arXiv subjects

J. I. Gonzalez-Serrano

Publications and source records attributed to J. I. Gonzalez-Serrano.

At least 19 recordsLinked to original sources

arXiv2017

A multi-wavelength continuum characterization of high-redshift broad absorption line quasars

We present the results of a multi-wavelength study of a sample of high-redshift Radio Loud (RL) Broad Absorption Line (BAL) quasars. This way we extend to higher redshift previous studies on the radio properties, and broadband optical colors of these objects. We have se- lected a sample of 22 RL BAL quasars with 3.6 z 4.8 cross-correlating the FIRST radio survey with the SDSS. Flux densities between 1.25 and 9.5 GHz have been collected with the JVLA and Effelsberg-100m telescopes for 15 BAL and 14 non-BAL quasars used as compar- ison sample. We determine the synchrotron peak frequency, constraining their age. A large number of GigaHertz Peaked Spectrum (GPS) and High Frequency Peakers (HFP) sources has been found in both samples (80% for BAL and 71% for non-BAL QSOs), not suggesting a younger age for BAL quasars. The spectral index distribution provides information about the orientation of these sources, and we find statistically similar distributions for the BAL and non-BAL quasars in contrast to work done on lower redshift samples. Our sample may be too small to convincingly find the same effect, or might represent a real evolutionary effect based on the large fraction of young sources. We also study the properties of broadband colors in both optical (SDSS) and near- and mid-infrared (UKIDSS and WISE) bands, finding that also at high redshift BAL quasars tend to be optically redder than non-BAL quasars. However, these differences are no more evident at longer wavelength, when comparing colors of the two samples by mean of the WISE survey.

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arXiv2015

The Spanish Square Kilometre Array White Book

The Square Kilometre Array (SKA) is called to revolutionise essentially all areas of Astrophysics. With a collecting area of about a square kilometre, the SKA will be a transformational instrument, and its scientific potential will go beyond the interests of astronomers. Its technological challenges and huge cost requires a multinational effort, and Europe has recognised this by putting the SKA on the roadmap of the European Strategy Forum for Research Infrastructures (ESFRI). The Spanish SKA White Book is the result of the coordinated effort of 120 astronomers from 40 different research centers. The book shows the enormous scientific interest of the Spanish astronomical community in the SKA and warrants an optimum scientific exploitation of the SKA by Spanish researchers, if Spain enters the SKA project.

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arXiv2015

Neural-network selection of high-redshift radio quasars, and the luminosity function at z~4

We obtain a sample of 87 radio-loud QSOs in the redshift range 3.6 1 mJy with star-like objects having r <20.2 in SDSS Data Release 7. Of these 87 QSOs, 80 are spectroscopically classified in previous work (mainly SDSS), and form the training set for a search for additional such sources. We apply our selection to 2,916 FIRST-DR7 pairs and find 15 likely candidates. Seven of these are confirmed as high-redshift quasars, bringing the total to 87. The candidates were selected using a neural-network, which yields 97% completeness (fraction of actual high-z QSOs selected as such) and an efficiency (fraction of candidates which are high-z QSOs) in the range of 47 to 60%. We use this sample to estimate the binned optical luminosity function of radio-loud QSOs at $z\sim 4$, and also the LF of the total QSO population and its comoving density. Our results suggest that the radio-loud fraction (RLF) at high z is similar to that at low-z and that other authors may be underestimating the fraction at high-z. Finally, we determine the slope of the optical luminosity function and obtain results consistent with previous studies of radio-loud QSOs and of the whole population of QSOs. The evolution of the luminosity function with redshift was for many years interpreted as a flattening of the bright end slope, but has recently been re-interpreted as strong evolution of the break luminosity for high-z QSOs, and our results, for the radio-loud population, are consistent with this.

