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1.
We present the first results of our X‐shooter observations for a sample of dwarf (–17 < MB < –15) galaxies in nearby (0.04 < z < 0.07) galaxy clusters. This luminosity range is fundamental to trace the evolution of higher‐z star‐forming cluster galaxies down to the present day, and to explore the galaxy scaling relations of early‐type galaxies over a broad mass range. Thanks to high resolution and availability of several lines we can derive the velocity dispersion of the galaxies in this range of luminosities and we begin the construction of the fundamental plane of faint early‐type galaxies (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
A simple, semi-analytic method is developed for obtaining the orbits of galaxies undergoing fast collisions in which the galaxies are represented by Plummer models. The results are found to agree fairly well with those of N-body simulations.A simple formula for obtaining the angle of deflection is deduced. The maximum angle of deflection is 180° forV p/V esc(p)=1.00, about 36° forV p/V esc(p)=1.50, and about 18° forV p/V esc(p)=2.00, whereV p is the velocity at closest approachp, andV esc(p) is the parabolic velocity of escape atp. The angle of deflection of a pair of colliding elliptical galaxies without halos is about twice that for a pair of galaxies with halos for the same relative velocity at infinite separation.  相似文献   

3.
In the course of investigation of Shakhbazian compact groups we studied the group ShCG 191 which has been identified also as the Abell cluster A1097. By its richness it may be classified as a rich compact group or a poor cluster. We determined redshifts of 14 objects in the area of the cluster and found that two of the supposed members of the group are stars. Redshifts of 12 galaxies show that the system is gravitationally bound. The V and R magnitudes of 23 member galaxies and their morphological types are determined. We present in this paper also the surface brightness contours of member galaxies in the central area of the cluster, the curves of isophotal twisting and the Fourier parameter a4. It is shown that some galaxies in the cluster are interacting with each other. Physical parameters of the group are close to those of ShCGs. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
In several nearby L ∼ L* early‐type galaxies, recent observations at large radii have shown indications of a lack of dark matter, substantially at odds with the prediction from the Cold Dark Matter (CDM) hierarchical merger models. Here we discuss a pilot observational project for the study of the internal kinematical and dynamical properties of this remarkable sample of galaxies. Using the VIMOS‐IFU in its high spectral resolution mode, it would be possible to investigate the regions up to ∼1.2 Re, taking advantage of the much larger field of view and telescope diameter. This will allow to disclose the presence of any kinematical substructures which could affect the conclusion on the mass modeling and definitely clarify the inner structure of this particular class of early‐type galaxies. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
We propose a classification of supermassive black holes (SMBHs) based on their efficiency in the conversion of infalling mass in emitted radiation. We use a theoretical model that assumes a conservation of angular momentum between the gas falling inside the hole and the photons emitted outwards, and suggests the existence of the scaling relation M•‐Reσ3, where M• is the mass of the central SMBH, whereas Re and σ are the effective radius and velocity dispersion of the host galaxies (bulges), respectively. We apply our model on a data set of 57 galaxies of different morphological types and with M• measurements, obtained through the analysis of Spitzer /IRAC 3.6‐µ m images. In order to find the best fit of the corresponding scaling law, we use the FITEXY routine to perform a least‐squares regression of M• on Reσ3 for the considered sample of galaxies. Our analysis shows that the relation is tight and our theoretical model allows to easily estimate the efficiency of mass conversion into radiation of the central SMBHs. Finally we propose a new appealing way to classify the SMBHs in terms of this parameter. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
We examine the XMM X-ray spectrum of the low-ionisation nuclear emission-line region (LINER)-AGN NGC 7213, which is best fit with a power law, Kα emission lines from Fe i, Fe xxv and Fe xxvi and a soft X-ray collisionally ionised thermal plasma with kT = 0.18+0.03−0.01 keV. We find a luminosity of 7× 10−4 LEdd, and a lack of soft X-ray excess emission, suggesting a truncated accretion disc. NGC 7213 has intermediate X-ray spectral properties, between those of the weak AGN found in the LINER M 81 and higher luminosity Seyfert galaxies. This supports the notion of a continuous sequence of X-ray properties from the Galactic Centre through LINER galaxies to Seyferts, likely determined by the amount of material available for accretion in the central regions. This work is based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).  相似文献   

