arXiv subjects

E. Bellocchi

Publications and source records attributed to E. Bellocchi.

30 records · Page 2Linked to original sources

arXiv2020

MUSE reveals extended circumnuclear outflows in the Seyfert 1 NGC 7469

NGC 7469 is a well known Luminous IR Galaxy, with a circumnuclear star formation ring ($\sim 830$ pc radius) surrounding a Seyfert 1 AGN. Nuclear unresolved winds were previously detected in X-rays and UV, as well as an extended biconical outflow in IR coronal lines. We search for extended outflows by measuring the kinematics of the $\mathrm{Hβ}$ and [O III] $λ5007$ optical emission lines, in data of the VLT/MUSE integral field spectrograph. We find evidence of two outflow kinematic regimes: one slower regime extending across most of the star formation ring -- possibly driven by the massive star formation -- and a faster regime (with a maximum velocity of $-715 \ \mathrm{km \ s^{-1}}$), only observed in [O III], in the western region between the AGN and the massive star forming regions of the ring, likely AGN-driven. This work shows a case where combined AGN/star-formation feedback can be effectively spatially-resolved, opening up a promising path toward a deeper understanding of feedback processes in the central kiloparsec of AGN.

astro-ph.GA↗

arXiv2020

Physics of ULIRGs with MUSE and ALMA: The PUMA project I. Properties of the survey and first MUSE data results

Ultraluminous infrared galaxies (ULIRGs) are characterised by extreme starburst (SB) and AGN activity, and are therefore ideal laboratories for studying the outflow phenomena. We have recently started a project called Physics of ULIRGs with MUSE and ALMA (PUMA), which is a survey of 25 nearby (z < 0.165) ULIRGs observed with the integral field spectrograph MUSE and the interferometer ALMA. This sample includes systems with both AGN and SB nuclear activity in the pre- and post-coalescence phases of major mergers. The main goals of the project are to study the prevalence of multi-phase outflows as a function of the galaxy properties, to constrain the driving mechanisms of the outflows (e.g. distinguish between SB and AGN winds), and to identify feedback effects on the host galaxy. In this first paper, we present details on the sample selection, MUSE observations, and derive first data products. MUSE data were analysed to study the dynamical status of each of the 21 ULIRGs observed so far, taking the stellar kinematics and the morphological properties inferred from MUSE narrow-band images into account. We also located the ULIRG nuclei, using near-IR (HST) and mm (ALMA) data, and studied their optical spectra to infer the ionisation state through BPT diagnostics, and outflows in both ionised and neutral gas. We show that the morphological and stellar kinematic classifications are consistent: post-coalescence systems are more likely associated with ordered motions, while interacting (binary) systems are dominated by non-ordered and streaming motions. We also find broad and asymmetric [OIII] and NaID profiles in almost all nuclear spectra, with line widths in the range 300-2000 km/s, possibly associated with AGN- and SB-driven winds. This result reinforces previous findings that indicated that outflows are ubiquitous during the pre- and post-coalescence phases of major mergers.

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arXiv2020

MUSE view of Arp220: Kpc-scale multi-phase outflow and evidence for positive feedback

Arp220 is the nearest and prototypical ULIRG, and shows evidence of pc-scale molecular outflows in its nuclear regions and strongly perturbed ionised gas kinematics on kpc scales. It is therefore the ideal system for investigating outflows and feedback phenomena in details. We investigate the feedback effects on the Arp220 ISM, deriving a detailed picture of the atomic gas in terms of physical and kinematic properties, with a spatial resolution never obtained before (0.56", i.e. ~ 210 pc). We use optical IFS observations from VLT/MUSE-AO to obtain spatially resolved stellar and gas kinematics, for both ionised ([N II]6583) and neutral (Na ID5891,96) components; we also derive dust attenuation, electron density, ionisation conditions and hydrogen column density maps to characterise the ISM properties. Arp220 kinematics reveal the presence of a disturbed, kpc-scale disk in the innermost nuclear regions, and highly perturbed, multi-phase (neutral and ionised) gas along the minor-axis of the disk, which we interpret as a galactic-scale outflow emerging from the Arp220 eastern nucleus. This outflow involves velocities up to ~ 1000 km/s at galactocentric distances of ~ 5 kpc, and has a mass rate of ~ 50 Msun/yr, and kinetic and momentum power of ~ 1e43 erg/s and ~ 1e35 dyne, respectively. The inferred energetics do not allow us to distinguish the origin of the outflows, i.e. whether they are AGN-driven or starburst-driven. We also present evidence for enhanced star formation at the edges of - and within - the outflow, with a star formation rate SFR ~ 5 Msun/yr (i.e. ~ 2% of the total SFR). Our findings suggest the presence of powerful winds in Arp220: they might be capable of removing or heating large amounts of gas from the host ("negative feedback"), but could be also responsible for triggering star formation ("positive feedback").