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arXiv2014

General Formulation for the Calibration and Characterization of Narrow-gap Etalons: the OSIRIS/GTC Tunable Filters Case

Tunable filters are a powerful way of implementing narrow-band imaging mode over wide wavelength ranges, without the need of purchasing a large number of narrow-band filters covering all strong emission or absorption lines at any redshift. However, one of its main features is a wavelength variation across the field of view, sometimes termed the phase effect. In this work, an anomalous phase effect is reported and characterized for the OSIRIS instrument at the 10.4m Gran Telescopio Canarias. The transmitted wavelength across the field of view of the instrument depends, not only on the distance to the optical centre, but on wavelength. This effect is calibrated for the red tunable filter of OSIRIS by measuring both normal-incidence light at laboratory and spectral lamps at the telescope at non-normal incidence. This effect can be explained by taking into account the inner coatings of the etalon. In a high spectral resolution etalon, the gap between plates is much larger than the thickness of the inner reflective coatings. In the case of a tunable filter, like that in OSIRIS, the coatings thickness could be of the order of the cavity, which changes drastically the effective gap of the etalon. We show that by including thick and dispersive coatings into the interference equations, the observed anomalous phase effect can be perfectly reproduced. In fact, we find that, for the OSIRIS red TF, a two-coatings model fits the data with a rms of 0.5Å at all wavelengths and incidence angles. This is a general physical model that can be applied to other tunable-filter instruments.

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arXiv2014

J-PAS: The Javalambre-Physics of the Accelerated Universe Astrophysical Survey

The Javalambre-Physics of the Accelerated Universe Astrophysical Survey (J-PAS) is a narrow band, very wide field Cosmological Survey to be carried out from the Javalambre Observatory in Spain with a purpose-built, dedicated 2.5m telescope and a 4.7 sq.deg. camera with 1.2Gpix. Starting in late 2015, J-PAS will observe 8500sq.deg. of Northern Sky and measure $0.003(1+z)$ photo-z for $9\times10^7$ LRG and ELG galaxies plus several million QSOs, sampling an effective volume of $\sim 14$ Gpc$^3$ up to $z=1.3$ and becoming the first radial BAO experiment to reach Stage IV. J-PAS will detect $7\times 10^5$ galaxy clusters and groups, setting constrains on Dark Energy which rival those obtained from its BAO measurements. Thanks to the superb characteristics of the site (seeing ~0.7 arcsec), J-PAS is expected to obtain a deep, sub-arcsec image of the Northern sky, which combined with its unique photo-z precision will produce one of the most powerful cosmological lensing surveys before the arrival of Euclid. J-PAS unprecedented spectral time domain information will enable a self-contained SN survey that, without the need for external spectroscopic follow-up, will detect, classify and measure $σ_z\sim 0.5\%$ redshifts for $\sim 4000$ SNeIa and $\sim 900$ core-collapse SNe. The key to the J-PAS potential is its innovative approach: a contiguous system of 54 filters with $145Å$ width, placed $100Å$ apart over a multi-degree FoV is a powerful "redshift machine", with the survey speed of a 4000 multiplexing low resolution spectrograph, but many times cheaper and much faster to build. The J-PAS camera is equivalent to a 4.7 sq.deg. "IFU" and it will produce a time-resolved, 3D image of the Northern Sky with a very wide range of Astrophysical applications in Galaxy Evolution, the nearby Universe and the study of resolved stellar populations.

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arXiv2013

The environments of luminous radio galaxies and type-2 quasars

We present the results of a comparison between the environments of 1) a complete sample of 46 southern 2Jy radio galaxies at intermediate redshifts (0.05 < z < 0.7), 2) a complete sample of 20 radio-quiet type-2 quasars (0.3 < z < 0.41), and 3) a control sample of 107 quiescent early-type galaxies at 0.2 < z < 0.7 in the Extended Groth Strip (EGS). The environments have been quantified using angular clustering amplitudes (Bgq) derived from deep optical imaging data. Based on these comparisons, we discuss the role of the environment in the triggering of powerful radio-loud and radio-quiet quasars. When we compare the Bgq distributions of the type-2 quasars and quiescent early-type galaxies, we find no significant difference between them. This is consistent with the radio-quiet quasar phase being a short-lived but ubiquitous stage in the formation of all massive early-type galaxies. On the other hand, PRGs are in denser environments than the quiescent population, and this difference between distributions of Bgq is significant at the 3 sigma level. This result supports a physical origin of radio loudness, with high density gas environments favouring the transformation of AGN power into radio luminosity, or alternatively, affecting the properties of the supermassive black holes themselves. Finally, focussing on the radio-loud sources only, we find that the clustering of weak-line radio galaxies (WLRGs) is higher than the strong-line radio galaxies (SLRGs), constituting a 3 sigma result. 82% of the 2Jy WLRGs are in clusters, according to our definition (Bgq > 400) versus only 31% of the SLRGs.

