Sánchez Blázquez, Patricia

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First Name
Last Name
Sánchez Blázquez
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Física de la Tierra y Astrofísica
Astronomía y Astrofísica
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Now showing 1 - 10 of 14
  • Publication
    Differences in carbon and nitrogen abundances between field and cluster early-type galaxies
    (IOP Publishing, 2003-06-20) Sánchez Blázquez, Patricia; Gorgas García, Francisco Javier; Cardiel López, Nicolás; Cenarro, J.; González, J. J.
    Central line-strength indices were measured in the blue spectral region for a sample of 98 early-type galaxies in different environments. For most indices (Mg b and [Fe] in particular), elliptical galaxies in rich clusters and in low-density regions follow the same index-sigma relations. However, striking spectral differences between field elliptical galaxies and their counterparts in the central region of the Coma Cluster are found for the first time, with galaxies in the denser environment showing significantly lower C4668 and CN2 absorption strengths. The most convincing interpretation of these results is that they represent a difference in abundance ratios arising from distinct star formation and chemical-enrichment histories of galaxies in different environments. A scenario in which elliptical galaxies in clusters are fully assembled at earlier stages than their low-density counterparts is discussed.
  • Publication
    Optical spectroscopic characterization of Fermi blazar candidates of uncertain type with TNG and DOT: first results
    (Oxford University Press., 2022-09-30) Olmo García, Amanda; Paliya, Vaidehi S.; Álvarez Crespo, Nuria; Kumar, Brajesh; Domínguez Díaz, Alberto; Gil de Paz, Armando; Sánchez Blázquez, Patricia
    The classification of gamma-ray-detected blazar candidates of uncertain type (BCU) is a relevant problem in extragalactic gamma-ray astronomy. Here we report the optical spectroscopic characterization, using two 3-4 m class telescopes, Telescopio Nazionale Galileo and Devasthal Optical Telescope, of 27 BCUs detected with the Fermi Large Area Telescope. Since the identification of emission lines is easier in broad-line blazars, which usually exhibit low frequency peaked (synchrotron peak frequency 1 and the farthest one is at z=2.55. The optical spectra of 2 of the 19 remaining objects are dominated by the absorption spectra of the host galaxy, and there is a tentative detection of the Lyman-alfa absorption feature in one source. The spectra of the remaining 16 objetcts, on the other hand, are found to be featureless.
  • Publication
    PHANGS-JWST first results: a combined HST and JWST analysis of the nuclear star cluster in NGC 628
    (IOP Publishing, 2023-02-01) Sánchez Blázquez, Patricia; otros, ...
    We combine archival Hubble Space Telescope and new James Webb Space Telescope imaging data covering the ultraviolet to mid-infrared regime to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a granddesign spiral galaxy. The cluster is located in a 200 pc × 400 pc cavity lacking both dust and gas. We find roughly constant values for the effective radius (r_(eff) ∼ 5 pc) and ellipticity (∈ ∼ 0.05), while the Sérsic index (n) and position angle (PA) drop from n ∼ 3 to ∼2 and PA ∼ 130° to 90°, respectively. In the mid-infrared, r_(eff) ∼ 12 pc, ∈ ∼ 0.4, and n ∼ 1–1.5, with the same PA ∼ 90°. The NSC has a stellar mass of log_(10) (M^(nsc)_(*) / M_(ꙩ) = 7.06  0.31, as derived through B − V, confirmed when using multiwavelength data, and in agreement with the literature value. Fitting the spectral energy distribution (SED), excluding the mid-infrared data, yields a main stellar population age of (8 ± 3) Gyr with a metallicity of Z = 0.012 ± 0.006. There is no indication of any significant star formation over the last few gigayears. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.
  • Publication
    Stellar populations of early-type galaxies in different environments - III. Line-strength gradients
    (EDP Sciencies, 2006-10) Sánchez Blázquez, Patricia; Gorgas García, Francisco Javier; Cardiel López, Nicolás
    Aims. This is the third paper of a series devoted to the study of the stellar content of early-type galaxies. The goal of the series is to set constraints on the evolutionary status of these objects. Methods. We present line-strength gradients for 22 spectral indices measured in a sample of 82 early-type galaxies in different environments, including the high-density cores of the Coma cluster, the Virgo cluster, poor groups, and isolated field galaxies. Using new evolutionary population synthesis models, we derive age and metallicity gradients, and compare the mean values with the predictions of different galaxy formation models. We explore the behaviour of individual chemical species by deriving the metallicity gradient with different indicators. Results. We find that the strength of the metallicity gradient inferred from stellar population models depends on the specific Lick index employed. In particular, metallicity gradients obtained with CN2 and C4668 combined with H beta are steeper than those measured using Ca4227 or Fe4383. The correlation of the metallicity gradients with other parameters also depends on the specific index employed. If the metallicity gradient is obtained using CN2 and Mgb, then it correlates with the central age of the galaxies. On the contrary, if Fe4383 or Ca4227 is used, the metallicity gradient correlates with the velocity dispersion gradient. Conclusions. This may suggest that several mechanisms have helped to set the age and metallicity gradients in early-type galaxies. While we do not find any correlation between the metallicity gradient and the central velocity dispersion for galaxies in low-density environments, we find a marginal correlation between the metallicity gradient and the mass for galaxies in the centre of the Coma cluster. We also find a trend for which galaxies in denser environments show a steeper metallicity gradient than galaxies in less dense environments. We interpret these results in light of the different mechanisms proposed to explain the observed changes between galaxies as a function of environment.
