arXiv subjects

S. Arribas

Publications and source records attributed to S. Arribas.

At least 73 records · Page 4Linked to original sources

arXiv2012

Spatially Resolved [FeII] 1.64 μm Emission in NGC 5135. Clues for Understanding the Origin of the Hard X-rays in Luminous Infrared Galaxies

Spatially resolved near-IR and X-ray imaging of the central region of the Luminous Infrared Galaxy NGC 5135 is presented. The kinematical signatures of strong outflows are detected in the [FeII]1.64 μm emission line in a compact region at 0.9 kpc from the nucleus. The derived mechanical energy release is consistent with a supernova rate of 0.05-0.1 yr$^{-1}$. The apex of the outflowing gas spatially coincides with the strongest [FeII] emission peak and with the dominant component of the extranuclear hard X-ray emission. All these features provide evidence for a plausible direct physical link between supernova-driven outflows and the hard X-ray emitting gas in a LIRG. This result is consistent with model predictions of starbursts concentrated in small volumes and with high thermalization efficiencies. A single high-mass X-ray binary (HMXB) as the major source of the hard X-ray emission although not favoured, cannot be ruled out. Outside the AGN, the hard X-ray emission in NGC 5135 appears to be dominated by the hot ISM produced by supernova explosions in a compact star-forming region, and not by the emission due to HMXB. If this scenario is common to U/LIRGs, the hard X-rays would only trace the most compact (< 100 pc) regions with high supernova and star formation densities, therefore a lower limit to their integrated star formation. The SFR derived in NGC 5135 based on its hard X-ray luminosity is a factor of two and four lower than the values obtained from the 24 μm and soft X-ray luminosities, respectively.

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arXiv2011

Integrated spectra extraction based on signal-to-noise optimization using Integral Field Spectroscopy

We propose and explore the potential of a method to extract high signal-to-noise (S/N) integrated spectra related to physical and/or morphological regions on a 2-dimensional field using Integral Field Spectroscopy (IFS) observations by employing an optimization procedure based on either continuum (stellar) or line (nebular) emission features. The optimization method is applied to a set of IFS VLT-VIMOS observations of (U)LIRG galaxies, describing the advantages of the optimization by comparing the results with a fixed-aperture, single spectrum case, and by implementing some statistical tests. We demonstrate that the S/N of the IFS optimized integrated spectra is significantly enhanced when compared with the single aperture unprocessed case. We provide an iterative user-friendly and versatile IDL algorithm that allows the user to spatially integrate spectra following more standard procedures. This is made available to the community as part of the PINGSoft IFS software package.

astro-ph.IM↗

arXiv2011

Star formation laws in Luminous Infrared Galaxies. New observational constraints on models

The observational study of star formation relations in galaxies is central to unraveling the physical processes at work on local and global scales. We wish to expand the sample of extreme starbursts, represented by local LIRGs and ULIRGs, with high quality observations in the 1-0 line of HCN. We study if a universal law can account for the star formation relations observed for the dense molecular gas in normal star forming galaxies and extreme starbursts. We have used the IRAM 30m telescope to observe a sample of 19 LIRGs in the 1-0 lines of CO, HCN and HCO+. The analysis of the new data proves that the efficiency of star formation in the dense molecular gas (SFE-dense) of extreme starbursts is a factor 3-4 higher compared to normal galaxies. We find a duality in Kennicutt-Schmidt (KS) laws that is reinforced if we account for the different conversion factor for HCN (alpha-HCN) in extreme starbursts and for the unobscured star formation rate in normal galaxies. This result extends to the higher molecular densities probed by HCN lines the more extreme bimodal behavior of star formation laws, derived from CO molecular lines by two recent surveys. We have confronted our observations with the predictions of theoretical models in which the efficiency of star formation is determined by the ratio of a constant star formation rate per free-fall time (SFR-ff) to the local free-fall time. We find that it is possible to fit the observed differences in the SFE-dense between normal galaxies and LIRGs/ULIRGs using a common constant SFR-ff and a set of physically acceptable HCN densities, but only if SFR-ff~0.005-0.01 and/or if alpha-HCN is a factor of a few lower than our favored values. Star formation recipes that explicitly depend on the galaxy global dynamical time scales do not significantly improve the fit to the new HCN data presented in this work.

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arXiv2011

Extranuclear Halpha-emitting complexes in low-z (U)LIRGs: Precursors of tidal dwarf galaxies?

