16 research outputs found
Improved constraints on the expansion rate of the Universe up to z~1.1 from the spectroscopic evolution of cosmic chronometers
We present new improved constraints on the Hubble parameter H(z) in the
redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic
evolution of early-type galaxies as a function of redshift. We extract a large
sample of early-type galaxies (\sim11000) from several spectroscopic surveys,
spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We
select the most massive, red elliptical galaxies, passively evolving and
without signature of ongoing star formation. Those galaxies can be used as
standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002),
whose differential age evolution as a function of cosmic time directly probes
H(z). We analyze the 4000 {\AA} break (D4000) as a function of redshift, use
stellar population synthesis models to theoretically calibrate the dependence
of the differential age evolution on the differential D4000, and estimate the
Hubble parameter taking into account both statistical and systematical errors.
We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in
H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z
\sim 1.1; for the first time, we place a constraint on H(z) at z \neq 0 with a
precision comparable with the one achieved for the Hubble constant (about 5-6%
at z \sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial
to distinguish many different quintessence cosmologies. These measurements have
been tested to best match a \Lambda CDM model, clearly providing a
statistically robust indication that the Universe is undergoing an accelerated
expansion. This method shows the potentiality to open a new avenue in constrain
a variety of alternative cosmologies, especially when future surveys (e.g.
Euclid) will open the possibility to extend it up to z \sim 2.Comment: 34 pages, 15 figures, 6 tables, published in JCAP. It is a companion
to Moresco et al. (2012b, http://arxiv.org/abs/1201.6658) and Jimenez et al.
(2012, http://arxiv.org/abs/1201.3608). The H(z) data can be downloaded at
http://www.physics-astronomy.unibo.it/en/research/areas/astrophysics/cosmology-with-cosmic-chronometer
Toward an internally consistent astronomical distance scale
Accurate astronomical distance determination is crucial for all fields in
astrophysics, from Galactic to cosmological scales. Despite, or perhaps because
of, significant efforts to determine accurate distances, using a wide range of
methods, tracers, and techniques, an internally consistent astronomical
distance framework has not yet been established. We review current efforts to
homogenize the Local Group's distance framework, with particular emphasis on
the potential of RR Lyrae stars as distance indicators, and attempt to extend
this in an internally consistent manner to cosmological distances. Calibration
based on Type Ia supernovae and distance determinations based on gravitational
lensing represent particularly promising approaches. We provide a positive
outlook to improvements to the status quo expected from future surveys,
missions, and facilities. Astronomical distance determination has clearly
reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press
(chapter 8 of a special collection resulting from the May 2016 ISSI-BJ
workshop on Astronomical Distance Determination in the Space Age
Astronomical Distance Determination in the Space Age: Secondary Distance Indicators
The formal division of the distance indicators into primary and secondary leads to difficulties in description of methods which can actually be used in two ways: with, and without the support of the other methods for scaling. Thus instead of concentrating on the scaling requirement we concentrate on all methods of distance determination to extragalactic sources which are designated, at least formally, to use for individual sources. Among those, the Supernovae Ia is clearly the leader due to its enormous success in determination of the expansion rate of the Universe. However, new methods are rapidly developing, and there is also a progress in more traditional methods. We give a general overview of the methods but we mostly concentrate on the most recent developments in each field, and future expectations. © 2018, The Author(s)