Virgo Cluster Elliptical Galaxies Research Articles

Artificial Broadcasts as Galactic Populations. II. Comparing Individualist and Collective Bounds on Broadcast Populations in Single Galaxies

The search for extraterrestrial intelligence includes efforts to constrain populations of artificial broadcasts in other galaxies. Previous efforts use individualist methods, searching for single broadcasts with high signal-to-noise ratio. These would be detected as observables with extreme values. This approach is limited to very bright broadcasts and also is subject to confusion, where a large number of broadcasts blend together to form a noise continuum. The mean value of the total emission provides an additional collective bound: the luminosity of the transmitters is no higher than the galaxy’s observed luminosity. Using the framework developed in Paper I, I evaluate how confusion affects individualist searches. I then compare individualist and collective approaches for radio broadcasts from the Milky Way, M31, and three Virgo Cluster elliptical galaxies. For current observations, confusion blurs narrowband radio broadcasts together in the Virgo ellipticals when there is one broadcast per gigahertz per 1000 stars. The collective bound implies fewer than ∼106(ℓ¯/1013W)−1 L-band broadcasts per star per gigahertz in the Milky Way wideband and is about 10 and 400 times stronger in M31 and M59, respectively. Applying the collective bound to the far-infrared–radio correlation yields constraints on radio broadcast populations in star-forming galaxies throughout the Universe. The collective bound allows us to rule out large regions of broadcast population parameter space even for distant galaxies. It also imposes constraints on gamma-ray, neutrino, and gravitational-wave broadcasts in the nearest galaxies.

Substructure in the Globular Cluster Populations of the Virgo Cluster Elliptical Galaxies M84 and M86

Abstract We have carried out a search for substructure within the globular cluster (GC) systems of M84 (NGC 4374) and M86 (NGC 4406), two giant elliptical galaxies in the Virgo Cluster. We use wide-field (36′ × 36′), multicolor broadband imaging to identify GC candidates in these two galaxies, as well as several other nearby lower-mass galaxies. Our analysis of the spatial locations of the GC candidates reveals several substructures, including a peak in the projected number density of GCs in M86 that is offset from the system center and may be at least partly due to the presence of the dwarf elliptical galaxy NGC 4406B, a bridge that connects the M84 and M86 GC systems, and a boxy isodensity contour along the southeast side of the M86 GC system. We divide our sample into red (metal-rich) and blue (metal-poor) GC candidates to look for differences in the spatial distributions of the two populations and find that the blue cluster candidates are the dominant population in each of the substructures we identify. We also incorporate the measurements from two radial velocity surveys of the GCs in the region and find that the bridge substructure is populated by GCs with a mix of velocities that are consistent with either M86 and M84, possibly providing further evidence for interaction signatures between the two galaxies.

The Infall of the Virgo Elliptical Galaxy M60 toward M87 and the Gaseous Structures Produced by Kelvin–Helmholtz Instabilities

Abstract We present Chandra observations of hot gas structures, which are characteristic of gas-stripping during infall, in the Virgo cluster elliptical galaxy M60 (NGC4649) located 1 Mpc east of M87. Chandra X-ray images at 0.5–2 keV show a sharp leading edge in the surface brightness that is 12.4 ± 0.1 kpc north and west of the galaxy center in the direction of M87 and characteristic of a merger cold front due to M60's motion through the Virgo ICM. We measured a temperature of 1.00 ± 0.02 keV for an abundance of inside the edge and for an abundance of in the Virgo ICM free stream region. We find that the observed jump in surface brightness yields a density ratio between gas inside the edge and in the cluster free stream region. If the edge is a cold front due solely to the infall of M60 in the direction of M87, we find a pressure ratio of and Mach number of . For 1.37 keV Virgo gas, we find a total infall velocity for M60 of . We calculate the motion in the plane of the sky to be , implying an inclination angle of °. Surface brightness profiles also show the presence of a faint, diffuse gaseous tail. We identify filamentary gaseous wing structures caused by the galaxy’s motion through the ICM. The structure and dimensions of these wings are consistent with simulations of Kelvin–Helmholtz instabilities, as expected if the gas-stripping is close to inviscid.

