-
[show abstract]
[hide abstract]
ABSTRACT: We used K-band photometry, maximum rotational velocities derived from
Fabry-Perot data and HI observed and predicted masses to study, for the first
time, the K-band, stellar and baryonic Tully-Fisher relations for galaxies in
Hickson compact groups. We compared these relations with the ones defined for
galaxies in less dense environments from the GHASP survey and from a sample of
gas-rich galaxies. We find that most of the Hickson compact group galaxies lie
on the K-band Tully-Fisher relation defined by field galaxies with a few
low-mass outliers, namely HCG 49b and HCG 96c, which appear to have had strong
recent burst of star formation. The stellar Tully-Fisher relation for compact
group galaxies presents a similar dispersion to that of the K-band relation,
and it has no significant outliers when a proper computation of the stellar
mass is done for the strongly star-forming galaxies. The scatter in these
relations can be reduced if the gaseous component is taken into account, i.e.,
if a baryonic Tully-Fisher relation is considered. In order to explain the
positions of the galaxies off the K-band Tully-Fisher relation we favour a
scenario in which their luminosities are brightened due to strong star
formation or AGN activity. We argue that strong bursts of star formation can
affect the B and K-band luminosities of HCG 49b and HCG 96c and in the case of
the latter also AGN activity may affect the K-band magnitude considerably,
without affecting their total masses.
04/2013;
-
[show abstract]
[hide abstract]
ABSTRACT: We present new Gemini spectra of 14 new objects found within the HI tails of
Hickson Compact Groups 92 and 100. Nine of them are GALEX Far-UV (FUV) and
Near-UV (NUV) sources. The spectra confirm that these objects are members of
the compact groups and have metallicities close to solar, with an average value
of 12+log(O/H)~8.5. They have average FUV luminosities 7 x 10^40 erg/s, very
young ages (< 100 Myr) and two of them resemble tidal dwarf galaxies (TDGs)
candidates. We suggest that they were created within gas clouds that were
ejected during galaxy-galaxy interactions into the intergalactic medium, which
would explain the high metallicities of the objects, inherited from the parent
galaxies from which the gas originated. We conduct a search for similar objects
in 6 interacting systems with extended HI tails, NGC 2623, NGC 3079, NGC 3359,
NGC 3627, NGC 3718, NGC 4656. We found 35 UV sources with ages < 100 Myr,
however most of them are on average less luminous/massive than the UV sources
found around HCG 92 and 100. We speculate that this might be an environmental
effect and that compact groups of galaxies are more favorable to TDG formation
than other interacting systems.
06/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We have searched for young star-forming regions around the merger remnant NGC
2782. By using GALEX FUV and NUV imaging and HI data we found seven UV sources,
located at distances greater than 26 kpc from the center of NGC 2782, and
coinciding with its western HI tidal tail. These regions were resolved in
several smaller systems when Gemini/GMOS r-band images were used. We compared
the observed colors to stellar population synthesis models and we found that
these objects have ages of ~1 to 11 Myr and masses ranging from 10^3.9 to
10^4.6 Msun. By using Gemini/GMOS spectroscopic data we confirm memberships and
derive high metallicities for three of the young regions in the tail
(12+log(O/H)=8.74\pm0.20, 8.81\pm0.20 and 8.78\pm0.20). These metallicities are
similar to the value presented by the nuclear region of NGC 2782 and also
similar to the value presented for an object located close to the main body of
NGC 2782. The high metallicities measured for the star-forming regions in the
gaseous tidal tail of NGC 2782 could be explained if they were formed out of
highly enriched gas which was once expelled from the center of the merging
galaxies when the system collided. An additional possibility is that the tail
has been a nursery of a few generations of young stellar systems which
ultimately polluted this medium with metals, further enriching the already
pre-enriched gas ejected to the tail when the galaxies collided.
