circumstellar envelopes based on the photochemical model is extended to include the temperature dependence of ion-molecule reactions with polar molecules, particularly HCN, and line self-shielding of CO dissociating radiation. The results are applied to the abundances of HCO(+) and HNC in C-rich circumstellar envelopes. With standard parameters for IRC + 10216, the model is found to be consistent with the new upper limit to the antenna temperature of the J = 1-0 line of HCO(+) obtained with the IRAM 30-m telescope. The photochemical model provides a natural explanation of the relatively large ratio of HCN to HNC observed for C-rich circumstellar envelopes, and good agreement is obtained for the H(C-13)N/HNC antenna temperature ratio measured for IRC + 10216.

The stellar luminosity function that has been measured in the visual band into the R, I, J, and K bands, where it has not yet been obtained directly, is transformed. The transformation is effected by subdividing the total visual function, which includes all stars, into subluminosity functions for each luminosity class (supergiants through white dwarfs), applying the known (V - D) color, D = R, I, J, K for each spectral type, and then summing the resultant transformed subluminosity functions into a total luminosity function for the band D. Simple analytic forms that accurately fit the transformed luminosity functions are given. Consideration is also given to the possibility of a systematic error resulting from the existence of a very red stellar population not accounted for in the visual band luminosity function