arXiv subjects

S. Oliver

Publications and source records attributed to S. Oliver.

At least 19 recordsLinked to original sources

arXiv2022

A new look at local ultraluminous infrared galaxies: the atlas and radiative transfer models of their complex physics

We present the ultraviolet to submillimetre spectral energy distributions (SEDs) of the HERschel Ultra Luminous Infrared Galaxy Survey (HERUS) sample of 42 local ultraluminous infrared galaxies (ULIRGs) and fit them with a Markov chain Monte Carlo (MCMC) code using the CYprus models for Galaxies and their NUclear Spectra (CYGNUS) radiative transfer models for starbursts, active galactic nucleus (AGN) tori and host galaxy. The Spitzer IRS spectroscopy data are included in the fitting. Our bayesian SED fitting method takes comparable time to popular energy balance methods but it is more physically motivated and versatile. All HERUS galaxies harbor high rates of star formation but we also find bolometrically significant AGN in all of the galaxies of the sample. We estimate the correction of the luminosities of the AGN in the ULIRGs due to the anisotropic emission of the torus and find that it could be up to a factor of $\sim10$ for nearly edge-on tori. We present a comparison of our results with the smooth torus model of Fritz et al. and the two-phase models of Siebenmorgen et al. and SKIRTOR. We find that the CYGNUS AGN torus models fit significantly better the SEDs of our sample compared to all other models. We find no evidence that strong AGN appear either at the beginning or end of a starburst episode or that starbursts and AGN affect each other. IRAS 01003-2238 and Mrk 1014 show evidence for dual AGN in their SED fits suggesting a minimum dual AGN fraction in the sample of 5%.

astro-ph.GA↗

arXiv2020

A Spitzer survey of Deep Drilling Fields to be targeted by the Vera C. Rubin Observatory Legacy Survey of Space and Time

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will observe several Deep Drilling Fields (DDFs) to a greater depth and with a more rapid cadence than the main survey. In this paper, we describe the ``DeepDrill'' survey, which used the Spitzer Space Telescope Infrared Array Camera (IRAC) to observe three of the four currently defined DDFs in two bands, centered on 3.6 $μ$m and 4.5 $μ$m. These observations expand the area which was covered by an earlier set of observations in these three fields by the Spitzer Extragalactic Representative Volume Survey (SERVS). The combined DeepDrill and SERVS data cover the footprints of the LSST DDFs in the Extended Chandra Deep Field-South field (ECDFS), the ELAIS-S1 field (ES1), and the XMM Large-Scale Structure Survey field (XMM-LSS). The observations reach an approximate $5σ$ point-source depth of 2 $μ$Jy (corresponding to an AB magnitude of 23.1; sufficient to detect a 10$^{11} M_{\odot}$ galaxy out to $z\approx 5$) in each of the two bands over a total area of $\approx 29\,$deg$^2$. The dual-band catalogues contain a total of 2.35 million sources. In this paper we describe the observations and data products from the survey, and an overview of the properties of galaxies in the survey. We compare the source counts to predictions from the SHARK semi-analytic model of galaxy formation. We also identify a population of sources with extremely red ([3.6]$-$[4.5] $>1.2$) colours which we show mostly consists of highly-obscured active galactic nuclei.

astro-ph.GA↗

arXiv2020

Building high accuracy emulators for scientific simulations with deep neural architecture search

Computer simulations are invaluable tools for scientific discovery. However, accurate simulations are often slow to execute, which limits their applicability to extensive parameter exploration, large-scale data analysis, and uncertainty quantification. A promising route to accelerate simulations by building fast emulators with machine learning requires large training datasets, which can be prohibitively expensive to obtain with slow simulations. Here we present a method based on neural architecture search to build accurate emulators even with a limited number of training data. The method successfully accelerates simulations by up to 2 billion times in 10 scientific cases including astrophysics, climate science, biogeochemistry, high energy density physics, fusion energy, and seismology, using the same super-architecture, algorithm, and hyperparameters. Our approach also inherently provides emulator uncertainty estimation, adding further confidence in their use. We anticipate this work will accelerate research involving expensive simulations, allow more extensive parameters exploration, and enable new, previously unfeasible computational discovery.

stat.ML↗

arXiv2019

Have we seen all the galaxies that comprise the cosmic infrared background at 250\,$μ$m $\le λ\le$ 500\,$μ$m?