01/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We studied, for the first time, the near-infrared, stellar and baryonic Tully–Fisher relations for a sample of field galaxies taken from a homogeneous Fabry–Perot sample of galaxies [the Gassendi HAlpha survey of SPirals (GHASP) survey]. The main advantage of GHASP over other samples is that the maximum rotational velocities were estimated from 2D velocity fields, avoiding assumptions about the inclination and position angle of the galaxies. By combining these data with 2MASS photometry, optical colours, H i masses and different mass-to-light ratio estimators, we found a slope of 4.48 ± 0.38 and 3.64 ± 0.28 for the stellar and baryonic Tully–Fisher relation, respectively. We found that these values do not change significantly when different mass-to-light ratio recipes were used. We also point out, for the first time, that the rising rotation curves as well as asymmetric rotation curves show a larger dispersion in the Tully–Fisher relation than the flat ones or the symmetric ones. Using the baryonic mass and the optical radius of galaxies, we found that the surface baryonic mass density is almost constant for all the galaxies of this sample. In this study we also emphasize the presence of a break in the NIR Tully–Fisher relation at MH, K∼−20 and we confirm that late-type galaxies present higher total-to-baryonic mass ratios than early-type spirals, suggesting that supernova feedback is actually an important issue in late-type spirals. Due to the well-defined sample selection criteria and the homogeneity of the data analysis, the Tully–Fisher relation for GHASP galaxies can be used as a reference for the study of this relation in other environments and at higher redshifts.
Monthly Notices of the Royal Astronomical Society 08/2011; 416(3):1936 - 1948. · 4.90 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We studied, for the first time, the near infrared, stellar and baryonic
Tully-Fisher relations for a sample of field galaxies taken from an homogeneous
Fabry-Perot sample of galaxies (the GHASP survey). The main advantage of GHASP
over other samples is that maximum rotational velocities were estimated from 2D
velocity fields, avoiding assumptions about the inclination and position angle
of the galaxies. By combining these data with 2MASS photometry, optical colors,
HI masses and different mass-to-light ratio estimators, we found a slope of
4.48\pm0.38 and 3.64\pm0.28 for the stellar and baryonic Tully-Fisher relation,
respectively. We found that these values do not change significantly when
different mass-to-light ratios recipes were used. We also point out, for the
first time, that rising rotation curves as well as asymmetric rotation curves
show a larger dispersion in the Tully-Fisher relation than flat ones or than
symmetric ones. Using the baryonic mass and the optical radius of galaxies, we
found that the surface baryonic mass density is almost constant for all the
galaxies of this sample. In this study we also emphasize the presence of a
break in the NIR Tully-Fisher relation at M(H,K)\sim-20 and we confirm that
late-type galaxies present higher total-to-baryonic mass ratios than early-type
spirals, suggesting that supernova feedback is actually an important issue in
late-type spirals. Due to the well defined sample selection criteria and the
homogeneity of the data analysis, the Tully-Fisher relation for GHASP galaxies
can be used as a reference for the study of this relation in other environments
and at higher redshifts.
06/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The formation of ultra-compact dwarf galaxies (UCDs) is believed to be interaction driven, and UCDs are abundant in the cores of galaxy clusters, environments that mark the end-point of galaxy evolution. Nothing is known about the properties of UCDs in compact groups of galaxies, environments where most of galaxy evolution and interaction is believed to occur and where UCDs in intermediate state of evolution may be expected. The main goal of this study is to detect and characterize, for the first time, the UCD population of compact groups. For that, 2 groups in different evolutionary stages, HCG 22 and HCG 90, were targeted with VLT/FORS2/MXU. We detect 16 and 5 objects belonging to HCG 22 and HCG 90, respectively, covering the magnitude range -10.0 > M_R > -11.5 mag. Their colours are consistent with old ages covering a broad range in metallicities. Photometric mass estimates put 4 objects in HCG 90 and 9 in HCG 22 in the mass range of UCDs (>2x10^6 M_Sun) for an assumed age of 12 Gyr. These UCDs are on average 2-3 times larger than typical Galactic GCs, covering a range of 2 >~ r_h >~ 21 pc. The UCDs in HCG 22 are more concentrated around the central galaxy than in HCG 90, at the 99% confidence level. They cover a broad range in [alpha/Fe] abundances from sub- to super-solar. The spectra of 3 UCDs show tentative evidence for intermediate age stellar populations. We calculate the specific frequency (S_N) of UCDs for both groups, finding that HCG 22 has about three times higher S_N than HCG 90. The ensemble properties of the detected UCDs supports 2 co-existing formation channels: a star cluster origin and an origin as tidally stripped dwarf nuclei. Our results imply that the UCDs detected in both groups do not, in their majority, originate from relatively recent galaxy interactions. Most of the detected UCDs have likely been brought into the group with their host galaxies.[abridged] Comment: Accepted for publication at A&A, 17 pages, 9 figures + 2 additional figures
