arXiv subjects

L. J. Kewley

Publications and source records attributed to L. J. Kewley.

At least 37 records · Page 2Linked to original sources

arXiv2014

The SAMI Galaxy Survey: Early Data Release

We present the Early Data Release of the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The SAMI Galaxy Survey is an ongoing integral field spectroscopic survey of ~3400 low-redshift (z<0.12) galaxies, covering galaxies in the field and in groups within the Galaxy And Mass Assembly (GAMA) survey regions, and a sample of galaxies in clusters. In the Early Data Release, we publicly release the fully calibrated datacubes for a representative selection of 107 galaxies drawn from the GAMA regions, along with information about these galaxies from the GAMA catalogues. All datacubes for the Early Data Release galaxies can be downloaded individually or as a set from the SAMI Galaxy Survey website. In this paper we also assess the quality of the pipeline used to reduce the SAMI data, giving metrics that quantify its performance at all stages in processing the raw data into calibrated datacubes. The pipeline gives excellent results throughout, with typical sky subtraction residuals in the continuum of 0.9-1.2 per cent, a relative flux calibration uncertainty of 4.1 per cent (systematic) plus 4.3 per cent (statistical), and atmospheric dispersion removed with an accuracy of 0."09, less than a fifth of a spaxel.

astro-ph.GA↗

arXiv2014

Strong Far-IR Cooling Lines, Peculiar CO Kinematics and Possible Star Formation Suppression in Hickson Compact Group 57

We present [C II] and [O I] observations from Herschel and CO(1-0) maps from the Combined Array for† Research in Millimeter Astronomy (CARMA) of the Hickson Compact Group HCG 57, focusing on the galaxies HCG 57a and HCG 57d. HCG 57a has been previously shown to contain enhanced quantities of warm molecular hydrogen consistent with shock and/or turbulent heating. Our observations show that HCG 57d has strong [C II] emission compared to L$_{\rm FIR}$ and weak CO(1-0), while in HCG 57a, both the [C II] and CO(1-0) are strong. HCG 57a lies at the upper end of the normal distribution of [C II]/CO and [C II]/FIR ratios, and its far-IR cooling supports a low density warm diffuse gas that falls close to the boundary of acceptable PDR models. However, the power radiated in the [C II] and warm H$_2$ emission have similar magnitudes, as seen in other shock-dominated systems and predicted by recent models. We suggest that shock-heating of the [C II] is a viable alternative to photoelectric heating in violently disturbed diffuse gas. The existence of shocks is also consistent with peculiar CO kinematics in the galaxy, indicating highly non-circular motions are present. These kinematically disturbed CO regions also show evidence of suppressed star formation, falling a factor of 10-30 below normal galaxies on the Kennicutt-Schmidt relation. We suggest that the peculiar properties of both galaxies are consistent with a highly dissipative off-center collisional encounter between HCG 57d and 57a, creating ring-like morphologies in both systems. Highly dissipative gas-on-gas collisions may be more common in dense groups because of the likelihood of repeated multiple encounters. The possibility of shock-induced SF suppression may explain why a subset of these HCG galaxies have been found previously to fall in the mid-infrared green valley.

astro-ph.GA↗

arXiv2014

The SAMI Galaxy Survey: The discovery of a luminous, low-metallicity H II complex in the dwarf galaxy GAMA J141103.98-003242.3

We present the discovery of a luminous unresolved H II complex on the edge of dwarf galaxy GAMA J141103.98-003242.3 using data from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. This dwarf galaxy is situated at a distance of ~100 Mpc and contains an unresolved region of H II emission that contributes ~70 per cent of the galaxy's H_alpha luminosity, located at the top end of established H II region luminosity functions. For the H II complex, we measure a star-formation rate of 0.147\pm0.041 M_solar yr^-1 and a metallicity of 12+log(O/H) = 8.01\pm0.05 that is lower than the rest of the galaxy by ~0.2 dex. Data from the H I Parkes All-Sky Survey (HIPASS) indicate the likely presence of neutral hydrogen in the galaxy to potentially fuel ongoing and future star-forming events. We discuss various triggering mechanisms for the intense star-formation activity of this H II complex, where the kinematics of the ionised gas are well described by a rotating disc and do not show any features indicative of interactions. We show that SAMI is an ideal instrument to identify similar systems to GAMA J141103.98-003242.3, and the SAMI Galaxy Survey is likely to find many more of these systems to aid in the understanding of their formation and evolution.

