arXiv subjects

Jesús Gallego

Publications and source records attributed to Jesús Gallego.

At least 37 records · Page 2Linked to original sources

arXiv2020

The OTELO survey. III. Demography, morphology, IR luminosity and environment of AGN hosts

We take advantage of the capabilities of the OTELO survey to select and study the AGN population in the field. We performed an analysis of the properties of these objects, including their demography, morphology, and IR luminosity. Focusing on the population of H$α$ emitters at $z \sim 0.4$, we also aim to study the environments of AGN and non-AGN galaxies at that redshift. We make use of the multiwavelength catalog of objects in the field compiled by the OTELO survey, unique in terms of minimum line flux and equivalent width. The OTELO pseudo-spectra allow the identification of emission lines and the spectral classification of the sources. We obtained a sample of 72 AGNs in the field of OTELO, selected with four different methods in the optical, X-rays, and mid-infrared bands. We find that using X-rays is the most efficient way to select AGNs. An analysis was performed on the AGN population of OTELO in order to characterize its members. At $z \sim 0.4$, we find that up to 26\% of our H$α$ emitters are AGNs. At that redshift, AGNs are found in identical environments to non-AGNs, although they represent the most clustered group when compared to passive and star-forming galaxies. The majority of our AGNs at any redshift were classified as late-type galaxies, including a 16\% proportion of irregulars. Another 16\% of AGNs show signs of interactions or mergers. Regarding the infrared luminosity, we are able to recover all the luminous infrared galaxies (LIRGs) in the field of OTELO up to $z\sim 1.6$. We find that the proportion of LIRGs and ultra-luminous infrared galaxies (ULIRGs) is higher among the AGN population, and that ULIRGs show a higher fraction of AGNs than LIRGs.

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arXiv2020

The OTELO survey. I. Description, data reduction, and multi-wavelength catalogue

The evolution of galaxies through cosmic time is studied observationally by means of extragalactic surveys. The OTELO survey aims to provide the deepest narrow-band survey to date in terms of minimum detectable flux and emission line equivalent width in order to detect the faintest extragalactic emission line systems. In this way, OTELO data will complements other broad-band, narrow-band, and spectroscopic surveys. The red tunable filter of the OSIRIS instrument on the 10.4 m Gran Telescopio Canarias (GTC) is used to scan a spectral window centred at $9175 Å$, which is free from strong sky emission lines, with a sampling interval of $6 Å$ and a bandwidth of $12 Å$ in the most deeply explored Extended Groth Strip region. Careful data reduction using improved techniques for sky ring subtraction, accurate astrometry, photometric calibration, and source extraction enables us to compile the OTELO catalogue. This catalogue is complemented with ancillary data ranging from deep X-ray to far-infrared, including high resolution HST images, which allow us to segregate the different types of targets, derive precise photometric redshifts, and obtain the morphological classification of the extragalactic objects detected. The OTELO multi-wavelength catalogue contains 11237 entries and is 50\% complete at AB magnitude 26.38. Of these sources, 6600 have photometric redshifts with an uncertainty $z_{phot}$ better than $0.2 (1+z_{phot})$. A total of 4336 of these sources correspond to preliminary emission line candidates, which are complemented by 81 candidate stars and 483 sources that qualify as absorption line systems. The OTELO survey products were released to the public on 2019.

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arXiv2020

The OTELO survey. II. The faint-end of the H$α$ luminosity function at z $\sim$ 0.40