astro-ph.GA↗

arXiv2019

Uncertainties in gas kinematics arising from stellar continuum modelling in integral field spectroscopy data: the case of NGC2906 observed with MUSE/VLT

We study how the use of several stellar subtraction methods and line fitting approaches can affect the derivation of the main kinematic parameters (velocity and velocity dispersion fields) of the ionized gas component. The target of this work is the nearby galaxy NGC 2906, observed with the MUSE instrument at Very Large Telescope. A sample of twelve spectra is selected from the inner (nucleus) and outer (spiral arms) regions, characterized by different ionization mechanisms. We compare three different methods to subtract the stellar continuum (FIT3D, STARLIGHT and pPXF), combined with one of the following stellar libraries: MILES, STELIB and GRANADA+MILES. The choice of the stellar subtraction method is the most important ingredient affecting the derivation of the gas kinematics, followed by the choice of the stellar library and by the line fitting approach. In our data, typical uncertainties in the observed wavelength and width of the Hαand [NII] lines are of the order of <δλ>_rms \sim 0.1Å and <δσ>_rms \sim 0.2Å (\sim 5 and 10km/s, respectively). The results obtained from the [NII] line seem to be slightly more robust, as it is less affected by stellar absorption than Hα. All methods considered yield statistically consistent measurements once a mean systemic contribution Δ\barλ=Δ\barσ=0.2xDelta_{MUSE} is added in quadrature to the line fitting errors, where Δ_{MUSE} = 1.1Å \sim 50 km/s denotes the instrumental resolution of the MUSE spectra. Although the subtraction of the stellar continuum is critical in order to recover line fluxes, any method (including none) can be used in order to measure the gas kinematics, as long as an additional component of 0.2 x Delta_MUSE is added to the error budget.

astro-ph.GA↗

arXiv2017

Star formation in a galactic outflow

Recent observations have revealed massive galactic molecular outflows that may have physical conditions (high gas densities) required to form stars. Indeed, several recent models predict that such massive galactic outflows may ignite star formation within the outflow itself. This star-formation mode, in which stars form with high radial velocities, could contribute to the morphological evolution of galaxies, to the evolution in size and velocity dispersion of the spheroidal component of galaxies, and would contribute to the population of high-velocity stars, which could even escape the galaxy. Such star formation could provide in-situ chemical enrichment of the circumgalactic and intergalactic medium (through supernova explosions of young stars on large orbits), and some models also predict that it may contribute substantially to the global star formation rate observed in distant galaxies. Although there exists observational evidence for star formation triggered by outflows or jets into their host galaxy, as a consequence of gas compression, evidence for star formation occurring within galactic outflows is still missing. Here we report new spectroscopic observations that unambiguously reveal star formation occurring in a galactic outflow at a redshift of 0.0448. The inferred star formation rate in the outflow is larger than 15 Msun/yr. Star formation may also be occurring in other galactic outflows, but may have been missed by previous observations owing to the lack of adequate diagnostics.

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arXiv2016

BaTMAn: Bayesian Technique for Multi-image Analysis

This paper describes the Bayesian Technique for Multi-image Analysis (BaTMAn), a novel image-segmentation technique based on Bayesian statistics that characterizes any astronomical dataset containing spatial information and performs a tessellation based on the measurements and errors provided as input. The algorithm iteratively merges spatial elements as long as they are statistically consistent with carrying the same information (i.e. identical signal within the errors). We illustrate its operation and performance with a set of test cases including both synthetic and real Integral-Field Spectroscopic data. The output segmentations adapt to the underlying spatial structure, regardless of its morphology and/or the statistical properties of the noise. The quality of the recovered signal represents an improvement with respect to the input, especially in regions with low signal-to-noise ratio. However, the algorithm may be sensitive to small-scale random fluctuations, and its performance in presence of spatial gradients is limited. Due to these effects, errors may be underestimated by as much as a factor of two. Our analysis reveals that the algorithm prioritizes conservation of all the statistically-significant information over noise reduction, and that the precise choice of the input data has a crucial impact on the results. Hence, the philosophy of BaTMAn is not to be used as a `black box' to improve the signal-to-noise ratio, but as a new approach to characterize spatially-resolved data prior to its analysis. The source code is publicly available at http://astro.ft.uam.es/SELGIFS/BaTMAn .

