Centaurus Group Research Articles

The Metallicity Distribution Function in Outer Halo Fields of Simulated Elliptical Galaxies Compared to Observations of NGC 5128

Stellar metallicity distribution functions (MDFs) have been measured for resolved stellar populations in the outer halos of many galaxies in nearby groups. Among them, the MDF of NGC 5128, the central giant elliptical in the Centaurus group, provides essential constraints for theories of massive galaxy formation and hierarchical assembly. To investigate the formation and chemical evolution history of the outer halo of giant elliptical galaxies, we examine the chemical properties of three zoom-in high-resolution cosmological hydrodynamical simulations of an NGC 5128–like giant elliptical galaxy and compare their outer halo MDFs to the observed one of NGC 5128. Even though the simulated galaxies have different merging histories and age distributions, all predicted MDFs are in good qualitative agreement with the observed one. The median metallicity of the simulated galaxies is, on average, [M/H] = −0.41 ± 0.06 compared to the observed value of [M/H] = −0.38 ± 0.02 for NGC 5128, and the dispersion in metallicity is ∼0.77 dex for both observed and simulated galaxies. We investigate the origin of the stars ending up in the outer halo field of simulated galaxies and show that most have an “accreted” origin, formed in other small galaxies and later accreted in mergers. Only ∼15% of the stars are formed in situ within the main progenitor of the galaxy and radially migrate outward. We show that the contribution of metal-rich in situ stars is subdominant in the outer halos of our simulated galaxies but can be prominent in the inner regions.

Star Formation History of Two Fields in the Halo of NGC 5128

AbstractNGC 5128 galaxy is a giant elliptical galaxy located in the Centaurus group of galaxies at 3.8 Mpc. We aim to study the star formation history (SFH) of two different fields of the galaxy. The northeastern field (Field 1) is located at a distance of 18.8 kpc, while the southern field (Field 2) is at 9.9 kpc. We use a photometric method that is based on identifying long period variable (LPV) stars and asymptotic giant branch (AGB) stars, as they are strong tracers of star formation and galaxy evolution due to their luminosity and variability; 395 LPVs in Field 1 and 671 LPVs in Field 2 have been identified. These two fields present similar SFHs, although the SF rate of Field 2 is more enhanced. We find that the galaxy has three major star formation episodes t ∼ 800 Myr ago, t ∼ 3.2 Gyr ago, and t ∼ 10 Gyr ago, where t is look-back time. The rate of star formation at ∼ 800 Myr ago agrees with previous studies suggesting that the galaxy experienced a merger around that time. Furthermore, NGC 5128 has experienced a lower star formation rate in its recent history which could have been driven by jet-induction star formation and multiple outbursts of AGN activity in this galaxy, as well as a minor merger around 400 Myr ago.

Metal-poor nuclear star clusters in two dwarf galaxies near Centaurus A suggesting formation from the in-spiraling of globular clusters

Studies of nucleated dwarf galaxies can constrain the scenarios for the formation and evolution of nuclear star clusters (NSC) in low-mass galaxies and give us insights on the origin of ultra compact dwarf galaxies (UCDs). We report the discovery of a NSC in the dwarf galaxy KKs58 and investigate its properties together with those of another NSC in KK197. Both NSCs are hosted by dwarf elliptical galaxies of the Centaurus group. Combining ESO VLT MUSE data with photometry from VLT FORS2, CTIO Blanco DECam, and HST ACS, as well as high-resolution spectroscopy from VLT UVES, we analyse the photometric, kinematic and stellar population properties of the NSCs and their host galaxies. We confirm membership of the NSCs based on their radial velocities and location close to the galaxy centres. We also confirm the membership of two globular clusters (GCs) and detect oblate rotation in the main body of KK197. Based on high signal-to-noise spectra taken with MUSE of the NSCs of both KKs58 and KK197 we measure low metallicities, [Fe/H] = −1.75 ± 0.06 dex and [Fe/H] = −1.84 ± 0.05 dex, and stellar masses of 7.3 × 105 M⊙ and 1.0 × 106 M⊙, respectively. Both NSCs are more metal-poor than their hosts that have metallicities of −1.35 ± 0.23 dex (KKs58) and −0.84 ± 0.12 dex (KK197). This can be interpreted as NSC formation via the in-spiral of GCs. The masses, sizes and metallicities of the two NSCs place them among other NSCs, but also among the known UCDs of the Centaurus group. This indicates that NSCs might constitute the progenitors of a part of the low-mass UCDs, although their properties are almost indistinguishable from typical GCs.