We take advantage of the capability of the OTELO survey to obtain the H$α$ luminosity function (LF) at ${\rm z}\sim0.40$. Because of the deepest coverage of OTELO, we are able to determine the faint end of the LF, and thus better constrain the star formation rate and the number of galaxies at low luminosities. The AGN contribution to this LF is estimated as well. We make use of the multi-wavelength catalogue of objects in the field compiled by the OTELO survey, which is unique in terms of minimum flux and equivalent width. We also take advantage of the pseudo-spectra built for each source, which allow the identification of emission lines and the discrimination of different types of objects. The H$α$ luminosity function at $z\sim0.40$ is obtained, which extends the current faint end by almost 1 dex, reaching minimal luminosities of $\log_{10}L_{\rm lim}=38.5$ erg s$^{-1}$ (or $\sim0.002\, \text{M}_\odot\text{ yr}^{-1})$. The AGN contribution to the total H$α$ luminosity is estimated. We find that no AGN should be expected below a luminosity of $\log_{10}L=38.6$ erg s$^{-1}$. From the sample of non-AGN (presumably, pure SFG) at $z\sim0.40$ we estimated a star formation rate density of $ρ_{\rm SFR}=0.012\pm0.005\ {\rm \text{M}_{\odot}\ yr^{-1}\ Mpc^{-3}}$.

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arXiv2019

The nature of the diffuse light near cities detected in nighttime satellite imagery

Diffuse glow has been observed around brightly lit cities in nighttime satellite imagery since at least the first publication of large scale maps in the late 1990s. In the literature, this has often been assumed to be an error related to the sensor, and referred to as "blooming", presumably in relation to the effect that can occur when using a CCD to photograph a bright source. Here we show that the effect is not instrumental, but in fact represents a real detection of light scattered by the atmosphere. Data from the Universidad Complutense Madrid sky brightness survey are compared to nighttime imagery from multiple sensors with differing spatial resolutions, and found to be strongly correlated. These results suggest that it should be possible for a future space-based imaging radiometer to monitor changes in the diffuse artificial skyglow of cities.

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arXiv2018

High-resolution MEGARA IFU spectroscopy and structural analysis of a fast-rotating, disky bulge in NGC 7025

Disky bulges in spiral galaxies are commonly thought to form out of disk materials (mainly) via bar driven secular processes, they are structurally and dynamically distinct from `classical bulges' built in violent merger events. We use high-resolution GTC/MEGARA integral-field unit spectroscopic observations of the Sa galaxy NGC 7025, obtained during the MEGARA commissioning run, together with detailed 1D and 2D decompositions of this galaxy's SDSS $i$-band data to investigate the formation of its disky (bulge) component which makes up $\sim 30\%$ of the total galaxy light. With a Sérsic index $n \sim 1.80 \pm 0.24$, half-light radius $R_{\rm e} \sim 1.70 \pm 0.43$ kpc and stellar mass $M_{*} \sim (4.34 \pm 1.70) \times10^{10} M_{\odot}$, this bulge dominates the galaxy light distribution in the inner $R \sim 15"$ ($\sim 4.7$ kpc). Measuring the spins ($λ$) and ellipticities ($ε$) enclosed within nine different circular apertures with radii $R \le R_{\rm e}$, we show that the bulge, which exhibits a spin track of an outwardly rising $λ$ and $ε$, is a fast rotator for all the apertures considered. Our findings suggest that this inner disky component is a pseudo-bulge, consistent with the stellar and dust spiral patterns seen in the galaxy down to the innermost regions but in contrast to the classical bulge interpretation favored in the past. We propose that a secular process involving the tightly wound stellar spiral arms of NGC 7025 may drive gas and stars out of the disk into the inner regions of the galaxy, building up the massive pseudo-bulge.

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arXiv2017

The GALEX/S4G Surface Brightness and Color Profiles Catalog - I. Surface Photometry and Color Gradients of Galaxies

