arXiv subjects

Evencio Mediavilla

Publications and source records attributed to Evencio Mediavilla.

18 recordsLinked to original sources

arXiv2024

The Abundance of Clustered Primordial Black Holes from Quasar Microlensing

While elementary particles are the favored candidate for the elusive dark matter, primordial black holes (PBHs) have also been considered to fill that role. Gravitational microlensing is a very well-suited tool to detect and measure the abundance of compact objects in galaxies. Previous studies based on quasar microlensing exclude a significant presence of substellar to intermediate-mass BHs ($\lesssim 100\,\mathrm{M}_\odot$). However, these studies were based on a spatially uniform distribution of BHs while, according to current theories of PBHs formation, they are expected to appear in clusters. We study the impact of clustering in microlensing flux magnification finding that at large scales clusters act like giant pseudo-particles, strongly affecting the emission coming from the Broad Line Region, which can no longer be used to define the zero microlensing baseline. As an alternative, we set this baseline from the intrinsic magnification ratios of quasar images predicted by macro lens models and compare them with the observed flux ratios in emission lines, infrared (IR), and radio. The (magnitude) differences are the flux-ratio anomalies attributable to microlensing, which we estimate for 35 image pairs corresponding to 12 lens systems. A Bayesian analysis indicates that the observed anomalies are incompatible with the existence of a significant population of clustered PBHs. Furthermore, we find that more compact clusters exhibit a stronger microlensing impact. Consequently, we conclude that clustering makes the existence of a significant population of BHs in the substellar to intermediate mass range even more unlikely.

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arXiv2021

HARMONI view of the host galaxies of active galactic nuclei around cosmic noon: Resolved stellar morpho-kinematics and the M$_{BH}$-$σ_{\star}$ relation

Context. The formation and evolution of galaxies appear linked to the growth of supermassive black holes, as evidenced by empirical scaling relations in nearby galaxies. Understanding this co-evolution over cosmic time requires the revelation of the dynamical state of galaxies and the measurement of the mass of their central black holes (MBH) at a range of cosmic distances. Bright active galactic nuclei (AGNs) are ideal for this purpose. Aims. The High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI), the first light integral-field spectrograph for the Extremely Large Telescope (ELT), will transform visible and near-infrared ground-based astrophysics thanks to its advances in sensitivity and angular resolution. We aim to analyse the capabilities of HARMONI to reveal the stellar morpho-kinematic properties of the host galaxies of AGNs at about cosmic noon. Methods. We made use of the simulation pipeline for HARMONI (HSIM) to create mock observations of representative AGN host galaxies at redshifts around cosmic noon. We used observations taken with the Multi-Unit Spectroscopic Explorer (MUSE) of nearby galaxies showing different morphologies and dynamical stages combined with theoretical AGN spectra to create the target inputs for HSIM. Results. According to our simulations, an on-source integration time of three hours should be enough to measure the MBH and to trace the morphology and stellar kinematics of the brightest host galaxies of AGNs beyond cosmic noon. For host galaxies with stellar masses $<$10$^{11}$ solar masses, longer exposure times are mandatory to spatially resolve the stellar kinematics.

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arXiv2020

White Paper on MAAT@GTC

MAAT is proposed as a visitor mirror-slicer optical system that will allow the OSIRIS spectrograph on the 10.4-m Gran telescopio CANARIAS (GTC) the capability to perform Integral Field Spectroscopy (IFS) over a seeing-limited FoV 14.20''x10'' with a slice width of 0.303''. MAAT@GTC will enhance the resolution power of OSIRIS by 1.6 times as compared to its 0.6'' wide long-slit. All the eleven OSIRIS grisms and volume-phase holographic gratings will be available to provide broad spectral coverage with moderate resolution (R=600 up to 4100) in the 3600 - 10000 Å wavelength range. MAAT unique observing capabilities will broaden its use to the needs of the GTC community to unveil the nature of most striking phenomena in the universe well beyond time-domain astronomy. The GTC equipped with OSIRIS+MAAT will also play a fundamental role in synergy with other facilities, some of them operating on the northern ORM at La Palma. This White Paper presents the different aspects of MAAT@GTC - including scientific and technical specifications, outstanding science cases, and an outline of the instrument concept.

