Fricke, Klaus J.

[["dc.bibliographiccitation.firstpage","115"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","127"],["dc.bibliographiccitation.volume","429"],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Cairos, L. M."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T08:34:49Z"],["dc.date.available","2018-11-07T08:34:49Z"],["dc.date.issued","2005"],["dc.description.abstract","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 3.6 m telescope. This work enlarges the samples presented in preceding papers of this study (Noeske et al. 2003, A A, 410, 481; Cairos et al. 2003, ApJ, 593, 312) 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."],["dc.identifier.doi","10.1051/0004-6361:20040221"],["dc.identifier.fs","38257"],["dc.identifier.isi","000225732700016"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9859"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/17913"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","E D P Sciences"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep near-infrared studies - II. The sample of northern BCDs"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","222"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","The Astrophysical Journal"],["dc.bibliographiccitation.lastpage","235"],["dc.bibliographiccitation.volume","560"],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Chaffee, F. H."],["dc.contributor.author","Foltz, C. B."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Green, R. F."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Guseva, N. G."],["dc.date.accessioned","2018-11-07T08:32:43Z"],["dc.date.available","2018-11-07T08:32:43Z"],["dc.date.issued","2001"],["dc.description.abstract","Long-slit Keck II,(1) 4 m Kitt Peak,(2) and 4.5 m MMT3 spectrophotometric data are used to investigate the stellar population and the evolutionary status of I Zw 18C, the faint C component of the nearby blue compact dwarf galaxy I Zw 18. Hydrogen H alpha and H beta emission lines are detected in the spectra of I Zw 18C, which implies that ionizing massive stars are present. High signal-to-noise Keck II spectra of different regions in I Zw 18C reveal H gamma, H delta, and higher order hydrogen lines in absorption. Several techniques are used to constrain the age of the stellar population in I Zw 18C. Ages derived from two different methods, one based on the equivalent widths of the H alpha, H beta emission lines and the other on H gamma, H delta absorption lines are consistent with a 15 Myr instantaneous burst model. We find that a small extinction in the range A(V) = 0.20-0.65 mag is needed to fit the observed spectral energy distribution of I Zw 18C with that model. In the case of constant star formation, all observed properties are consistent with stars forming continuously between similar to 10 and less than or similar to 100 Myr ago. We use all available observational constraints for I Zw 18C, including those obtained from Hubble Space Telescope color-magnitude diagrams, to argue that the distance to I Zw 18 should be as high as similar to 15 Mpc. The deep spectra also reveal extended ionized gas emission around I Zw 18. H alpha emission is detected as far as 30\" from it. To a B surface brightness limit of similar to 27 mag arcsec(-2), we find no observational evidence for extended stellar emission in the outermost regions at distances less than or similar to 15\" from I Zw 18."],["dc.identifier.doi","10.1086/322494"],["dc.identifier.isi","000171587300023"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/17405"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Univ Chicago Press"],["dc.relation.issn","0004-637X"],["dc.title","A spectroscopic study of component C and the extended emission around I Zw 18"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","45"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","59"],["dc.bibliographiccitation.volume","457"],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2019-07-09T11:54:53Z"],["dc.date.available","2019-07-09T11:54:53Z"],["dc.date.issued","2006-10-01"],["dc.description.abstract","Aims. Aiming to find new extremely metal-deficient star-forming galaxies we extracted from the Two-Degree Field Galaxy Redshift Survey (2dFGRS) 100 K Data Release 14 emission-line galaxies with relatively strong [O iii] λ4363 emission. Methods. 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. Results. 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."],["dc.identifier.doi","10.1051/0004-6361:20054458"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9875"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60757"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","New southern blue compact dwarf galaxies in the 2dF Galaxy redshift survey"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","75"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","90"],["dc.bibliographiccitation.volume","407"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Green, R. F."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Noeske, K. G."],["dc.date.accessioned","2018-11-07T10:37:06Z"],["dc.date.available","2018-11-07T10:37:06Z"],["dc.date.issued","2003"],["dc.description.abstract","Spectroscopy and V, I CCD photometry of the dwarf irregular galaxy SBS 1129+576 are presented for the first time. The CCD images reveal a chain of compact H II regions within the elongated low-surface-brightness (LSB) component of the galaxy. Star formation takes place mainly in two high-surface-brightness H II regions. The mean (V-I) colour of the LSB component in the surface brightness interval mu(V) between 23 and 26 mag arcsec(-2) is relatively blue similar to0.56 +/- 0.03 mag, as compared to the (V-I) similar to 0.9-1.0 for the majority of known dwarf irregular and blue compact dwarf (BCD) galaxies. Spectroscopy shows that the galaxy is among the most metal-deficient galaxies with an oxygen abundance 12 + log (O/H) = 7.36 +/- 0.10 in the brightest H II region and 7.48 +/- 0.12 in the second brightest H II region, or 1/36 and 1/28 of the solar value(star), respectively. Hbeta and Halpha emission lines and Hdelta and Hgamma absorption lines are detected in a large