Author: Itziar Aretxaga

UNCOVERING THE DEEPLY EMBEDDED ACTIVE GALACTIC NUCLEUS ACTIVITY IN THENUCLEAR REGIONS OF THE INTERACTING GALAXY Arp 299

Itziar Aretxaga (2013)

We present mid-infrared (MIR) 8–13μm spectroscopy of the nuclear regions of the interacting galaxy Arp 299(IC 694+NGC 3690) obtained with CanariCam (CC) on the 10.4 m Gran Telescopio Canarias (GTC). The highangular resolution (∼0”.3–0”.6) of the data allows us to probe nuclear physical scales between 60 and 120 pc,which is a factor of 10 improvement over previous MIR spectroscopic observations ofthis system. The GTC/CCspectroscopy displays evidence of deeply embedded active galactic nucleus (AGN) activity in both nuclei. The GTC/CC nuclear spectrum of NGC 3690/Arp 299-B1 can be explained as emission from AGN-heated dustin a clumpy torus with both a high covering factor and high extinction along the line of sight. The estimatedbolometric luminosity of the AGN in NGC 3690 is 3.2 ± 0.6 × 10⁴⁴ erg s⁻¹. The nuclear GTC/CC spectrum ofIC 694/Arp 299-A shows 11.3μm polycyclic aromatic hydrocarbon emission stemming from a deeply embedded (Av∼ 24 mag) region of less than 120 pc in size. There is also a continuum-emitting dust component. If associatedwith the putative AGN in IC 694, we estimate that it would be approximately five times less luminous than the AGN in NGC 3690. The presence of dual AGN activity makes Arp 299 a good example to study such phenomena in the early coalescence phase of interacting galaxies.

Article

Galaxies: individual (Arp 299, IC 694, NGC 3690) Galaxies: nuclei Galaxies: Seyfert Infrared: galaxies CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA

The SCUBA-2 Cosmology Legacy Survey: blank-field number counts of 450-μm-selected galaxies and their contribution to the cosmic infrared Background

Itziar Aretxaga David Hughes (2013)

The first deep blank-field 450 μm map (1σ≈ 1.3 mJy) from the Submillimetre Common- User Bolometer Array-2 SCUBA-2 Cosmology Legacy Survey (S2CLS), conducted with the James Clerk Maxwell Telescope (JCMT) is presented. Our map covers 140 arcmin² of the Cosmological Evolution Survey field, in the footprint of the Hubble Space Telescope (HST) Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. Using 60 submillimetre galaxies detected at ≥3.75σ, we evaluate the number counts of 450-μm-selected galaxies with flux densities S₄₅₀>5 mJy. The 8 arcsec JCMT beam and high sensitivity of SCUBA-2 now make it possible to directly resolve a larger fraction of the cosmic infrared background (CIB, peaking at λ∼ 200 μm) into the individual galaxies responsible for its emission than has previously been possible at this wavelength. At S₄₅₀>5 mJy, we resolve (7.4 ± 0.7) × 10¯² MJy sr¯¹ of the CIB at 450 μm (equivalent to 16 ± 7 per cent of the absolute brightness measured by the Cosmic Background Explorer at this wavelength) into point sources. Afurther ∼40 per cent of the CIB can be recovered through a statistical stack of 24 μm emitters in this field, indicating that the majority (≈60 per cent) of the CIB at 450 μm is emitted by galaxies with S₄₅₀>2 mJy. The average redshift of 450 μm emitters identified with (LIR ≈ 1.1 × 10¹² L⊙). If the galaxies contributing to the statistical stack lie at similar redshifts, then the majority of the CIB at 450 μm is emitted by galaxies in the luminous infrared galaxy (LIRG) class with LIR>3.6 × 10¹¹ L⊙.

Article

Galaxies: high-redshift Cosmology: observations Submillimetre: galaxies CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA

X-ray detections of submillimetre galaxies: active galactic nuclei versus starburst contribution

Itziar Aretxaga David Hughes (2013)

