arXiv subjects

J. A. Muñoz

Publications and source records attributed to J. A. Muñoz.

At least 37 records · Page 2Linked to original sources

arXiv2021

Microlensing of the broad emission lines in 27 gravitationally lensed quasars. Broad line region structure and kinematics

We aim to study the structure and kinematics of the broad line region (BLR) of a sample of 27 gravitationally lensed quasars with up to five different epochs of observation. This sample is composed of ~100 spectra from the literature plus 22 unpublished spectra of 11 systems. We measure the magnitude differences in the broad emission line (BEL) wings and statistically model the distribution of microlensing magnifications to determine a maximum likelihood estimate for the sizes of the C IV, C III], and Mg II emitting regions. The BELs in lensed quasars are expected to be magnified differently owing to the different sizes of the regions from which they originate. Focusing on the most common BELs in our spectra (C IV, C III], and Mg II), we find that the low-ionization line Mg II is only weakly affected by microlensing. In contrast, the high-ionization line C IV shows strong microlensing in some cases, indicating that its emission region is more compact. Thus, the BEL profiles are deformed differently depending on the geometry and kinematics of the corresponding emitting region. We detect microlensing in either the blue or the red wing (or in both wings with different amplitudes) of C IV in more than 50% of the systems and find outstanding asymmetries in the wings of QSO 0957+561, SDSS J1004+4112, SDSS J1206+4332, and SDSS J1339+1310. This observation indicates that the BLR is, in general, not spherically symmetric and supports the existence of two regions in the BLR, one insensitive to microlensing and another that only shows up when it is magnified by microlensing.

astro-ph.GA↗

arXiv2020

The Impact of the Mass Spectrum of Lenses in Quasar Microlensing Studies. Constraints on a Mixed Population of Primordial Black Holes and Stars

We show that quasar microlensing magnification statistics induced by a population of point microlenses distributed according to a mass-spectrum can be very well approximated by that of a single-mass, "monochromatic", population. When the spatial resolution (physically defined by the source size) is small as compared with the Einstein radius, the mass of the monochromatic population matches the geometric mean of the mass-spectrum. Otherwise, the best-fit mass can be larger. Taking into account the degeneracy with the geometric mean, the interpretation of quasar microlensing observations under the hypothesis of a mixed population of primordial black holes and stars, makes the existence of a significant population of intermediate mass black holes ($\sim$ 100$M_\odot$) unlikely but allows, within a two-$σ$ confidence interval, the presence of a large population ($\gtrsim 40\%$ of the total mass) of substellar black holes ($\sim$ 0.01$M_\odot$).

astro-ph.CO↗

arXiv2020

Individual Estimates of the Virial Factor in 10 Quasars: Implications on the Kinematics of the Broad Line Region

Assuming a gravitational origin for the Fe III$λλ$2039-2113 redshift and using microlensing based estimates of the size of the region emitting this feature, we obtain individual measurements of the virial factor, $f$, in 10 quasars. The average values for the Balmer lines, $\langle f_{Hβ}\rangle={\bf 0.43\pm 0.20}$ and $\langle f_{Hα}\rangle={\bf 0.50\pm 0.24}$, are in good agreement with the results of previous studies for objects with lines of comparable widths. In the case of Mg II, consistent results, $f_{Mg II} \sim {\bf 0.44}$, can be also obtained accepting a reasonable scaling for the size of the emitting region. The modeling of the cumulative histograms of individual measurements, $CDF(f)$, indicates a {relatively} high value for the ratio between isotropic and cylindrical motions, $a\sim {\bf 0.4}-0.7$. On the contrary, we find very large values of the virial factor associated to the Fe III$λλ$2039-2113 blend, $f_{FeIII}=14.3\pm2.4$, which can be explained if this feature arises from a flattened nearly face-on structure, similar to the accretion disk.

astro-ph.GA↗

arXiv2018

Photometric and Spectroscopic Properties of Type Ia Supernova 2018oh with Early Excess Emission from the $Kepler$ 2 Observations

Supernova (SN) 2018oh (ASASSN-18bt) is the first spectroscopically-confirmed type Ia supernova (SN Ia) observed in the $Kepler$ field. The $Kepler$ data revealed an excess emission in its early light curve, allowing to place interesting constraints on its progenitor system (Dimitriadis et al. 2018, Shappee et al. 2018b). Here, we present extensive optical, ultraviolet, and near-infrared photometry, as well as dense sampling of optical spectra, for this object. SN 2018oh is relatively normal in its photometric evolution, with a rise time of 18.3$\pm$0.3 days and $Δ$m$_{15}(B)=0.96\pm$0.03 mag, but it seems to have bluer $B - V$ colors. We construct the "uvoir" bolometric light curve having peak luminosity as 1.49$\times$10$^{43}$erg s$^{-1}$, from which we derive a nickel mass as 0.55$\pm$0.04M$_{\odot}$ by fitting radiation diffusion models powered by centrally located $^{56}$Ni. Note that the moment when nickel-powered luminosity starts to emerge is +3.85 days after the first light in the Kepler data, suggesting other origins of the early-time emission, e.g., mixing of $^{56}$Ni to outer layers of the ejecta or interaction between the ejecta and nearby circumstellar material or a non-degenerate companion star. The spectral evolution of SN 2018oh is similar to that of a normal SN Ia, but is characterized by prominent and persistent carbon absorption features. The C II features can be detected from the early phases to about 3 weeks after the maximum light, representing the latest detection of carbon ever recorded in a SN Ia. This indicates that a considerable amount of unburned carbon exists in the ejecta of SN 2018oh and may mix into deeper layers.

astro-ph.SR↗

arXiv2018

Estimate of the Accretion Disk Size in the Gravitationally Lensed Quasar HE 0435-1223 using Microlensing Magnification Statistics

We present a measurement of the accretion disk size of the quadruple lensed quasar HE 0435-1223 from well-sampled 13-yr COSMOGRAIL optical light curves. Using accurate time delays for the images A, B, C, and D, we modeled and removed the intrinsic quasar variability, and found microlensing events of amplitude up to 0.6, 0.4, and 0.5 mag in the images A, C and D respectively. From the statistics of microlensing magnifications in these images we use Bayesian methods to estimate the size of the quasar accretion disk. We have inferred the half-light radius for the accretion disk using two different methods, $R_{1/2} = 7.6_{-1.1}^{+12.0} \sqrt{M/0.3M_{\odot}}$ light-days (histogram product) and $R_{1/2} = 7.7_{-1.2}^{+7.0} \sqrt{M/0.3M_{\odot}}$ light-days ($χ^2$ criterion). The results are self-consistent and in good agreement with the continuum size predicted by single-epoch spectroscopy and previous studies making use of narrow-band photometry of HE 0435-1223.

astro-ph.GA↗

arXiv2018

Microlensing and Intrinsic Variability of the Broad Emission Lines of Lensed Quasars

We study the BELs in a sample of 11 gravitationally lensed quasars with at least two epochs of observation to identify intrinsic variability and to disentangle it from microlensing. To improve our statistical significance we also include 15 systems with single-epoch spectra. MgII and CIII] emission lines are only weakly affected by microlensing, but CIV shows strong microlensing in some cases, even for regions of the line core, associated with small projected velocities. However, excluding the strongly microlensed cases, there is a strikingly good match between the red wings of the CIV and CIII] profiles. Analysis of these results supports the existence of two regions in the BLR, one that is insensitive to microlensing (of size $\gtrsim$ 50 light-days and kinematics not confined to a plane) and another that shows up only when it is magnified by microlensing (of size of a few light-days, comparable to the accretion disk). Both regions can contribute in different proportions to the emission lines of different species and, within each line profile, to different velocity bins, all of which complicates detailed studies of the BLR based on microlensing size estimates. The strength of the microlensing indicates that some spectral features that make up the pseudo-continuum, such as the shelf-like feature at λ1610 or several FeIII blends, may in part arise from an inner region of the accretion disk. In the case of FeII, microlensing is strong in some blends but not in others. This opens up interesting possibilities to study quasar accretion disk kinematics.

astro-ph.GA↗

arXiv2016

Size of the accretion disk in the gravitationally lensed quasar SDSS J1004+4112 from the statistics of microlensing magnifications

