DSpace Angular :: Browsing by Author "Farrah, D."

Browsing by Author "Farrah, D."

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A GROWTH-RATE INDICATOR FOR COMPTON-THICK ACTIVE GALACTIC NUCLEI
(2016) Brightman, M.; Masini, A.; Ballantyne, D. R.; Balokovic, M.; Brandt, W. N.; Chen, C. -T.; Comastri, A.; Farrah, D.; Gandhi, P.; Harrison, F. A.; Ricci, C.; Stern, D.; Walton, D. J.
Due to their heavily obscured central engines, the growth rate of Compton-thick (CT) active galactic nuclei (AGNs) is difficult to measure. A statistically significant correlation between the Eddington ratio, lambda(Edd), and the X-ray power-law index, Gamma, observed in unobscured AGNs offers an estimate of their growth rate from X-ray spectroscopy (albeit with large scatter). However, since X-rays undergo reprocessing by Compton scattering and photoelectric absorption when the line of sight to the central engine is heavily obscured, the recovery of the intrinsic Gamma is challenging. Here we study a sample of local, predominantly CT megamaser AGNs, where the black hole mass, and thus Eddington luminosity, are well known. We compile results of the X-ray spectral fitting of these sources with sensitive high-energy (E > 10 keV) NuSTAR data, where X-ray torus models, which take into account the reprocessing effects have been used to recover the intrinsic Gamma values and X-ray luminosities, L-X. With a simple bolometric correction to L-X to calculate lambda(Edd), we find a statistically significant correlation between Gamma and lambda(Edd) (p = 0.007). A linear fit to the data yields Gamma = (0.41 +/- 0.18)log(10)lambda(Edd) + (2.38 +/- 0.20), which is statistically consistent with results for unobscured AGNs. This result implies that torus modeling successfully recovers the intrinsic AGN parameters. Since the megamasers have low-mass black holes (M-BH approximate to 10(6)-10(7) M-circle dot) and are highly inclined, our results extend the Gamma-lambda(Edd) relationship to lower masses and argue against strong orientation effects in the corona, in support of AGN unification. Finally this result supports the use of Gamma as a growth-rate indicator for accreting black holes, even for CT AGNs.
A New Compton-thick AGN in Our Cosmic Backyard: Unveiling the Buried Nucleus in NGC 1448 with NuSTAR
(2017) Annuar, A.; Alexander, D.; Gandhi, P.; Lansbury, G.; Asmus, D.; Ballantyne, D.; Bauer, Franz Erik; Boggs, S.; Boorman, P.; Brandt W.; Brightman, M.|Christensen, F.; Craig, W.; Farrah, D.; Goulding, A.; Hailey, C.; Harrison, F.; Koss, M.; Lamassa, S.; Murray, S.; Ricci, Claudio; Rosario, D.; Stanley, F.; Stern, D.; Zhang, W.
Broad-band X-ray spectral analysis of the Seyfert 1 galaxy GRS 1734-292
(2017) Tortosa, A.; Marinucci, A.; Matt, G.; Bianchi, S.; La Franca, F.; Ballantyne, D. R.; Boorman, P. G.; Fabian, A. C.; Farrah, D.; Ricci, Claudio; Fuerst, F.; Gandhi, P.; Harrison, F. A.; Koss, M. J.; Stern, D.; Ursini, F.; Walton, D. J.
CONSTRAINING THE Lyα ESCAPE FRACTION WITH FAR- INFRARED OBSERVATIONS OF Lyα EMITTERS
(2014) Wardlow, Julie L.; Malhotra, S.; Zheng, Z.; Finkelstein, S.; Bock, J.; Bridge, C.; Calanog, J.; Ciardullo, R.; Conley, A.; Cooray, A.; Farrah, D.; Gawiser, E.; Gronwall, C.; Heinis, S.; Ibar, E.; Ivison, R. J.; Marsden, G.; Oliver, S. J.; Rhoads, J.; Riechers, D.; Schulz, B.; Smith, A. J.; Viero, M.; Wang, L.; Zemcov, M.