We present a large-scale study of the X-ray properties and near-IR-to-radio spectral energy distributions (SEDs) of submillimetre galaxies (SMGs) detected at 1.1 mm with the AzTEC instrument across a ∼1.2 square degree area of the sky. Combining deep 2–4 Ms Chandra data with Spitzer IRAC/MIPS and Very Large Array data within the Great Observatories Origins Deep Survey North (GOODS-N), GOODS-S and COSMOS fields, we find evidence for active galactic nucleus (AGN) activity in ∼14 per cent of 271 AzTEC SMGs, ∼28 per cent considering only the two GOODS fields. Through X-ray spectral modelling and multiwavelength SED fitting using Monte Carlo Markov chain techniques to Siebenmorgen et al. (AGN) and Efstathiou, Rowan-Robinson & Siebenmorgen (starburst) templates, we find that while star formation dominates the IR emission, with star formation rates (SFRs) ∼100–1000M⊙ yr⁻¹, the X-ray emission for most sources is almost exclusively from obscured AGNs, with column densities in excess of 10²³ cm⁻². Only for ∼6 per cent of our sources do we find an X-ray-derived SFR consistent with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR, preventing significant contribution from the AGN template. Our SED modelling further shows that the AGN and starburst templates typically lack the required 1.1 mm emission necessary to match observations, arguing for an extended, cool dust component. The cross-correlation function between the full samples of X-ray sources and SMGs in these fields does not indicate a strong correlation between the two populations at large scales, suggesting that SMGs and AGNs do not necessarily trace the same underlying large-scale structure. Combined with the remaining X-ray-dim SMGs, this suggests that sub-mm-bright sources may evolve along multiple tracks, with X-ray-detected SMGs representing transitionary objects between periods of high star formation and AGN activity, while X-ray-faint SMGs represent a brief starburst phase of more normal galaxies.

Article

Galaxies: active Galaxies: high-redshift Galaxies: starburst Submillimetre: galaxies X-rays: galaxies CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA

Submm/mm Galaxy Counterpart Identification Using a Characteristic Density Distribution

Itziar Aretxaga David Hughes (2013)

We present a new submm/mm galaxy counterpart identification technique whichbuilds on the use of Spitzer IRAC colors as discriminators between likely counter-parts and the general IRAC galaxy population. Using 102 radio- and SMA-confirmedcounterparts to AzTEC sources across three fields (GOODS-N, GOODS-S, and COSMOS), we develop a non-parametric IRAC color-color characteristic density distribution (CDD), which, when combined with positional uncertainty information vialikelihood ratios, allows us to rank all potential IRAC counterparts around SMGsand calculate the significance of each ranking via the reliability factor. We reportall robust and tentative radio counterparts to SMGs, the first such list available forAzTEC/COSMOS, as well as the highest ranked IRAC counterparts for all AzTECSMGs in these fields as determined by our technique. We demonstrate that the technique is free of radio bias and thus applicable regardless of radio detections. For observations made with a moderate beamsize (∼18′′), this technique identifies ∼85 percent of SMG counterparts. For much larger beamsizes (≳30′′), we report identificationrates of 33-49 per cent. Using simulations, we demonstrate that this technique is animprovement over using positional information alone for observations with facilities such as AzTEC on the LMT and SCUBA-2 on JCMT.

Article

Submillimetre: galaxies Radio continuum: galaxies Infrared: galaxies Galaxies: high redshift Techniques: photometric Methods: data analysis CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA RADIOASTRONOMÍA RADIOASTRONOMÍA

A massive bubble of extremely metal-poor gas around a collapsing Lyα blob at z = 2.54

Andrew Humphrey Itziar Aretxaga (2013)

Using long-slit optical spectroscopy obtained at the 10.4 m Gran Telescopio Canarias, we have examined the gaseous environment of the radio-loud quasar TXS 1436+157 (z = 2.54),previously known to be associated with a large Lyαnebula and a spatially extended Lyα-absorbing structure. From the Lyαnebula, we measure kinematic properties consistent withinfall at a rate of ∼10–100 M⊙ yr⁻¹ – more than sufficient to power a quasar at the top of theluminosity function.The absorbing structure lies outside of the Lyαnebula, at a radius of ≳40 kpc from thequasar. Against the bright unresolved continuum and line emission from the quasar, we detectin absorption the NVλλ1239, 1241, CIVλλ1548, 1551 and Si IVλλ1394, 1403 doublets, withno unambiguous detection of absorption lines from any low-ionization species of metal. Themetal column densities, taken together with the HI column density measurement from the literature, indicate that the absorbing gas is predominantly ionized by the quasar, has a massof hydrogen of ≳1.6 × 10¹¹ M⊙, a gas density of ≤18 cm⁻³, a line-of-sight thickness of≥18 pc and a covering factor approaching unity. While this absorbing structure is clearly notcomposed of pristine gas, it has an extremely low metallicity, with ionizationmodels providinga 3σ limit of 12+log(O/H) ≤ 7.3.To explain these results, we discuss a scenario involving starburst-driven superbubbles andthe creation of infalling filaments of cold gas which fuel/trigger the quasar. We also discussthe possibility of detecting large-scale absorbers such as this in emission when illuminated bya powerful quasar.

Article

Galaxies: active Galaxies: evolution Galaxies: ISM Quasars: absorption lines Qasars: emission lines Quasars: individual: TXS 1436+157 CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA