Unveiling the nature of the most luminous galaxies at the cosmic noon.

This thesis focus on understanding the physical properties of galaxies at redshifts 2.3 < z < 3.3, a time period called Cosmic Noon when galaxies were actively forming stars and evolving rapidly. The work involves the study of different galaxy populations, from young Lyα emitters (LAEs) and Lyman break galaxies (LBGs), to more evolved, and very actively star forming submillimeter galaxies (SMGs) detected with the Herschel Space Observatory. Because of the faintness of these high redshift galaxies, this work employ the power of the gravitational lens effect in high signal-to-noise (S/N) studies to probe deeply into their physical properties in a multi-wavelength approach, with particular emphasis to the rest-frame ultra-violet (UV) emission. First, the BELLS GALLERY project is presented, a dedicated survey aimed to search for strong gravitationally lensed systems with 2 < z < 3 LAEs as background sources. Within this project, the thesis work reports the discovery of two very bright lensed LAEs, that are within the brightest and intrinsically most luminous LAEs known so far at any redshift. In addition, results from a deep optical imaging and spectroscopic survey with the Gran Telescopio Canarias and the William Herschel Telescope targeting six of this new type of strong galaxy-scale lensed LAEs are described and discussed. The main properties of these lensed LAEs are derived, such as their Lyα and UV luminosities, star formation rates, and dust attenuation. Several rest-frame UV diagnostics are also employed on their high S/N spectra to study the kinematics of the interstellar medium and the observed spatial distribution of the UV continuum and Lyα emission. Second, a detailed imaging and spectroscopic analysis of one of the brightest gravitationally lensed SMG, HLock01 at z = 2.96, is presented. It is shown that HLock01 is a merger system composed of a massive Herschel-selected SMG and an optically bright, satellite LBG, separated by only 3.3 kpc in projection. The high S/N rest-frame UV spectrum of the LBG also shows evidence of large scale gas motions, including gas outflows from the LBG, inflowing gas falling onto the Herschel SMG, and an extended reservoir of neutral gas at an impact parameter of 110 kpc. These results are one of the first observational confirmation that gas accretion, along with on-going mergers, are the main mechanisms responsible for the extremely large star formation rates seen in many SMGs. Lastly, the serendipitous discovery of a large, extended Lyα nebula at z = 3.325 is presented. The nebula shows Lyα emission extended over 110 kpc with a total luminosity L(Lyα) = (6.00±0.08)×10^44 erg s^(-1) , being one of the most luminous Lyα nebula known so far. It also shows extended emission of C IV, He II, and C III] over ~ 90, 50, and 35 kpc, respectively. The origin of this nebula is likely associated with a massive type 2 active galaxy and the two faint radio lobes or jets contained within its central ~ 8 kpc

The BOSS Emission-Line Lens Survey. III. : Strong Lensing of Lyα\alpha Emitters by Individual Galaxies

We introduce the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey (BELLS) for GALaxy-Ly$\alpha$ EmitteR sYstems (BELLS GALLERY) Survey, which is a Hubble Space Telescope program to image a sample of galaxy-scale strong gravitational lens candidate systems with high-redshift Ly$\alpha$ emitters (LAEs) as the background sources. The goal of the BELLS GALLERY Survey is to illuminate dark substructures in galaxy-scale halos by exploiting the small-scale clumpiness of rest-frame far-UV emission in lensed LAEs, and to thereby constrain the slope and normalization of the substructure-mass function. In this paper, we describe in detail the spectroscopic strong-lens selection technique, which is based on methods adopted in the previous Sloan Lens ACS (SLACS) Survey, BELLS, and SLACS for the Masses Survey. We present the BELLS GALLERY sample of the 21 highest-quality galaxy--LAE candidates selected from $\approx 1.4 \times 10^6$ galaxy spectra in the BOSS of the Sloan Digital Sky Survey III. These systems consist of massive galaxies at redshifts of approximately 0.5 strongly lensing LAEs at redshifts from 2--3. The compact nature of LAEs makes them an ideal probe of dark substructures, with a substructure-mass sensitivity that is unprecedented in other optical strong-lens samples. The magnification effect from lensing will also reveal the structure of LAEs below 100 pc scales, providing a detailed look at the sites of the most concentrated unobscured star formation in the universe. The source code used for candidate selection is available for download as a part of this release.Comment: 14 pages, 5 figures, accepted for publication in the ApJ (ApJ, 824, 86). Minor edits to match the ApJ published versio

