arXiv subjects

E. Carrasco

Publications and source records attributed to E. Carrasco.

At least 19 recordsLinked to original sources

arXiv2026

MEGARA Stellar Spectral Library. Second Release

We present the second release of the MEGARA spectral library, MEGASTAR, which now includes all spectra collected during ten observing semesters at the Gran Telescopio CANARIAS. This new release supersedes our first release and incorporates a substantial number of additional observations (2000 new spectra), obtained at high spectral resolution, R(FWHM)$\sim$20000, in two wavelength ranges centred on H${\alpha}$ (6420 - 6790 A) and on the CaII triplet (8370 - 8885 A). The aim of this paper is to introduce MEGASTAR DR2 to the community as its high-resolution spectra can serve as a valuable resource for numerous types of research. In particular, we will use MEGASTAR spectra to construct SSP blocks within the HR-PyPopStar evolutionary synthesis models. The stars were observed using the integral field spectroscopy mode of the instrument. We process the data in a uniform way with the MEGARA data reduction pipeline. We estimate the stellar flux by adding the spectra from 37 spaxels, centred on the spaxel with the highest flux in the IFU reconstructed image. This approach guarantees that the effective slit width, and therefore the spectral resolution, are the same for all spectra. The second MEGASTAR release consists of 2838 spectra corresponding to 1408 stars, providing a better coverage of the stellar parameter space than the first release. The spectra were acquired with an average continuum S/N of about 215. This second release meets the standards of a modern empirical library: it offers reliable calibrations, data free from slit effects, observations of a large number of stars, and provides high spectral resolution to model both individual stellar clusters and entire galaxies observed with MEGARA.

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arXiv2026

WEAVE imaging spectroscopy of NGC 6720: an iron bar in the Ring

We present spatially resolved spectroscopic observations of the planetary nebula NGC 6720, the Ring Nebula, taken during the science verification phase of WEAVE, a new instrument mounted on the William Herschel Telescope on La Palma. We use the instrument's Large Integral Field Unit (LIFU) to obtain spectra of the Ring Nebula, covering its entire optically bright inner regions as well as parts of its much fainter outer molecular halo. We report the discovery of emission from [Fe~{\sc v}] and [Fe~{\sc vi}] confined to a narrow ``bar'' extending across the central regions of the nebula. No lines of other elements share this morphology or, at the spectral resolving power used ($R \sim 2500$), the same radial velocity. The extent to which iron in this bar is depleted is presently unclear; comparison with JWST-detected dust continuum emission suggests that some dust grain destruction may be occurring in the region, but there is currently no observational evidence for the $>$ 50~km\,s$^{-1}$ shock waves or $T > 10^6$~K X-ray emitting gas needed to enable this. Where the bar is located along the line of sight through the nebula, and how it was created, are new puzzles to be solved for this iconic planetary nebula.

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arXiv2025

MEGADES: MEGARA galaxy disc evolution survey. Ionised gas diagnosis

We present the ionised gas properties and metallicity gradients of 43 galaxies observed by the MEGADES survey. Using the MEGARA (Multi-Espectrografo en GTC de Alta Resolucion para Astronomia) instrument, our data combine relatively high spectral (R ~ 6000) and spatial (0.62 arcsec) resolution to study the ionised gas through classic BPT diagnostics in the [N II] and [S II] variants. We examine how these diagrams vary with radius and with the velocity dispersion of the H-alpha line, and we propose a new diagnostic based on the ratio between the velocity dispersions of the [N II] 6584 and H-alpha lines to disentangle the relative roles of AGN, shocks and H II regions. Many regions, regardless of galactocentric distance, show shock-like emission, inferred from their line ratios (high [N II]6584/H-alpha and intermediate [O III]5007/H-beta) and their location between H II and AGN regimes. This improved selection of H II-like regions enables robust oxygen abundance estimates using the N2 indicator. Most galaxies show negligible metallicity gradients, especially low-abundance (<8.37 dex) fast rotators, with an average slope of 0.005 dex Re^-1 and a dispersion of 0.42 dex Re^-1. Above 8.37 dex, fast rotators display mildly negative gradients (mean -0.68 dex Re^-1, dispersion 0.93). For the full MEGADES sample, the mean gradient is -0.03 dex Re^-1 with a dispersion of 0.77. We discuss the implications for the influence of galactic winds on abundance gradients.