(Abridged)This paper characterizes the physical and kinematic properties of external massive star-forming regions in a sample of (U)LIRGs. We use high angular resolution ACS images from the HST B and I bands, as well as Halpha-line emission maps obtained with IFS. We find 31 external Halpha-emitting (young star-forming) complexes in 11 (U)LIRGs. These complexes have in general similar sizes, luminosities, and metallicities to extragalactic giant HII regions and TDG candidates found in less luminous mergers and compact groups of galaxies. We assess the mass content and the likelihood of survival as TDGs of the 22 complexes with simple structures in the HST images based on their photometric, structural, and kinematic properties. The dynamical tracers used (radius-sigma and luminosity-sigma diagrams) indicate that most of the complexes might be self-gravitating entities. The resistance to forces from the parent galaxy is studied by considering the tidal mass of the candidate and its relative velocity with respect to the parent galaxy. After combining the results of previous studies of TDG searches in ULIRGs a total of 9 complexes satisfy most of the applied criteria and thus show a high-medium or high likelihood of survival, their total mass likely being compatible with that of dwarf galaxies. They are defined as TDG candidates. We propose that they probably formed more often during the early phases of the interaction. Combining all data for complexes with IFS data where a significant fraction of the system is covered, we infer a TDG production rate of 0.3 candidates with the highest probabilities of survival per system for the (U)LIRGs class. This rate, though, might decrease to 0.1 after the systems in (U)LIRGs have evolved for 10 Gyr, for long-lived TDGs, which would imply that no more than 5-10 % of the overall dwarf population could be of tidal origin.

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arXiv2011

Ionized outflows in SDSS type 2 quasars at z~0.3-0.6

We have analyzed the spatially integrated kinematic properties of the ionized gas within the inner r ~2). While the quiescent gas shows small or null velocity shifts relative to the systemic velocity, the highly perturbed gas trends to show larger shifts which, moreover, are blueshifts in general. Within a given object, the most perturbed gas trends to have the largest blueshift as well. All together support that the perturbed gas, which is responsible for the blue asymmetries of the line profiles, is outflowing. Although some bias affects the sample, we argue that ionized gas outflows are a common phenomenon in optically selected type 2 quasars at 0.3< z < 0.6.

astro-ph.CO↗

arXiv2011

Integral Field Spectroscopy surveys of nearby spiral and U-LIRG galaxies

We describe the observations and preliminary results of the gas-phase analysis based on two ongoing, wide-field Integral Field Spectroscopy (IFS) surveys: the PPAK IFS Nearby Galaxies Survey (PINGS), targeting disc galaxies; and the VIMOS-IFU observations of low-z (Ultra)Luminous Infrared Galaxies (U-LIRGs), the local counterpart of massive, dusty high-z star-forming galaxies. We describe how these observations are allowing to discover and characterise abundance differentials between galactic substructures and differences depending on the morphologically/dynamically distinct types of objects, which in turn will allow us to interpret the gas-phase abundances of analogue high-z systems.

astro-ph.CO↗

arXiv2011

The local LIRG NGC5135: AGN and SN activity traced by NIR IFU spectroscopy

By observing the local luminous infrared galaxy NGC5135 with the near-IR IFU spectrograph SINFONI (ESO-VLT), we report an approx. 600 pc (in projection) AGN outflow traced by [SiVI]1.96mum emission. This is the largest outflow traced by a coronal line ever reported. Its large spatial scale suggests that shocks, in addition to AGN continuum emission, are needed to locally produce [SiVI] emission. We also show, for the first time, clear kinematical evidence of the AGN-outflow vs. ISM interaction through variations in the 2D velocity fields of different gas phases. Such local perturbations in the kinematics clearly match the outflow structure. We use the [FeII]1.64mum emission, a supernovae tracer, to estimate the supernovae rate in different star-forming knots (approx. 250 pc across) within the central 2.3 kpc of NGC5135. The estimated supernovae rates go from 0.02 to 0.08 yr^{-1} being in excellent agreement with predictions from 6 cm radio emission in the same areas.

