L. N. Makarova

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.

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.

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.

The EFIGI catalogue of 4458 nearby galaxies with detailed morphology

Now that large databases of resolved galaxy images are provided by modern imaging surveys, advanced morphological studies can be envisioned, urging for well defined calibration samples. We present the EFIGI catalogue, a multiwavelength database specifically designed for a dense sampling of all Hubble types. The catalogue merges data from standard surveys and catalogues (Principal Galaxy Catalogue, Sloan Digital Sky Survey, Value-Added Galaxy Catalogue, HyperLeda, and the NASA Extragalactic Database) and provides detailed morphological information. Imaging data are obtained from the SDSS DR4 in the u, g, r, i, and z bands for a sample of 4458 PGC galaxies, whereas photometric and spectroscopic data are obtained from the SDSS DR5 catalogue. Point-Spread Function models are derived in all five bands. Composite colour images of all objects are visually examined by a group of astronomers, and galaxies are staged along the Hubble sequence and classified according to 16 morphological attributes describing their structure, texture, as well as environment and appearance on a five-level scale. The EFIGI Hubble sequence shows remarkable agreement with the RC3 Revised Hubble Sequence. The main characteristics and reliability of the catalogue are examined, including photometric completeness, type mix, systematic trends and correlations. The final EFIGI database is a large sub-sample of the local Universe, with a dense sampling of Sd, Sdm, Sm and Im types compared to magnitude-limited catalogues. We estimate the photometric catalogue to be more than ~ 80% complete for galaxies with 10 < g < 14. More than 99.5% of EFIGI galaxies have a known redshift in the HyperLeda and NED databases.

Photometric properties of the Local Volume dwarf galaxies

We present surface photometry and metallicity measurements for 104 nearby dwarf galaxies imaged with the Advanced Camera for Surveys and Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. In addition, we carried out photometry for 26 galaxies of the sample and for Sextans B on images of the Sloan Digital Sky Survey. Our sample comprises dwarf spheroidal, irregular and transition type galaxies located within ∼10 Mpc in the field and in nearby groups: M81, Centaurus A, Sculptor, and Canes Venatici I cloud. It is found that the early-type galaxies have on average higher metallicity at a given luminosity in comparison to the late-type objects. Dwarf galaxies with MB ≥ −12 ÷ −13 m deviate toward larger scale lengths from the scale length – luminosity relation common for spiral galaxies, h ∝ L 0.5 B . The following correlations between fundamental parameters of the galaxies are consistent with expectations if there is pronounced gas-loss through galactic winds: 1) between the luminosity of early-type dwarf galaxies and the mean metallicity of constituent red giant branch stars, Z ∼ L 0.4 , 2) between mean surface brightness within the 25 m /⊓ ′′ isophote and the corresponding absolute magnitude in the V and I bands, SB25 ∼ 0.3M25, and 3) between the central surface brightness (or effective surface brightness) and integrated absolute magnitude of galaxies in the V and I bands, SB0 ∼ 0.5ML, SBe ∼ 0.5Me. The knowledge of basic photometric parameters for a large sample of dwarf galaxies is essential for a better understanding of their evolution.

The stellar content and distance of UGC 4483

We present HST/WFPC2 observations of UGC 4483, an irregular galaxy in the M81/NGC 2403 complex. Stellar photometry was carried out with HSTphot, and is complete to V ~ 26.0 and I ~ 24.7. We measure the red giant branch tip at I = 23.56 +/- 0.10 and calculated a distance modulus of (m-M)o = 27.53 +/- 0.12 (corresponding to a distance of 3.2 +/- 0.2 Mpc), placing UGC 4483 within the NGC 2403 subgroup. We were able to measure properties of a previously-known young star cluster in UGC 4483, finding integrated magnitudes of V = 18.66 +/- 0.21 and I = 18.54 +/- 0.10 for the stellar contribution (integrated light minus Halpha and [OIII] contribution), corresponding to an age of ~10-15 Myr and initial mass of ~10^4 Msun. This is consistent with the properties of the clusters brightest stars, which were resolved in the data for the first time. Finally, a numerical analysis of the galaxys stellar content yields a roughly constant star formation rate of 1.3x10^-3 Msun/yr and mean metallicity of [Fe/H] = -1.3 dex from 15 Gyr ago to the present.