Cepheid and SNIa Distance Scales

We review the possibility that metallicity could provide a diagnostic for the age of a galaxy, hence that the most metal-poor star forming galaxies in the local universe may be genuinely young. Indeed, observational evidence for “downsizing” shows the average age of the stars in a galaxy to decrease with decreasing mass and metallicity. However, we conclude both from observational and theoretical viewpoints that metallicity is not an arrow of time. Consequently the most metal–poor galaxies of our local universe are not necessarely young. Current observations suggest that an old stellar population is present in all metal-poor galaxies, although a couple of cases, e.g. IZw18, remain under debate. Further observations with more sentitive equipement should settle this question in the coming years.

Using single channel K -band photometric data from the literature, a provisional infrared diameter-velocity dispersion relation for elliptical galaxies in the Coma and Virgo clusters is derived. The Coma cluster relation has ~1.5 times lower scatter at K band than in B or V. Excluding 4 outliers, the rms scatter at K for 24 galaxies in Coma is only 4.8% in distance, close to the limit implied by the observational errors. Distance estimates based on the IR D - σ, relation will be more accurate than those derived from optical data. The improvement in the infrared is attributed to a decrease in sensitivity to stellar population parameters (age, metallicity, and slope of the IMF), as well as lower internal extinction from dust compared to the optical. That the D - σ, relation has a larger scatter in the optical indicates that there are detectable, but small, stellar population or dust content differences among the Coma ellipticals. Since the D -σ relations are based on the fundamental plane, this result promises that the fundamental plane is thinner in the infrared than it is in the optical. Infrared photometric data available for Virgo are limited to just 13 objects; the spread in distance due to the depth of the cluster precludes any significant improvement over B and V. A relative Coma-Virgo distance of 5.56 is derived from the K band data, in agreement with estimates in other colors and using other techniques, indicating that there is no significant age difference between Virgo and Coma ellipticals.

Theoretical models and observations of collapsar-created gamma-ray bursts, typically long-duration gamma-ray bursts (LGRBs), both suggest that these transients cannot occur at high metallicity, likely due to angular momentum losses via stellar winds for potential progenitor stars. However, the precise metallicity threshold (if it is a hard threshold) above which the formation of LGRBs is suppressed is still a topic of discussion. We investigated observed LGRBs and the properties of their host galaxies to constrain this metallicity dependence. In order to compute LGRB rates we modelled the cosmic history of star formation as a function of host galaxy metallicity and stellar mass, and added a LGRB efficiency function that can include various shapes including abrupt cutoffs and more gradual variations in the GRB yield with metallicity. In contrast to previous work, this model includes scatters in the relations between mass, metallicity, and star formation rate, as well as a scatter in the metallicity distribution inside galaxies. We then varied both the threshold value and the shape, and compared the results of our model to observed LGRBs and the properties of their host galaxies. In our model a sharp cutoff at an oxygen abundance Z_ O/H =12+łog( O/H )=8.6±0.1 (corresponding to ∼0.6,Z_ provides the best explanation for the observed LGRB data. In contrast, a lower threshold proposed in the literature (i.e. at Z_ O/H =8.3 or ∼0.3,Z_ fits the observations poorly. We therefore conclude that, in contrast to most theoretical LGRB models, a relatively high metallicity threshold at near solar values provides the best match between our model and observed LGRBs.

The nearest large groups of elliptical galaxies, in the Virgo and Fornax clusters, play a central role in determinations of the Hubble constant, H0, and hence the cosmological rate of expansion. Because the relative distances between these two clusters and more remote clusters are well known, absolute distance determinations to Virgo and Fornax should establish the Hubble constant for the local Universe. In addition, elliptical galaxies reside predominantly in the cores of clusters, so distance calibrations for ellipticals should minimize the uncertainties due to the possibly large extent of the clusters along the line of sight. A powerful and direct way of establishing such distances is to use thebrightest red-giant stars, which have nearly uniform luminosities1,2. Here we report the direct observation of old red-giant stars in a dwarf elliptical galaxy in the Virgo cluster. We determine a distance to this galaxy, and thus to the core of the Virgo cluster, of 15.7 ± 1.5 megaparsecs, from which we estimate a Hubble constant of H0 = 77 ± 8 km s−1 Mpc−1. Under the assumption of a low-density Universe with the simplest cosmology, the age of the Universe is no more than 12–13 billion years.