The cosmic infrared background (CIB) provides a fundamental observational constraint on the star-formation history of galaxies over cosmic history. We estimate the contribution to the CIB from catalogued galaxies in the COSMOS field by using a novel map fitting technique on the \textit{Herschel} SPIRE maps. Prior galaxy positions are obtained using detections over a large range in wavelengths in the $K_{\rm s}$--3\,GHz range. Our method simultaneously fits the galaxies, the system foreground, and the leakage of flux from galaxies located in masked areas and corrects for an "over-fitting" effect not previously accounted for in stacking methods. We explore the contribution to the CIB as a function of galaxy survey wavelength and depth. We find high contributions to the CIB with the deep $r$ ($m_{\rm AB} \le 26.5$), $K_{\rm s}$ ($m_{\rm AB} \le 24.0$) and 3.6\,$μ$m ($m_{\rm AB} \le 25.5$) catalogues. We combine these three deep catalogues and find a total CIB contributions of 10.5 $\pm$ 1.6, 6.7 $\pm$ 1.5 and 3.1 $\pm$ 0.7\,nWm$^{-2}$sr$^{-1}$ at 250, 350 and 500\,$μ$m, respectively. Our CIB estimates are consistent with recent phenomenological models, prior based SPIRE number counts and with (though more precise than) the diffuse total measured by FIRAS. Our results raise the interesting prospect that the CIB contribution at $λ\le 500\,μ$m from known galaxies has converged. Future large-area surveys like those with the Large Synoptic Survey Telescope are therefore likely to resolve a substantial fraction of the population responsible for the CIB at 250\,$μ$m $\leq λ\leq$ 500\,$μ$m.

astro-ph.GA↗

arXiv2019

Discovery of a giant and luminous Lya+CIV+HeII nebula at z=3.326 with extreme emission line ratios

We present the discovery of HLock01-LAB, a luminous and large Lya nebula at z=3.326. Medium-band imaging and long-slit spectroscopic observations with the Gran Telescopio Canarias reveal extended emission in the Lya 1215Å, CIV1550Å, and HeII 1640Ålines over ~100kpc, and a total luminosity L(Lya)=(6.4+/-0.1)x10^44 erg s^-1. HLock01-LAB presents an elongated morphology aligned with two faint radio sources contained within the central ~8kpc of the nebula. The radio structures are consistent to be faint radio jets or lobes of a central galaxy, whose spectrum shows nebular emission characteristic of a type-II active galactic nucleus (AGN). The continuum emission of the AGN at short wavelengths is, however, likely dominated by stellar emission of the host galaxy, for which we derive a stellar mass M* = 2.3x10^11 Msun. The detection of extended emission in CIV and CIII] indicates that the gas within the nebula is not primordial. Feedback may have enriched the halo at at least 50 kpc from the nuclear region. Using rest-frame UV emission-line diagnostics, we find that the gas in the nebula is likely heated by the AGN. Nevertheless, at the center of the nebula we find extreme emission line ratios of Lya/CIV~60 and Lya/HeII~80, one of the highest values measured to date, and well above the standard values of photoionization models (Lya/HeII~30 for case B photoionization). Our data suggest that jet-induced shocks are likely responsible for the increase of the electron temperature and, thus, the observed Lya enhancement in the center of the nebula. This scenario is further supported by the presence of radio structures and perturbed kinematics in this region. The large Lya luminosity in HLock01-LAB is likely due to a combination of AGN photoionization and jet-induced shocks, highlighting the diversity of sources of energy powering Lya nebulae. [abridged]

astro-ph.GA↗

arXiv2018

Probing the High-Redshift Universe with SPICA: Toward the Epoch of Reionization and Beyond