  • Publication
    Gaseous-phase metallicities and stellar populations in the centres of barred galaxies
    (Wiley, 2014-08-11) Cacho, R.; Sánchez Blázquez, Patricia; Gorgas García, Francisco Javier; Pérez, I.
    Numerical simulations predict that bars represent a very important agent for triggering gas inflows, which in turn could lead to central star formation. Bars thus are thought to contribute to the formation of the bulge. This process changes both the gaseous-phase and the stellar-phase metallicities in the centres of galaxies. With the aim of quantifying the importance of this process, we present a comparative study of the gaseous-phase and stellar-phase metallicities in the centres of members of a sample of barred and unbarred galaxies from SDSS. We do not find a significant difference in the metallicity (neither gaseous nor stellar) between barred and unbarred galaxies, but we find different trends in the metallicities of early- and late-type galaxies, with larger differences in the metallicity in the early-type subsample. Our results contradict some previous research in this field, but we find a possible origin of the discrepancies between previous works and our results.
  • Publication
    Improving star cluster age estimates in PHANGS-HST galaxies and the impact on cluster demographics in NGC 628
    (Oxford University Press., 2023-01-28) Sánchez Blázquez, Patricia; otros, ...
    A long-standing problem when deriving the physical properties of stellar populations is the degeneracy between age, reddening, and metallicity. When a single metallicity is used for all the star clusters in a galaxy, this degeneracy can result in 'catastrophic' errors for old globular clusters. Typically, approximately 10-20 per cent of all clusters detected in spiral galaxies can have ages that are incorrect by a factor of 10 or more. In this paper, we present a pilot study for four galaxies (NGC 628, NGC 1433, NGC 1365, and NGC 3351) from the PHANGS-HST survey. We describe methods to correct the age-dating for old globular clusters, by first identifying candidates using their colours, and then reassigning ages and reddening based on a lower metallicity solution. We find that young 'Interlopers' can be identified from their H alpha flux. CO (2-1) intensity or the presence of dust can also be used, but our tests show that they do not work as well. Improvements in the success fraction are possible at the approximate to 15 per cent level (reducing the fraction of catastrophic age-estimates from between 13 and 21 per cent, to between 3 and 8 per cent). A large fraction of the incorrectly age-dated globular clusters are systematically given ages around 100 Myr, polluting the younger populations as well. Incorrectly age-dated globular clusters significantly impact the observed cluster age distribution in NGC 628, which affects the physical interpretation of cluster disruption in this galaxy. For NGC 1365, we also demonstrate how to fix a second major age-dating problem, where very dusty young clusters with E(B - V) > 1.5 mag are assigned old, globular-cluster like ages. Finally, we note the discovery of a dense population of approximate to 300 Myr clusters around the central region of NGC 1365 and discuss how this results naturally from the dynamics in a barred galaxy.
  • Publication
    Variations in the Σ_(SFR)−Σ_(mol)−Σ_(*) plane across galactic environments in PHANGS galaxies
    (EDP Sciencies, 2022-07-12) Sánchez Blázquez, Patricia; otros, ...
    Aims. There exists some consensus that the stellar mass surface density (Σ_(*)) and molecular gas mass surface density (Σ_(mol)) are the main quantities responsible for locally setting the star formation rate. This regulation is inferred from locally resolved scaling relations between these two quantities and the star formation rate surface density (Σ_(SFR)), which have been extensively studied in a wide variety of works. However, the universality of these relations is debated. Here, we probe the interplay between these three quantities across different galactic environments at a spatial resolution of 150 pc. Methods. We performed a hierarchical Bayesian linear regression to find the best set of parameters C_(*), C_(mol), and C_(norm) that describe the starforming plane conformed by Σ_(*), Σ_(mol), and Σ_(SFR), such that log Σ_(SFR) = C_(*) log Σ(*) + C_(mol) log Σ_(mol) + C_(norm). We also explored variations in the determined parameters across galactic environments, focusing our analysis on the C_(*) and C_(mol) slopes. Results. We find signs of variations in the posterior distributions of C(*) and C_(mol) across different galactic environments. The dependence of Σ_(SFR) on Σ_(*) spans a wide range of slopes, with negative and positive values, while the dependence of Σ_(SFR) on Σ_(mol) is always positive. Bars show the most negative value of C_(*) (−0.41), which is a sign of longer depletion times, while spiral arms show the highest C_(*) among all environments (0.45). Variations in C_(mol) also exist, although they are more subtle than those found for C_(*). Conclusions. We conclude that systematic variations in the interplay of Σ_(*), Σ_(mol), and Σ_(SFR) across different galactic environments exist at a spatial resolution of 150 pc, and we interpret these variations to be produced by an additional mechanism regulating the formation of stars that is not captured by either Σ_(*) or Σ_(mol). Studying environmental variations in single galaxies, we find that these variations correlate with changes in the star formation efficiency across environments, which could be linked to the dynamical state of the gas that prevents it from collapsing and forming stars, or to changes in the molecular gas fraction.
  • Publication
    Early-type galaxies in the Coma Cluster: A new piece in the calcium puzzle
    (IOP Publishing, 2004-10-20) Cenarro, A. J.; Sánchez Blázquez, Patricia; Cardiel López, Nicolás; Gorgas García, Francisco Javier
    We present measurements of the Ca II triplet and the Ca4227 Lick index for a sample of early-type galaxies in the Coma Cluster, deriving, for the first time, their corresponding relationships with velocity dispersion. Compared with a similar subsample of elliptical galaxies in the field, Coma galaxies with velocity dispersions in the range approximate to180-270 km s(-1) exhibit significant differences in the strengths of the Ca features, suggesting an influence of the environment on the star formation histories of these galaxies. We argue that the main scenarios previously proposed to explain the relatively low Ca II triplet of galaxies are not able by themselves to simultaneously reconcile the strengths of the two Ca indices in both environments.
  • Publication
    Optically faint massive Balmer break galaxies at z > 3 in the CANDELS/GOODS fields
    (IOP Publishing LTD, 2019-05-10) Alcalde Pampliega, Belén; Pérez González, Pablo Guillermo; Barro, Guillermo; Domínguez Sánchez, Helena; Eliche Moral, M. Carmen; Cardiel López, Nicolás; Hernán Caballero, Antonio; Rodríguez Muñoz, Lucía; Sánchez Blázquez, Patricia; Esquej, Pilar
    We present a sample of 33 Balmer break galaxies (BBGs) selected as Hubble Space Telescope/F160W dropouts in the deepest CANDELS/GOODS fields (H >/~ 27.3 mag) but relatively bright in Spitzer/IRAC ([3.6], [4.5] < 24.5 mag), implying red colors (median and quartiles: {H - [3.6]} = 3.1^(3.4)_(2.8) mag ). Half of these BBGs are newly identified sources. Our BBGs are massive ({ log (M/ M_(☉))} = 10.8_(10.4)^( 11.0)), high-redshift ({z} = 4.8_(4.4)^(5.1)), dusty ({A(V)} = 2.0_(1.5)^(2.0) mag) galaxies. The spectral energy distributions (SEDs) of half of our sample indicate that they are star-forming galaxies with typical specific star formation rates (SFRs) of 0.5–1.0 Gyr^(−1), qualifying them as main-sequence (MS) galaxies at 3 < z < 6. One-third of these SEDs indicate the presence of prominent emission lines (Hβ + [O III], Hα + [N II]) boosting the IRAC fluxes and red colors. Approximately 20% of the BBGs are very dusty (A (V) ∼ 2.5 mag) starbursts with strong mid-to-far-infrared detections and extreme SFRs (SFR > 10^(3) M_(☉) yr^(−1)) that place them above the MS. The rest, 30%, are post-starbursts or quiescent galaxies located >2σ below the MS with mass-weighted ages older than 700 Myr. Only two of the 33 galaxies are X-ray-detected active galactic nuclei (AGNs) with optical/near-infrared SEDs dominated by stellar emission, but the presence of obscured AGNs in the rest of the sources cannot be discarded. Our sample accounts for 8% of the total number density of log(M / M_(☉)) > 10 galaxies at z > 3, but it is a significant contributor (30%) to the general population of red log(M / M_(☉) > 11 galaxies at 4 < z < 6. Finally, our results point out that one of every 30 massive log (M / M_(☉) > 11 galaxies in the local universe was assembled in the first 1.5 Gyr after the big bang, a fraction that is not reproduced by state-of-the-art galaxy formation simulations.
  • Publication
    Medium-resolution Isaac Newton Telescope library of empirical spectra
    (Wiley, 2006-09-11) Sánchez Blázquez, Patricia; Peletier, R. F.; Jiménez Vicente, J.; Cardiel López, Nicolás; Cenarro, A. J.; Falcón Barroso, J.; Gorgas García, Francisco Javier; Selam, S.; Vazdekis, A.
    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.