astro-ph.GA↗

arXiv2014

The FMOS-Cosmos Survey of Star-Forming Galaxies at z~1.6 II. The Mass-Metallicity Relation and the Dependence on Star Formation Rate and Dust Extinction

We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate, and dust content of star-forming galaxies at z$\sim$1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity relation at $z\sim1.6$ is steeper than the relation observed in the local Universe. The steeper MZ relation at $z\sim1.6$ is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at $z\sim1.6$. The most massive galaxies at $z\sim1.6$ ($\sim 10^{11}M_\odot$) are enriched to the level observed in massive galaxies in the local Universe. The mass-metallicity relation we measure at $z\sim1.6$ supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and star formation rate for galaxies at a fixed stellar mass at $z\sim1.6$ which is similar to trends observed in the local Universe. We do not find a relation between stellar mass, metallicity and star formation rate that is independent of redshift; our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity and dust extinction. We find that at a fixed stellar mass dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs and dust extinctions we conclude that stellar mass is most closely related to dust extinction.

astro-ph.CO↗

arXiv2014

The FMOS-COSMOS survey of star-forming galaxies at z ~ 1.6. I. Hα-based star formation rates and dust extinction

We present the first results from a near-IR spectroscopic survey of the COSMOS field, using the Fiber Multi-Object Spectrograph on the Subaru telescope, designed to characterize the star-forming galaxy population at $1.4<z<1.7$. The high-resolution mode is implemented to detect H$α$ in emission between $1.6{\rm -}1.8 \mathrm{μm}$ with $f_{\rm Hα}\gtrsim4\times10^{-17}$ erg cm$^{-2}$ s$^{-1}$. Here, we specifically focus on 271 sBzK-selected galaxies that yield a H$α$ detection thus providing a redshift and emission line luminosity to establish the relation between star formation rate and stellar mass. With further $J$-band spectroscopy for 89 of these, the level of dust extinction is assessed by measuring the Balmer decrement using co-added spectra. We find that the extinction ($0.6\lesssim A_\mathrm{Hα} \lesssim 2.5$) rises with stellar mass and is elevated at high masses compared to low-redshift galaxies. Using this subset of the spectroscopic sample, we further find that the differential extinction between stellar and nebular emission \hbox{$E_\mathrm{star}(B-V)/E_\mathrm{neb}(B-V)$} is 0.7--0.8, dissimilar to that typically seen at low redshift. After correcting for extinction, we derive an H$α$-based main sequence with a slope ($0.81\pm0.04$) and normalization similar to previous studies at these redshifts.

astro-ph.CO↗

arXiv2013

Systematics in Metallicity Gradient Measurements I : Angular Resolution, Signal-to-Noise and Annuli Binning

With the rapid progress in metallicity gradient studies at high-redshift, it is imperative that we thoroughly understand the systematics in these measurements. This work investigates how the [NII]/Halpha ratio based metallicity gradients change with angular resolution, signal-to-noise (S/N), and annular binning parameters. Two approaches are used: 1. We downgrade the high angular resolution integral-field data of a gravitationally lensed galaxy and re-derive the metallicity gradients at different angular resolution; 2. We simulate high-redshift integral field spectroscopy (IFS) observations under different angular resolution and S/N conditions using a local galaxy with a known gradient. We find that the measured metallicity gradient changes systematically with angular resolution and annular binning. Seeing-limited observations produce significantly flatter gradients than higher angular resolution observations. There is a critical angular resolution limit beyond which the measured metallicity gradient is substantially different to the intrinsic gradient. This critical angular resolution depends on the intrinsic gradient of the galaxy and is < 0.02 arcsec for our simulated galaxy. We show that seeing-limited high-redshift metallicity gradients are likely to be strongly affected by resolution-driven gradient flattening. Annular binning with a small number of annuli produces a more flattened gradient than the intrinsic gradient due to weak line smearing. For 3-annuli bins, a minimum S/N of ~ 5 on the [NII] line is required for the faintest annulus to constrain the gradients with meaningful errors.

astro-ph.CO↗

arXiv2013

Mid-Infrared Properties of Nearby Luminous Infrared Galaxies I: Spitzer IRS Spectra for the GOALS Sample

