arXiv subjects

G. A. Mamon

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

At least 73 records · Page 4Linked to original sources

arXiv2013

Paired galaxies with different activity levels and their supernovae

We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The statistical study of SN hosts shows that there is no significant difference between morphologies of hosts in our sample and the larger general sample of SN hosts in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are consistent with previous results compiled with the larger sample. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies. SN types are not correlated with the luminosity ratio of host and neighbor galaxies in pairs. The orientation of SNe with respect to the preferred direction toward neighbor galaxy is found to be isotropic and independent of kinematical properties of the galaxy pair.

astro-ph.CO↗

arXiv2013

On the Nature of Unconfirmed Supernovae

We study the nature of 39 unconfirmed supernovae (SNe) from the sky area covered by the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8), using available photometric and imaging data and intensive literature search. We confirm that 21 objects are real SNe, 2 are Galactic stars, 4 are probable SNe, and 12 remain unconfirmed events. The probable types for 4 objects are suggested: 3 SNe are of probable type Ia, and SN 1953H is probable type II SN. In addition, we identify the host galaxy of SN 1976N and correct the offsets/coordinates of SNe 1958E, 1972F, and 1976N.

astro-ph.CO↗

arXiv2013

Five Supernova Survey Galaxies in the Southern Hemisphere: Supernova Ia Rates

Based on the database of 56 supernovae (SNe) events discovered in 3838 galaxies of the southern hemisphere, we compute the rate of SNe of different types along the Hubble sequence normalized to the optical and near-infrared (NIR) luminosities as well as to the stellar mass of the galaxies. We find that the rates of Type Ia SNe show a dependence on both morphology and colors of the galaxies, and therefore, on the star-formation activity. The rate of SNe Ia can be explained by assuming that at least 15% of Ia events in spiral galaxies originate in relatively young stellar populations. We also find that the rates show no modulation with nuclear activity or environment.

astro-ph.CO↗

arXiv2013

Why does the Jeans Swindle work?

When measuring the mass profile of any given cosmological structure through internal kinematics, the distant background density is always ignored. This trick is often refereed to as the "Jeans Swindle". Without this trick a divergent term from the background density renders the mass profile undefined, however, this trick has no formal justification. We show that when one includes the expansion of the Universe in the Jeans equation, a term appears which exactly cancels the divergent term from the background. We thereby establish a formal justification for using the Jeans Swindle.

astro-ph.CO↗

arXiv2012

Supernovae and their host galaxies. I. The SDSS DR8 database and statistics

(Abridged) In this first paper of a series, we report the creation of large and well-defined database that combines extensive new measurements and a literature search of 3876 supernovae (SNe) and their 3679 host galaxies located in the sky area covered by the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). This database should be much larger than previous ones, and should contain a homogenous set of global parameters of SN hosts, including morphological classifications and measures of nuclear activity. The measurements of apparent magnitudes, diameters (D25), axial ratios (b/a), and position angles (PA) of SN host galaxies were made using the images extracted from the SDSS g-band. For each host galaxy, we analyzed RGB images of the SDSS to accurately measure the position of its nucleus to provide the SDSS name. With these images, we also provide the host galaxy's morphological type, and note if it has a bar, a disturbed disk, and whether it is part of an interacting or merging system. In addition, the SDSS nuclear spectra were analyzed to diagnose the central power source of the galaxies. Special attention was paid to collect accurate data on the spectroscopic classes, coordinates, offsets of SNe, and heliocentric redshifts of the host galaxies. The creation of this large database will help to better understand how the different types of SNe are correlated with the properties of the nuclei and global physical parameters of the host galaxies, and minimize possible selection effects and errors that often arise when data are selected from different sources and catalogs.

astro-ph.CO↗

arXiv2012

Compact Groups of Galaxies selected by stellar mass: The 2MASS Compact Group Catalogue

We present a photometric catalogue of compact groups of galaxies (p2MCGs) automatically extracted from the 2MASS extended source catalogue. A total of 262 p2MCGs are identified, following the criteria of Hickson (1982), of which 230 survive visual inspection. Only 1/4 of these groups were previously known compact groups (CGs). Among the 144 p2MCGs that have all their galaxies with known redshifts, 85 have 4 or more accordant galaxies. This v2MCG sample of velocity-filtered p2MCGs constitutes the largest sample of CGs catalogued to date, with both well-defined selection criteria and velocity filtering, and is the first CG sample selected by stellar mass. We compared the properties of the 78 v2MCGs with > 3000 km/s with the properties of other CG samples, as well as those (mvCGs) extracted from the semi-analytical model of Guo et al. (2011) run on the high-resolution Millennium-II simulation. In this mvCG sample, 2/3 of the groups are physically dense. The space density of v2MCGs within 6000 km/s is 4 times that of the Hickson sample up to the same distance and with the same criteria used here, but still 40% less than that of mvCGs. The v2MCG constitutes the first group catalogue showing statistically significant signs of wide magnitude gaps (according to Tremaine-Richstone statistics) and centrally located 1st-ranked galaxies, both consistent with the predictions obtained from mvCGs. By virtue of its automatic selection with the popular Hickson criteria, its size, its selection on stellar mass, and its statistical signs of mergers and centrally located brightest galaxies, the v2MCG catalogue appears to be the laboratory of choice to study compact groups of 4 or more galaxies of comparable luminosity. [Abridged]

