arXiv subjects

J. P. U. Fynbo

Publications and source records attributed to J. P. U. Fynbo.

318 records · Page 18Linked to original sources

arXiv2003

The Building the Bridge survey for z=3 Ly-alpha emitting galaxies I: method and first results

We present the first results of an observational programme at the ESO Very Large Telescope aimed at detecting a large sample of high-redshift galaxies fainter than the current spectroscopic limit of R=25.5 for Lyman-Break galaxies. In this paper, we describe the results of deep narrow and broad-band imaging and subsequent follow-up multi-object spectroscopy of faint high-redshift galaxies in the fields of the BRI1346-0322 and Q2138-4427. These QSOs have intervening absorbers, at redshifts z=2.85 and z=3.15 respectively, for which redshifted Ly-alpha emission falls within less than a few AA from the central wavelengths of existing VLT (~60 AA wide) narrow-band filters. We selected 37 and 27 candidate emission-line galaxies in the two fields respectively. About 85% of the candidates have R-band magnitudes fainter than R=25.5. The first spectroscopic follow-up of a sub-sample of the candidates resulted in 41 confirmed candidates and 4 foreground galaxies (three [OII] emitters and one CIV emitter). The confirmation rate is 82% and 68% in the field of BRI1346-0322 and Q2138-4427 respectively. In addition, we serendipitously detect a number of other emission-line sources on some of the slitlets not used for candidates. Of these, 9 are also most likely Ly-alpha emitters with redshifts ranging from 1.98 to 3.47. The redshift distribution of confirmed candidates in the field of BRI1346-0322 is consistent with being drawn from a uniform distribution weighted by the filter response curve, whereas the galaxies in the field of Q2138-4427 have redshifts clustering very close to the redshift of the damped Ly-alpha absorber. This latter fact indicates the existence of a large `pancake'-like structure confirming the earlier suggestions of Francis & Hewitt (1993).

astro-ph↗

arXiv2003

Optical and near-infrared observations of the GRB020405 afterglow

(Abridged) We report on observations of the optical and NIR afterglow of GRB020405. Ground-based optical observations started about 1 day after the GRB and spanned a period of ~10 days; archival HST data extended the coverage up to 70 days after the GRB. We report the first detection of the afterglow in NIR bands. The detection of emission lines in the optical spectrum indicates that the GRB is located at z = 0.691. Absorptions are also detected at z = 0.691 and at z = 0.472. The latter system is likely caused by clouds in a galaxy located 2 arcsec southwest of the GRB host. Hence, for the first time, the galaxy responsible for an intervening absorption system in the spectrum of a GRB afterglow is identified. Optical and NIR photometry indicates that the decay in all bands follows a single power law of index alpha = 1.54. The late-epoch VLT and HST points lie above the extrapolation of this power law, so that a plateau is apparent in the VRIJ light curves at 10-20 days after the GRB. The light curves at epochs later than day ~20 after the GRB are consistent with a power-law decay with index alphaprime = 1.85. We suggest that this deviation can be modeled with a SN having the same temporal profile as SN2002ap, but 1.3 mag brighter at peak, and located at the GRB redshift. Alternatively, a shock re-energization may be responsible for the rebrightening. A polarimetric R-band measurement shows that the afterglow is polarized, with P = 1.5 % and theta = 172 degrees. Optical-NIR spectral flux distributions show a change of slope across the J band which we interpret as due to the presence of nu_c. The analysis of the multiwavelength spectrum within the fireball model suggests that a population of relativistic electrons produces the optical-NIR emission via synchrotron in an adiabatically expanding blastwave, and the X-rays via IC.

astro-ph↗

arXiv2003

Ly-alpha emission from GRB host galaxies

Ly-alpha emission is indicative of on-going star formation in a dust-poor environment. Ly-alpha imaging is therefore a probe of the star formation rate and of the dust-content of Gamma-Ray Burst host galaxies. Both of these parameters are central to our understanding of GRB progenitors and of how the environments affect the propagation of afterglow emission out of host galaxies. We have started a program aimed at imaging high redshift (z>2) host galaxies of GRBs at the Ly-alpha resonance line from neutral hydrogen. Here were report the results from imaging of the fields of GRB 000301C and GRB 000926 and outline upcoming observations of further hosts.

astro-ph↗

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.