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arXiv2019

Astro2020 Science White Paper - Quasar Microlensing: Revolutionizing our Understanding of Quasar Structure and Dynamics

Microlensing by stars within distant galaxies acting as strong gravitational lenses of multiply-imaged quasars, provides a unique and direct measurement of the internal structure of the lensed quasar on nano-arcsecond scales. The measurement relies on the temporal variation of high-magnification caustic crossings which vary on timescales of days to years. Multiwavelength observations provide information from distinct emission regions in the quasar. Through monitoring of these strong gravitational lenses, a full tomographic view can emerge with Astronomical-Unit scale resolution. Work to date has demonstrated the potential of this technique in about a dozen systems. In the 2020s there will be orders of magnitude more systems to work with. Monitoring of lens systems for caustic-crossing events to enable triggering of multi-platform, multi-wavelength observations in the 2020s will fulfill the potential of quasar microlensing as a unique and comprehensive probe of active black hole structure and dynamics.

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arXiv2019

The Most Powerful Lenses in the Universe: Quasar Microlensing as a Probe of the Lensing Galaxy

Optical and X-ray observations of strongly gravitationally lensed quasars (especially when four separate images of the quasar are produced) determine not only the amount of matter in the lensing galaxy but also how much is in a smooth component and how much is composed of compact masses (e.g., stars, stellar remnants, primordial black holes, CDM sub-halos, and planets). Future optical surveys will discover hundreds to thousands of quadruply lensed quasars, and sensitive X-ray observations will unambiguously determine the ratio of smooth to clumpy matter at specific locations in the lensing galaxies and calibrate the stellar mass fundamental plane, providing a determination of the stellar $M/L$. A modest observing program with a sensitive, sub-arcsecond X-ray imager, combined with the planned optical observations, can make those determinations for a large number (hundreds) of the lensing galaxies, which will span a redshift range of $\sim$$0.25<z<1.5$

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arXiv2018

A Second-Order Moment of Microlensing Variability as a Novel Tool in Extragalactic Research

We define a second-order moment of the observational differential microlensing curves that can be used to impose constraints on physical properties of lensed quasars. We show that this quantity is sensitive both to variations in the source size and the deflector mass. We formulize a methodology to recover the source size from the observational measurements when the mass spectrum is fixed. As a case study, we test it with a sample of four quadruple lenses, both in simulated scenarios and with real data from the $\textit{Chandra X-ray Observatory}$. In our simulations with a uniform stellar population the method works best to detect sources around $0.1$ Einstein radii, giving correct upper/lower limits for much smaller/bigger sizes without requiring a big leap in additional computational effort as compared to a single-epoch approach, yet taking advantage of multi-epoch information. We apply the method to a small sample of X-ray data from four objects assuming a range of star masses, and obtain a degeneracy relation between the source size and deflector mass. Combined with previous estimates for the size of the X-ray corona, the degeneracy relation suggests that X-ray microlensing is mainly induced by planetary mass objects.

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arXiv2014

Strong Chromatic Microlensing in HE0047-1756 and SDSS1155+6346

We use spectra of the double lensed quasars HE0047-1756 and SDSS1155+6346 to study their unresolved structure through the impact of microlensing. There is no significant evidence of microlensing in the emission line profiles except for the Ly$α$ line of SDSS1155+6346, which shows strong differences in the shapes for images A and B. However, the continuum of the B image spectrum in SDSS1155+6346 is strongly contaminated by the lens galaxy and these differences should be considered with caution. Using the flux ratios of the emission lines for image pairs as a baseline to remove macro-magnification and extinction, we have detected strong chromatic microlensing in the continuum measured by CASTLES (http://www.cfa.harvard.edu/castles/), in both lens systems, with amplitudes $0.09 (λ16000) \lesssim |Δm |\lesssim 0.8 (λ5439)$ for HE0047-1756, and $0.2 (λ16000) \lesssim |Δm |\lesssim 0.8 (λ5439)$ for SDSS1155+6346. Using magnification maps to simulate microlensing, and modeling the accretion disk as a Gaussian source (I $\propto$ exp(-R$^{2}$/2r$^2_s$)) of size r$_{s}$ $\propto$ $ λ^{p} $ we find, r$_{s}$ = 2.5$_{-1.4}^{+3.0}$ $\sqrt{M/0.3M_{\odot}}$ light days and p = 2.3 $\pm$ 0.8, at the rest frame for $λ$ = 2045, for HE0047-1756 (log prior), and r$_{s}$ = 5.5$_{-3.3}^{+8.2}$ $\sqrt{M/0.3M_{\odot}}$ light days and p = 1.5 $\pm$ 0.6 at the rest frame of $λ$ = 1398, for SDSS1155+6346 (log prior). Contrary to other studied lens systems, the chromaticity detected in HE0047-1756 and SDSS1155+6346 is large enough to fulfill the thin disk prediction. The inferred sizes, however, are very large compared to the predictions of this model, especially in the case of SDSS1155+6346.

