171,485 research outputs found
The redshift dependence of the MBH–Mhost relation in quasars.
No full textThis Thesis is focused on the study of the evolution of the MBH–Lhost, Mhost relations
as a function of redshift. The aim is to probe whether (and how) the black hole – host galaxy relations evolve during Cosmic ages. This would contribute in constraining the possible formation histories of galaxies and in unveiling the mechanisms regulating the co-existence of black holes and galaxies.
The present study addresses the joint evolution of black holes and galaxies from an observational point of view. Our sample consists of 96 quasars with 0 < z < 3, half of which are radio loud (chapter 2). The stellar luminosities of the host galaxies are taken from imaging studies available in the literature, and from new observations led by our group (chapter 3). The stellar mass is derived from the host galaxy luminosity, under certain assumptions on
the star formation history of the galaxy (chapter 4). Spectroscopic determinations of the black hole masses are derived from the analysis of new data taken on purpose (chapters 3 and 5). The whole dataset is available in the appendix sections A and B. From the study of the MBH/Mhost ratio at low-z, where evolutionary effects are negligible, we infer some constraints
on the geometry of the broad line region. When moving to high redshift (z = 2−3),
we find that the MBH–Lhost relation is practically unchanged. On the other hand, because of the evolution of the stellar mass-to-light ratio, the MBH–Mhost relation shows a clear evolution, in the sense that, for a given host galaxy mass, black holes at high redshift are ∼ 8 times more massive than their low-z counter-parts. This trend cannot be explained in terms of selection effects, and is confirmed after relaxing some operative assumptions. Our results are compared to those of similar works available in the literature. Sketches of possible
interpretative scenarios are also discussed (chapter 6). Conclusions and future perspectives are presented in chapter 7.
The present work principally deals with the analyses and studies published in Decarli et
al. (2008a, on the broad line region geometry), Kotilainen et al. (2009, on the luminosity of quasar host galaxies at z > 2), Decarli et al. (2009b, on the spectroscopic dataset) and Decarli et al. (2009c, on the evolution of the BH–host galaxy relations). A complete list of my publications during the PhD is provided in appendix C
Trends in mortality from cerebrovascular disease in Italy, 1955-78
No full textTrends in age-specific and age-standardized death certification rates from all cerebrovascular diseases and various diagnostic subcategories in Italy during the period 1955-78 have been analysed. In both sexes, a decrease in excess of 25% was evident in the overall age-standardized cerebrovascular disease mortality. However, rates were roughly stable in males up to age 50 and in females up to age 45, and slightly but consistently increasing in the younger age groups (under 40), mostly in females. The largest downward trends were for both sexes in the 55 to 74 age groups, and the declines were more marked in females, averaging 3% per year. Since death certification is most reliable in the younger age groups and it is difficult to imagine any modification of risk factors which should affect mortality in later middle age but not in younger age groups, there is no obvious and simple interpretation of this pattern of trends. A comparison with similar trends in ischemic heart disease and other causes of death suggests that the decline in overall cerebrovascular disease mortality might be partially or largely artefactual, though a between-sexes comparison indicates that at least part of the decrease registered in females may well be real. The extent of the decline, however, has been almost certainly more limited in Italy than in most other Western countries. Only in the younger age group (30-34) did rates show a larger increase in females, which might be related to increased prevalence of cigarette smoking, or the use of oral contraceptives
Trends in childhood cancer mortality in Italy, 1955-78
No full textTrends in childhood cancer death rates in Italy from 1955 to 1978 were analyzed. All cancer age-standardized mortality below age 15 fell about 20%, with a clear downward trend since the early 1970's. Declines were evident for leukemias (-25%), Hodgkin's disease (-56%), non-Hodgkin's lymphomas (-27%), kidney cancer (-25%), retinoblastoma (-50%), and bone sarcomas (-31%), for a total number of about 200-250 fewer deaths per year in the late 1970's compared to the expected values using rates of the 1950's. The observed fall was apparently confined within the first age group considered (0-4 years), but the age-specific patterns of trend were partly influenced by simple postponement of some deaths to older age groups. Comparisons with similar data in other developed countries suggest that, although there has undoubtedly been some progress, there is still wide scope for further reduction in childhood cancer mortality in Italy, simply through more rational use of currently available diagnostic and therapeutic knowledge
Decline of childhood cancer mortality in Italy, 1955-1980
No full textThe decline in childhood cancer mortality in Italy from 1955 to 1980 has been evaluated through (1) comparison of age-specific and age-standardized (0-14 years) rates for the periods 1955-1960 and 1979-1980 and (2) computation of expected numbers of deaths by application of the age-specific rates for the period 1955-1960 to the population structure of subsequent periods. Certified mortality fell by 35% for leukaemias, 90% for Hodgkin's disease, 30% for non-Hodgkin's lymphomas, 40% for bone sarcomas, 30% for kidney (Wilms') tumours, 65% for retinoblastoma. No clear trend was reported for other neoplasms, including neuroblastoma. About 300 cancer deaths per year were avoided in the period 1979-1980 compared with the expected number based on the 1955-1960 rates (170 for leukaemias alone). Although clearly encouraging, these trends are substantially less favourable than those from several other developed countries. It is therefore likely that several dozen other deaths from childhood cancer could be avoided each year through earlier (or more accurate) application of effective therapies, particularly for neoplasms requiring radiotherapy or surgical treatment
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