Bright Elliptical Galaxies Research Articles

Do elliptical galaxies have dark matter?

We present constraints on the structure of dark matter halos in elliptical galaxies from the relationship between X-ray temperature and velocity dispersion observed in an optically complete sample. We demonstrate the ubiquity of dark matter in L>L ∗ galaxies, present limits on the dark matter structural parameters, and discuss the scaling of these parameters with optical luminosity. We find that the dark matter is characterized by velocity dispersions that are greater than those of the luminous stars, and that the mass-to-light ratio within six half-light radii for bright elliptical galaxies has a universal value, M/ L V ≈25 h 80 M ⊙/ L V ⊙ . The latter conclusion is consistent with gravitational lensing studies, but conflicts with the simplest extension of CDM theories of large scale structure formation to galactic scales.

Stellar Kinematics of Merging Galaxies: Clues to the Origins of Elliptical Galaxies

There is significant evidence suggesting that mergers of galaxies produce elliptical galaxies. To determine whether the known kinematic properties of elliptical galaxies are consistent with those of their suggested progenitors, we have examined the stellar velocity dispersion in 11 nuclear regions within starbursting infrared-luminous galaxies. All of these galaxies are in some stage of merging. The new data are presented and statistically analyzed in combination with data from the literature. We find that the kinematic and photometric properties of these galaxies suggest that they are the progenitors of low-luminosity (L < L*) elliptical galaxies. Dissipative collapse of gas followed by star formation is apparently not producing a core of high-density high-velocity dispersion stars like those found in very bright elliptical galaxies. We suggest that only the ultraluminous infrared galaxies can possibly produce L* ellipticals. We further present the results of population synthesis models that show that intermediate-age stellar populations should contribute significantly to the light of merger remnants even after the morphological signs of merging have vanished.

The Distribution of BCDGs in Voids

Generally the density of the environment is important for the formation and evolution of galaxies: bright elliptical galaxies reside in the centers of galaxy clusters, whereas late type galaxies preferentially populate small groups, filaments or the outskirts of rich clusters of galaxies. Furthermore, fainter galaxies define smaller voids than bright galaxies. Our investigation of void catalogues in the Northern Local Void region shows that large voids are interlaced by systems of faint galaxies dividing them into smaller subvoids (Lindner et al., 1995). This void hierarchy is an important property of the Large Scale Structure in the nearby Universe and can help to solve problems concerning the distribution of dwarf galaxies and BCDGs.

X-Ray Observations and the Structure of Elliptical Galaxies

We compare optical and high-quality X-ray data for three bright elliptical galaxies in the Virgo Cluster, NGC 4472, 4649, and 4636. The distribution of total mass in NGC 4472 and 4649 determined from X-ray data is sensitive to the stellar mass over a considerable range in galactic radius extending to r ≈ re, the effective radius. The agreement of X-ray and optically determined stellar masses provides a unique verification of the stellar mass-to-light ratio, which is essentially constant over the range 0.1 r/re 1. However, for NGC 4636 the dark matter is important at all radii 0.35re. Evidently, the dark to stellar mass ratio varies in quite different ways in elliptical galaxies of comparable optical luminosity, implying that the radial structure of dark halos may not be universal. There is some evidence in NGC 4636 for additional support of the hot interstellar gas at r 0.35re; either a field B ~ 10-4 G or a small (mechanically unstable) central region of high gas temperature (T ~ 107 K) is required. The global temperature structure in the hot interstellar medium of many recently observed elliptical galaxies is very similar, reaching a maximum near 3re-4re. This feature, which may suggest a new structural scale in these galaxies, is inconsistent with current theoretical gasdynamical models.

