arXiv subjects

K. J. Fricke

Publications and source records attributed to K. J. Fricke.

At least 37 records · Page 2Linked to original sources

arXiv2011

A nearby GRB host galaxy: VLT/X-shooter observations of HG 031203

(abridged) Long-duration gamma-ray bursts (LGRBs) occur in galaxies of generally low metallicity. We aim at a spectroscopic analysis of HG 031203, the host galaxy of a LRGB burst, to obtain its properties. Based on VLT/X-shooter spectroscopic observations in the wavelength range 3200-24000A, we use standard direct methods to evaluate physical conditions and element abundances. The resolving power of the instrument also allowed us to trace the kinematics of the ionised gas. We derive an interstellar oxygen abundance of 12+logO/H=8.20+/-0.03. The observed fluxes of hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value C(Hbeta)=1.67. We produce the CLOUDY photoionisation HII region model that reproduces observed emission-line fluxes of different ions in the optical range. This model also predicts emission-line fluxes in the near-infrared (NIR) and mid-infrared (MIR) ranges that agree well with the observed ones. This implies that the star-forming region observed in the optical range is the only source of ionisation and there is no additional source of ionisation seen in the NIR and MIR ranges that is hidden in the optical range.We find that the heavy element abundances, Halpha luminosity, stellar mass, star-formation rate and specific star-formation rate of HG 031203 are in the range that is covered by the luminous compact galaxies (LCGs).This implies that the LCGs with extreme star-formation that also comprise green pea galaxies as a subclass may harbour LGRBs.

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arXiv2011

VLT/X-shooter observations of the low-metallicity blue compact dwarf galaxy PHL 293B including a luminous blue variable star

(abridged) We present VLT/X-shooter spectroscopic observations in the wavelength range 3000-23000A of the extremely metal-deficient blue compact dwarf (BCD) galaxy PHL 293B containing a luminous blue variable (LBV) star. We determine abundances of N, O, Ne, S, Ar, and Fe and study the properties of the LBV from the fluxes and widths of broad emission lines. We derive an interstellar oxygen abundance of 12+log O/H = 7.71+/-0.02, which is in agreement with previous determinations. The observed fluxes of narrow Balmer, Paschen and Brackett hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value C(Hbeta) = 0.225. This implies that the star-forming region observed in the optical range is the only source of ionisation and there is no additional source of ionisation that is seen in the NIR range but is hidden in the optical range. For the LBV star in PHL 293B we find broad emission with P Cygni profiles in several Balmer hydrogen emission lines and for the first time in several Paschen hydrogen lines and in several HeI emission lines, implying temporal evolution of the LBV on a time scale of 8 years. The Halpha luminosity of the LBV star is by one order of magnitude higher than the one obtained for the LBV star in NGC 2363=Mrk 71 which has a slightly higher metallicity 12+logO/H = 7.87. The terminal velocity of the stellar wind in the low-metallicity LBV of PHL293B is high, ~800 km/s, and is comparable to that seen in spectra of some extragalactic LBVs during outbursts. We find that the averaged terminal velocities derived from the Paschen and HeI emission lines are by some ~40-60 km/s lower than those derived from the Balmer emission lines. This probably indicates the presence of the wind accelerating outward.

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arXiv2010

Tol 2240-384 - a new low-metallicity AGN candidate

Active galactic nuclei (AGNs) have typically been discovered in massive galaxies of high metallicity. We attempt to increase the number of AGN candidates in low metallicity galaxies. We present VLT/UVES and archival VLT/FORS1 spectroscopic and NTT/SUSI2 photometric observations of the low-metallicity emission-line galaxy Tol 2240-384 and perform a detailed study of its morphology, chemical composition, and emission-line profiles. We determine abundances of nitrogen, O, Ne, S, Cl, Ar, and Fe by analyzing the fluxes of narrow components of the emission lines using empirical methods. We verify with a photoionisation model that the physics of the narrow-line component gas is similar to that in common metal-poor galaxies. Image deconvolution reveals two high-surface brightness regions in Tol 2240-384 separated by 2.4 kpc.The brightest southwestern region is surrounded by intense ionised gas emission on a spatial scale of ~5 kpc. The profiles of the strong emission lines in the UVES spectrum are asymmetric and all these lines apart from Halpha and Hbeta can be fitted by two Gaussians of FWHM ~75-92 km/s separated by ~80 km/s implying that there are two regions of ionised gas emitting narrow lines. The shapes of the Halpha and Hbeta lines are more complex. In particular, the Halpha emission line consists of two broad components of FWHM ~700 km/s and 2300 km/s, in addition to narrow components of two regions revealed from profiles of other lines. The extraordinarily high luminosity of the broad Halpha line of 3x10e41 erg/s cannot be accounted for by massive stars at different stages of their evolution. The broad Halpha emission persists over a period of 7 years, which excludes supernovae as a powering mechanism of this emission. This emission most likely arises from an accretion disc around a black hole of mass ~10e7 Msun.

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arXiv2009

An investigation of the luminosity-metallicity relation for a large sample of low-metallicity emission-line galaxies

(abridged) We present 8.2m VLT spectroscopic observations of 28 HII regions in 16 emission-line galaxies and 3.6m ESO telescope spectroscopic observations of 38 HII regions in 28 emission-line galaxies. These emission-line galaxies were selected mainly from the Data Release 6 (DR6) of the Sloan Digital Sky Survey (SDSS) as metal-deficient galaxy candidates. We collect photometric and high-quality spectroscopic data for a large uniform sample of star forming galaxies including new observations. Our aim is to study the luminosity-metallicity (L-Z) relation for nearby galaxies, especially at its low-metallicity end and compare it with that for higher-redshift galaxies. From our new observations we find that the oxygen abundance in 61 out of the 66 HII regions of our sample ranges from 12+logO/H=7.05 to 8.22. Our sample includes 27 new galaxies with 12+logO/H<7.6 which qualify as extremely metal-poor star-forming galaxies (XBCDs). Among them are 10 HII regions with 12+logO/H<7.3. The new sample is combined with a further 93 low-metallicity galaxies with accurate oxygen abundance determinations from our previous studies, yielding in total a high-quality spectroscopic data set of 154 HII regions. 9000 more galaxies with oxygen abundances, based mainly on the Te-method, are compiled from the SDSS. Our data set spans a range of 8 mag with respect to its absolute magnitude in SDSS g (-12>Mg>-20) and nearly 2 dex in its oxygen abundance (7.0<12+logO/H<8.8), allowing us to probe the L-Z relation in the nearby universe down to the lowest currently studied metallicity level. The L-Z relation established on the basis of the present sample is consistent with previous ones obtained for emission-line galaxies.

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arXiv2009

SBS 0335-052E+W: deep VLT/FORS+UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies

(abridged) We present deep archival VLT/FORS1+UVES spectroscopic observations of the system of two blue compact dwarf (BCD) galaxies SBS 0335-052E and SBS 0335-052W. Our aim is to derive element abundances in different HII regions of this unique system of galaxies and to study spatial abundance variations. We determine abundances of helium, nitrogen, oxygen, neon, sulfur, chlorine, argon and iron. The oxygen abundance in the brighter eastern galaxy varies in the range 7.11 to 7.32 in different HII regions supporting previous findings and suggesting the presence of oxygen abundance variations on spatial scales of ~1-2 kpc. The oxygen abundance in the brightest region No.1 of SBS 0335-052W is 7.22+/-0.07, consistent with previous determinations.Three other HII regions are much more metal-poor with an unprecedently low oxygen abundance of 12+logO/H=7.01+/-0.07 (region No.2), 6.98+/-0.06 (region No.3), and 6.86+/-0.14 (region No.4). These are the lowest oxygen abundances ever derived in emission-line galaxies. Helium abundances derived for the brightest HII regions of both galaxies are mutually consistent. We derive weighted mean He mass fractions of 0.2485+/-0.0012 and 0.2514+/-0.0012 for two different sets of HeI emissivities. The N/O abundance ratio in both galaxies is slightly higher than that derived for other BCDs with 12+logO/H<7.6. This implies that the N/O in extremely metal-deficient galaxies could increase with decreasing metallicity.

