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We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), alpha-element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low-a disk, high-alpha disk, and total population independently. The low-alpha disk exhibits a negative radial metallicity gradient of -0.06 +/- 0.001 dex kpc(-1), which flattens with distance from the midplane. The high-alpha disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]-[Fe/H] plane and in the [Mg/Fe]-age relation persist across the entire disk. The age estimates have typical uncertainties of similar to 0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy.

Beitia-Antero, L., De Castro, A. I. G., & De La Fuente Marcos, R. (2020). High reddening patches in gaia DR2: Possible artifacts or indication of star formation at the edge of the galactic disk. Astronomy and Astrophysics, 634 doi:10.1051/0004-6361/201936881 © ESO 2020, Context. Deep GALEX UV data show that the extreme outskirts of some spiral galaxies are teeming with star formation. Such young stellar populations evolving so far away from the bulk of their host galaxies challenge our overall understanding of how star formation proceeds at galactic scales. It is at present unclear whether our own Milky Way may also exhibit ongoing and recent star formation beyond the conventional edge of the disk (∼15 kpc). Aims. Using Gaia DR2 data, we aim to determine if such a population is present in the Galactic halo, beyond the nominal radius of the Milky Way disk. Methods. We studied the kinematics of Gaia DR2 sources with parallax values between 1/60 and 1/30 milliarcseconds towards two regions that show abnormally high values of extinction and reddening; the results are compared with predictions from GALAXIA Galactic model. We also plotted the color–magnitude (CM) diagrams with heliocentric distances computed inverting the parallaxes, and studied the effects of the large parallax errors by Monte Carlo sampling. Results. The kinematics point towards a Galactic origin for one of the regions, while the provenance of the stars in the other is not clear. A spectroscopic analysis of some of the sources in the first region confirms that they are located in the halo. The CM diagram of the sources suggests that some of them are young., Ministerio de Economía y Competitividad (MINECO), Universidad Complutense de Madrid /Banco de Santander, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, TRUE, pub

Studying the resolved stellar populations of the different structural components that build massive galaxies directly unveils their assembly history. We aim at characterizing the stellar population properties of a representative sample of bulges and pure spheroids in massive galaxies (M ∗ > 1010 M o˙) in the GOODS-N field. We take advantage of the spectral and spatial information provided by SHARDS and Hubble Space Telescope data to perform the multi-image spectrophotometric decoupling of the galaxy light. We derive the spectral energy distribution separately for bulges and disks in the redshift range 0.14 < z ≤ 1 with spectral resolution R ∼ 50. Analyzing these spectral energy distributions, we find evidence of a bimodal distribution of bulge formation redshifts. We find that 33% of them present old mass-weighted ages, implying a median formation redshift form=6.2_-1.7+1.5. They are relics of the early universe embedded in disk galaxies. A second wave, dominant in number, accounts for bulges formed at median redshift form=1.3_-0.6+0.6. The oldest (first-wave) bulges are more compact than the youngest. Virtually all pure spheroids (i.e., those without any disk) are coetaneous with the second-wave bulges, presenting a median redshift of formation form=1.1_-0.3+0.3 The two waves of bulge formation are distinguishable not only in terms of stellar ages but also in star formation mode. All first-wave bulges formed fast at z ∼ 6, with typical timescales around 200 Myr. A significant fraction of the second-wave bulges assembled more slowly, with star formation timescales as long as 1 Gyr. The results of this work suggest that the centers of massive disk-like galaxies actually harbor the oldest spheroids formed in the universe.

Deep surveys have allowed us to precisely chart the evolution of galaxies from billions of years ago through to the present day. We’ve found that galaxies in the distant past are dramatically different than those in the local universe: the stellar masses, sizes, structures, star formation rates, gas contents, and kinematics of galaxies all evolve with redshift. One of the few constants is the bimodality between star-forming and quiescent galaxies, which persists across a wide redshift range. Despite these observational advances, the exact nature of the physical processes governing the growth and transformation of galaxies remain unknown.The first section of this thesis concentrates on the growth of galaxies. Previous studies have used half-light radii to trace the evolution of galaxy sizes. However, radial color gradients cause the light and mass profiles of galaxies to differ, biasing these measurements. I develop and test multiple techniques for measuring the mass profiles of galaxies from high-resolution multi-band Hubble Space Telescope imaging, then use these techniques to create the largest- ever catalog of galaxy half-mass radii at 0 ≤ z ≤ 2.5. This unique catalog enables me to correct for biases in previous studies of size evolution and discover that galaxies grow much more slowly than previously thought. I then examine how the structures of galaxies change as they age along the quiescent sequence, providing support for a merger-driven “inside-out” growth mechanism. Finally, I investigate how the structures of galaxies change as they gradually move up the star-forming sequence towards quiescence. These results pave the way for a new interpretation of the star-forming size-mass relation, and provide evidence for multiple distinct pathways for galaxies to shut down their star formation.The second section of this thesis addresses the transformation of galaxies from star-forming to quiescent. Because stars form out of cold molecular gas, most theoretical mechani