We present eight monitoring seasons of the four brightest images of the gravitational lens SDSS J1004+4112 observed between December 2003 and October 2010. Using measured time delays for the images A, B and C and the model predicted time delay for image D we have removed the intrinsic quasar variability, finding microlensing events of about 0.5 and 0.7 mag of amplitude in the images C and D. From the statistics of microlensing amplitudes in images A, C, and D, we have inferred the half-light radius (at λ rest = 2407 Å) for the accretion disk using two different methods, $R_{1/2}=8.7^{+18.5}_{-5.5} \sqrt{M/0.3 M_\odot}$ (histograms product) and $R_{1/2} = 4.2^{+3.2}_{-2.2} \sqrt{M/0.3 M_\odot}$ light-days ($χ^2$). The results are in agreement within uncertainties with the size predicted from the black hole mass in SDSS J1004+4112 using the thin disk theory.

astro-ph.GA↗

arXiv2015

Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile TiO$_2$

Although the rutile structure of TiO$_2$ is stable at high temperatures, the conventional quasiharmonic approximation predicts that several acoustic phonons decrease anomalously to zero frequency with thermal expansion, incorrectly predicting a structural collapse at temperatures well below 1000\,K. Inelastic neutron scattering was used to measure the temperature dependence of the phonon density of states (DOS) of rutile TiO$_2$ from 300 to 1373\,K. Surprisingly, these anomalous acoustic phonons were found to increase in frequency with temperature. First-principles calculations showed that with lattice expansion, the potentials for the anomalous acoustic phonons transform from quadratic to quartic, stabilizing the rutile phase at high temperatures. In these modes, the vibrational displacements of adjacent Ti and O atoms cause variations in hybridization of $3d$ electrons of Ti and $2p$ electrons of O atoms. With thermal expansion, the energy variation in this "phonon-tracked hybridization" flattens the bottom of the interatomic potential well between Ti and O atoms, and induces a quarticity in the phonon potential.

cond-mat.mtrl-sci↗

arXiv2015

Probing the dark matter radial profile in lens galaxies and the size of X-ray emitting region in quasars with microlensing

We use X-ray and optical microlensing measurements to study the shape of the dark matter density profile in the lens galaxies and the size of the (soft) X-ray emission region. We show that single epoch X-ray microlensing is sensitive to the source size. Our results, in good agreement with previous estimates, show that the size of the X-ray emission region scales roughly linearly with the black hole mass, with a half light radius of $R_{1/2}\simeq(24\pm14) r_g$ where $r_g=GM_{BH}/c^2$. This corresponds to a size of $\log(R_{1/2}/cm)=15.6^{+0.3}_{-0.3}$ or $\sim$ 1 light day for a black hole mass of $M_{BH}=10^9 M_\sun$. We simultaneously estimated the fraction of the local surface mass density in stars, finding that the stellar mass fraction is $α=0.20\pm0.05$ at an average radius of $\sim 1.9 R_{e}$, where $R_e$ is the effective radius of the lens. This stellar mass fraction is insensitive to the X-ray source size and in excellent agreement with our earlier results based on optical data. By combining X-ray and optical microlensing data, we can divide this larger sample into two radial bins. We find that the surface mass density in the form of stars is $α=0.31\pm0.15$ and $α=0.13\pm0.05$ at $(1.3\pm0.3) R_{e}$ and $(2.3\pm0.3) R_{e}$, respectively, in good agreement with expectations and some previous results.

astro-ph.GA↗

arXiv2014

Dark Matter Fraction in Lens Galaxies: New Estimates from Microlensing

We present a joint estimate of the stellar/dark matter mass fraction in lens galaxies and the average size of the accretion disk of lensed quasars from microlensing measurements of 27 quasar image pairs seen through 19 lens galaxies. The Bayesian estimate for the fraction of the surface mass density in the form of stars is $α=0.21\pm0.14$ near the Einstein radius of the lenses ($\sim 1 - 2$ effective radii). The estimate for the average accretion disk size is $R_{1/2}=7.9^{+3.8}_{-2.6}\sqrt{M/0.3M_\sun}$ light days. The fraction of mass in stars at these radii is significantly larger than previous estimates from microlensing studies assuming quasars were point-like. The corresponding local dark matter fraction of 79\% is in good agreement with other estimates based on strong lensing or kinematics. The size of the accretion disk inferred in the present study is slightly larger than previous estimates.