AN IN-DEPTH STUDY OF THE ABUNDANCE PATTERN IN THE HOT INTERSTELLAR MEDIUM IN NGC 4649

We present our X-ray imaging spectroscopic analysis of data from deep Suzaku and XMM-Newton Observatory exposures of the Virgo Cluster elliptical galaxy NGC 4649 (M60), focusing on the abundance pattern in the hot interstellar medium (ISM). All measured elements show a radial decline in abundance, with the possible exception of Oxygen. We construct steady state solutions to the chemical evolution equations that include infall in addition to stellar mass return and SNIa enrichment, and consider recently published SNIa yields. By adjusting a single model parameter to obtain a match to the global abundance pattern in NGC 4649 we infer that introduction of subsolar metallicity external gas has reduced the overall ISM metallicity and diluted the effectiveness of SNIa to skew the pattern towards low alpha-to-Fe ratios, and estimate the combination of SNIa rate and level of dilution. Evidently, newly-introduced gas is heated as it is integrated into, and interacts with, the hot gas that is already present. These results indicate a complex flow and enrichment history for NGC 4649, reflecting the continual evolution of elliptical galaxies beyond the formation epoch. The heating and circulation of accreted gas may help reconcile this dynamic history with the mostly passive evolution of elliptical stellar populations. In an appendix we examine the effects of the recent updated atomic database AtomDB in spectral fitting of thermal plasmas with hot ISM temperatures in the elliptical galaxy range.

THE GAS DYNAMICS OF NGC 4472 REVEALED BYXMM-NEWTON

We present results from a 100 ks XMM-Newton observation of the hot gas in the Virgo cluster elliptical galaxy NGC 4472. We find a surface brightness discontinuity {approx}21 kpc north of the nucleus, consistent with being a contact discontinuity between two moving fluids. We also detect a >60 kpc long ram-pressure stripped tail. The pressure across the discontinuity implies an infall velocity, v{sub infall}, of 1000 km s{sup -1} < v{sub infall}< 2200 km s{sup -1} depending on what assumptions are made about the density and pressure of the external gas. We suggest that the NGC 4472 group is falling into a collapsing filament, which is itself falling into the Virgo cluster. The gas of a collapsing filament is rapidly decelerated as it crosses the standoff shock, but the apparent high velocity of infall for NGC 4472 could be simply due to the fact that the gravitating potential of the NGC 4472 group is unaffected by this shock. While the group falls through the shock its gas will be stripped as it passes through the stalled gas of the filament. Additionally, we find two sets of cool filamentary arms to the east and the southwest of the nucleus. One ofmore » the southwest arms is coincident with a sharp filament seen with Chandra. We interpret these arms as filaments of cool gas that have been driven out from the center of the galaxy by the buoyant evolution of a radio bubble. The age of this outburst is {approx}10{sup 8} yr assuming that the buoyant bubble rises with a velocity of {approx}0.4c{sub s} = 200 km s{sup -1}; the energy of the outburst is a modest {approx}2 x 10{sup 56} erg.« less

Optical/near-infrared colours of early-type galaxies and constraints on their star formation histories

We introduce and discuss the properties of a theoretical (B−K)(J−K) integrated colour diagram for single-age, single-metallicity stellar populations. We show how this combination of integrated colours is able to largely disentangle the well-known age–metallicity degeneracy when the age of the population is greater than ∼300 Myr, and thus provides valuable estimates of both age and metallicity of unresolved stellar systems. We discuss in detail the effect on this colour–colour diagram of α-enhanced metal abundance ratios (typical of the oldest populations in the Galaxy), the presence of blue horizontal branch stars unaccounted for in the theoretical calibration and of statistical colour fluctuations in low-mass stellar systems. In the case of populations with multiple stellar generations, the luminosity-weighted mean age obtained from this diagram is shown to be heavily biased towards the youngest stellar components. We then apply this method to several data sets for which optical and near-infrared photometry are available in the literature. We find that Large Magellanic Cloud and M31 clusters have colours which are consistent with the predictions of the models, but these do not provide a sensitive test due to the fluctuations which are predicted by our modelling of the Poisson statistics in such low-mass systems. For the two Local Group dwarf galaxies NGC 185 and 6822, the mean ages derived from the integrated colours are consistent with the star formation histories inferred independently from photometric observations of their resolved stellar populations. The methods developed here are applied to samples of nearby early-type galaxies with high-quality aperture photometry in the literature. A sample of bright field and Virgo cluster elliptical galaxies is found to exhibit a range of luminosity-weighted mean ages from 3 to 14 Gyr, with a mean of ∼8 Gyr, independent of environment, and mean metallicities at or just above the solar value. Colour gradients are found in all of the galaxies studied, in the sense that central regions are redder. Apart from two radio galaxies, where the extreme central colours are clearly driven by the active galactic nucleus, and one galaxy which also shows a radial age gradient, these colour changes appear consistent with metallicity changes at a constant mean age. Finally, aperture data for five Virgo early-type dwarf galaxies show that these galaxies appear to be shifted to lower mean metallicities and lower mean ages (range 1–6 Gyr) than their higher luminosity counterparts.

