arXiv subjects

G. A. Mamon

Publications and source records attributed to G. A. Mamon.

90 records · Page 5Linked to original sources

arXiv2004

The origin of HI-deficiency in galaxies on the outskirts of the Virgo cluster. II. Companions and uncertainties in distances and deficiencies

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).

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arXiv2003

The origin of HI-deficiency in galaxies on the outskirts of the Virgo cluster. I. How far can galaxies bounce out of clusters?

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.

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arXiv2001

Where the Very Bright Matter is a Standard Ruler

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\^ıtre-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.

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arXiv2001

The Cosmological Constant and Quintessence from a Correlation Function Comoving Fine Feature in the 2dF Quasar Redshift Survey

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 ξ(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 ξ(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 Ω_Λare constrained to \Omm= 0.25\pm0.10, Ω_Λ=0.65\pm0.25 (68% confidence), \Omm= 0.25\pm0.15, Ω_Λ=0.60\pm0.35 (95%), respectively, *from the 2QZ-10K alone*. Independently of the SNe Ia data, the zero cosmological constant model (Ω_Λ=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*.

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arXiv2001

Star formation losses due to tidal debris in `hierarchical' galaxy formation

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.

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arXiv2000

The DENIS Point Source Catalogue towards the Magellanic Clouds

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.

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arXiv2000

Multi-wavelength Observations of Galaxies in the Southern Zone of Avoidance

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.

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arXiv1999

Clumpy diffuse X-ray emission from the spiral-rich compact galaxy group HCG16

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)

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arXiv1999

Understanding low and high velocity dispersion compact groups

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.

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arXiv1999

Near-Infrared Galaxy Surveys in 2D, 3D & 4D

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.

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arXiv1999

DENIS Observations of Multibeam Galaxies in the Zone of Avoidance

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.

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arXiv1997

Galaxies with DENIS: Preliminary star/galaxy separation and first results

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.

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arXiv1997

Galaxies and Cosmology with DENIS

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 (Δm < 0.1) for J \leq 14.

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arXiv1997

Large-Scale Structures Behind the Milky Way from Near-IR Surveys

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.

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arXiv1997

DENIS Galaxies in the Zone of Avoidance

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.

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arXiv1996

The Surface Density Profiles and Lensing Characteristics of Hickson's Compact Groups of Galaxies

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.

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arXiv1996

Preliminary galaxy extraction from DENIS images

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.

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arXiv1996

Near-infrared surface photometry of spiral galaxies

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 $A_V < 2$.

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