Scaling Laws for Advection‐dominated Flows: Applications to Low‐Luminosity Galactic Nuclei

We present analytical scaling laws for self-similar advection dominated flows. The spectra from these systems range from 10$^{8}$ - 10$^{20}$ Hz, and are determined by considering cooling of electrons through synchrotron, bremsstrahlung, and Compton processes. We show that the spectra can be quite accurately reproduced without detailed numerical calculations, and that there is a strong testable correlation between the radio and X-ray fluxes from these systems. We describe how different regions of the spectrum scale with the mass of the accreting black hole, $M$, the accretion rate of the gas, $\dot{M}$, and the equilibrium temperature of the electrons, $T_e$. We show that the universal radio spectral index of 1/3 observed in most elliptical galaxies (Slee et al. 1994) is a natural consequence of self-absorbed synchrotron radiation from these flows. We also give expressions for the total luminosity of these flows, and the critical accretion rate, $\dot{M}_{crit}$, above which the advection solutions cease to exist. We find that for most cases of interest the equilibrium electron temperature is fairly insensitive to $M$, $\dot{M}$, and parameters in the model. We apply these results to low luminosity black holes in galactic nuclei. We show that the problem posed by Fabian & Canizares (1988) of whether bright elliptical galaxies host dead quasars is resolved, as pointed out recently by Fabian & Rees (1995), by considering advection-dominated flows.

The Globular Cluster Systems of NGC 1400 and NGC 1407

view Abstract Citations (21) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Globular Cluster Systems of NGC 1400 and NGC 1407 Perrett, Kathryn M. ; Hanes, David A. ; Butterworth, Steven T. ; Kavelaars, Jj ; Geisler, Doug ; Harris, William E. Abstract The two brightest elliptical galaxies in the Eridanus A group, NGC 1400 and NGC 1407, have been observed in both the Washington T_1 and Kron-Cousins I filters to obtain photometry of their globular cluster systems (GCSs). This group of galaxies is of particular interest due to its exceptionally high M/L value, previously estimated at ~ 3000h, making this cluster highly dark-matter-dominated (Gould 1993). NGC 1400's radial velocity (549 km/s) is extremely low compared to that of the central galaxy of Eridanus A (NGC 1407 with v_sun=1766 km/s) and the other members of the system, suggesting that it is a foreground galaxy projected by chance onto the cluster. Using the shapes of the globular cluster luminosity functions, however, we derive distances of 17.6 +/- 3.1 Mpc to NGC 1407 and 25.4 +/- 7.0 Mpc to NGC 1400. These results support earlier conclusions that NGC 1400 is at the distance of Eridanus A and therefore has a large peculiar velocity. Specific frequencies are also derived for these galaxies, yielding values of S_N=4.0 +/- 1.3 for NGC 1407 and S_N = 5.2 +/- 2.0 for NGC 1400. In this and other respects, these two galaxies have GCSs which are consistent with those observed in other galaxies. Publication: The Astronomical Journal Pub Date: March 1997 DOI: 10.1086/118309 arXiv: arXiv:astro-ph/9611052 Bibcode: 1997AJ....113..895P Keywords: Astrophysics E-Print: 14 pages (AASTeX), 3 postscript figures, submitted to the Astronomical Journal full text sources arXiv | ADS | data products SIMBAD (51) NED (49)

Support for X‐Ray Deduced Abundances in Galaxies and Clusters: The Consistency of Iron Abundances from L and K Emission

Significantly subsolar metallicities have been reported in X-rays for a variety of sources, often in disagreement with theoretical expectations or with measurements at other wavelengths. As a test of the reliability of the X-ray abundances in systems dominated by thermal emission from hot gas in collisional ionization equilibrium, we compare Fe abundances determined independently from the Fe L and Fe K emission regions in simple one- and two-temperature thermal fits to ASCA X-ray spectra of the elliptical galaxy M87 and five galaxy clusters. We find that the Fe L and Fe K abundances are consistent within or near their 90% confidence errors, which would not necessarily be the case if there were severe problems with the atomic physics or with the instrument calibrations. Our data cover a range of plasma temperatures kT = 2-4 keV, where the Fe L emission arises primarily from Fe XXIII and XXIV and the Fe K emission arises primarily from Fe XXV. There is also a contribution from less ionized gas at lower temperatures in M87. For M87, the abundances from Fe K are systematically lower by 30%-50% than those from Fe L, and the differences are attributable to the complicated temperature structure in the central cooling flow. Allowing for the possibility of excess absorption of the emission from the cooling flow increases the systematic offset of the Fe L and Fe K abundances to 40%-80% in the simple model we consider. The cluster spectra, on the other hand, are for nearly isothermal regions outside any central cooling flow and the abundances have no systematic offset. The consistency between the Fe K and Fe L abundances, which is also seen in other clusters and in the corona of Ar Lac, indicates that whatever atomic physics uncertainties exist in the current codes are not likely to render Fe abundance measurements unreliable within the ~30%-50% agreement we find for the systems we examined. The results using various thermal emission codes differ by 15%-20%, showing the level of scatter due just to different assumptions about the atomic physics. The atomic rates for H- and He-like ions, which are relevant for the determination of abundances in elements other than Fe, are more accurately known than those for less ionized species that dominate the complicated Fe L emission. In light of the support our results give to the abundances derived from ASCA data for clusters and bright elliptical galaxies, we consider briefly the plausibility of subsolar abundances in elliptical galaxies.