The results from the ESA Gaia astrometric mission and deep photometric surveys have revolutionized our knowledge of the Milky Way. There are many ongoing efforts to search these data for stellar substructure to find evidence of individual accretion events that built up the Milky Way and its halo. One of these newly identified features, called Nyx, was announced as an accreted stellar stream traveling in the plane of the disk. Using a combination of elemental abundances and stellar parameters from the GALAH and Apache Point Observatory Galactic Evolution Experiment (APOGEE) surveys, we find that the abundances of the highest likelihood Nyx members are entirely consistent with membership of the thick disk, and inconsistent with a dwarf galaxy origin. We conclude that the postulated Nyx stream is most probably a high-velocity component of the Milky Way's thick disk. With the growing availability of large data sets including kinematics, stellar parameters, and detailed abundances, the probability of detecting chance associations increases, and hence new searches for substructure require confirmation across as many data dimensions as possible.

The Milky Way's nuclear stellar disk (NSD) and nuclear star cluster (NSC) are the main features of the Galactic center. Nevertheless, their observation is hampered by the extreme source crowding and high extinction. Hence, their relation and formation scenario are not fully clear yet. We aim to detect the stellar populations from the NSC and the NSD along the line of sight toward the NSC and assess whether they have different stellar populations and star formation histories. We analyzed the color-magnitude diagram, K s versus H-K s, of a region of 8.′2 2.′8 centered on the NSC, and detected two different stellar groups with different extinctions. We studied their red clumps to find the features associated with each of the stellar populations. We obtained that the two groups of stars correspond to the NSD and the NSC and found that they have significantly different stellar populations and star formation histories. We detected a double red clump for the NSD population, in agreement with previous work, whereas the NSC presents a more complex structure well fitted by three Gaussian features. We created extinction maps to analyze the extinction variation between the detected stellar groups. We found that the high-extinction layer varies on smaller scales (arcseconds) and that there is a difference of AKs ∼ 0.6 mag between both extinction layers. Finally, we obtained that the distance toward each of the stellar populations is compatible with the Galactic center distance and found some evidence of a slightly closer distance for the NSD stars (∼360 200 pc). © 2021. The Author(s). Published by the American Astronomical Society.

Beitia-Antero, L., De Castro, A. I. G., & De La Fuente Marcos, R. (2020). High reddening patches in gaia DR2: Possible artifacts or indication of star formation at the edge of the galactic disk. Astronomy and Astrophysics, 634 doi:10.1051/0004-6361/201936881 © ESO 2020, Context. Deep GALEX UV data show that the extreme outskirts of some spiral galaxies are teeming with star formation. Such young stellar populations evolving so far away from the bulk of their host galaxies challenge our overall understanding of how star formation proceeds at galactic scales. It is at present unclear whether our own Milky Way may also exhibit ongoing and recent star formation beyond the conventional edge of the disk (∼15 kpc). Aims. Using Gaia DR2 data, we aim to determine if such a population is present in the Galactic halo, beyond the nominal radius of the Milky Way disk. Methods. We studied the kinematics of Gaia DR2 sources with parallax values between 1/60 and 1/30 milliarcseconds towards two regions that show abnormally high values of extinction and reddening; the results are compared with predictions from GALAXIA Galactic model. We also plotted the color–magnitude (CM) diagrams with heliocentric distances computed inverting the parallaxes, and studied the effects of the large parallax errors by Monte Carlo sampling. Results. The kinematics point towards a Galactic origin for one of the regions, while the provenance of the stars in the other is not clear. A spectroscopic analysis of some of the sources in the first region confirms that they are located in the halo. The CM diagram of the sources suggests that some of them are young., Ministerio de Economía y Competitividad (MINECO), Universidad Complutense de Madrid /Banco de Santander, Unidad Deptal. de Astronomía y Geodesia, Fac. de Ciencias Matemáticas, TRUE, pub