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arXiv2023

The MEGARA view of outflows in LINERs

Outflows are believed to be ubiquitous in all AGNs, although their presence in low luminosity AGNs, in particular, for LINERs, has only started to be explored. Their properties (geometry, mass and energetics) are still far from being properly characterised. We use integral field spectroscopic data from the MEGARA instrument, at GTC, to analyse a small sample of nine LINERs, candidates of hosting ionised gas outflows. We aim to study the main emission lines in the optical to identify their properties and physical origin. We obtained data cubes at the lowest (R$\sim$6000) and highest (R$\sim$20000) spectral resolution of MEGARA. We modelled and subtracted the stellar continuum to obtain the ionised gas contribution, and then fitted the emission lines to extract their kinematics (velocity and velocity dispersion). We identified outflows as a secondary component in the emission lines. The primary component of the emission lines was typically associated to gas in the galactic disc. For some objects, there is an enhanced-$σ$ region co-spatial with the secondary component. We associated it to turbulent gas produced due to the interaction with the outflows. We find signatures of outflows in six LINERs, with mass outflow rates ranging from 0.004 to 0.4 M$_{sun}$yr$^{-1}$ and energy rates from $\sim$10$^{38}$ to $\sim$10$^{40}$ erg s$^{-1}$. Their mean electronic density is 600cm$^{-3}$, extending to distances of $\sim$400 pc at an (absolute) velocity of $\sim$340 km s$^{-1}$ (on average). They tend to be compact and unresolved, although for some sources they are extended with a bubble-like morphology. Our results confirm the existence of outflows in the best LINER candidates identified using previous long-slit spectroscopic and imaging data. These outflows do not follow the scaling relations obtained for more luminous AGNs. For some objects we discuss jets as the main drivers of the outflows

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arXiv2023

MEGADES: MEGARA Galaxy Discs Evolution Survey. Data Release I: central fields

The main interest of the Science Team for the exploitation of the MEGARA instrument at the 10.4m Gran Telescopio Canarias (GTC hereafter) is devoted to the study of nearby galaxies, with focus on the research of the history of star formation, and chemical and kinematical properties of disc systems. We refer to this project as MEGADES: MEGARA Galaxy Discs Evolution Survey. The initial goal of MEGADES is to provide a detailed study of the inner regions of nearby disc galaxies, both in terms of their spectrophotometric and chemical evolution, and their dynamical characterisation, by disentangling the contribution of in-situ and ex-situ processes to the history of star formation and effective chemical enrichment of these regions. In addition, the dynamical analysis of these inner regions naturally includes the identification and characterization of galactic winds potentially present in these regions. At a later stage, we will extend this study further out in galactocentric distance. The first stage of this project encompasses the analysis of the central regions of a total of 43 nearby galaxies observed with the MEGARA Integral Field Unit for 114 hours, including both Guaranteed Time and Open Time observations. In this paper we provide a set of all the processed data products available to the community and early results from the analysis of these data regarding stellar continuum, ionized and neutral gas features.

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arXiv2022

MEGASTAR (III). Stellar parameters and data products for DR1 late-type stars

MEGARA is the optical integral field and multi-object spectrograph at the Gran Telescopio Canarias. We have created MEGASTAR, an empirical library of stellar spectra obtained using MEGARA at high resolution $R=20\,000$ (FWHM), available in two wavelength ranges: one centered in H$α$, from 6420 to 6790\,Å and the other centered in the \ion{Ca}{ii} triplet, from 8370 to 8885\,Å (\mbox{HR-R} and \mbox{HR-I} VPH-grating configurations). In this work, we use MEGASTAR spectra, combination of these two short wavelength intervals, to estimate the stellar parameters namely effective temperature, surface gravity and metallicity (and their associated errors) for a sample of 351 MEGASTAR members with spectral types earlier than B2. We have applied a $χ^2$ technique by comparing MEGASTAR data to theoretical stellar models. For those stars with stellar parameters derived in the literature, we have obtained a good agreement between those published parameters and ours. Besides the stellar parameters, we also provide several products like the rectified spectra, radial velocities and stellar indices for this sample of stars. In a near future, we will use MEGASTAR spectra and their derived stellar parameters to compute stellar population evolutionary synthesis models, which will contribute to a better interpretation of star clusters and galaxies spectra obtained with MEGARA.