We present new, spatially resolved, surface photometry in FUV and NUV from images obtained by the $\textit{Galaxy Evolution Explorer}$ (GALEX), and IRAC1 (3.6 $μ$m) photometry from the $\textit{Spitzer Survey of Stellar Structure in Galaxies}$ (S$^{4}$G) (Sheth et al. 2010). We analyze the radial surface brightness profiles $μ_{FUV}$, $μ_{NUV}$, and $μ_{[3.6]}$, as well as the radial profiles of (FUV $-$ NUV), (NUV $-$ [3.6]), and (FUV $-$ [3.6]) colors in 1931 nearby galaxies (z $<$ 0.01). The analysis of the 3.6 $μ$m surface brightness profiles also allows us to separate the bulge and disk components in a quasi-automatic way, and to compare their light and color distribution with those predicted by the chemo-spectrophotometric models for the evolution of galaxy disks of Boissier & Prantzos (2000). The exponential disk component is best isolated by setting an inner radial cutoff and an upper surface brightness limit in stellar mass surface density. The best-fitting models to the measured scale length and central surface brightness values yield distributions of spin and circular velocity within a factor of two to those obtained via direct kinematic measurements. We find that at a surface brightness fainter than $μ_{[3.6]}=20.89$ mag arcsec$^{-2}$, or below $3\times 10^{8}$ $M_{\odot}$ kpc$^{-2}$ in stellar mass surface density, the average specific star formation rate for star forming and quiescent galaxies remains relatively flat with radius. However, a large fraction of GALEX Green Valley galaxies (defined in Bouquin et al. 2015) shows a radial decrease in specific star formation rate. This behavior suggests that an outside-in damping mechanism, possibly related to environmental effects, could be testimony of an early evolution of galaxies from the blue sequence of star forming galaxies towards the red sequence of quiescent galaxies.

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arXiv2017

A comparison between the soft X-ray and [O III] morphologies of active galactic nuclei

Several studies of nearby active galactic nuclei (AGN) have shown that the soft X-ray emission presents a size and morphology that resembles that of the narrow-line region (NLR) traced by [O III]. Since the NLR is mainly constituted by gas photoionised by the AGN, it seems logical to assume that this is also the primary source of the soft X-ray emission. However, these results are based on individual sources or small samples, particularly focused on type-2 Seyfert galaxies. Very little has been said concerning other types of AGN. The purpose of this work is to compare the circumnuclear morphologies of soft X-ray and [O III] images to test whether they match in different optical classes of AGN. Our sample is composed of 27 AGN: nine type-1 Seyferts, 10 type-2 Seyferts, and eight low ionisation nuclear emission-line regions (LINERs). We find a good match in 100% of the type-2 Seyferts in our sample. This correspondence is less frequent in type-1 Seyferts (22%) and it is not seen in LINERs. The good resemblance in type-2 Seyferts constitutes an evidence for a common physical origin. We argue that the lack of correspondence in type-1 Seyferts might be due to the line of sight perpendicular to the accretion disk. Based on the morphologies of the eight LINERs in our sample, we discard a common origin for the soft X-ray and [O III] emissions in these objects. Regarding the X-ray properties, both high column density and hard X-ray luminosity are associated with matched morphologies.

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arXiv2016

Constraining the epoch of reionization from the observed properties of the high-z Universe

We combine observational data on a dozen independent cosmic properties at high-$z$ with the information on reionization drawn from the spectra of distant luminous sources and the cosmic microwave background (CMB) to constrain the interconnected evolution of galaxies and the intergalactic medium since the dark ages. The only acceptable solutions are concentrated in two narrow sets. In one of them reionization proceeds in two phases: a first one driven by Population III stars, completed at $z\sim 10$, and after a short recombination period a second one driven by normal galaxies, completed at $z\sim 6$. In the other set both kinds of sources work in parallel until full reionization at $z\sim 6$. The best solution with double reionization gives excellent fits to all the observed cosmic histories, but the CMB optical depth is 3-$σ$ larger than the recent estimate from the Planck data. Alternatively, the best solution with single reionization gives less good fits to the observed star formation rate density and cold gas mass density histories, but the CMB optical depth is consistent with that estimate. We make several predictions, testable with future observations, that should discriminate between the two reionization scenarios. As a byproduct our models provide a natural explanation to some characteristic features of the cosmic properties at high-$z$, as well as to the origin of globular clusters.

