[show abstract][hide abstract] ABSTRACT: We have followed up on the results of a 65 square degree CFHT/MegaCam imaging
survey of the nearby M81 Group searching for faint and ultra-faint dwarf
galaxies. The original survey turned up 22 faint candidate dwarf members. Based
on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as
dwarf galaxy members of the group. Distances and stellar population
characteristics are discussed for each. To a completeness limit of M_r' = -10,
we find a galaxy luminosity function slope of -1.27+-0.04 for the M81 group. In
this region, there are now 36 M81 group members known, including 4 blue compact
dwarfs, 8 other late types including the interacting giants M81, NGC 3077, and
M82, 19 early type dwarfs, and at least 5 potential tidal dwarf galaxies. We
find that the dSph galaxies in M81 appear to lie in a flattened distribution,
similar to that found for the Milky Way and M31. One of the newly discovered
dSph galaxies has properties similar to the ultra-faint dwarfs being found in
the Local Group with a size R_e ~ 100 pc and total magnitude estimates M_r' =
-6.8 and M_I ~ -9.1.
[show abstract][hide abstract] ABSTRACT: Cosmicflows-2 is a compilation of distances and peculiar velocities for over
8000 galaxies. Numerically the largest contributions come from the
luminosity-linewidth correlation for spirals, the 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, Surface Brightness Fluctuation, SNIa, and
several miscellaneous but accurate procedures. Our collaboration is making
important contributions to two of these inputs: Tip of the Red Giant Branch and
TFR. A large body of new distance material is presented. In addition, an effort
is made to assure that all the contributions, 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/Mpc. 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 Astronomical Journal 07/2013; 146(4). · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: A CFHT/MegaCam search for faint dwarf galaxies over 65 square degrees in
the nearby M81 group turned up 22 new candidates. This survey is
complete down to M_r' = -10 within the virial radius of the group. Using
HST/ACS and WFPC2 two-color photometry, we have confirmed 14 of these as
bona-fide M81 group dwarf galaxy members from tip of the red giant
branch distances. These include 3 blue compact dwarfs, a likely tidal
dwarf, 1 dwarf irregular, and 9 dwarf spheroidals, one of which, at M_r'
-6.8 with effective radius R_e 90 pc , is similar to the ultra-faint
dwarf spheroidals being discovered in the Local Group. To a completeness
limit of M_r' = -10, we find no evidence for a steep galaxy luminosity
function slope; the faint-end slope of -1.3 is inconsistent with
theoretical cosmological predictions. With the color-magnitude diagrams
we investigate the stellar populations and evolutionary histories of
these very faint and small dwarfs in an environment more dynamically
active than the Local Group.
[show abstract][hide abstract] ABSTRACT: The Numerical Action Method (NAM) is a fully non-linear technique that
can be used to analyze galaxy dynamics. We apply NAM to a catalog that
includes a complete volume-limited sample of 150 galaxies within 4.5
Mpc. Each of these nearby galaxies' distances have been measured in a
consistent manner by applying the Tip of the Red Giant Method to
observations from the Hubble Space Telescope. The combination of
distance information and location on the sky with the assumption that
galaxies' peculiar motions go to zero at early times set the boundary
conditions for minimizing the action of each galaxy. The results from
NAM yield complete phase-space information for each galaxy through time.
These solutions are not unique, but are assessed based on the degree
that they match with each galaxy's measured peculiar radial velocity.
This agreement depends on the mass of the galaxies, and thus NAM
provides constraints on the galaxies' total dynamical masses. We present
a reconstruction of the orbits and estimates of the masses of the
galaxies of the M81 group. This work is supported through HST program:
[show abstract][hide abstract] ABSTRACT: Recent observations of UGC 4879 with the Advanced Camera for Surveys on the Hubble Space Telescope confirm that it is a nearby isolated dwarf irregular galaxy. We measure a distance of 1.36 ± 0.03 Mpc using the tip of the red giant branch method. This distance puts UGC 4879 beyond the radius of first turnaround of the Local Group and ~700 kpc from its nearest neighbor Leo A. This isolation makes this galaxy an ideal laboratory for studying pristine star formation uncomplicated by interactions with other galaxies. We present the star formation history of UGC 4879 derived from simulated color-magnitude diagrams.
The Astronomical Journal 02/2011; 141(4):106. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: In a CFHT/Megacam imaging survey of the M81 Group to search for the smallest dwarf galaxies, we identified 22 new candidate dwarf galaxies. Follow-up HST ACS and WFPC2 imaging in F814W and F606W bands was used to produce color-magnitude diagrams down to 1.5-3 mag below the tip of the red giant branch. From tip of the red giant branch distances, we establish 14 out of the 22 candidates as bona-fide group members, including 3 blue compact dwarfs, 1 likely tidal dwarf, and a dwarf spheroidal galaxy as faint as MR = -6.9. The latter is within the domain of the ultra-faint dwarf galaxies recently discovered in the Local Group. As the original survey extended out to the group second turnaround radius, and based on detection limits determined from simulations, we believe our sample of M81 group galaxy members is largely complete down to MR = -9.5. We discuss the properties of the M81 Group dwarf galaxy population.