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arXiv2022

Spatially-resolved properties of the ionized gas in the HII galaxy J084220+115000

We present a spatially resolved spectroscopic study for the metal poor HII galaxy J084220+115000 using MEGARA Integral Field Unit observations at the Gran Telescopio Canarias. We estimated the gas metallicity using the direct method for oxygen, nitrogen and helium and found a mean value of 12+$\log$(O/H)=$8.03\pm$0.06, and integrated electron density and temperature of $\sim161$ cm$^{-3}$ and $\sim15400$ K, respectively. The metallicity distribution shows a large range of $Δ$(O/H) = 0.72 dex between the minimum and maximum (7.69$\pm$0.06 and 8.42$\pm$0.05) values, unusual in a dwarf star-forming galaxy. We derived an integrated $\log$(N/O) ratio of $-1.51\pm0.05$ and found that both N/O and O/H correspond to a primary production of metals. Spatially resolved maps indicate that the gas appears to be photoionized by massive stars according to the diagnostic line ratios. Between the possible mechanisms to explain the starburst activity and the large variation of oxygen abundance in this galaxy, our data support a possible scenario where we are witnessing an ongoing interaction triggering multiple star-forming regions localized in two dominant clumps.

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arXiv2022

The nature of the Cygnus extreme B-supergiant 2MASS J20395358+4222505

2MASS J20395358+4222505 is an obscured early B supergiant near the massive OB star association Cyg OB2. Despite its bright infrared magnitude (K$_{s}$=5.82) it has remained largely ignored because of its dim optical magnitude (B=16.63, V=13.68). In a previous paper we classified it as a highly reddened, potentially extremely luminous, early B-type supergiant. We obtained its spectrum in the U, B and R spectral bands during commissioning observations with the instrument MEGARA@GTC. It displays a particularly strong H$α$ emission for its spectral type, B1 Ia. The star seems to be in an intermediate phase between super- and hypergiant, a group that it will probably join in the near (astronomical) future. We observe a radial velocity difference between individual observations and determine the stellar parameters, obtaining T$_{eff}$ = 24000 K, logg$_{c}$= 2.88 $\pm$ 0.15. The rotational velocity found is large for a B-supergiant, vsini= 110 $\pm$ 25 km s$^{-1}$. The abundance pattern is consistent with solar, with a mild C underabundance (based on a single line). Assuming that J20395358+4222505 is at the distance of Cyg OB2 we derive the radius from infrared photometry, finding R= 41.2 $\pm$ 4.0 R$_{\odot}$, log(L/L$_{\odot}$)= 5.71 $\pm$ 0.04 and a spectroscopic mass of 46.5 $\pm$ 15.0 M$_{\odot}$. The clumped mass-loss rate (clumping factor 10) is very high for the spectral type, $\dot{M}$ = 2.4x10$^{-6}$ M$_{\odot}$ a$^{-1}$. The high rotational velocity and mass-loss rate place the star at the hot side of the bi-stability jump. Together with the nearly solar CNO abundance pattern, they may also point to evolution in a binary system, J20395358+4222505 being the initial secondary.

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arXiv2021

A new insight of AGC198691 (Leoncino) galaxy with MEGARA at the GTC

We describe the observations of the low-metallicity nearby galaxy AGC198691 (Leoncino dwarf) obtained with the Integral Field Unit of the instrument MEGARA at the Gran Telescopio Canarias. The observations cover the wavelength ranges 4304 - 5198 A and 6098 - 7306 A with a resolving power R ~ 6000. We present 2D maps of the ionized gas, deriving the extension of the HII region and gas kinematics from the observed emission lines. We have not found any evidence of recent gas infall or loss of metals by means of outflows. This result is supported by the closed-box model predictions, consistent with the oxygen abundance found by other authors in this galaxy and points towards Leoncino being a genuine XMD galaxy. We present for the first time spatially resolved spectroscopy allowing the detailed study of a star forming region. We use PopStar+Cloudy models to simulate the emission-line spectrum. We find that the central emission line spectrum can be explained by a single young ionizing cluster with an age ~ 3.5 +/- 0.5Myr and a stellar mass of about 2000 solar masses. However, the radial profiles of [OIII]5007 A and the Balmer lines in emission demand photoionization by clusters of different ages between 3.5 and 6.5Myr that might respond either to the evolution of a single cluster evolving along the cooling time of the nebula (about 3Myr at the metallicity of Leoncino, Z ~ 0.0004) or to mass segregation of the cluster, being both scenarios consistent with the observed equivalent widths of the Balmer lines