Ram Pressure Stripping in the Low-Luminosity Virgo Cluster Elliptical Galaxy NGC 4476

We present a deep VLA search for H I emission from the low-luminosity Virgo Cluster elliptical galaxy NGC 4476, which contains 1.1 × 108 M⊙ of molecular gas in an undisturbed disk in regular rotation. No H I was detected. The rms noise in the final image corresponds to a 3 σ column density sensitivity of 1.2 × 1020 cm-2 at the position of NGC 4476, averaged over the 4 kpc beam. The total H I mass is less than 1.5 × 107 M⊙. If we compare our H I upper limit with the H2 content, we find that NGC 4476 is extremely deficient in H I compared with other galaxies detected in these two species. The H2/H mass ratio for NGC 4476 is greater than 7, whereas typical H2/H ratios for elliptical galaxies detected in both H I and H2 are less than 2. On the basis of this extreme H I deficiency and the intracluster medium density at the projected distance from M87, we argue that either NGC 4476 has undergone ram pressure stripping while traveling through the Virgo Cluster core or its average molecular gas density is larger and its interstellar UV field is smaller than in typical spiral galaxies. NGC 4476 is located 12' in projection from M87, which causes extreme continuum confusion problems. We also discuss in detail the techniques used for continuum subtraction. The spectral dynamic range of our final image is 50,000 to 1.

Infrared Surface Brightness Fluctuations in Virgo Cluster Elliptical Galaxies

view Abstract Citations (33) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Surface Brightness Fluctuations in Virgo Cluster Elliptical Galaxies Jensen, Joseph B. ; Luppino, Gerard A. ; Tonry, John L. Abstract We imaged seven Virgo Cluster elliptical galaxies and the bulge of M31 in the near-infrared K' band (2.1 micron). The amplitude of the spatial surface brightness fluctuations (SBFs) was measured for each galaxy. Using the I-band SBF distance measurements for the Virgo galaxies, and a distance of 0.77 Mpc for M31, we determined a mean absolute fluctuation magnitude of M^bar^_K'_ = -5.62 +/- 0.29. Our calibration is consistent with Luppino & Tonry's Local Group determination of M^bar^_K'_ = -5.61 +/- 0.09 for M31, and it is also consistent with, but somewhat fainter than, Pahre & Mould's value of M^bar^_K_ = -5.77 +/- 0.18 from observations of six Virgo elliptical galaxies. Our results also compare favorably with theoretical predictions based on simple stellar populations. The scatter in our measurements is significant and appears to result from both observational uncertainty and variations in stellar populations. Nevertheless, the consistency of the IR observations on average and the relative brightness of fluctuations at K' suggest that IR SBFs may be a useful tool for measuring galaxy distances out to ~8000 km s^-1^. We find that the key observational limitations in using IR SBFs are accurately measuring the point-spread function (PSF) and subtracting the sky background, both of which strongly influence the fluctuation amplitude measured. A relationship was found between the fluctuation amplitude and the signal-to-noise ratio (S/N) of the observation: fluctuation amplitudes are systematically larger in low- S/N measurements. We attribute this relationship to present-day limitations of infrared arrays, which have sensitivity and dark current variations on scales comparable to those of the surface brightness fluctuations. In low-S/N observations, variations due to imperfect dark current subtraction and flat-fielding contribute significantly to the power spectrum, resulting in a biased measurement of the fluctuation power. To measure accurate IR SBF distances, a S/N ~> 4 is required. Significant radial variations in fluctuation power were not conclusively observed in any of the elliptical galaxies for which our S/N was sufficiently high to permit radial SBF analysis. Publication: The Astrophysical Journal Pub Date: September 1996 DOI: 10.1086/177711 Bibcode: 1996ApJ...468..519J Keywords: GALAXIES: CLUSTERS: INDIVIDUAL NAME: VIRGO; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: ELLIPTICAL AND LENTICULAR; CD; GALAXIES: PHOTOMETRY; INFRARED: GALAXIES; TECHNIQUES: IMAGE PROCESSING full text sources ADS | data products SIMBAD (11) NED (9)

Hubble Space Telescope photometry of the central regions of Virgo cluster elliptical galaxies. II: Isophote shapes.

The isophotal shapes of a magnitude limited sample of Virgo ellipticals are presented. These are derived from high resolution Hubble Space Telescope (HST) photometry. The absence of atmospheric seeing and accurate knowledge of the Point Spread Function (PSF) allows us to perform an accurate deconvolution. Model galaxies were constructed to test the deconvolution algorithms used, and showed that we can accurately recover isophotal shape parameters down to 0.5 sec. From the isophotal parameters we can classify the galaxies in two subsamples: disky and non-disky galaxies. In three of these disky galaxies we found evidence for a nuclear stellar disk in the inner 1.5 sec. In addition these galaxies also have an outer disk, that seems to break up inside 2 sec - 3 sec. In the two galaxies for which there is kinematic evidence from the literature of a decoupled core, we found no indication for such subsystem from the isophotal shape analysis. In 80% of these early type galaxies there are indications for dust. For eight of these galaxies the dust has not been detected before.

