Wide Field Spectrograph Research Articles

Probing the physics of narrow-line regions of Seyfert galaxies

We have used the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope at Siding Spring to observe the nearby, nearly face-on, Seyfert 2 galaxy, NGC 5427. We have obtained integral field spectroscopy of both the nuclear regions and the HII regions in the spiral arms. We have constrained the chemical abundance in the interstellar medium of the extended narrow line region (ENLR) by measuring the abundance gradient in the circum-nuclear \ion{H}{ii} regions to determine the nuclear chemical abundances, and to use these to in turn determine the EUV spectral energy distribution for comparison with theoretical models. We find a very high nuclear abundance, $\sim 3.0$ times solar, with clear evidence of a nuclear enhancement of N and He, possibly caused by massive star formation in the extended ($\sim 100$pc) central disk structure. The circum-nuclear narrow-line region spectrum is fit by a radiation pressure dominated photoionisation model model with an input EUV spectrum from a Black Hole with mass $5\times10^7 M_{\odot}$ radiating at $\sim 0.1$ of its Eddington luminosity. The bolometric luminosity is closely constrained to be $\log L_{\mathrm bol.} = 44.3\pm 0.1$ erg s$^{-1}$. The EUV spectrum characterised by a soft accretion disk and a harder component extending to above 15keV. The ENLR region is extended in the NW-SE direction. The line ratio variation in circum-nuclear spaxels can be understood as the result of mixing \ion{H}{ii} regions with an ENLR having a radius-invariant spectrum.

SEVEN NEW CARBON-ENHANCED METAL-POOR RR LYRAE STARS

We report estimated carbon-abundance ratios, [C/Fe], for seven newly-discovered carbon-enhanced metal-poor (CEMP) RR Lyrae stars. These are well-studied RRab stars that had previously been selected as CEMP candidates based on low-resolution spectra. For this pilot study, we observed eight of these CEMP RR Lyrae candidates with the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope. Prior to this study, only two CEMP RR Lyrae stars had been discovered: TY Gru and SDSS J1707+58. We compare our abundances to new theoretical models of the evolution of low-mass stars in binary systems. These simulations evolve the secondary stars, post accretion from an AGB donor, all the way to the RR Lyrae stage. The abundances of CEMP RR Lyrae stars can be used as direct probes of the nature of the donor star, such as its mass, and the amount of material accreted onto the secondary. We find that the majority of the sample of CEMP RR Lyrae stars is consistent with AGB donor masses of around 1.5 - 2.0 solar masses and accretion masses of a few hundredths of a solar mass. Future high-resolution studies of these newly-discovered CEMP RR Lyrae stars will help disentangle the effects of the proposed mixing processes that occur in such objects.

