arXiv subjects

L. Christensen

Publications and source records attributed to L. Christensen.

At least 109 records · Page 6Linked to original sources

arXiv2009

The integral field spectroscopy (IFS) wiki

In this article we present the integral field spectroscopy (IFS) wiki site, http://ifs.wikidot.com; what the wiki is, our motivation for creating it, and a short introduction to IFS. The IFS wiki is designed to be a central repository of information, tips, codes, tools, references, etc., regarding the whole subject of IFS, which is accessible and editable by the whole community. Currently the wiki contains a broad base of information covering topics from current and future integral field spectrographs, to observing, to data reduction and analysis techniques. We encourage everyone who wants to know more about IFS to look at this web-site, and any question you may have you can post from there. And if you have had any experience with IFS yourself, we encourage you to contribute your knowledge and help the site develop its full potential. Before re-inventing the wheel, consult the wiki...

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arXiv2008

Highly ionized gas on galaxy scales: mapping the interacting Seyfert galaxy LEDA 135736

We have used the VIMOS IFU to map the properties of the Seyfert 1.9 galaxy LEDA 135736. These maps reveal a number of interesting features including: an Extended Narrow Line Region detectable out to 9 kpc, an area of intense star formation located at a projected distance of 12 kpc from the centre, an elliptical companion galaxy, and kinematic features, aligned along the long-axis of the ENLR, that are consistent with radio jet-driven mass outflow. We propose that the ENLR results from extra-planar gas ionized by the AGN, and that the AGN in turn might be triggered by interaction with the companion galaxy, which can also explain the burst of star formation and morphological features. Only about two percent of the ENLR's kinetic energy is in the mass outflow. We infer from this that the bulk of mechanical energy imparted by the jet is used to heat this gas.

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arXiv2008

IFU observations of the GRB 980425/SN 1998bw host galaxy: emission line ratios in GRB regions

The collapsar model predicts that the progenitors of Gamma-ray Bursts (GRBs) are metal poor in Fe group elements. The existence of low metallicity stellar populations could manifest itself through special characteristics of the immediate environment of the GRB site in the host galaxy. We analyse the strong emission lines from the sub-luminous host galaxy of GRB 980425, which showed the first connection with a supernova explosion (SN 1998bw). The host has a sufficient size to allow detailed resolved spectroscopy of individual HII regions and to look for regions with special properties close to the the GRB site. Using integral field spectroscopy with VIMOS we cover most of the high surface brightness part of the host including the HII region where the supernova and GRB occurred. The star formation rate, reddening, equivalent width and stellar mass in the GRB region is similar to other HII regions in the host. Extreme values arise in the only region that shows emission lines from Wolf-Rayet stars; a region that lies 800 pc in projection from the GRB site. Strong emission line diagnostics of all HII regions imply oxygen abundances between 0.3 and 0.8 solar with the lowest values arising in the WR and GRB regions. Comparing the measured emission line ratios for a sample of low redshift GRB hosts to theoretical models and to observations of field galaxies, we find that GRBs arise in a range of metallicity environments while the regions are consistently very young. The similar line ratios of GRB hosts compared to the WR region can arise in spatially unresolved galaxies with bright HII regions near the GRB location. (Abridged)

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arXiv2007

An integral field spectroscopic survey for high redshift damped Lyman-alpha galaxies

We search for galaxy counterparts to damped Lyman-alpha absorbers (DLAs) at z>2 towards nine quasars, which have 14 DLAs and 8 sub-DLAs in their spectra. We use integral field spectroscopy to search for Ly-alpha emission line objects at the redshifts of the absorption systems. Besides recovering two previously confirmed objects, we find six statistically significant candidate Ly-alpha emission line objects. The candidates are identified as having wavelengths close to the DLA line where the background quasar emission is absorbed. In comparison with the six currently known Ly-alpha emitting DLA galaxies the candidates have similar line fluxes and line widths, while velocity offsets between the emission lines and systemic DLA redshifts are larger. The impact parameters are larger than 10 kpc, and lower column density systems are found at larger impact parameters. Assuming that a single gas cloud extends from the QSO line of sight to the location of the candidate emission line, we find that the average candidate DLA galaxy is surrounded by neutral gas with an exponential scale length of ~5 kpc.