With the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z>5 that are hyper-luminous in the infrared ($μ$$L_{\rm IR}>10^{13}$ L$_{\odot}$, where $μ$ is a lensing magnification factor), the possibility has opened up for SPICA, the proposed ESA M5 mid-/far-infrared mission, to extend its spectroscopic studies toward the epoch of reionization and beyond. In this paper, we examine the feasibility and scientific potential of such observations with SPICA's far-infrared spectrometer SAFARI, which will probe a spectral range (35-230 $μ$m) that will be unexplored by ALMA and JWST. Our simulations show that SAFARI is capable of delivering good-quality spectra for hyper-luminous infrared galaxies (HyLIRGs) at z=5-10, allowing us to sample spectral features in the rest-frame mid-infrared and to investigate a host of key scientific issues, such as the relative importance of star formation versus AGN, the hardness of the radiation field, the level of chemical enrichment, and the properties of the molecular gas. From a broader perspective, SAFARI offers the potential to open up a new frontier in the study of the early Universe, providing access to uniquely powerful spectral features for probing first-generation objects, such as the key cooling lines of low-metallicity or metal-free forming galaxies (fine-structure and H2 lines) and emission features of solid compounds freshly synthesized by Population III supernovae. Ultimately, SAFARI's ability to explore the high-redshift Universe will be determined by the availability of sufficiently bright targets (whether intrinsically luminous or gravitationally lensed). With its launch expected around 2030, SPICA is ideally positioned to take full advantage of upcoming wide-field surveys such as LSST, SKA, Euclid, and WFIRST, which are likely to provide extraordinary targets for SAFARI.

astro-ph.GA↗

arXiv2018

HELP: modelling the spectral energy distributions of Herschel detected galaxies in the ELAIS N1 field

The HELP project focuses on the data from ESA's Herschel mission, which covered over 1300$deg^2$ and is preparing to publish a multi-wavelength catalogue of millions of objects. Our main goal is to find the best approach to simultaneously fitting SEDs of millions of galaxies across a wide redshift range to obtain homogeneous estimates of the main physical parameters of detected IR galaxies. We perform SED fitting on the UV/NIR to FIR emission of 42 047 galaxies from the pilot HELP field: ELAIS N1. We use the latest release of CIGALE, a galaxy SED fitting code relying on energy balance, to deliver the main physical parameters such as $M_{star}$, SFR, and $L_{dust}$. We implement additional quality criteria to the fits by calculating $χ^2$ values for the stellar and dust part of the spectra independently. These criteria allow us to identify the best fits and to identify peculiar galaxies. We perform the SED fitting by assuming three different dust attenuation laws separately allowing us to test the impact of the assumed law on estimated physical parameters. We implemented two additional quality value checks for the SED fitting method based on $M_{star}$ estimation and energy budget. This method allows us to identify possible objects with incorrect matching in the catalogue and peculiar galaxies; we found 351 possible candidates of lensed galaxies using two complementary $χ^2$s criteria (stellar and IR) and $z_{phot}$ calculated for the IR part of the spectrum only. We find that the attenuation law has an important impact on the $M_{star}$ estimate (on average leading to disparities of a factor of two). We derive the relation between $M_{star}$ estimates obtained by different attenuation laws and we find the best recipe for our sample. We also make independent estimates of the total $L_{dust}$ parameter from stellar emission by fitting the galaxies with and without IR data separately.

astro-ph.GA↗

arXiv2018

ALMA observations of lensed Herschel sources : Testing the dark-matter halo paradigm