Metals in 3D: A Cosmic View from Integral Field Spectroscopy

Integral field spectroscopy (IFS) is an observational technique that has revolutionized our understanding of extended objects in the Universe since the last decade. IFS provides unique contributions to the study ofGalactic ionized nebulae, extragalactic HII regions, and galaxies in the local and in the early Universe, which in some aspects are complementary to the high precision performance of existing wide area photometric and single-aperture spectroscopic surveys. The power of this technique is the possibility of gathering complete spectroscopic information across the spatial extension of astrophysical objects, thus allowing the study of physical spatial variations of their properties, this being specially significant for those properties related to their metal content and star formation activity. With this special issue we want to cover the most relevant aspects related to IFS, in order to illustrate to the reader the wide scope opened by this observational technique. In what follows we present the main contents of this special issue split by subject. Two papers of this issue are devoted to modeling the chemical evolution of spiral and dwarf galaxies by M. Molla and S. Recchi. Theoretical models are a key ingredient in order to be compared with the observational data since either their predictions open new observational avenues or they are constrained by new observational results. Both aspects must walk hand in hand to make progress in the field. Two papers follow, dealing with the study of Galactic objects. The one by L. Lopez-Martin mostly addresses some aspects of the particular technical problems of IFS data handling. A paper by A. Mesa-Delgado faces the chemical abundance discrepancy problem applied to Galactic Herbig Haro objects in the Orion nebula, illustrating how IFS can help to shed light on this issue. A set of four papers follows focused on extragalactic studies with fiber-fed spectrographs: the first two papers, by E. Perez-Montero et al. and P. Lagos and P. Papaderos, deal with the chemical properties of star-forming (HII/BCD) dwarf galaxies and with the interplay of theWR stellar population on the metal enrichment of the interstellar medium. The remaining two papers of this block, by F. F. RosalesOrtega and S. F. Sanchez, are focused on the properties of the HII regions in spiral galaxies and review most recent results on chemical abundance gradients obtained from IFS observations. Last but not least, a set of two papers of this issue are devoted to the description and main properties of two ongoing experiments/instruments. One is a wide-field integral field spectrograph, by G. A. Blanc, with applications in several astrophysical fields, in particular in the study of the properties of nearby galaxies. The second one, by L. Drissen et al., explains the basics of the operation of imaging Fourier transform spectrometers (IFTS), an interesting alternative to the traditional dispersive spectrographs due to their wide field of view, and it shows the main goals that can be achieved using them in the study of the chemical evolution of astrophysical objects.

Spaxel analysis: probing the physics of star formation in ultraluminous infrared galaxies

This paper presents a detailed spectral pixel (spaxel) analysis of the ten Luminous Infrared Galaxies (LIRGs) previously observed with the Wide Field Spectrograph (WiFeS), an integral field spectrograph mounted on the ANU 2.3m telescope, and for which an abundance gradient analysis has already been presented by Rich et al. (2012). Here we use the strong emission line analysis techniques developed by Dopita et al. (2013) to measure the ionisation parameter and the oxygen abundance in each spaxel. In addition, we use the observed H$\alpha$ flux to determine the surface rate of star formation ($M_{\odot}$ yr$^{-1}$ kpc$^{-2}$) and use the [\ion{S}{2}] $\lambda\lambda6717/6731$ ratio to estimate the local pressure in the ionised plasma. We discuss the correlations discovered between these physical quantities, and use them to infer aspects of the physics of star formation in these extreme star forming environments. In particular, we find a correlation between the star formation rate and the inferred ionisation parameter. We examine the possible reasons for this correlation, and determine that the most likely explanation is that the more active star forming regions have a different distribution of molecular gas which favour higher ionisation parameters in the ionised plasma.

PyWiFeS: a rapid data reduction pipeline for the Wide Field Spectrograph (WiFeS)

We present PyWiFeS, a new Python-based data reduction pipeline for the Wide Field Spectrograph (WiFeS). PyWiFeS consists of a series of core data processing routines built on standard scientific Python packages commonly used in astronomical applications. Included in PyWiFeS is an implementation of a new global optical model of the spectrograph which provides wavelengths solutions accurate to ∼0.05 Å (RMS) across the entire detector. The core PyWiFeS package is designed to be scriptable to enable batch processing of large quantities of data, and we present a default format for handling of observation metadata and scripting of data reduction.

The physical parameters of the microquasar S26 in the Sculptor Group galaxy NGC 7793

NGC 7793 - S26 is an extended source (350 pc $\times$ 185 pc) previously studied in the radio, optical and x-ray domains. It has been identified as a micro-quasar which has inflated a super bubble. We used Integral Field Spectra from the Wide Field Spectrograph on the ANU 2.3 m telescope to analyse spectra between 3600--7000 \AA. This allowed us to derive fluxes and line ratios for selected nebular lines. Applying radiative shock model diagnostics, we estimate shock velocities, densities, radiative ages and pressures across the object. We show that S26 is just entering its radiative phase, and that the northern and western regions are dominated by partially-radiative shocks due to a lower density ISM in these directions. We determine a velocity of expansion along the jet of 330 km s$^{-1}$, and a velocity of expansion of the bubble in the minor axis direction of 132 km s$^{-1}$. We determine the age of the structure to be $4.1\times10^5$ yr, and the jet energy flux to be $ (4-10)\times10^{40}$ erg s$^{-1}$ The jet appears to be collimated within $\sim0.25$ deg, and to undergo very little precession. If the relativistic $\beta \sim 1/3$, then some 4 M$_{\odot}$ of relativistic matter has already been processed through the jet. We conclude that the central object in S26 is probably a Black Hole with a mass typical of the ultra-luminous X-ray source population which is currently consuming a fairly massive companion through Roche Lobe accretion.