7.
We report three new or updated techniques for probing the parameters of active galaxies based on the masses of their central black holes MBH). First, we derived a near-IR analog of the bulge luminosity versus MBH relationship. The low scatter makes it a promising new tool to study the black hole demographics. Next, we present relations between MBH and the10 μm and 2-10 keV nuclear luminosity. They may help to study the MBH evolution over wide redshift ranges. Finally, we measured MBH in quasars from z ∼ 3.4 to z ∼ 0.3 to search directly for MBH growth. Surprisingly, we found no evidence for growth implying that the majority of quasar host galaxies have undergone their last major merger at z ≥ 3. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

8.
We present R-band galaxy luminosity functions (GLFs) from aspectroscopic sample of six nearby rich galaxy clusters. In addition to individual cluster GLFs, extending to, in one case, M R=–14, we also present composite GLFs for cluster and field galaxies toM R=–17. All six cluster samples are consistent with the composite GLF, but there is evidence that the GLF of the quiescent population in clusters is not universal. Furthermore, the GLF of quiescent galaxies is significantly steeper in clusters than in the field. The overall GLF in clusters is consistent with that of field galaxies, except for the luminous tip, which is enhanced in clusters versus the field. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

9.
Using two volume‐limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6) with the luminosity –20.0 ≤ Mr ≤ –18.5 and –22.40 ≤ Mr ≤–20.16, we have explored the environmental dependence of the fractions of red star‐forming and blue passive galaxies. It is found that the fractions of red star‐forming and blue passive galax‐ies decline mildly with increasing local density in the luminous volume‐limited sample, but in the faint volume‐limited sample these fractions rise slightly with increasing local density except that the fraction of red star‐forming decreases with density in the densest regime. Only according to statistical results of this study, it is difficult to reach the conclusion: there is an environmental dependence for color beyond that for star formation activities or for star formation activities beyond that for color. In this condition, we preferentially believe that star formation activities and color possiblely have equally strong environmental dependence. In the faint volume‐limited sample, we observe that the fraction of star‐forming galaxies‐the density relation has a “critical density” at the projected local density PLD ≈ 1 h–2 Mpc–2: below this density the fraction of star‐forming galaxies is high and nearly constant, while above this density this fraction drops rapidly. Thus, it is possible that in the densest regime of the faint volume‐limited sample, there is an environmental dependence for star formation activities beyond that for color, which leads to the fraction of red star‐forming decreasing with density in the densest regime of the faint volume‐limited sample (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
We present SALT spectroscopy of a globular cluster in the center of the nearby isolated dSph galaxy KKs3 situated at a distance of 2.12 Mpc. Its heliocentric radial velocity is 316 ± 7 km s–1 that corresponds to VLG = 112 km s–1 in the Local Group (LG) reference frame. We use its distance and velocity along with the data on other 35 field galaxies in the proximity of the LG to trace the local Hubble flow. The following basic properties of the local field galaxies are briefly discusse: morphology, absolute magnitudes, average surface brightnesses, specific star formation rates, and hydrogen mass‐to‐stellar mass ratios. Surprisingly, the sample of the neighboring isolated galaxies displays no signs of compression under the influence of the expanding Local Void. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
The 395 late-type spiral galaxies brighter than 15m in r-band are selected from the Data Release 2 of Sloan Digital Sky Survey and the colormagnitude relations of these galaxies and their disks are investigated. It is found that the colors g − r, r − z and g − z of these galaxies and their disks are strongly correlated with the r-band absolute magnitudes, i.e., the more luminous galaxies (or disks) have the redder colors than the less luminous galaxies (or disks). And the correlation of galaxies is stronger than that of their disks.  相似文献   