Evidence From Intrinsic Shapes for Two Families of Elliptical Galaxies

Bright elliptical galaxies have a markedly different distribution of Hubble types than faint ellipticals; the division occurs near M_B=-20 and bright ellipticals are rounder on average. The Hubble types of galaxies in both groups are narrowly clustered, around E1.5 in the case of the bright galaxies and around E3 for the fainter ones. The Hubble-type distribution of the faint ellipticals is consistent with oblate symmetry, but the oblate hypothesis fails for the bright ellipticals. However a distribution of triaxial intrinsic shapes can successfully reproduce the apparent shape data for either group. The distribution of intrinsic, short-to-long axis ratios is peaked around 0.75 for bright galaxies and 0.65 for faint galaxies. Our results provide further evidence that elliptical galaxies should be divided into two, morphologically distinct families.

Metal Abundance of an X-Ray Emitting Gas in Two Groups of Galaxies: The NGC 5044 Group and HCG 51

We observed two groups of galaxies, the NGC 5044 group (WP 23) and Hickson's compact group HCG 51, with ASCA. We detected an extended bright soft X-ray emission, which indicates the existence of large amounts of a hot X-ray emitting gas in both targets. The temperature of the hot gas is ∼ 1 keV for both objects, which is equivalent to their galaxy velocity dispersion. The metal abundance of the gas is 0.3–0.5 solar value for both objects, which is similar to that of rich clusters of galaxies. The Si to Fe abundance ratio is smaller than that of rich clusters of galaxies, although the iron abundances determined by the Fe-L lines are somewhat uncertain. The X-ray luminosities in the 0.5–10 keV band are 1 × 1043 erg s−1 and 5 × 1042 erg s−1 for the NGC 5044 group and HCG 51, respectively, which are higher by an order of magnitude than those of X-ray bright elliptical galaxies. This makes HCG 51 one of the most X-ray luminous compact groups. Both objects have a total gravitating mass of Mtotal ∼ 2.0 × 1013M⊙, and a gas mass and a galaxy mass of Mgas ∼ Mgalaxy ∼ 1.5 × 1012M⊙. The ratios among these mass components are Mgas/Mgalaxy ∼ 1 and (Mgas + Mgalaxy)/ Mtotal ∼ 0.2 within ∼ 350 kpc for both objects. The latter is similar to previous ROSAT results for many groups of galaxies, while the former is larger than the average value of the ROSAT-observed groups. Moreover, the metal abundances of the present two groups are significantly higher than those of the NGC 2300 group and HCG 62, and are comparable to those of clusters. These suggest that the hot-gas mass and metal abundances can scatter widely among groups, compared to the small variance found among rich clusters.

Interpreting Central Surface Brightness and Color Profiles in Elliptical Galaxies

Hubble Space Telescope imagery has revealed dust features in the central regions of many (50%-80%) nearby bright elliptical galaxies. If these features are an indication of an underlying smooth diffuse dust distribution, then the interpretation of central surface brightness and color profiles in elliptical galaxies becomes significantly more difficult. In this Letter, diagnostics for constraining the presence of such an underlying central dust distribution are presented. We show that easily detectable central color gradients and flattened central surface brightness profiles can be induced by even small amounts of smoothly distributed dust (~100 M☉). Conversely, combinations of flat surface brightness profiles and flat color gradients or steep surface brightness profiles and steep color gradients are unlikely to be caused by dust. Taken as a whole, these results provide a simple observational tautology for constraining the existence of smooth diffuse dust distributions in the central regions of elliptical galaxies.