The dwarf galaxy satellite system of Centaurus A

Dwarf galaxy satellite systems are essential probes to test models of structure formation, making it necessary to establish a census of dwarf galaxies outside of our own Local Group. We present deep FORS2 VI band images from the ESO Very Large Telescope (VLT) for 15 dwarf galaxy candidates in the Centaurus group of galaxies. We confirm nine dwarfs to be members of Cen A by measuring their distances using a Bayesian approach to determine the tip of the red giant branch luminosity. We have also fit theoretical isochrones to measure their mean metallicities. The properties of the new dwarfs are similar to those in the Local Group in terms of their sizes, luminosities, and mean metallicities. Within our photometric precision, there is no evidence of a metallicity spread, but we do observe possible extended star formation in several galaxies, as evidenced by a population of asymptotic giant branch stars brighter than the red giant branch tip. The new dwarfs do not show any signs of tidal disruption. Together with the recently reported dwarf galaxies by the complementary PISCeS survey, we study the luminosity function and 3D structure of the group. By comparing the observed luminosity function to the high-resolution cosmological simulation IllustrisTNG, we find agreement within a 90% confidence interval. However, Cen A seems to be missing its brightest satellites and has an overabundance of the faintest dwarfs in comparison to its simulated analogs. In terms of the overall 3D distribution of the observed satellites, we find that the whole structure is flattened along the line-of-sight, with a root-mean-square (rms) height of 130 kpc and an rms semi-major axis length of 330 kpc. Future distance measurements of the remaining dwarf galaxy candidates are needed to complete the census of dwarf galaxies in the Centaurus group.

The origin of lopsided satellite galaxy distribution in galaxy pairs

ABSTRACT It is well known that satellite galaxies are not isotropically distributed among their host galaxies as suggested by most interpretations of the Λ cold dark matter (ΛCDM) model. One type of anisotropy recently detected in the Sloan Digital Sky Survey (and seen when examining the distribution of satellites in the Local Group and in the Centaurus group) is a tendency to be so-called lopsided. Namely, in pairs of galaxies (like Andromeda and the Milky Way) the satellites are more likely to inhabit the region in between the pair, rather than on opposing sides. Although recent studies found a similar set-up when comparing pairs of galaxies in ΛCDM simulations indicating that such a set-up is not inconsistent with ΛCDM, the origin has yet to be explained. Here we examine the origin of such lopsided set-ups by first identifying such distributions in pairs of galaxies in numerical cosmological simulations, and then tracking back the orbital trajectories of satellites (which at z = 0 display the effect). We report two main results: first, the lopsided distribution was stronger in the past and weakens towards z = 0. Secondly, the weakening of the signal is due to the interaction of satellite galaxies with the pair. Finally, we show that the z = 0 signal is driven primarily by satellites that are on first approach, who have yet to experience a ‘flyby’. This suggests that the signal seen in the observations is also dominated by dynamically young accretion events.

A whirling plane of satellite galaxies around Centaurus A challenges CDM cosmology

AbstractThe phase-space correlation of dwarf galaxies around the Milky Way and the Andromeda galaxy pose a serious challenge to our understanding of structure formation. Recently, another planar structure was discovered around Cen A, the major galaxy of the Centaurus group. We have surveyed this galaxy group for new dwarf galaxies and presented the discovery of 57 new dwarf member candidates. Furthermore, we have studied the kinematics of previously known dwarfs and again found a kinematic coherence in their movement, similar to the Local Group satellites. In CDM simulations, such an alignment appears in less than 0.5 percent.

