arXiv subjects

P. Møller

Publications and source records attributed to P. Møller.

63 records · Page 4Linked to original sources

arXiv2004

Discovery of the Near-IR Afterglow and of the Host of GRB 030528

The rapid dissemination of an arcmin-sized HETE-2 localization of the long-duration X-ray flash GRB 030528 led to a ground-based multi-observatory follow-up campaign. We report the discovery of the near-IR afterglow, and also describe the detection of the underlying host galaxy in the optical and near-IR bands. The afterglow is classified as "optically dark" as it was not detected in the optical band. The K-band photometry presented here suggests that the lack of optical detection was simply the result of observational limitations (lack of rapid and deep observations plus high foreground extinction). Simple power law fits to the afterglow in the K-band suggest a typically decay with a slope of alpha=1.2. The properties of the host are consistent with the idea that GRB hosts are star forming blue galaxies. The redshift of GRB 030528 can not be determined accurately, but the data favour redshifts less than unity. In addition, we present an optical and near-IR analysis of the X-ray source CXOU J170354.0--223654 from the vicinity of GRB 030528.

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arXiv2004

The host of GRB 030323 at z=3.372: a very high column density DLA system with a low metallicity

We present photometry and spectroscopy of the afterglow of GRB 030323. VLT spectra of the afterglow show damped Lya (DLA) absorption and low- and high-ionization lines at a redshift z=3.3718+-0.0005. The inferred neutral hydrogen column density, log N(HI)=21.90+-0.07, is larger than any (GRB- or QSO-) DLA HI column density inferred directly from Lya in absorption. From the afterglow photometry, we derive a conservative upper limit to the host-galaxy extinction: A(V)<0.5 mag. The iron abundance is [Fe/H]=-1.47+-0.11, while the metallicity of the gas as measured from sulphur is [S/H]=-1.26+-0.20. We derive an upper limit on the H2 molecular fraction of 2N(H2)/(2N(H2)+N(HI))<~10^-6. In the Lya trough, a Lya emission line is detected, which corresponds to a star-formation rate (not corrected for dust extinction) of roughly 1 Msun per year. All these results are consistent with the host galaxy of GRB 030323 consisting of a low metallicity gas with a low dust content. We detect fine-structure lines of silicon, SiII*, which have never been clearly detected in QSO-DLAs; this suggests that these lines are produced in the vicinity of the GRB explosion site. Under the assumption that these fine-structure levels are populated by particle collisions, we estimate the HI volume density to be n_HI=100-10000 cm^-3. HST/ACS imaging 4 months after the burst shows an extended AB(F606W)=28.0+-0.3 mag object at a distance of 0.14" (1kpc) from the early afterglow location, which presumably is the host galaxy of GRB 030323.

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arXiv2003

Very high column density and small reddening towards GRB 020124 at z = 3.20

We present optical and near-infrared observations of the dim afterglow of GRB 020124, obtained between 2 and 68 hours after the gamma-ray burst. The burst occurred in a very faint (R > 29.5) Damped Ly-alpha Absorber (DLA) at a redshift of z = 3.198 +- 0.004. The derived column density of neutral hydrogen is log(N_H) = 21.7 +- 0.2 and the rest-frame reddening is constrained to be E(B-V) < 0.065, i.e., A_V < 0.20 for standard extinction laws with R_V ~ 3. The resulting dust-to-gas ratio is less than 11 % of that found in the Milky Way, but consistent with the SMC and high-redshift QSO DLAs, indicating a low metallicity and/or a low dust-to-metals ratio in the burst environment. A grey extinction law (large R_V), produced through preferential destruction of small dust grains by the GRB, could increase the derived A_V and dust-to-gas ratio. The dimness of the afterglow is however fully accounted for by the high redshift: If GRB 020124 had been at z = 1 it would have been approximately 1.8 mag brighter--in the range of typical bright afterglows.

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arXiv2002

Absorption Systems in the Spectrum of GRB 021004

We report on a 3600 s spectrum of GRB 021004 obtained with the Nordic Optical Telecope on La Palma 10.71 hours after the burst. We identify absorption lines from five systems at redshifts 1.3806, 1.6039, 2.2983, 2.3230, and 2.3292. In addition we find an emission line which, if due to Ly-alpha from the host galaxy, gives a redshift of 2.3351. The nearest absorber is blueshifted by 530 km/s with respect to this line, consistent with shifts seen in Damped Ly-alpha and Lyman-Break galaxies at similar redshifts. The emission line flux is 2.46+-0.50 x 10^-16 erg/s/cm^2. Some of the absorption systems are "line-locked", an effect often seen in QSO absorption systems believed to originate close to the QSO central engine.

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arXiv2002

Are high-redshift DLA galxies Lyman-break galaxies?

We use deep HST STIS and NICMOS images of three spectroscopically confirmed galaxy counterparts of high-redshift damped Ly-alpha (DLA) absorbers (one of which is a new discovery) to test the hypothesis that high-redshift DLA galaxies are Lyman-break galaxies. If this hypothesis is correct the emission properties of DLA galaxies must lie within the range of emission properties measured for Lyman-break galaxies of similar absolute magnitude. This will be true regardless of selection biases in the sample of detected DLA galaxies. We test this prediction using several emission properties: half-light radius, radial profile (Sersic n parameter), optical-to-near-infrared colour, morphology, Ly alpha emission equivalent width, and Ly alpha emission velocity structure. In all cases the measured values for the DLA galaxies lie within the range measured for the population of Lyman-break galaxies. None of the measurements is in conflict with the prediction. We conclude that the measured emission properties of the three DLA galaxies studied here are consistent with the conjecture that high-redshift DLA galaxies are Lyman-break galaxies. We show that this result does not conflict with the observation that the few high-redshift DLA galaxies discovered are mostly fainter than spectroscopically confirmed L* Lyman-break galaxies.