THE BOSS EMISSION-LINE LENS SURVEY. IV. SMOOTH LENS MODELS for the BELLS GALLERY SAMPLE

We present \textsl{Hubble Space Telescope} (\textsl{HST}) F606W-band imaging observations of 21 galaxy-Ly$\alpha$ emitter lens candidates in the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey (BELLS) for GALaxy-Ly$\alpha$ EmitteR sYstems (BELLS GALLERY) survey. 17 systems are confirmed to be definite lenses with unambiguous evidence of multiple imaging. The lenses are primarily massive early-type galaxies (ETGs) at redshifts of approximately $0.55$, while the lensed sources are Ly$\alpha$ emitters (LAEs) at redshifts from 2 to 3. Although the \textsl{HST} imaging data are well fit by smooth lens models consisting of singular isothermal ellipsoids in an external shear field, a thorough exploration of dark substructures in the lens galaxies is required. The Einstein radii of the BELLS GALLERY lenses are on average $60\%$ larger than those of the BELLS lenses because of the much higher source redshifts which will allow a detailed investigation of the radius evolution of the mass profile in ETGs. With the aid of the average $\sim 13 \times$ lensing magnification, the LAEs are resolved to comprise individual star-forming knots of a wide range of properties with characteristic sizes from less than 100 pc to several kpc, rest-frame far UV apparent AB magnitudes from 29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.Comment: 15 pages, 4 figures, minor edits to match the ApJ published versio

The Low-redshift Lyman Continuum Survey: Radio continuum properties of low-zz Lyman continuum emitters

The sources that leak Lyman-continuum (LyC) photons and lead to the reionisation of the universe are intensely studied using multiple observing facilities. Recently, the Low-redshift LyC Survey (LzLCS) has found the first large sample of LyC emitting galaxies at low redshift ($z\sim 0.3$) with the Hubble Space Telescope/Cosmic Origins Spectrograph. The LzLCS sample contains a robust estimate of the LyC escape fraction ($f_\mathrm{esc}^\mathrm{LyC}$) for 66 galaxies spanning a wide range of $f_\mathrm{esc}^\mathrm{LyC}$. Here we, for the first time, aim to study the radio continuum (RC) properties of LzLCS sources and their dependence on $f_\mathrm{esc}^\mathrm{LyC}$. We present Karl G. Jansky Very Large Array RC observations at C (4-8 GHz), S (2-4 GHz) and L (1-2 GHz) bands for a sub-sample of the LzLCS sources. The radio spectral index ($\alpha^{\mathrm{3GHz}}_\mathrm{6GHz}$) spans a wide range from being flat ( $\geq -0.1$) to very steep ($\leq -1.0$). We find that the strongest leakers in our sample show flat $\alpha^{\mathrm{3GHz}}_\mathrm{6GHz}$, weak leakers have $\alpha^{\mathrm{3GHz}}_\mathrm{6GHz}$ close to normal star-forming galaxies, and non-leakers are characterized by steep $\alpha^{\mathrm{3GHz}}_\mathrm{6GHz}$. We argue that a combination of young ages, free-free absorption, and a flat cosmic-ray energy spectrum can altogether lead to a flat $\alpha^{\mathrm{3GHz}}_\mathrm{6GHz}$ for strong leakers. Non-leakers are characterized by steep spectra which can arise due to break/cutoff at high frequencies. Such a cutoff in the spectrum can arise in a single injection model of CRs characteristic of galaxies which have recently stopped star formation. Such a relation between $\alpha^{\mathrm{3GHz}}_\mathrm{6GHz}$ and $f_\mathrm{esc}^\mathrm{LyC}$ hints at the interesting role of supernovae, CRs, and magnetic fields in facilitating the escape (and/or the lack) of LyC photons.Comment: 25 pages, 14 figures, 3 tables, Submitted to Astronomy & Astrophysic

SHARDS frontier fields: physical properties of a low-mass Lyα emitter at z = 5.75