Distances from the tip of the red giant branch to the dwarf galaxies dw1335-29 and dw1340-30 in the Centaurus group

Context. The abundance and spatial distribution of dwarf galaxies are excellent empirical benchmarks against which to test models of structure formation on small scales. The nearby Centaurus group, with its two subgroups centered on Cen A and M 83, stands out as an important alternative to the Local Group for scrutinizing cosmological model predictions in a group of galaxies context. Aims. We have obtained deep optical images of three recently discovered M 83 satellite galaxy candidates with the FORS2 instrument mounted on the Very Large Telescope. We aim to confirm their group membership and study their stellar population. Methods. Deep V I-band photometry was used to resolve the brightest stars in our targets. Artificial star tests are performed to estimate the completeness and uncertainties of the photometry. The color-magnitude diagrams reveal the red giant branch (RGB) stars, allowing us to use the Sobel edge detection method to measure the magnitude of the RGB tip and thus derive distances and group membership for our targets. The mean metallicity of the dwarf galaxies were further determined by fitting BASTI model isochrones to the mean RGB locus. Results. We confirm the two candidates, dw1335-29 and dw1340-30, to be dwarf satellites of the M 83 subgroup, with estimated distances of 5.03 ± 0.24 Mpc and 5.06 ± 0.24 Mpc, respectively. Their respective mean metallicities of ⟨[Fe/H]⟩ = −1.79 ± 0.4 and ⟨[Fe/H]⟩ = −2.27 ± 0.4 are consistent with the metallicity–luminosity relation for dwarf galaxies. The third candidate, dw1325-33, could not be resolved into stars due to insufficiently deep images, implying its distance must be larger than 5.3 Mpc. Using the two newly derived distances we assess the spatial distribution of the galaxies in the M 83 subgroup and discuss a potential plane-of-satellites around M 83.

New low surface brightness dwarf galaxies in the Centaurus group

We conducted an extensive CCD search for faint, unresolved dwarf galaxies of very low surface brightness in the whole Centaurus group region encompassing the Cen A and M 83 subgroups lying at a distance of roughly 4 and 5 Mpc, respectively. The aim is to significantly increase the sample of known Centaurus group members down to a fainter level of completeness, serving as a basis for future studies of the 3D structure of the group. Following our previous survey of 60 square degrees covering the M 83 subgroup, we extended and completed our survey of the Centaurus group region by imaging another 500 square degrees area in the g and r bands with the wide-field Dark Energy Survey Camera at the 4m Blanco telescope at CTIO. The limiting central surface brightness reached for suspected Centaurus members is $\mu_r \approx 29$ mag arcsec$^{-2}$, corresponding to an absolute magnitude $M_r \approx -9.5$. The images were enhanced using different filtering techniques. We found 41 new dwarf galaxy candidates, which together with the previously discovered 16 dwarf candidates in the M 83 subgroup amounts to almost a doubling of the number of known galaxies in the Centaurus complex, if the candidates are confirmed. We carried out surface photometry in g and r, and report the photometric parameters derived therefrom, for all new candidates as well as previously known members in the surveyed area. The photometric properties of the candidates, when compared to those of LG dwarfs and previously known Centaurus dwarfs, suggest membership in the Centaurus group. The sky distribution of the new objects is generally following a common envelope around the Cen A and M 83 subgroups. How the new dwarfs are connected to the intriguing double-planar feature recently reported by Tully et al. (2015) must await distance information for the candidates.

Testing the two planes of satellites in the Centaurus group

The existence of satellite galaxy planes poses a major challenge for the standard picture of structure formation with non-baryonic dark matter. Recently Tully et al. (2015) reported the discovery of two almost parallel planes in the nearby Cen A group using mostly high-mass galaxies (M$_B$ $<$ -10 mag) in their analysis. Our team detected a large number of new group member candidates in the Cen A group (M\"uller et al. 2016). This dwarf galaxy sample combined with other recent results from the literature enables us to test the galaxy distribution in the direction of the Cen A group and to determine the statistical significance of the geometric alignment. Taking advantage of the fact that the two galaxy planes lie almost edge-on along the line of sight, the newly found 13 group members by Crnojevic et al. (2014, 2016) and our 16 new Cen A group candidates (M\"uller et al. 2016) can be assigned relative to the two planes. We use various statistical methods to test whether the distribution of galaxies follows a single normal distribution or shows evidence of bimodality as it has been reported earlier. We confirm that the data used for the Tully et al. (2015) study support the picture of a bimodal structure. However, when the new galaxy samples are included, the gap between the two galaxy planes is closing and the significance level of the bimodality is reduced. Instead, the plane that contains Cen A becomes more prominent. We found evidence that the galaxy system around Cen A is made up of only one plane of satellites. This plane is almost orthogonal to the dust plane of Cen A. Accurate distances to the new dwarf galaxies will be required to measure the precise 3D distribution of the galaxies around Cen A.

