Context. Fossil galaxy groups are speculated to be old and highly evolved systems of galaxies that formed early in the universe and had enough time to deplete their L∗ galaxies through successive ...mergers of member galaxies, building up one massive central elliptical, but retaining the group X-ray halo. Aims. Considering that fossils are the remnants of mergers in ordinary groups, the merger history of the progenitor group is expected to be imprinted in the fossil central galaxy (FCG). We present for the first time radial gradients of single-stellar population (SSP) ages and metallicites in a sample of FCGs to constrain their formation scenario. We also measure line-strength gradients for the strongest absorption features in these galaxies. Methods. We took deep spectra with the long-slit spectrograph ISIS at the William Herschel Telescope (WHT) for six FCGs. The obtained spectra are fit with Pegase HR SSP models within the full-spectrum fitting package ULySS yielding SSP ages and metallicities of the stellar populations. We measure radial gradients of SSP ages and metallicities along the major axes. Lick indices are measured for the strongest absorption features to determine line-strength gradients and compare with the full-spectrum fitting results. Results. Our sample comprises some of the most massive galaxies in the universe exhibiting an average central velocity dispersion of σ0 = 271 ± 28 km s-1. Metallicity gradients are throughout negative with comparatively flat slopes of ∇Fe/H = −0.19 ± 0.08 while age gradients are found to be insignificant (∇age = 0.00 ± 0.05). All FCGs lie on the fundamental plane, suggesting that they are virialised systems. We find that gradient strengths and central metallicities are similar to those found in cluster ellipticals of similar mass. Conclusions. The comparatively flat metallicity gradients with respect to those predicted by monolithic collapse (∇Z = −0.5) suggest that fossils are indeed the result of multiple major mergers. Hence we conclude that fossils are not “failed groups” that formed with a top-heavy luminosity function. The low scatter of gradient slopes suggests a similar merging history for all galaxies in our sample.
ABSTRACT We study the intrinsic shapes of a sample of over 400 quiescent galaxies in the cores of the Virgo and Fornax clusters with luminosities 106 ≤ Lg/L⊙ ≤ 108. Similar to satellites of the Local ...Group and Centaurus A, these faint, low surface brightness cluster galaxies are best described as a family of thick (〈C/A〉 > 0.5), oblate-triaxial spheroids. However, the large sample size allows us to show that the flattening of their stellar distribution depends both on luminosity and on the presence of a nuclear star cluster. Nucleated satellites are thicker at all luminosities compared to their non-nucleated counterparts, and fainter galaxies are systematically thicker as well, regardless of nucleation. Once nucleation is accounted for, we find no evidence that the environment the satellites live in plays a relevant role in setting their 3D structure. We interpret both the presence of stellar nuclei and the associated thicker shapes as the result of preferential early and rapid formation, effectively making these faint nucleated galaxies the first generation of cluster satellites.
RX J1548.9+0851, a fossil cluster? Eigenthaler, P.; Zeilinger, W. W.
Astronomy and astrophysics (Berlin),
04/2012, Letnik:
540
Journal Article
Recenzirano
Odprti dostop
Context. Fossil galaxy groups are spatially extended X-ray sources with X-ray luminosities above \hbox{$L_{{\rm X},\,\textrm{\scriptsize bol}} \ge 10^{42}~h_{50}^{-2}$}LX, bol≥1042 h50-2 erg s-1 and ...a central elliptical galaxy dominating the optical, the second-brightest galaxy being at least 2 mag fainter in the R band. Whether these systems are a distinct class of objects resulting from exceptional formation and evolution histories is still unclear, mainly due to the small number of objects studied so far, mostly lacking spectroscopy of group members for group membership confirmation and a detailed kinematical analysis. Aims. To complement the scarce sample of spectroscopically studied fossils down to their faint galaxy populations, the fossil candidate RX J1548.9+0851 (z = 0.072) is studied in this work. Our results are compared with existing data from fossils in the literature. Methods. We use ESO VLT VIMOS multi-object spectroscopy to determine redshifts of the faint galaxy population and study the luminosity-weighted dynamics and luminosity function of the system. The full-spectrum fitting package ULySS is used to determine ages and metallicities of group members. VIMOS imaging data are used to study the morphology of the central elliptical. Results. We identify 40 group members spectroscopically within the central ~300 kpc of the system and find 31 additional redshifts from the literature, resulting in a total number of 54 spectroscopically confirmed group members within 1 Mpc. RX J1548.9+0851 is made up of two bright ellipticals in the central region with a magnitude gap of Δm1,2 = 1.34 in the SDSS r′ band leaving the definition of RX J1548.9+0851 being a fossil to the assumption of the virial radius. We find a luminosity-weighted velocity dispersion of 568 km s-1 and a mass of ~2.5 × 1014 M⊙ for the system confirming previous studies that revealed fossils to be massive. An average mass-to-light ratio of M/L ~ 400 M⊙/L⊙ is derived from the SDSS g′, r′, and i′ bands. The central elliptical is well-fitted by a pure deVaucouleurs r1/4 law without a cD envelope. Symmetric shells are revealed along the major axis of the galaxy indicating a recent minor merger. RX J1548.9+0851 shows a steep, increasing luminosity function with a faint-end slope of α = −1.4 ± 0.1. Satellite galaxies show a clear spatial segregation with respect to their stellar populations – objects with old stars are confined to an elongated, central distribution aligned with the major axis of the central elliptical. Conclusions. Although RX J1548.9+0851 shows similar properties compared to other fossils studied recently, it might not be a fossil at all, being dominated by 2 bright central ellipticals. Comparing RX J1548.9+0851 with scaling relations from ordinary poor groups and clusters confirm the idea that fossils might simply be normal clusters with the richness and optical luminosity of poor groups.
Context. Low-luminosity galaxies are known to outnumber the bright galaxy population in poor groups and clusters of galaxies. Yet, the investigation of low-luminosity galaxy populations outside the ...Local Group remains rare and the dependence on different group environments is still poorly understood. Previous investigations have uncovered the photometric scaling relations of early-type dwarfs and a strong dependence of morphology with environment. Aims. The present study aims to analyse the photometric and spectroscopic properties of the low-luminosity galaxy population in the nearby, well-evolved and early-type dominated NGC 5846 group of galaxies. It is the third most massive aggregate of early-type galaxies after the Virgo and Fornax clusters in the local universe. Photometric scaling relations and the distribution of morphological types as well as the characteristics of emission-line galaxies are investigated. Methods. Spectroscopically selected low-luminosity group members from the Sloan Digital Sky Survey with cz < 3000 km s-1 within a radius of 2° = 0.91 Mpc around NGC 5846 are analysed. Surface brightness profiles of early-type galaxies are fit by a Sérsic model $\propto$$r^{1/n}$. Star formation rates, oxygen abundances, and emission characteristics are determined for emission-line galaxies. Results. Seven new group members showing no entry in previous catalogues are identified in the outer (>1.33°) parts of the system. Several photometric scaling relations for dEs as well as the morphology-density relation for dwarf galaxies are reproduced. The correlation between host and satellite morphologies in poor groups of galaxies is also confirmed. Nucleated dwarfs are found to be located in the vicinity to the brightest ellipticals in the group. Only two faint galaxies exhibit fine structure. Emission-line dwarfs show no interaction-induced activity.
Abstract
The formation of Low mass X-ray binaries (LMXB) is favored within dense stellar systems such as Globular Clusters (GCs). The connection between LMXB and Globular Clusters has been ...extensively studied in the literature, but these studies have always been restricted to the innermost regions of galaxies. We present a study of LMXB in GCs within the central 1.5
deg
2
of the Fornax cluster with the aim of confirming the existence of a population of LMXB in intra-cluster GCs and understand if their properties are related to the host GCs, to the environment or/and to different formation channels.
RX J1548.9+0851, a fossil cluster? Eigenthaler, P; Zeilinger, W W
Astronomy and astrophysics (Berlin),
04/2012, Letnik:
540
Journal Article
Recenzirano
Fossil galaxy groups are spatially extended X-ray sources with X-ray luminosities above... and a central elliptical galaxy dominating the optical, the second-brightest galaxy being at least 2 mag ...fainter in the R band. To complement the scarce sample of spectroscopically studied fossils down to their faint galaxy populations, the fossil candidate RX J1548.9+0851 is studied in this work. The authors use ESO VLT VIMOS multi-object spectroscopy to determine redshifts of the faint galaxy population and study the luminosity-weighted dynamics and luminosity function of the system. RX J1548.9+0851 is made up of two bright ellipticals in the central region with a magnitude gap of... in the SDSS r' band leaving the definition of RX J1548.9+0851 being a fossil to the assumption of the virial radius. Although RX J1548.9+0851 shows similar properties compared to other fossils studied recently, it might not be a fossil at all, being dominated by 2 bright central ellipticals. (ProQuest: ... denotes formulae/symbols omitted.)
The Fossil Candidate RX J1548.9+0851 Eigenthaler, P.; Zeilinger, W. W.
Environment and the Formation of Galaxies: 30 years later,
05/2011
Book Chapter
Numerical simulations as well as optical and X-ray observations have shown that poor groups of galaxies can evolve to what is called a fossil group. Dynamical friction as the driving process leads to ...the coalescence of individual galaxies in ordinary poor groups, leaving behind nothing more than a central, massive elliptical galaxy supposed to contain the merger history of the whole group. Due to longer merging timescales for less-massive galaxies, a surrounding faint-galaxy population and an extended X-ray halo similar to that found in ordinary poor groups, is expected. Multi-object spectroscopy with VIMOS has been performed to study the faint galaxy population of the fossil candidate RX J1548.9 + 0851.
We introduce our Radial Velocity Survey for Planets around Young stars (RVSPY), characterise our target stars, and search for substellar companions at orbital separations smaller than a few au from ...the host star. We use the FEROS spectrograph to obtain high signal-to-noise spectra and time series of precise radial velocities (RVs) of 111 stars most of which are surrounded by debris discs. Our target stars have spectral types between early F and late K, a median age of 400 Myr, and a median distance of 45 pc. We determine for all target stars their basic stellar parameters and present the results of the high-cadence RV survey and activity characterization. We achieve a median single-measurement RV precision of 6 m/s and derive the short-term intrinsic RV scatter of our targets (median 22 m/s), which is mostly caused by stellar activity and decays with age from >100 m/s at <20 Myr to <20 m/s at >500 Myr. We discover six previously unknown close companions with orbital periods between 10 and 100 days, three of which are low-mass stars, and three are in the brown dwarf mass regime. We detect no hot companion with an orbital period <10 days down to a median mass limit of ~1 M_Jup for stars younger than 500 Myr, which is still compatible with the established occurrence rate of such companions around main-sequence stars. We find significant RV periodicities between 1.3 and 4.5 days for 14 stars, which are, however, all caused by rotational modulation due to starspots. We also analyse the TESS photometric time series data and find significant periodicities for most of the stars. For 11 stars, the photometric periods are also clearly detected in the RV data. We also derive stellar rotation periods ranging from 1 to 10 days for 91 stars, mostly from TESS data. From the intrinsic activity-related short-term RV jitter, we derive the expected mass-detection thresholds for longer-period companions.
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