The Great Observatories All-Sky LIRG Survey (GOALS) is a multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer spectra covering 5-38um and provide a basic analysis of the mid-IR spectral properties for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra. The GOALS sample of 244 nuclei in 180 luminous and 22 ultraluminous IR galaxies represents a complete subset of the IRAS RBGS and covers a range of merger stages, morphologies and spectral types. The majority (>60%) of GOALS LIRGs have high 6.2um PAH equivalent widths (EQW > 0.4um) and low levels of silicate absorption (s_9.7um >-1.0). There is a general trend among the U/LIRGs for silicate depth and MIR slope to increase with LIR. U/LIRGs in the late stages of a merger also have on average steeper MIR slopes and higher levels of dust obscuration. Together these trends suggest that as gas & dust is funneled towards the center of a coalescing merger, the nuclei become more compact and obscured. The sources that depart from these correlations have very low PAH EQW (EQW < 0.1um) consistent with their MIR emission being dominated by an AGN. The most heavily dust obscured sources are the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst. As the merger progresses a marked decline is seen for the fraction of high EQW (star formation dominated) sources while the fraction of composite sources increases but the fraction of AGN-dominated sources remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z~2, the average GOALS LIRG is more absorbed at 9.7um and has more PAH emission. However, when the AGN contributions to both the local LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starbursting SMGs.

astro-ph.CO↗

arXiv2012

The Metallicity Evolution of Star-Forming Galaxies from Redshift 0 to 3: Combining Magnitude Limited Survey with Gravitational Lensing

We present a comprehensive observational study of the gas phase metallicity of star-forming galaxies from z ~ 0 -> 3. We combine our new sample of gravitationally lensed galaxies with existing lensed and non-lensed samples to conduct a large investigation into the mass-metallicity (MZ) relation at z > 1. We apply a self-consistent metallicity calibration scheme to investigate the metallicity evolution of star-forming galaxies as a function of redshift. The lensing magnification ensures that our sample spans an unprecedented range of stellar mass (3*10^{7}-6*10^{10} M_sun). We find that at the median redshift of z=2.07, the median metallicity of the lensed sample is 0.35 dex lower than the local SDSS star-forming galaxies and 0.18 dex lower than the z ~ 0.8 DEEP2 galaxies. We also present the z ~ 2 MZ relation using 19 lensed galaxies. A more rapid evolution is seen between z ~ 1->3 than z ~ 0 -> 1 for the high-mass galaxies (10^{9.5-11} M_sun), with almost twice as much enrichment between z ~ 1 -> 3 than between z ~ 1 -> 0. We compare this evolution with the most recent cosmological hydrodynamic simulations with momentum driven winds. We find that the model metallicity is consistent with the observed metallicity within the observational error for the low mass bins. However, for higher masses, the model over-predicts the metallicity at all redshifts. The over-prediction is most significant in the highest mass bin of 10^{10-11} M_sun.

astro-ph.CO↗

arXiv2012

The A2667 Giant Arc at z=1.03: Evidence for Large-scale Shocks at High Redshift

We present the spatially resolved emission line ratio properties of a ~10^10 M_sun star-forming galaxy at redshift z=1.03. This galaxy is gravitationally lensed as a triple-image giant arc behind the massive lensing cluster Abell 2667. The main image of the galaxy has magnification factors of 14+/-2.1 in flux and ~ 2 by 7 in area, yielding an intrinsic spatial resolution of 115-405 pc after AO correction with OSIRIS at KECK II. The HST morphology shows a clumpy structure and the Hα kinematics indicates a large velocity dispersion with V_{max} sin(i)/σ~ 0.73, consistent with high redshift disk galaxies of similar masses. From the [NII]/Hα line ratios, we find that the central 350 parsec of the galaxy is dominated by star formation. The [NII]/Hα line ratios are higher in the outer-disk than in the central regions. Most noticeably, we find a blue-shifted region of strong [NII]/Hα emission in the outer disk. Applying our recent HII region and slow-shock models, we propose that this elevated [NII]/Hα ratio region is contaminated by a significant fraction of shock excitation due to galactic outflows. Our analysis suggests that shocked regions may mimic flat or inverted metallicity gradients at high redshift.