The Study of H a from Dwarf Emissions (SHaDE) is a high spectral resolution (R = 13 500) H a integral field survey of 69 dwarf galaxies with stellar masses 106 < M* < 109 MO. The survey used FLAMES on the ESO Very Large Telescope. SHaDE is designed to study the kinematics and stellar populations of dwarf galaxies using consistent methods applied to massive galaxies and at matching level of detail, connecting these mass ranges in an unbiased way. In this paper, we set out the science goals of SHaDE, describe the sample properties, outline the data reduction, and analysis processes. We investigate the log M*-log S0.5 mass-kinematics scaling relation, which has previously shown potential for combining galaxies of all morphologies in a single scaling relation. We extend the scaling relation from massive galaxies to dwarf galaxies, demonstrating this relation is linear down to a stellar mass of M* ~ 108.6 MO. Below this limit, the kinematics of galaxies inside one effective radius appears to be dominated by the internal velocity dispersion limit of the H a-emitting gas, giving a bend in the log M*-log S0.5 relation. Replacing stellar mass with total baryonic mass using gas mass estimate reduces the severity but does not remove the linearity limit of the scaling relation. An extrapolation to estimate the galaxies' dark matter halo masses, yields a log Mh-log S0.5 scaling relation that is free of any bend, has reduced curvature over the whole mass range, and brings galaxies of all masses and morphologies on to the virial relation.

23 páginas, Comunidad de Madrid, Ministerio de Ciencia, Innovación y Universidades (España), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, Instituto de Física de Partículas y del Cosmos (IPARCOS), TRUE, pub

We derive the synchrotron distribution in the Milky Way disc from H II region absorption observations over -40° < l < 40° at six frequencies of 76.2, 83.8, 91.5, 99.2, 106.9, and 114.6 MHz with the GaLactic and Extragalactic All-sky Murchison widefield array survey (GLEAM). We develop a new method of emissivity calculation by taking advantage of the Haslam et al. (1981) map and known spectral indices, which enable us to simultaneously derive the emissivity and the optical depth of H II regions at each frequency. We show our derived synchrotron emissivities based on 152 absorption features of H II regions using both the method previously adopted in the literature and our improved method. We derive the synchrotron emissivity from H II regions to the Galactic edge along the line of sight and, for the first time, derive the emissivity from H II regions to the Sun. These results provide direct information on the distribution of the Galactic magnetic field and cosmic ray electrons for future modelling.

Understanding the physical processes governing galaxy growth and evolution remains an outstanding challenge in astronomy. Constraining these processes requires observations at multiple epochs, but despite exquisite observations of galaxies in the local universe, relatively little is known about galaxies at early times. In the last decade, large photometric surveys have revealed many details about galaxies across the past 10 billion years. However, fully understanding galaxies in the early universe and how they connect to today's galaxy population requires observations of their physical properties through spectroscopy as well as photometry. Recent instrumentation advances have now paved the way for spectroscopic surveys of large samples of distant galaxies, which provide key insights into the earlier phases of galaxy evolution. In this dissertation, I use detailed photometric and spectroscopic observations and simulations to investigate the dust content, masses, and kinematic structures of star-forming galaxies at z~1.5-3, near the peak of cosmic star formation. I present results using Hubble Space Telescope (HST) grism observations of an unbiased sample of galaxies at z~1.5 from the 3D-HST survey to measure the relation between nebular and stellar dust attenuation. These constraints on the dust content of distant galaxies enable accurate measurements of star formation rates, and help to characterize the dust distribution in early galaxies. I also investigate the internal kinematics of galaxies at z~1.5-3 using moderate-resolution near-infrared spectra from the MOSDEF survey with Keck/MOSFIRE together with high spatial-resolution HST imaging. I develop a set of models to measure and interpret kinematics from spectra taken with galaxy-slit misalignments, including galaxies without spatially-resolved spectra. I then use these models to derive independent, dynamical estimates of the galaxy masses, and to constrain the amount of support from ordered versus random motions