We have undertaken a detailed comparison of the colours of early-type galaxies in the Virgo and Coma clusters. In Paper I (this issue), we presented our system of homogeneous U,V,J and K photometric measurements for these galaxies. In this paper, we use this data set to investigate the universality of the colour–magnitude correlation. Our work reassesses the anomaly noted by Aaronson, Persson & Frogel. Following these authors, we initially compare the relative distances of the two clusters derived from the L – σ and U – V and V – K colour–magnitude correlations. However, in contrast to their result, we find that all three relations give compatible relative distance moduli: Δmᵤ−ᵥ=4.01±0.20,Δmᵥ−ₖ=3.58±0.23, ΔmḺ−σ=3.62±0.16. A similar result is found by correlating the colours and velocity dispersions with photometric diameters. Again, we find that all three comparisons give consistent distance estimates: Δmᵤ−ᵥ=3.87±0.15, Δmᵥ−ₖ=3.42±0.21, ΔmḎ−σ=3.67±0.11, with a mean relative distance modulus of 3.69±0.08. These results show that the colour–magnitude relation has the same form in both Coma and Virgo. An alternative approach is to compare, the colours of the galaxies directly through the distance- independent correlation between colour and velocity dispersion. We find that the median colours are offset by −0.009±0.012(U−V), 0.005±0.016(V−K) and −0.038±0.012(J−K), with an estimated systematic error of 0.02, 0.03 and 0.04 mag in each case. All of these offsets are therefore consistent with there being no intrinsic difference between the colours of early-type galaxies in Virgo and Coma. We conclude that the colour–magnitude relation has the same form in both clusters, and hence can provide a reliable cosmic distance estimator for clusters of galaxies, giving relative distances accurate to ~ 20 per cent per galaxy.
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\nIn addition, our data constrain the intrinsic scatter of early-type galaxies about the mean colour–magnitude relation. We measure an rms scatter of typically 0.05 mag, of which ~ 0.03 mag can be accounted for by observational error. By examining the correlation of residuals, we show that this intrinsic variation is unlikely to be dominated by differences in the star formation histories of elliptical galaxies. We use the stellar population synthesis model of Bruzual to quantify the implications of this result. First, we present simple time-scale arguments to suggest that the spheroidal components of early-type galaxies are unlikely to have formed below a redshift of 2(q₀=0.5). Secondly, we show that our data are only marginally consistent with the strong bursts of star formation required to explain the spectra of galaxies in moderate-redshift clusters.

We attempted to predict the spatial (radial) distribution of the iron abundance in the intracluster gas of the Fornax cluster of galaxies, by combining the available models for elliptical galaxy formation with the observed spatial distribution of galaxy luminosities. We found that the galaxy formation models can provide the total mass of intracluster iron comparable to that observed in the Fornax cluster, as is the case in the Virgo cluster (Okazaki et al. 1993, AAA 58.160.101). The model predictions show that the galaxy formation efficiency in the Fornax cluster is higher (by about a factor of three) than that in the Virgo cluster. The inferred spatial distribution of the iron abundance depends sensitively on the models for elliptical galaxy formation, and is especially affected by the total wind energy from galaxies, compared to the gravitational energy in the cluster; for instance, model which supplies a large amount of wind energy suggests large-scale mixing of intracluster gas, which does not allow any large-scale systematic variation in the abundance distribution. This indicates that poor clusters of galaxies, such as the Fornax, are favorable sites for estimating the total energy of galactic winds, by comparing the observed iron abundance gradient with the results of theoretical models.