astro-ph.IM↗

arXiv2015

Deconstructing the narrow-line region of the nearest obscured quasar

We study the physical and kinematic properties of the narrow line region (NLR) of the nearest obscured quasar MRK 477 (z=0.037), using optical and near-infrared spectroscopy. We explore a diversity of aspects that provide a more complete understanding of the nature of this object, example of a type 2 quasar in the nearby Universe, as well as a starburst-AGN hybrid system [abridged].

astro-ph.GA↗

arXiv2014

Spatially resolved kinematics, galactic wind, and quenching of star formation in the luminous infrared galaxy IRAS F11506-3851

We present a multi-wavelength integral field spectroscopic study of the low-z LIRG IRAS F11506-3851, on the basis of VIMOS and SINFONI (ESO-VLT) observations. The morphology and the 2D kinematics of the gaseous (neutral and ionized) and stellar components have been mapped using the NaD doublet, the H$α$ line, and the near-IR CO(2-0) and CO(3-1) bands. The kinematics of the ionized gas and the stars are dominated by rotation, with large observed velocity amplitudes and centrally peaked velocity dispersion maps. The stars lag behind the warm gas and represent a dynamically hotter system, as indicated by the observed dynamical ratios. Thanks to these IFS data we have disentangled the contribution of the stars and the ISM to the NaD feature, finding that it is dominated by the absorption of neutral gas clouds in the ISM. The neutral gas 2D kinematics shows a complex structure dominated by two components. On the one hand, the thick slowly rotating disk lags significantly compared to the ionized gas and the stars, with an irregular and off-center velocity dispersion map. On the other hand, a kpc-scale neutral gas outflow is observed along the semi-minor axis of the galaxy, as revealed by large blueshifted velocities (30-154 km/s). We derive an outflowing mass rate in neutral gas of about 48 $\dot{M_{\rm w}}$/yr. Although this implies a global mass loading factor of 1.4, the 2D distribution of the ongoing SF suggests a much larger value of mass loading factor associated with the inner regions (R$<$200 pc), where the current SF represents only 3 percent of the total. All together these results strongly suggest that we are witnessing (nuclear) quenching due to SF feedback in IRAS F11506-3851. However, the relatively large mass of molecular gas detected in the nuclear region via the H2 1-0 S(1) line suggests that further episodes of SF may take place again.

astro-ph.GA↗

arXiv2012

Studying the kinematic asymmetries of disks and post-coalescence mergers using a new `kinemetry' criterion

We have obtained VIMOS/VLT optical integral field spectroscopy (IFS) data for a sample of 4 LIRGs which have been selected at a similar distance ($\sim$ 70 Mpc) to avoid relative resolution effects. They have been classified in two groups (isolated disk and post-coalescence mergers) according to their morphology. The $kinemetry$ method (developed by Krajnovic and coworkers) is used to characterize the kinematic properties of these galaxies and to discuss new criteria for distinguishing their status. We present and discuss new kinematic maps (i.e., velocity field and velocity dispersion) for these four galaxies. The morphological and kinematic classifications of these systems are consistent, with disks having lower kinematic asymmetries than post-coalescence mergers. We then propose and discuss a new kinematic criterion to differentiate these two groups. This criterion distinguishes better these two categories and has the advantage of being less sensitive to angular resolution effects. According to the previous criteria,the present post-coalescence systems would have been classified as disks. This indicates that the separation of disks from mergers is subjective to the definition of `merger'. It also suggests that previous estimates of the merger/disk ratio could have been underestimated, but larger samples are necessary to establish a firmer conclusion.