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arXiv2012

SAFIR: testing the coexistence of AGN and star formation activity and the nature of the dusty torus in the local universe

We present the Seyfert and star formation Activity in the Far-InfraRed (SAFIR) project, a small (15.1h) Herschel guaranteed time proposal performing PACS and SPIRE imaging of a small sample of nearby Seyfert galaxies. This project is aimed at studying the physical nature of the nuclear IR emission by means of multi-component spectral energy distribution (SED) fitting and the star formation properties of AGN hosts, as traced by cold dust. We summarize the results achieved so far and outline the on-going work.

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arXiv2012

Status of the OTELO Project

The OTELO project is the extragalactic survey currently under way using the tunable filters of the OSIRIS instrument at the GTC. OTELO is already providing the deepest emission line object survey of the universe up to a redshift 7. In this contribution, the status of the survey and the first results obtained are presented.

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arXiv2012

Probing the Nuclear and Circumnuclear Activity of NGC1365 in the Infrared

We present new far-infrared (70-500micron) Herschel PACS and SPIRE imaging observations as well as new mid-IR Gemini/T-ReCS imaging (8.7 and 18.3micron) and spectroscopy of the inner Lindblad resonance (ILR) region (R<2.5kpc) of the spiral galaxy NGC1365. We complemented these observations with archival Spitzer imaging and spectral mapping observations. The ILR region of NGC1365 contains a Seyfert 1.5 nucleus and a ring of star formation with an approximate diameter of 2kpc. The strong star formation activity in the ring is resolved by the Herschel/PACS imaging data, as well as by the Spitzer 24micron continuum emission, [NeII]12.81micron line emission, and 6.2 and 11.3micron PAH emission. The AGN is the brightest source in the central regions up to lambda~24micron, but it becomes increasingly fainter in the far-infrared when compared to the emission originating in the infrared clusters (or groups of them) located in the ring. We modeled the AGN unresolved infrared emission with the CLUMPY torus models and estimated that the AGN contributes only to a small fraction (~5%) of the infrared emission produced in the inner ~5kpc. We fitted the non-AGN 24-500micron spectral energy distribution of the ILR region and found that the dust temperatures and mass are similar to those of other nuclear and circumnuclear starburst regions. Finally we showed that within the ILR region of NGC1365 most of the on-going star formation activity is taking place in dusty regions as probed by the 24micron emission.

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arXiv2011

Resolving the nuclear dust distribution of the Seyfert 2 galaxy NGC 3081

We report far-infrared (FIR) imaging of the Seyfert 2 galaxy NGC 3081 in the range 70-500 micron, obtained with an unprecedented angular resolution, using the Herschel Space Observatory instruments PACS and SPIRE. The 11 kpc (~70 arcsec) diameter star-forming ring of the galaxy appears resolved up to 250 micron. We extracted infrared (1.6-500 micron) nuclear fluxes, that is active nucleus-dominated fluxes, and fitted them with clumpy torus models, which successfully reproduce the FIR emission with small torus sizes. Adding the FIR data to the near- and mid-infrared spectral energy distribution (SED) results in a torus radial extent of Ro=4(+2/-1) pc, as well as in a flat radial distribution of the clouds (i.e. the q parameter). At wavelengths beyond 200 micron, cold dust emission at T=28+/-1 K from the circumnuclear star-forming ring of 2.3 kpc (~15 arcsec) in diameter starts making a contribution to the nuclear emission. The dust in the outer parts of the galaxy is heated by the interstellar radiation field (19+/-3 K).