With the advent of wide-area submillimeter surveys, a large number of high-redshift gravitationally lensed dusty star-forming galaxies (DSFGs) has been revealed. Due to the simplicity of the selection criteria for candidate lensed sources in such surveys, identified as those with $S_{500μm} > 100$ mJy, uncertainties associated with the modelling of the selection function are expunged. The combination of these attributes makes submillimeter surveys ideal for the study of strong lens statistics. We carried out a pilot study of the lensing statistics of submillimetre-selected sources by making observations with the Atacama Large Millimetre Array (ALMA) of a sample of strongly-lensed sources selected from surveys carried out with the Herschel Space Observatory. We attempted to reproduce the distribution of image separations for the lensed sources using a halo mass function taken from a numerical simulation which contains both dark matter and baryons. We used three different density distributions, one based on analytical fits to the halos formed in the EAGLE simulation and two density distributions (Singular Isothermal Sphere (SIS) and SISSA) that have been used before in lensing studies. We found that we could reproduce the observed distribution with all three density distributions, as long as we imposed an upper mass transition of $\sim$$10^{13} M_{\odot}$ for the SIS and SISSA models, above which we assumed that the density distribution could be represented by an NFW profile. We show that we would need a sample of $\sim$500 lensed sources to distinguish between the density distributions, which is practical given the predicted number of lensed sources in the Herschel surveys.

astro-ph.GA↗

arXiv2018

Red, redder, reddest: SCUBA-2 imaging of colour-selected \textit{Herschel} sources

High-redshift, luminous, dusty star forming galaxies (DSFGs) constrain the extremity of galaxy formation theories. The most extreme are discovered through follow-up on candidates in large area surveys. Here we present 850 $μ$m SCUBA-2 follow-up observations of 188 red DSFG candidates from the \textit{Herschel} Multi-tiered Extragalactic Survey (HerMES) Large Mode Survey, covering 274 deg$^2$. We detected 87 per cent with a signal-to-noise ratio $>$ 3 at 850~$μ$m. We introduce a new method for incorporating the confusion noise in our spectral energy distribution fitting by sampling correlated flux density fluctuations from a confusion limited map. The new 850~$μ$m data provide a better constraint on the photometric redshifts of the candidates, with photometric redshift errors decreasing from $σ_z/(1+z)\approx0.21$ to $0.15$. Comparison spectroscopic redshifts also found little bias ($\langle (z-z_{\rm spec})/(1+z_{\rm spec})\rangle = 0.08 $). The mean photometric redshift is found to be 3.6 with a dispersion of $0.4$ and we identify 21 DSFGs with a high probability of lying at $z > 4$. After simulating our selection effects we find number counts are consistent with phenomenological galaxy evolution models. There is a statistically significant excess of WISE-1 and SDSS sources near our red galaxies, giving a strong indication that lensing may explain some of the apparently extreme objects. Nevertheless, our sample should include examples of galaxies with the highest star formation rates in the Universe ($\gg10^3$ M$_\odot$yr$^{-1}$).

astro-ph.GA↗

arXiv2017

Witnessing the birth of the red sequence: the physical scale and morphology of dust emission in hyper-luminous starbursts in the early Universe