view Abstract Citations (266) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Potential, Velocity, and Density Fields from Redshift-Distance Samples: Application: Cosmography within 6000 Kilometers per Second Bertschinger, Edmund ; Dekel, Avishai ; Faber, Sandra M. ; Dressler, Alan ; Burstein, David Abstract We present the first results of applying a potential flow reconstruction algorithm to the real universe. The method, described in detail in the preceding paper, takes as input radial peculiar velocities and distances for a set of objects that trace large-scale motions. Our sample is based on 544 early-type galaxies with D_n_ - σ distance estimates and 429 spirals with infrared Tully-Fisher distances. From these data, the method reconstructs the three- dimensional potential, velocity, and mass density fields smoothed on large scales. The results are shown as maps of these fields, revealing the three-dimensional structure within 6000 km s^-1^ distance from the Local Group. For each map we provide an error map based on Monte Carlo simulations. The dominant recovered structure is an extended, deep potential well in the Hydra-Centaurus region, stretching across the Galactic plane toward Pavo, broadly confirming the "great attractor" (GA) model of Lynden-Bell et al. (1988). The peak density contrast in this region is given by {OMEGA}^4/7deltaρ/ρ = 1.2 +/- 0.4 with a Gaussian smoothing window of radius ~ 1400 km s^-1^. The Local Supercluster appears to be an extended ridge on the near flank of the GA, proceeding through the Virgo Southern Extension to the Virgo and Ursa Major clusters. The Virgo cluster and the Local Group are both falling toward the bottom of the GA potential well, with peculiar velocities (smoothed on a scale of 500 km s^-1^) of 658 +/- 121 km s^-1^ and 565 +/- 125 km s^-1^, respectively. Several large regions of below-average mass density are discovered that match known voids in the galaxy distribution. A general correlation exists between the mass and galaxy distributions, except for a significant disagreement in the Perseus- Pisces supercluster, which is practically invisible in the reconstructed mass distribution. However, the very sparse sampling of measured distances in the current sample may cause us to underestimate the amplitude of both positive and negative density perturbations in that direction. The average velocities in spheres of radii 4000 and 6000 km s^-1^ centered on the Local Group (with prior, additional smoothing by a Gaussian of radius 1200 km s^-1^) are 388 +/- 67 km s^-1^ toward L = 177^deg^, B = -15^deg^, and 327 +/- 82 km s^-1^ toward L = 194^deg^, B = 5^deg^, respectively, compared with predicted rms velocities of 287 and 224 km s^-1^ for the unbiased cold dark matter model. Publication: The Astrophysical Journal Pub Date: December 1990 DOI: 10.1086/169419 Bibcode: 1990ApJ...364..370B Keywords: Dark Matter; Galactic Clusters; Galactic Evolution; Potential Fields; Radial Velocity; Red Shift; Space Density; Algorithms; Astronomical Maps; Computational Astrophysics; Cosmology; Density Distribution; Monte Carlo Method; Astrophysics; COSMOLOGY; DARK MATTER; GALAXIES: CLUSTERING; GALAXIES: FORMATION full text sources ADS | data products SIMBAD (3)

To properly quantify the possible residual systematic errors affecting the classical Cepheid distance scale, a detailed theoretical scenario is recommended. By extending the set of nonlinear, convective pulsation models published for Z = 0.02 to Z = 0.004, Z = 0.008, and Z = 0.03, we provide a detailed homogeneous, nonlinear model grid taking into account simultaneous variations of the mass–luminosity relation, the efficiency of superadiabatic convection, and the chemical composition. The dependence of the inferred period–radius, period–mass–radius, and period–mass–luminosity–temperature relations on the input parameters is discussed for both the fundamental and first overtone modes. The trend of the instability strip getting redder as the metallicity increases is confirmed for the additional mass–luminosity assumptions and mixing length values. From the obtained multifilter light curves, we derive the mean magnitudes and colors, and in turn the period–luminosity–color and period–Wesenheit relations, for each assumed chemical composition, mass–luminosity relation, and efficiency of superadiabatic convection. Application to a well-studied sample of Cepheids in the Large Magellanic Cloud allows us to constrain the dependence of the inferred distance modulus on the assumed mass–luminosity relation, and the inclusion of the metallicity term in the derivation of the period–Wesenheit relations allows us, for each assumed mass–luminosity relation, to predict the metallicity dependence of the Cepheid distance scale. The obtained metal-dependent, period–Wesenheit relations are compared with recent results in the literature and applied to a sample of Gaia Early Data Release 3 Galactic Cepheids with known metal abundances to derive individual parallaxes. The comparison of these predictions with Gaia results is finally discussed.