part of the LSB component. We use two extinction-insensitive methods based on the equivalent widths of (1) emission and (2) absorption Balmer lines to put constraints on the age of the stellar populations in the galaxy. In addition, we use two extinction-dependent methods based on (3) the spectral energy distribution (SED) and (4) the (V-I) colour. Several scenarios of star formation were explored using all 4 methods. The observed properties of the LSB component can be reproduced by a stellar population forming continuously since 10 Gyr ago, provided that the star formation rate has increased during the last 100 Myr by a factor of 6 to 50 and no extinction is present. However, the observational properties of the LSB component in SBS 1129+576 can be reproduced equally well by continuous star formation which started not earlier than 100 Myr ago and stopped at 5 Myr, if some extinction is assumed. Hence, the ground-based spectroscopic and photometric observations are not sufficient for distinguishing between a young and an old age for SBS 1129+576."],["dc.identifier.doi","10.1051/0004-6361:20030806"],["dc.identifier.isi","000184435000013"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9799"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/45481"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies - I. SBS 1129+576"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","885"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","893"],["dc.bibliographiccitation.volume","464"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2019-07-09T11:54:59Z"],["dc.date.available","2019-07-09T11:54:59Z"],["dc.date.issued","2007-03-04"],["dc.description.abstract","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, ApJ, 644, 890) we focus here on 3.6 m 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 ( $Z_{\\odot}/60 \\la Z \\la Z_{\\odot}/3$) and, combined with the sample of 47 H II regions from Guseva et al. (2006), yields the largest spectroscopic data set ever used to derive the electron temperature in the H+ zone. Methods.In the same way as in Guseva et al. (2006) we have used a Monte Carlo technique to vary free parameters and to calculate a series of model spectral energy distributions (SEDs) for each H II region. The electron temperature in the H+ zones was derived from the best fitting synthetic and observed SEDs in the wavelength range ~3200-5100 Å, which includes the Balmer jump. Results.On the base of the present large spectroscopic sample we find that in hot ($T_{\\rm e}$(H+) $\\ga$ 11 000 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 $T_{\\rm e}$(H+) and $T_{\\rm e}$(O III)."],["dc.identifier.doi","10.1051/0004-6361:20066067"],["dc.identifier.fs","297790"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9939"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60774"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.access","openAccess"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.title","Balmer jump temperature determination in a large sample of low-metallicity HII regions"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","91"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","104"],["dc.bibliographiccitation.volume","407"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Green, R. F."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Noeske, K. G."],["dc.date.accessioned","2018-11-07T10:37:06Z"],["dc.date.available","2018-11-07T10:37:06Z"],["dc.date.issued","2003"],["dc.description.abstract","We present broad-band V and I imaging and long-slit spectroscopy in the optical range lambdalambda3600-7500 Angstrom of the dwarf irregular galaxy HS 1442+4250. The oxygen abundance 12 + log (O/H) = 7.63 +/- 0.02 (Z = Z(circle dot)19)(star) in the brightest H II region of HS 1442+4250 places the galaxy among the most metal-deficient emission-line galaxies. The low metallicity and blue colour (V-I) similar to0.4 mag of the low-surface-brightness (LSB) component make HS 1442+4250 a likely rare young dwarf galaxy candidate. We use four methods to estimate the stellar population age in the LSB component of HS 1442+4250. Different star formation histories are considered. The equivalent widths of hydrogen Halpha and Hbeta emission lines, and of hydrogen Hgamma and Hdelta absorption lines, the spectral energy distribution and the observed (V-I) colours of the LSB regions are reproduced quite well by models with only young and intermediate-age stellar populations. By contrast, the observational data cannot be reproduced by a stellar population formed continuously with a constant star formation rate in the age range from 0 to greater than or equal to 2 Gyr. While a faint old stellar population in HS 1442+4250 with an age greater than or equal to2 Gyr is not excluded, we find no evidence for such a population from the present data."],["dc.identifier.doi","10.1051/0004-6361:20030807"],["dc.identifier.isi","000184435000014"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9800"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/45483"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies - II. HS 1442+4250"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A149"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","529"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Stasinska, G."