We present high-spatial-resolution ($\sim 0.12''$ or $\approx 800 \, {\rm pc}$ at $z = 4.5$) ALMA $870\,μ$m dust continuum observations of a sample of 44 ultrared dusty star-forming galaxies (DSFGs) selected from the H-ATLAS and HerMES far-infrared surveys because of their red colors from 250 to 500 $μ$m: $S_{500} / S_{250} > 1.5$ and $S_{500} / S_{350} > 1.0$. With photometric redshifts in the range $z \sim 4$-6, our sample includes the most luminous starbursting systems in the early Universe known so far, with total obscured star-formation rates (SFRs) of up to $\sim 4,500 \, M_\odot \, {\rm yr}^{-1}$, as well as a population of lensed, less intrinsically luminous sources. The lower limit on the number of ultrared DSFGs at 870 $μ$m (with flux densities measured from the ALMA maps and thus not affected by source confusion) derived in this work is in reasonable agreement with models of galaxy evolution, whereas there have been reports of conflicts at 500 $μ$m (where flux densities are derived from SPIRE). Ultrared DSFGs have a variety of morphologies (from relatively extended disks with smooth radial profiles, to compact sources, both isolated and interacting) and an average size, $θ_{\rm FWHM}$, of $1.46 \pm 0.41\, {\rm kpc}$, considerably smaller than the values reported in previous work for less-luminous DSFGs at lower redshifts. The size and the estimated gas-depletion times of our sources are compatible with their being the progenitors of the most massive, compact, red-and-dead galaxies at $z \sim 2$-3, and ultimately of local ultra-massive elliptical galaxies or massive galaxy clusters. We are witnessing the birth of the high-mass tail of the red sequence of galaxies.

astro-ph.GA↗

arXiv2017

The MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey

The MIGHTEE large survey project will survey four of the most well-studied extragalactic deep fields, totalling 20 square degrees to $μ$Jy sensitivity at Giga-Hertz frequencies, as well as an ultra-deep image of a single ~1 square degree MeerKAT pointing. The observations will provide radio continuum, spectral line and polarisation information. As such, MIGHTEE, along with the excellent multi-wavelength data already available in these deep fields, will allow a range of science to be achieved. Specifically, MIGHTEE is designed to significantly enhance our understanding of, (i) the evolution of AGN and star-formation activity over cosmic time, as a function of stellar mass and environment, free of dust obscuration; (ii) the evolution of neutral hydrogen in the Universe and how this neutral gas eventually turns into stars after moving through the molecular phase, and how efficiently this can fuel AGN activity; (iii) the properties of cosmic magnetic fields and how they evolve in clusters, filaments and galaxies. MIGHTEE will reach similar depth to the planned SKA all-sky survey, and thus will provide a pilot to the cosmology experiments that will be carried out by the SKA over a much larger survey volume.

astro-ph.GA↗

arXiv2017

OCAMS: The OSIRIS-REx Camera Suite

The requirements-driven OSIRIS-REx Camera Suite (OCAMS) acquires images essential to collecting a sample from the surface of Bennu. During proximity operations, these images document the presence of satellites and plumes, record spin state, enable an accurate digital terrain model of the shape of the asteroid and identify any surface hazards. They confirm the presence of sampleable regolith on the surface, observe the sampling event itself, and image the sample head in order to verify its readiness to be stowed. They document the history of Bennu as an example of early solar system material, as a microgravity body with a planetesimal size-scale, and as a carbonaceous object. OCAMS is fitted with three cameras. The MapCam records point-source color images on approach to the asteroid in order to connect ground-based point-source observations of Bennu to later higher-resolution surface spectral imaging. The SamCam documents the sample site before, during, and after it is disturbed by the sample mechanism. The PolyCam, using its focus mechanism, observes the sample site at sub-centimeter resolutions, revealing surface texture and morphology. While their imaging requirements divide naturally between the three cameras, they preserve a strong degree of functional overlap. OCAMS and the other spacecraft instruments allow the OSIRIS-REx mission to collect a sample from a microgravity body on the same visit during which it was first optically acquired from long range, a useful capability as humanity explores near-Earth, Main-Belt and Jupiter Trojan asteroids.

astro-ph.IM↗

arXiv2016

The faint end of the 250 micron luminosity function at z < 0.5

Aims. We aim to study the 250 micron luminosity function (LF) down to much fainter luminosities than achieved by previous efforts. Methods. We developed a modified stacking method to reconstruct the 250 micron LF using optically selected galaxies from the SDSS survey and Herschel maps of the GAMA equatorial fields and Stripe 82. Our stacking method not only recovers the mean 250 micron luminosities of galaxies that are too faint to be individually detected, but also their underlying distribution functions. Results. We find very good agreement with previous measurements in the overlapping luminosity range. More importantly, we are able to derive the LF down to much fainter luminosities (around 25 times fainter) than achieved by previous studies. We find strong positive luminosity evolution \propto (1 + z)^4.89\pm1.07 and moderate negative density evolution \propto (1 + z)^-1.02\pm0.54 over the redshift range z=[0.02, 0.5].