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arXiv2011

A Study of Gravitational Lens Chromaticity with the Hubble Space Telescope

We report Hubble Space Telescope observations of 6 gravitational lenses with the Advanced Camera for Surveys. We measured the flux ratios between the lensed images in 6 filters from 8140Å to 2200Å. In 3 of the systems, HE0512$-$3329, B1600+434, and H1413+117, we were able to construct UV extinction curves partially overlapping the 2175Å feature and characterize the properties of the dust relative to the Galaxy and the Magellanic Clouds. In HE1104$-$1804 we detect chromatic microlensing and use it to study the physical properties of the quasar accretion disk. For a Gaussian model of the disk $\exp(-r^2/2 r_s^2)$, scaling with wavelength as $r_s \propto λ^p$, we estimate $r_s(\lambda3363)=4^{+4}_{-2}$ ($7\pm 4$) light-days and $p=1.1\pm 0.6$ ($1.0\pm 0.6$) for a logarithmic (linear) prior on $r_s$. The remaining two systems, FBQ0951+2635 and SBS1520+530, yielded no useful estimates of extinction or chromatic microlensing.

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arXiv2011

A Study of Gravitational Lens Chromaticity using Ground-based Narrow Band Photometry

We present observations of wavelength-dependent flux ratios for four gravitational lens systems (SDSS~J1650+4251, HE~0435$-$1223, FBQ 0951+2635, and Q~0142$-$100) obtained with the Nordic Optical Telescope. The use of narrowband photometry, as well as the excellent seeing conditions during the observations, allows us to study their chromatic behavior. For SDSS~J1650+4251, we determine the extinction curve of the dust in the $z_L=0.58$ lens galaxy and find that the 2175 Å\ feature is absent. In the case of HE~0435$-$1223, we clearly detect chromatic microlensing. This allows us to estimate the wavelength-dependent size of the accretion disk. We find an R-band disk size of $r^{R}_s=13\pm5$ light days for a linear prior on $r^{R}_s$ and $r^{R}_s=7\pm6$ light days for a logarithmic prior. For a power-law size-wavelength scaling of $r_s\proptoλ^{p}$, we were able to constrain the value of the exponent to $p=1.3\pm0.3$ for both $r^{R}_s$ priors, which is in agreement with the temperature profiles of simple thin disk models ($p=4/3$).

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arXiv2006

Hidden Trigger for the Giant Starburst Arc in M 83?

The huge star formation events that occur at some galactic centers do not provide enough clues as to their origin, since the morphological signatures of the triggering mechanism are smeared out in the timescale of a few orbital revolutions of the galaxy core. Our high spatial resolution three-dimensional near-infrared spectroscopy for the first time reveals that a previously known hidden mass concentration is located exactly at the youngest end of a giant star-forming arc. This location, the inferred average cluster ages, and the dynamical times clearly indicate that the interloper has left behind a spur of violent star formation in M 83, in a transient event lasting less than one orbital revolution. The study of the origin (bar funneling or cannibalized satellite) and fate (black hole merging or giant stellar cluster) of this system could provide clues to the question of core growing and morphological evolution in grand-design spiral galaxies. In particular, our TreeSPH numerical modeling suggests that the two nuclei could coalesce, forming a single massive core in about 60 million years or less.