New dwarf galaxy candidates in the Centaurus group

Recent studies of the distribution and kinematics of the Milky Way and Andromeda satellite galaxy systems have confirmed the existence of coplanar, corotating structures of galaxies. In addition to the 'missing satellite problem', these structures pose a major challenge to the standard $\Lambda$CDM scenario of structure formation. We complement the efforts made by the dwarf galaxy community to extend these studies to other nearby galaxy groups by systematically searching for faint, unresolved dwarf members with a low surface brightness in the Southern Centaurus group of galaxies. The aim is to determine whether these coplanar, corotating structures are a universal phenomenon. We imaged an area of 60 square degrees (0.3 Mpc$^2$) around the M83 subgroup with the wide-field Dark Energy Camera (DECam) at the CTIO 4 m Blanco telescope in $g$ and $r$ down to a limiting surface brightness of $\mu_r\approx 30$ mag arcsec$^{-2}$. Various image-filtering techniques were applied to the DECam data to enhance the visibility of extremely low-surface brightness objects. We report the discovery of 16 new dwarf galaxy candidates in the direction of the M83 subgroup, roughly doubling the number of known dwarfs in that region. The photometric properties of the candidates, when compared to those of the Local Group, suggest membership in the M83 subgroup. The faintest objects have a central star density of $\approx1.3 L_\odot$ pc$^{-2}$ and a total magnitude of $g = 20.25$, corresponding to $M_g = -9.55$ at the nominal distance of 4.9 Mpc. The sky distribution of the new objects is significantly prolonged toward Cen A, suggesting that many of them belong to the Cen A subgroup or a common halo. We also provide updated surface photometry for the brighter, known dwarf members in the surveyed area.

Resolved Stellar Population of Distant Galaxies in the ELT Era

ABSTRACTThe expected imaging capabilities of future Extremely Large Telescopes (ELTs) will offer the unique possibility to investigate the stellar populations of distant galaxies from the photometry of the stars in very crowded fields. Using simulated images and photometric analysis we explore here two representative science cases aimed at recovering the characteristics of the stellar populations in the inner regions of distant galaxies. Specifically, case (1) at the center of the disk of a giant spiral in the Centaurus Group (μB ∼ 21, distance of 4.6 Mpc) and case (2) at half of the effective radius of a giant elliptical in the Virgo Cluster (μI ∼ 19.5, distance of 18 Mpc). We generate synthetic frames by distributing model stellar populations and adopting a representative instrumental setup, i.e., a 42 m telescope operating close to the diffraction limit. The effect of crowding is discussed in detail, showing how stars are measured preferentially brighter than they really are as the confusion limit is approached. We find that (1) accurate photometry (σ ∼ 0.1, completeness ≳90%) can be obtained for case 2 down to I ∼ 28.5, J ∼ 27.5, allowing us to recover the stellar metallicity distribution in the inner regions of ellipticals in Virgo to within ∼0.1 dex; (2) the same photometric accuracy holds for the science case 1 down to J ∼ 28.0, K ∼ 27.0, enabling reconstruction of the star formation history up to the Hubble time via simple star counts in diagnostic boxes. For the latter case, we discuss the possibility of deriving more detailed information on the star formation history from the analysis of their horizontal-branch stars. We show that the combined features of high sensitivity and angular resolution of ELTs may open a new era for our knowledge of the stellar content of galaxies of different morphological types up to the distance of the Virgo cluster.

