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.Comment: Accepted by MNRAS. 20 pages, 9 figure

AGN in the CALIFA survey: X-ray detection of nuclear sources

A complete demographic of active galactic nuclei (AGN) is essential to understand the evolution of the Universe. Optical surveys estimate the population of AGN in the local Universe to be of $\sim$ 4%. However, these results could be biased towards bright sources, not affected by the host galaxy attenuation. An alternative method for detecting these objects is through the X-ray emission. In this work, we aim to complement the AGN population of the optical CALIFA survey (941 sources), by using X-ray data from Chandra, which provides the best spatial resolution to date, essential to isolate the nuclear emission from the host galaxy. We study a total of 138 sources with available data. We find 34 new bonafide AGN and 23 AGN candidates, which could increase the AGN population to 7-10\% among the CALIFA survey. X-rays are particularly useful for low-luminosity AGN since they are excluded by the criterion of large equivalent width of the $H\alpha$ emission line when applied to optical selections. Indeed, placing such a restrictive criteria might cause a loss of up to 70% of AGN sources. X-ray detected sources are preferentially located in the right side of the [$OIII$]/$H\beta$ versus [$NII$]/$H\alpha$ diagram, suggesting that this diagram might be the most reliable at classifying AGN sources. Our results support the idea that multi-wavelength studies are the best way to obtain a complete AGN population.Comment: 18 pages, 8 figures, 7 tables, 5 pages of supplementary online material available. Accepted for publication in MNRA

The inner view of NGC 1052 using multiple X-ray observations

In this paper, we make a multi-epoch analysis of NGC 1052, one of the prototypical LLAGN, using XMM-Newton, Suzaku and NuSTAR observations, taken from 2001 to 2017. This is the first time that results from NuSTAR observations are reported for NGC 1052. On the technical aspects, we found a wavelength-dependent calibration issue between simultaneous XMM-Newton and NuSTAR spectra. It is described by a change on the photon index of $\rm{ \Gamma_{NuSTAR}- \Gamma_{XMM-Newton}=0.17\pm0.04}$. We use ancillary Chandra data to decontaminate the nuclear spectrum from circumnuclear contributors. We find that two baseline models can fit the broad (0.5-50 keV) X-ray spectrum of the source. One consists of a power-law like continuum which is absorbed by a uniform absorber, reflection from neutral material, and a separate power-law component in the soft band. The second model presents a clumpy absorber. The reflection component is still present, but not the soft band power-law. Instead, absorption by a warm absorber is necessary to fit the spectra. This is the first time that a reflection component is established in this object, thanks to high energy data from NuSTAR. This component is constant in flux and shape, supporting the idea that is produced away from the central source (probably the torus). We find flux, spectral slope and absorption variations on timescales of months to years. We also find that a patchy-absober can explain the behaviour of this source better as it is $\sim$ 200 times more likely than the uniform absober while it yields to smaller intrinsic variations.Comment: 11 pages, 6 figures, 2 tables. Accepted for publication in MNRA

Resolving the AGN and host emission in the mid-infrared using a model-independent spectral decomposition

We present results on the spectral decomposition of 118 Spitzer Infrared Spectrograph (IRS) spectra from local active galactic nuclei (AGN) using a large set of Spitzer/IRS spectra as templates. The templates are themselves IRS spectra from extreme cases where a single physical component (stellar, interstellar, or AGN) completely dominates the integrated mid-infrared emission. We show that a linear combination of one template for each physical component reproduces the observed IRS spectra of AGN hosts with unprecedented fidelity for a template fitting method, with no need to model extinction separately. We use full probability distribution functions to estimate expectation values and uncertainties for observables, and find that the decomposition results are robust against degeneracies. Furthermore, we compare the AGN spectra derived from the spectral decomposition with sub-arcsecond resolution nuclear photometry and spectroscopy from ground-based observations. We find that the AGN component derived from the decomposition closely matches the nuclear spectrum, with a 1-sigma dispersion of 0.12 dex in luminosity and typical uncertainties of ~0.19 in the spectral index and ~0.1 in the silicate strength. We conclude that the emission from the host galaxy can be reliably removed from the IRS spectra of AGN. This allows for unbiased studies of the AGN emission in intermediate and high redshift galaxies -currently inaccesible to ground-based observations- with archival Spitzer/IRS data and in the future with the Mid-InfraRed Instrument of the James Webb Space Telescope. The decomposition code and templates are available at http://www.denebola.org/ahc/deblendIRS.Comment: 16 pages, 15 figures, 2 tables, accepted for publication in Ap