Cooling-Flow Models of the X-Ray Emission and Temperature Profiles of Elliptical Galaxies

We compare the results of a spherical, steady-state cooling-flow model with gas loss with the observed X-ray emission profiles and temperatures for five bright elliptical galaxies in Virgo and Fornax. We adopt a “thermal-instability” mass-loss prescription (following Sarazin &amp; Ashe 1989) and refer to galaxy models constrained by radially extended stellar dynamical data (Saglia et al. 1992). Our cooling-flow models are specified by three free parameters: the mass accretion rate and the pressure pext at some external radius rext, and a dimensionless constant q, which regulates the mass deposition rate along the flow. We find that models with confining pressures of pext ≃ 4 ÷ 14 × 103K cm–3 and significant accretion rates of external material, up to 4M⊙/yr, provide emission and temperature profiles in good agreement with present-day data. The trend shown in the right frame of the lower panel in the Figure suggests a possible correlation between LX/LB and the iron abundance in the gas inside ellipticals. A full account of this work, together with all the relevant references, is given in Bertin &amp; Toniazzo (1995); here below, we add a comparison of the models with some recent ASCA data (Loewenstein et al. 1994; Mushotzky et al. 1994).This work was partially supported by ASI (under contract 94RS94-202/3 FAE) of Italy.

X-Ray Observations of Elliptical Galaxies by ASCA Satellite

Using ASCA, we have confirmed that the ISM of X-ray bright elliptical galaxies are surprisingly metal poor, as compared to the theoretical predictions. In fact the exact values of the derived metallicity depend considerably on the plasma emission codes. However, the overall metallicity cannot be larger than ∼ 1 solar. For low LX/LB galaxies, all the available plasma codes suggest abundances less than half a solar. The ASCA spectra may be compatible with somewhat higher metallicity if we assume there is an additional low-temperature component (e.g. kTe ∼ 0.3 keV). However, the derived abundance can not be over 1 solar. In particular, the Si abundance turns out to be &lt; 1.5 solar, confirming the metal-poor nature of the ISM. These ASCA results are in severe contradiction with most of the SN Ia rate, particularly that of Tammann (1982). Considering further that a fairly long time (109–10yr) is needed for the stellar mass loss to accumulates into the ISM, it is suggested that the SN Ia rate has remained quite low throughout Hubble time.

Cooling Flow Models of the X-Ray Emission and Temperature Profiles for a Sample of Elliptical Galaxies

A simple spherically-symmetric, steady-state, cooling-flow description with gas loss (following Sarazin \& Ashe 1989), within galaxy models constrained by radially extended stellar dynamical data, is shown to provide generally reasonable fits to the existing data on X-ray emission profiles and temperatures for a set of bright elliptical galaxies in Virgo and Fornax. Three free parameters are needed to specify the model: the external mass flux, the external pressure, and a dimensionless factor, which regulates the mass deposition rate along the flow. Three different assumptions on the supernova rate have been considered. A moderate value for the supernova rate in elliptical galaxies is found to be preferred. Confining pressures of $p_{ext}\sim4\div15\times10^3\kelvin$ cm$^{-3}$ and significant accretion rates of external material, up to $4\msolar/\yr$, are suggested by our models. A possible correlation between $L_X/L_B$ and the iron abundance in the gas inside ellipticals is pointed out.

Detections of hard X-ray emissions from bright early-type galaxies with ASCA

Five bright elliptical galaxies in the Virgo Cluster, NGC 4365, NGC 4374 (M84), NGC 4406 (M86), NGC 4472 (M49), and NGC 4636, were observed with ASCA. In addition to the extended thermal X-ray emission of temperature kT approximately 1 keV, harder X-rays with color temperature kT greater than or equal to 2 keV were detected from all of them. The 2-10 keV luminosities of this hard component for the five galaxies, integrated within 5 min, are distributed within a relatively narrow range of (1-4) x 10(exp 40) ergs/s. The hard X-ray component is primarily attributed to the integrated emission from discrete X-ray sources. In NGC 4406 and NGC 4374 the data indicate that the hard component is contributed additionally by foreground/background emission from the hot intracluster medium (ICM) of the Virgo Cluster. The hard component of NGC 4472 seems also contributed by the Virgo ICM emission, but in this case there is evidence that the ICM brightness is locally enhanced within approximately 10 min of NGC 4472.