NGC 5253 and ESO 269-G058: Dwarf Galaxies with a Past

Deep r' and i' images obtained with GMOS on Gemini South are used to probe the bright stellar content in the outer regions of the Centaurus Group dwarf galaxies NGC 5253 and ESO 269-G058. Red giant branch (RGB) stars are traced out to a distance of 8 kpc along the major axis of NGC 5253 and 6 kpc in ESO 269-G058. The outer regions of both galaxies are metal-poor; RGB stars located between projected major axis distances of 2 and 4 kpc in NGC 5253 have [Fe/H] ∼ -1, whereas RGB stars in the corresponding portion of ESO 269-G058 have [Fe/H] ∼ -1.8. Stars with metallicities that differ from the mean by more than a few tenths of a dex make only a modest contribution to the stellar content in the outer regions of both galaxies. A population of bright asymptotic giant branch (AGB) stars is seen in both galaxies. In the particular case of NGC 5253, roughly 1%-10% of the stellar mass may have formed during the past few hundred million years, and it is suggested that the progenitors of the two recent Type Ia supernovae in this galaxy may have formed at this time. That NGC 5253 has experienced either episodic or continuing elevated levels of star formation during the past few hundred million years is reminiscent of what is seen in other dwarf starburst galaxies, such as NGC 3077, and it is argued that the current episodes of star formation in NGC 5253 and ESO 269-G058 may have been triggered up to ∼1 Gyr in the past. Finally, a distance modulus is computed for each galaxy based on the brightness of the RGB tip, and the results are μ0 = 27.48 ± 0.14 for NGC 5253 and 27.93 ± 0.18 for ESO 269-G058.

The Centaurus Group and the Outer Halo of NGC 5128: Are They Dynamically Connected?

NGC 5128, a giant elliptical galaxy only $\sim 4$ Mpc away, is the dominant member of a galaxy group of over 80 probable members. The Centaurus group provides an excellent sample for a kinematic comparison between the halo of NGC 5128 and its surrounding satellite galaxies. A new study, presented here, shows no kinematic difference in rotation amplitude, rotation axis, and velocity dispersion between the halo of NGC 5128, determined from over $\sim340$ of its globular clusters, and those of the Centaurus group as a whole. These results suggest NGC 5128 could be behaving in part as the inner component to the galaxy group, and could have begun as a large initial seed galaxy, gradually built up by minor mergers and satellite accretions, consistent with simple cold dark matter models. The mass and mass-to-light ratios in the B-band, corrected for projection effects, are determined to be $(1.3\pm0.5) \times 10^{12}$ M$_{\sun}$ and $52\pm22$ M$_{\sun}$/L$_{\sun}$ for NGC 5128 out to a galactocentric radius of 45 kpc, and $(9.2\pm3.0) \times 10^{12}$ M$_{\sun}$ and $153\pm50$ M$_{\sun}$/L$_{\sun}$ for the Centaurus group, consistent with previous studies.

HiDetection of Two Dwarf S0 Galaxies in Nearby Groups: ESO 384-016 and NGC 59

A H I survey of 10 dE/dS0 galaxies in the nearby Sculptor and Centaurus A groups was made using the Australia Telescope Compact Array. The observed galaxies have accurate distances derived by Jerjen et al. using the surface brightness fluctuation technique. Their absolute magnitudes are in the range -9.5 > MB > -15.3. Only two of the 10 galaxies were detected at our detection limit (~1.0 × 106 M⊙ for the Centaurus group and ~5.3 × 105 M⊙ for the Sculptor group): the two dS0 galaxies ESO 384-016 in the Centaurus A group and NGC 59 in the Sculptor group, with H I masses of × 106 and × 107 M⊙, respectively. Those two detections were confirmed using the Green Bank Telescope. These small H I reservoirs could fuel future generations of low-level star formation and could explain the bluer colors seen at the center of the detected galaxies. Similar to what is seen with the Virgo dwarf ellipticalss, the two objects with H I appear to be on the outskirts of the groups.

Wide-Field Washington Photometry of the NGC 5128 Globular Cluster System. II. Large-Scale Properties of the System

Building on the CMT1 photometric database presented in Paper I, in this paper we derive the large-scale properties of the globular cluster system (GCS) in NGC 5128, the nearest giant elliptical and the dominant galaxy in the Centaurus group. In global terms, it has a smaller total population than previously thought: we estimate 980 ± 120 clusters over all magnitudes, yielding a specific frequency SN = 1.4 ± 0.2, with a steep projected radial distribution σ ~ r-2. The luminosity distribution of the clusters resembles that of an old, normal GC luminosity function (Gaussian-like with peak at MV -7.4 and dispersion of 1.3 mag), but these parameters are unfortunately quite uncertain because of the system's low population and the heavy field contamination. Using the metallicity-sensitive C - T1 color index, we discuss the metallicity distribution function (MDF) for a subsample of 211 previously identified clusters, all on a homogeneous photometric system. We find the MDF to be strongly bimodal, with metallicity peaks at [Fe/H] = -1.55 and -0.55 and with nearly equal numbers of clusters in each of the metal-poor and metal-rich modes. The combined evidence from the system's low specific frequency, the MDF, and the isophotal shell features in the halo light make a major merger a plausible model for the formation history of this giant E galaxy. However, the progenitor galaxies must have been more gas-rich than in any present-day mergers or starbursts. Finally, we present a list of 327 new cluster candidates not identified in any previous surveys; most of these are in the less well studied bulge region of the galaxy and along the minor axis.