astro-ph.GA↗

arXiv2016

HELP: XID+, The Probabilistic De-blender for Herschel SPIRE maps

We have developed a new prior-based source extraction tool, XID+, to carry out photometry in the Herschel SPIRE maps at the positions of known sources. XID+ is developed using a probabilistic Bayesian framework which provides a natural framework in which to include prior information, and uses the Bayesian inference tool, Stan, to obtain the full posterior probability distribution on flux estimates. In this paper, we discuss the details of XID+ and demonstrate the basic capabilities and performance by running it on simulated SPIRE maps resembling the COSMOS field, and comparing to the current prior-based source extraction tool DESPHOT. We show that not only does XID+ perform better on metrics such as flux accuracy and flux uncertainty accuracy, we illustrate how obtaining the posterior probability distribution can help overcome some of the issues inherent with maximum likelihood based source extraction routines. We run XID+ on the COSMOS SPIRE maps from HerMES, using a 24 $\mathrm{μm}$ catalogue as a prior and show the marginalised SPIRE colour-colour plot and marginalised contribution to the cosmic infrared background at the SPIRE wavelengths. XID+ is a core tool arising from the Herschel Extragalactic Legacy Project (HELP) and we discuss how additional work within HELP providing prior information on fluxes can and will be utilised. The software is available at https://github.com/H-E-L-P/XID_plus. We also provide the data product for COSMOS. We believe this is the first time that the full posterior probability of galaxy photometry has been provided as a data product.

astro-ph.GA↗

arXiv2016

HELP: star formation as function of galaxy environmentwith Herschel

The Herschel Extragalactic Legacy Project (HELP) brings together a vast range of data from many astronomical observatories. Its main focus is on the Herschel data, which maps dust obscured star formation over 1300 deg$^2$. With this unprecedented combination of data sets, it is possible to investigate how the star formation vs stellar mass relation (main-sequence) of star-forming galaxies depends on environment. In this pilot study we explore this question between 0.1 < z < 3.2 using data in the COSMOS field. We estimate the local environment from a smoothed galaxy density field using the full photometric redshift probability distribution. We estimate star formation rates by stacking the SPIRE data from the Herschel Multi-tiered Extragalactic Survey (HerMES). Our analysis rules out the hypothesis that the main-sequence for star-forming systems is independent of environment at 1.5 < z < 2, while a simple model in which the mean specific star formation rate declines with increasing environmental density gives a better description. However, we cannot exclude a simple hypothesis in which the main-sequence for star-forming systems is independent of environment at z < 1.5 and z > 2. We also estimate the evolution of the star formation rate density in the COSMOS field and our results are consistent with previous measurements at z < 1.5 and z > 2 but we find a $1.4^{+0.3}_{-0.2}$ times higher peak value of the star formation rate density at $z \sim 1.9$.