The processes that fuel and quench star formation in galaxies are expected to leave imprints on their structure. Moreover, these imprints can serve as signposts to identify galaxies at various stages of their evolution. In this dissertation, we describe our efforts to characterize changes in galaxy structure (1) as star formation is going out, (2) after star formation has ostensibly quenched, and (3) during active star formation, with the goal of elucidating the relevant processes that regulate star formation in each case.In Chapter 2, we use a local (z~0) sample of galaxies drawn from the Sloan Digital Sky Survey (SDSS) to investigate the first two cases. We find that, as galaxies quench, their outer stellar mass density profiles remain essentially constant. However, their inner stellar mass density (within 1 kpc) increases, even while galaxies are still star-forming, until it reaches a mass-dependent threshold, at which point quenching can occur. The existence of this threshold indicates that quenching is connected with processes that grow bulges. In Chapter 3, we then study the morphologies and color profiles of 19 z~0 early-type galaxies located in the green valley. Combining high-resolution Hubble ultraviolet images with SDSS optical photometry, we find that these objects harbor low-level star formation that is clearly detectable in the ultraviolet. Moreover, the recently formed stars are distributed in symmetric rings that often span the entire optical extent of the galaxy. The presence of an old underlying population in their outer parts suggests that star formation in these galaxies is either gradually fading out or possibly rejuvenated by smooth accretion from the intergalactic medium. Such galaxies comprise ~13% of green valley galaxies of similar mass and color, and they may linger in the green valley for several Gyr. Finally, in Chapter 4, we focus on the evolution of star-forming galaxies since z=2.5, leveraging the rich multi-wavelength datasets produc

A fundamental pursuit of astronomy is to understand galaxy evolution. The enormous scales and complex physics involved in this endeavor guarantees a never-ending journey that has enamored both astronomers and laymen alike. But despite the difficulty of this task, astronomers have still attempted to further this goal. Among of these astronomers is Edwin Hubble. His work, which includes the famous Hubble sequence, has immeasurably influenced our understanding of galaxy evolution. In this thesis, we present three works that continues Hubble's line of study by using galaxy structure to learn about galaxy evolution. First, we examine the dependence of galaxy quiescence on inner galactic structure with the AEGIS/ DEEP2 survey at 0.5

Spectral features absorbed against some radio quasars exhibit ~50 mJy variations, with the lines varying both relative to the continuum and, when several lines are present, even relative to one another. We point out that such variability can be expected as a consequence of refractive scintillation caused by the interstellar medium of our Galaxy. Scintillation can cause independent variations between closely-spaced spectral lines, and can even alter the line profile. The background source need not he compact to exhibit spectral variability. The variability can he used to infer the parsec to sub-parsec scale structure of the intervening absorbing material. We discuss the importance of scintillation relative to other possible origins of spectral variability. The present theory is applied to account for the variations observed in the HI-absorbed quasar PKS I 127-145.

Strong galaxy-scale gravitational lensing provides a powerful means of studying galaxy formation, constraining cosmology and understanding the evolution of large-scale structure. The presence of a foreground lensing galaxy deflects the light rays of a background source into multiple images, with their configuration dependent upon the lens mass distribution. Modelling of this distribution to reproduce the lensed images not only aids in measuring the dark matter content of the foreground galaxy, but allows for the reconstruction of the background source in order to study high-redshift galaxy populations. Modelling is typically performed by relatively slow parametric parameter-fitting techniques requiring manual inspection. However, upcoming large-scale surveys like the Legacy Survey of Space and Time (LSST) and Euclid will discover tens of thousands of strong lenses, with this vast quantity driving the growing use of automated machine learning for both identifying and modelling such systems extremely quickly. Convolutional neural networks (CNNs) can extract information from lensed images in order to predict parameters of the lens mass model, but require large simulated data sets for training and testing. In this thesis, I explore the effectiveness of deep learning CNNs for estimating strong galaxy-scale lens mass model parameters when applied to upcoming wide-field survey data, investigating the practicalities they face and comparing and combining them with conventional modelling methods. I construct a CNN and train it on my own simulated lensing images with the imaging characteristics of the Euclid VIS band, LSST r-band, and LSST gri multiband. The CNN is trained to predict parameters of a smooth singular isothermal ellipsoid (SIE) projected mass profile that would best fit the observed image. Multiple aspects of this method are investigated, beginning with a comparison of its accuracy and reliability when applied to the survey data sets. The impact of multiband imag