astro-ph.GA↗

arXiv2014

Statistics of Microlensing Caustic Crossings in Q~2237+0305: Peculiar Velocity of the Lens Galaxy and Accretion Disk Size

We use the statistics of caustic crossings induced by microlensing in the lens system Q~2237+0305 to study the lens galaxy peculiar velocity. We calculate the caustic crossing rates for a comprehensive family of stellar mass functions and find a dependence of the average number of caustic crossings with the effective transverse velocity and the average mass, $\langle n \rangle \propto {v_{eff} / \sqrt{\langle m \rangle}}$, equivalent to the theoretical prediction for the case of microlenses with identical masses. We explore the possibilities of the method to measure $v_{eff}$ using the $\sim$12 years of OGLE monitoring of the four images of Q 2237+0305. To determine a lower limit for $v_{eff}$ we count, conservatively, a single caustic crossing for each one of the 4 high magnification events identified in the literature (plus one additional proposed by us) obtaining $v_{eff} \gtrsim 240\sqrt{\langle m \rangle/0.17M_\odot}\rm\,km\, s^{-1}$ at 68\% of confidence. From this value and the average $FWHM$ of 4 high magnification events we obtain a lower limit of $r_s \gtrsim 1.4 \sqrt{\langle m \rangle/0.17M_\odot}$ light-days for the radius of the source ($r_s=FWHM/2.35$). Tentative identification of 3 additional caustic crossing events leads to estimates of $v_{eff}\simeq (493\pm 246)\sqrt{\langle m \rangle/0.17M_\odot}\rm\,km\, s^{-1}$ for the effective transverse velocity and of $r_s \simeq (2.7\pm 1.3)\sqrt{\langle m \rangle/0.17M_\odot}$ light-days for the source size. The estimated transverse peculiar velocity of the galaxy is $v_t \simeq(429\pm246)\sqrt{\langle m \rangle/0.17M_\odot}\rm\,km\, s^{-1}$.

astro-ph.CO↗

arXiv2014

Nonharmonic Phonons in $α$-Iron at High Temperatures

Phonon densities of states (DOS) of bcc $α$-$^{57}$Fe were measured from room temperature through the 1044K Curie transition and the 1185K fcc $γ$-Fe phase transition using nuclear resonant inelastic x-ray scattering. At higher temperatures all phonons shift to lower energies (soften) with thermal expansion, but the low transverse modes soften especially rapidly above 700K, showing strongly nonharmonic behavior that persists through the magnetic transition. Interatomic force constants for the bcc phase were obtained by iteratively fitting a Born-von Kármán model to the experimental phonon spectra using a genetic algorithm optimization. The second-nearest-neighbor fitted axial force constants weakened significantly at elevated temperatures. An unusually large nonharmonic behavior is reported, which increases the vibrational entropy and accounts for a contribution of 35 meV/atom in the free energy at high temperatures. The nonharmonic contribution to the vibrational entropy follows the thermal trend of the magnetic entropy, and may be coupled to magnetic excitations. A small change in vibrational entropy across the $α$-$γ$ structural phase transformation is also reported.

cond-mat.mtrl-sci↗

arXiv2014

The Average Size and Temperature Profile of Quasar Accretion Disks

We use multi-wavelength microlensing measurements of a sample of 10 image pairs from 8 lensed quasars to study the structure of their accretion disks. By using spectroscopy or narrow band photometry we have been able to remove contamination from the weakly microlensed broad emission lines, extinction and any uncertainties in the large-scale macro magnification of the lens model. We determine a maximum likelihood estimate for the exponent of the size versus wavelength scaling ($r_s\propto λ^p$ corresponding to a disk temperature profile of $T\propto r^{-1/p}$) of $p=0.75^{+0.2}_{-0.2}$, and a Bayesian estimate of $p=0.8\pm0.2$, which are significantly smaller than the prediction of thin disk theory ($p=4/3$). We have also obtained a maximum likelihood estimate for the average quasar accretion disk size of $r_s=4.5^{+1.5}_{-1.2} $ lt-day at a rest frame wavelength of $λ= 1026~{\mathrm Å}$ for microlenses with a mean mass of $M=1 M_\sun$, in agreement with previous results, and larger than expected from thin disk theory.