[show abstract][hide abstract] ABSTRACT: The several hundred galaxies that make up the Local Volume (within 10 Mpc) can be resolved into stars with the Hubble Space Telescope (HST). To date 300 of these galaxies have been observed with HST, including a nearly complete volume-limited sample of 150 galaxies within 4.5 Mpc. We announce the availability of a database of photometry from these observations, from which we measure distances to each galaxy based on the Tip of the Red Giant Branch (TRGB) method. Combining the TRGB distances with radial velocity information allows us to identify new members of groups and to measure group masses. Furthermore, these data can be used in the reconstruction of galaxy orbits using a numerical least-action method. Additionally, the HST photometry is well-suited to analyses of galaxy star formation histories via the color-magnitude diagram synthesis technique. This dataset, therefore, holds clues to the nature of dark matter, Large Scale Structure, and galaxy evolution. We present early results from each of these types of studies. This work is supported through HST program: GO-11584.
[show abstract][hide abstract] ABSTRACT: We have identified a complete, flux-limited (S 160>120 mJy) sample of 160 mum selected sources from Spitzer observations of the 1 deg2 Infrared Space Observatory (ISO) Deep Field region in the Lockman Hole (LH). Ground-based UV, optical, and near-infrared (NIR) photometry and optical spectroscopy have been used to determine colors, redshifts, and masses for the complete sample of 40 galaxies. Spitzer-IRAC+MIPS photometry, supplemented by ISOPHOT data at 90 mum and 170 mum, has been used to calculate accurate total infrared luminosities, L IR(8-1000 mum), and to determine the IR luminosity function (LF) of luminous infrared galaxies (LIRGs). The maximum observed redshift is z ~ 0.80 and the maximum total infrared luminosity is log (L IR/L sun) = 12.74. Over the luminosity range log (L IR/L sun) = 10-12, the LF for LIRGs in the LH Deep Field is similar to that found previously for local sources at similar infrared luminosities. The mean host galaxy mass, log (M/M sun) = 10.7, and dominance of H II-region spectral types, is also similar to what has been found for local LIRGs, suggesting that intense starbursts likely power the bulk of the infrared luminosity for sources in this range of L IR. However for the most luminous sources, log (L IR/L sun)>12.0, we find evidence for strong evolution in the LF vprop(1 + z)6±1, assuming pure number density evolution. These ultraluminous infrared galaxies (ULIRGs) have a larger mean host mass, log (M/M sun) = 11.0, and exhibit disturbed morphologies consistent with strong interactions/mergers, and they are also more likely to be characterized by starburst-active galactic nucleus (AGN) composite or AGN spectral types.
The Astronomical Journal 01/2011; 141(4). · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: The manner in which galaxies in the Local Volume are distributed in space represents the most detailed example available of the result of the formation of structure. In particular, the galaxies can be taken as test particles whose motions betray the presence of both luminous and dark matter. We construct a self-consistent volume-limited sample of 150 galaxy distances out to 4.5Mpc using stars at the Tip of the Red Giant Branch (TRGB) as standard candles. These distances are derived from archival data taken with the WFPC2 and ACS instruments on HST. Combining the spatial configuration of galaxies with radial velocity information we use numerical action methods to characterize the distribution of matter within this volume.
[show abstract][hide abstract] ABSTRACT: The quantitative spectral analysis of medium resolution optical spectra of A and B supergiants obtained with DEIMOS and ESI at the Keck Telescopes is used to determine a distance modulus of 24.93 ± 0.11 mag (968 ± 50 kpc) for the Triangulum Galaxy M33. The analysis yields stellar effective temperatures, gravities, interstellar reddening, and extinction, the combination of which provides a distance estimate via the flux-weighted gravity-luminosity relationship (FGLR). This result is based on an FGLR calibration that is continually being polished. An average reddening of E(B – V) ~ 0.08 mag is found, with a large variation ranging from 0.01 to 0.16 mag, however, demonstrating the importance of accurate individual reddening measurements for stellar distance indicators in galaxies with evident signatures of interstellar absorption. The large-distance modulus found is in good agreement with recent work on eclipsing binaries, planetary nebulae, long-period variables, RR Lyrae stars, and also with Hubble Space Telescope (HST) observations of Cepheids, if reasonable reddening assumptions are made for the Cepheids. Since distances based on the tip of the red giant branch (TRGB) method found in the literature give conflicting results, we have used HST Advanced Camera for Surveys V- and I-band images of outer regions of M33 to determine a TRGB distance of 24.84 ± 0.10 mag, in basic agreement with the FGLR result. We have also determined stellar metallicities and discussed the metallicity gradient in the disk of M33. We find metallicity of Z ☉ at the center and 0.3 Z ☉ in the outskirts at a distance of one isophotal radius. The average logarithmic metallicity gradient is –0.07 ± 0.01 dex kpc–1. However, there is a large scatter around this average value, very similar to what has been found for the H II regions in M33.
The Astrophysical Journal 09/2009; 704(2):1120. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The CMDs/TRGB (Color-Magnitude Diagrams/Tip of the Red Giant Branch) 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.
The Astronomical Journal 03/2009; · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: 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 are presented arising from ongoing observational programs at the University of Hawaii 2.2m telescope, radio telescopes at Green Bank, Arecibo, and Parkes and with Hubble Space Telescope. This new observational material is made available in tandem with related material drawn from archives and passed through common analysis pipelines.
The Astronomical Journal 03/2009; · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: We use a complete sample of 70mum and 160mum selected sources from Spitzer observations of a 1 square-degree region in the Lockman Hole, supplemented by ISOPHOT data at 90mum and 170mum, to determine the evolution of the far-infrared luminosity function (LF) of luminous infrared galaxies (LIGs) out to redshift z 1. Keck spectroscopy is available for the majority of these sources and for the remainder we use photometric redshifts obtained from a combination of multi-wavelength ground-based optical/NIR photometry and Spitzer-IRAC data. We present evidence for strong evolution in the LF for LIGs in the luminosity range log(Lir/Lsun) = 11 12.5.