astro-ph.CO↗

arXiv2012

Five supernova survey galaxies in the southern hemisphere. II. The supernova rates

Based on the database compiled in the first article of this series, with 56 SN events discovered in 3838 galaxies of the southern hemisphere, we compute the rate of supernovae (SNe) of different types along the Hubble sequence normalized to the optical and near-infrared luminosities as well as to the stellar mass of the galaxies. We find that the rates of all SN types show a dependence on both morphology and colors of the galaxies, and therefore, on the star-formation activity. The rate of core-collapse (CC) SNe is confirmed to be closely related to the Star Formation Rate (SFR) and only indirectly to the total mass of the galaxies. The rate of SNe Ia can be explained by assuming that at least 15% of Ia events in spiral galaxies originates in relatively young stellar populations. We find that the rates show no modulation with nuclear activity or environment. The ratio of SN rates between types Ib/c and II shows no trend with spiral type.

astro-ph.CO↗

arXiv2011

How do galaxies acquire their mass?

We introduce a toy model that describes (in a single equation) the mass in stars as a function of halo mass and redshift. Our model includes the suppression of gas accretion from gravitational shock heating and AGN jets mainly for M_halo > M_shock ~ 10^12 M_Sun and from a too hot IGM onto haloes with v_circ < 40 km/s, as well as stellar feedback that drives gas out of haloes mainly with v_circ < 120 km/s. We run our model on the merger trees of the haloes and subhaloes of a high-resolution dark matter cosmological simulation. The galaxy mass is taken as the maximum between the mass given by the model and the sum of the masses of its progenitors (reduced by tidal stripping). Designed to reproduce the present-day stellar mass function of galaxies, our model matches fairly well the evolution of the cosmic stellar density. It leads to the same z=0 relation between central galaxy stellar and halo mass as the one found by abundance matching and also as that previously measured at high mass on SDSS centrals. Our model also predicts a bimodal distribution (centrals and satellites) of stellar masses for given halo mass, in good agreement with SDSS observations. The relative importance of mergers depends much more on stellar than halo mass. Galaxies with m_stars > 10^11 M_Sun/h acquire most of their mass through mergers (mostly major and gas-poor), as expected from our model's shutdown of gas accretion at high M_halo. However, mergers are rare for m_stars < 10^11 M_Sun/h (greater than our mass resolution), a consequence of the curvature of the stellar vs. halo mass relation. So gas accretion must be the dominant growth mechanism for intermediate and low mass galaxies, e.g. dwarf ellipticals in clusters, except that gas-rich galaxy mergers account for the bulk of the growth of ellipticals with m_stars ~ 10^10.5 M_Sun/h, which we predict must be the typical mass of ULIRGs.

astro-ph.CO↗

arXiv2010

Deprojecting the quenching of star formation in and near clusters

Using H_delta and D_n4000 as tracers of recent or ongoing efficient star formation, we analyze the fraction of SDSS galaxies with recent or ongoing efficient star formation (GORES) in the vicinity of 268 clusters. We confirm the well-known segregation of star formation, and using Abel deprojection, we find that the fraction of GORES increases linearly with physical radius and then saturates. Moreover, we find that the fraction of GORES is modulated by the absolute line-of-sight velocity (ALOSV): at all projected radii, higher fractions of GORES are found in higher ALOSV galaxies. We model this velocity modulation of GORES fraction using the particles in a hydrodynamical cosmological simulation, which we classify into virialized, infalling and backsplash according to their position in radial phase space at z=0. Our simplest model, where the GORES fraction is only a function of class does not produce an adequate fit to our observed GORES fraction in projected phase space. On the other hand, assuming that in each class the fraction of GORES rises linearly and then saturates, we are able to find well-fitting 3D models of the fractions of GORES. In our best-fitting models, in comparison with 18% in the virial cone and 13% in the virial sphere, GORES respectively account for 34% and 19% of the infalling and backsplash galaxies, and as much as 11% of the virialized galaxies, possibly as a result of tidally induced star formation from galaxy-galaxy interactions. At the virial radius, the fraction of GORES of the backsplash population is much closer to that of the virialized population than to that of the infalling galaxies. This suggests that the quenching of efficient star formation is nearly complete in a single passage through the cluster.