09/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: We obtained new Fabry-Perot data cubes and derived velocity fields, monochromatic and velocity dispersion maps for 28 galaxies in the Hickson compact groups 37, 40, 47, 49, 54, 56, 68, 79 and 93. We find that one third of the non-barred compact group galaxies have position angle misalignments between the stellar and gaseous components. This and the asymmetric rotation curves are clear signatures of kinematic perturbations, probably due to interactions among compact group galaxies. A comparison between the B-band Tully-Fisher relation for compact group galaxies and that for the GHASP field-galaxy sample shows that, despite the high fraction of compact group galaxies with asymmetric rotation curves, these lie on the Tully-Fisher relation defined by galaxies in less dense environments, although with more scatter. This is in agreement with previous results, but now confirmed for a larger sample of 41 galaxies. We confirm the tendency for compact group galaxies at the low-mass end of the Tully-Fisher relation (HCG 49b, 89d, 96c, 96d and 100c) to have either a magnitude that is too bright for its mass (suggesting brightening by star formation) and/or a low maximum rotational velocity for its luminosity (suggesting tidal stripping). These galaxies are outside the Tully Fisher relation, at the 1 sigma level, even when the minimum acceptable values of inclinations are used to compute their maximum velocities. The inclusion of such galaxies with v<100 km/s in the determination of the zero point and slope of the compact group B-band Tully-Fisher relation would strongly change the fit, making it different from the relation for field galaxies, a fact that has to be kept in mind when studying scaling relations of interacting galaxies, specially at high redshifts. Comment: 17 figures. Accepted for publication in Astronomy and Astrophysics. Hickson compact groups Fabry-Perot data are available at http://fabryperot.oamp.fr/PerotFabry/
03/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: We present the results of a multiwavelength campaign searching for young objects in the intragroup medium of seven compact groups of galaxies: HCG 2, 7, 22, 23, 92, 100 and NGC 92. We used Fabry-Perot velocity fields and rotation curves together with GALEX NUV and FUV images, optical R-band and HI maps to evaluate the stage of interaction of each group. We conclude that groups (i) HCG 7 and HCG 23 are in an early stage of interaction, (ii) HCG 2 and HCG 22 are mildly interacting, and (iii) HCG 92, HCG 100 and NGC 92 are in a late stage of evolution. Evolved groups have a population of young objects in their intragroup medium while no such population is found within the less evolved groups. We also report the discovery of a tidal dwarf galaxy candidate in the tail of NGC 92. These three groups, besides containing galaxies which have peculiar velocity fields, also show extended HI tails. Our results indicate that the advanced stage of evolution of a group together with the presence of intragroup HI clouds may lead to star formation in the intragroup medium. Comment: 2 pages, submitted to the Proceedings of IAU Symposium No. 262, 'Stellar Populations - Planning for the Next Decade', 2009, G. R. Bruzual and S. Charlot, ed
12/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: We present a new insight on NGC 6034 and UGC 842, two groups of galaxies previously reported in the literature as being fossil groups. The study is based on optical photometry and spectroscopy obtained with the CTIO Blanco telescope and Sloan Digital Sky Survey archival data. We find that NGC 6034 is embedded in a large structure, dominated by three rich clusters and other small groups. Its first and next four ranked galaxies have magnitude differences in the r band and projected distances which violate the optical criteria to classify it as a fossil group. We confirm that the UGC 842 group is a fossil group, but with about half the velocity dispersion that is reported in previous works. The velocity distribution of its galaxies reveals the existence of two structures in its line of sight, one with σ v ~ 223 km s–1 and another with σ v ~ 235 km s–1, with a difference in velocity of ~820 km s–1. The main structure is dominated by passive galaxies, while these represent ~60% of the second structure. The X-ray temperature for the intragroup medium of a group with such a velocity dispersion is expected to be kT ~0.5-1 keV, against the observed value of kT ~1.9 keV reported in the literature. This result makes UGC 842 a special case among fossil groups because (1) it represents more likely the interaction between two small groups, which warms the intragroup medium and/or (2) it could constitute evidence that member galaxies lost energy in the process of spiraling toward the group center, and decreased the velocity dispersion of the system. As far as we know, UGC 842 is the first low-mass fossil group studied in detail.