Absorption line gradients in the blue and near-ultraviolet spectra of bright elliptical galaxies, and implications for studies of intermediate redshift objects

view Abstract Citations (37) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Absorption Line Gradients in the Blue and Near-Ultraviolet Spectra of Bright Elliptical Galaxies, and Implications for Studies of Intermediate Redshift Objects Davidge, T. J. ; Clark, C. C. Abstract Long-slit spectroscopic observations covering the wavelength interval 3000-4500 A are used to investigate the radial behavior of atomic and molecular absorption features in the elliptical galaxies NGC 2693, NGC 3348, NGC 3379, NGC 4278, NGC 4486, and NGC 5044. There is a general tendency for metallic absorption features to weaken and continuum indices to flatten with increasing radius, in qualitative agreement with what is seen at visible wavelengths. All six galaxies contain significant (i.e., at the 3σ level) gradients in the 4000 A break. The rate of change of the 4000 A break with radius, {DELTA}4000/{DELTA} log(r), is correlated with {DELTA}Mg_2_/{DELTA} log(r), and the galaxy-to-galaxy scatter in {DELTA}4000/{DELTA} log(r) is larger than expected from experimental uncertainties alone. We compare the spectral indices of the various galaxies at the radius where Mg_2_ = 0.28, which corresponds roughly to [Fe/H] = 0, and find small galaxy-to-galaxy scatter. NGC 4486 is peculiar in that it has a very steep 4000 A break gradient and relatively weak absorption features at Mg_2_ = 0.28, suggesting that the evolution of this galaxy has been very different from that of most other ellipticals. The data are also used to investigate aperture effects in spectroscopic observations of intermediate redshift galaxies. It is demonstrated that the failure to compensate for aperture effects in galaxies out to z = 0.2 can introduce an apparent redshift dependence in the strength of the 4000 A break which closely follows trends previously attributed to evolution. Publication: The Astronomical Journal Pub Date: March 1994 DOI: 10.1086/116908 Bibcode: 1994AJ....107..946D Keywords: Atomic Spectra; Elliptical Galaxies; Molecular Absorption; Radial Distribution; Red Shift; Stellar Spectra; Ultraviolet Astronomy; Charge Coupled Devices; Data Reduction; Spectrographs; Spectroscopic Telescopes; Astrophysics; GALAXIES: ELLIPTICAL AND LENTICULAR; ULTRAVIOLET: GALAXIES; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: EVOLUTION full text sources ADS | data products SIMBAD (25) NED (6)

The Heavy Element Abundance in the Hot Corona of the Bright Elliptical Galaxy NGC 4472

view Abstract Citations (50) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Heavy Element Abundance in the Hot Corona of the Bright Elliptical Galaxy NGC 4472 Forman, W. ; Jones, C. ; David, L. ; Franx, M. ; Makishima, K. ; Ohashi, T. Abstract From a 25 ks ROSAT PSPC observation of the elliptical galaxy NGC 4472, we measured the iron abundance with arcminute spatial resolution to a radial distance of 16' (74 kpc) in the hot corona. The heavy element abundance is roughly constant at approximately 1-2 [Fe/H]_sun_ from 4' to 16'. A comparison of these measurements to models of the heavy element enrichment of hot galactic coronae around elliptical galaxies provides new insights and constraints for the evolution with time of the Type Ia supernova rate and for its present epoch value. In particular, the near-solar value of the iron abundance and its constancy throughout the corona suggest a relatively constant supernova rate over time with a present epoch value at the low end of the range derived by van den Bergh & Tammann. Publication: The Astrophysical Journal Pub Date: December 1993 DOI: 10.1086/187115 Bibcode: 1993ApJ...418L..55F Keywords: GALAXIES: ABUNDANCES; GALAXIES: ISM; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4472; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (4) NED (1) HEASARC (1)