We study the far-infrared properties of 498 Ly alpha emitters (LAEs) at z = 2.8, 3.1, and 4.5 in the Extended Chandra Deep Field-South, using 250, 350, and 500 mu m data from the Herschel Multi-tiered Extragalactic Survey and 870 mu m data from the LABOCA ECDFS Submillimeter Survey. None of the 126, 280, or 92 LAEs at z = 2.8, 3.1, and 4.5, respectively, are individually detected in the far-infrared data. We use stacking to probe the average emission to deeper flux limits, reaching 1 sigma depths of similar to 0.1 to 0.4 mJy. The LAEs are also undetected at >= 3 sigma in the stacks, although a 2.5 sigma signal is observed at 870 mu m for the z = 2.8 sources. We consider a wide range of far-infrared spectral energy distributions (SEDs), including an M82 and an Sd galaxy template, to determine upper limits on the far-infrared luminosities and far-infrared-derived star formation rates of the LAEs. These star formation rates are then combined with those inferred from the Ly alpha and UV emission to determine lower limits on the LAEs' Lya escape fraction (f(esc)(Ly alpha)). For the Sd SED template, the inferred LAEs fesc(Ly alpha) are greater than or similar to 30% (1 sigma) at z = 2.8, 3.1, and 4.5, which are all significantly higher than the global fesc(Ly alpha) at these redshifts. Thus, if the LAEs fesc(Ly alpha) follows the global evolution, then they have warmer far-infrared SEDs than the Sd galaxy template. The average and M82 SEDs produce lower limits on the LAE fesc(Ly alpha) of similar to 10%-20% (1 sigma), all of which are slightly higher than the global evolution of fesc(Ly alpha), but consistent with it at the 2 sigma-3 sigma level.
Environment of the submillimeter-bright massive starburst HFLS3 at z similar to 6.34
(2015) Laporte, Nicolás; Perez, I.; Calanog, J.; Cooray, A.; Wardlow, J.; Bock, J.; Bridge, C.; Burgarella, D.; Bussmann, R.; Cabrera, Alejandro Leopoldo; Casey, C.; Clements, D.; Conley, A.; Dannerbauer, H.; Farrah, D.; Fu, H.
GRAVITATIONAL LENS MODELS BASED ON SUBMILLIMETER ARRAY IMAGING OF HERSCHEL-SELECTED STRONGLY LENSED SUB-MILLIMETER GALAXIES AT z > 1.5
(2013) Bussmann, R. S.; Perez-Fournon, I.; Amber, S.; Calanog, J.; Gurwell, M. A.; Dannerbauer, H.; De Bernardis, F.; Fu, Hai; Harris, A. I.; Krips, M.; Lapi, A.; Maiolino, R.; Omont, A.; Riechers, D.; Wardlow, J.; Baker, A. J.; Birkinshaw, M.; Bock, J.; Bourne, N.; Clements, D. L.; Cooray, A.; De Zotti, G.; Dunne, L.; Dye, S.; Eales, S.; Farrah, D.; Gavazzi, R.; Nuevo, J. Gonzalez; Hopwood, R.; Ibar, E.; Ivison, R. J.; Laporte, N.; Maddox, S.; Martinez-Navajas, P.; Michalowski, M.; Negrello, M.; Oliver, S. J.; Roseboom, I. G.; Scott, Douglas; Serjeant, S.; Smith, A. J.; Smith, Matthew; Streblyanska, A.; Valiante, E.; van der Werf, P.; Verma, A.; Vieira, J. D.; Wang, L.; Wilner, D.