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arXiv2008

Extremely metal-poor star-forming galaxies. New detections and general morphological and photometric properties

(abridged) We present long-slit spectroscopy with the 3.6m ESO telescope of eight HII regions in seven star-forming (SF) dwarf galaxies, discovered in SDSS DR4 and 6dFGRS. In addition, we use SDSS imaging data to study the photometric structure of the sample galaxies. From the 3.6m telescope spectra, we determine the oxygen abundance of these systems to be 7.3<12+log(O/H)<7.6, placing them among the most metal-poor SF galaxies ever discovered. Our photometric analysis reveals a moderately blue, stellar host galaxy in all sample galaxies. The detection of a stellar host in all galaxies studied here and all previously studied extremely metal-deficient SF galaxies implies that they are unlikely to be forming their first generation of stars. With regard to the structural properties of their host galaxy, we demonstrate that these systems are indistinguishable from blue compact dwarf (BCD) galaxies. However, in contrast to the majority (>90%) of BCDs that are characterised by red elliptical host galaxies, extremely metal-poor SF dwarfs (hereafter XBCDs) reveal moderately blue and irregular hosts. This is consistent with a young evolutionary status and in the framework of standard star formation histories implies that several XBCDs formed most of their stellar mass in the past 2 Gyr. A large fraction of XBCDs reveal a cometary morphology due to the presence of intense SF activity at one edge of an elongated host galaxy with a gradually decreasing surface brightness towards its antipodal end.

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arXiv2007

Balmer jump temperature determination in a large sample of low-metallicity H II regions

Aims. Continuing the systematic determination of the electron temperature of H II regions using the Balmer and/or Paschen discontinuities by Guseva et al. (2006) we focus here on 3.6m ESO telescope observations of a large new sample of 69 H II regions in 45 blue compact dwarf (BCD) galaxies. This data set spans a wide range in metallicity (Zsun/60 11000 K) H II regions the temperature of the O2+ zone, determined from doubly ionised oxygen forbidden lines, does not differ statistically from the temperature of the H+ zone. Thus, we confirm and strengthen the finding by Guseva et al. (2006). We emphasize that due to a number of modelling assumptions and the observational uncertainties for individual objects, only a large, homogeneous sample, as the one used here, can enable a conclusive study of the relation between Te(H+) and Te(O III).

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arXiv2006

New southern blue compact dwarf galaxies in the 2dF Galaxy Redshift Survey

Aiming to find new extremely metal-deficient star-forming galaxies we extracted from the Two-Degree Field Galaxy Redshift Survey (2dFGRS) 100K Data Release 14 emission-line galaxies with relatively strong [OIII] 4363 emission. Spectroscopic and photometric studies of this sample and, in addition, of 7 Tololo and 2 UM galaxies were performed on the basis of observations with the ESO 3.6m telescope. All sample galaxies qualify with respect to their photometric and spectroscopic properties as blue compact dwarf (BCD) galaxies. Additionally, they show a good overlap with a comparison sample of 100 well-studied emission-line galaxies on the 12+log(O/H) vs. log(Ne/O), log(Ar/O) and log(Fe/O) planes. From the analysis of the 2dFGRS subsample we report the discovery of two new extremely metal-deficient BCDs with an oxygen abundance 12+log(O/H) < 7.6 and of another seven galaxies with 12+log(O/H) < 7.8. Furthermore, we confirm previous oxygen abundance determinations for the BCDs Tol 1304-353, Tol 2146-391, UM 559 and UM 570 to be 12+log(O/H) < 7.8.

