Astrofísica

Over the past couple of years a clear gravitational anomaly has been reported and confirmed by two independent research groups carefully considering relative velocities, v and separations, s, on the plane of the sky, for wide binary star samples from the most recent GAIA catalogue. Over various studies covering a range of sample selection strategies and statistical analysis techniques, a surprising phenomenology has emerged. While the small separation samples for s<2000 au accurately conform to Newtonian expectations, for separations above 3000 au, a clear and systematic departure from Newtonian predictions appears. This high separation regime shows a v proportional to s^(-1/2) scaling, but corresponding to Keplerian orbits under an effective gravitational constant of 1.5G. Given the narrow range of total masses of around 1.6 M_{sun} in the samples considered, the critical separation at which a change in regime appears corresponds to approaching the a0 threshold, where a0 is the characteristic acceleration scale of MOND, as inferred from galactic rotation curve observations. Further, the precise distribution of wide binary relative velocities measured, closely corresponds to MOND expectations for such solar neighbourhood systems under the external field effect predicted by MOND. Now that a low acceleration validity limit for Newtonian gravity has been found, precisely at the acceleration scales over which the presence of dark matter has been proposed, astrophysical inferences for such hypothetical component become suspect.

Presentación de libro

Over twenty years ago, Type Ia Supernovae (SNe Ia) observations revealed an accelerating Universe's expansion, suggesting a significant dark energy presence, often modelled as a cosmological constant, \( \Lambda \). Despite its pivotal role in cosmology, the standard $\Lambda$CDM model remains largely underexplored in the redshift range between distant SNe Ia and the Cosmic Microwave Background (CMB). This study harnesses the James Webb Space Telescope's advanced capabilities to extend the Hubble flow mapping across an unprecedented redshift range, from \( z \approx 0 \) to \( z \approx 7.5 \). Utilising a dataset of 231 HII galaxies and extragalactic HII regions, we employ the \(\text{L}-\sigma\) relation, correlating the luminosity of Balmer lines with their velocity dispersions, to define a competitive technique for measuring cosmic distances. This approach maps the Universe's expansion over 12 billion years, covering over 95\% of its age. Our analysis, using Bayesian inference, constrains the parameter space $\lbrace h, \Omega_m, w_0\rbrace = \lbrace 0.731\pm0.039, 0.302^{+0.12}_{-0.069}, -1.01^{+0.52}_{-0.29}\rbrace $ (statistical) for a flat Universe. These results provide new insights into cosmic evolution and suggest uniformity in the photo-kinematical properties of young massive ionizing clusters in giant HII regions and HII galaxies across most of the Universe's history.

El Telescopio Espacial James Webb (JWST) está revolucionando la mayoría de las áreas de la astrofísica. Uno de los hallazgos más interesantes y desconcertantes ha sido el descubrimiento de una población de galaxias brillantes en el universo temprano (menos de 500 millones de años después del Big Bang) que parece difícil de explicar con los actuales modelos de formación de galaxias utilizados y cuyas propiedades físicas aún no se han entendido completamente y tienen implicaciones importantes para la formación de galaxias y sus poblaciones estelares. El espectrógrafo del infrarrojo cercano del JWST (NIRSpec) proporciona una visión de las propiedades físicas de las galaxias hasta z de 7-9 gracias a la detección de líneas de emisión del gas ionizado, pero a edades del Universo más tempranas, las características espectrales más brillantes están desplazadas más al rojo. en el régimen de infrarrojo medio donde esas observaciones no son posibles. Discutiré la primera detección de hidrógeno ionizado (Halpha) y oxígeno doblemente ionizado ([OIII]4959,5007 Angstroms) a z > 10 utilizando el instrumento de infrarrojo medio MIRI del JWST. Estas detecciones sitúan a la galaxia GHZ2/GLASS-z12, a z=12,36 + - 0,02, convirtiéndola en el objeto astronómico más distante con detección espectroscópica directa de estas líneas y el objeto más brillante de esta época. Su abundancia estimada de oxígeno es cercana al 10% del valor solar, lo que indica un rápido enriquecimiento de metales durante las primeras fases de formación de galaxias, es decir, unos 300 millones de años después de recombinación. Esto confirma las condiciones únicas de las galaxias más brillantes y distantes descubiertas recientemente por JWST y el enorme potencial de las observaciones del IR medio para caracterizar estos sistemas, abriendo una gama de nuevas posibilidades en el estudio del Universo temprano.

En la siguiente charla les mostraré el estudio que realicé sobre una muestra de galaxias con núcleo activo (AGN) para estudiar simultáneamente la región central donde se localiza el agujero negro supermasivo y el resto de la galaxia anfitriona. Para lograrlo, se utilizaron los datos del catastro MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), el cual, se dedicó a observar con la técnica de espectroscopía de campo integral (IFS) a una selección de ∼10,000 galaxias cercanas (z<0.15). Con el desarrolló de una herramienta que utiliza la intensidad de la componente ancha de Hα se identificaron 103 AGNs tipo 1. Se hablará de esta técnica, los métodos que se utilizaron para sustraer la componente estelar de los espectros, el ajuste de líneas de emisión y los parámetros generales estimados de estos AGNs. Así mismo, se mostrarán diversos parámetros encontrados en sus galaxias anfitrionas y algunas relaciones de escala encontradas hasta el momento entre las propiedades de ambas regiones.

Main sequence stars hosting extreme quantities of inner planetary system debris are likely between rocky planetary embryos or planets orbiting in the stars' terrestrial planet zone and that the nature of these events can inform us on the formation and/or evolution of rocky Earth-like planets. Some systems present challenges to our understanding of such processes: stars that could potentially host carbon-dominated solid bodies, a system whose infrared excess emission (and hence dust) suddenly disappeared in 2009 and has yet to return, the dustiest main sequence star known whose dust intercepts 16% of the incoming stellar light and could be heralding the formation of a Mercury analog, and an intermediate-age star that experiences "dipper"-like lightcurve behavior due to transiting clumps of dust. I will discuss relevant processes that could produce the observed characteristics of the population of extremely dusty main sequence stars and outline tests that may distinguish between possible models.

The Pleiades has always been an important benchmark object for stellar astrophysics. The star cluster unites stars of nearly the same age and chemical abundance, making it an ideal natural laboratory. Stellar multiplicity is an important but still poorly defined characteristic of the stellar population; the estimates of the binarity fraction for the star clusters vary significantly. Recent data releases from the Gaia mission have provided a significant boost for related studies. Correct member selection is essential for the cluster's characterization. The Pleiades are known to be particularly well-separated in parameter space from the field stars compared to other clusters. Notably, binary stars often possess poorly reliable astrometric Gaia DR3 solutions marked by the RUWE excess, which may hamper membership classification. Fortunately, the prominent cluster's proper motion allows for taking advantage of long-term ground-based observations and including such problematic entries into consideration, along with the often neglected sources with two-parameter Gaia DR3 solutions. The astrometric data is further complemented by radial velocity measurements from Gaia, APOGEE, LAMOST, GALAH, and the CfA&CORAVEL dedicated Pleiades monitoring program. Stars with a magnitude of G<15 within two degrees from the cluster's center are selected for speckle interferometry survey conducted at 2.5-meter telescope of the SAI MSU Caucasian Observatory. Overall, the 409 Gaia DR3 sources are identified as probable cluster's members, including 14 objects without an available parallax solution. This number is almost 10% larger compared to previous studies based on Gaia DR3 alone for the considered parameter space. After the comparison of several theoretical models against the empirical sequence in the color-magnitude diagram, the 100-Myr age PARSEC isochrone is chosen. According to the preliminary results, not less than 10% of Pleiades members have a companion within 0.2-1 arcsec range (27-135 AU).

Unveiling the emergence of massive/bright galaxies within the first 600 million years of the Universe is pivotal in astronomy. However, the mechanisms driving their rapid growth remain unclear. Millimeter/submillimeter spectroscopic observations of the far-infrared [OIII] and [CII] lines present a critical pathway to explore this. Here we present the science and development of FINER, a dual-polarization SIS mixer receiver for LMT exploiting ALMA's wideband sensitivity upgrade technology. Covering 120−350 GHz, FINER will offer an instantaneous intermediate frequency (IF) of 3−21 GHz per sideband per polarization which corresponds to a 5x wider bandwidth than ALMA, promising an unparalleled spectral scanning capability among sub/mm facilities in the northern hemisphere. We also mention a broad range of science cases affordable with FINER, which includes planetary sciences, star-formation and astrochemistry, and distant dusty star-forming galaxies.