astro-ph↗

arXiv2002

Building the bridge between Damped Ly-alpha Absorbers and Lyman Break galaxies

In 2000, we started the program ``Building the Bridge between Damped Ly-alpha Absorbers and Lyman-Break Galaxies: Ly-alpha Selection of Galaxies'' at the European Southern Observatory's Very Large Telescope. This project is an attempt to use Ly-alpha selection of high-z galaxies to bridge the gap between absorption- and emission-selected galaxies by creating a large database of z=3 galaxies belonging to the abundant population of faint (R>25.5) galaxies probed by the Damped Ly-alpha Absorbers (DLAs). Here we present the first results of our program, namely the results from a deep Ly-alpha study of the field of the z=2.85 DLA towards Q2138-4427.

astro-ph↗

arXiv2002

Constraints on (Omega_m,Omega_Lambda) using distributions of inclination angles for high redshift filaments

In this paper we present a scale free method to determine the cosmological parameters (Omega_m, Omega_Lambda). The method is based on the requirement of isotropy of the distribution of orientations of cosmological filaments. The current structure formation paradigm predicts that the first structures to form are voids and filaments, causing a web-like structure of the matter distribution at high redshifts. Recent observational evidence suggests that the threads, or filaments, of the cosmic web most easily are mapped in Ly-alpha emission. We describe how such a 3D map can be used to constrain the cosmological parameters in a way which, contrary to most other cosmological tests, does not require the use of a standard rod or a standard candle. We perform detailed simulations in order to define the optimal survey parameters for the definition of an observing programme aimed to address this test, and to investigate how statistical and observational errors will influence the results. We conclude that observations should target filaments of comoving size 15-50 Mpc in the redshift range 2-4, and that each filament must be defined by at least four Ly-alpha emitters. Detection of 20 filaments will be sufficient to obtain a result, while 50 filaments will make it possible to place significant new constraints on the values of Omega_m and Omega_Lambda permitted by the current supernova observations. In a future paper we study how robust these conclusions are to systematic velocities in the survey box.

astro-ph↗

arXiv2002

An HST study of three very faint GRB host galaxies

As part of the HST/STIS GRB host survey program we present the detection of three faint gamma-ray burst (GRB) host galaxies based on an accurate localisation using ground-based data of the optical afterglows (OAs). A common property of these three hosts is their extreme faintness. The location at which GRBs occur with respect to their host galaxies and surrounding environments are robust indicators of the nature of GRB progenitors. The bursts studied here are among the four most extreme outliers, in terms of relative distance from the host center, in the recent comprehensive study of Bloom et al. 2002. We obtain a revised and much higher probability that the galaxies identified as hosts indeed are related to the GRBs (P(n_chance)=0.78, following Bloom et al. 2002), thereby strengthening the conclusion that GRBs are preferentially located in star-forming regions in their hosts. Apart from being faint, the three hosts consist of multiple structures, indicative of merging and active star-formation. For one of the hosts, GRB 980329, we estimate a photometric redshift of z~3.5.

astro-ph↗

arXiv2002

Deep Ly-alpha imaging of two z=2.04 GRB host galaxy fields

We report on the results of deep narrow-band Ly-alpha, U and I imaging of the fields of two GRBs at z=2.04 (GRB 000301C and GRB 000926). We find that the host galaxy of GRB 000926 is an extended, strong Ly-alpha emitter with a rest-frame equivalent width of 71+20-15 AA. The galaxy consists of two main components and several fainter knots. GRB 000926 occurred in the western component, whereas most of the Ly-alpha luminosity (about 65%) originates in the eastern component. Using archival HST images of the host galaxy we measure the spectral slopes (f_lambda prop. to lambda^beta) of the two components to beta = -2.4+-0.3 (east) and -1.4+-0.2 (west). This implies that both components contain at most small amounts of dust, consistent with the observed strong Ly-alpha emission. The western component has a slightly redder V-I colour than the eastern component, suggesting the presence of at least some dust. We do not detect the host galaxy of GRB 000301C in neither Ly-alpha emission nor in U and I-band images. We infer a limit of U(AB)>27.7 (2-sigma limit per arcsec^2). The upper limits on the Ly-alpha flux implies a Ly-alpha equivalent width upper limit of 150AA. We find 11 and 8 other galaxies with excess emission in the narrow filter in the fields of GRB 000301C and GRB 000926 respectively. Based on these detections we conclude that GRB 000926 occurred in one of the strongest centres of star formation within several Mpc, whereas GRB 000301C occurred in an intrinsically very faint galaxy far from being the strongest centre of star formation in its galactic environment. Under the hypothesis that GRBs trace star formation, the wide range of GRB host galaxy luminosities implies a very steep faint end slope of the high redshift galaxy luminosity function.