All the previously cataloged ultracompact dwarf (UCD) galaxies in the Fornax and Virgo clusters have 17.5 <b J < 20. Using the 2dF spectrograph on the Anglo-Australian Telescope, we have carried out a search for fainter UCDs in the Fornax Cluster. In the magnitude interval 19.5 <b J < 21.5, we have found 54 additional compact cluster members within a projected radius of 0. 9 (320 kpc) of the cluster center, all of which meet our selection and observational criteria to be UCDs. These newly identified objects, however, overlap in luminosity and spatial distribution with objects classified as globular clusters (GCs) belonging to the central cluster galaxy NGC 1399; in fact, about half of the objects in our sample are included in recent catalogs of NGC 1399/Fornax GCs. The numbers, luminosity function, and spatial distributions of our compact object sample are consistent with being the bright tail of the Fornax cluster-wide GC population. Yet, our present larger sample of intergalactic compact objects forms a dynamically distinct population from both the NGC1399 GCs and the nucleated dwarf ellipticals in Fornax. This supports the interpretation that the UCDs, which populate the bright tail of the GC luminosity function, are, in some respects, a separate class of objects, at least to the extent that they have experienced a distinct dynamical history and origin, which differs from the bulk of the NGC1399 GCs. Correcting for our spectroscopic incompleteness, we estimate that there are ∼105 ± 13 of these brighter compact cluster objects down to bJ < 21.5 in the central region of the Fornax, and hence these UCDs/globulars outnumber other galaxy types in this space. The differences in their dynamics and distribution compared to dwarf ellipticals (dEs) may be consistent with a threshing or tidal destruction origin, if they have come from a subpopulation of dE galaxies on initial orbits that rendered them susceptible to such processes.

Given the growing interest in gravitational-wave and cosmological parity-violating effects in dynamical Chern-Simons (dCS) gravity, it is crucial to investigate whether the scalar-gravitational Pontryagin term in dCS gravity persists when formulated in the context of the U(1)B−L anomaly in the standard model (SM). In particular, it has been argued that dCS gravity can be reduced to Einstein gravity after “rotating away” the gravitational-Pontryagin coupling into the phase of the Weinberg operator—analogous to the rotation of the axion zero mode into the quark mass matrix. We find that dCS gravity is nontrivial if the scalar field ϕ has significant spacetime dependence from dynamics. We provide a comprehensive consideration of the dCS classical and quantum symmetries relevant for embedding a dCS sector in the SM. We find that, because of the baryon/lepton number chiral gravitational anomaly, the scalar-Pontryagin term cannot be absorbed by a field redefinition. Assuming a minimal extension of the SM, we also find that a coupling of the dCS scalar with right-handed neutrinos induces both the scalar-Pontryagin coupling and an axionlike phase in the dimension-five Weinberg operator. We comment on the issue of gauging the U(1)B−L, the observational effects with these two operators present for upcoming experiments, and the origin of dCS gravity in string theory. Published by the American Physical Society 2024

Statistics on the nearest neighbors of bright galaxies (MBt ≤ -17n) in the Virgo and Fornax clusters are compared. Some differences are found between the surroundings of bright SB and S galaxies.

