arXiv subjects

Eduardo Gonzalez-Solares

Publications and source records attributed to Eduardo Gonzalez-Solares.

12 recordsLinked to original sources

arXiv2014

Detailed modelling of a large sample of Herschel sources in the Lockman Hole: identification of cold dust and of lensing candidates through their anomalous SEDs

We have studied in detail a sample of 967 SPIRE sources with 5-sigma detections at 350 and 500 micron and associations with Spitzer-SWIRE 24 micron galaxies in the HerMES-Lockman survey area, fitting their mid- and far-infrared, and submillimetre, SEDs in an automatic search with a set of six infrared templates. For almost 300 galaxies we have modelled their SEDs individually to ensure the physicality of the fits. We confirm the need for the new cool and cold cirrus templates, and also of the young starburst template, introduced in earlier work. We also identify 109 lensing candidates via their anomalous SEDs and provide a set of colour-redshift constraints which allow lensing candidates to be identified from combined Herschel and Spitzer data. The picture that emerges of the submillimetre galaxy population is complex, comprising ultraluminous and hyperluminous starbursts, lower luminosity galaxies dominated by interstellar dust emission, lensed galaxies and galaxies with surprisingly cold (10-13K) dust. 11 % of 500$μ$m selected sources are lensing candidates. 70 % of the unlensed sources are ultraluminous infrared galaxies and 26 % are hyperluminous. 34 % are dominated by optically thin interstellar dust ('cirrus') emission, but most of these are due to cooler dust than is characteristic of our Galaxy. At the highest infrared luminosities we see SEDs dominated by M82, Arp220 and young starburst types, in roughly equal proportions.

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arXiv2012

Hyper-luminous Reddened Broad-Line Quasars at z~2 from the VISTA Hemisphere Survey and WISE All Sky Survey

We present the first sample of spectroscopically confirmed heavily reddened broad-line quasars selected using the new near infra-red VISTA Hemisphere Survey and WISE All-Sky Survey. Observations of four candidates with (J-K)>2.5 and K<=16.5 over ~180 sq deg, leads to confirmation that two are highly dust-reddened broad-line Type 1 quasars at z~2. The typical dust extinctions are AV ~ 2-2.5 mags. We measure black-hole masses of ~10^9 M0 and extinction corrected bolometric luminosities of ~10^47 erg/s, making these among the brightest Type 1 quasars currently known. Despite this, these quasars lie well below the detection limits of wide-field optical surveys like the SDSS with iAB > 22. We also present WISE photometry at 3--22um, for our full sample of spectroscopically confirmed reddened quasars including those selected from the UKIDSS Large Area Survey (Banerji et al. 2012a). We demonstrate that the rest-frame infrared SEDs of these reddened quasars are similar to UV-luminous Type 1 quasars with significant hot dust emission and starburst quasar hosts like Mrk231. The average 12um flux density of our reddened quasars is similar to that of the recently discovered HyLIRG WISE1814+3412 (z=2.452) at similar redshifts, with two of our reddened quasars also having comparable 22um flux densities to this extreme HyLIRG. These optically faint, heavily reddened broad-line quasars are therefore among the most mid infrared luminous galaxies at z~2, now being discovered using WISE.

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arXiv2012

Revised SWIRE photometric redshifts

We have revised the SWIRE Photometric Redshift Catalogue to take account of new optical photometry in several of the SWIRE areas, and incorporating 2MASS and UKIDSS near infrared data. Aperture matching is an important issue for combining near infrared and optical data, and we have explored a number of methods of doing this. The increased number of photometric bands available for the redshift solution results in improvements both in the rms error and, especially, in the outlier rate. We have also found that incorporating the dust torus emission into the QSO templates improves the performance for QSO redshift estimation. Our revised redshift catalogue contains over 1 million extragalactic objects, of which 26288 are QSOs.