astro-ph.GA↗

arXiv2015

The host galaxies of micro-Jansky radio sources

We combine a deep 0.5~deg$^2$, 1.4~GHz deep radio survey in the Lockman Hole with infrared and optical data in the same field, including the SERVS and UKIDSS near-infrared surveys, to make the largest study to date of the host galaxies of radio sources with typical radio flux densities $\sim 50 \;μ$Jy. 87% (1274/1467) of radio sources have identifications in SERVS to $AB\approx 23.1$ at 3.6 or 4.5$μ$m, and 9% are blended with bright objects (mostly stars), leaving only 4% (59 objects) which are too faint to confidently identify in the near-infrared. We are able to estimate photometric redshifts for 68% of the radio sources. We use mid-infrared diagnostics to show that the source population consists of a mixture of star forming galaxies, rapidly accreting (cold mode) AGN and low accretion rate, hot mode AGN, with neither AGN nor starforming galaxies clearly dominating. We see the breakdown in the $K-z$ relation in faint radio source samples, and show that it is due to radio source populations becoming dominated by sources with radio luminosities $\sim 10^{23}\;{\rm WHz^{-1}}$. At these luminosities, both the star forming galaxies and the cold mode AGN have hosts with stellar luminosities about a factor of two lower than those of hot mode AGN, which continue to reside in only the most massive hosts. We show that out to at least $z\sim 2$, galaxies with stellar masses $>10^{11.5}\, M_{\odot}$ have a radio-loud fraction up to $\sim 30$%. This is consistent with there being a sufficient number of radio sources that radio-mode feedback could play a role in galaxy evolution.

astro-ph.GA↗

arXiv2015

The composite nature of Dust-Obscured Galaxies (DOGs) at z~2-3 in the COSMOS field: I. A Far-Infrared View

Dust-Obscured galaxies (DOGs) are bright 24 um-selected sources with extreme obscuration at optical wavelengths. They are typically characterized by a rising power-law continuum of hot dust (T_D ~ 200-1000K) in the near-IR indicating that their mid-IR luminosity is dominated by an an active galactic nucleus (AGN). DOGs with a fainter 24 um flux display a stellar bump in the near-IR and their mid-IR luminosity appears to be mainly powered by dusty star formation. Alternatively, it may be that the mid-IR emission arising from AGN activity is dominant but the torus is sufficiently opaque to make the near-IR emission from the AGN negligible with respect to the emission from the host component. In an effort to characterize the astrophysical nature of the processes responsible for the IR emission in DOGs, this paper exploits Herschel data (PACS + SPIRE) on a sample of 95 DOGs within the COSMOS field. We derive a wealth of far-IR properties (e.g., total IR luminosities; mid-to-far IR colors; dust temperatures and masses) based on SED fitting. Of particular interest are the 24 um-bright DOGs (F_24um > 1mJy). They present bluer far-IR/mid-IR colors than the rest of the sample, unveiling the potential presence of an AGN. The AGN contribution to the total 8-1000 um flux increases as a function of the rest-frame 8 um-luminosity irrespective of the redshift. This confirms that faint DOGs (L_8 um< 10^12 L_sun) are dominated by star-formation while brighter DOGs show a larger contribution from an AGN.

astro-ph.GA↗

arXiv2015

Mapping the average AGN accretion rate in the SFR-M* plane for Herschel selected galaxies at 0<z<2.5

We study the relation of AGN accretion, star formation rate (SFR), and stellar mass (M$_*$) using a sample of $\approx$ 8600 star-forming galaxies up to z=2.5 selected with \textit{Herschel} imaging in the GOODS and COSMOS fields. For each of them we derive SFR and M$_*$, both corrected, when necessary, for emission from an active galactic nucleus (AGN), through the decomposition of their spectral energy distributions (SEDs). About 10 per cent of the sample are detected individually in \textit{Chandra} observations of the fields. For the rest of the sample we stack the X-ray maps to get average X-ray properties. After subtracting the X-ray luminosity expected from star formation and correcting for nuclear obscuration, we derive the average AGN accretion rate for both detected sources and stacks, as a function of M$_{*}$, SFR and redshift. The average accretion rate correlates with SFR and with M$_*$. The dependence on SFR becomes progressively more significant at z$>$0.8. This may suggest that SFR is the original driver of these correlations. We find that average AGN accretion and star formation increase in a similar fashion with offset from the star-forming "main-sequence". Our interpretation is that accretion onto the central black hole and star formation broadly trace each other, irrespective of whether the galaxy is evolving steadily on the main-sequence or bursting.

astro-ph.GA↗