492 research outputs found
Surface Brightness Fluctuations as Primary and Secondary Distance Indicators
The surface brightness fluctuations (SBF) method measures the variance in a
galaxy's light distribution arising from fluctuations in the numbers and
luminosities of individual stars per resolution element. Once calibrated for
stellar population effects, SBF measurements with HST provide distances to
early-type galaxies with unrivaled precision. Optical SBF data from HST for the
Virgo and Fornax clusters give the relative distances of these nearby fiducial
clusters with 2% precision and constrain their internal structures.
Observations in hand will allow us to tie the Coma cluster, the standard of
comparison for distant cluster studies, into the same precise relative distance
scale. The SBF method can be calibrated in an absolute sense either empirically
from Cepheids or theoretically from stellar population models. The agreement
between the model and empirical zero points has improved dramatically,
providing an independent confirmation of the Cepheid distance scale. SBF is
still brighter in the near-IR, and an ongoing program to calibrate the method
for the F110W and F160W passbands of the WFC3 IR channel will enable accurate
distance derivation whenever a large early-type galaxy or bulge is observed in
these passbands at distances reaching well out into the Hubble flow.Comment: 8 pages, invited review at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", to appear in
Astrophysics and Space Scienc
The Dependence of Globular Cluster Number on Density for Abell Cluster Central Galaxies
A study of the globular cluster systems of 23 brightest, or central, galaxies
in 19 Abell clusters has recently been completed. This Letter presents some of
the newly discovered correlations of the globular cluster specific frequency
in these galaxies with other galaxy and cluster properties and puts forth
an interpretation of these results. is found to correlate strongly with
measures of the cluster density, such as the velocity dispersion of the cluster
galaxies and the cluster X-ray temperature and luminosity (especially ``local''
X-ray luminosity). Within a cluster, galaxies at smaller projected distances
from the X-ray center are found to have higher values of . Taken together,
the scaling of with cluster density and the relative constancy of central
galaxy luminosity suggest a scenario in which globular clusters form in
proportionate numbers to the available mass, but galaxy luminosity
``saturates'' at a maximum threshold, resulting in higher \sn\ values for
central galaxies in denser clusters as well as the suitability of these
galaxies as ``standard candles.'' Thus, these galaxies do not have too many
globular clusters for their luminosity; rather, they are underluminous for
their number of globular clusters.Comment: 10 pages, with 4 included postscript figures; AASTeX (aaspp4.sty); to
appear in ApJ Letter
Stellar Populations and Surface Brightness Fluctuations: New Observations and Models
We examine the use of surface brightness fluctuations (SBF) for both stellar
population and distance studies. New V-band SBF data are reported for five
Fornax cluster galaxies and combined with literature data to define a new
V-band SBF distance indicator. We use new stellar population models, based on
the latest Padua isochrones transformed empirically to the observational plane,
to predict SBF magnitudes and integrated colours for a wide range of population
ages and metallicities. We examine the sensitivity of the predictions to
changes in the isochrones, transformations, and IMF. The new models reproduce
the SBF data for globular clusters fairly well, especially if higher
metallicity globulars are younger. The models also give a good match to the
"fluctuation colors" of elliptical galaxies. In order to obtain theoretical
calibrations of the SBF distance indicators, we combine our single-burst models
into composite population models. These models reproduce the observed behavior
of the SBF magnitudes as a function of stellar population parameters, including
the steep colour dependence found for HST/WFPC2 F814W SBF data. Because the
theoretical SBF calibrations are fairly sensitive to uncertain details of
stellar evolution, the empirical calibrations are more secure. However, the
sensitivity of SBF to these finer details potentially makes it a powerful
constraint for stellar evolution and population synthesis. [abbridged]Comment: 24 pages with 17 embedded figures. MNRAS, in pres
Reconciliation of the Surface Brightness Fluctuations and Type Ia Supernovae Distance Scales
We present Hubble Space Telescope measurements of surface brightness
fluctuations (SBF) distances to early-type galaxies that have hosted Type Ia
supernovae (SNIa). The agreement in the relative SBF and SNIa multicolor light
curve shape and delta-m_15 distances is excellent. There is no systematic scale
error with distance, and previous work has shown that SBF and SNIa give
consistent ties to the Hubble flow. However, we confirm a systematic offset of
about 0.25 mag in the distance zero points of the two methods, and we trace
this offset to their respective Cepheid calibrations. SBF has in the past been
calibrated with Cepheid distances from the H_0 Key Project team, while SNIa
have been calibrated with Cepheid distances from the team composed of Sandage,
Saha, and collaborators. When the two methods are calibrated in a consistent
way, their distances are in superb agreement. Until the conflict over the
``long'' and ``short'' extragalactic Cepheid distances among many galaxies is
resolved, we cannot definitively constrain the Hubble constant to better than
about 10%, even leaving aside the additional uncertainty in the distance to the
Large Magellanic Cloud, common to both Cepheid scales. However, recent
theoretical SBF predictions from stellar population models favor the Key
Project Cepheid scale, while the theoretical SNIa calibration lies between the
long and short scales. In addition, while the current SBF distance to M31/M32
is in good agreement with the RR Lyrae and red giant branch distances,
calibrating SBF with the longer Cepheid scale would introduce a 0.3 mag offset
with respect to the RR Lyrae scale.Comment: 13 pages, 3 PostScript figures, LaTeX with AASTeX 5.02 and natbib.sty
v7.0 (included). Accepted for publication in The Astrophysical Journa
Independent Analysis of the Distance to NGC1052-DF2
The conclusion that the diffuse galaxy NGC1052-DF2 is deficient in dark
matter depends critically on the distance, as noted in the original publication
and subsequent works. The results of our preliminary assessment of the SBF
distance have already been referenced on the web. Here we present the details
of a more careful analysis, supply some context, and comment on the remaining
uncertainty.Comment: 2 pages, accepted by Research Notes of the American Astronomical
Society; text is a bit laconic because of the RNAAS word limi
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