astro-ph.CO↗

arXiv2010

Five supernova survey galaxies in the southern hemisphere. I. Optical and near-infrared database

The determination of the supernova (SN) rate is based not only on the number of detected events, but also on the properties of the parent galaxy population. This is the first paper of a series aimed at obtaining new, refined, SN rates from a set of five SN surveys, by making use of a joint analysis of near-infrared (NIR) data. We describe the properties of the 3838 galaxies that were monitored for SNe events, including newly determined morphologies and their DENIS and POSS-II/UKST I, 2MASS and DENIS J and Ks and 2MASS H magnitudes. We have compared 2MASS, DENIS and POSS-II/UKST IJK magnitudes in order to find possible systematic photometric shifts in the measurements. The DENIS and POSS-II/UKST I band magnitudes show large discrepancies (mean absolute difference of 0.4 mag), mostly due to different spectral responses of the two instruments, with an important contribution (0.33 mag rms) from the large uncertainties in the photometric calibration of the POSS-II and UKST photographic plates. In the other wavebands, the limiting near infrared magnitude, morphology and inclination of the galaxies are the most influential factors which affect the determination of photometry of the galaxies. Nevertheless, no significant systematic differences have been found between of any pair of NIR magnitude measurements, except for a few percent of galaxies showing large discrepancies. This allows us to combine DENIS and 2MASS data for the J and Ks filters.

astro-ph.CO↗

arXiv2009

The nature of compact groups of galaxies from cosmological simulations

The nature of compact groups (CGs) of galaxies, apparently so dense that the galaxies often overlap, is still a subject of debate: Are CGs roughly as dense in 3D as they appear in projection? Or are they caused by chance alignments of galaxies along the line-of-sight, within larger virialized groups or even longer filamentary structures? The nature of CGs is re-appraised using the z=0 outputs of three galaxy formation models, applied to the dissipationless Millennium Simulation. The same selection criteria are applied to mock galaxy catalogs from these models as have been applied by Hickson and co-workers in redshift space. We find 20 times as many mock CGs as the `HCGs' found by Hickson within a distance corresponding to 9000 km/s. This very low (5%) HCG completeness is caused by Hickson missing groups that were either faint, near the surface brightness threshold, of small angular size, or with a dominant brightest galaxy. We find that most velocity-filtered CGs are physically dense, regardless of the precise threshold used in 3D group size and line-of-sight elongation, and of the galaxy formation model used. This result also holds for mock CGs with the same selection biases as was found for the HCGs.

astro-ph.CO↗

arXiv2009

The radial distribution of core-collapse supernovae in spiral host galaxies

With the goal of providing constraints on the nature of the progenitors of core-collapse supernovae, we compare their radial distribution within their spiral host galaxies with the distributions of stars and ionized gas in the spiral disks. The normalized radial distribution of all CCSNe is consistent with an exponential law, with a possible depletion of CCSNe within one-fifth of the isophotal radius. The scale length of the distribution of type II SNe appears to be significantly larger than that of the stellar disks of their host galaxies, but consistent with the scale lengths of Freeman disks. SNe Ib/c have a significantly smaller scale length than SNe II, with little difference between types Ib and Ic. The radial distribution of type Ib/c SNe is more centrally concentrated than that of the stars in a Freeman disk, but is similar to the stellar disk distribution that we infer for the host galaxies. The scale length of the CCSN radial distribution shows no significant correlation with the host galaxy morphological type, or the presence of bars. However, low luminosity as well as inclined hosts have a less concentrated distribution of CCSNe, which are probably a consequence of metallicity and selection effects, respectively. The exponential distribution of CCSNe shows a scale length consistent with that of the ionized gas confirming the generally accepted hypothesis that the progenitors of these SNe are young massive stars. Given the lack of correlation of the normalized radial distances of CCSNe with the morphological type of the host galaxy, we conclude that the more concentrated distribution of SNe Ib/c relative to SNe II must arise from the higher metallicity of their progenitors or possibly from a shallower initial mass function in the inner regions of spirals.

astro-ph.CO↗

arXiv2008

An optical view of the filament region of Abell 85

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.

astro-ph↗

arXiv2007

The galaxy luminosity function of the Abell 496 cluster and its spatial variations

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.

astro-ph↗

arXiv2006

The highly obscured region around PKS1343-601 - I. Galactic interstellar extinctions using DENIS galaxy colours

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.

astro-ph↗

arXiv2006

Kinematical and Dynamical Modeling of Elliptical Galaxies

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.

astro-ph↗

arXiv2005

Lost & Found Dark Matter in Elliptical Galaxies

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.

astro-ph↗

arXiv2005

GALICS -- VI. Modelling Hierarchical Galaxy Formation in Clusters

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.

astro-ph↗