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arXiv2009

Integral field optical spectroscopy of a representative sample of ULIRGs: I. The Data

We present a project aimed at studying the structure, dust distribution, ionization state, and kinematics of a representative sample of 22 ULIRGs. The galaxies in the sample undergo different merger phases (they are evenly divided between pre- and post-coalescence systems) and ionization stages (27% HII, 32% LINER, 18% Seyfert, and 23% mixed classifications) over a wide infrared luminosity range (11.8<Lir/Lsun<12.6), which also includes some galaxies of low luminosity. The main aims of this paper are to present the sample and discuss the structure of the stellar and ionized gas components. Our results imply that evolution caused by a merger is occurring in the ionized gas structure of ULIRGs. The present study relies on the use of integral field optical spectroscopy data obtained with the INTEGRAL instrument at the 4.2 m William Herschel Telescope.

astro-ph.CO↗

arXiv2009

Integral field optical spectroscopy of a representative sample of ULIRGs: II. Two-dimensional kpc-scale extinction structure

We investigate the two-dimensional kpc-scale structure of the extinction in a representative sample of local ULIRGs using the Halpha/Hbeta line ratio.We use optical integral field spectroscopy obtained with the INTEGRAL instrument at the William Herschel Telescope. Complementary optical and near-IR high angular resolution HST images have also been used. The extinction exhibits a very complex and patchy structure in ULIRGs on kpc scales, from basically transparent regions to others deeply embedded in dust (Av~0.0 to Av~8.0 mag). Nuclear extinction covers a broad range in Av from 0.6 to 6 mag, 69% of the nuclei having Av>2.0 mag. Extinction in the external regions is substantially lower than in the nuclei with 64% of the ULIRGs in the sample having median Av of less than 2 mag for the entire galaxy. While post-coalescence nuclei tend to cluster around Av values of 2 to 3 mag, pre-coalescence nuclei appear more homogeneously distributed over the entire 0.4 mag <Av< 7.7 mag range. For the average extinction (Av~2.0 derived for the ULIRGs of the sample, the ratio of the de-reddened to observed SFR values is 6. The extinction-corrected, Halpha-based SFR ranges from 10 to 300 Msun/yr. For only 28% of the cases the de-reddened SFR is <20 Msun/yr, whereas for the observed SFR this percentage increases to 72%. The IR-based SFR is always higher than the optical-based one, with differences ranging from about 2 to up to 30. The nuclear observed SFR has an average contribution to the total one of 16% for the entire sample. Once corrected for extinction, the average value becomes 31%. Because of mostly extinction effects, the optical (I-band) half-light radius in the sample galaxies is on average a factor 2.3 larger than the corresponding near-IR (H-band) value.

astro-ph.CO↗

arXiv2009

Near-IR Integral Field Spectroscopy study of the Star Formation and AGN of the LIRG NGC 5135

We present a study of the central 2.3 kpc of NGC 5135, a nearby Luminous Infrared Galaxy (LIRG) with an AGN and circumnuclear starburst. Our main results are based on intermediate spectral resolution (~ 3000-4000) near infrared data taken with the SINFONI integral field spectrograph at the ESO VLT. The ionization of the different phases of the interstellar gas and the complex structures of the star formation have been mapped. Individual regions of interest have been identified and studied in detail. For the first time in this galaxy, we have detected the presence of a high excitation ionization cone centered on the AGN by using the [SiVI] (1.96 micron) line. So far, this structure is the largest reported in the literature for this coronal line, extending (in projection) as far as ~ 600 pc from the galaxy nucleus. In a complex spatial distribution, a variety of mechanisms are driving the gas ionization, including SNe remnant shocks, young stars and AGN photoionization. The excitation of the molecular gas, however, is mainly produced by X-rays and SNe remnant shocks. UV-mechanisms like fluorescence represent a marginal overall contribution to this process, contrary to the expectations we might have for a galaxy with a recent and strong star formation. Our SNe rate estimations from [FeII] (1.64 micron) are in excellent agreement with 6 cm radio emission predictions. Typical SNe rates between 0.01-0.04 yr^-1 were found for individual ~ 200 pc-scale regions, with an overall SNe rate of 0.4-0.5 yr^-1. Even though NGC 5135 has suffered a recent starburst (6-7 Myr ago), the data strongly suggest the presence of a second, older stellar population dominated by red giant/supergiant stars.

astro-ph.CO↗

arXiv2008

Photometric and Kinematic Characterization of Tidal Dwarf Galaxy candidates

Tidal Dwarf Galaxies (TDG), or self-graviting objects created from the tidal forces in interacting galaxies, have been found in several merging systems. This work will focus on identifying TDG candidates among a sample of Luminous and Ultraluminous Infrared Galaxies (U)LIRGs, where these interactions are occurring, in order to study their formation and evolution. High angular resolution imaging from Hubble Space Telescope (HST) in B, I and H band will be used to detect these sources. Photometric measurements of these regions compared to Stellar Synthesis Population models will allow us to roughly estimate the age and the mass. Complementary optical Integral Field spectroscopy we will be able to explore the physical, kinematic and dynamical properties in TDGs. We present preliminary photometric results for IRAS 0857+3915, as an example of the study that will be held for the entire sample of (U)LIRGs.