astro-ph.CO↗

arXiv2013

Long-term monitoring, time delay and microlensing in the gravitational lens system Q0142-100

We present twelve years of monitoring of the gravitational lens Q0142-100 from the Teide Observatory. The data, taken from 1999 to 2010, comprise 105 observing nights with the IAC80 telescope. The application of the delta2-method to the dataset leads to a value of the time delay between both components of the system of 72+/-22 days (68 per cent confidence level), consistent within the uncertainties with the latest previous results. With this value in mind a possible microlensing event is detected in Q0142-100.

astro-ph.CO↗

arXiv2013

Microlensing of Quasar UV Iron Emission

We measure the differential microlensing of the UV Fe II and Fe III emission line blends between 14 quasar image pairs in 13 gravitational lenses. We find that the UV iron emission is strongly microlensed in 4 cases with amplitudes comparable to that of the continuum. Statistically modeling the magnifications we infer a typical size of r ~ 4*sqrt(M/Msun) light-days for the Fe line emitting regions which is comparable to the size of the region generating the UV continuum (3 ~ 7 light-days). This may indicate that a significant part of the UV Fe II and Fe III emission originates in the quasar accretion disk.

astro-ph.CO↗

arXiv2013

The Host Halos of OI Absorbers in the Reionization Epoch

We use a radiation hydrodynamic simulation of the hydrogen reionization epoch to study OI absorbers at z~6. The intergalactic medium (IGM) is reionized before it is enriched, hence OI absorption originates within dark matter halos. The predicted abundance of OI absorbers is in reasonable agreement with observations. At z=10, roughly 70% of sightlines through atomically-cooled halos encounter a visible (N_OI > 10^14 cm^-2) column. Reionization ionizes and removes gas from halos less massive than 10^8.4 M_0, but 20% of sightlines through more massive halos encounter visible columns even at z=5. The mass scale of absorber host halos is 10-100 times smaller than the halos of Lyman break galaxies and Lyman-alpha emitters, hence absorption probes the dominant ionizing sources more directly. OI absorbers have neutral hydrogen columns of 10^19-10^21 cm^-2, suggesting a close resemblance between objects selected in OI and HI absorption. Finally, the absorption in the foreground of the z=7.085 quasar ULASJ1120+0641 cannot originate in a dark matter halo because halo gas at the observed HI column density is enriched enough to violate the upper limits on the OI column. By contrast, gas at less than one third the cosmic mean density satisfies the constraints. Hence the foreground absorption likely originates in the IGM.

astro-ph.CO↗

arXiv2013

Does Singlet Fission Enhance the Performance of Organic Solar Cells?

Singlet fission, in which the optical spin-singlet exciton dissociates into two low energy triplet excitons, has been proposed as a viable approach to enhance the quantum efficiency of organic solar cells. We show that even when singlet fission is occurring in the donor molecule, the electronic structure at the donor$-$acceptor interface must satisfy specific requirements for the solar cell performance to be enhanced by this process. We focus on the pentacene$-$C$_{60}$ solar cell, and on the basis of our calculations and available experimental data, we conclude that there is not enough evidence that these requirements are met by the donor$-$acceptor interface here. We propose experiments that can determine whether the minimal requirement for enhanced performance driven by singlet fission is met in this and other solar cells.

cond-mat.str-el↗

arXiv2013

Microlensing of Quasar Broad Emission Lines: Constraints on Broad Line Region Size

We measure the differential microlensing of the broad emission lines between 18 quasar image pairs in 16 gravitational lenses. We find that high ionization lines such as CIV are more strongly microlensed than low ionization lines, indicating that the high ionization line emission regions are more compact. If we statistically model the distribution of microlensing magnifications, we obtain estimates for the broad line region radius of 24 (-15/+22) and 55 (-35/+150) light-days (90% confidence) for the high and low ionization lines, respectively. When the sample is divided attending to quasar luminosity, we find that the line emission regions of more luminous quasars are larger, with a slope consistent with the expected scaling from photoionization models. Our estimates also agree well with the results from local reveberation mapping studies.

astro-ph.CO↗