The Astronomical Journal 12/2009; 139(1):216. · 4.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study presents the mass distribution for a sample of 18 late-type galaxies in nine Hickson Compact Groups. We used rotation curves from high resolution 2D velocity fields of Fabry-Perot observations and J-band photometry from the 2MASS survey, in order to determine the dark halo and the visible matter distributions. The study compares two halo density profile, an isothermal core-like distribution and a cuspy one. We also compare their visible and dark matter distributions with those of galaxies belonging to cluster and field galaxies coming from two samples: 40 cluster galaxies of Barnes et al (2004) and 35 field galaxies of Spano et al. (2008). The central halo surface density is found to be constant with respect to the total absolute magnitude similar to what is found for the isolated galaxies. This suggests that the halo density is independent to galaxy type and environment. We have found that core-like density profiles fit better the rotation curves than cuspy-like ones. No major differences have been found between field, cluster and compact group galaxies with respect to their dark halo density profiles. Comment: 35 pages, 21 figures. Accept for publication in Astronomical Journal
09/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: Context: Compact groups of galaxies are entities that have high densities of galaxies and serve as laboratories to study galaxy interactions, intergalactic star formation and galaxy evolution. Aims: The main goal of this study is to search for young objects in the intragroup medium of seven compact groups of galaxies: HCG 2, 7, 22, 23, 92, 100 and NGC 92 as well as to evaluate the stage of interaction of each group. Methods: We used Fabry-Perot velocity fields and rotation curves together with GALEX NUV and FUV images and optical R-band and HI maps. Results: (i) HCG 7 and HCG 23 are in early stages of interaction, (ii) HCG 2 and HCG 22 are mildly interacting, and (iii) HCG 92, HCG 100 and NGC 92 are in late stages of evolution. We find that all three evolved groups contain populations of young blue objects in the intragroup medium, consistent with ages < 100 Myr, of which several are younger than < 10 Myr. We also report the discovery of a tidal dwarf galaxy candidate in the tail of NGC 92. These three groups, besides containing galaxies that have peculiar velocity fields, also show extended HI tails. Conclusions: Our results indicate that the advanced stage of evolution of a group, together with the presence of intragroup HI clouds, may lead to star formation in the intragroup medium. A table containing all intergalactic HII regions and tidal dwarf galaxies confirmed to date is appended. Comment: 26 pages, 19 figures. Accepted for publication in Astronomy and Astrophysics
08/2009;
-
[show abstract]
[hide abstract]
ABSTRACT: We present observations of Hα emission of Stephan's Quintet obtained with a scanning Fabry-Perot interferometer and samplings of ~11 km s-1 and ~1''. Our observations show an intragroup arclike feature formed of bright Hα knots and diffuse gas distributed along tidal tails associated with NGC 7318B and possibly also NGC 7318A. New velocities for 23 emitting regions detected along the Hα structure are presented. South of NGC 7318B, along a path covering ~12 h−175 kpc, H II regions with velocities ranging from 5540 to 6700 km s-1 are detected, suggesting that two or more overlapping tidal tails and/or a bow-shock region may have been formed through several interaction events within the group.
The Astrophysical Journal 12/2008; 516(2):L69. · 6.02 Impact Factor
-
P. Amram, C. Mendes de Oliveira,
H. Plana,
C. Balkowski,
O. Hernandez,
C. Carignan,
E. S. Cypriano,
L. Sodré,
Jr,
J. L. Gach,
and J. Boulesteix
[show abstract]
[hide abstract]
ABSTRACT: We have obtained high spectral resolution (R = 45,900) Fabry-Perot velocity maps of the Hickson compact group HCG 31 in order to revisit the important problem of the merger nature of the central object A+C and to derive the internal kinematics of the candidate tidal dwarf galaxies in this group. Our main findings are as follows: (1) double kinematic components are present throughout the main body of A+C, which strongly suggests that this complex is an ongoing merger; (2) regions A2 and E, to the east and south of complex A+C, present rotation patterns with velocity amplitudes of ~25 km s-1, and they counterrotate with respect to A+C; and (3) region F, which was previously thought to be the best example of a tidal dwarf galaxy in HCG 31, presents no rotation and negligible internal velocity dispersion, as is also the case for region A1. HCG 31 presents an undergoing merger in its center (A+C), and it is likely that it has suffered additional perturbations due to interactions with the nearby galaxies B, G, and Q.