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arXiv2006

Extended Lyman alpha emission around bright quasars

Quasars trace the most massive structures at high redshifts and their presence may influence the evolution of the massive host galaxies. We study the extended Lyman alpha emission line regions (EELRs) around seven bright, mostly radio-quiet quasars (QSOs) at 2.7<z<4.5, and compare luminosities with EELRs around radio-loud QSOs reported in the literature. Using integral field spectroscopy, we analyse the morphology and kinematics of the quiescent Lya EELRs around the QSOs. We find evidence for the presence of EELRs around four radio-quiet and one radio-loud QSO. All EELRs appear asymmetric and the optically brightest QSOs also have the brightest Lya nebulae. For the two brightest nebulae we find velocities between ~600 km s^-1 at the QSO position to ~200 km s^-1 at a distance of 3-4 arcsec from the QSO and surface flux densities up to 2-3*10^{-16} erg cm^-2 s^-1 arcsec^-2. The five EELRs have total Lya luminosities which correspond to ~0.5% of the luminosities from the QSOs broad Lya emission lines. This fraction is an order of magnitude smaller than found for EELRs around radio-loud, steep spectrum QSOs reported in the literature. While the nebulae luminosities are correlated with the QSO Lya luminosities, we find that nebulae luminosities are not correlated with the central QSO ionising fluxes. The presence of gas in the EELRs can be interpreted based on two competing scenarios: either from quasar feedback mechanisms, or from infalling matter. Apart from these two effects, the Lya flux around radio-loud objects can be enhanced due to interactions with the radio jets. The relatively fainter nebulae around radio-quiet QSOs compared to lobe-dominated radio-loud QSOs can be ascribed to this effect, or to significant differences in the environments between the two classes.

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arXiv2006

Strange magnification pattern in the large separation lens SDSS J1004+4112 from optical to X-rays

We present simultaneous XMM-Newton UV and X-ray observations of the quadruply lensed quasar SDSS J1004+4112 (RBS 825). Simultaneously with the XMM-Newton observations we also performed integral field spectroscopy on the two closest lens images A and B using the Calar Alto PMAS spectrograph. In X-rays the widely spaced components C and D are clearly resolved, while the closer pair of images A and B is marginally resolved in the XMM-EPIC images. The integrated X-ray flux of the system has decreased by a factor of 6 since it was observed in the ROSAT All Sky Survey in 1990, while the X-ray spectrum became much harder with the power law index evolving from Gamma=-2.3 to -1.86. By deblending the X-ray images of the lensed QSO we find that the X-ray flux ratios between the lens images A and B are significantly different from the simultaneously obtained UV ratios and previously measured optical flux ratios. Our optical spectrum of lens image A shows an enhancement in the blue emission line wings, which has been observed in previous epochs as a transient feature. We propose a scenario where intrinsic UV and X-ray variability gives rise to line variations which are selectively magnified in image A by microlensing. The extended emission of the lensing cluster of galaxies is clearly detected in the EPIC images, we measure a 0.5-2.0 keV luminosity of 1.4 E44 erg/s. Based on the cluster X-ray properties, we estimate a mass of 2-6 E14 solar masses.

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arXiv2006

A jet-cloud interaction in the 3C 196 environment

Powerful radio galaxies and radio-loud quasars at high redshifts are frequently associated with extended emission-line regions (EELRs). Here we investigate the [O II] EELR around the quasar 3C 196 at z=0.871 using integral field spectroscopy. We also detect extended [Ne II] emission at a distance of about 30 kpc from the core. The emission is aligned with the radio hot spots and shows a redshifted and a blueshifted component with a velocity difference of ~800 km s^-1. The alignment effect and large velocities support the hypothesis that the EELR is caused by a jet-cloud interaction, which is furthermore indicated by the presence of a pronounced bend in the radio emission at the location of the radio hot spots. We also report observations of two other systems which do not show as clear indications of interactions. We find a weaker alignment of an [O II] EELR from the z=0.927 quasar 3C 336, while no EELR is found around the core-dominated quasar OI 363 at z=0.63.