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arXiv2016

Properties of galaxies at the faint end of the H$α$ luminosity function at $z\sim0.62$

Studies measuring the star formation rate density, luminosity function, and properties of star-forming galaxies are numerous. However, it exists a gap at $0.5<z<0.8$ in H$α$-based studies. Our main goal is to study the properties of a sample of faint H$α$ emitters at $z\sim0.62$. We focus on their contribution to the faint end of the luminosity function and derived star formation rate density, characterising their morphologies and basic photometric and spectroscopic properties. We use a narrow-band technique in the near-infrared, with a filter centred at 1.06 $μ$m. The data come from ultra-deep VLT/HAWK-I observations in the GOODS-S field with a total of 31.9 h in the narrow-band filter. We perform a visual classification of the sample and study their morphologies from structural parameters available in CANDELS. Our 28 H$α$-selected sample of faint star-forming galaxies reveals a robust faint-end slope of the luminosity function $α=-1.46_{-0.08}^{+0.16}$. The derived star formation rate density at $z\sim0.62$ is $ρ_\mathrm{SFR} = 0.036_{-0.008}^{+0.012} M_{\odot}~\mathrm{yr^{-1}~Mpc^{-3}}$. The sample is mainly composed of disks, but an important contribution of compact galaxies with Sérsic indexes $n\sim2$ display the highest specific star formation rates. The luminosity function at $z\sim0.62$ from our ultra-deep data points towards a steeper $α$ when an individual extinction correction for each object is applied. Compact galaxies are low-mass, low-luminosity, and starburst-dominated objects with a light profile in an intermediate stage from early to late types.

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arXiv2016

FRIDA: diffraction-limited imaging and integral-field spectroscopy for the GTC

FRIDA is a diffraction-limited imager and integral-field spectrometer that is being built for the adaptive-optics focus of the Gran Telescopio Canarias. In imaging mode FRIDA will provide scales of 0.010, 0.020 and 0.040 arcsec/pixel and in IFS mode spectral resolutions of 1500, 4000 and 30,000. FRIDA is starting systems integration and is scheduled to complete fully integrated system tests at the laboratory by the end of 2017 and to be delivered to GTC shortly thereafter. In this contribution we present a summary of its design, fabrication, current status and potential scientific applications.

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arXiv2016

Creating lenticular galaxies with major mergers

Lenticular galaxies (S0s) represent the majority of early-type galaxies in the local Universe, but their formation channels are still poorly understood. While galaxy mergers are obvious pathways to suppress star formation and increase bulge sizes, the marked parallelism between spiral and lenticular galaxies (e.g. photometric bulge-disc coupling) seemed to rule out a potential merger origin. Here, we summarise our recent work in which we have shown, through N-body numerical simulations, that disc-dominated lenticulars can emerge from major mergers of spiral galaxies, in good agreement with observational photometric scaling relations. Moreover, we show that mergers simultaneously increase the light concentration and reduce the angular momentum relative to their spiral progenitors. This explains the mismatch in angular momentum and concentration between spirals and lenticulars recently revealed by CALIFA observations, which is hard to reconcile with simple fading mechanisms (e.g. ram-pressure stripping).

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arXiv2015

Testing sky brightness models against radial dependency: a dense two dimensional survey around the city of Madrid, Spain

We present a study of the night sky brightness around the extended metropolitan area of Madrid using Sky Quality Meter (SQM) photometers. The map is the first to cover the spatial distribution of the sky brightness in the center of the Iberian peninsula. These surveys are neccessary to test the light pollution models that predict night sky brightness as a function of the location and brightness of the sources of light pollution and the scattering of light in the atmosphere. We describe the data-retrieval methodology, which includes an automated procedure to measure from a moving vehicle in order to speed up the data collection, providing a denser and wider survey than previous works with similar time frames. We compare the night sky brightness map to the nocturnal radiance measured from space by the DMSP satellite. We find that i) a single source model is not enough to explain the radial evolution of the night sky brightness, despite the predominance of Madrid in size and population, and ii) that the orography of the region should be taken into account when deriving geo-specific models from general first-principles models. We show the tight relationship between these two luminance measures. This finding sets up an alternative roadmap to extended studies over the globe that will not require the local deployment of photometers or trained personnel.