AN INTEGRAL FIELD STUDY OF ABUNDANCE GRADIENTS IN NEARBY LUMINOUS INFRARED GALAXIES

We present for the first time metallicity maps generated using data from the Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies (LIRGs) and discuss the abundance gradients and distribution of metals in these systems. We have carried out optical integral field spectroscopy (IFS) of several several LIRGs in various merger phases to investigate the merger process. In a major merger of two spiral galaxies with preexisting disk abundance gradients, the changing distribution of metals can be used as a tracer of gas flows in the merging system as low metallicity gas is transported from the outskirts of each galaxy to their nuclei. We employ this fact to probe merger properties by using the emission lines in our IFS data to calculate the gas-phase metallicity in each system. We create abundance maps and subsequently derive a metallicity gradient from each map. We compare our measured gradients to merger stage as well as several possible tracers of merger progress and observed nuclear abundances. We discuss our work in the context of previous abundance gradient observations and compare our results to new galaxy merger models which trace metallicity gradient. Our results agree with the observed flattening of metallicity gradients as a merger progresses. We compare our results with new theoretical predictions that include chemical enrichment. Our data show remarkable agreement with these simulations.

KINEMATICS AND CHEMISTRY OF HALO SUBSTRUCTURES: THE VICINITY OF THE VIRGO OVERDENSITY

We present observations obtained with the AAT's 2dF wide field spectrograph AAOmega of K-type stars located within a region of the sky which contains the Virgo Over-Density and the leading arm of the Sagittarius Stream. On the basis of the resulting velocity histogram we isolate halo substructures in these overlapping regions including Sagittarius and previously discovered Virgo groups. Through comparisons with N-body models of the Galaxy-Sagittarius interaction, we find a tri-axial dark matter halo is favoured and we exclude a prolate shape. This result is contradictory with other observations along the Sagittarius leading arm, which typically favour prolate models. We have also uncovered K-giant members of Sagittarius that are notably more metal poor ([Fe/H] = -1.7 +/- 0.3 dex) than previous studies. This suggests a significantly wider metallicity distribution exists in the Sagittarius Stream than formerly considered. We also present data on five carbon stars which were discovered in our sample.

Stellar population gradients in the cores of nearby field E+A galaxies

We have selected a sample of local E+A galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 7 for follow-up integral field spectroscopy with the Wide Field Spectrograph (WiFeS) on the Australian National University's (ANU) 2.3-m telescope. The sample was selected using the Hα line in place of the [O ii] λ3727 line as the indicator of ongoing star formation (or lack thereof). This allowed us to select a lower redshift sample of galaxies than available in the literature since the [O ii] λ3727 falls off the blue end of the wavelength coverage in the SDSS for the very lowest redshift objects. This low-redshift selection means that the galaxies have a large angular to physical scale which allows us to resolve the central ∼1 kpc region of the galaxies; the region where stellar population gradients are expected. Such observations have been difficult to make using other higher redshift samples because even at redshifts z∼ 0.1 the angular to physical scale is similar to the resolution provided by ground-based seeing. Our integral field spectroscopy has enabled us to make the first robust detections of Balmer line gradients in the centres of E+A galaxies. Six out of our sample of seven, and all the galaxies with regular morphologies, are observed to have compact and centrally concentrated Balmer line absorption. This is evidence for compact young cores and stellar population gradients which are predicted from models of mergers and tidal interactions which funnel gas into the galaxy core. Given the generally isolated nature of our sample, this argues for the galaxies being seen in the late stage of a merger where the progenitors have already coalesced.

