In the distant past, telescopes were known, first and foremost, for the sizesof their apertures. Advances in technology are now enabling astronomers tobuild extremely powerful instruments to the extent that instruments have nowachieved importance comparable or even exceeding the usual importance accordedto the apertures of the telescopes. However, the cost of successive generationsof instruments has risen at a rate noticeably above that of the rate ofinflation. Here, given the vast sums of money now being expended on opticaltelescopes and their instrumentation, I argue that astronomers must undertake"cost-benefit" analysis for future planning. I use the scientific output of thefirst two decades of the W. M. Keck Observatory as a laboratory for thispurpose. I find, in the absence of upgrades, that the time to reach peak paperproduction for an instrument is about six years. The prime lifetime ofinstruments (sans upgrades), as measured by citations returns, is about adecade. Well thought out and timely upgrades increase and sometimes even doublethe useful lifetime. I investigate how well instrument builders are rewarded. Ifind acknowledgements ranging from almost 100% to as low as 60%. Next, giventhe increasing cost of operating optical telescopes, the management of existingobservatories continue to seek new partnerships. This naturally raises thequestion "What is the cost of a single night of telescope time". I provide arational basis to compute this quantity. I then end the paper with somethoughts on the future of large ground-based optical telescopes, bearing inmind the explosion of synoptic precision photometric, astrometric and imagingsurveys across the electromagnetic spectrum, the increasing cost ofinstrumentation and the rise of mega instruments.

We present two novel designs for a telescope suitable formassively-multiplexed spectroscopy. The first is a very wide field Cassegraintelescope optimised for fibre feeding. It provides a Field Of View (FOV) of 2.5degrees diameter with a 10m primary mirror. It is telecentric and works at F/3,optimal for fibre injection. As an option, a gravity invariant focus for thecentral 10 arc-minutes can be added, to host, for instance, a giant integralfield unit (IFU). It has acceptable performance in the 360-1300 nm wavelengthrange. The second concept is an innovative five mirror telescope design basedon a Three Mirror Anastigmatic (TMA) concept. The design provides a large FOVin a convenient, gravity- invariant focal plane, and is scalable to a range oftelescope diameters. As specific example, we present a 10m telescope with a 1.5degree diameter FOV and a relay system that allows simultaneous spectroscopywith 10,000 mini-IFUs over a square degree, or, alternatively a 17.5 squarearcminutes giant IFU, by using 240 MUSE-type spectrographs. We stress theimportance of developing the telescope and instrument designs for both cases.

Based on an almost complete sample of Galactic open star clusters within 1.8kpc, we perform a comprehensive statistical analysis of various clusterparameters like spatial position, age, size, mass and extinction in order tounderstand the general properties of the open cluster system in the Galaxy andthe Galactic structure. Based on the distribution of 1241 open clusters aboutthe Galactic plane and in different age bins, we find the average Galacticscale height as Zh = 60+/-2 pc for the youngest cluster population having Age<700 Myr, however, it increases up to 64+/-2 pc when we also include olderpopulation of clusters. The solar offset is found to be 6.2+/-1.1 pc above theformal Galactic plane. We derive a local mass density of \rho_0 = 0.090+/-0.005Msun/pc^3 and found a negligibly small amount of dark matter in the solarneighbourhood. The reddening in the direction of clusters suggests a strongcorrelation with their vertical distance from the Galactic plane having arespective slope of dE(B-V)/dz = 0.40+/-0.04 and 0.42+/-0.05 mag/kpc below andabove the GP. We observe a linear mass-radius and mass-age relations in theopen clusters and derive a slope of dR/d(logM) = 2.08+/-0.10 andd(logM)/d(logT) = -0.36+/-0.05,respectively.

Many observed globular clusters (GCs) seem to show a central overabundance ofmass whose nature has not yet fully understood. Indeed, it is not clear whetherit is due to a central intermediate mass black hole (IMBH) or to a massivestellar system (MSS) composed of mass segregated stars. In this contribution wepresent a semi-analytic approach to the problem complemented by 12 $N$-bodysimulations in which we followed the formation of MSSs in GCs with masses up to$3\times 10^5$ \Ms. Some implications for the formation of IMBHs andgravitational waves emission are discussed in perspective of a future work.