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arXiv2008

Use of neural networks for the identification of new z>=3.6 QSOs from FIRST-SDSS DR5

We aim to obtain a complete sample of redshift > 3.6 radio QSOs from FIRST sources having star-like counterparts in the SDSS DR5 photometric survey (r<=20.2). We found that simple supervised neural networks, trained on sources with SDSS spectra, and using optical photometry and radio data, are very effective for identifying high-z QSOs without spectra. The technique yields a completeness of 96 per cent and an efficiency of 62 per cent. Applying the trained networks to 4415 sources without DR5 spectra we found 58 z>=3.6 QSO candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z QSOs. Spectra of 13 additional candidates from the literature and from SDSS DR6 revealed 7 more z>=3.6 QSOs, giving and overall efficiency of 60 per cent. None of the non-candidates with spectra from NED or DR6 is a z>=3.6 QSO, consistently with a high completeness. The initial sample of z>=3.6 QSOs is increased from 52 to 76, i.e. by a factor 1.46. From the new identifications and candidates we estimate an incompleteness of SDSS for the spectroscopic classification of FIRST 3.6<=z<=4.6 QSOs of 15 percent for r<=20.2.

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arXiv2008

Radio spectra and polarisation properties of radio-loud Broad Absorption Line Quasars

We present multi-frequency observations of a sample of 15 radio-emitting Broad Absorption Line Quasars (BAL QSOs), covering a spectral range between 74 MHz and 43 GHz. They display mostly convex radio spectra which typically peak at about 1-5 GHz (in the observer's rest-frame), flatten at MHz frequencies, probably due to synchrotron self-absorption, and become steeper at high frequencies, i.e., >~ 20 GHz. VLA 22-GHz maps (HPBW ~ 80 mas) show unresolved or very compact sources, with linear projected sizes of <= 1 kpc. About 2/3 of the sample look unpolarised or weakly polarised at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarised intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non-BAL QSOs, both in the observed and the rest-frame, finding steeper spectra among non-BAL QSOs. However constraining this comparison to compact sources results in no significant differences between both distributions. This comparison is consistent with BAL QSOs not being oriented along a particular line of sight. In addition, our analysis of the spectral shape, variability and polarisation properties shows that radio BAL QSOs share several properties common to young radio sources like Compact Steep Spectrum (CSS) or Gigahertz-Peaked Spectrum (GPS) sources.

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arXiv2006

A FIRST-APM-SDSS survey for high-redshift radio QSOs

We selected from VLA-FIRST a sample of 94 objects starlike in SDSSS, and with APM colour O-E>2, i.e. consistent with their being high-z QSOs. 78 candidates were classified spectroscopically from published data (mainly SDSS) or observations reported here. The fractions of QSOs (51/78) and z > 3 QSOs (23/78) are comparable to those found in other photometric searches for high-z QSOs. We confirm that O-E>2 ensures inclusion of all QSOs with 3.7 < z < 4.4. The fraction of broad absorption line (BAL) QSOs for 2 < z < 4.4 is 27+-10 per cent (7/26), and the estimated BAL fraction for radio loud (RL) QSOs is at least as high as for optically selected QSOs (about 13 per cent). The high BAL fraction and the high fraction of LoBALs in our sample are likely due to the red colour selection. The space density of RL QSOs for 3.7 < z < 4.4, MAB (1450 A) < -26.6 and P(1.4 GHz) > 10^25.7 W Hz^(-1) is 1.7+-0.6 Gpc^(-3). Adopting a RL fraction 13.4+-3 per cent, this corresponds to rho = 12.5+-5.6 Gpc^(-3), in good agreement with the SDSS QSO luminosity function in Fan et al. (2001). We note the unusual QSO FIRST 1413+4505 (z=3.11), which shows strong associated Lyalpha absorption and an extreme observed luminosity, L about 2 x 10^(15) solar luminosities.

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arXiv2006

OSIRIS Software: The Mask Designer Tool

OSIRIS is a Day One instrument that will be available at the 10m GTC telescope which is being built at La Palma observatory in the Canary Islands. This optical instrument is designed to obtain wide-field narrow-band images using tunable filters and to do low-resolution spectroscopy in both long-slit and multislit modes. For the multislit spectroscopy mode, we have developed a software to assist the observers to design focal plane masks. In this paper we describe the characteristics of this Mask Designer tool. We discuss the main design concepts, the functionality and particular features of the software.