THE SMALL ISOLATED GAS-RICH IRREGULAR DWARF (SIGRID) GALAXY SAMPLE: DESCRIPTION AND FIRST RESULTS

Using an optically-unbiased selection process based on the HIPASS neutral hydrogen survey, we have selected a sample of 83 spatially isolated, gas-rich dwarf galaxies in the southern hemisphere with cz between 350 and 1650 km s-1, and with R-band luminosities and HI masses less than that of the Small Magellanic Cloud. The sample is an important population of dwarf galaxies in the local Universe, all with ongoing star formation, and most of which have no existing spectroscopic data. We are measuring the chemical abundances of these galaxies, using the Integral Field Spectrograph on the ANU 2.3m telescope, the Wide Field Spectrograph (WiFeS). This paper describes our survey criteria and procedures, lists the survey sample, and reports on initial observations.

EXTENDED NARROW-LINE EMISSION IN THE BRIGHT SEYFERT 1.5 GALAXY HE 2211-3903

Extended narrow-line regions (ENLRs) and extended emission-line regions (EELRs) have been the focus of integral field spectroscopy aiming at the inner kiloparsecs of nearby Seyfert galaxies as well as the larger environment of high redshift QSOs. Based on observations with the Wide Field Spectrograph WiFeS at the 2.3 m telescope of the Australian National University, we present spatially resolved emission-line diagnostics of the bright Seyfert 1.5 galaxy HE 2211-3903 which is drawn from a sample of the brightest Seyfert galaxies at z<0.06 with luminosities around the classical Seyfert/QSO demarcation. In addition to the previously known spiral arms of HE 2211-3903, the emission-line maps reveal a large scale ring with a radius of about 6 kpc which is connected to the active galactic nucleus (AGN) through a bar-like structure. The overall gas kinematics indicates a disk rotation pattern. The emission-line ratios show Seyfert-type, HII region-type, and composite classifications, while there is no strong evidence of LINER-type ratios. Shock ionization is likely to be negligible throughout the galaxy. The composite line ratios are explained via a mixing line between AGN and HII region photoionization. Composite line ratios are predominantly found in between the HII regions in the circum-nuclear region, the bar-like structure to the east of the nucleus, and the eastern half of the ring, suggesting AGN photoionization of the low-density interstellar medium in an ENLR on galaxy scales. The line ratios in the nucleus indicate N-enrichment, which is discussed in terms of chemical enrichment by Wolf-Rayet and Asymptotic Giant Branch stars during past and ongoing nuclear starburst activity.

FRD in optical fibres at low temperatures: investigations for Gemini's Wide-field Fibre Multi-Object Spectrograph

While there is no direct evidence for the deterioration in Focal Ratio Degradation (FRD) of optical fibres in severe temperature gradients, the fibre ends inserted into metallic containment devices such as steel ferrules can be a source of stress, and hence increased FRD at low temperatures. In such conditions, instruments using optical fibres may suffer some increase in FRD and consequent loss of system throughput when they are working in environments with significant thermal gradients, a common characteristic of ground-based observatories. In this paper we present results of experiments with optical fibres inserted in different materials as a part of our prototyping study for Gemini's Wide-field Multi-Object Spectrograph (WFMOS) project. Thermal effects and the use of new holding techniques will be discussed in the context of Integral Field Units and multi-fibres systems. In this work, we have used careful methodologies that give absolute measurements of FRD to quantify the advantages of using epoxy-based composites rather than metals as support structures for the fibre ends. This is shown to be especially important in minimizing thermally induced stresses in the fibre terminations. Not only is this important for optimizing fibre spectrograph performance but the benefits of using such materials are demonstrated in the minimization of positional variations and the avoidance of metal-to-glass delamination. Furthermore, by impregnating the composites with small zirconium oxide particles the composite materials supply their own fine polishing grit which aids significantly to the optical quality of the finished product.