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arXiv2015

Creating S0s with major mergers: a 3D view

A number of simulators have argued that major mergers can sometimes preserve discs (e.g. Springel & Hernquist 2005), but the possibility that they could explain the emergence of lenticular galaxies (S0s) has been generally neglected. In fact, observations of S0s reveal a strong structural coupling between their bulges and discs, which seems difficult to reconcile with the idea that they come from major mergers. However, in Querejeta et al. (2015a) we have used N-body simulations of binary mergers to show that, under favourable conditions, discs are first destroyed but soon regrow out of the leftover debris, matching observational photometric scaling relations (e.g. Laurikainen et al. 2010). Additionally, in Querejeta et al. (2015b) we have shown how the merger scenario agrees with the recent discovery that S0s and most spirals are not compatible in an angular momentum--concentration plane. This important result from CALIFA constitutes a serious objection to the idea that spirals transform into S0s mainly by fading (e.g. via ram-pressure stripping, as that would not explain the observed simultaneous change in $λ_\mathrm{Re}$ and concentration), but our simulations of major mergers do explain that mismatch. From such a 3D comparison we conclude that mergers must be a relevant process in the build-up of the current population of S0s.

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arXiv2015

The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence

We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6$μ$m photometry for > 2000 galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which is populated by irregular and spiral galaxies, and is mainly driven by changes in the formation timescale ($τ$) and a degeneracy between $τ$ and dust reddening. The tightness of the GBS provides an unprecedented way of identifying star-forming galaxies and objects that are just evolving to (or from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS, at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the optical red sequence. We find no such dichotomy in terms of stellar mass (measured by $\rm{M}_{[3.6]}$), since both massive ($M_{\star} > 10^{11} M_{\odot}$) blue and red sequence galaxies are identified. The type that is proportionally more often found in the GGV are the S0-Sa's and most of these are located in high-density environments. We discuss evolutionary models of galaxies that show a rapid transition from the blue to the red sequence on timescale of $10^{8}$years.

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arXiv2014

Recent stellar mass assembly of low-mass star-forming galaxies at redshifts 0.3 < z < 0.9

The epoch when low-mass star forming galaxies (LMSFGs) form the bulk of their stellar mass is uncertain. While some models predict an early formation, others favor a delayed scenario until later ages of the universe. We present constraints on the star formation histories (SFHs) of a sample of LMSFGs obtained through the analysis of their spectral energy distributions using a novel approach that (1) consistently combines photometric (broadband) and spectroscopic (equivalent widths of emission lines) data, and (2) uses physically motivated SFHs with non-uniform variations of the star formation rate (SFR) as a function of time. The sample includes 31 spectroscopically confirmed LMSFGs (7.3 < log M*/Msun < 8.0) at 0.3 < z_spec < 0.9 in the Extended-Chandra Deep Field-South field (E-CDF-S). Among them, 24 were selected with photometric stellar mass log M*/Msun < 8.0, 0.3 < z_phot < 1.0, and NB816 < 26 AB mag; the remaining 7 were selected as blue compact dwarfs (BCDs) within the same photometric redshift and magnitude ranges. We also study a secondary sample of 43 more massive spectroscopically confirmed galaxies (8.0 < log M*/Msun < 9.1), selected with the same criteria. The SFRs and stellar masses derived for both samples place our targets on the standard main sequence of star forming galaxies. The median SFH of LMSFGs at intermediate redshifts appears to form 90% of the median stellar mass inferred for the sample in the 0.5-1.8 Gyr immediately preceding the observation. These results suggest a recent stellar mass assembly for LMSFGs, consistent with the cosmological downsizing trends. We find similar median SFH timescales for the more massive secondary sample.

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arXiv2014

Formation of S0 galaxies through mergers. V. Antitruncated stellar discs resulting from major mergers