Hubble Space Telescope photometry of the central regions of Virgo Cluster elliptical galaxies. 1: Observations, discussion, and conclusions

Using the Hubble Space Telescope we have observed at 10 pc resolution the nuclei of a luminosity-limited sample of 14 E and E/SO galaxies in the Virgo Cluster with magnitudes B(sub T) = 9.4 to 13.4. In this paper we present the images, and discuss the results of the detailed analysis of the surface photometry given in two companion papers. We find that the nuclear and near-nuclear morphologies confirm and strengthen the previously recognized dichotomy of 'E' galaxies into 'true' and 'disky' subtypes. The latter, usually classified E4 or later, often show a bright nuclear disk of radius approximately 100 pc. Essentially all early-type galaxies with -18 greater than M(sub B) greater than -20 are disky. Most true E galaxies are classified E4 or earlier. Most galaxies of both types show dust in the nuclear regions, the most remarkable example being a compact dust disk in NGC 4261. Other than dust, no anomalies were detected in the centers of the three galaxies in our sample which show clear kinematic evidence for a decoupled component.

Hubble Space Telescope photometry of the central regions of Virgo cluster elliptical galaxies. 3: Brightness profiles

We have used the Planetary Camera on the Hubble Space Telescope (HST) to study the morphology and surface brightness parameters of a luminosity-limited sample of fourteen elliptical galaxies in the Virgo cluster. The total apparent blue magnitudes of the galaxies range between 9.4 and 13.4. In this paper, the core brightness profiles are presented, while the overall morphology and the isophotal shapes are discussed in two companion papers (Jaffe et al. (1994); van den Bosch et al. (1994)). We show that, in spite of the spherical aberration affecting the HST primary mirror, deconvolution techniques allow recovery of the brightness profile up to 0.2 arcsec from the center of the galaxies. We find that none of the galaxies has an isothermal core. On the basis of their morphological and photometrical properties, the galaxies can be divided in two physically distinct groups, referred to as Type I and Type II. All of the Type I galaxies are classified as E1 to E3 in the Revised Shapley Ames Catalog (Sandage & Tammann 1981), while Type II galaxies are classified as E5 to E7. The characteristics of Type II galaxies are explained by the presence of disks component on both the 1 arcsec and the 10 arcsec scales, while Type I galaxies correspond to the classical disk-free ellipticals.

The luminosity function of compact groups of galaxies

We present an analysis of the luminosity function of the galaxies in Hickson's sample of compact groups (HCG). The luminosities of compact group galaxies are consistent with their being drawn from a Schechter luminosity function with α = -0.2^+0.8^_-0.9_, L^*^ = 1.1 +/- 0.2 x 10^10^ h^-2^L_sun_ and {PHI}^*^ = 1.3^+0.2^_-0.8_ x 10^-4^ h^3^ Mpc^-3^ (99% confidence level). Individual morphological-type luminosity functions were also determined. Both the total and morphological-type specific luminosity functions of compact group galaxies are significantly different from those of field, loose-group, and cluster galaxies. In particular, the luminosity function of HCG elliptical galaxies has a mean magnitude which is significantly brighter than the mean magnitude of Virgo cluster elliptical galaxies (28% of HCG elliptical galaxies are more luminous than M87). The mean luminosity density of galaxies in compact groups is estimated to be L = 1.3^+0.1^_-0.8_ x 10^6^ h L_sun_ Mpc^-3^, which constitutes 0.8% of the total luminosity density of galaxies in the universe. This result is consistent with the conventional scenario in which compact groups merge to form elliptical galaxies on a relatively short time scale.

Observations of novae in the Virgo cluster

view Abstract Citations (96) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Novae in the Virgo Cluster Pritchet, Christopher J. ; van den Bergh, Sidney Abstract During 15 nights of observations in 1986 March and April the authors have detected nine novae in Virgo cluster elliptical galaxies. From six novae with reasonably well-observed light curves it is found that the distance modulus of the Virgo cluster is 6.8±0.4 (estimated error) larger than that of M31. Using a distance modulus of 24.65±0.15 for M31 then gives a Virgo cluster distance of D = 19.5±3.9 Mpc. With a cosmological redshift of 1336±54 km s-1 for the Virgo cluster this yields a value H0 = 69±14 km s-1 Mpc-1 for the Hubble parameter. Publication: The Astrophysical Journal Pub Date: July 1987 DOI: 10.1086/165387 Bibcode: 1987ApJ...318..507P Keywords: Light Curve; Novae; Virgo Galactic Cluster; Cosmology; Red Shift; Star Distribution; Stellar Magnitude; Astrophysics; COSMOLOGY; GALAXIES: GENERAL; STARS: NOVAE full text sources ADS | data products SIMBAD (15) NED (12)