OPTICAL IFU OBSERVATIONS OF THE BRIGHTEST CLUSTER GALAXY NGC 4696: THE CASE FOR A MINOR MERGER AND SHOCK-EXCITED FILAMENTS

We present deep optical integral-field spectroscopic observations of the nearby (z ~ 0.01) brightest cluster galaxy NGC 4696 in the core of the Centaurus Cluster, made with the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope at Siding Spring Observatory. We investigate the morphology, kinematics, and excitation of the emission-line filaments and discuss these in the context of a model of a minor merger. We suggest that the emission-line filaments in this object have their origin in the accretion of a gas-rich galaxy and that they are excited by v ~100-200 km/s shocks driven into the cool filament gas by the ram pressure of the transonic passage of the merging system through the hot halo gas of NGC 4696.

The 3D structure of N132D in the LMC: a late-stage young supernova remnant

We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the resultant data cube, we have been able to reconstruct the full 3D structure of the system of [O III] filaments. The majority of the ejecta form a ring of ~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We conclude that SNR N132D is approaching the end of the reverse shock phase before entering the fully thermalized Sedov phase of evolution. We speculate that the ring of oxygen-rich material comes from ejecta in the equatorial plane of a bipolar explosion, and that the overall shape of the SNR is strongly influenced by the pre-supernova mass loss from the progenitor star. We find tantalizing evidence of a polar jet associated with a very fast oxygen-rich knot, and clear evidence that the central star has interacted with one or more dense clouds in the surrounding ISM.

THE CAS A-LIKE SNR 1E 0102.2-7219 IN THE SMALL MAGELLANIC CLOUD: AN ASYMMETRIC BIPOLAR EXPLOSION

We have used the Wide Field Spectrograph on the 2.3 m telescope at Siding Spring Observatory to map the [O III] λ5007 dynamics of the young oxygen-rich supernova remnant 1E 0102.2-7219 in the Small Magellanic Cloud. From the resultant data cube, we have been able to reconstruct the full three-dimensional structure of the system of [O III] filaments. From this we are able to deduce that the ejecta trace an asymmetric bipolar structure. The redshifted gas contains fainter clumps but with higher velocities than the blueshifted gas. The major axis of the explosion is inclined at ~40° to the line of sight. This structure shows that the supernova explosion has been influenced both by the rotation of the progenitor star and, presumably, by a global rotational instability following core collapse.

NGC 839: SHOCKS IN AN M82-LIKE SUPERWIND

We present observations of NGC 839 made with the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope. Our data cover a region 25" x 60" at a spatial resolution of ~1.5". The long axis of the field is aligned with the superwind we have discovered in this starburst galaxy. The data cover the range of 3700-7000 {\AA}, with a spectral resolution R~7000 in the red, and R~3000 in the blue. We find that the stellar component of the galaxy is strongly dominated by a fast rotating intermediate-age (~400 Myr) A-Type stellar population, while the gas is concentrated in a bi-conical polar funnel. We have generated flux distributions, emission line ratio diagnostics and velocity maps in both emission and absorption components. We interpret these in the context of a new grid of low-velocity shock models appropriate for galactic-scale outflows. These models are remarkably well fit to the data, providing for the first time model diagnostics for shocks in superwinds and strongly suggesting that shock excitation is largely responsible for the extended LINER emission in the outflowing gas in NGC 839. Our work may have important implications both for extended LINER emission seen in other galaxies, as well as in the interpretation of objects with "composite" spectra. Finally, we present a scenario for the formation of E+A galaxies based upon our observations of NGC 839, and its relation to M82.

The Wide Field Spectrograph (WiFeS): performance and data reduction

This paper describes the on-telescope performance of the Wide Field Spectrograph (WiFeS). The design characteristics of this instrument, at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) and mounted on the ANU 2.3 m telescope at the Siding Spring Observatory has been already described in an earlier paper (Dopita et al. in Astrophys. Space Sci. 310:255, 2007). Here we describe the throughput, resolution and stability of the instrument, and describe some minor issues which have been encountered. We also give a description of the data reduction pipeline, and show some preliminary results.