The Astrophysical Journal 12/2008; 612(1):L5. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have discovered four intergalactic H II regions in Stephan's quintet, which is more than a 25 kpc projected distance from the center of the nearest group galaxy, with no apparent optical connection to it. They have MB ranging from -11.9 to -12.5 mag, colors B-R = 0.7-1.1 mag, radial velocities from 6565 to 6651 km s-1, and they are superposed onto the H I tail east of NGC 7319, with a mean radial velocity of 6610 km s-1. In addition, they have metallicities of the order of 12 + log(O/H) = 8.58 ± 0.25, which suggests that they were formed from preenriched material. We derive a mean age of 4.6 ± 0.6 Myr and a mean stellar mass of (2.9 ± 1.4) × 104 M☉ for the four objects. The masses, ages, colors, velocities, metallicities, and location of the objects suggest that they are H II regions that were formed far away from the galaxies through compression of the intergalactic H I gas by galaxy collisions.
The Astrophysical Journal 12/2008; 605(1):L17. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This continuing study of intragroup light in compact groups of galaxies aims to establish new constraints to models of formation and evolution of galaxy groups, specially of compact groups, which are a key part in the evolution of larger structures, such as clusters. In this paper we present three additional groups (HCG 15, 35 and 51) using deep wide field $B$ and $R$ band images observed with the LAICA camera at the 3.5m telescope at the Calar Alto observatory (CAHA). This instrument provides us with very stable flatfielding, a mandatory condition for reliably measuring intragroup diffuse light. The images were analyzed with the OV\_WAV package, a wavelet technique that allows us to uncover the intragroup component in an unprecedented way. We have detected that 19, 15 and 26% of the total light of HCG 15, 35 and 51, respectively, is in the diffuse component, with colours that are compatible with old stellar populations and with mean surface brightness that can be as low as $28.4 {\rm B mag arcsec^{-2}}$. Dynamical masses, crossing times and mass to light ratios were recalculated using the new group parameters. Also tidal features were analyzed using the wavelet technique. Comment: 12 pages, 5 figures. Accepted for publication in MNRAS. See http://www.eso.org/~cdarocha/publications/DaRochaetal2008_IGL_HCG.pdf for full resolution version. Complementary reference added
05/2008;
-
[show abstract]
[hide abstract]
ABSTRACT: We present a multiwavelength study of the poor cluster RX J1117.4+0743 ([VMF 98] 097) at z=0.485, based on GMOS/Gemini South g', r' photometry and spectroscopy, and XMM-Newton observations. We examine its nature and surroundings by analyzing the projected galaxy distribution, the galaxy velocity distribution, the weak-lensing mass reconstruction, and the X-ray spectroscopy and imaging. The cluster shows a complex morphology. It is composed by at least two structures along the line-of-sight, with velocity dispersions of 592+-82 km s^-1 and 391+-85 km s^-1 respectively. Other structures are also detected in X-ray, in the galaxy projected number density map, and by weak-lensing. One of these clumps, could be gravitationally bound and associated to the main cluster. The derived temperature and bolometric X-ray luminosity reveal that [VMF 98] 097 behave like a normal cluster, in agreement with Lx-Tx correlation found for both local (z=0) and moderate redshift (z~0.4) clusters. We find that the mass determination inferred from weak-lensing is in average 3 to 4.8 times higher (depending on the model assumed) than the X-ray mass. We have two possible explanations for this discrepancy: i) the cluster is in non-equilibrium, then the deviation of the X-ray estimated mass from the true value can be as high as a factor of two; ii) the intervening mass along the line-of-sight of the cluster is producing an over-estimation of the weak-lensing mass. Based on the analysis presented, we conclude that [VMF 98] 097 is a perturbed cluster with at least two substructures in velocity space and with other nearby structures at projected distances of about 1 h^-1 Mpc. This cluster is an example of a poor cluster caught in the process of accreting sub-structures to become a rich cluster. Comment: 16 pages, 11 figures.emulateapj.cls style. Accepted for publication in The Astrophysical Journal
04/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: We have studied the photometric properties of four fields around the
high-redshift quasar pairs QP1310+0007, QP1355-0032, QP0110-0219, and
QP0114-3140 at z ~ 1 with the aim of identifying large-scale structures- galaxy
clusters or groups- around them. This sample was observed with GMOS in Gemini
North and South telescopes in the g', r', i', and z' bands, and our photometry
is complete to a limiting magnitude of i' ~ 24 mag (corresponding to ~ M*_i' +
2 at the redshift of the pairs). Our analysis reveals that QP0110-0219 shows
very strong and QP1310+0007 and QP1355-0032 show some evidence for the presence
of rich galaxy clusters in direct vicinity of the pairs. On the other hand,
QP0114-3140 could be an isolated pair in a poor environment. This work suggest
that z ~ 1 quasar pairs are excellent tracers of high density environments and
this same technique may be useful to find clusters at higher redshifts.