Strong gravitational lenses are now being routinely discovered in wide-field surveys at (sub-)millimeter wavelengths. We present Submillimeter Array (SMA) high-spatial resolution imaging and Gemini-South and Multiple Mirror Telescope optical spectroscopy of strong lens candidates discovered in the two widest extragalactic surveys conducted by the Herschel Space Observatory: the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) and the Herschel Multi-tiered Extragalactic Survey (HerMES). From a sample of 30 Herschel sources with S-500 > 100 mJy, 21 are strongly lensed (i.e., multiply imaged), 4 are moderately lensed (i.e., singly imaged), and the remainder require additional data to determine their lensing status. We apply a visibility-plane lens modeling technique to the SMA data to recover information about the masses of the lenses as well as the intrinsic (i.e., unlensed) sizes (r(half)) and far-infrared luminosities (L-FIR) of the lensed submillimeter galaxies (SMGs). The sample of lenses comprises primarily isolated massive galaxies, but includes some groups and clusters as well. Several of the lenses are located at z(lens) > 0.7, a redshift regime that is inaccessible to lens searches based on Sloan Digital Sky Survey spectroscopy. The lensed SMGs are amplified by factors that are significantly below statistical model predictions given the 500 mu m flux densities of our sample. We speculate that this may reflect a deficiency in our understanding of the intrinsic sizes and luminosities of the brightest SMGs. The lensed SMGs span nearly one decade in L-FIR (median L-FIR = 7.9 x 10(12) L-circle dot) and two decades in FIR luminosity surface density (median Sigma(FIR) = 6.0 x 10(11) L-circle dot kpc(-2)). The strong lenses in this sample and others identified via (sub-) mm surveys will provide a wealth of information regarding the astrophysics of galaxy formation and evolution over a wide range in redshift.
HerMES: CANDIDATE HIGH-REDSHIFT GALAXIES DISCOVERED WITH HERSCHEL/SPIRE
(2014) Dowell, C. Darren; Conley, A.; Glenn, J.; Arumugam, V.; Asboth, V.; Aussel, H.; Bertoldi, F.; Bethermin, M.; Bock, J.; Boselli, A.; Bridge, C.; Buat, V.; Burgarella, D.; Cabrera-Lavers, A.; Casey, C. M.; Chapman, S. C.; Clements, D. L.; Conversi, L.; Cooray, A.; Dannerbauer, H.; De Bernardis, F.; Ellsworth-Bowers, T. P.; Farrah, D.; Franceschini, A.; Griffin, M.; Gurwell, M. A.; Halpern, M.; Hatziminaoglou, E.; Heinis, S.; Ibar, E.; Ivison, R. J.; Laporte, N.; Marchetti, L.; Martinez-Navajas, P.; Marsden, G.; Morrison, G. E.; Nguyen, H. T.; O'Halloran, B.; Oliver, S. J.; Omont, A.; Page, M. J.; Papageorgiou, A.; Pearson, C. P.; Petitpas, G.; Perez-Fournon, I.; Pohlen, M.; Riechers, D.; Rigopoulou, D.; Roseboom, I. G.; Rowan-Robinson, M.; Sayers, J.; Schulz, B.; Scott, Douglas; Seymour, N.; Shupe, D. L.; Smith, A. J.; Streblyanska, A.; Symeonidis, M.; Vaccari, M.; Valtchanov, I.; Vieira, J. D.; Viero, M.; Wang, L.; Wardlow, J.; Xu, C. K.; Zemcov, M.
We present a method for selecting z > 4 dusty, star-forming galaxies (DSFGs) using Herschel/Spectral and Photometric Imaging Receiver 250/350/500 mu m flux densities to search for red sources. We apply this method to 21 deg(2) of data from the HerMES survey to produce a catalog of 38 high-z candidates. Follow-up of the first five of these sources confirms that this method is efficient at selecting high-z DSFGs, with 4/5 at z = 4.3-6.3 (and the remaining source at z = 3.4), and that they are some of the most luminous dusty sources known. Comparison with previous DSFG samples, mostly selected at longer wavelengths (e. g., 850 mu m) and in single-band surveys, shows that our method is much more efficient at selecting high-z DSFGs, in the sense that a much larger fraction are at z > 3. Correcting for the selection completeness and purity, we find that the number of bright (S-500 (mu m) >= 30 mJy), red Herschel sources is 3.3 +/- 0.8 deg(-2). This is much higher than the number predicted by current models, suggesting that the DSFG population extends to higher redshifts than previously believed. If the shape of the luminosity function for high-z DSFGs is similar to that at z similar to 2, rest-frame UV based studies may be missing a significant component of the star formation density at z = 4-6, even after correction for extinction.