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arXiv2005

Multi-Wavelength Studies of the Optically Dark Gamma-Ray Burst 001025A

We identify the fading X-ray afterglow of GRB 001025A from XMM-Newton observations obtained 1.9-2.3 days, 2 years, and 2.5 years after the burst. The non-detection of an optical counterpart to an upper limit of R=25.5, 1.20 days after the burst, makes GRB 001025A a ``dark'' burst. Based on the X-ray afterglow spectral properties of GRB 001025A, we argue that some bursts appear optically dark because their afterglow is faint and their cooling frequency is close to the X-ray band. This interpretation is applicable to several of the few other dark bursts where the X-ray spectral index has been measured. The X-ray afterglow flux of GRB 001025A is an order of magnitude lower than for typical long-duration gamma-ray bursts. The spectrum of the X-ray afterglow can be fitted with an absorbed synchrotron emission model, an absorbed thermal plasma model, or a combination thereof. For the latter, an extrapolation to optical wavelengths can be reconciled with the R-band upper limit on the afterglow, without invoking any optical circumburst absorption, provided the cooling frequency is close to the X-ray band. Alternatively, if the X-ray afterglow is due to synchrotron emission only, seven magnitudes of extinction in the observed R-band is required to meet the R-band upper limit, making GRB 001025A much more obscured than bursts with detected optical afterglows. Based on the column density of X-ray absorbing circumburst matter, an SMC gas-to-dust ratio is insufficient to produce this amount of extinction. The X-ray tail of the prompt emission enters a steep temporal decay excluding that the tail of the prompt emission is the onset of the afterglow (abridged).

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arXiv2005

Spectro-photometric study of the GRB 030329 host galaxy

In this study optical/near-infrared(NIR) broad band photometry and optical spectroscopic observations of the GRB 030329 host galaxy are presented. The Spectral Energy Distribution (SED) of the host is consistent with a starburst galaxy template with a dominant stellar population age of ~150 Myr and an extinction Av ~0.6. Analysis of the spectral emission lines shows that the host is likely a low metallicity galaxy. Two independent diagnostics, based on the restframe UV continuum and the [OII] line flux, provide a consistent unextincted star formation rate of SFR ~0.6 Mo yr^-1. The low absolute magnitude of the host (M_B ~ -16.5) implies a high specific star formation rate value, SSFR = ~34 Mo yr^-1 (L/L*)^-1.

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arXiv2005

Photometric redshift of the GRB 981226 host galaxy

No optical afterglow was found for the dark burst GRB 981226 and hence no absorption redshift has been obtained. We here use ground-based and space imaging observations to analyse the spectral energy distribution (SED) of the host galaxy. By comparison with synthetic template spectra we determine the photometric redshift of the GRB 981226 host to be z_phot = 1.11+/-0.06 (68% confidence level). While the age-metallicity degeneracy for the host SED complicates the determination of accurate ages, metallicity, and extinction, the photometric redshift is robust. The inferred z_phot value is also robust compared to a Bayesian redshift estimator which gives z_phot=0.94+/-0.13. The characteristics for this host are similar to other GRB hosts previously examined. Available low resolution spectra show no emission lines at the expected wavelengths. The photometric redshift estimate indicates an isotropic energy release consistent with the Amati relation for this GRB which had a spectrum characteristic of an X-ray flash.

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arXiv2005

The GRB 030329 host: a blue low metallicity subluminous galaxy with intense star formation

We present broad band photometry and spectroscopic observations of the host galaxy of GRB 030329. Analysis of the spectral emission lines shows that the host is likely a low metallicity galaxy (Z~0.004). The spectral energy distribution (SED) constructed with the photometric points has been fitted using synthetic and observational templates. The best SED fit is obtained with a starburst template with an age of ~150 Myr and an extinction Av~0.6. We find that the GRB 030329 host galaxy is a subluminous galaxy (L~0.016 L*) with a stellar mass of >~10^8 Mo. Three independent diagnostics, based on the restframe UV continuum, the [OII], and the Balmer emission lines, provide a consistent unextincted star formation rate of ~0.6 Mo yr^-1, implying a high unextincted specific star formation rate (~34 Mo yr^-1 (L/L*)^-1). We estimate that the unextincted specific star formation rate of the GRB 030329 host is higher than ~93.5% of the galaxies at a similar redshift.

