In many astronomical problems one often needs to determine the upper and/or lower boundary of a given data set. An automatic and objective approach consists in fitting the data using a generalized ...least-squares method, where the function to be minimized is defined to handle asymmetrically the data at both sides of the boundary. In order to minimize the cost function, a numerical approach, based on the popular downhill simplex method, is employed. The procedure is valid for any numerically computable function. Simple polynomials provide good boundaries in common situations. For data exhibiting a complex behaviour, the use of adaptive splines gives excellent results. Since the described method is sensitive to extreme data points, the simultaneous introduction of error weighting and the flexibility of allowing some points to fall outside of the fitted frontier, supplies the parameters that help to tune the boundary fitting depending on the nature of the considered problem. Two simple examples are presented, namely the estimation of spectra pseudo-continuum and the segregation of scattered data into ranges. The normalization of the data ranges prior to the fitting computation typically reduces both the numerical errors and the number of iterations required during the iterative minimization procedure.
A new stellar library developed for stellar population synthesis modelling is presented. The library consists of 985 stars spanning a large range in atmospheric parameters. The spectra were obtained ...at the 2.5-m Isaac Newton Telescope and cover the range λλ 3525–7500 Å at 2.3 Å (full width at half-maximum) spectral resolution. The spectral resolution, spectral-type coverage, flux-calibration accuracy and number of stars represent a substantial improvement over previous libraries used in population-synthesis models.
We present synthetic spectral energy distributions (SEDs) for single-age, single-metallicity stellar populations (SSPs) covering the full optical spectral range at moderately high resolution full ...width at half-maximum (FWHM) = 2.3 Å. These SEDs constitute our base models, as they combine scaled-solar isochrones with an empirical stellar spectral library Medium resolution INT Library of Empirical Spectra (MILES), which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients, not just on the stellar spectra, but also on extensive photometric libraries, which are used to determine the transformations from the theoretical parameters of the isochrones to observational quantities. The unprecedented stellar parameter coverage of the MILES stellar library allowed us to safely extend our optical SSP SED predictions from intermediate- to very-old-age regimes and the metallicity coverage of the SSPs from super-solar to M/H=−2.3. SSPs with such low metallicities are particularly useful for globular cluster studies. We have computed SSP SEDs for a suite of initial mass function shapes and slopes. We provide a quantitative analysis of the dependence of the synthesized SSP SEDs on the (in)complete coverage of the stellar parameter space in the input library that not only shows that our models are of higher quality than those of other works, but also in which range of SSP parameters our models are reliable. The SSP SEDs are a useful tool to perform the analysis of stellar populations in a very flexible manner. Observed spectra can be studied by means of full spectrum fitting or by using line indices. For the latter, we propose a new line index system to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. Apart from constant resolution as a function of wavelength, the system is also based on flux-calibrated spectra. Data can be analysed at three different resolutions: 5, 8.4 and 14 Å (FWHM), which are appropriate for studying globular cluster, low- and intermediate-mass galaxies, and massive galaxies, respectively. Furthermore, we provide polynomials to transform current Lick/IDS line index measurements to the new system. We provide line index tables in the new system for various popular samples of Galactic globular clusters and galaxies. We apply the models to various stellar clusters and galaxies with high-quality spectra, for which independent studies are available, obtaining excellent results. Finally, we designed a web page from which not only these models and stellar libraries can be downloaded but which also provides a suite of on-line tools to facilitate the handling and transformation of the spectra.