HerMES: COSMIC INFRARED BACKGROUND ANISOTROPIES AND THE CLUSTERING OF DUSTY STAR-FORMING GALAXIES
(2013) Viero, M. P.; Wang, L.; Zemcov, M.; Addison, G.; Amblard, A.; Arumugam, V.; Aussel, H.; Bethermin, M.; Bock, J.; Boselli, A.; Buat, V.; Burgarella, D.; Casey, C. M.; Clements, D. L.; Conley, A.; Conversi, L.; Cooray, A.; De Zotti, G.; Dowell, C. D.; Farrah, D.; Franceschini, A.; Glenn, J.; Griffin, M.; Hatziminaoglou, E.; Heinis, S.; Ibar, E.; Ivison, R. J.; Lagache, G.; Levenson, L.; Marchetti, L.; Marsden, G.; Nguyen, H. T.; O'Halloran, B.; Oliver, S. J.; Omont, A.; Page, M. J.; Papageorgiou, A.; Pearson, C. P.; Perez-Fournon, I.; Pohlen, M.; Rigopoulou, D.; Roseboom, I. G.; Rowan-Robinson, M.; Schulz, B.; Scott, D.; Seymour, N.; Shupe, D. L.; Smith, A. J.; Symeonidis, M.; Vaccari, M.; Valtchanov, I.; Vieira, J. D.; Wardlow, J.; Xu, C. K.
We present measurements of the auto-and cross-frequency power spectra of the cosmic infrared background (CIB) at 250, 350, and 500 mu m (1200, 860, and 600 GHz) from observations totaling similar to 70 deg(2) made with the SPIRE instrument aboard the Herschel Space Observatory. We measure a fractional anisotropy delta I/I = 14% +/- 4%, detecting signatures arising from the clustering of dusty star-forming galaxies in both the linear (2-halo) and nonlinear (1-halo) regimes; and that the transition from the 2- to 1-halo terms, below which power originates predominantly from multiple galaxies within dark matter halos, occurs at k(theta) similar to 0.10-0.12 arcmin(-1) (l similar to 2160-2380), from 250 to 500 mu m. New to this paper is clear evidence of a dependence of the Poisson and 1-halo power on the flux-cut level of masked sources-suggesting that some fraction of the more luminous sources occupy more massive halos as satellites, or are possibly close pairs. We measure the cross-correlation power spectra between bands, finding that bands which are farthest apart are the least correlated, as well as hints of a reduction in the correlation between bands when resolved sources are more aggressively masked. In the second part of the paper, we attempt to interpret the measurements in the framework of the halo model. With the aim of fitting simultaneously with one model the power spectra, number counts, and absolute CIB level in all bands, we find that this is achievable by invoking a luminosity-mass relationship, such that the luminosity-to-mass ratio peaks at a particular halo mass scale and declines toward lower and higher mass halos. Our best-fit model finds that the halo mass which is most efficient at hosting star formation in the redshift range of peak star-forming activity, z similar to 1-3, is log( M-peak/M-circle dot) similar to 12.1 +/- 0.5, and that the minimum halo mass to host infrared galaxies is log(Mmin/M-circle dot) similar to 10.1 +/- 0.6.
HerMES: THE CONTRIBUTION TO THE COSMIC INFRARED BACKGROUND FROM GALAXIES SELECTED BY MASS AND REDSHIFT
(2013) Viero, M. P.; Moncelsi, L.; Quadri, R. F.; Arumugam, V.; Assef, R. J.; Bethermin, M.; Bock, J.; Bridge, C.; Casey, C. M.; Conley, A.; Cooray, A.; Farrah, D.; Glenn, J.; Heinis, S.; Ibar, E.; Ikarashi, S.; Ivison, R. J.; Kohno, K.; Marsden, G.; Oliver, S. J.; Roseboom, I. G.; Schulz, B.; Scott, D.; Serra, P.; Vaccari, M.; Vieira, J. D.; Wang, L.; Wardlow, J.; Wilson, G. W.; Yun, M. S.; Zemcov, M.
