arXiv subjects

L.

Publications and source records attributed to L..

10 recordsLinked to original sources

arXiv2024

Disentangling the co-evolution of galaxies and supermassive black holes with PRIMA

The most active phases of star formation and black hole accretion are strongly affected by dust extinction, making far-infrared (far-IR) observations the best way to disentangle and study the co-evolution of galaxies and super massive black holes. The plethora of fine structure lines and emission features from dust, ionised and neutral atomic and warm molecular gas in the rest-frame mid- and far-IR provide unmatched diagnostic power to determine the properties of gas and dust, measure gas-phase metallicities and map cold galactic outflows in even the most obscured galaxies. By combining multi-band photometric surveys with low and high-resolution far-IR spectroscopy, the PRobe far-Infrared Mission for Astrophysics (PRIMA), a concept for a far-IR, 1.8m-diameter, cryogenically cooled observatory, will revolutionise the field of galaxy evolution by taking advantage of this IR toolkit to find and study dusty galaxies across galactic time. In this work, we make use of the phenomenological simulation SPRITZ and the Santa Cruz semi-analytical model to describe how a moderately deep multi-band PRIMA photometric survey can easily reach beyond previous IR missions to detect and study galaxies down to $10^{11}\,L_{\odot}$ beyond cosmic noon and at least up to z=4, even in the absence of gravitational lensing. By decomposing the spectral energy distribution (SED) of these photometrically selected galaxies, we show that PRIMA can be used to accurately measure the relative AGN power, the mass fraction contributed by polycyclic aromatic hydrocarbon (PAH) and the total IR luminosity. At the same time, spectroscopic follow up with PRIMA will allow to trace both the star formation and black hole accretion rates (SFR, BHAR), the gas phase metallicities and the mass outflow rates of cold gas in hundreds to thousands of individual galaxies to z=2.

astro-ph.GA↗

arXiv2023

Beyond the disk: EUV coronagraphic observations of the Extreme Ultraviolet Imager on board Solar Orbiter

Most observations of the solar corona beyond 2 Rs consist of broadband visible light imagery from coronagraphs. The associated diagnostics mainly consist of kinematics and derivations of the electron number density. While the measurement of the properties of emission lines can provide crucial additional diagnostics of the coronal plasma (temperatures, velocities, abundances, etc.), these observations are comparatively rare. In visible wavelengths, observations at these heights are limited to total eclipses. In the VUV range, very few additional observations have been achieved since the pioneering results of UVCS. One of the objectives of the Full Sun Imager (FSI) channel of the EUI telescope on board the Solar Orbiter mission has been to provide very wide field-of-view EUV diagnostics of the morphology and dynamics of the solar atmosphere in temperature regimes that are typical of the lower transition region and of the corona. FSI carries out observations in two narrowbands of the EUV spectrum centered on 17.4 nm and 30.4 nm that are dominated, respectively, by lines of Fe IX/X (formed in the corona around 1 MK) and by the resonance line of He II (formed around 80 kK in the lower transition region). Unlike previous EUV imagers, FSI includes a moveable occulting disk that can be inserted in the optical path to reduce the amount of instrumental stray light to a minimum. FSI detects signals at 17.4 nm up to the edge of its FOV (7~Rs), which is about twice further than was previously possible. Comparisons with observations by the LASCO and Metis coronagraphs confirm the presence of morphological similarities and differences between the broadband visible light and EUV emissions, as documented on the basis of prior eclipse and space-based observations. The very-wide-field observations of FSI are paving the way for future dedicated instruments.

astro-ph.SR↗

arXiv2020

The CARMENES search for exoplanets around M dwarfs -- LP 714-47b (TOI 442.01): Populating the Neptune desert

We report the discovery of a Neptune-like planet (LP 714-47 b, P = 4.05204 d, m_b = 30.8 +/- 1.5 M_earth , R_b = 4.7 +/- 0.3 R_earth ) located in the 'hot Neptune desert'. Confirmation of the TESS Object of Interest (TOI 442.01) was achieved with radial-velocity follow-up using CARMENES, ESPRESSO, HIRES, iSHELL, and PFS, as well as from photometric data using TESS, Spitzer, and ground-based photometry from MuSCAT2, TRAPPIST- South, MONET-South, the George Mason University telescope, the Las Cumbres Observatory Global Telescope network, the El Sauce telescope, the TUBITAK National Observatory, the University of Louisville Manner Telescope, and WASP-South. We also present high-spatial resolution adaptive optics imaging with the Gemini Near-Infrared Imager. The low uncertainties in the mass and radius determination place LP 714-47 b among physically well-characterised planets, allowing for a meaningful comparison with planet structure models. The host star LP 714-47 is a slowly rotating early M dwarf (T_eff = 3950 +/- 51 K) with a mass of 0.59 +/- 0.02 M_sun and a radius of 0.58 +/- 0.02 R_sun. From long-term photometric monitoring and spectroscopic activity indicators, we determine a stellar rotation period of about 33 d. The stellar activity is also manifested as correlated noise in the radial-velocity data. In the power spectrum of the radial-velocity data, we detect a second signal with a period of 16 days in addition to the four-day signal of the planet. This could be shown to be a harmonic of the stellar rotation period or the signal of a second planet. It may be possible to tell the difference once more TESS data and radial-velocity data are obtained.

astro-ph.EP↗

arXiv2019

Optical Spectroscopic Observations of Gamma-Ray Blazar Candidates. VII. Follow-up Campaign in the Southern Hemisphere