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arXiv2012

Heavily Reddened Quasars at z~2 in the UKIDSS Large Area Survey: A Transitional Phase in AGN Evolution

We present a new sample of purely near infra-red selected KVega<16.5 extremely red ((J-K)>2.5) quasar candidates at z~2 from 900 sq deg of data in the UKIDSS Large Area Survey (LAS). Five of these are spectroscopically confirmed to be heavily reddened Type 1 AGN with broad emission lines bringing our total sample of reddened quasars from the UKIDSS-LAS to 12 at z=1.4-2.7. At these redshifts, Ha (6563A) is in the K-band. However, the mean Ha equivalent width of the reddened quasars is only ten per cent larger than that of the optically selected population and cannot explain the extreme colours. Instead, dust extinction of Av~2-6 mags is required to reproduce the continuum colours of our sources. This is comparable to the dust extinctions seen in submillimetre galaxies at similar redshifts. We argue that the AGN are likely being observed in a relatively short-lived breakout phase when they are expelling gas and dust following a massive starburst, subsequently turning into UV-luminous quasars. Some of our quasars show direct evidence for strong outflows (v~800-1000 km/s) affecting the Ha line consistent with this scenario. We predict that a larger fraction of reddened quasar hosts are likely to be submillimetre bright compared to the UV-luminous quasar population. We use our sample to place new constraints on the fraction of obscured Type 1 AGN likely to be missed in optical surveys. Taken at face-value our findings suggest that the obscured fraction depends on quasar luminosity. The space density of obscured quasars is ~5x that inferred for UV-bright quasars from the SDSS luminosity function at Mi<-30 but seems to drop at lower luminosities even accounting for various sources of incompleteness in our sample (abridged).

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arXiv2011

A first catalogue of automatically selected UV-excess sources from the UVEX survey

We present the first catalogue of point-source UV-excess sources selected from the UVEX survey. UVEX images the Northern Galactic Plane in the U, g, r and HeI5875 bands in the Galactic latitude range -5deg<b<+5deg. Through an automated algorithm, which works on a field-to-field basis, we select blue UV-excess sources in 211 square degrees from the (U-g) vs. (g-r) colour-colour diagram and the g vs. (U-g) and g vs. (g-r) colour-magnitude diagrams. The UV-excess catalogue covers the magnituderange 14<g<22.5, contains 2170 sources and consists of a mix of white dwarfs, post-common-envelope objects, interacting binaries, quasars and AGN. Two other samples of outliers were found during the selection: i) a 'subdwarf' sample, consisting of no less than 9872 candidate metal-poor stars or lightly reddened main-sequence stars, and ii) a 'purple' sample consisting of 803 objects, most likely a mix of reddened late M-giants, T Tauri stars, planetary nebulae, symbiotic stars and carbon stars. Cross-matching the selected UV-excess catalogue with other catalogues aids with the first classification of the different populations and shows that more than 99% of our selected sources are unidentified sources.

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arXiv2009

Scale Length of Disk Galaxies

As a part of a Euro-VO research initiative, we have undertaken a programme aimed at studying the scale length of 54909 Sa-Sd spiral galaxies from the SDSS DR6 catalogue. We have retrieved u,g,r,i,z-band images for all galaxies in order to derive the light profiles. We also calculate asymmetry parameters to select non-disturbed disks for which we will derive exponential disk scale lengths. As images in different bands probe different optical depths and stellar populations, it is likely that a derived scale length value should depend on waveband, and our goal is to use the scale length variations with band pass, inclination, galaxy type, redshift, and surface brightness, in order to better understand the nature of spiral galaxies.