We quantify the fraction of the cosmic infrared background (CIB) that originates from galaxies identified in the UV/optical/near-infrared by stacking 81,250 (similar to 35.7 arcmin(-2)) K-selected sources (K-AB < 24.0) split according to their rest-frame U-V versus V-J colors into 72,216 star-forming and 9034 quiescent galaxies, on maps from Spitzer/MIPS (24 mu m), Herschel/PACS (100, 160 mu m), Herschel/SPIRE (250, 350, 500 mu m), and AzTEC (1100 mu m). The fraction of the CIB resolved by our catalog is (69% +/- 15%) at 24 mu m, (78% +/- 17%) at 70 mu m, (58% +/- 13%) at 100 mu m, (78% +/- 18%) at 160 mu m, (80% +/- 17%) at 250 mu m, (69% +/- 14%) at 350 mu m, (65% +/- 12%) at 500 mu m, and (45% +/- 8%) at 1100 mu m. Of that total, about 95% originates from star-forming galaxies, while the remaining 5% is from apparently quiescent galaxies. The CIB at lambda less than or similar to 200 mu m appears to be sourced predominantly from galaxies at z less than or similar to 1, while at. greater than or similar to 200 mu m the bulk originates from 1 less than or similar to z less than or similar to 2. Galaxies with stellar masses log(M/M-circle dot) = 9.5-11 are responsible for the majority of the CIB, with those in the log(M/M-circle dot) = 9.5-10 bin contributing mostly at lambda < 250 mu m, and those in the log(M/M circle dot) = 10-11 bin dominating at lambda > 350 mu m. The contribution from galaxies in the log(M/M-circle dot) = 9.0-9.5 (lowest) and log(M/M-circle dot) = 11.0-12.0 (highest) stellar-mass bins contribute the least-both of order 5%-although the highest stellar-mass bin is a significant contributor to the luminosity density at z greater than or similar to 2. The luminosities of the galaxies responsible for the CIB shifts from combinations of "normal" and luminous infrared galaxies (LIRGs) at lambda less than or similar to 160 mu m, to LIRGs at 160 less than or similar to lambda less than or similar to 500 mu m, to finally LIRGs and ultra-luminous infrared galaxies at lambda greater than or similar to 500 mu m. Stacking analyses were performed using SIMSTACK, a novel algorithm designed to account for possible biases in the stacked flux density due to clustering. It is made available to the public at www.astro.caltech.edu/similar to viero/viero_homepage/toolbox.html.
Herschel reveals the obscured star formation in HiZELS Hα emitters at z=1.47
(2013) Ibar, E.; Sobral, D.; Best, P. N.; Ivison, R. J.; Smail, I.; Arumugam, V.; Berta, S.; Bethermin, M.; Bock, J.; Cava, A.; Conley, A.; Farrah, D.; Geach, J.; Ikarashi, S.; Kohno, K.; Le Floc'h, E.; Lutz, D.; Magdis, G.; Magnelli, B.; Marsden, G.; Oliver, S. J.; Page, M. J.; Pozzi, F.; Riguccini, L.; Schulz, B.; Seymour, N.; Smith, A. J.; Symeonidis, M.; Wang, L.; Wardlow, J.; Zemcov, M.
