D. I. Makarov

THE EXTRAGALACTIC DISTANCE DATABASE

A database can be accessed on the Web at http://edd.ifa.hawaii.edu that was developed to promote access to information related to galaxy distances. The database has three functional components. First, tables from many literature sources have been gathered and enhanced with links through a distinct galaxy naming convention. Second, comparisons of results both at the levels of parameters and of techniques have begun and are continuing, leading to increasing homogeneity and consistency of distance measurements. Third, new material is presented arising from ongoing observational programs at the University of Hawaii 2.2 m telescope, radio telescopes at Green Bank, Arecibo, and Parkes and with the Hubble Space Telescope. This new observational material is made available in tandem with related material drawn from archives and passed through common analysis pipelines.

Tip of the Red Giant Branch Distances. II. Zero-Point Calibration

The luminosity of the tip of the red giant branch (TRGB) provides an excellent measure of galaxy distances and is easily determined in the resolved images of nearby galaxies observed with Hubble Space Telescope. There is now a large amount of archival data that are relevant to the TRGB methodology and offer comparisons with other distance estimators. Zero-point issues related to the TRGB distance scale are reviewed in this paper. Consideration is given to the metallicity dependence of the TRGB, the transformations between HST flight systems and Johnson-Cousins photometry, the absolute magnitude scale based on horizontal branch measurements, and the effects of reddening. The zero point of the TRGB is established with a statistical accuracy of 1%, modulo the uncertainty in the magnitude of the horizontal branch, with a typical rms uncertainty of 3% in individual galaxy distances at high Galactic latitude. The zero point is consistent with the Cepheid period-luminosity relation scale but invites reconsideration of the claimed metallicity dependence with that method. The maser distance to NGC 4258 is consistent with TRGB but presently has lower accuracy.

Cosmicflows-2: The Data

Cosmicflows-2 is a compilation of distances and peculiar velocities for over 8000 galaxies. Numerically the largest contributions come from the luminosity-line width correlation for spirals, the Tully-Fisher relation (TFR), and the related fundamental plane relation for E/S0 systems, but over 1000 distances are contributed by methods that provide more accurate individual distances: Cepheid, tip of the red giant branch (TRGB), surface brightness fluctuation, Type Ia supernova, and several miscellaneous but accurate procedures. Our collaboration is making important contributions to two of these inputs: TRGB and TFR. A large body of new distance material is presented. In addition, an effort is made to ensure that all the contributions, both our own and those from the literature, are on the same scale. Overall, the distances are found to be compatible with a Hubble constant H 0 = 74.4 ? 3.0?km?s?1?Mpc?1. The great interest going forward with this data set will be with velocity field studies. Cosmicflows-2 is characterized by a great density and high accuracy of distance measures locally, falling to sparse and coarse sampling extending to z = 0.1.

Local galaxy flows within 5 Mpc

We present Hubble Space Telescope/WFPC2 images of sixteen dwarf galaxies as part of our snapshot survey of nearby galaxy candidates. We derive their distances from the luminosity of the tip of the red giant branch stars with a typical

The Hubble Flow around the Centaurus A/M83 Galaxy Complex

We present Hubble Space Telescope ACS images and color-magnitude diagrams for 24 nearby galaxies in and near the constellation of Centaurus with radial velocities VLG < 550 km s-1. Distances are determined based on the luminosities of stars at the tip of the red giant branch that range from 3.0 to 6.5 Mpc. The galaxies are concentrated in two spatially separated groups around Cen A (NGC 5128) and M83 (NGC 5236). The Cen A group itself has a mean distance of 3.76 ± 0.05 Mpc, a velocity dispersion of 136 km s-1, a mean harmonic radius of 192 kpc, and an estimated orbital/virial mass of (6.4-8.1) × 1012 M⊙. This elliptical-dominated group is found to have a relatively high mass-to-light ratio: M/LB = 125 M⊙/L⊙. For the M83 group we derived a mean distance of 4.79 ± 0.10 Mpc, a velocity dispersion of 61 km s-1, a mean harmonic radius of 89 kpc, and an estimated orbital/virial mass of (0.8-0.9) × 1012 M⊙. This spiral-dominated group is found to have a relatively low M/LB = 34 M⊙/L⊙. The radius of the zero-velocity surface around Cen A lies at R0 = 1.40 ± 0.11 Mpc, implying a total mass within R0 of MT = (6.0 ± 1.4) × 1012 M⊙. This value is in good agreement with the Cen A orbital/virial mass estimates and provides confirmation of the relatively high M/LB of this elliptical-dominated group. The centroids of both groups, as well as surrounding field galaxies, have very small peculiar velocities, <25 km s-1, with respect to the local Hubble flow with H0 = 68 km s-1 Mpc-1.