astro-ph.CO↗

arXiv2010

Extreme Starbursts in the Local Universe

The "Extreme starbursts in the local universe" workshop was held at the Insituto de Astrofisica de Andalucia in Granada, Spain on 21-25 June 2010. Bearing in mind the advent of a new generation of facilities such as JWST, Herschel, ALMA, eVLA and eMerlin, the aim of the workshop was to bring together observers and theorists to review the latest results. The purpose of the workshop was to address the following issues: what are the main modes of triggering extreme starbursts in the local Universe? How efficiently are stars formed in extreme starbursts? What are the star formation histories of local starburst galaxies? How well do the theoretical simulations model the observations? What can we learn about starbursts in the distant Universe through studies of their local counterparts? How important is the role of extreme starbursts in the hierarchical assembly of galaxies? How are extreme starbursts related to the triggering of AGN in the nuclei of galaxies? Overall, 41 talks and 4 posters with their corresponding 10 minutes short talks were presented during the workshop. In addition, the workshop was designed with emphasis on discussions, and therefore, there were 6 discussion sessions of up to one hour during the workshop. Here is presented a summary of the purposes of the workshop as well as a compilation of the abstracts corresponding to each of the presentations. The summary and conclusions of the workshop along with a description of the future prospects by Sylvain Veilleux can be found in the last section of this document. A photo of the assistants is included.

astro-ph.CO↗

arXiv2010

The HELLAS2XMM survey. XIII. Multi-component analysis of the spectral energy distribution of obscured AGN

We combine near-to-mid-IR Spitzer data with shorter wavelength observations (optical to X-rays) to get insights on the properties of a sample of luminous, obscured Active Galactic Nuclei (AGN). We aim at modeling their broad-band Spectral Energy Distributions (SEDs) in order to estimate the main parameters related to the dusty torus. The sample comprises 16 obscured high-redshift (0.9<z<2.1) xray luminous quasars (L_2-10 ~ 10^44 erg s-1) selected from the HELLAS2XMM survey. The SEDs are described by a multi-component model including a stellar component, an AGN component and a starburst. The majority (~80%) of the sources show moderate optical depth (tau_9.7um<3) and the derived column densities N_H are consistent with the xray inferred values (10^22 <N_H< 3x10^23 cm-2) for most of the objects, confirming that the sources are moderately obscured Compton-thin AGN. Accretion luminosities in the range 5x10^44 < Lbol < 4x10^46 erg s-1 are inferred. We compare model luminosities with those obtained by integrating the observed SED, finding that the latter are lower by a factor of ~2 in the median. The discrepancy can be as high as an order of magnitude for models with high optical depth (tau_9.7um=10). The ratio between the luminosities obtained by the fitting procedure and from the observed SED suggest that, at least for Type~2 AGN, observed bolometric luminosities are likely to underestimate intrinsic ones and the effect is more severe for highly obscured sources. Bolometric corrections from the hard X-ray band are computed and have a median value of k_2-10kev ~ 20. The obscured AGN in our sample are characterized by relatively low Eddington ratios (median lambda_Edd~0.08). On average, they are consistent with the Eddington ratio increasing at increasing bolometric correction (e.g. Vasudevan & Fabiam 2009).

astro-ph.CO↗

arXiv2009

The HELLAS2XMM Survey. XII. The infrared/sub-millimeter view of an X-ray selected Type 2 quasar at z=2

We present multi-wavelength observations (from optical to sub-millimeter, including Spitzer and SCUBA) of H2XMMJ 003357.2-120038 (also GD158_19), an X-ray selected, luminous narrow-line (Type 2) quasar at z=1.957 selected from the HELLAS2XMM survey. Its broad-band properties can be reasonably well modeled assuming three components: a stellar component to account for the optical and near-IR emission, an AGN component (i.e., dust heated by an accreting active nucleus), dominant in the mid-IR, with an optical depth at 9.7 micron along the line of sight (close to the equatorial plane of the obscuring matter) of tau(9.7)=1 and a full covering angle of the reprocessing matter (torus) of 140 degrees, and a far-IR starburst component (i.e., dust heated by star formation) to reproduce the wide bump observed longward of 70 micron. The derived star-formation rate is about 1500 solar masses per year. The overall modeling indicates that GD158_19 is a high-redshift X-ray luminous, obscured quasar with coeval powerful AGN activity and intense star formation. It is probably caught before the process of expelling the obscuring gas has started, thus quenching the star formation.

astro-ph.GA↗