Spectroscopic gradients in bright elliptical galaxies

view Abstract Citations (41) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopic Gradients in Bright Elliptical Galaxies Davidge, T. J. Abstract Long-slit spectra of eleven bright elliptical galaxies are used to investigate the radial behavior of various atomic and molecular absorption features in these objects. The majority of features weaken with radius, with the Mg_2_ and Na5895 indices showing the strongest gradients. However, the strengths of Hβ and Hα absorption typically remain constant. The rate of change of the Mg_2_ index with log(r), δ Mg_2_/δ log( r), shows a galaxy-to-galaxy dispersion which is larger than expected from experimental uncertainties, indicating that the galaxies in this study have not been selected from a sample in which all systems have identical radial properties. This suggests that there are system-to-system differences in the star formation histories of elliptical galaxies. Moreover, the rates with which most atomic and molecular features change with respect to Mg_2_ in the outer envelopes of these systems appears to be in better agreement with trends defined by globular clusters than galaxy nuclei. Gorgas et al. [MNRAS, 245,217(1990)] reached similar conclusions in their study of early type galaxies. Values of δ Mg_2_/δ log(r) derived in this study are combined with those published in the literature to search for correlations with various galaxy properties. δ Mg_2_/δ log(r) appears to be loosely correlated with the central velocity dispersion, σ_0_ and the dynamical anisotropy parameter, (v/σ)^*^; although both relations are significant at roughly the 95% confidence level, a larger body of observations is required to establish unambiguously the reality of these relations. A significant relation does not exist between δ Mg_2_/δlog (r) and the integrated galaxy brightness M_B_. Publication: The Astronomical Journal Pub Date: May 1992 DOI: 10.1086/116164 Bibcode: 1992AJ....103.1512D Keywords: Absorption Spectra; Astronomical Spectroscopy; Elliptical Galaxies; Abundance; H Lines; Luminosity; Molecular Absorption; Spectral Line Width; Astrophysics; GALAXIES: ELLIPTICAL AND LENTICULA; GALAXIES: KINEMATICS AND DYNAMICS; TECHNIQUES: SPECTROSCOPIC full text sources ADS | data products SIMBAD (28) NED (11)

The velocity dispersion anisotropy and mass-to-light ratio of elliptical galaxies

Axisymmetric dynamical models are constructed for 37 bright elliptical galaxies for which high-quality photometrical, and both major and minor axis kinematical data are available in the literature. The models are of the type used previously by Binney, Davies & Illingworth and van der Marel, Binney & Davies. The projected kinematics are predicted from the observed surface photometry, assuming a constant mass-to-light ratio, and a velocity ellipsoid with σ r =σ θ [i.e. f=f(E,L z )].

Interstellar matter in early-type galaxies - Optical observations

Results of optical observations of 26 bright elliptical galaxies selected on the basis of IRAS data are discussed. Optical broadband imaging (using B and R filters) and narrow-band imaging (using H-alpha interference filters) have been performed to study dust patches and ionized gas. Long-split spectroscopy has also been made to determine gas kinematics and relative line ratios. The spectroscopic data confirm the presence and distribution of interstellar matter (dust lanes and ionized gas) seen in the direct imaging. Decoupled kinematics of interstellar gas and stars favors an external origin of the interstellar matter. However, for one isolated galaxy, an internal origin is not excluded. The rotation curves determined by optical emission lines are symmetric around the center in most galaxies observed. Galaxy masses and mass-to-light ratios are estimated using the rotation curves of the ionized gas.

Spectroscopy and photometry of elliptical galaxies. VI - Sample selection and data summary

Photometric and spectroscopic data are presented for a survey of the nearest and brightest elliptical galaxies. Distances, velocities relative to the cosmic rest frame, and residual velocities relative to a velocity-flow model are calculated for individual galaxies and groups. Information is provided on the selection and completeness of the target and observed samples. Both samples appear to be noticeably deeper in the north than in the south. A new diameter system for ellipticals is described that is easy to measure on survey prints and is a useful indicator of B_T_ magnitude.