astro-ph↗

arXiv2001

The optical afterglow and host galaxy of GRB 000926

In this paper we illustrate with the case of GRB 000926 how Gamma Ray Bursts (GRBs) can be used as cosmological lighthouses to identify and study star forming galaxies at high redshifts. The optical afterglow of the burst was located with optical imaging at the Nordic Optical Telescope 20.7 hours after the burst. Rapid follow-up spectroscopy allowed the determination of the redshift of the burst and a measurement of the host galaxy HI-column density in front of the burst. With late-time narrow band Ly-alpha as well as broad band imaging, we have studied the emission from the host galaxy and found that it is a strong Ly-alpha emitter in a state of active star formation.

astro-ph↗

arXiv2001

Detecting filaments at z=3

We present the detection of a filament of Ly-alpha emitting galaxies in front of the quasar Q1205-30 at z=3.04 based on deep narrow band imaging and follow-up spectroscopy obtained at the ESO NTT and VLT. We argue that Ly-alpha selection of high redshift galaxies with relatively modest amounts of observing time allows the detection and redshift measurement of galaxies with sufficiently high space densities that we can start to map out the large scale structure at z=2-3 directly. Even more interesting is it that a 3D map of the filaments will provide a new cosmological test for the value of the cosmological constant, Omega_Lambda.

astro-ph↗

arXiv2001

HST/STIS observations of GRB000301C: CCD imaging and NUV MAMA spectroscopy

We present HST/STIS observations of the optical counterpart (OT) of the gamma-ray burster GRB 000301C obtained on 2000 March 6, five days after the burst. CCD clear aperture imaging reveals a R ~ 21.50+/-0.15 source with no apparent host galaxy. An 8000 s, 1150 < lambda/A < 3300 NUV-MAMA prism spectrum shows a relatively flat continuum (in f_lambda) between 2800 and 3300 A, with a mean flux 8.7 (+0.8,-1.6)+/- 2.6 10^(-18) ergs/s/cm^2/A, and a sharp break centered at 2797+/-25 A. We interpret it as HI Lyman break at z = 2.067+/-0.025 indicating the presence of a cloud with a HI column density log(HI) > 18 on the line-of-sight to the OT. This value is conservatively a lower limit to the GRB redshift. However, the facts that large N(HI) system are usually considered as progenitors of present day galaxies and that other OTs are found associated with star forming galaxies strongly suggest that it is the GRB redshift. In any case, this represents the largest direct redshift determination of a gamma-ray burster to date. Our data are compatible with an OT spectrum represented by a power-law with an intrinsic index α= 1.2((f_nu \propto nu^-alpha) and no extinction in the host galaxy or with alpha = 0.5 and extinction by a SMC-like dust in the OT rest-frame with A_V = 0.15. The large N(HI) and the lack of detected host is similar to the situation for damped Ly-alpha absorbers at z > 2.

astro-ph↗

arXiv2001

The Host Galaxy and Optical Light Curve of the Gamma-Ray Burst GRB 980703

We present deep HST/STIS and ground-based photometry of the host galaxy of the gamma-ray burst GRB 980703 taken 17, 551, 710, and 716 days after the burst. We find that the host is a blue, slightly over-luminous galaxy with V_gal = 23.00 +/- 0.10, (V-R)_gal = 0.43 +/- 0.13, and a centre that is approximately 0.2 mag bluer than the outer regions of the galaxy. The galaxy has a star-formation rate of 8-13 M_sun/yr, assuming no extinction in the host. We find that the galaxy is best fit by a Sersic R^(1/n) profile with n ~= 1.0 and a half-light radius of 0.13 arcsec (= 0.72/h_100 proper kpc). This corresponds to an exponential disk with a scale radius of 0.22 arcsec (= 1.21/h_100 proper kpc). Subtracting a fit with elliptical isophotes leaves large residuals, which suggests that the host galaxy has a somewhat irregular morphology, but we are unable to connect the location of GRB 980703 with any special features in the host. The host galaxy appears to be a typical example of a compact star forming galaxy similar to those found in the Hubble Deep Field North. The R-band light curve of the optical afterglow associated with this gamma-ray burst is consistent with a single power-law decay having a slope of alpha = -1.37 +/- 0.14. Due to the bright underlying host galaxy the late time properties of the light-curve are very poorly constrained. The decay of the optical light curve is consistent with a contribution from an underlying Type Ic supernova like SN1998bw, or a dust echo, but such contributions cannot be securely established.

astro-ph↗