Associations of Dwarf Galaxies

The Hubble Space Telescope Advanced Camera for Surveys has been used to determine accurate distances for 20 galaxies from measurements of the luminosity of the brightest red giant branch stars. Five associations of dwarf galaxies that had originally been identified based on strong correlations on the plane of the sky and in velocity are shown to be equally well correlated in distance. Two more associations with similar properties have been discovered. Another association is identified that is suggested to be unbound through tidal disruption. The associations have the spatial and kinematic properties expected of bound structures with ? 1011 M?. However, these entities have little light, with the consequence that the mass-to-light ratios are in the range 100-1000 M? L. Within a well-surveyed volume extending to a 3 Mpc radius, all but one known galaxy lie within one of the groups or associations that have been identified.

The Extragalactic Distance Database: Color-Magnitude Diagrams

The color-magnitude diagrams/tip of the red giant branch (CMDs/TRGB) section of the Extragalactic Distance Database contains a compilation of observations of nearby galaxies from the Hubble Space Telescope. Approximately 250 (and increasing) galaxies in the Local Volume have CMDs and the stellar photometry tables used to produce them available through the Web. Various stellar populations that make up a galaxy are visible in the CMDs, but our primary purpose for collecting and analyzing these galaxy images is to measure the TRGB in each. We can estimate the distance to a galaxy by using stars at the TRGB as standard candles. In this paper, we describe the process of constructing the CMDs and make the results available to the public.

Advanced Camera for Surveys Imaging of 25 Galaxies in Nearby Groups and in the Field

We present Hubble Space Telescope Advanced Camera for Surveys images and color-magnitude diagrams for 25 nearby galaxies with radial velocities VLG < 500 km s-1. Distances are determined based on the luminosities of stars at the tip of the red giant branch that range from 2 to 12 Mpc. Two of the galaxies, NGC 4163 and IC 4662, are found to be the nearest known representatives of blue compact dwarf objects. Using high-quality data on distances and radial velocities of 110 nearby field galaxies, we derive their mean Hubble ratio to be 68 km s-1 Mpc-1 with a standard deviation of 15 km s-1 Mpc-1. Peculiar velocities of most of the galaxies, Vpec = VLG - 68D, follow a Gaussian distribution with σv = 63 km s-1 but with a tail toward high negative values. Our data display the known correlation between peculiar velocity and galaxy elevation above the Local Supercluster plane. The small observed fraction of galaxies with high peculiar velocities, Vpec < -500 km s-1, may be understood as objects associated with nearby groups (Coma I, Eridanus) outside the local volume.

The Hubble flow around the Local Group

We use updated data on distances and velocities of galaxies in the proximity of the Local Group (LG) in order to establish properties of the local Hubble flow. For 30 neighbouring galaxies with distances 0.7 < D LG < 3.0 Mpc, the local flow is characterized by the Hubble parameter H loc = (78 ± 2)km s -1 Mpc -1 , the mean-square peculiar velocity σ v = 25 km s -1 , corrected for errors of radial velocity measurements (∼4 km s -1 ) and distance measurements (∼10km s -1 ), as well as the radius of the zero-velocity surface R 0 = (0.96±0.03) Mpc. The minimum value for σ v is achieved when the barycentre of the LG is located at the distance Dc = (0.55 ± 0.05) D M31 towards Andromeda galaxy (M31) corresponding to the Milky Way (MW)-to-M31 mass ratio M MW /M M31 ≃ 4/5. In the reference frame of the 30 galaxies at 0.7-3.0 Mpc, the LG barycentre has a small peculiar velocity ∼(24 ± 4) km s -1 towards the Sculptor constellation. The derived value of R 0 corresponds to the total mass M T (LG) = (1.9 ± 0.2) 10 12 M ⊙ with Ω m = 0.24 and a topologically flat universe, a value in good agreement with the sum of virial mass estimates for the MW and M31.

Tip of the Red Giant Branch Distances. I. Optimization of a Maximum Likelihood Algorithm

Accurate distances to galaxies can be determined from the luminosities of stars at the tip of the red giant branch (TRGB). We use a maximum likelihood algorithm to locate the TRGB in galaxy color-magnitude diagrams. The algorithm is optimized by introducing reliable photometric errors and a completeness characterization determined with artificial star experiments. The program is extensively tested using Monte Carlo simulations, artificial galaxies, and a sample of nearby dwarf galaxies observed with the Hubble Space Telescope WFPC2 and ACS. Our procedure is shown to be reliable, to have good accuracy, and to not introduce any systematic errors. The methodology is especially useful in cases in which the TRGB approaches the photometric limit and/or the RGB is poorly populated.