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arXiv2006

Oxygen abundance variations in the system of the two blue compact dwarf galaxies SBS 0335-052E and SBS 0335-052W

We present 3.6m ESO telescope spectroscopic observations of the system of the two blue compact dwarf galaxies SBS 0335-052W and SBS 0335-052E. The oxygen abundance in SBS 0335-052W is 12 + log O/H = 7.13 +/- 0.08, confirming that this galaxy is the most metal-deficient emission-line galaxy known. We find that the oxygen abundance in SBS 0335-052E varies from region to region in the range from 7.20 to 7.31, suggesting the presence of an abundance gradient over a spatial scale of 1 kpc. Signatures of early carbon-type Wolf-Rayet stars are detected in cluster 3 of SBS 0335-052E, corresponding to the emission of three to eighteen WC4 stars, depending on the adopted luminosity of a single WC4 star in the CIV 4658 emission line.

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arXiv2006

Two extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey

We present spectroscopic observations with the 3.6m ESO telescope of two emission-line galaxies, J2104-0035 and J0113+0052, selected from the Data Release 4 (DR4) of the Sloan Digital Sky Survey (SDSS). From our data we determine the oxygen abundance of these systems to be respectively 12+logO/H = 7.26+/-0.03 and 7.17+/-0.09, making them the two most metal-deficient galaxies found thus far in the SDSS and placing them among the five most metal-deficient emission-line galaxies ever discovered. Their oxygen abundances are close to those of the two most metal-deficient emission-line galaxies known, SBS0335-052W with 12+logO/H = 7.12+/-0.03 and I Zw 18 with 12+logO/H = 7.17+/-0.01.

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arXiv2004

New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared studies: II. The sample of northern BCDs

This paper is part of a series of publications which present a systematic study of Blue Compact Dwarf (BCD) Galaxies in the Near Infrared (NIR). Compared to the visible light, NIR data allow a better separation of the starburst emission from the light distribution of the old stellar low-surface brightness (LSB) host galaxy. We analyze deep NIR broad band images of a sample of 11 BCDs, observed with the Calar Alto 3.6m telescope. This work enlarges the samples presented in preceding papers of this study (Noeske et al. 2003, Cairos et al. 2003) by BCDs of the most common morphological type, displaying a regular elliptical LSB host galaxy. The data presented here allow the detection and quantitative study of the extended stellar LSB host galaxy in all sample BCDs. The NIR surface brightness profiles (SBPs) of the LSB host galaxies agree at large galactocentric radii with those from optical studies, showing also an exponential intensity decrease and compatible scale lengths. Similar to Noeske et al. (2003), we find centrally flattening exponential (type V) SBPs of the host galaxy for several BCDs. Such SBPs remain mostly undetected in optical bands, due to the comparatively stronger starburst emission at these wavelengths. We apply a modified exponential distribution to decompose and quantitatively analyze SBPs of LSB hosts with a type V intensity distribution. We present the results of the surface photometry and the decomposition of SBPs, and discuss individual objects with respect to morphological details of their star-forming regions.

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arXiv2004

Deep VLT spectroscopy of the blue compact dwarf galaxies Tol 1214-277 and Tol 65

We present VLT spectroscopic observations with different spectral resolutions and different slit orientations of the two metal-deficient blue compact dwarf (BCD) galaxies Tol 1214-277 and Tol 65. The oxygen abundances in the brightest HII regions of Tol 1214-277 and Tol 65 are found to be 12+log O/H = 7.55+/-0.01 and 7.54+/-0.01, or Zsun/24. The nitrogen-to-oxygen abundance ratios in the two galaxies are log N/O =-1.64+/-0.03 and -1.60+/-0.02 and lie in the narrow range found for other most metal-deficient BCDs. The helium mass fraction derived in several HII regions in both galaxies is consistent with a high primordial helium mass fraction, Yp ~ 0.244. We confirm the detection of the high-ionization forbidden emission line [FeV]4227 in the spectrum of Tol 1214-277. Additionally, weak [NeIV]4725, [FeVI]5146, 5177, and [FeVII]5721, 6087 emission lines are detected in the high-resolution spectrum of Tol 1214-277. The detection of these lines implies the presence of hard radiation with photon energy in the range ~ 4-8 Ryd. Emission lines are detected in the spectra of eight galaxies in the fields of Tol 1214-277 and Tol 65. Seven of these galaxies are background objects, while one galaxy has a redshift close to that of Tol 1214-277. Situated at a projected distance of ~ 14.5 kpc from Tol 1214-277, this galaxy is probably a companion of the BCD.