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arXiv2009

IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys

We have identified 17 A-type stars in the Galactic Plane that have mid-IR excesses at 8 micron. From the observed colors in the (r'-H_alpha)-(r'-i') plane, we first identified 23050 early A-type main sequence (MS) star candidates in the Isaac Newton Photometric H-Alpha Survey (IPHAS) point source database that are located in Spitzer GLIMPSE Galactic Plane fields. Imposing the requirement that they be detected in all seven 2MASS and IRAC bands led to a sample of 2692 candidate A-type stars with fully sampled 0.6 to 8 micron SEDs. Optical classification spectra of 18 of the IPHAS candidate A-type MS stars showed that all but one could be well fitted using main sequence A-type templates, with the other being an A-type supergiant. Out of the 2692 A-type candidates 17 (0.6%) were found to have 8-micron excesses above the expected photospheric values. Taking into account non-A-Type contamination estimates, the 8-micron excess fraction is adjusted to ~0.7%. The distances to these sources range from 0.7-2.5 kpc. Only 10 out of the 17 excess stars had been covered by Spitzer MIPSGAL survey fields, of which 5 had detectable excesses at 24 micron. For sources with excesses detected in at least two mid-IR wavelength bands, blackbody fits to the excess SEDs yielded temperatures ranging from 270 to 650 K, and bolometric luminosity ratios L_IR/L* from 2.2x10^{-3}-1.9x10^{-2}, with a mean value of 7.9x10^{-3} (these bolometric luminosities are lower limits as cold dust is not detectable by this survey). Both the presence of mid-IR excesses and the derived bolometric luminosity ratios are consistent with many of these systems being in the planet-building transition phase between the early protoplanetary disk phase and the later debris disk phase.

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arXiv2007

High-Redshift QSOs in the SWIRE Survey and the z~3 QSO Luminosity Function

We use a simple optical/infrared (IR) photometric selection of high-redshift QSOs that identifies a Lyman Break in the optical photometry and requires a red IR color to distinguish QSOs from common interlopers. The search yields 100 z~3 (U-dropout) QSO candidates with 19<r'<22 over 11.7 deg^2 in the ELAIS-N1 (EN1) and ELAIS-N2 (EN2) fields of the Spitzer Wide-area Infrared Extragalactic (SWIRE) Legacy Survey. The z~3 selection is reliable, with spectroscopic follow-up of 10 candidates confirming they are all QSOs at 2.83<z<3.44. We find that our z~4$ (g'-dropout) sample suffers from both unreliability and incompleteness but present 7 previously unidentified QSOs at 3.50<z<3.89. Detailed simulations show our z~3 completeness to be ~80-90% from 3.0<z<3.5, significantly better than the ~30-80% completeness of the SDSS at these redshifts. The resulting luminosity function extends two magnitudes fainter than SDSS and has a faint end slope of beta=-1.42 +- 0.15, consistent with values measured at lower redshift. Therefore, we see no evidence for evolution of the faint end slope of the QSO luminosity function. Including the SDSS QSO sample, we have now directly measured the space density of QSOs responsible for ~70% of the QSO UV luminosity density at z~3. We derive a maximum rate of HI photoionization from QSOs at z~3.2, Gamma = 4.8x10^-13 s^-1, about half of the total rate inferred through studies of the Ly-alpha forest. Therefore, star-forming galaxies and QSOs must contribute comparably to the photoionization of HI in the intergalactic medium at z~3.

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arXiv2006

Parametric modelling of the 3.6um to 8um colour distributions of galaxies in the SWIRE Survey

We fit a parametric model comprising a mixture of multi-dimensional Gaussian functions to the 3.6 to 8um colour and optical photo-z distribution of galaxy populations in the ELAIS-N1 and Lockman Fields of SWIRE. For 16,698 sources in ELAIS-N1 we find our data are best modelled (in the sense of the Bayesian Information Criterion) by the sum of four Gaussian distributions or modes (C_a, C_b, C_c and C_d). We compare the fit of our empirical model with predictions from existing semi-analytic and phenomological models. We infer that our empirical model provides a better description of the mid-infrared colour distribution of the SWIRE survey than these existing models. This colour distribution test is thus a powerful model discriminator and complementary to comparisons of number counts. We use our model to provide a galaxy classification scheme and explore the nature of the galaxies in the different modes of the model. C_a consists of dusty star-forming systems such as ULIRG's. Low redshift late-type spirals are found in C_b, where PAH emission dominates at 8um. C_c consists of dusty starburst systems at intermediate redshifts. Low redshift early-type spirals and ellipticals dominate C_d. We thus find a greater variety of galaxy types than one can with optical photometry alone. Finally we develop a new technique to identify unusual objects, and find a selection of outliers with very red IRAC colours. These objects are not detected in the optical, but have very strong detections in the mid-infrared. These sources are modelled as dust-enshrouded, strongly obscured AGN, where the high mid-infrared emission may either be attributed to dust heated by the AGN or substantial star-formation. These sources have z_ph ~ 2-4, making them incredibly infrared luminous, with a L_IR ~ 10^(12.6-14.1) L_sun.