We describe the far-infrared (far-IR; rest-frame 8-1000-mu m) properties of a sample of 443 H alpha-selected star-forming galaxies in the Cosmic Evolution Survey (COSMOS) and Ultra Deep Survey (UDS) fields detected by the High-redshift Emission Line Survey (HiZELS) imaging survey. Sources are identified using narrow-band filters in combination with broad-band photometry to uniformly select H alpha (and [O ii] if available) emitters in a narrow redshift slice at z = 1.47 +/- 0.02. We use a stacking approach in Spitzer-MIPS mid-IR, Herschel-PACS/SPIRE far-IR [from the PACS Evolutionary Prove (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES)] and AzTEC mm-wave images to describe their typical far-IR properties. We find that HiZELS galaxies with observed H alpha luminosities of L(H alpha)(obs) approximate to 10(8.1-9.1) L-circle dot ( approximate to 10(41.7-42.7) erg s(-1)) have bolometric far-IR luminosities of typical luminous IR galaxies, L(8-1000 mu m) approximate to 10(-0.006)(11.41)(+0.04) L-circle dot. Combining the H alpha and far-IR luminosities, we derive median star formation rates (SFRs) of SFRH alpha, FIR = 32 +/- 5 M-circle dot yr(-1) and H alpha extinctions of A(H alpha) = 1.0 +/- 0.2 mag. Perhaps surprisingly, little difference is seen in typical HiZELS extinction levels compared to local star-forming galaxies. We confirm previous empirical stellar mass (M-*) to A(H alpha) relations and the little or no evolution up to z = 1.47. For HiZELS galaxies (or similar samples) we provide an empirical parametrization of the SFR as a function of rest-frame (u - z) colours and 3.6-mu m photometry - a useful proxy to aid in the absence of far-IR detections in high-z galaxies. We find that the observed H alpha luminosity is a dominant SFR tracer when rest-frame (u - z) colours are less than or similar to 0.9 mag or when Spitzer-3.6-mu m photometry is fainter than 22 mag (Vega) or when stellar masses are lower than 10(9.7) M-circle dot. We do not find any correlation between the [O ii]/H alpha and far-IR luminosity, suggesting that this emission line ratio does not trace the extinction of the most obscured star-forming regions, especially in massive galaxies where these dominate. The luminosity-limited HiZELS sample tends to lie above of the so-called main sequence for star-forming galaxies, especially at low stellar masses, indicating high star formation efficiencies in these galaxies. This work has implications for SFR indicators and suggests that obscured star formation is linked to the assembly of stellar mass, with deeper potential wells in massive galaxies providing dense, heavily obscured environments in which stars can form rapidly.
HERSCHEL-ATLAS: A BINARY HyLIRG PINPOINTING A CLUSTER OF STARBURSTING PROTOELLIPTICALS
(2013) Ivison, R. J.; Swinbank, A. M.; Smail, Ian; Harris, A. I.; Bussmann, R. S.; Cooray, A.; Cox, P.; Fu, H.; Kovacs, A.; Krips, M.; Narayanan, D.; Negrello, M.; Neri, R.; Penarrubia, J.; Richard, J.; Riechers, D. A.; Rowlands, K.; Staguhn, J. G.; Targett, T. A.; Amber, S.; Baker, A. J.; Bourne, N.; Bertoldi, F.; Bremer, M.; Calanog, J. A.; Clements, D. L.; Dannerbauer, H.; Dariush, A.; De Zotti, G.; Dunne, L.; Eales, S. A.; Farrah, D.; Fleuren, S.; Franceschini, A.; Geach, J. E.; George, R. D.; Helly, J. C.; Hopwood, R.; Ibar, E.; Jarvis, M. J.; Kneib, J. -P.; Maddox, S.; Omont, A.; Scott, D.; Serjeant, S.; Smith, M. W. L.; Thompson, M. A.; Valiante, E.; Valtchanov, I.; Vieira, J.; van der Werf, P.
Panchromatic observations of the best candidate hyperluminous infrared galaxies from the widest Herschel extragalactic imaging survey have led to the discovery of at least four intrinsically luminous z = 2.41 galaxies across an approximate to 100 kpc region-a cluster of starbursting protoellipticals. Via subarcsecond interferometric imaging we have measured accurate gas and star formation surface densities. The two brightest galaxies span similar to 3 kpc FWHM in submillimeter/radio continuum and CO J = 4-3, and double that in CO J = 1-0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks-a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have M-dyn of several x 10(11) M-circle dot, and gas fractions of similar to 40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star formation rates place them greater than or similar to 5x above the main sequence, which supposedly comprises large gas disks like these. Their high star formation efficiencies are difficult to reconcile with a simple volumetric star formation law. N-body and dark matter simulations suggest that this system is the progenitor of a B(inary)-type approximate to 10(14.6)-M-circle dot cluster.