Wide-Field Washington Photometry of the NGC 5128 Globular Cluster System. I. The Database

To investigate the global properties of the globular cluster system (GCS) around NGC 5128, the central giant elliptical galaxy in the nearby Centaurus group, we have obtained deep CCD imaging for an area of almost 2 deg2 centered on the galaxy. Our data, in the CMT1 Washington photometric system, reach an approximate limiting magnitude of T1 R 22 and contain magnitudes, colors, and coordinates for more than 100,000 objects. Of these, the vast majority (about 99%) are either foreground stars or faint background galaxies; the old-halo globular clusters make up the remaining tiny fraction of the sample. Our database, however, provides the material for understanding the large-scale features of the GCS, including its metallicity distribution (MDF), luminosity distribution, and spatial structure.

The distance to the giant elliptical galaxy NGC 5128

The distance to NGC 5128, the central galaxy of the Centaurus group and the nearest giant elliptical to us, has been determined using two independent distance indicators: the Mira period-luminosity (PL) relation and the luminosity of the tip of the red giant branch (RGB). The data were taken at two different locations in the halo of NGC 5128 with the ISAAC near-IR array on ESO VLT. From more than 20 hours of observations with ISAAC a very deep K s -band luminosity function was constructed. The tip of the RGB is detected at K s = 21.24 ± 0.05 mag. Using an empirical calibration of the K-band RGB tip magnitude, and assuming a mean metallicity of [M/H] = -0.4 dex and reddening of E(B - V) = 0.11, a distance modulus of NGC 5128 of (m - M) 0 = 27.87 ± 0.16 was derived. The comparison of the H-band RGB tip magnitude in NGC 5128 and the Galactic Bulge implies a distance modulus of NGC 5128 of (m - M) 0 = 27.9 ± 0.2 in good agreement with the K-band RGB tip measurement. The inner halo field has larger photometric errors, brighter completeness limits and a larger number of blends. Thus the RGB tip feature is not as sharp as in the outer halo field. The population of stars above the tip of the RGB amounts to 2176 stars in in the outer halo field (Field 1) and 6072 stars in the inner halo field (Field 2). The large majority of these sources belong to the asymptotic giant branch (AGB) population in NGC 5128 with numerous long period variables. Mira variables were used to determine the distance of NGC 5128 from a period-luminosity relation calibrated using the Hipparcos parallaxes and LMC Mira period-luminosity relation in the K-band. This is the first Mira period-luminosity relation outside the Local Group. A distance modulus of 27.96 ± 0.1 was derived, adopting the LMC distance modulus of 18.50 ± 0.04. The mean of the two methods yields a distance modulus to NGC 5128 of 27.92 ± 0.19 corresponding to D = 3.84 ± 0.35 Mpc.

Interactions between weaver ants Oecophylla smaragdina, homopterans, trees and lianas in an Australian rain forest canopy