12.
The formulation of the tensor virial equations is generalized to unrelaxed configurations, where virial equilibrium does not coincide with dynamical (or hydrostatic) equilibrium. Homeoidally striated, Jacobi ellipsoids, which generalize classical Jacobi ellipsoids, are studied in detail. Further investigation is devoted to the generation of sequences of virial equilibrium configurations where the anisotropy parameters are left unchanged, including both flattened and elongated, triaxial configurations, and the determination of the related bifurcation points. An application is made to dark matter haloes hosting giant galaxies (M ≈ 1012 m⊙), with regard to assigned initial and final configuration, following and generalizing to many respects a procedure conceived by Thuan & Gott (1975). The dependence of the limiting axis ratios, below which no configuration is allowed for the sequence under consideration, on the change in mass, total energy, and angular momentum, during the evolution, is illustrated in some representative situations. The dependence of the axis ratios, ε31 and ε21, on a parameter, related to the initial conditions of the density perturbation, is analysed in connection with a few special cases. The same is done for the rotation parameters. Within the range of the rotation parameter, λ, deduced from high‐resolution numerical simulations, the shape of dark matter haloes is mainly decided by the amount of anisotropy in residual velocity distribution. On the other hand, the contribution of rotation has only a minor effect on the meridional plane, and no effect on the equatorial plane, as bifurcation points occur for larger values of λ. To this respect, dark matter haloes are found to resemble giant elliptical galaxies. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
We present UBVRCIC magnitudes of 49 comparison stars in the fields of the Seyfert galaxies Mrk 335, Mrk 79, Mrk 279, Mrk 506, 3C 382, 3C 390.3, NGC 6814, Mrk 304, Ark 564, and NGC 7469 in order to facilitate the photometric monitoring of these objects; 36 of the stars have not been calibrated before. The comparison stars are situated in 5 × 5 arcmin fields centred on the Seyfert galaxies, their V band flux ranges from 11.7 to 18.2 mag with a median value of 16.3 mag, and their B – V colour index ranges from 0.4 to 1.6 mag with a median value of 0.8 mag. The median errors of the calibrated UBVRCIC magnitudes are 0.08, 0.04, 0.03, 0.04, and 0.06 mag, respectively. Comparison stars were calibrated for the first time in three of the fields (Mrk 506, 3C 382, and Mrk 304). The comparison sequences in the other fields were improved in various aspects. Extra stars were calibrated in four fields (Mrk 335, Mrk 79, NGC 6814, and NGC 7469) – most of these stars are fainter and are situated closer to the Seyfert galaxies compared to the existing comparison stars. The passband coverage of the sequences in five fields (Mrk 335, Mrk 79, Mrk 279, NGC 6814, and Ark 564) was complemented with the U band. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
Our aim is to explore the relation between gas, atomic and molecular, and dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO line emission maps. To estimate the dust content, we use the disk opacity as inferred from the number of distant galaxies identified in twelve HST/WFPC2 fields of ten nearby spiral galaxies. The observed number of distant galaxies is calibrated for source confusion and crowding with artificial galaxy counts and here we verify our results with sub‐mm surface brightnesses from archival Herschel ‐SPIRE data. We find that the opacity of the spiral disk does not correlate well with the surface density of atomic (H I) or molecular hydrogen (H2) alone implying that dust is not only associated with the molecular clouds but also the diffuse atomic disk in these galaxies. Our result is a typical dust‐to‐gas ratio of 0.04, with some evidence that this ratio declines with galactocentric radius, consistent with recent Herschel results. We discuss the possible causes of this high dust‐to‐gas ratio; an over‐estimate of the dust surface‐density, an under‐estimate of the molecular hydrogen density from CO maps or a combination of both. We note that while our value of the mean dust‐to‐gas ratio is high, it is consistent with the metallicity at the measured radii if one assumes the Pilyugin & Thuan (2005) calibration of gas metallicity. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
It is shown that the radial velocity dispersion of the elongated HCGs (b/a ≤ 0.2) with smaller two‐dimensional galaxy‐galaxy median projected separation R is, on average, higher than those of the groups with larger R. It shows that galaxies in a group move preferentially along its elongation. Inspection of radial velocities of member galaxies in chain‐like and in roundish HCGs shows that galaxies in HCGs most probably rotate around the gravitational center of the corresponding group. Other two possible mechanisms: flying apart of galaxies from the group in opposite directions, and infall of field galaxies upon the group are excluded. It follows that HCGs are, probably, more stable formations, than it has been assumed. In this case the known inconsistencies between the results of the N‐body simulations and the observational facts are being excluded.  相似文献   