Integral Field Unit Spectrograph for Extremely Large Telescopes

ABSTRACTWe have carried out a concept study for a wide-field monolithic integral field unit (IFU) spectrograph for extremely large telescopes (ELTs). We target in this paper the technological challenges that have to be faced in order to build such an instrument, focusing on the adaptive optics (AO) requirements, the image slicer technology, and the detectors status. We also address the main science drivers, together with the concept design and the expected performance applied to the European-ELT (E-ELT) case. A monolithic wide-field spectrograph provides a continuous field of view (FOV) separated by a field splitter in several subfields, each of them feeding a module featuring an image slicer, a collimator and a spectrograph. The use of image slicers provides 3D spectrographic images of the complete FOV, allowing for detection and study of sources without need of targeting them, a very useful property especially for the deep observation of faint high-redshift objects, whose density on the sky is expected to be quite high. In light of this discussion, we suggest the advantages of using shorter wavelengths and its implication in both the scientific program and the budget.

The Wide Field Spectrograph (WiFeS)

This paper describes the Wide Field Spectrograph (WiFeS) under construction at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) for the ANU 2.3 m telescope at the Siding Spring Observatory. WiFeS is a powerful integral field, double-beam, concentric, image-slicing spectrograph designed to deliver excellent throughput, wavelength stability, spectrophotometric performance and superb image quality along with wide spectral coverage throughout the 320–950 nm wavelength region. It provides a 25×38 arcsec field with 0.5 arcsec sampling along each of twenty five 38×1 arcsec slitlets. The output format is optimized to match the 4096×4096 pixel CCD detectors in each of two cameras individually optimized for the blue and the red ends of the spectrum, respectively. A process of “interleaved nod-and-shuffle” will be applied to permit quantum noise-limited sky subtraction. Using VPH gratings, spectral resolutions of 3000 and 7000 are provided. The full spectral range is covered in a single exposure at R=3000, and in two exposures in the R=7000 mode. The use of transmissive coated optics, VPH gratings and optimized mirror coatings ensures a throughput (including telescope atmosphere and detector) >30% over a wide spectral range. The concentric image-slicer design ensures an excellent and uniform image quality across the full field. To maximize scientific return, the whole instrument is configured for remote observing, pipeline data reduction, and the accumulation of calibration image libraries.

The metallicity gradient of M 33: chemical abundances of H ii regions

Context. We present spectroscopic observations of a sample of 72 emission-line objects, including mainly H ii regions, in the spiral galaxy M 33. Spectra were obtained with the multi-object, wide field spectrograph AF2/WYFFOS at the 4.2 m WHT telescope. Line intensities, extinction, and electron density were determined for the whole sample of objects. Aims. The aim of the present work was to derive chemical and physical parameters of a set of H ii regions, and from them the metallicity gradient. Methods. Electron temperatures and chemical abundances were derived for the 14 H ii regions where both [O ii ]a nd [Oiii ]e mission line fluxes were measured, including the electron temperature sensitive emission line [O iii] 436.3 nm and in a few cases [N ii] 575.5 nm. The ionization correction factor (ICF) method was used to derive the total chemical abundances. Results. The presence of abundance gradients was inferred from the radial behaviour of several emission-line ratios, and accurately measured from chemical abundances directly derived in 14 H ii regions. The oxygen abundances of our H ii regions, located in the radial region from ∼ 2t o∼7.2 kpc, gave an oxygen gradient −0.054 ± 0.011 dex kpc −1 Conclusions. The overall oxygen gradient for M 33 obtained using ours and previous oxygen determinations in a large number of H ii regions with direct electron temperature determination as well as abundance in young stars presented a two slope shape: −0.19 dex kpc −1 for the central regions (R < 3 kpc), and −0.038 dex kpc −1 for the outer regions (R ≥ 3 kpc).