astro-ph.CO↗

arXiv2012

Eliminating Error in the Chemical Abundance Scale for Extragalactic HII Regions

In an attempt to remove the systematic errors which have plagued the calibration of the HII region abundance sequence, we have theoretically modeled the extragalactic HII region sequence. We then used the theoretical spectra so generated in a double blind experiment to recover the chemical abundances using both the classical electron temperature + ionization correction factor technique, and the technique which depends on the use of strong emission lines (SELs) in the nebular spectrum to estimate the abundance of oxygen. We find a number of systematic trends, and we provide correction formulae which should remove systematic errors in the electron temperature + ionization correction factor technique. We also provide a critical evaluation of the various semi-empirical SEL techniques. Finally, we offer a scheme which should help to eliminate systematic errors in the SEL-derived chemical abundance scale for extragalactic HII regions.

astro-ph.CO↗

arXiv2012

An Integral Field Study of Abundance Gradients in Nearby LIRGs

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.

astro-ph.CO↗

arXiv2012

The Metallicities of Low Stellar Mass Galaxies and the Scatter in the Mass-Metallicity Relation

In this investigation we quantify the metallicities of low mass galaxies by constructing the most comprehensive census to date. We use galaxies from the SDSS and DEEP2 survey and estimate metallicities from their optical emission lines. We also use two smaller samples from the literature which have metallicities determined by the direct method using the temperature sensitive [OIII]4363 line. We examine the scatter in the local mass-metallicity (MZ) relation determined from ~20,000 star-forming galaxies in the SDSS and show that it is larger at lower stellar masses, consistent with the theoretical scatter in the MZ relation determined from hydrodynamical simulations. We determine a lower limit for the scatter in metallicities of galaxies down to stellar masses of ~10^7 M_solar that is only slightly smaller than the expected scatter inferred from the SDSS MZ relation and significantly larger than what is previously established in the literature. The average metallicity of star-forming galaxies increases with stellar mass. By examining the scatter in the SDSS MZ relation, we show that this is mostly due to the lowest metallicity galaxies. The population of low mass, metal-rich galaxies have properties which are consistent with previously identified galaxies that may be transitional objects between gas-rich dwarf irregulars and gas-poor dwarf spheroidals and ellipticals.

astro-ph.CO↗

arXiv2011

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 Å, 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.

astro-ph.CO↗

arXiv2011

The High-Metallicity Explosion Environment of the Relativistic Supernova 2009bb

We investigate the environment of the nearby (d ~ 40Mpc) broad-lined Type Ic supernova SN 2009bb. This event was observed to produce a relativistic outflow likely powered by a central accreting compact object. While such a phenomenon was previously observed only in long-duration gamma-ray bursts (LGRBs), no LGRB was detected in association with SN 2009bb. Using an optical spectrum of the SN 2009bb explosion site, we determine a variety of ISM properties for the host environment, including metallicity, young stellar population age, and star formation rate. We compare the SN explosion site properties to observations of LGRB and broad-lined SN Ic host environments on optical emission line ratio diagnostic diagrams. Based on these analyses, we find that the SN 2009bb explosion site has a very high metallicity of ~2x solar, in agreement with other broad-lined SN Ic host environments and at odds with the low-redshift LGRB host environments and recently proposed maximum metallicity limits for relativistic explosions. We consider the implications of these findings and the impact that SN 2009bb's unusual explosive properties and environment have on our understanding of the key physical ingredient that enables some SNe to produce a relativistic outflow.

astro-ph.HE↗

arXiv2011

Metallicity Gradient of a Lensed Face-on Spiral Galaxy at Redshift 1.49

We present the first metallicity gradient measurement for a grand-design face-on spiral galaxy at z~1.5. This galaxy has been magnified by a factor of 22$\times$ by a massive, X-ray luminous galaxy cluster MACS\,J1149.5+2223 at z=0.544. Using the Laser Guide Star Adaptive Optics aided integral field spectrograph OSIRIS on KECK II, we target the Halpha emission and achieve a spatial resolution of 0.1", corresponding to a source plane resolution of 170 pc. The galaxy has well-developed spiral arms and the nebular emission line dynamics clearly indicate a rotationally supported disk with V_{rot}/σ~4. The best-fit disk velocity field model yields a maximum rotation of V_{rot} sin{i}=150$\pm$15 km s^{-1}, and a dynamical mass of M_{dyn}=1.3$\pm0.2\times10^{10}csc^2(i) M_{\odot} (within 2.5\,kpc), where the inclination angle i=45$\pm10^{\circ}$. Based on the [NII] and Halpha ratios, we measured the radial chemical abundance gradient from the inner hundreds of parsecs out to ~5 kpc. The slope of the gradient is -0.16$\pm$0.02 dex kpc$^{-1}$, significantly steeper than the gradient of late-type or early-type galaxies in the local universe. If representative of disk galaxies at z~1.5, our results support an "inside-out" disk formation scenario in which early infall/collapse in the galaxy center builds a chemically enriched nucleus, followed by slow enrichment of the disk over the next 9 Gyr.