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arXiv2021

Stellar populations with MEGARA: the inner regions of NGC 7025

Context. We aim to determine the capabilities of the MEGARA@GTC instrument integral-field unit to study stellar populations and exploit its combination of high spectral (R \sim 6,000, 12,000 and 20,000) and spatial (0.62") resolutions within its 12.5"x11.3" field of view. Aims. We pursue to establish a systematic method through which we can determine the properties of the stellar populations in the observations made with MEGARA, more specifically within the MEGADES legacy project and, for this paper, those of the stellar populations of NGC 7025. Methods. We use MEGARA observations of galaxy NGC 7025. We apply different approaches to estimate the properties of the stellar populations with the highest possible certainty. Numerous tests were also performed to check the reliability of the study. Results. All the studies we conduct (both full spectral fitting and absorption line indices) on the stellar populations of NGC 7025 indicate that the stars that form its bulge have supersolar metallicity and considerably old ages (\sim 10 Gyr), in general. We determined that the bulge of NGC 7025 has a mild negative mass-weighted age gradient using three different combinations of MEGARA spectral setups. Regarding its more detailed star formation history, our results indicate that, besides a rather constant star formation at early epochs, a peak in formation history of the stars in the bulge is also found 3.5-4.5 Gyr ago, partly explaining the mass-weighted age gradients measured. Conclusions. The scenario presented in NGC 7025 is that of an isolated galaxy under secular evolution that about 3.5-4.5 Gyr ago likely experimented a minor merger (mass ratio 1/10) that induced an increase in star formation and also perturbed the morphology of its outer disc. We report on different lessons learned for the ongoing exploitation of the MEGADES survey with GTC.

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arXiv2020

MEGARA-GTC Stellar Spectral Library (II). MEGASTAR First Release

MEGARA is an optical integral field and multiobject fibre based spectrograph for the 10.4m Gran Telescopio CANARIAS that offers medium to high spectral resolutions (FWHM) of R $\simeq$ 6000, 12000, 20000. Commissioned at the telescope in 2017, it started operation as a common-user instrument in 2018. We are creating an instrument-oriented empirical spectral library from MEGARA-GTC stars observations, MEGASTAR, crucial for the correct interpretation of MEGARA data. This piece of work describes the content of the first release of MEGASTAR, formed by the spectra of 414 stars observed with R $\simeq$ 20000 in the spectral intervals from 6420 to 6790 $Å$ and from 8370 to 8885 $Å$, and obtained with a continuum average signal to noise ratio around 260. We describe the release sample, the observations, the data reduction procedure and the MEGASTAR database. Additionally, we include in Appendix A, an atlas with the complete set of 838 spectra of this first release of the MEGASTAR catalogue.

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arXiv2020

Mapping the ionized gas of the metal-poor HII galaxy PHL 293B with MEGARA

Here we report the first spatially resolved spectroscopic study for the galaxy PHL293B using the high-resolution GTC/MEGARA IFU. PHL293B is a local, extremely metal-poor, high ionization galaxy. This makes PHL 293B an excellent analogue for galaxies in the early Universe. The MEGARA aperture (~12.5''x 11.3'') covers the entire PHL 293B main body and its far-reaching ionized gas. We created and discussed maps of all relevant emission lines, line ratios and physical-chemical properties of the ionized ISM. The narrow emission gas appears to be ionized mainly by massive stars according to the observed diganostic line ratios, regardless of the position across the MEGARA aperture. We detected low intensity broad emission components and blueshifted absorptions in the Balmer lines (H$α$,H$β$) which are located in the brightest zone of the galaxy ISM. A chemically homogeneity, across hundreds of parsecs, is observed in O/H. We take the oxygen abundance 12+log(O/H)=7.64 $\pm$ 0.06 derived from the PHL293B integrated spectrum as the representative metallicity for the galaxy. Our IFU data reveal for the first time that the nebular HeII4686 emission from PHL 293B is spatially extended and coincident with the ionizing stellar cluster, and allow us to compute its absolute HeII ionizing photon flux. Wolf-Rayet bumps are not detected excluding therefore Wolf-Rayet stars as the main HeII excitation source. The origin of the nebular HeII4686 is discussed.