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arXiv2005

PMAS, the Potsdam Multi-Aperture Spectrophotometer. I. Design, Manufacture, and Performance

We describe the design, manufacture, commissioning, and performance of PMAS, the Potsdam Multi-Aperture Spectrophotometer. PMAS is a dedicated integral field spectrophotometer, optimized to cover the optical wavelength regime of 0.35--1um. It is based on the lens array -- fiber bundle principle of operation. The instrument employs an all-refractive fiber spectrograph, built with CaF2 optics, to provide good transmission and high image quality over the entire nominal wavelength range. A set of user-selectable reflective gratings provides low to medium spectral resolution in first order of approx. 1.5, 3.2, and 7 A, depending on the groove density (1200, 600, 300 gr/mm). While the standard integral field unit (IFU) uses a 16x16 element lens array, which provides seeing-limited sampling in a relatively small field-of-view (FOV) in one of three magnifications (8x8, 12x12, or 16x16 arcsec^2, respectively), a recently retrofitted bare fiber bundle IFU (PPak) expands the FOV to a hexagonal area with a footprint of 65x74 arcsec^2. Other special features include a cryogenic CCD camera for field acquisition and guiding, a nod-shuffle mode for beam switching and improved sky background subtraction, and a scanning Fabry-Perot etalon in combination with the standard IFU (PYTHEAS mode). PMAS was initially designed and built as an experimental traveling instrument with optical interfaces to various telescopes (Calar Alto 3.5m, ESO-VLT, LBT). It is offered as a common user instrument at Calar Alto under contract with MPIA Heidelberg since 2002.

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arXiv2004

The merging/AGN connection II. Ionization of the circumnuclear regions

We report the first results of a study of a sample of 20 galaxy mergers/interacting systems, using the VIMOS and PMAS integral field spectrographs. For each object, we extracted the integrated spectrum of the central regions and analyzed the ionization state using classical diagnostic diagrams (Veilleux & Osterbrock 1987). There is evidence of AGN ionization in 4 of the objects, i.e. 20% of the sample, a considerably higher fraction than found in previous studies ~4%

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arXiv2004

Integral Field Spectroscopy of the Central Regions of 3C 120: Evidence of a Past Merging Event

IFS combined with HST WFPC imaging were used to characterize the central regions of the Seyfert 1 radio galaxy 3C 120. We carried out the analysis of the data, deriving intensity maps of different emission lines and the continua at different wavelengths from the observed spectra. Applying a 2D modeling to the HST images we decoupled the nucleus and the host galaxy, and analyzed the host morphology. The host is a highly distorted bulge dominated galaxy, rich in substructures. We developed a new technique to model the IFS data extending the 2D modeling. Using this technique we separated the Seyfert nucleus and the host galaxy spectra, and derived a residual data cube with spectral and spatial information of the different structures in 3C 120. Three continuum-dominated structures (named A, B, and C) and other three extended emission line regions (EELRs, named E1, E2 and E3) are found in 3C 120 which does not follow the general behavior of a bulge dominated galaxy. We also found shells in the central kpc that may be remnants of a past merging event in this galaxy. The origin of E1 is most probably due to the interaction of the radio-jet of 3C 120 with the intergalactic medium. Structures A, B, and the shell at the southeast of the nucleus seem to correspond to a larger morphological clumpy structure that may be a tidal tail, consequence of the past merging event. We found a bright EELR (E2) in the innermost part of this tidal tail, nearby the nucleus, which shows a high ionization level. The kinematics of the E2 region and its connection to the tidal tail suggest that the tail has channeled gas from the outer regions to the center.