IC 3639—A NEW BONA FIDE COMPTON-THICK AGN UNVEILED BY NuSTAR
(2016) Boorman, Peter G.; Gandhi, P.; Alexander, D. M.; Annuar, A.; Ballantyne, D. R.; Bauer, Franz Erik; Boggs, S. E.; Brandt, W. N.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Farrah, D.; Hailey, C. J.; Harrison, F. A.; Hönig, S. F.; Koss, M.; LaMassa, S. M.; Masini, A. C.; Ricci, G.; Risaliti, D.; Stern, W.; Zhang, W.
New spectral model for constraining torus covering factors from broadband X-ray spectra of active galactic nuclei
(2018) Baloković, M.; Brightman, M.; Harrison, F.A.; Comastri, A.; Ricci, Claudio; Buchner, J.; Gandhi, P.; Farrah, D.; Stern, D.
NuSTAR observations of four nearby X-ray faint AGNs: low luminosity or heavy obscuration?
(OUP, 2020) Annuar, A.; Alexander, D. M.; Gandhi, P.; Lansbury, G. B.; Asmus, D.; Balokovic, M.; Ballantyne, D. R.; Bauer, Franz Erik; Boorman, P. G.; Brandt, W. N.; Brightman, M.; Chen, C. T. J.; Del Moro, A.; Farrah, D.; Harrison, F. A.; Koss, M. J.; Lanz, L.; Marchesi, S.; Masini, A.; Nardini, E.; Ricci, Claudio; Stern, D.; Zappacosta, L.
We present NuSTAR (Nuclear Spectroscopic Telescope Array) observations of four active galactic nuclei (AGNs) located within 15 Mpc. These AGNs, namely ESO 121-G6, NGC 660, NGC 3486, and NGC 5195, have observed X-ray luminosities of L 2–10 keV,obs ≲ 10 39 erg s −1 , classifying them as low-luminosity AGN (LLAGN). We perform broad-band X-ray spectral analysis for the AGN by combining our NuSTAR data with Chandra or XMM–Newton observations to directly measure their column densities (N H ) and infer their intrinsic power. We complement our X-ray data with archival and new high-angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured (N H > 10 23 cm −2 ; L 2–10 keV,int ∼ 10 41 erg s −1 ), and NGC 660 may be Compton thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with L 2–10 keV,int < 10 39 erg s −1 , i.e. genuine LLAGN. Both of the heavily obscured AGNs have L bol > 10 41 erg s −1 and λ Edd ≳ 10 −3 , and are detected in high-angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486, however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN.
The Phoenix galaxy as seen by NuSTAR
(2017) Masini, A.; Comastri, A.; Puccetti, S.; Balokovic, M.; Gandhi, P.; Guainazzi, M.; Boggs, S.; Ricci, Claudio; Bauer, Franz Erik; Boorman, P.; Brightman, M.; Christensen, F.; Craig, W.; Farrah, D.; Hailey, C.; Harrison, F.; Koss, M.
The roles of star formation and AGN activity of IRS sources in the HerMES fields
(2013) Feltre, A.; Hatziminaoglou, E.; Hernan-Caballero, A.; Fritz, J.; Franceschini, A.; Bock, J.; Cooray, A.; Farrah, D.; Solares, E. A. Gonzalez; Ibar, E.; Isaak, K. G.; Lo Faro, B.; Marchetti, L.; Oliver, S. J.; Page, M. J.; Rigopoulou, D.; Roseboom, I. G.; Symeonidis, M.; Vaccari, M.
In this work, we explore the impact of the presence of an active galactic nucleus (AGN) on the mid- and far-infrared (IR) properties of galaxies as well as the effects of simultaneous AGN and starburst activity in the same galaxies. To do this, we apply a multicomponent, multiband spectral synthesis technique to a sample of 250 mu m selected galaxies of the Herschel Multi-tiered Extragalactic Survey (HerMES), with Infrared Spectrograph (IRS) spectra available for all galaxies. Our results confirm that the inclusion of the IRS spectra plays a crucial role in the spectral analysis of galaxies with an AGN component improving the selection of the best-fitting hot dust (torus) model.

Browsing by Author "Farrah, D."

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