et al. 2008; D’Onofrio et al. 2016). If luminosity is proportional to mass then the virial theorem implies that L ∝ Ref fσ2 where Ref f is the effective radius and σ is the line-of-sight velocity dispersion.
1.4.2 Late-Type Galaxies
Analogous scaling relations are found for LTGs, and we list here below
• size–mass; similarly o ETGs also late–type galaxies show a correlation between size and mass but the slope is different with respect to the one of the ETGs (see Shen et al. 2003), suggesting different assembly mechanisms between the two classes.
• Tully–Fisher relation (TFR): Empirical relationship between the mass or in-trinsic luminosity and angular velocity or emission line width of a spiral galaxy (Tully & Fisher 1977. The TFR is one of the most widely used methods of measuring extragalactic distances since spiral galaxies are relatively common and contain young, massive stars. The rotational velocity serves as a predic-tor of the luminosity, or absolute magnitude, of the galaxy. The distance is calculated from the distance modulus. It is analogous to the FJR relation for ETGs.
Using the above mentioned relation for different types of galaxies, one can study the evolution of galaxies from past to present. The existence of different correlations of the physical properties indicates that for all galaxies within a particular galaxy type follows a similar the formation and evolution path. The relations therefore provide insights into both the formation and evolution of galaxies, and many are also used to measure the distances to galaxies.
1.5 Galaxy Evolution from Observations
Early–type galaxies (ETGs) play an important role in the observational studies of galaxy formation and evolution as they contain the traces of evolution from past to present. We quantify this evolution by correlating the galaxy physical properties at different redshifts. ETGs are known to follow well–defined empirical scaling laws that relate their global observational properties: the Faber–Jackson (FJ; Faber &
Jackson 1976), Kormendy (1977), fundamental plane (FP; Djorgovski & Davis 1987;
Dressler et al. 1987), size–mass (Shen et al. 2003, Hyde & Bernardi 2009), color–
mass ), color–σ (Bower et al. 1992), Mg2–σ (e.g., Guzman et al. 1992; Bernardi et al.
2003), MBH− M⋆ or MBH− σ (de Zeeuw 2001; Magorrian et al. 1998; Ferrarese &
Merritt 2000; Gebhardt et al. 2000; Tremaine et al. 2002), color gradient vs mass (La Barbera et al. 2010a; Tortora et al. 2010), dynamical vs stellar mass (Tortora
et al. 2009, 2012) relations. These scaling relations provide invaluable information about the formation and evolution of ETGs, setting stringent constraints to galaxy formation models. In particular, studying the structural and mass properties of galaxies at different redshifts can thus give more insights into the formation and evolution of galaxies over time.
Early–type galaxies (ETGs) follow a steep relation between their size and the stellar mass, the so called, size–mass relation. They are also found to be much more compact in the past with respect to local counterparts (Daddi et al. 2005; Trujillo et al. 2006; Trujillo et al. 2007; Saglia et al. 2010; Trujillo et al. 2011, etc.). A simple monolithic–like scenario, where the bulk of the stars is formed in a single dissipative event, followed by a passive evolution, is not longer supported by these observations.
Thus, several explanations have been offered for the dramatic size difference between local massive galaxies and quiescent galaxies at high redshift. The simplest is related to measurement systematics, since observers could have underestimated the sizes and/or overestimated the masses. However, recent studies suggest that it is difficult to change the sizes and the masses by more than a factor of 1.5, unless the initial mass function (IMF) is strongly altered (e.g., Muzzin et al. 2009; Cassata et al.
2010; Szomoru et al. 2010). Other explanations include extreme mass loss due to a quasar–driven wind (Fan et al. 2008), strong radial age gradients leading to large differences between mass–weighted and luminosity–weighted ages (Hopkins et al.
2009b; La Barbera & de Carvalho 2009), star formation due to gas accretion (Franx et al. 2008), and selection effects (e.g., van Dokkum et al. 2008; van der Wel et al.
2009).
The best candidate to represent the galaxy evolution scenario is galaxy merging.
Over time, galaxies were attracted to one another by the force of their gravity, and collided together in a series of mergers. As cosmic time evolves the high–z “red nuggets” are thought to merge and evolve into the present–day massive and extended galaxies. ETGs undergo mergings at different epochs, becoming metal rich, massive and red in color (Kauffmann 1996). Better then major mergers, the most plausible mechanism to explain this size and mass accretion is minor merging (e.g., Bezanson et al. 2009; Naab et al. 2009; van Dokkum et al. 2010; Hilz et al. 2013; Tortora et al. 2014b). Numerical simulations predict that such mergers are frequent (Guo &
White 2008; Naab et al. 2009), leading to observed stronger size growth than mass growth (Bezanson et al. 2009. The minor merging scenario can also explain the joint observed evolution of size and central dark matter (Tortora et al. (2014b); Tortora et al. 2017, in preparation). However, interestingly, recently it has been found that a tiny fraction of the high–z red nuggets might survive intact till the present epoch, without any merging experience, resulting in compact, relic systems in the nearby Universe (Tortora et al. 2016; Trujillo et al. 2012).