Massive galaxies at higher redshifts ($\emph{z}$ $>$ 2) show differentcharacteristics from their local counterparts: They are compact and most likelyhave a disk. In this study, we trace the evolution of local massive galaxies byperforming a detailed morphological analysis, namely, fitting single S\'{e}rsicprofiles and performing bulge+disk decompositions. We analyze $\sim$ 250massive galaxies selected from all CANDELS fields (COSMOS, UDS, EGS,GOODS-South and GOODS-North). We confirm that both star-forming and quiescentgalaxies increase their sizes significantly from $\emph{z}$ $\approx$ 2.5 tothe present day. The global S\'{e}rsic index of quiescent galaxies increasesover time (from $n$ $\approx$ 2.5 to $n$ $>$ 4), while that of star-forminggalaxies remains roughly constant ($n$ $\approx$ 2.5). By decomposing galaxyprofiles into bulge+disk components, we find that massive galaxies at highredshift have prominent stellar disks, which are also evident from visualinspection of the images. By $z$ $\approx$ 0.5, the majority of the disksdisappear and massive quiescent galaxies begin to resemble the local ellipticalgalaxies. Star-forming galaxies have lower bulge-to-total ratios ($B/T$) thantheir quiescent counterparts at each redshift bin. The bulges of star-formingand quiescent galaxies follow different evolutionary histories, while theirdisks evolve similarly. We conclude that major mergers, along with minormergers, have played a crucial role in the significant size increase ofhigh-\emph{z} galaxies and the destruction of their massive and large-scaledisks.

We introduce the ALMA Redshift 4 Survey (AR4S), a systematic ALMA survey ofall the known galaxies with stellar mass (M*) larger than 5e10 Msun at 3.5<z<5in the GOODS--south, UDS and COSMOS CANDELS fields. The sample we have analyzedin this paper is composed of 96 galaxies observed with ALMA at 890um (180umrest-frame) with an on-source integration time of 1.3 min per galaxy. Wedetected 32% of the sample at more than 3 sigma significance. Using the stackedALMA and Herschel photometry, we derived an average dust temperature of 40+/-2K for the whole sample, and extrapolate the Lir and SFR for all our galaxiesbased on their ALMA flux. We then used a forward modeling approach to estimatetheir intrinsic sSFR distribution, deconvolved of measurement errors andselection effects: we find a linear relation between SFR and M*, with a mediansSFR=2.8+/-0.8 Gyr and a dispersion around that relation of 0.28+/-0.13 dex.This latter value is consistent with that measured at lower redshifts, which isproof that the main sequence of star-forming galaxies was already in place atz=4, at least among massive galaxies. These new constraints on the propertiesof the main sequence are in good agreement with the latest predictions fromnumerical simulations, and suggest that the bulk of star formation in galaxiesis driven by the same mechanism from z=4 to the present day, that is, over atleast 90% of the cosmic history. We also discuss the consequences of ourresults on the population of early quiescent galaxies. This paper is part of aseries that will employ these new ALMA observations to explore the starformation and dust properties of the massive end of the z=4 galaxy population.

Recently a population of large, very low surface brightness, spheroidalgalaxies was identified in the Coma cluster. The apparent survival of theseUltra Diffuse Galaxies (UDGs) in a rich cluster suggests that they have veryhigh masses. Here we present the stellar kinematics of Dragonfly 44, one of thelargest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Keck IItelescope. We find a velocity dispersion of 47 km/s, which implies a dynamicalmass of M_dyn=0.7x10^10 M_sun within its deprojected half-light radius ofr_1/2=4.6 kpc. The mass-to-light ratio is M/L=48 M_sun/L_sun, and the darkmatter fraction is 98 percent within the half-light radius. The high mass ofDragonfly 44 is accompanied by a large globular cluster population. From deepGemini imaging taken in 0.4" seeing we infer that Dragonfly 44 has 94 globularclusters, similar to the counts for other galaxies in this mass range. Ourresults add to other recent evidence that many UDGs are "failed" galaxies, withthe sizes, dark matter content, and globular cluster systems of much moreluminous objects. We estimate the total dark halo mass of Dragonfly 44 bycomparing the amount of dark matter within r=4.6 kpc to enclosed mass profilesof NFW halos. The enclosed mass suggests a total mass of ~10^12 M_sun, similarto the mass of the Milky Way. The existence of nearly-dark objects with thismass is unexpected, as galaxy formation is thought to be maximally-efficient inthis regime.