A bright radio HH object with large proper motions in the massive star-forming region W75N

We analyze radio continuum and line observations from the archives of the Very Large Array, as well as X-ray observations from the \emph{Chandra} archive of the region of massive star formation W75N. Five radio continuum sources are detected: VLA 1, VLA 2, VLA 3, Bc, and VLA 4. VLA 3 appears to be a radio jet; we detect J=1-0, v=0 SiO emission towards it, probably tracing the inner parts of a molecular outflow. The radio continuum source Bc, previously believed to be tracing an independent star, is found to exhibit important changes in total flux density, morphology, and position. These results suggest that source Bc is actually a radio Herbig-Haro object, one of the brightest known, powered by the VLA~3 jet source. VLA 4 is a new radio continuum component, located a few arcsec to the south of the group of previously known radio sources. Strong and broad (1,1) and (2,2) ammonia emission is detected from the region containing the radio sources VLA~1, VLA~2, and VLA~3. Finally, the 2-10 keV emission seen in the \emph{Chandra}/ACIS image shows two regions that could be the termination shocks of the outflows from the multiple sources observed in W75N.Comment: 26 pages, 7 figure

Differences between CO- and calcium triplet-derived velocity dispersions in spiral galaxies: evidence for central star formation?

et al.We examine the stellar velocity dispersions (σ) of a sample of 48 galaxies, 35 of which are spirals, from the Palomar nearby galaxy survey. It is known that for ultra-luminous infrared galaxies (ULIRGs) and merger remnants, the σ derived from the near-infrared CO band heads is smaller than that measured from optical lines, while no discrepancy between these measurements is found for early-type galaxies. No such studies are available for spiral galaxies – the subject of this paper. We used cross-dispersed spectroscopic data obtained with the Gemini Near-Infrared Spectrograph, with spectral coverage from 0.85 to 2.5 μm, to obtain σ measurements from the 2.29 μm CO band heads (σCO) and the 0.85 μm calcium triplet (σCaT). For the spiral galaxies in the sample, we found that σCO is smaller than σCaT, with a mean fractional difference of 14.3 per cent. The best fit to the data is given by σopt = (46.0 ± 18.1) + (0.85 ± 0.12)σCO. This ‘σ-discrepancy’ may be related to the presence of warm dust, as suggested by a slight correlation between the discrepancy and the infrared luminosity. This is consistent with studies that have found no σ-discrepancy in dust-poor early-type galaxies, and a much larger discrepancy in dusty merger remnants and ULIRGs. That σCO is lower than σopt may also indicate the presence of a dynamically cold stellar population component. This would agree with the spatial correspondence between low-σCO and young/intermediate-age stellar populations that has been observed in spatially resolved spectroscopy of a handful of galaxies.RAR acknowledges support from FAPERGS (project no. 12/1209-6) and CNPq (project no. 470090/2013-8). LCH acknowledges support from the Kavli Foundation, Peking University, and grant no. XDB09030102 (Emergence of Cosmological Structures) from the Strategic Priority Research Program of the Chinese Academy of Sciences. ARA acknowledges CNPq for partial support to this work through grant 307403/2012-2. LM thanks CNPq through grant 305291/2012-2. LC acknowledges support from the Special Visiting Researcher Fellowship (PVE 313945/2013-6) under the Brazilian Scientific Mobility Program ‘Ciencias sem Fronteiras’. RR acknowledges funding from FAPERGs (ARD 11/1758-5) and CNPq (PeP 304796/2011-5). CRA is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934) and by the Spanish Ministry of Science and Innovation (MICINN) through project PN AYA2010-21887-C04.04.Peer Reviewe