Searching for low energy counterparts of gamma-ray sources is one of the major challenges in modern gamma-ray astronomy. In the third Fermi source catalog about 30 % of detected sources are unidentified/unassociated Gamma-ray Sources (UGSs). We recently started an optical spectroscopic follow up campaign to confirm the blazar-like nature of candidates counterparts of UGSs. Here we report the spectra of 61 targets collected with the Southern Astrophysical Research Telescope (SOAR) between 2014 and the 2017. Our sample includes 33 potential counterparts of UGSs, selected on the basis of WISE colors, and 27 blazar candidates of uncertain type associated with gamma-ray sources of the last release of the Fermi catalog. We confirm the BZB nature of 20 sources lying within the positional uncertainty region of the UGSs. All the observed BCUs show blazar-like spectra, classified as 2 BZQs and 25 BZBs, for which we obtained 6 redshift estimates. Within the BCUs observations we report the redshift estimate for the BZB associated with, 3FGL J1106.4-3643 that is the second most distant BL Lac known to date, at z>1.084.

astro-ph.GA↗

arXiv2019

Accurate Identification of Galaxy Mergers with Imaging

Merging galaxies play a key role in galaxy evolution, and progress in our understanding of galaxy evolution is slowed by the difficulty of making accurate galaxy merger identifications. We use GADGET-3 hydrodynamical simulations of merging galaxies with the dust radiative transfer code SUNRISE to produce a suite of merging galaxies that span a range of initial conditions. This includes simulated mergers that are gas poor and gas rich and that have a range of mass ratios (minor and major). We adapt the simulated images to the specifications of the SDSS imaging survey and develop a merging galaxy classification scheme that is based on this imaging. We leverage the strengths of seven individual imaging predictors ($Gini$, $M_{20}$, concentration, asymmetry, clumpiness, S\'ersic index, and shape asymmetry) by combining them into one classifier that utilizes Linear Discriminant Analysis. It outperforms individual imaging predictors in accuracy, precision, and merger observability timescale (>2 Gyr for all merger simulations). We find that the classification depends strongly on mass ratio and depends weakly on the gas fraction of the simulated mergers; asymmetry is more important for the major mergers, while concentration is more important for the minor mergers. This is a result of the relatively disturbed morphology of major mergers and the steadier growth of stellar bulges during minor mergers. Since mass ratio has the largest effect on the classification, we create separate classification approaches for minor and major mergers that can be applied to SDSS imaging or adapted for other imaging surveys.

astro-ph.GA↗

arXiv2011

Measuring the spatial extent of individual localized photonic states

We measure the spatial extent of individual localized photonic states in a slow-light photonic crystal waveguide. The size of the states is measured by perturbing each state individually through a local electromagnetic interaction with a near-field probe. We find localized states which are not observed in transmission and show that these states are shorter than the waveguide. We also directly obtain near-field measurements of the participation ratio, from which the size of the states can be derived, in quantitative agreement with the size measured with the perturbation method.

physics.optics↗

arXiv2010

Three-dimensional negative index of refraction at optical frequencies by coupling plasmonic waveguides

We identify a route towards achieving a negative index of refraction at optical frequencies based on coupling between plasmonic waveguides that support backwards waves. We show how modal symmetry can be exploited in metal-dielectric waveguide pairs to achieve negative refraction of both phase and energy. By properly controlling coupling between adjacent waveguides, a metamaterial consisting of a one-dimensional multilayer stack exhibiting an isotropic index of -1 can be achieved at a free-space wavelength of 400 nm. The general concepts developed here may inspire new low-loss metamaterial designs operating close to the metal plasma frequency.

physics.optics↗

arXiv2008

Scattering of acoustic waves by a magnetic cylinder

With the aim of studying magnetic effects in time-distance helioseismology, we use the first-order Born approximation to compute the scattering of acoustic plane waves by a magnetic cylinder embedded in a uniform medium. We show, by comparison with the exact solution, that the travel-time shifts computed in the Born approximation are everywhere valid to first order in the ratio of the magnetic to the gas pressures. We also show that, for arbitrary magnetic field strength, the Born approximation is not valid in the limit where the radius of the magnetic cylinder tends to zero.

astro-ph↗

arXiv2006

Relativistic MHD Winds from Rotating Neutron Stars

We solve the time-dependent dynamics of axisymmetric, general relativistic MHD winds from rotating neutron stars. The mass loss rate is obtained self consistently as a solution of the MHD equations, subject to a finite thermal pressure at the stellar surface. Conditions are chosen to be representative of the neutrino driven phase in newly born magnetars, which have been considered as a possible engine for GRBs. We compute the angular momentum and energy losses as a function of $\sigma$ and compare them with the analytic expectation from the classical theory of pulsar winds. We observe the convergence to the force-free limit in the energy loss and we study the evolution of the closed zone for increasing magnetization. Results also show that the dipolar magnetic field and the presence of a closed zone do not modify significantly the acceleration and collimation properties of the wind.

astro-ph↗

arXiv1999

Integrating the BeppoSAX Gamma-Ray Burst Monitor into the 3rd Interplanetary Network

We have added the BeppoSAX Gamma-Ray Burst Monitor to the 3rd Interplanetary Network of burst detectors. We analyze 16 bursts whose positions are known to good accuracy from measurements at other wavelengths. We show that there is excellent agreement between the Ulysses/BeppoSAX triangulation annuli and the known positions of these events, and that these annuli can in many cases provide useful constraints on the positions of bursts detected by the BeppoSAX Wide Field Camera and Narrow Field Instruments.

astro-ph↗