Lenticular galaxies (S0s) are more likely to host antitruncated (Type-III) stellar discs than galaxies of later Hubble types. Major mergers are popularly considered too violent mechanisms to form these breaks. We have investigated whether major mergers can result into S0-like remnants with realistic antitruncated stellar discs or not. We have analysed 67 relaxed S0 and E/S0 remnants resulting from dissipative N-body simulations of major mergers from the GalMer database. We have simulated realistic R-band surface brightness profiles of the remnants to identify those with antitruncated stellar discs. Their inner and outer discs and the breaks are quantitatively characterized to compare with real data. Nearly 70% of our S0-like remnants are antitruncated, meaning that major mergers that result in S0s have a high probability of producing Type-III stellar discs. Our remnants lie on top of the extrapolations of the observational trends (towards brighter magnitudes and higher break radii) in several photometric diagrams. In scale-free photometric diagrams, simulations and observations overlap and the remnants reproduce the observational trends, so the physical mechanism after antitruncations is highly scalable. We have found novel photometric scaling relations between the characteristic parameters of the antitruncations in real S0s, which are also reproduced by our simulations. The trends in all the photometric planes can be derived from three basic scaling relations that real and simulated Type-III S0s fulfill: h_i \prop R_brkIII, h_o \prop R_brkIII, and mu_brkIII \prop R_brkIII, where h_i and h_o are the scalelenghts of the inner and outer discs, and mu_brkIII and R_brkIII are the surface brightness and radius of the breaks. Mayor mergers provide a feasible mechanism to form realistic antitruncated S0 galaxies (abridged).

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arXiv2014

Higher prevalence of X-ray selected AGN in intermediate age galaxies up to z~1

We analyse the stellar populations in the host galaxies of 53 X-ray selected optically dull active galactic nuclei (AGN) at 0.34 10^10.5 M_sun) and that the observed fraction of galaxies hosting an AGN increases with the stellar mass. A careful selection of random control samples of inactive galaxies allows us to remove the stellar mass and redshift dependencies of the AGN fraction to explore trends with several stellar age indicators. We find no significant differences in the distribution of the rest-frame U-V colour for AGN hosts and inactive galaxies, in agreement with previous results. However, we find significantly shallower 4000 AA breaks in AGN hosts, indicative of younger stellar populations. With the help of a model-independent determination of the extinction, we obtain extinction-corrected U-V colours and light-weighted average stellar ages. We find that AGN hosts have younger stellar populations and higher extinction compared to inactive galaxies with the same stellar mass and at the same redshift. We find a highly significant excess of AGN hosts with Dn(4000)~1.4 and light weighted average stellar ages of 300-500 Myr, as well as a deficit of AGN in intrinsic red galaxies. We interpret failure in recognising these trends in previous studies as a consequence of the balancing effect in observed colours of the age-extinction degeneracy.

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arXiv2014

Evolution induced by dry minor mergers onto fast-rotator S0 galaxies

We analysed collisionless N-body simulations of intermediate and minor dry mergers onto S0s to test whether these mergers can generate S0 galaxies with kinematics intermediate between fast and slow rotators. We find that minor mergers induce a lower decrease of the global rotational support than encounters of lower mass ratios, which results in S0s with properties intermediate between fast and slow rotators. The resulting remnants are intrinsically more triaxial, less flattened, and span the whole range of apparent ellipticities up to $ε_\mathrm{e} \sim 0.8$. They do not show lower apparent ellipticities in random projections than initially; on the contrary, the formation of oval distortions and the disc thickening increase the percentage of projections at $0.4 < ε_\mathrm{e} < 0.7$. In the experiments with S0b progenitor galaxies, minor mergers tend to spin up the bulge and to decrease slightly its intrinsic ellipticity, whereas in the cases of primary S0c galaxies they keep the rotational support of the bulge nearly constant and decrease significantly its intrinsic ellipticity. The remnant bulges remain nearly spherical ($B/A \sim C/A > 0.9$), but exhibit a wide range of triaxialities ($0.20 < T < 1.00$). In the plane of global anisotropy of velocities ($δ$) vs. intrinsic ellipticity ($ε_\mathrm{e,intr}$), some of our models extend the linear trend found in previous major merger simulations towards higher $ε_\mathrm{e,intr}$ values, while others depart from it. This is consistent with the wide dispersion exhibited by real S0s in this diagram compared with ellipticals, which follow the linear trend drawn by major merger simulations. The different trends exhibited by ellipticals and S0 galaxies in the $δ$ - $ε_\mathrm{e}$ diagram may be pointing to the different role played by major mergers in the build-up of each morphological type.

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