03/2007;
-
[show abstract]
[hide abstract]
ABSTRACT: AIMS: We analyse the photometric properties of the early-type Fornax cluster dwarf galaxy population, based on a wide field imaging study of the central cluster area in V and I. We used the instrument/telescope combination IMACS/Magellan at Las Campanas Observatory, providing much larger light collecting area and better image resolution than previous surveys. METHODS: We create a fiducial sample of Fornax cluster dwarf ellipticals (dEs) in the following three steps: (1) To verify cluster membership, we measured I-band surface brightness fluctuation (SBF) distances to candidate dEs; (2) We re-assessed morphological classifications for candidate dEs too faint for SBF detection; and (3) We searched for new candidate dEs in the size-luminosity regime close to the resolution limit of previous surveys. RESULTS: (1) We confirm cluster membership for 28 candidate dEs in the range -16.6<M_V<-10.1 mag by means of SBF distances. We find no SBF background galaxy. (2) Of 51 further candidate dEs in the range -13.2<M_V<-8.6 mag, 2/3 are confirmed as probable cluster members by morphological re-assessment, while 1/3 are re-classified as probable background objects. (3) We find 12 new dE candidates in the range -12.3<M_V<-8.8 mag. The surface brightness-magnitude relation defined by the resulting fiducial dE sample shows that Fornax dEs are about 40% larger than Local Group dEs. The Fornax dE sample furthermore defines a colour-magnitude relation that appears slightly shallower than that of Local Group dEs. The early-type dwarf galaxy luminosity function in Fornax has a faint end slope alpha = -1.1 +/- 0.1. We discuss these findings in the context of structure formation theories. (ABRIDGED)
11/2006;
-
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of Cl 2334+48, a rich cluster of galaxies in the Zone of Avoidance, identified in public images from the XMM-Newton archive. We present the main properties of this cluster using the XMM-Newton X-ray data, along with new optical spectroscopic and photometric observations. Cl 2334+48 is located at z = 0.271 +/- 0.001, as derived from the optical spectrum of the brightest member galaxy. Such redshift agrees with a determination from the X-ray spectrum (z = 0.263 (+0.012/-0.010)), in which an intense emission line is matched to the rest wavelength of the Fe Kalpha complex. Its intracluster medium has a plasma temperature of 4.92 (+0.50/-0.48) keV, sub-solar abundance (0.38 +/- 0.12 Zsun), and a bolometric luminosity of 3.2 x 10^44 erg/s. A density contrast delta = 2500 is obtained in a radius of 0.5 Mpc/h70, and the corresponding enclosed mass is 1.5 x 10^14 Msun. Optical images show an enhancement of g'-i' > 2.5 galaxies around the central galaxy, as expected if these were cluster members. The central object is a luminous E-type galaxy, which is displaced ~ 40 kpc/h70 from the cluster X-ray center. In addition, it has a neighbouring arc-like feature (~ 22" or 90 kpc/h70 from it), probably due to strong gravitational lensing. The discovery of Cl 2334+48 emphasises the remarkable capability of the XMM-Newton to reveal new clusters of galaxies in the Zone of Avoidance. Comment: 9 pages, 11 figures, Accepted for publication in A&A (on July 12, 2006)
06/2006;
-
[show abstract]
[hide abstract]
ABSTRACT: We present a photometric search for UCD candidates in the nearby galaxy group NGC 1023 (d=11 Mpc) -- the poorest environment searched for UCDs yet --, based on wide field imaging with CFHT. After photometric and morphological selection, we obtain a sample of 21 UCD candidates with -12<M_V<-11 mag, if located at NGC 1023's distance. From spectroscopy taken at Calar Alto observatory, we identify the UCD candidate in closest projection to NGC 1023 as an emission line background galaxy. Our photometric data show that in the NGC 1023 group, the mass spectrum of analogs to Fornax/Virgo UCD is restricted to about 1/4 of the maximum Fornax/Virgo UCD mass. More spectroscopy is needed to further constrain the mass range of UCDs in this galaxy group. Comment: 5 pages, 4 figures, to appear in the proceedings of ESO Astrophysics Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V. Ivanov, J. Borissova
03/2006;