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arXiv2001

The evolution of field early-type galaxies to z~0.7

We have measured the Fundamental Plane (FP) parameters for a sample of 30 field early-type galaxies (E/S0) in the redshift range 0.1 5Åin 22% of an enlarged sample of 42 massive E/S0 in the range 0.1<z<0.73, in contrast with the quiescent population observed in clusters at similar z. We interpret these findings as evidence that a significant fraction of massive field E/S0 experiences secondary episodes of star-formation at z<1.

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arXiv2001

The properties of field elliptical galaxies at intermediate redshift. III: the Fundamental Plane and the evolution of stellar populations from z~0.4 to z=0

We report on the study of a sample of 25 field early-type galaxies, in the redshift range z~0.1-0.5, selected on the basis of colours and morphology from the HST-MDS. Field early-type galaxies define a tight Fundamental Plane (FP) out to z~0.4, with scatter unchanged with respect to local samples, within the observational errors. The intermediate redshift FP is offset with respect to the FP of the Coma Cluster. The offset of the FP is found to increase with redshift. The evolution of the FP is studied quantitatively with a Bayesian-Montecarlo technique. By applying this technique, we find that the offset of the intercept of the FP (Δγ) with respect to the local FP increases as Δγ= τz with the following 68 per cent limits: 0.33<τ<0.44 (for Ω=1, Ω_Λ=0) or 0.44<τ<0.56 (for Ω=0.3,Ω_Λ=0.7). In addition, we interpret the results in terms of the evolution of the stellar populations, under the assumption of passive evolution. In a single-burst scenario, the observed properties are consistent with those of a stellar population formed at z>2 (for Ω=1, Ω_Λ=0, H_0=50 \kms Mpc^{-1}) or 0.8<z<1.6 (for Ω=0.3, Ω_Λ=0.7, H_0=65 \kms Mpc^{-1}). If a small fraction of the stellar mass is formed in a secondary burst, the primary burst may have occurred at higher z. Finally, the intercept and scatter of the FP found for field early-type galaxies and for cluster data at z~0.4 are mutually consistent, within the observational errors. If higher redshift (up to z=0.83) cluster data are considered, the ages of the stellar populations of field early-type galaxies inferred from a single-burst scenario are found to be marginally smaller than the ages derived for the cluster galaxies. [shortened]

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arXiv2001

The properties of field elliptical galaxies at intermediate redshift. II: photometry and spectroscopy of an HST selected sample

A sample of field early-type galaxies (E/S0) at intermediate redshift ($z\sim0.1-0.6$) is selected, based on morphology and colours from HST-WFPC2 parallel images. Photometric structural parameters (effective radius $R_{\tx{e}}$ and effective surface brightness $SB_{\tx{e}}$) are derived through the F606W and F814W filters, using luminosity profile fitting and two-dimensional fitting techniques. The combined parameter that enters the Fundamental Plane ($\log R_{\tx{e}}-βSB_{\tx{e}}$, with $β\approx0.32$) is shown to suffer from significantly smaller uncertainties (r.m.s. 0.03) than the individual structural parameters (e.g. $\sim 15$ per cent r.m.s. on the effective radius). High signal-to-noise intermediate resolution spectra, taken at the ESO-3.6m, yield redshifts for 35 galaxies and central velocity dispersions for 22 galaxies. Central velocity dispersions are derived using a library of stellar templates covering a wide range of spectral types, in order to study the effects of templates mismatches. The average random error on the central velocity dispersion is found to be 8 per cent and the average systematic error due to template mismatch is found to be 5 per cent. The errors on velocity dispersion measurement and the effects of template mismatches are studied by means of extensive Montecarlo simulations. In addition, we investigate whether the determination of the velocity dispersion is sensitive to the spectral range used, finding that the value of velocity dispersion is unchanged when the spectral regions that include the absorption features Ca HK and NaD are masked out during the fit.

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arXiv1999

The Properties of Field Elliptical Galaxies at Intermediate Redshift. I: Empirical Scaling Laws

We present measurements of the Fundamental Plane (FP) parameters (the effective radius, the mean effective surface brightness, and the central velocity dispersion) of six field elliptical galaxies at intermediate redshift. The imaging is taken from the Medium Deep Survey of the Hubble Space Telescope, while the kinematical data are obtained from long-slit spectroscopy using the 3.6-m ESO telescope. The Fundamental Plane appears well defined in the field even at redshift $\approx$ 0.3. The data show a shift in the FP zero point with respect to the local relation, possibly indicating modest evolution, consistent with the result found for intermediate redshift cluster samples. The FP slopes derived for our field data, plus other cluster ellipticals at intermediate redshift taken from the literature, differ from the local ones, but are still consistent with the interpretation of the FP as a result of homology, of the virial theorem and of the existence of a relation between luminosity and mass, $L \propto M^η$. We also derive the surface brightness vs. effective radius relation for nine galaxies with redshift up to $z \approx0.6$, and data from the literature; the evolution that can be inferred is consistent with what is found using the FP.

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