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arXiv2020

MEGARA-IFU detection of extended HeII4686 nebular emission in the central region of NGC1569 and its ionization budget

We here report the detection of extended HeII4686 nebular emission in the central region of NGC1569 using the integral field spectrograph MEGARA at the 10.4-m Gran Telescopio Canarias. The observations cover a Field of View (FoV) of 12.5 arcsec x 11.3 arcsec at seeing-limited spatial resolution of ~15 pc and at a spectral resolution of R=6000 in the wavelength range 4330--5200 Angstrom. The emission extends over a semi-circular arc of ~40 pc width and ~150 pc diameter around the super star cluster A (SSC-A). The Av derived using Balmer decrement varies from the Galactic value of 1.6 mag to a maximum of ~4.5 mag, with a mean value of 2.65+/-0.60 mag. We infer 124+/-11 Wolf-Rayet (WR) stars in SSC-A using the HeII4686 broad feature and Av=2.3 mag. The He+ ionizing photon rate from these WR stars is sufficient to explain the luminosity of the HeII4686 nebula. The observationally-determined total He+ and H0 ionizing photon rates, their ratio, and the observed number of WR stars in SSC-A are all consistent with the predictions of simple stellar population models at an age of 4.0+/-0.5 Myr, and mass of (5.5+/-0.5)x10^5 Msun. Our observations reinforce the absence of WR stars in SSC-B, the second most massive cluster in the FoV. None of the other locations in our FoV where HeII4686 emission has been reported from narrow-band imaging observations contain WR stars.

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arXiv2020

NGC 7469 as seen by MEGARA: new results from high-resolution IFU spectroscopy

We present our analysis of high-resolution (R $\sim$ 20 000) GTC/MEGARA integral-field unit spectroscopic observations, obtained during the commissioning run, in the inner region (12.5 arcsec x 11.3 arcsec) of the active galaxy NGC7469, at spatial scales of 0.62 arcsec. We explore the kinematics, dynamics, ionisation mechanisms and oxygen abundances of the ionised gas, by modelling the H$α$-[NII] emission lines at high signal-to-noise (>15) with multiple Gaussian components. MEGARA observations reveal, for the first time for NGC7469, the presence of a very thin (20 pc) ionised gas disc supported by rotation (V/$σ$ = 4.3), embedded in a thicker (222 pc), dynamically hotter (V/$σ$ = 1.3) one. These discs nearly co-rotate with similar peak-to-peak velocities (163 vs. 137 km/s ), but with different average velocity dispersion (38 vs. 108 km/s ). The kinematics of both discs could be possibly perturbed by star-forming regions. We interpret the morphology and the kinematics of a third (broader) component ($σ$ > 250 km/s) as suggestive of the presence of non-rotational turbulent motions possibly associated either to an outflow or to the lense. For the narrow component, the [NII]/H$α$ ratios point to the star-formation as the dominant mechanism of ionisation, being consistent with ionisation from shocks in the case of the intermediate component. All components have roughly solar metallicity. In the nuclear region of NGC7469, at r < 1.85 arcsec, a very broad (FWHM = 2590 km/s ) Hα component is contributing (41%) to the global H$α$ -[NII]profile, being originated in the (unresolved) broad line region of the Seyfert 1.5 nucleus of NGC7469.