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arXiv2006

Integral field spectroscopy of the Luminous Infrared Galaxy Arp299 (IC694+NGC3690)

The luminous infrared galaxy Arp299 (IC694+NGC3690) is studied using optical integral field spectroscopy obtained with the INTEGRAL system, together with archival Hubble Space Telescope WFPC2 and NICMOS images. The stellar and ionized gas morphology shows lambda-dependent variations due to the combined effects of the dust internal extinction, and the nature and spatial distribution of the different ionizing sources. The two-dimensional ionization maps have revealed an off-nuclear conical structure of about 4 kpc in length, characterized by high excitation conditions and a radial gradient in the gas electron density. The apex of this structure coincides with B1 region of NGC3690 which, in turn, presents Seyfert-like ionization, high extinction and a high velocity dispersion. These results strongly support the hypothesis that B1 is the true nucleus of NGC3690, where an AGN is located. In the circumnuclear regions HII-like ionization dominates, while LINER-like ionization is found elsewhere. The Halpha emitting sources with ages from 3.3 to 7.2x10^6 years, have masses of between 6 and 680x10^6 Msun and contribute (extinction corrected) about 45% to the bolometric luminosity. The ionized (Halpha) and neutral (NaD) gas velocity fields show similar structure on scales of several hundred to about 1 kpc, indicating that these gas components are kinematically coupled. The kinematic structure is complex and on scales of about 0.2 kpc does not appear to be dominated by the presence of ordered, rotational motions. The large velocity dispersion measured in NGC3690 indicates that this galaxy is the most massive of the system. The low velocity amplitude and dispersion of the interface suggest that the ionized gas is slowly rotating or in a close to quiescent phase.

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arXiv2005

Exploring the Potential of Integral Field Spectroscopy Observing Extrasolar Planet Transits: Ground Based Observations of the Atmospheric Na in HD209458b

We explore the use of Integral Field Spectroscopy (IFS) to observe extrasolar planet transits. Although this technique should find its full potential in space observations (e.g. JWST, TPF), we have tested its basics with ground based time series observations of HD209458b obtained with WHT+INTEGRAL during a transit. For this analysis we used 5550 spectra, obtained in 150 exposures during a period of >7 hours. We found that IFS offers 3 fundamental advantages with respect to previously used methods. (i) It improves the effective S/N in photon limited observations by distributing the light coming from the star into the 2 dimensions of the detector. (ii) This type of IFS data allows to 'auto-calibrate' instrumental and background effects. (iii) Since the star image characteristics as well as its photometric properties are extracted from the same data-cube, it is possible to decorrelate photometric instabilities induced by PSF variations. These data have also allowed us to explore the accuracy limits of ground based 'relative' spectrophotometry. This was done using a photometric index that probes the NaD lines, for which we obtained a nominal 1-sigma error of ~1.0x10^-4. This result, based on observations of only 1 transit, indicates that this type of ground observation can constrain the characterization of the transmission spectrum of extrasolar planets. The present observations are compatible with no extra NaD depression during the transit. Though this result seems to be inconsistent with the recently reported HST-STIS findings we point out its limited statistical meaning: the results disagree within 1-sigma, but agree within 2-sigma. We also give some recommenda-tions to instrument developers in order to enhance the efficiency of the method.

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arXiv2003

GLITP Optical Monitoring of QSO 0957+561: VR Light Curves and Variability

The GLITP collaboration observed the first gravitational lens system (QSO 0957+561) from 2000 February 3 to 2000 March 31. The daily VR observations were made with the 2.56-m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma (Spain). We have derived detailed and robust VR light curves of the two components Q0957+561A and Q0957+561B. In spite of the excellent sampling rate, we have not found evidence in favor of true daily variability. With respect to variability on time-scales of several weeks, we measure VR gradients of about -0.8 mmag/day in Q0957+561A and + 0.3 mmag/day in Q0957+561B. The gradients are very probably originated in the far source, thus adopting this reasonable hypothesis (intrinsic variability), we compare them to the expected gradients during the evolution of a compact supernova remnant at the redshift of the source quasar. The starburst scenario is roughly consistent with some former events, but the new gradients do not seem to be caused by supernova remnant activity.