We probe the merging channel of massive galaxies over the z = 0.3–1.3 redshift window by studying close pairs in a sample of 238 galaxies with stellar mass ≳1011 M⊙, from the SHARDS (Survey for ...High-z Absorption Red and Dead Sources) survey. SHARDS provides medium-band photometry equivalent to low-resolution optical spectra (R ∼ 50), allowing us to obtain extremely accurate photometric redshifts (median |Δz|/(1 + z) ∼ 0.55 per cent) and to improve the constraints on the age distribution of the stellar populations. Our data set is volume limited, probing merger progenitors with mass ratios 1:100 (μ ≡ M
sat/M
cen = 0.01) out to z = 1.3. A strong correlation is found between the age difference of host and companion galaxy and stellar mass ratio, from negligible age differences in major mergers to age differences ∼4 Gyr for 1:100 minor mergers. However, this correlation is simply a reflection of the mass–age trend in the general population. The dominant contributor to the growth of massive galaxies corresponds to mass ratios μ ≳ 0.3, followed by a decrease in the fractional mass growth rate linearly proportional to log μ, at least down to μ ∼ 0.01, suggesting a decreasing role of mergers involving low-mass companions, especially if dynamical friction time-scales are taken into account. A simple model results in an upper limit for the average mass growth rate of massive galaxies of (ΔM/M)/Δt ∼ 0.08 ± 0.02 Gyr−1, over the z ≲ 1 range, with an ∼70 per cent fractional contribution from (major) mergers with μ ≳ 0.3. The majority of the stellar mass contributed by mergers does not introduce significantly younger populations, in agreement with the small radial age gradients observed in present-day early-type galaxies.
ABSTRACT
We present the first release of the Calar Alto CAFOS direct imaging data, a project led by the Spanish Virtual Observatory with the goal of enhancing the use of the Calar Alto archive by the ...astrophysics community. Data Release 1 contains 23 903 reduced and astrometrically calibrated images taken from 2008 March to 2019 July with a median of the mean uncertainties in the astrometric calibration of 0.04 arcsec. The catalogue associated to 6132 images in the Sloan griz filters provides accurate astrometry and PSF calibrated photometry for 139 337 point-like detections corresponding to 21 985 different sources extracted from a selection of 2338 good-quality images. The mean internal astrometric and photometric accuracies are 0.05 arcsec and 0.04 mag, respectively. In this work we describe the approach followed to process and calibrate the images, and the construction of the associated catalogue, together with the validation quality tests carried out. Finally, we present three cases to prove the science capabilities of the catalogue: discovery and identification of asteroids, identification of potential transients, and identification of cool and ultracool dwarfs.
ABSTRACT
We present our analysis of high-resolution (R ∼ 20 000) GTC/MEGARA integral-field unit spectroscopic observations, obtained during the commissioning run, in the inner region (12.5 arcsec × ...11.3 arcsec) of the active galaxy NGC 7469, at spatial scales of 0.62 arcsec. We explore the kinematics, dynamics, ionization mechanisms, and oxygen abundances of the ionized gas, by modelling the H α-N ii emission lines at high signal-to-noise (> 15) with multiple Gaussian components. MEGARA observations reveal, for the first time for NGC 7469, the presence of a very thin (20 pc) ionized 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 corotate with similar peak-to-peak velocities (163 versus 137 km s−1), but with different average velocity dispersion (38 ± 1 versus 108 ± 4 km s−1). 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−1) 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 N ii/H α ratios point to the star-formation as the dominant mechanism of ionization, being consistent with ionization from shocks in the case of the intermediate component. All components have roughly solar metallicity. In the nuclear region of NGC 7469, at r ≤ 1.85 arcsec, a very broad (FWHM = 2590 km s−1) H α component is contributing (41 per cent) to the global H α-N ii profile, being originated in the (unresolved) broad line region of the Seyfert 1.5 nucleus of NGC 7469.
ABSTRACT
We present a spatially resolved spectroscopic study for the metal poor H ii 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 ± 0.06, and integrated electron density and temperature of ∼161 cm−3 and ∼15400 K, respectively. The metallicity distribution shows a large range of Δ(O/H) = 0.72 dex between the minimum and maximum (7.69 ± 0.06 and 8.42 ± 0.05) values, unusual in a dwarf star-forming galaxy. We derived an integrated log (N/O) ratio of −1.51 ± 0.05 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.