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arXiv2006

Understanding Infrared Galaxy Populations: the SWIRE Legacy Survey

We discuss spectral energy distributions, photometric redshifts, redshift distributions, luminosity functions, source-counts and the far infrared to optical luminosity ratio for sources in the SWIRE Legacy Survey. The spectral energy distributions of selected SWIRE sources are modelled in terms of a simple set of galaxy and quasar templates in the optical and near infrared, and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and AGN dust torus) in the mid infrared. The optical data, together with the IRAC 3.6 and 4.5 mu data, have been used to determine photometric redshifts. For galaxies with known spectroscopic redshifts there is a notable improvement in the photometric redshift when the IRAC data are used, with a reduction in the rms scatter from 10% in (1+z) to 5%. While further spectroscopic data are needed to confirm this result, the prospect of determining good photometric redshifts for the 2 million extragalactic objects in SWIRE is excellent. The distribution of the different infrared sed types in the L{ir}/L{opt} versus L{ir} plane, where L{ir} and L{opt} are the infrared and optical bolometric luminosities, is discussed. Source-counts at 24, 70 and 160 mu are discussed, and luminosity functions at 3.6 and 24 mu are presented.

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arXiv2004

Angular Clustering of Galaxies at 3.6 micron from the SWIRE survey

We present the first analysis of large-scale clustering from the Spitzer Wide-area InfraRed Extragalactic legacy survey: SWIRE. We compute the angular correlation function of galaxies selected to have 3.6 micron fluxes brighter than 32 muJy in three fields totaling two square degrees in area. In each field we detect clustering with a high level of significance. The amplitude and slope of the correlation function is consistent between the three fields and is modeled as $w(theta)=Aθ^{1-γ}$ with $A=(0.6\pm0.3)\times10^{-3}, γ=2.03\pm0.10$. With a fixed slope of $γ=1.8$, we obtain an amplitude of $A=(1.7\pm0.1)\times10^{-3}$. Assuming an equivalent depth of K~18.7 mag we find our errors are smaller but our results are consistent with existing clustering measurements in K-band surveys and with stable clustering models. We estimate our median redshift $z\simeq 0.75$ and this allows us to obtain an estimate of the three-dimensional correlation function $ξ(r)$, for which we find $r_0=4.4\pm0.1 h^{-1}$ Mpc.

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arXiv2004

Dust and gas obscuration in ELAIS Deep X-ray Survey reddened quasars

Hard X-ray surveys have uncovered a large population of heavily obscured AGN. They also reveal a population of quasars with moderate obscuration at both visible and X-ray wavelengths. We use Chandra selected samples of quasars from the ELAIS Deep X-ray Survey (EDXS) and CDF-N to investigate the obscuration towards the nuclei of moderately obscured AGN. We find an inverse correlation between the optical to X-ray flux ratio and the X-ray hardness ratio which can be interpreted as due to obscuration at visible and X-ray wavelengths. We present detailed optical and near-infrared data for a sample of optically-faint (R>23) quasars from the EDXS. These are used to constrain the amount of rest-frame UV/optical reddening towards these quasars. It is found that optically-faint quasars are mostly faint due to obscuration, not because they are intrinsically weak. After correcting for reddening, the optical magnitudes of most of these quasars are similar to the brighter quasars at these X-ray fluxes. Combining with gas column densities inferred from the X-ray observations we consider the gas-to-dust ratios of the obscuring matter. We find that the quasars generally have higher gas-to-dust absorption than that seen in the Milky Way - similar to what has been found for nearby Seyfert galaxies. We consider the possible existence of a large population of X-ray sources which have optical properties of Type 1 (unobscured) quasars, but X-ray properties of Type 2 (obscured) quasars. We show that the observed distribution of optical-to-X-ray flux ratios of quasars at z>1 is skewed to low values compared to the intrinsic distribution...

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