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arXiv2002

Around the Clock Observations of the Q0957+561 A,B Gravitationally Lensed Quasar II: Results for the second observing season

We report on an observing campaign in March 2001 to monitor the brightness of the later arriving Q0957+561 B image in order to compare with the previously published brightness observations of the (first arriving) A image. The 12 participating observatories provided 3543 image frames which we have analyzed for brightness fluctuations. From our classical methods for time delay determination, we find a 417.09 +/- 0.07 day time delay which should be free of effects due to incomplete sampling. During the campaign period, the quasar brightness was relatively constant and only small fluctuations were found; we compare the structure function for the new data with structure function estimates for the 1995--6 epoch, and show that the structure function is statistically non-stationary. We also examine the data for any evidence of correlated fluctuations at zero lag. We discuss the limits to our ability to measure the cosmological time delay if the quasar's emitting surface is time resolved, as seems likely.

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arXiv2001

Optical observations of the dark Gamma-Ray Burst GRB 000210

We report on optical observations on GRB 000210 obtained with the 2.56-m Nordic Optical Telescope and the 1.54-m Danish Telescope starting 12.4 hours after the gamma-ray event. The content of the X-ray error box determined by the Chandra satellite is discussed.

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arXiv2001

'Round the Clock Observations of the Q0957+561 A,B Gravitationally Lensed Quasar

An observing campaign with 10 participating observatories has undertaken to monitor the optical brightness of the Q0957 gravitationally lensed quasar for 10 consecutive nights in January 2000. The resulting A image brightness curve has significant brightness fluctuations and makes a photometric prediction for the B image light curve for a second campaign planned for 12-21 March 2001. The ultimate purpose is to determine the gravitational lens time delay to a fraction of an hour, and to seek evidence for rapid microlensing.

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arXiv2000

Short-timescale Fluctuations in the Difference Light Curves of QSO 0957+561A,B: Microlensing or Noise?

From optical R band data of the double quasar QSO 0957+561A,B, we made two new difference light curves (about 330 days of overlap between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image). We observed noisy behaviours around the zero line and no short-timescale events (with a duration of months), where the term event refers to a prominent feature that may be due to microlensing or another source of variability. Only one event lasting two weeks and rising - 33 mmag was found. Measured constraints on the possible microlensing variability can be used to obtain information on the granularity of the dark matter in the main lensing galaxy and the size of the source. In addition, one can also test the ability of the observational noise to cause the rms averages and the local features of the difference signals. We focused on this last issue. The combined photometries were related to a process consisting of an intrinsic signal plus a Gaussian observational noise. The intrinsic signal has been assumed to be either a smooth function (polynomial) or a smooth function plus a stationary noise process or a correlated stationary process. Using these three pictures without microlensing, we derived some models totally consistent with the observations. We finally discussed the sensitivity of our telescope (at Teide Observatory) to several classes of microlensing variability.

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arXiv1999

Two-Dimensional Line Strength Maps in Three Well-studied Early-Type Galaxies

Integral field spectroscopy has been obtained for the nuclear regions of 3 large, well-studied, early-type galaxies. From these spectra we have obtained line strength maps for about 20 absorption lines, mostly belonging to the Lick system. An extensive comparison with multi-lenslet spectroscopy shows that accurate kinematic maps can be obtained, and also reproducible line strength maps. Comparison with long-slit spectroscopy also produces good agreement. We show that Mg is enhanced with respect to Fe in the inner disk of one of the three galaxies studied, the Sombrero. [Mg/Fe] there is larger than in the rest of the bulge. The large values of Mg/Fe in the central disk are consistent with the centres of other early-type galaxies, and not with large disks, like the disk of our Galaxy, where [Mg/Fe] is approximately 0. We confirm with this observation a recent result of Worthey (1998) that Mg/Fe is determined by the central kinetic energy, or escape velocity, of the stars, only, and not by the formation time scale of the stars. A stellar population analysis using the models of Vazdekis et al. (1996) shows that our observed H gamma agrees well with what is predicted based on the other lines. Using the line strength of the Ca II IR triplet as an indicator of the abundance of Ca, we find that Ca follows Fe, and not Mg, in these galaxies. This is peculiar, given the fact that Ca is an alpha-element. Finally, by combining the results of this paper with those of Vazdekis et al. (1997) we find that the line strength gradients in the three galaxies are primarily caused by variations in metallicity.

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