arXiv subjects

L. Infante

Publications and source records attributed to L. Infante.

137 records · Page 8Linked to original sources

arXiv1999

The central region of the Fornax cluster -- III. Dwarf galaxies, globular clusters, and cD halo - are there interrelations?

In this paper we briefly review the properties of the dwarf galaxy population at the core of the Fornax cluster, as well as the properties of the extraordinary rich globular cluster system and the cD halo around the central galaxy NGC 1399. In turn, the question whether a scenario in which dwarf galaxies have been accreted and dissolved in the cluster center can explain the observed properties is addressed. The possibility of accretion of a certain number of dwarf galaxies, the stripping of their globular clusters and gas, and the formation of new globular clusters from stripped infalling gas are discussed. An increase in the specific frequency of the central globular cluster system is only possible, if the infalling gas from stripped dwarfs formed globulars very efficiently and/or accreted and stripped dwarf galaxies possessed a rich globular cluster system themselves. In conclusion, we argue that although the dwarf galaxy infall is a very attractive scenario to explain a number of properties in the system there are probably other physical mechanisms that also take place.

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arXiv1998

The central region of the Fornax cluster -- I. A catalog and photometric properties of galaxies in selected CCD fields

We present a photometric catalog (based on V and I photometry) of galaxies in the central regions of the Fornax galaxy cluster. Our 11 CCD fields cover 0.17 degrees in total. The limiting surface brightness is around 24 mag arsec^-2, similar to that of Ferguson's (1989, AJ 98, 367) catalog, whereas our limiting total magnitude is around V = 22 mag, about two magnitudes fainter. It is the surface brightness limit, however, that prevents us from detecting the counterparts of the faintest Local Group dwarf spheroidals. The photometric properties of all objects are presented as a catalog. The properties and fit parameters of the surface brightness profiles for a sub-sample are presented as a second catalog (both catalogs are available in electronic form at the CDS). We can only add 4 new dwarf galaxies to Ferguson's catalog. However, we confirm that the dwarf galaxies in Fornax follow a similar surface brightness-magnitude relation as the Local Group dwarfs. They also follow the color (metallicity) - relation seen in other galaxy clusters. A formerly suspected excess of dwarf galaxies surrounding the central cD galaxy NGC 1399 can finally be ruled out. An enhanced density of objects around NGC 1399 can indeed be seen, but it appears displaced with respect to the central galaxy and is identified as a background cluster at z = 0.11 in Paper II of these series, which will discuss spectroscopic results for our sample.

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arXiv1998

The central region of the Fornax cluster -- II. Spectroscopy and radial velocities of member and background galaxies

Radial velocities of 94 galaxies brighter than about V_tot = 20 mag in the direction of the central Fornax cluster have been measured. Except for 8 Fornax members, all galaxies lie in the background. Among the 8 members, there are 5 nucleated dwarf ellipticals that are already listed in the FCC (Ferguson 1989, AJ 98, 367). Two of the 3 ``new'' members are very compact and have surface brightnesses comparable to globular clusters, however their luminosities are in the range of dwarf elliptical nuclei. The measured line indices (especially Mg2, H beta, and iron) of the brighter of the compact objects suggest a solar metallicity, whereas the fainter compact object as well as the dE,Ns have line indices that are similar to those of old metal-poor globular clusters (GCs). However, with these data it is not possible to clearly classify the compact objects either as very bright globular clusters, isolated nuclei of dE,Ns, or even compact ellipticals. A background galaxy cluster at z = 0.11 has been found just behind the center of the Fornax cluster. This explains the excess population of galaxies reported in Paper I. The brightest galaxy of the background cluster lies only 1.1 arcmin south of NGC 1399 and is comparable in absolute luminosity with the central Fornax galaxy itself.