Summary Tritrophic interactions between the weaver ant Oecophylla smaragdina (Fabricius) (Hymenoptera: Formicidae), plants and honeydew‐producing trophobionts (Hemiptera: Sternorrhyncha and Auchenorrhyncha, Lepidoptera: Lycaenidae) were studied in a rain forest canopy in Northern Queensland, Australia. Most commonly attended trophobionts by O. smaragdina at this study site were Coccidae ( Coccus sp., Milviscutulus sp.) and Membracidae ( Sextius sp.), followed by Toxoptera aurantii (Aphidae), Planococcus citri (Pseudococcidae), Icerya sp. (Margarodidae), an unidentified species of Eriococcidae, Austrotartessus sp. (Cicadellidae), and lycaenid butterfly larvae ( Anthene seltuttus , Arhopala centaurus group). Most trophobionts were highly polyphagous, and trees and lianas from many plant species and families acted as homopteran hosts. However, lianas were found to play a key role. First, the majority (68%) of aggregation sites was found on lianas, especially on the legumes Entada phaseoloides and Caesalpinia traceyi , and secondly, per capita ant visitation rate ( VR ) at coccoids was significantly higher on lianas compared to trees. In total, VR to homopterans was 64% higher on lianas. Sites of ant–homopteran aggregations were regularly replaced by new locations on fresh plant growth. The mean longevity of nests of this polydomous ant species was 131 days, of individual aggregation sites with membracids 54 days and with coccoids 130 days. Our results suggest that plant‐specific differences in suitability for honeydew production (especially the availability of lianas) and the availability of preferred trophobionts have a strong influence on the vigour of Oecophylla colonies.

Search for HI in Dwarf Spheroidal Galaxies

AbstractAfter reviewing the HI content and distribution in extreme dwarf irregular (dIrr) and dwarf elliptical (dE) galaxies, previous searches for HI in dwarf spheroidal (dSph) galaxies will be discussed. I will report on the recent detections of HI probably associated with the Local Group (LG) dSph Sculptor and dIrr/dSph Phoenix, obtained with the ATCA, along with a similar detection in the Centaurus Group dSph CEN_41. Data obtained for Sculptor, using the Parkes Multibeam system, will also be presented and the advantage of the wide field for such nearby objects will be emphasised. Finally, the possible origin of the gas and the general problem of the missing ISM in dSph galaxies will be discussed.

Nebular spectra of type IA supernovae as probes for extragalactic distances, reddening, and nucleosynthesis

view Abstract Citations (55) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nebular Spectra of Type IA Supernovae as Probes for Extragalactic Distances, Reddening, and Nucleosynthesis Ruiz-Lapuente, P. ; Lucy, L. B. Abstract We investigate the feasability of extracting basic information contained in the nebular spectra of supernovae: the amount of Ni synthesized in the explosion, the intervening reddening, and the distance to the parent galaxy. These physical quantities have correlated effects on the observed nebular spectra. Nevertheless, discrimination is possible by the use of least-squares theory, which allows one to find the best estimates of the model parameters, their statistical errors, and their mutual correlations. A spectral synthesis code for Type Ia supernovae (SNs Ia) in the nebular phase has been developed that includes the basic physics needed to reproduce the spectra. Intrinsic characteristics of nebular spectra of SNs Ia, such as the dependence of the observed luminosity of Fe III and Fe II forbidden lines at different wavelengths on the initial ^56^Ni mass and on the reddening, provide the basis for the multiparameter determination. It is shown that this procedure can yield estimates of the distance to the host galaxy, of the total reddening, and of the Ni mass synthesized in the explosion. The method, when applied to nebular spectra of SN 1986G in Cen A, gives as best values for the model parameters a production of 0.38 +/- 0.03 M_sun_ of ^56^Ni, a distance to Cen A (and thus to the Centaurus Group) of 3.3 +/- 0.3 Mpc, and a reddening E(B- V) of 1.09 +/- 0.02. These results are compared with determinations of the same quantities by traditional methods. In addition, the least-squares fitting indicates the presence of 0.039 +/- 0.003 M_sun_ of stable isotopes of Ni. The ^56^Ni mass derived for SN 1986G is a clue to the understanding of the peculiar properties of this supernova, suggesting that this event was intrinsically fainter than other SNs Ia. For comparison purposes, the case of SN 1972E is also discussed, although the least-squares technique is not applied. Publication: The Astrophysical Journal Pub Date: November 1992 DOI: 10.1086/171978 Bibcode: 1992ApJ...400..127R Keywords: Astrometry; Interstellar Extinction; Nebulae; Nuclear Fusion; Stellar Spectra; Supernovae; Computational Astrophysics; Feasibility Analysis; Least Squares Method; Nuclear Reactions; Astrophysics; GALAXIES: INDIVIDUAL NAME: CENTAURUS A; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES; STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1986G; STARS: SUPERNOVAE: GENERAL full text sources ADS | data products SIMBAD (3) NED (3)