We analyze the properties of a multiply-imaged Lyman-alpha (Lya) emitter at z=5.75 identified through SHARDS Frontier Fields intermediate-band imaging of the Hubble Frontier Fields (HFF) cluster Abell 370. The source, A370-L57, has low intrinsic luminosity (M_UV~-16.5), steep UV spectral index (\beta=-2.4+/-0.1), and extreme rest-frame equivalent width of Lya (EW(Lya)=420+180-120 \AA). Two different gravitational lens models predict high magnification (\mu~10--16) for the two detected counter-images, separated by 7", while a predicted third counter-image (\mu~3--4) is undetected. We find differences of ~50% in magnification between the two lens models, quantifying our current systematic uncertainties. Integral field spectroscopy of A370-L57 with MUSE shows a narrow (FWHM=204+/-10 km/s) and asymmetric Lya profile with an integrated luminosity L(Lya)~10^42 erg/s. The morphology in the HST bands comprises a compact clump (r_e<100 pc) that dominates the Lya and continuum emission and several fainter clumps at projected distances <1 kpc that coincide with an extension of the Lya emission in the SHARDS F823W17 and MUSE observations. The latter could be part of the same galaxy or an interacting companion. We find no evidence of contribution from AGN to the Lya emission. Fitting of the spectral energy distribution with stellar population models favors a very young (t<10 Myr), low mass (M*~10^6.5 Msun), and metal poor (Z<4x10^-3) stellar population. Its modest star formation rate (SFR~1.0 Msun/yr) implies high specific SFR (sSFR~2.5x10^-7 yr^-1) and SFR density (Sigma_SFR ~ 7-35 Msun/yr/kpc^2). The properties of A370-L57 make it a good representative of the population of galaxies responsible for cosmic reionization.Comment: 14 pages, 8 figures, 4 tables. Accepted for publication in Ap

Vacuole-mitochondrial crosstalk during apoptosis induced by acetic acid in yeast

This work was supported by the FCT project PTDC/BIA-BCM/69448/200

What yeast can tell us about how cells commit suicide?

Multicellular organisms developed a complex system to balance cell proliferation and cell death in order to guarantee correct embryonic development and tissue homeostasis. Failure of cells to undergo programmed cell death (PCD) can potentially lead to severe diseases, including neural degeneration, autoimmunity and cancer. Identifying the molecules involved in PCD and understanding the regulation of the process are crucial for prevention and management of these diseases. Evidence of the enormous impact of PCD, of which apoptosis is the most frequent morphological phenotype, on human health makes it one of the today’s main research topics. Since PCD was initially considered specific of metazoans, biological models were first restricted to animal cells. Actually, based on the absence of known crucial PCD regulators, as indicated by plain homologies searches, as well as on the difficulty to explain the sense of cell suicide in a unicellular organism, it was not accepted that these organisms could possess a PDC mechanism. However, evidence has been reported in the last decade indicating that the process of self-destruction in different unicellular organisms, namely in yeast, can also take place. In the present communication, I will present the research we have been developing on PCD, based on the exploration/exploitation of yeast as a simple eukaryotic unicellular model system. Particular focus will be given to our more recent studies suggesting a complex regulation and interplay between mitochondria and the vacuole in acetic acid induced PCD. The validation in mammalian cell lines of the hypothesis postulated with the yeast model will be also discussed.Fundação para a Ciência e a Tecnologia (FCT

The Low-Redshift Lyman Continuum Survey. Unveiling the ISM properties of low-zz Lyman continuum emitters

Combining 66 ultraviolet (UV) spectra and ancillary data from the Low-Redshift Lyman Continuum Survey (LzLCS) and 23 LyC observations by earlier studies, we form a statistical sample of star-forming galaxies at $z \sim 0.3$ to study the role of the cold interstellar medium (ISM) gas in the leakage of ionizing radiation. We first constrain the massive star content (ages and metallicities) and UV attenuation, by fitting the stellar continuum with a combination of simple stellar population models. The models, together with accurate LyC flux measurements, allow to determine the absolute LyC photon escape fraction for each galaxy ($f_{\rm esc}^{\rm abs}$). We measure the equivalent widths and residual fluxes of multiple HI and low-ionization state (LIS) lines, and the geometrical covering fraction adopting the picket-fence model. The $f_{\rm esc}^{\rm abs}$ spans a wide range, with a median (0.16, 0.84 quantiles) of 0.04 (0.02, 0.20), and 50 out of the 89 galaxies detected in the LyC. The HI and LIS line equivalent widths scale with the UV luminosity and attenuation, and inversely with the residual flux of the lines. The HI and LIS residual fluxes are correlated, indicating that the neutral gas is spatially traced by the LIS transitions. We find the observed trends of the absorption lines and the UV attenuation are primarily driven by the covering fraction. The non-uniform gas coverage demonstrates that LyC photons escape through low-column density channels in the ISM. The equivalent widths and residual fluxes of the UV lines strongly correlate with $f_{\rm esc}^{\rm abs}$: strong LyC leakers show weak absorption lines, low UV attenuation, and large Ly$\alpha$ equivalent widths. We finally show that simultaneous UV absorption line and dust attenuation measurements can predict, on average, the escape fraction of galaxies and the method can be applied to galaxies across a wide redshift range.Comment: 30 pages, 16 figures, 3 tables; accepted for publication in Astronomy and Astrophysics on December 16, 2021. Tables A1 to A4 are part of the LzLCS science products and will be publicly available in a dedicated websit