Investigation on size evolution of galaxies over time have been performed in the recent years based on different surveys. The most prominent surveys that have been
1.5 Galaxy Evolution from Observations 19
done in the last two decades are DEEP2 (galaxies within the redshift range 0.75 <
z < 1.4 Davis et al. 2003); GAMA (250 square degrees with galaxies up to redshift 0.4: Driver et al. 2011; Driver et al. 2011); 2dFGRS (measuring redshifts for 250 000 galaxies; Colless et al. 2001a), and SDSS (10000 square degrees in northern sky in u, g, r, i and z bands; York et al. 2000). SDSS is one of the most successful surveys in the field of galaxy evolution studies (Kauffmann et al. 2003) in the recent years.
Better quality instrumentations and telescopes mean better database and sci-entific results. And some more recent surveys, like KiDS@VST, are aiming at im-proving the data quality, pushing the SDSS results to larger redshifts and lower masses. KiDS is a large scale optical imaging survey, which will cover 1500 square degrees over u, g, r and i bands, using VLT Survey telescope (VST) and Omega-CAM (de Jong et al. 2015; de Jong et al. 2017). The high spatial resolution of VST (0.2”/pixel), the better seeing conditions and the depth (KiDS is ∼ 2 magnitudes deeper than SDSS, de Jong et al. (2015)) makes the survey good for the galaxy evolution studies, and more promising for our scientific goals. Extrapolating the re-sults presented in this paper to the whole survey, we plan to measure the structural parameters in the four KiDS wavebands for 4 million galaxies, at redshifts z . 0.7 (Tortora et al. 2016).
Chapter 2
Kilo Degree Survey
Sky surveys serves as a basic data in the field of astronomy. They represents nowa-days the largest data generators in astronomy, propelled by the advances in in-formation and computation technology, and have transformed the ways in which astronomy is done. This trend is bound to continue, especially with the new gen-eration of synoptic sky surveys that cover wide areas of the sky repeatedly, and open a new time domain of discovery. Surveys enable a very wide range of science, and that is perhaps their key unifying characteristic. They can be used to generate large, statistical samples of objects that can be studied as populations, or as tracers of larger structures to which they belong.
2.1 VLT Survey Telescope
The VLT Survey Telescope (VST) is the latest telescope added to ESO’s Paranal Observatory in the Atacama Desert of northern Chile (Capaccioli & Schipani 2011;
Kuijken 2011). It is placed in an enclosure adjacent to the four Very Large Tele-scope (VLT) Unit TeleTele-scopes on the summit of Cerro Paranal. The VST (Fig. 2.1) is a wide-field survey telescope with a field of view twice as broad as the full Moon.
It is the largest telescope in the world designed to exclusively survey the sky in visible light. Like the VLT, the new survey telescope covers a wide-range of wave-lengths from ultraviolet through optical to the near-infrared (0.3 to 1.0 microns).
But whereas the largest telescopes, such as the VLT, can only study a small part of the sky at any one time, the VST is designed to photograph large areas quickly and deeply. With a total field view of 1o x 1o, twice as broad as the full Moon, the VST was conceived to support the VLT with wide-angle imaging by detecting and pre-characterising sources, which the VLT Unit Telescopes can then observe further.
The VST is comprised of two mirrors, a primary mirror (M1) with a diameter of 2.61 m and a smaller secondary mirror (M2) with a 93.8 cm diameter. The telescope
Figure 2.1: The VLT Survey Telescope(left) and OmegaCAM camera lies at the heart of the VST. This view shows its 32 CCD detectors that together create 268-megapixel images(right).
is equipped with pixel scale of 0.2”/pixel, is equipped with 5 filters (the Sloan-like filters ugriz). OmegaCAM was built by an international consortium of five institu-tions: Netherlands Research School for Astronomy (NOVA), Kapteyn Astronomical Institute, Universit¨ats-Sternwarte M¨unchen, Astronomical Observatory of Padova and ESO.
The VST project is a joint venture between the European Southern Observatory and the Capodimonte Astronomical Observatory (OAC), part of the Italian National Institute for Astrophysics (INAF). The Italian center designed the telescope while ESO is responsible for the civil engineering works at the site. The VST will be dedi-cated to survey programs. With its state-of-the-art camera, the quality of its optics, and the exceptional seeing conditions of Paranal, the VST is making important ad-vances in many fields of research, from the Milky Way to cosmology. Most of the tele-scope time is dedicated to survey programs solicited by ESO (the ESO Public Sur-veys), but a fraction of the telescope time is also dedicated to GTO large programs, handled by the telescope and camera consortia, plus there is a 10% of time dedi-cated to Chilean programs. To give a perspective of the science currently done by the VST, we briefly summarize the three ESO Public Surveys (see also the ESO webpage:
www.eso.org/sci/observing/PublicSurveys/sciencePublicSurveys.html#VST) VPHAS+: The VST Photometric H-α Survey of the Southern Galactic Plane. PI Janet Drew (Imperial College of London). This survey will combine H-α and broad-band ugri imaging over an area of 1800 square degrees capturing the whole of the