The stellar spectral features of nearby galaxies in the near infrared: tracers of thermally pulsing asymptotic giant branch stars?

et al.We analyse the stellar absorption features in high signal-to-noise ratio (S/N) near-infrared (NIR) spectra of the nuclear region of 12 nearby galaxies, mostly spirals. The features detected in some or all of the galaxies in this sample are the TiO (0.843 and 0.886 μm), VO (1.048 μm), CN (1.1 and 1.4 μm), H2O (1.4 and 1.9 μm) and CO (1.6 and 2.3 μm) bands. The C2 (1.17 and 1.76 μm) bands are generally weak or absent, although C2 (1.76 μm) may be weakly present in the mean galaxy spectrum. A deep feature near 0.93 μm, likely caused by CN, TiO and/or ZrO, is also detected in all objects. Fitting a combination of stellar spectra to the mean spectrum shows that the absorption features are produced by evolved stars: cool giants and supergiant stars in the early- or thermally pulsing asymptotic giant branch (E-AGB or TP-AGB) phases. The high luminosity of TP-AGB stars, and the appearance of VO and ZrO features in the data, suggest that TP-AGB stars dominate these spectral features. However, a contribution from other evolved stars is also likely. Comparison with evolutionary population synthesis models shows that models based on empirical libraries that predict relatively strong NIR features provide a more accurate description of the data. However, none of the models tested accurately reproduces all of the features observed in the spectra. To do so, the models will need to not only improve the treatment of TP-AGB stars, but also include good quality spectra of red giant and E-AGB stars. The uninterrupted wavelength coverage, high S/N and quantity of features we present here will provide a benchmark for the next generation of models aiming to explain and predict the NIR properties of galaxies.The Brazilian authors thank CNPq and FAPERGS support. LCH acknowledges support by the Chinese Academy of Science through grant no. XDB09030102 (Emergence of Cosmological Structures) from the Strategic Priority Research Program and by the National Natural Science Foundation of China through grant No. 11473002. CRA is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934).Peer Reviewe

Particle acceleration in the Herbig–Haro objects HH 80 and HH 81

We present an analysis of radio (Karl G. Jansky Very Large Array (VLA)), optical (HST), and X-ray (Chandra and XMM-Newton) observations and archival data of the Herbig-Haro objects HH 80 and HH 81 in the context of jet-cloud interactions. Our radio images are the highest angular resolution to date of these objects, allowing to spatially resolve the knots and compare the regions emitting in the different spectral ranges. We found that soft X-ray thermal emission is located ahead of the non-thermal radio peak. This result is consistent with a radiative forward shock that heats the shocked gas up to 106K, and an adiabatic reverse shock able to accelerate particles and produce synchrotron radiation detectable at radio frequencies. These high angular resolution radio images also reveal a bow shock structure in the case of HH 80N, being the first time this morphology is detected in a Herbig-Haro object at these frequencies.Fil: Rodríguez Kamenetzky, Adriana Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Carrasco Gonzalez, Carlos Eugenio. Universidad Nacional Autónoma de México. Instituto de Radioastronomía y Astrofísica; MéxicoFil: González Martín, Omaira. Universidad Nacional Autónoma de México. Instituto de Radioastronomía y Astrofísica; MéxicoFil: Araudo, Anabella Teresa. Czech Academy of Sciences; República ChecaFil: Rodríguez, Luis Felipe. Universidad Nacional Autónoma de México. Instituto de Radioastronomía y Astrofísica; MéxicoFil: Vig, Sarita. Indian Institute of Space Science and Technology. Department of Earth and Space Science; IndiaFil: Hofner, Peter. New Mexico Tech. Physics Department; Estados Unido