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arXiv2005

XMM-Newton and Deep Optical Observations of the OTELO fields: the Groth-Westphal Strip

OTELO (OSIRIS Tunable Emission Line Object Survey) will be carried out with the OSIRIS instrument at the 10 m GTC telescope at La Palma, and is aimed to be the deepest and richest survey of emission line objects to date. The deep narrow-band optical data from OSIRIS will be complemented by means of additional observations that include: (i) an exploratory broad-band survey that is already being carried out in the optical domain, (ii) FIR and sub-mm observations to be carried with the Herschel space telescope and the GTM, and (iii) deep X-Ray observations from XMM-Newton and Chandra.Here we present a preliminary analysis of public EPIC data of one of the OTELO targets,the Groth-Westphal strip, gathered from the XMM-Newton Science Archive (XSA). EPIC images are combined with optical BVRI data from our broadband survey carried out with the 4.2m WHT at La Palma. Distance-independent diagnostics (involving X/O ratio, hardness ratios, B/T ratio) are tested.

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arXiv2005

Unusual high-redshift radio BAL quasar 1624+3758

We present observations of the most radio-luminous BAL quasar known, 1624+3758, at redshift z = 3.377. The quasar has several unusual properties: (1) The FeII UV191 1787-A emission line is very prominent. (2) The BAL trough (BALnicity index 2990 km/s) is detached by 21000 km/s and extends to velocity v = -29000 km/s. There are additional intrinsic absorbers at -1900 and -2800 km/s. (3) The radio rotation measure of the quasar, 18350 rad/m^2, is the second-highest known. The radio luminosity is P(1.4GHz) = 4.3 x 10^27 W/Hz (H0 = 50 km/s/Mpc, q0 = 0.5), radio loudness R* = 260. The radio source is compact (<~ 2.8 kpc) and the radio spectrum is GHz-peaked, consistent with it being relatively young. The width of the CIV emission line, in conjunction with the total optical luminosity, implies black-hole mass ~ 10^9 M(sun), L/L(Eddington) ~ 2. The high Eddington ratio, and the radio-loudness, place this quasar in one corner of Boroson's (2002) 2-component scheme for the classification of AGN, implying a very high accretion rate, and this may account for some of the unusual observed properties. A complex mini-BAL absorber at v = -3000 km/s is detected in each of CIV, NV and OVI. The blue and red components of the CIV doublet happen to be unblended, allowing both the covering factor and optical depth to be determined as a function of velocity. Variation of covering factor with velocity dominates the form of the mini-BAL...

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arXiv2004

Integral Field Spectroscopy of the Central Regions of 3C 120: Evidence of a Past Merging Event

IFS combined with HST WFPC imaging were used to characterize the central regions of the Seyfert 1 radio galaxy 3C 120. We carried out the analysis of the data, deriving intensity maps of different emission lines and the continua at different wavelengths from the observed spectra. Applying a 2D modeling to the HST images we decoupled the nucleus and the host galaxy, and analyzed the host morphology. The host is a highly distorted bulge dominated galaxy, rich in substructures. We developed a new technique to model the IFS data extending the 2D modeling. Using this technique we separated the Seyfert nucleus and the host galaxy spectra, and derived a residual data cube with spectral and spatial information of the different structures in 3C 120. Three continuum-dominated structures (named A, B, and C) and other three extended emission line regions (EELRs, named E1, E2 and E3) are found in 3C 120 which does not follow the general behavior of a bulge dominated galaxy. We also found shells in the central kpc that may be remnants of a past merging event in this galaxy. The origin of E1 is most probably due to the interaction of the radio-jet of 3C 120 with the intergalactic medium. Structures A, B, and the shell at the southeast of the nucleus seem to correspond to a larger morphological clumpy structure that may be a tidal tail, consequence of the past merging event. We found a bright EELR (E2) in the innermost part of this tidal tail, nearby the nucleus, which shows a high ionization level. The kinematics of the E2 region and its connection to the tidal tail suggest that the tail has channeled gas from the outer regions to the center.

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arXiv2004

Clean optical spectrum of the radio jet of 3C 120

We present integral field spectroscopy (IFS) of the central region of 3C 120. We have modeled the nuclear and host galaxy 3D spectra using techniques normally applied to imaging, decoupling both components, and obtained a residual datacube. Using this residual datacube, we detected the extended emission line region associated with the radio jet. We obtained, for the first time, a clean spectrum of this region and found compelling evidences of a jet-cloud interaction. The jet compresses and splits the gas cloud which is ionized by the AGN and/or by the strong local UV photon field generated by a shock process. We cannot confirm the detection of an extended emission line region associated with the counter-jet reported by Axon (1989).

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