astro-ph↗

arXiv2008

Kinemetry of SINS High-Redshift Star-Forming Galaxies: Distinguishing Rotating Disks from Major Mergers

We present a simple set of kinematic criteria that can distinguish between galaxies dominated by ordered rotational motion and those involved in major merger events. Our criteria are based on the dynamics of the warm ionized gas (as traced by H-alpha) within galaxies, making this analysis accessible to high-redshift systems, whose kinematics are primarily traceable through emission features. Using the method of kinemetry (developed by Krajnovic and co-workers), we quantify asymmetries in both the velocity and velocity dispersion maps of the warm gas, and the resulting criteria enable us to empirically differentiate between non-merging and merging systems at high redshift. We apply these criteria to 11 of our best-studied rest-frame UV/optical-selected z~2 galaxies for which we have near infrared integral field spectroscopic data from SINFONI on the VLT. Of these 11 systems, we find that >50% have kinematics consistent with a single rotating disk interpretation, while the remaining systems are more likely undergoing major mergers. This result, combined with the short formation timescales of these systems, provides evidence that rapid, smooth accretion of gas plays a significant role in galaxy formation at high redshift.

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arXiv2007

Search for Tidal Dwarf Galaxies Candidates in a Sample of Ultraluminous Infrared Galaxies

(ABRIDGED) Star-forming small galaxies made out of collisional debris have been found in a variety of merging systems. So far only a few of them are known in ULIRGs although they show clear signs of interactions. Whether external star formation may take place in such objects is an open question. The aim of this paper is to identify and characterise the physical and kinematic properties of the external star forming regions in a sample of ULIRGs, including TDG candidates, using optical IFS and high angular resolution HST imaging. We have found that the presence of external star-forming regions is common with 12 objects being identified in 5 ULIRGs. These regions show a large range of dynamical mass up to 1x10^{10} M_sun, with average sizes of ~750 pc. In addition, the line ratios, metallicities and Hαequivalent widths are typical of young bursts of star formation (age ~ 5-8 Myr), and similar to those of other TDG candidates. Their extinction corrected Hαluminosities lead to masses for the young stellar component of ~2x10^6 - 7x10^8 M_sun. The likelihood of survival of these regions as TDGs is discussed based on their structural and kinematic properties. Most of these systems follow the relation between effective radius and velocity dispersion found for globular clusters and Ellipticals, which suggests they are stable against internal motions. The stability against forces from the parent galaxy have been studied and a comparison of the data with the predictions of dynamical evolutionary models is also performed. Five regions out of twelve show High-Medium or High likelihood of survival. Our best candidate, which satisfy all the utilized criteria, is located in the advanced merger IRAS15250+3609 and presents a velocity field decoupled from the relatively distant parent galaxy.

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arXiv2006

Recurrence of the blue wing enhancements in the high ionization lines of SDSS 1004+4112 A

We present integral field spectroscopic observations of the quadruple-lensed QSO SDSS 1004+4112 taken with the fiber system INTEGRAL at the William Herschel Telescope on 2004 January 19. In May 2003 a blueward enhancement in the high ionization lines of SDSS 1004+4112A was detected and then faded. Our observations are the first to note a second event of similar characteristics less than one year after. Although initially attributed to microlensing, the resemblance among the spectra of both events and the absence of microlensing-induced changes in the continuum of component A are puzzling. The lack of a convincing explanation under the microlensing or intrinsic variability hypotheses makes the observed enhancements particularly relevant, calling for close monitoring of this object.