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arXiv2004

Pox 186: an ultracompact galaxy with dominant ionized gas emission

We present a ground-based optical spectroscopic and HST U, V, I photometric study of the blue compact dwarf (BCD) galaxy Pox 186. It is found that the emission of the low-surface brightness (LSB) component in Pox 186 at radii < 3'' (< 270 pc in linear scale) is mainly gaseous in origin. We detect Halpha emission out to radii as large as 6''. At radii > 3'' the light of the LSB component is contaminated by the emission of background galaxies complicating the study of the outermost regions. The surface brightness distribution in the LSB component can be approximated by an exponential law with a scale length alpha < 120 pc. This places Pox 186 among the most compact dwarf galaxies known. The derived alpha is likely to be an upper limit to the scale length of the LSB component because of the strong contribution of the gaseous emission. The oxygen abundance in the bright HII region derived from the 4.5m Multiple Mirror Telescope (MMT) and 3.6m ESO telescope spectra are 12+log(O/H)= 7.76+/-0.02 and 7.74+/-0.01 (~ Zsun/15), respectively, in accordance with previous determinations. The helium mass fractions found in this region are Y=0.248+/-0.009 (MMT) and Y=0.248+/-0.004 (3.6m) suggesting a high primordial helium abundance.

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arXiv2004

The evolution of the luminosity functions in the FORS Deep Field from low to high redshift: I. The blue bands

We use the very deep and homogeneous I-band selected dataset of the FORS Deep Field (FDF) to trace the evolution of the luminosity function over the redshift range 0.5 < z < 5.0. We show that the FDF I-band selection down to I(AB)=26.8 misses of the order of 10 % of the galaxies that would be detected in a K-band selected survey with magnitude limit K(AB)=26.3 (like FIRES). Photometric redshifts for 5558 galaxies are estimated based on the photometry in 9 filters (U, B, Gunn g, R, I, SDSS z, J, K and a special filter centered at 834 nm). A comparison with 362 spectroscopic redshifts shows that the achieved accuracy of the photometric redshifts is (Delta z / (z_spec+1)) < 0.03 with only ~ 1 % outliers. This allows us to derive luminosity functions with a reliability similar to spectroscopic surveys. In addition, the luminosity functions can be traced to objects of lower luminosity which generally are not accessible to spectroscopy. We investigate the evolution of the luminosity functions evaluated in the restframe UV (1500 Angstroem and 2800 Angstroem), u', B, and g' bands. Comparison with results from the literature shows the reliability of the derived luminosity functions. Out to redshifts of z ~ 2.5 the data are consistent with a slope of the luminosity function approximately constant with redshift, at a value of -1.07 +- 0.04 in the UV (1500 Angstroem, 2800 Angstroem) as well as u', and -1.25 +- 0.03 in the blue (g', B). We do not see evidence for a very steep slope (alpha < -1.6) in the UV at z ~ 3.0 and z ~ 4.0 favoured by other authors. There may be a tendency for the faint-end slope to become shallower with increasing redshift but the effect is marginal. We find a brightening of M_star and a decrease of Phi_star with redshift for all analyzed wavelengths. [abridged]