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arXiv2020

MEGARA-GTC Stellar Spectral Library (I)

MEGARA (Multi Espectr{ó}grafo en GTC de Alta Resoluci{ó}n para Astronom{\'ı}a) is an optical (3650~--~9750Å), fibre-fed, medium-high spectral resolution (R = 6000, 12000, 20000) instrument for the GTC 10.4m telescope, commissioned in the summer of 2017, and currently in operation. The scientific exploitation of MEGARA demands a stellar-spectra library to interpret galaxy data and to estimate the contribution of the stellar populations. This paper introduces the MEGARA-GTC spectral library, detailing the rationale behind the catalogue building. We present the spectra of 97 stars (21 individual stars and 56 members of the globular cluster M15, being both sub-samples taken during the commissioning runs; and 20 stars from our on-going GTC Open-Time program). The spectra have R~=~20000 in the HR-R and HR-I setups, centred at 6563 and 8633~Å respectively. We describe the procedures to reduce and analyse the data. Then, we determine the best-fitting theoretical models to each spectrum through a $χ^{2}$ minimisation technique to derive the stellar physical parameters and discuss the results. We have also measured some absorption lines and indices. Finally, this article introduces our project to complete the library and the database to make the spectra available to the community.

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arXiv2019

Spatially-resolved analysis of neutral winds, stars and ionized gas kinematics with MEGARA/GTC: new insights on the nearby galaxy UGC 10205

We present a comprehensive analysis of the multi-phase structure of the interstellar medium (ISM) and the stellar kinematics in the edge-on nearby galaxy UGC 10205 using integral field spectroscopy (IFS) data taken with MEGARA at the GTC. We explore both the neutral and the ionized gas phases using the interstellar Na ${\small I}$ D doublet absorption (LR$-$V set-up, R $\sim$ 6000) and the H$α$ emission line (HR$-$R set-up, R $\sim$ 18000), respectively. The high-resolution data show the complexity of the H$α$ emission line profile revealing the detection of up to three kinematically distinct gaseous components. Despite of this fact, a thin disk model is able to reproduce the bulk of the ionized gas motions in the central regions of UGC 10205. The use of asymmetric drift corrections is needed to reconciliate the ionized and the stellar velocity rotation curves. We also report the detection of outflowing neutral gas material blueshifted by $\sim$ 87 km s$^{-1}$. The main physical properties that describe the observed outflow are a total mass M$_{out}$ $=$ (4.55 $\pm$ 0.06) $\times$ 10$^{7}$ M$_{\odot}$ and a cold gas mass outflow rate $\dot{M}$$_{out}$ $=$ 0.78 $\pm$ 0.03 M$_{\odot}$ yr$^{-1}$. This work points out the necessity of exploiting high-resolution IFS data to understand the multi-phase components of the ISM and the multiple kinematical components in the central regions of nearby galaxies.

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arXiv2018

Implementation of a single-shot receiver for quaternary phase-shift keyed coherent states

We experimentally investigate a strategy to discriminate between quaternary phase-shift keyed coherent states based on single-shot measurements that is compatible with high-bandwidth communications. We extend previous theoretical work in single-shot measurements to include critical experimental parameters affecting the performance of practical implementations. Specifically, we investigate how the visibility of the optical displacement operations required in the strategy impacts the achievable discrimination error probability, and identify the experimental requirements to outperform an ideal heterodyne measurement. Our experimental implementation is optimized based on the experimental parameters and allows for the investigation of realistic single-shot measurements for multistate discrimination.

quant-ph↗

arXiv2017

GTC Observations of an Overdense Region of LAEs at z=6.5

We present the results of our search for the faint galaxies near the end of the Reionisation Epoch. This has been done using very deep OSIRIS images obtained at the Gran Telescopio Canarias (GTC). Our observations focus around two close, massive Lyman Alpha Emitters (LAEs) at redshift 6.5, discovered in the SXDS field within a large-scale overdense region (Ouchi et al. 2010). The total GTC observing time in three medium band filters (F883w35, F913w25 and F941w33) is over 34 hours covering $7.0\times8.5$ arcmin$^2$ (or $\sim30,000$ Mpc$^3$ at $z=6.5$). In addition to the two spectroscopically confirmed LAEs in the field, we have identified 45 other LAE candidates. The preliminary luminosity function derived from our observations, assuming a spectroscopic confirmation success rate of $\frac{2}{3}$ as in previous surveys, suggests this area is about 2 times denser than the general field galaxy population at $z=6.5$. If confirmed spectroscopically, our results will imply the discovery of one of the earliest protoclusters in the universe, which will evolve to resemble the most massive galaxy clusters today.

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