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arXiv2005

LINER-like Extended Nebulae in ULIRGs: Shocks Generated by Merger Induced Flows

In this work we studied the two-dimensional ionization structure of the circumnuclear and extranuclear regions in a sample of six low-z Ultraluminous Infrared Galaxies using Integral Field Spectroscopy. The ionization conditions in the extranuclear regions of these galaxies (~5-15 kpc) are typical of LINERs as obtained from the Veilleux-Osterbrock line ratio diagnostic diagrams. The range of observed line ratios is best explained by the presence of fast shocks with velocities of 150 to 500 km s^{-1}, while the ionization by an AGN or nuclear starburst is in general less likely. The comparison of the two-dimensional ionization level and velocity dispersion in the extranuclear regions of these galaxies shows a positive correlation, further supporting the idea that shocks are indeed the main cause of ionization. The origin of these shocks is also investigated. Despite the likely presence of superwinds in the circumnuclear regions of these systems, no evidence for signatures of superwinds such as double velocity components are found in the extended extranuclear regions. We consider a more likely explanation for the presence of shocks, the existence of tidally induced large scale gas flows caused by the merging process itself, as evidenced by the observed velocity fields characterized by peak-to-peak velocities of 400 km s^{-1}, and velocity dispersions of up to 200 km s^{-1}.

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arXiv2004

Asymmetrical structure of ionization and kinematics in the Seyfert galaxy NGC 5033

We present integral field spectroscopy of NGC 5033, a low luminosity Seyfert galaxy. The observations were made with INTEGRAL, a fiber based system operating at the WHT. The intensity map of the H$β$ emission line represents a spiral or ring-like pattern of HII regions. On the contrary, the [OIII] intensity map morphology is markedly anisotropic. The strong morphological differences imply that the [OIII] emitters represent highly ionized gas illuminated by the central source. The [OIII] map morphology is compatible with a biconical structure of ionization induced by strong extinction in the galaxy disc that also obscures half of the spheroidal stellar bulge. We identify the spectrum corresponding to the Seyfert 1 nucleus from the presence of H$β$ broad emission lines. This spectrum is located in a region where strong extinction is expected but exhibits the bluest spectral energy distribution. The Seyfert 1 nucleus seems to be offcenter with respect to the stellar rotation center. This result has been also found in other Seyfert galaxies and interpreted in terms of a past merger. The offcentering could indicate the presence of nonsymmetric departures in the gravitational potential which could be fueling the active nucleus. The kinematics of the [OIII] emitters show important deviations at a kpc scale with respect to the stellar velocity field and show features related to the asymmetrical morphology of the high ionization region.

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arXiv2004

The X-Ray Binary X2127+119 in M15: Evidence for a Very-Low-Mass, Stripped-Giant Companion

We present integral field spectroscopy of X2127+119, the luminous X-ray binary in the globular cluster M15, obtained with INTEGRAL/WYFFOS on the William Herschel Telescope. We find that tomograms of HeII 4686 line profiles appear to be incompatible with the previously-assumed view of X2127+119, in which the binary consists of a 1.4-solar-mass neutron star and a 0.8-solar-mass sub-giant companion near the main-sequence turn-off for M15. Our data imply a much smaller mass ratio M_2/M_x of 0.1. We find that models of X2127+119 with black-hole compact objects give a poor fit to our data, while a neutron-star compact object is consistent with the data, implying that X2127+119's companion may have a much lower mass (~0.1 solar masses) than previously assumed. As an 0.1-solar-mass main-sequence star would be unable to fill its Roche lobe in a binary with X2127+119's orbital period (17.1 hours), the companion is likely to be the remnant of a significantly more massive star which has had most of its envelope stripped away.

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arXiv2003

INTEGRAL Field Spectroscopy of the Extended Ionized Gas in Arp 220

Integral field optical spectroscopy with the INTEGRAL system has been used to investigate for the first time the two-dimensional kinematic and ionization properties of the extended, warm ionized gas in Arp 220 over an area of 28 kpc by 15 kpc. The structure of the ionized gas is divided into well identified regions associated with the X-ray emitting plumes and extended lobes. Changes in the ionization state of the gas along the major axis of the plumes are detected, in particular in the outer regions of the northwestern plume where the transition between the main stellar body of the galaxy and a broad, low surface brightness tidal tail is located. If the plumes are produced by a starburst-driven galactic wind, the efficiency in the conversion of mechanical to radiation energy is a factor of at least 10 smaller than in galactic winds developed in edge-on spirals with well defined rotation and outflowing axis. The kinematic properties of the lobes are to a first order in agreement with the predictions of the merger scenario according to which the lobes are tidal-induced gas condensations produced during the merging process. The largest velocity gradients and velocity deviations from the systemic velocity are not associated with the plumes, but with the outer stellar envelope and broad tidal tails at distances of up to 7.5 kpc, indicating that the large scale kinematics of the extended ionized gas in Arp 220, is most likely dominated by the tidal-induced motions, and not by galactic winds associated with nuclear starbursts.

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