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arXiv2004

The Tully-Fisher relation at intermediate redshift

Using the Very Large Telescope in Multi Object Spectroscopy mode, we have observed a sample of 113 field spiral galaxies in the FORS Deep Field (FDF) with redshifts in the range 0.1<z<1.0. The galaxies were selected upon apparent brightness (R<23) and encompass all late spectrophotometric types from Sa to Sdm/Im. Spatially resolved rotation curves have been extracted for 77 galaxies and fitted with synthetic velocity fields taking into account all observational effects from inclination and slit misalignment to seeing and slit width. We also compared different shapes for the intrinsic rotation curve. To gain robust values of V_max, our analysis is focussed on galaxies with rotation curves which extend well into the region of constant rotation velocity at large radii. If the slope of the local Tully-Fisher relation (TFR) is held fixed, we find evidence for a mass-dependent luminosity evolution which is as large as up to 2 mag for the lowest-mass galaxies, but is small or even negligible for the highest-mass systems in our sample. In effect, the TFR slope is shallower at z~0.5 in comparison to the local sample. We argue for a mass-dependent evolution of the mass-to-light ratio. An additional population of blue, low-mass spirals does not seem a very appealing explanation. The flatter tilt we find for the distant TFR is in contradiction to the predictions of recent semi-analytic simulations.

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arXiv2004

Motion and Properties of Nuclear Radio Components in Seyfert Galaxies Seen with VLBI

We report EVN, MERLIN and VLBA observations at 18 cm, 6 cm and 3.6 cm of the Seyfert galaxies NGC 7674, NGC 5506, NGC 2110 and Mrk 1210 to study their structure and proper motions on pc scales and to add some constraints on the many possible causes of the radio-quietness of Seyferts. The component configurations in NGC 7674 and NGC 2110 are simple, linear structures, whereas the configurations in NGC 5506 and Mrk 1210 have multiple components with no clear axis of symmetry. We suggest that NGC 7674 is a low-luminosity compact symmetric object. Comparing the images at different epochs, we find a proper motion in NGC 7674 of (0.92+-0.07) c between the two central components separated by 282 pc and, in NGC 5506, we find a 3 sigma upper limit of 0.50 c for the components separated by 3.8 pc. Our results confirm and extend earlier work showing that the outward motion of radio components in Seyfert galaxies is non-relativistic on pc scales. We briefly discuss whether this non-relativistic motion is intrinsic to the jet-formation process or results from deceleration of an initially relativistic jet by interaction with the pc or sub-pc scale interstellar medium. We combined our sample with a list compiled from the literature of VLBI observations made of Seyfert galaxies, and found that most Seyfert nuclei have at least one flat-spectrum component on the VLBI scale, which was not seen in the spectral indices measured at arcsec resolution. We found also that the bimodal alignment of pc and kpc radio structures displayed by radio galaxies and quasars is not displayed by this sample of Seyferts, which shows a uniform distribution of misalignment between 0 deg and 90 deg. The frequent misalignment could result from jet precession or from deflection of the jet by interaction with gas in the interstellar medium.

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arXiv2004

Discovery of the high--ionization emission line [Ne V] 3426 in the blue compact dwarf galaxy Tol 1214-277

The discovery of the high-ionization [Ne V] 3426A emission line in the spectrum of the blue compact dwarf (BCD) galaxy Tol 1214-277 is reported. The detection of this line implies the presence of intense ionizing X-ray emission with a luminosity in the range 10^39-10^40 erg/s. Such a high X-ray luminosity cannot be reproduced by models of massive stellar populations. Other mechanisms, such as fast shocks or accretion of gas in high-mass X-ray binaries need to be invoked to account for the high intensity of the [Ne V] 3426A emission line.

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arXiv2003

The regeneration of stellar bars by tidal interactions. Numerical simulations of fly-by encounters

We study the regeneration of stellar bars triggered by a tidal interaction, using numerical simulations of either purely stellar or stellar+gas disc galaxies. We find that interactions which are sufficiently strong to regenerate the bar in the purely stellar models do not lead to a regeneration in the dissipative models, owing to the induced gas inflow in those models. In models in which the bar can be regenerated, we find a tight correlation between the strength and the pattern speed of the induced bar. This relation can be explained by a significant radial redistribution of angular momentum in the disc due to the interaction, similar to the processes and correlations found for isolated barred spirals. We furthermore show that the regenerated bars show the same dynamical properties as their isolated counterparts.

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