16.
Using the multi-band photometric data of all five CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) fields and the near-infrared (F125W and F160W) high-resolution images of HST WFC3 (Hubble Space Telescope Wide Field Camera 3), a quantitative study of morphology and structure of mass-selected galaxies is presented. The sample includes 8002 galaxies with a redshift 1 < z < 3 and stellar mass M*> 1010M⊙. Based on the Convolutional Neural Network (ConvNet) criteria, we classify the sample galaxies into SPHeroids (SPH), Early-Type Disks (ETD), Late-Type Disks (LTD), and IRRegulars (IRR) in different redshift bins. The findings indicate that the galaxy morphology and structure evolve with redshift up to z ～ 3, from irregular galaxies in the high-redshift universe to the formation of the Hubble sequence dominated by disks and spheroids. For the same redshift interval, the median values of effective radii (re) of different morphological types are in a descending order: IRR, LTD, ETD, and SPH. But for the Sérsic index (n), the order is reversed (SPH, ETD, LTD, and IRR). In the meantime, the evolution of galaxy size (re) with the redshift is explored for the galaxies of different morphological types, and it is confirmed that their size will enlarge with time. However, such a phenomenon is not found in the relations between the redshift (1 < z < 3) and the mean axis ratio (b/a), as well as the Sérsic index (n).  相似文献   

17.
Observations are presented of the isolated dwarf irregular galaxy And IV made with the Hubble Space Telescope Advanced Camera for Surveys and the Giant Metrewave Radio Telescope in the 21 cm HI line. We determine the galaxy distance of 7.17 ± 0.31 Mpc using the Tip of Red Giant Branch method. The galaxy has a total blue absolute magnitude of –12.81 mag, linear Holmberg diameter of 1.88 kpc, and an HI ‐disk extending to 8.4 times the optical Holmberg radius. The HI massto‐blue luminosity ratio for And IV amounts 12.9 M⊙/L⊙. From the GMRT data we derive the rotation curve for the HI and fit it with different mass models. We find that the data are significantly better fit with an iso‐thermal dark matter halo, than by an NFW halo. We also find that MOND rotation curve provides a very poor fit to the data. The fact that the isothermal dark matter halo provides the best fit to the data supports models in which star formation feedback results in the formation of a dark matter core in dwarf galaxies. The total mass‐to‐blue luminosity ratio of 162 M⊙/L⊙ makes And IV among the darkest dIrr galaxies known. However, its baryonic‐to‐dark mass ratio (Mgas + M *)/MT = 0.11 is close to the average cosmic baryon fraction of 0.15. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
The Eridanus galaxies follow the well-known radio—FIR correlation. The majority (70%) of these galaxies have their star formation rates below that of the Milky Way. The galaxies that have a significant excess of radio emission are identified as low luminosity AGNs based on their radio morphologies obtained from the GMRT observations. There are no powerful AGNs (L 20cm > 1023 W Hz−1) in the group. The two most far-infrared and radio luminous galaxies in the group have optical and HI morphologies suggestive of recent tidal interactions. The Eridanus group also has two far-infrared luminous but radio-deficient galaxies. It is believed that these galaxies are observed within a few Myr of the onset of an intense star formation episode after being quiescent for at least a 100 Myr. The upper end of the radio luminosity distribution of the Eridanus galaxies (L 20cm ∼ 1022 W Hz−1) is consistent with that of the field galaxies, other groups, and late-type galaxies in nearby clusters.  相似文献   

19.
To investigate the environmental dependence of u ‐, g ‐, r ‐, i ‐, and z ‐band luminosities, we perform comparative studies of luminosity distributions between galaxy members of compact groups (CGs) and isolated galaxies. It is found that for the r, i, and z bands isolated galaxies have a higher proportion of faint galaxies and a lower proportion of luminous galaxies than galaxy members of CGs, but for the u band an opposite trend is observed. The correlation between the g ‐band luminosity and the environment has different trends in different luminosity regions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
Data from the H I Parkes All-Sky Survey (HIPASS) of the southern sky in the neutral hydrogen line are used to determine the radial velocities and widths of the H I line for flat spiral galaxies of the Revised Flat-Galaxy Catalog (RFGC) seen edge-on. The sample of 103 flat galaxies detected in HIPASS is characterized by a median radial velocity of +2037 km/sec and a median width of the H I line at the level of 50% of maximum of 242 km/sec. For RFGC galaxies the 50% detection level in HIPASS corresponds to an apparent magnitude B t = 14 m .5 or an angular diameter a = 2.9. The relative number of detected galaxies increases from 2% for the morphological types Sbc and Sc to 41% for the type Sm. The median value of the ratio of hydrogen mass to total mass for RFGC galaxies is 0.079. With allowance for the average internal extinction for edge-on galaxies, <B t< = 0 m .75, the median ratio of hydrogen mass to luminosity, M H I/L B = 0.74 M /L , is typical for late-type spirals. Because of its small depth, HIPASS reveals only a few RFGC galaxies with previously unknown velocities and line widths.  相似文献   

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