The dynamic characteristics of spiral galaxies with absolute magnitudes M ≥ −20m.6 in the Virgo and Fornax clusters are studied using data from the Merged Catalog of Galaxies MERCG. The galactic diameters from MERCG are used to determine the radius RD that defines the region of possible concentration of dark matter, and the dynamic parameters Mdyn and Mdyn/LB of the spiral galaxies are calculated based on the centrifugal equilibrium condition. Results from the theory of angular momentum transfer are used to estimate the central surface density m0 and angular momentum K of stars in these galaxies. A comparison of the dynamic parameters of the spiral galaxies with M ≥ −20.6 and M ≤ −20.6 reveals a statistically significant higher fraction of dark matter in the spiral galaxies with M ≤ −20.6, at 26.3% in Virgo and 27% in Fornax.

We summarize findings from imaging surveys of 143 early-type galaxies in the Virgo and Fornax Clusters. Using deep HST images in the F475W (g) and F850LP (z) band-passes obtained with the Advanced Camera for Surveys (ACS), we have examined the central structure of the program galaxies, finding clear evidence for a compact stellar nucleus in ∼ 75% of the sample. The formation of early-type galaxies of low- and intermediate-mass is often – but not always – accompanied by the formation of a compact stellar nucleus.

Surface brightness fluctuations (SBFs) are much brighter in the infrared than they are at optical wavelengths, making it possible to measure greater distances using IR SBFs. We report new K' (2.1 ?m) SBF measurements of nine galaxies in the Fornax and Eridanus clusters using a 10242 pixel HgCdTe array. We used improved analysis techniques to remove contributions to the SBFs from globular clusters and background galaxies, and we assess the relative importance of other sources of residual variance. We applied the improved methodology to our Fornax and Eridanus images and to our previously published Virgo cluster data. Apparent fluctuation magnitudes were used in conjunction with Cepheid distances to M31 and the Virgo cluster to calibrate the K' SBF distance scale. We find the absolute fluctuation magnitude ${u{M}{7016}}$ -->$K{′}$ -->=-5.61?0.12, with an intrinsic scatter of 0.06 mag to the calibration. No statistically significant change in ${u{M}{7016}}$ -->$K{′}$ --> is detected as a function of (V-I). Our calibration is consistent with simple (constant age and metallicity) stellar population models. The lack of a correlation with (V-I) in the context of the stellar population models implies that elliptical galaxies bluer than (V-I) = 1.2 have SBFs dominated by younger (5-8 Gyr) populations and metallicities comparable to redder ellipticals. Significant contributions to the SBFs from anomalous populations of asymptotic giant branch stars are apparently uncommon in giant ellipticals. K' SBFs prove to be a reliable distance indicator as long as the residual variance from globular clusters and background galaxies is properly removed. Also, it is important that a sufficiently high signal-to-noise ratio be achieved to allow reliable sky subtraction because residual spatial variance can bias the measurement of the SBF power spectrum.

Côté (1995) surveyed the nearby Centaurus A (Cen A) and Sculptor (Sci) group regions in the search for gas-rich, dwarf irregular galaxies (Irr) which are associated with these galaxy aggregates. 36 Irrs have been found and confirmed as new group members via 21cm/Hα redshifts. In finding this large number of Irrs, the question rises whether systems from the other dwarf galaxy family, the gas-poor dwarf ellipticals (dE), also exist in the two groups. So far nothing is known about dE membership but taking into account the morphology-density relation for dwarfs (Binggeli et al. 1990) a number ratio Irr/dE≈ 1 - 2 would be expected. Prompted by these “missing” dEs we started a large program to identify and study dEs in Cen A and Sci. The main scientific goals are (1) to find dE candidates and to establish group membership via velocity or distance and (2) to estimate the luminosity function (LF) of dwarf galaxies to the faintest possible luminosities. For the two groups, being respectively at a mean distance of 4.0 Mpc and 2.5 Mpc, we will be able to reach dwarf galaxies 4-5 magnitudes fainter than in the previous studies in the Virgo and Fornax clusters and the five groups Leo I, Dorado, NGC1400, NGC5044, and Antlia (Sandage et al. 1985, Ferguson &amp;: Sandage 1990). We briefly outline here first results from the CenA group. All details about the complete survey including Scl will be presented in Jerjen et al. (1997)