astro-ph.CO↗

arXiv2011

The Mass-Metallicity and Luminosity-Metallicity Relation from DEEP2 at z ~ 0.8

We present the mass-metallicity (MZ) and luminosity-metallicity (LZ) relations at z ~ 0.8 from ~1350 galaxies in the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey. We determine stellar masses by fitting the spectral energy distribution inferred from photometry with current stellar population synthesis models. This work raises the number of galaxies with metallicities at z ~ 0.8 by more than an order of magnitude. We investigate the evolution in the MZ and LZ relations in comparison with local MZ and LZ relations determined in a consistent manner using ~21,000 galaxies in the Sloan Digital Sky Survey. We show that high stellar mass galaxies (log(M/M_solar)~10.6) at z ~ 0.8 have attained the chemical enrichment seen in the local universe, while lower stellar mass galaxies (log(M/M_solar)~9.2) at z ~ 0.8 have lower metallicities (Delta log(O/H)~0.15 dex) than galaxies at the same stellar mass in the local universe. We find that the LZ relation evolves in both metallicity and B-band luminosity between z ~ 0.8 and z~ 0, with the B-band luminosity evolving as a function of stellar mass. We emphasize that the B-band luminosity should not be used as a proxy for stellar mass in chemical evolution studies of star-forming galaxies. Our study shows that both the metallicity evolution and the B-band luminosity evolution for emission-line galaxies between the epochs are a function of stellar mass, consistent with the cosmic downsizing scenario of galaxy evolution.

astro-ph.CO↗

arXiv2010

COLA III. Radio Detection of AGN in Compact Moderate Luminosity Infra-Red Galaxies

We present results from 4.8 GHz VLA and Global-VLBI observations of the northern half of the moderate FIR luminosity (median L_IR = 10^11.01 L_Sol) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores (~10^21 W/Hz) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by AGN. These sub-parsec scale radio cores are preferentially detected toward galaxies whose VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star-formation we conclude that the AGN powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central super-massive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity.

astro-ph.CO↗

arXiv2010

The Double-Peaked 2008 Outburst of the Accreting Milli-Second X-ray Pulsar, IGR J00291+5934

In August 2008, the accreting milli-second X-ray pulsar (AMXP), IGR J00291+5934, underwent an outburst lasting ~ 100 days, the first since its discovery in 2004. We present data from the double-peaked outburst from Faulkes Telescope North, the INT, the Keck Telescope, PAIRITEL, the Westerbork Synthesis Radio Telescope and the Swift, XMM-Newton and RXTE X-ray missions. We study the outburst's evolution at various wavelengths. We study the light curve morphology, presenting the first radio-X-ray Spectral Energy Distributions (SEDs) for this source and the most detailed UV-IR SEDs for any outbursting AMXP. We show simple models that attempt to identify the emission mechanisms responsible. We analyse short-timescale optical variability, and compare a medium resolution optical spectrum with those from 2004. The outburst morphology is unusual for an AMXP, comprising two peaks, the second containing a 'plateau' of ~ 10 days at maximum brightness within 30 days of the initial activity. This has implications on duty cycles of short-period X-ray transients. The X-ray spectrum can be fitted by a single, hard power-law. We detect optical variability of ~ 0.05 magnitudes, on timescales of minutes, but find no periodic modulation. In the optical, the SEDs contain a blue component, indicative of an irradiated disc, and a transient near-infrared (NIR) excess. This excess is consistent with a simple model of an optically thick synchrotron jet (as seen in other outbursting AMXPs). The optical spectrum shows a double-peaked H alpha profile, a diagnostic of an accretion disc, but we do not clearly see other lines (e.g. He I, II) reported in 2004. Optical/IR observations of AMXPs are excellent for studying the evolution of both the outer accretion disc and the inner jet, and may eventually provide us with tight constraints to model disc-jet coupling in accreting neutron stars.

astro-ph.HE↗