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arXiv2004

Abundances and kinematics of a candidate sub-damped Lyman-alpha galaxy toward PHL 1226

The spectrum of the quasar PHL 1226 is known to have a strong Mg II and sub-damped Lyman-alpha (sub-DLA) absorption line system with N(HI)=(5+/-2)*10^19 cm^-2 at z=0.1602. Using integral field spectra from the Potsdam Multi Aperture Spectrophotometer (PMAS) we investigate a galaxy at an impact parameter of 6".4 which is most probably responsible for the absorption lines. A fainter galaxy at a similar redshift and a slightly larger distance from the QSO is known to exist, but we assume that the absorption is caused by the more nearby galaxy. From optical Balmer lines we estimate an intrinsic reddening consistent with 0, and a moderate star formation rate of 0.5 M_sun yr^-1, is inferred from the Halpha luminosity. Using nebular emission line ratios we find a solar oxygen abundance 12+log(O/H)=8.7+/-0.1 and a solar nitrogen to oxygen abundance ratio log(N/O)=-1.0+/-0.2. This abundance is larger than those of all known sub-DLA systems derived from analyses of metal absorption lines in quasar spectra. On the other hand, the properties are compatible with the most metal rich galaxies responsible for strong Mg II absorption systems. These two categories can be reconciled if we assume an abundance gradient similar to local galaxies. Under that assumption we predict abundances 12+log(O/H)=7.1 and log(N/O)=-1.9 for the sub-DLA cloud, which is similar to high redshift DLA and sub-DLA systems. We find evidence for a rotational velocity of ~200 km s^-1 over a length of ~7 kpc. From the geometry and kinematics of the galaxy we estimate that the absorbing cloud does not belong to a rotating disk, but could originate in a rotating halo.

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arXiv2004

Integral field observations of DLA galaxies

We report preliminary results from a targeted investigation on quasars containing damped Lyman-alpha absorption (DLA) lines as well strong metal absorption lines, carried out with the Potsdam Multi Aperture Spectrophotometer (PMAS). We search for line-emitting objects at the same redshift as the absorption lines and close to the line of sight of the QSOs. We have observed and detected the already confirmed absorbing galaxies in Q2233+131 (z_abs=3.15) and Q0151+045 (z_abs=0.160), while failing to find spectral signatures for the z=0.091 absorber in Q0738+313. From the Q2233+131 DLA galaxy, we have detected extended Ly-alpha emission from an area of 3"*5".

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arXiv2004

Clean optical spectrum of the radio jet of 3C 120

We present integral field spectroscopy (IFS) of the central region of 3C 120. We have modeled the nuclear and host galaxy 3D spectra using techniques normally applied to imaging, decoupling both components, and obtained a residual datacube. Using this residual datacube, we detected the extended emission line region associated with the radio jet. We obtained, for the first time, a clean spectrum of this region and found compelling evidences of a jet-cloud interaction. The jet compresses and splits the gas cloud which is ionized by the AGN and/or by the strong local UV photon field generated by a shock process. We cannot confirm the detection of an extended emission line region associated with the counter-jet reported by Axon (1989).

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arXiv2004

UV star-formation rates of GRB host galaxies

We study a magnitude-limited sample of 10 gamma-ray burst (GRB) host galaxies with known spectroscopic redshifts (0.43 < z < 2.04). From an analysis of the spectral energy distributions (SEDs), based on published broad-band optical and near-infrared photometry, we derive photometric redshifts, galaxy types, ages of the dominant stellar populations, internal extinctions, and ultraviolet (UV) star-formation rates (SFRs) of the host galaxies. The photometric redshifts are quite accurate despite the heterogeneous nature of the sample: The r.m.s. errors are sigma(z) = 0.21 and sigma(Delta z/(1+z_spec)) = 0.16 with no significant systematic offsets. All the host galaxies have SEDs similar to young starburst galaxies with moderate to low extinction. A comparison of specific SFRs with those of high-redshift galaxies in the Hubble Deep Fields shows that GRB hosts are most likely similar to the field galaxies with the largest specific SFRs. On the other hand, GRB hosts are not significantly younger than starburst field galaxies at similar redshifts, but are found to be younger than a sample of all types of field galaxies.

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