19 research outputs found
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)
A photometric study of the ages and metallicities of early-type galaxies in A 2218
We present deep optical and near-infrared imaging of the rich cluster A2218
at z=0.17. Our optical imaging comes from new multicolour Hubble Space
Telescope WFPC2 observations in the F450W (B), F606W (V) and F814W (I)
passbands. These observations are complemented by deep near-infrared, Ks-band,
imaging from the new INGRID imager on the 4.2-m William Herschel Telescope.
This combination provides unique high-precision multicolour optical-infrared
photometry and morphological information for a large sample of galaxies in the
core of this rich cluster at a lookback time of ~3Gyrs. We analyse the (B-I),
(V-I) and (I-Ks) colours of galaxies spanning a range of a factor of 100 in
K-band luminosity in this region and compare these with grids of stellar
population models. We find that the locus of the colours of the stellar
populations in the luminous (>0.5L*) early-type galaxies, both ellipticals and
S0s, traces a sequence of varying metallicity at a single age. At fainter
luminosities (<0.1L*), this sequence is extended to lower metallicities by the
morphologically-classified ellipticals. However, the faintest S0s exhibit very
different behaviour, showing a wide range in colours, including a large
fraction (30%) with relatively blue colours which appear to have younger
luminosity-weighted ages for their stellar populations, 2-5Gyrs. We show that
the proportion of these young S0s in the cluster population is consistent with
the observed decrease in the S0 population seen in distant clusters when
interpreted within the framework of a two-step spectroscopic and morphological
transformation of accreted spiral field galaxies into cluster S0s.Comment: 11 pages, 1 jpeg figure, Submitted to M
Limits on the Spatial Extent of AGN Measured with the Fine Guidance Sensors of the HST
Accepted for publication in the Astrophysical JournalConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal