Supernovae As Probes Of The Cosmological Star Formation Rate And Distance Scale
Creators: name: Altavilla, Giuseppe
Publisher: name: Zenodo
Year: 2003
Subjects: Supernovae, distance scale, star formation rate

description: Supernovae (SNe) can  give useful hints in a variety of studies spanning different astrophysical and cosmological issues. SNe in general represent in fact useful "laboratory'' where matter experiences extreme conditions that cannot be produced in terrestrial laboratories. SNe can give information on stellar evolution,  mass loss processes or<br>
accretion mechanisms,  explosions physics. Supernovae explosions are tight related to  the kinematics and enrichment of the interstellar  matter. SNe can also shed light on the study of pulsars, cosmic rays, neutrinos,  gravitational waves and  gamma-ray bursts. Besides, because of their brightness, SNe are also an important tool to investigate  the Universe to very large distances, providing us with information on its properties.

In this Thesis we will not discuss the physics of Supernovae but we will focus our attention on the last issue mentioned, i.e. role of SNe as probes.<br>
In particular we will discuss the use of Type Ia SNe as distance indicator, their use as cosmological tool for determining the cosmological parameters and, together with Core Collapse SNe, we will discuss their role as star<br>
formation rate tracers. Understanding the global history of the Universe is a fundamental goal of cosmology and one of the conceptually simplest test is observing how<br>
a standard (or standardizable!) candle dims as a function of redshift. Type Ia SNe in particular are invaluable cosmological tool that can be used to measure global properties of  our Universe,  like the Hubble<br>
constant H<sub>0</sub> (e.g. Rust 1974; Hamuy et al. 1996b; Tripp and Branch 1999; Freedman et al. 2001), the cosmological  parameters q<sub>0</sub>, Ω<sub>M</sub>, Ω<sub>Λ </sub>(e.g. Schmidt et al. 1998; Perlmutter et al. 1999; Riess et al. 1998).<br>
The  nearby SNe in particular provides the current expansion rate, while  more  distant objects allow us  to search for the effects of cosmic curvature and the Universe expansion history.

The thesis is made up of two parts: in the first one  we will analyse a sample of nearby SNe, while in the second part we will study an intermediate redshift SN sample.<br>
In particular, the topics discussed in this Thesis are the following:

 


	 The intrinsic brightness, the relatively uniform light curves and spectral evolution of SNe Ia  suggested very soontheir use as  standard candles. Yet, as it will be discussed in  Chapter 2,  observations of an  increasing number  of SNe  showed a great variety of objects  also  inside  SN Ia. Fortunately for their use  as distance indicators,  correlations between observables and absolute magnitude at maximum seem to exist. So, although not strictly homogeneous,  after proper calibration, SNe  Ia represent the most accurate  distance indicators on  cosmological scales. In  Chapter 2 we use  data from literature and new unpublished data of nearby SNe Ia  to estimate the   parameters of the  luminosity-width relation and we examine how different   metallicity-dependent calibrations of the Cepheid absolute magnitude affect the type Ia calibration and, in turn, the Hubble constant. We also focus the attention on the absorption estimate and  correction, which turn out  to play a crucial role in the SN absolute magnitude calibration.


 


	To date observational estimates of the SN rate at high redshift have been based on the SN searches  aimed to use SN Ia as cosmological probes and no estimates for CCSNe rate are  available. For this reason in 1999 we started a SN search  mainly aimed to estimate the supernovae rate  at intermediate   redshift  (z~0.3) for both Thermonuclear SNe (SNe Ia) and  Core Collapse SNe. In Chapter 3, after a brief overview on SN searches in general, we describe   our  Southern  inTermediate Redshift ESO Supernova Search (STRESS). The technical details of the instrumentation used, the observations scheduling and strategy, the data collection as well as the software development and the data reduction of the STRESS project are reported. The spectroscopically confirmed SNe as well as the  byproducts of the search are also presented. In Chapter 4  we combine our intermediate redshift SNe with the local sample used in  Chapter 2, exploiting  the results found  in the same chapter to calibrate the whole sample. The  resulting Hubble diagram is then used to estimate  the cosmological  parameters  Ω<sub>M</sub>, Ω<sub>Λ </sub>. In order to get better constraints on the cosmological parameters, we  also combine our intermediate redshift SN sample with data from literature, obtaining a significantly larger sample and  extending the hubble diagram  to higher redshifts. In both cases Supernovae  at high redshift seem to be  fainter  than expected, as if  the rate of expansion of the Universe is accelerating. This  behavior, already noticed a few years ago, can be explained in the framework of the standard Friedmann-Robertson-Walker cosmology through the presence of a vacuum energy ("dark energy'' or a cosmological constant), but alternative hypotheses are presented too.The explosion rate of Supernovae (SNR) is important for several reasons. Supernova rates in  galaxies depend  on the star formation processes, on  stellar evolution (which depends on  metallicity and hence  on the galaxy age), and on the binary system population. A comparison between  SN explosion frequencies at different redshifts may provide important constraints on the evolutionary scenario of the SN progenitors and on the star formation rate (SFR). In particular,  because of the short lifetime of massive progenitors (M &gt; 8M<sub>sun</sub>), the rate of Core Collapse SNe (CCSNe) is correlated with the instantaneous SFR, while the rate of Type Ia SNe, originating  in evolved binary system, can give information about the  long term star formation history. Moreover  Supernovae are among the main drivers of the chemical evolution of a  galaxy, it is thus important  to follow the temporal evolution   of their rates  as accurate as possible. In Chapter 5  we exploit the data collected during our SN search to estimate the SN rates at intermediate redshift (z~0.3), for both type Ia and CCSNe. This is the first attempt to measure the CCSNe rate beyond the local Universe! Our data show an increase of the supernova explosion frequencies with z  for both SN classes, but much more steeper for Core Collapse Supernovae, in agreement with the expected star formation rate evolution in the same redshift range. Other modern studies on type Ia SN rates suggest a shallower evolution with redshift, but the large uncertainties do not allow to  claim adisagreement and leave the problem open to further study.


The results obtained in this Thesis and future perspectives are summarized<br>
in Chapter 6.