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arXiv1997

The Dynamics of the cD Clusters Abell 119 and Abell 133

A dynamical analysis of the structure of the clusters of galaxies Abell 119 and Abell 133 is presented, using new redshift data combined with existing data from the literature. We compare our results with those from the X-ray data for these clusters, and with those from radio data for the central cD galaxy in each cluster. A comparison of the mass estimate based on X-ray data and that obtained here after subgroups are eliminated shows them to be comparable. After the elimination of subgroups, 125 galaxy members in Abell 119 and 120 in Abell 133 give dispersions of 472 km/s and 735 km/s respectively. However, our dynamical analysis of the optical data shows little substructure in the velocity field of Abell 133, conflicting with what is seen in the Rosat X-ray map. Abell 119 seems to have multiple structures along the line of sight. We derive virial mass estimates of 3.05 X 10E14 Solar Masses for Abell 119 and 7.79 X 10E14 Solar Masses for Abell 133 within 1.5 Mpc, which agree well with the X-ray-derived masses within errors.

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arXiv1997

NGC 1427A - an LMC type galaxy in the Fornax Cluster

We have discovered that the Fornax irregular galaxy NGC 1427A is in very many respects a twin of the Large Magellanic Cloud. Based on B, V, I, and H alpha images, we find the following. The light of the galaxy is dominated by high surface brightness regions in the south-west that are superimposed by a half-ring of OB associations and H II regions indicating recent star formation. The colors of the main stellar body are (V-I) = 0.8 mag and (B-V) = 0.4 mag, comparable to the LMC colors. A low surface brightness cloud north of the main body as well as a LSB tail in the west have colors (V-I = 0.2 mag) that are more typical for blue compact dwarf galaxies. We identified a system of cluster candidates with mean ages < 2 Gyr (assuming a LMC metallicity) comprising the richest cluster system in an irregular galaxy observed up to now outside the Local Group. In X-ray wavelengths NGC 1427A appears with a relatively soft and complex spectrum.

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arXiv1996

Globular cluster systems of early--type galaxies in Fornax

We studied the properties of the globular cluster systems of five early--type galaxies in the Fornax galaxy cluster: NGC 1374, NGC 1379, NGC 1387, NGC 1427, and the central giant elliptical NGC 1399. From the investigation of their number of globular clusters, specific frequency, color distribution, surface density profile, and spatial distribution, we conclude that our faint ellipticals have no more globular clusters than spirals of the same mass, and neither differ in their other properties. For these galaxies there is no need to imply a different formation scenario of the globular cluster system. The central giant elliptical has far more globular clusters and show signatures of a different history in the building up of its globular cluster system.

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arXiv1996

Strong Clustering of Faint Galaxies at Small Angular Scales

The 2-point angular correlation function of galaxies, \wt, has been computed on equatorial fields observed with the CTIO 4m prime focus, within a total area of 2.31 deg$^2$. In the magnitude range $19\le m_R \le 21.5$, corresponding to $ \approx 0.35$, we find an excess of power in \wt at scales $2''\leθ\le6''$ over what would be expected from an extrapolation of \wt measured at larger $θ$. The significance of this excess is $\approx 5σ$. At larger scales, $6''< θ\le 24''$, the amplitude of \wt is 1.6 times smaller than the standard no evolutionary model. At these scales there is remarkable agreement between the present data and Infante \& Pritchet (1995). At large angular scales ($6''< θ\le 24''$) the data is best described by a model where clustering evolution in $ξ(r,z)$ has taken place. Strong luminosity evolution cannot be ruled out with the present data. At smaller scales, $2''\le θ\le 6''$, our data are formally fit by models where $ε=-2.4 (Ω=0.2, r_o=5.1h^{-1}$Mpc) or $r_o = 7.3h^{-1}$Mpc $(Ω=0.2, ε=0)$. If the mean redshift of our sample is 0.35 then our data show a clear detection of the scale ($\approx 19h^{-1}kpc$) where the clustering evolution approaches a highly non linear regime, i.e., $ε\le 0$. The rate at which galaxies merge has been computed. If this rate is proportional to $(1+z)^m$, then $m=2.2 \pm 0.5$.

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arXiv1996

The distance of the Fornax Cluster based on Globular Cluster Luminosity Functions

We present Globular Cluster Luminosity Functions for four ellipticals and one S0-Galaxy in the Fornax cluster of galaxies, derived from CCD photometry in V and I. The averaged turnover magnitudes are $V_{TO} = 23.80 \pm 0.06$ and $I_{TO} =22.39 \pm 0.05$, respectively. We derive a relative distance modulus $(m-M)_{Fornax} - (m-M)_{M87} = 0.08 \pm 0.09$ mag using the turnover of M87 based on HST data.

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arXiv1994

The Medium Redshift Clusters CL0017-20 and CL0500-24

We present magnitudes and redshifts of galaxies in the cluster of galaxies CL0017-20 and in the double cluster CL0500-24. Luminosity functions and velocity distributions have been derived. CL0017-20 possesses a virial mass of $2.9 \times 10^{14}$ M$_\odot$ and a \vmag band luminosity of $2.3 \pm 0.5 \times 10^{12}$ L$_\odot$ ($M/L_{\rm V} = 127$), much of it in a very compact core of size 113 kpc. Our new velocities and photometry of CL0500-24 confirm its double nature. Our group algorithm clearly detects two subconcentrations with masses 1.9 and $2.2 \times 10^{14}$ M$_{\odot}$. Its total \vmag band luminosity amounts to $2.7 \pm 0.8 \times 10^{12}$ L$_{\odot}$ ($M/L_{\rm V}$ of 157). Since the crossing and collapse times in both clusters are smaller than the age of the Universe, they appear bound and virialized. It is surprising that although $M/L$ is small in these clusters, giant arcs have been detected in both.

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arXiv1994

Counts and Colours of Faint Stars in 5 Fields Near the North Galactic Pole

Faint star number counts in the photographic \jmag band and \bvcol colour distributions are presented for a 1.08 deg$^2$ field near the North Galactic Pole. Due to the excellent star/galaxy discrimination we count stars as faint as \jmag = 23. We compare the number counts and colour distributions in 5 adjacent fields near SA57. The number counts and colour distributions are in very good agreement with previous data. However, we find that the large field-to-field scatter in the colour distributions, which we argue is real, might prevent us setting strong limits on Galactic structure. A simple two component standard model, Bahcall and Soneira (1984), fits the number counts reasonably well at the bright \jmag $< 21$, but fails notably at the faint end, even if a third component is added, as in Reid and Majewski (1993). The standard models are in good agreement with both the number counts and colour distribution at $20 < $\vmag$< 21$. Although the standard models bimodal shape of the colour distribution compares well with the data at $21 < $\vmag$< 21.5$, the number counts of stars are underestimated.

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arXiv1994

The Clustering Properties of Faint Galaxies

The two-point angular correlation function of galaxies, \wte, has been computed from a new survey of faint galaxies covering a 2 deg$^2$ area near the North Galactic Pole. This survey, which is complete to limiting magnitudes \jmag=24 and \fmag=23, samples angular scales as large as $1\degpoint5$. Faint galaxies are found to be more weakly clustered (by a factor of at least two) compared to galaxies observed locally. Clustering amplitudes are closer to model predictions in the red than in the blue. The weak clustering of faint galaxies cannot be explained by any plausible model of clustering evolution with redshift. However, one possible explanation of the clustering properties of intermediate redshift galaxies is that they resemble those of starburst galaxies and H II region galaxies, which are observed locally to possess weak clustering amplitudes. Our clustering amplitudes are also similar to those of nearby late-type galaxies, which are observed to be more weakly clustered than early-type galaxies A simple, self-consistent model is presented that predicts the fraction of galaxies in the ``excess'' population at intermediate redshifts, and correctly matches observed color distributions. The available data on the clustering properties of faint galaxies are consistent with this model if the ``excess'' population of faint blue galaxies is also the weakly clustered population. Evidence is presented that the power-law slope of the angular correlation function becomes shallower at fainter magnitudes. A similar effect is seen locally both for dwarf galaxies and for galaxies with late morphological type;

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