The optical spectroscopic classification of active galactic nuclei (AGN) into type 1 and type 2 can be understood in the frame of the AGN unification models. However, it remains unclear which ...physical properties are driving the classification into intermediate sub-types (1.0, 1.2, 1.5, 1.8, 1.9). To shed light on this issue, we present an analysis of the effect of extinction and AGN and host galaxy luminosities on sub-type determination for a sample of 159 X-ray selected AGN with a complete and robust optical spectroscopic classification. The sample spans a rest-frame 2–10 keV X-ray luminosity range of 10 42 –10 46 erg s −1 and redshifts between 0.05 and 0.75. From the fitting of their ultraviolet-to-mid-infrared spectral energy distributions, we extracted the observed AGN over total AGN+galaxy contrast, optical/ultraviolet line-of-sight extinction, as well as host galaxy and AGN luminosities. The observed contrast exhibits a clear decline with sub-type, distinguishing two main groups: 1.0–5 and 1.8–2. This difference is partly driven by an increase in extinction following the same trend. Nevertheless, 50% of 1.9s and 2s lack sufficient extinction to explain the lack of detection of broad emission lines, unveiling the necessity of an additional effect. Our findings show that 1.8–2s preferentially live in host galaxies with higher luminosities while displaying similar intrinsic AGN luminosities to 1.0–5s. Consequently, the AGN to host galaxy luminosity ratio diminishes, hindering the detection of the emission of the broad emission lines, resulting in the 1.8–2 classification of those with insufficient extinction. Thus, the combination of increasing extinction and decreasing AGN over galaxy luminosity ratio, mainly driven by an increasing host galaxy luminosity, constitutes the main reasons behind the sub-type classification into 1.0–5 and 1.8–2.
One of the major challenges in studying the cosmic evolution of relativistic jets is the identification of the high-redshift (z > 3) BL Lacertae objects (BL Lacs), a class of jetted active galactic ...nuclei characterized by their quasi-featureless optical spectra. Here we report the identification of the first γ-ray emitting BL Lac, 4FGL J1219.0+3653 (J1219), beyond z = 3, i.e., within the first two billion years of the age of the universe. The optical and near-infrared spectra of J1219 taken from 10.4 m Gran Telescopio Canarias exhibit no emission lines down to an equivalent width of ∼3.5 supporting its BL Lac nature. The detection of a strong Ly break at ∼5570 , on the other hand, confirms that J2119 is indeed a high-redshift (z ∼ 3.59) quasar. Based on the prediction of a recent BL Lac evolution model, J1219 is one of the only two such objects expected to be present within the comoving volume at z = 3.5. Future identifications of more z > 3 γ-ray emitting BL Lac sources, therefore, will be crucial to verify the theories of their cosmic evolution.
ABSTRACT
MEGARA (Multi Espectrógrafo en Gran Telescopio Canarias de Alta Resolución para Astronomía) 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, $R=20\, 000$ (full width at half-maximum), available in two wavelength ranges: one centred on Hα, from 6420 to 6790 Å; and the other centred on the Ca ii triplet, from 8370 to 8885 Å (HR-R and HR-I volume phase holographic (VPH)-grating configurations). In this work, we use MEGASTAR spectra, a combination of these two short wavelength intervals, to estimate the stellar parameters, namely the effective temperature, surface gravity, and metallicity (and their associated errors), for a sample of 351 MEGASTAR members with spectral types earlier than B2. We applied a χ2-technique by comparing MEGASTAR data with theoretical stellar models. For those stars with stellar parameters derived in the literature, we obtained a good agreement between the published parameters and ours. In addition to the stellar parameters, we also provide several products, such as the rectified spectra, radial velocities, and stellar indices, for this sample of stars. In the 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 cluster and galactic spectra obtained with MEGARA.
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