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Henkel, Cornelia"],["dc.contributor.author","Papaderos, P."],["dc.date.accessioned","2018-11-07T08:56:17Z"],["dc.date.available","2018-11-07T08:56:17Z"],["dc.date.issued","2011"],["dc.description.abstract","Context. We present deep spectroscopy of a large sample of low-metallicity emission-line galaxies. Aims. The main goal of this study is to derive element abundances in these low-metallicity galaxies. Methods. We analyze 121 VLT spectra of H II regions in 46 low-metallicity emission-line galaxies. Of these spectra 83 are archival VLT/FORS1 + UVES spectra of H II regions in 31 low-metallicity emission-line galaxies that are studied for the first time with standard direct methods to determine the electron temperatures, the electron number densities, and the chemical abundances. Results. The oxygen abundance of the sample lies in the range 12 + log O/H = 7.2-8.4. We confirm previous findings that Ne/O increases with increasing oxygen abundance, likely because of a higher depletion of oxygen in higher-metallicity galaxies. The Fe/O ratio decreases from roughly solar at the lowest metallicities to about one tenth of solar, indicating that the degree of depletion of iron into dust grains depends on metallicity. The N/O ratio in extremely low-metallicity galaxies with 12 + log O/H < 7.5 shows a slight increase with decreasing oxygen abundance, which could be the signature of enhanced production of primary nitrogen by rapidly rotating stars at low metallicity. We present the first empirical relation between the electron temperature derived from [S III]lambda 6312/lambda 9069 or [N II]lambda 5755/lambda 6583 and the one derived from [O III]lambda 4363/lambda(4959 + 5007) in low-metallicity galaxies. We also present an empirical relation between t(e) derived from [O II]lambda 3727/(lambda 7320 + lambda 7330) or [S II]lambda 4068/(lambda 6717 + lambda 6730) and [O III]lambda 4363/lambda(4959 + 5007). The electron number densities N-e(Cl III) and N-e(Ar IV) were derived in a number of objects and are found to be higher than N-e(O II) and N-e(S II). This has potential implications for the derivation of the pregalactic helium abundance. In a number of objects, the abundances of C++ and O++ could be derived from recombination lines. Our study confirms the discrepancy between abundances found from recombination lines (RLs) and collisionally excited lines (CELs) and that C/O increases with O/H."],["dc.identifier.doi","10.1051/0004-6361/201016291"],["dc.identifier.fs","590499"],["dc.identifier.isi","000294240700024"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/8604"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/23104"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","VLT spectroscopy of low-metallicity emission-line galaxies: abundance patterns and abundance discrepancies"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","519"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","528"],["dc.bibliographiccitation.volume","421"],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T10:47:20Z"],["dc.date.available","2018-11-07T10:47:20Z"],["dc.date.issued","2004"],["dc.description.abstract","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 less than or similar to3\" (5270 pc in linear scale) is mainly gaseous in origin. We detect Ha emission out to radii as large as 6\". At radii greater than or similar to3\" 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 less than or similar to 120 pc. This places Pox 186 among the most compact dwarf galaxies known. The derived a 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 H II region derived from the 4.5 m Multiple Mirror Telescope (MMT) and 3.6 m ESO telescope spectra are 12 + log (O/H) = 7.76 +/- 0.02 and 7.74 +/- 0.01 (-Z(circle dot)/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 (3.6 m) suggesting a high primordial helium abundance."],["dc.identifier.doi","10.1051/0004-6361:20035949"],["dc.identifier.fs","21429"],["dc.identifier.isi","000222897700017"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9820"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/47940"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","E D P Sciences"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Pox 186: An ultracompact galaxy with dominant ionized gas emission"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","169"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","The Astronomical Journal"],["dc.bibliographiccitation.lastpage","181"],["dc.bibliographiccitation.volume","121"],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Thuan, T. X."],["dc.date.accessioned","2018-11-07T09:29:17Z"],["dc.date.available","2018-11-07T09:29:17Z"],["dc.date.issued","2001"],["dc.description.abstract","We present a spectrophotometric study based on VLT/FORS I observations of one of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol 1214-277 (Z similar to Z(.)/25). The data show that roughly half of the total luminosity of the BCD originates from a bright and compact starburst region located at the northeastern tip of a faint dwarf galaxy with cometary appearance. The starburst has ignited less than 4 Myr ago and its emission is powered by several thousand O7V stars and similar to 170 late-type nitrogen Wolf-Rayet stars located within a compact region with less than or similar to 500 pc in diameter. For the first time in a BCD, a relatively strong [Fe V] lambda 4227 emission line is seen which together with intense He II lambda 4686 emission indicates the presence of a very hard radiation field in Tol 1214-277. We argue that this extraordinarily hard radiation originates from both Wolf-Rayet stars and radiative shocks in the starburst region. The structural properties of the low surface brightness (LSB) component underlying the starburst have been investigated by means of surface photometry down to 28 B mag arcsec(-2). We find that, for a surface brightness level fainter than similar to 24.5 B mag arcsec(-2), an exponential fitting law provides an adequate approximation to its radial intensity distribution. The broadband colors in the outskirts of the LSB component of Tol 1214-277 are nearly constant and are consistent with an age below one Gyr. This conclusion is supported by the comparison of the observed spectral energy distribution (SED) of the LSB host with theoretical SEDs."],["dc.identifier.doi","10.1086/318016"],["dc.identifier.isi","000166173300013"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30987"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Univ Chicago Press"],["dc.relation.issn","0004-6256"],["dc.title","An imaging and spectroscopic study of the very metal-deficient blue compact dwarf galaxy Tol 1214-277"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","113"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","129"],["dc.bibliographiccitation.volume","491"],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T11:09:17Z"],["dc.date.available","2018-11-07T11:09:17Z"],["dc.date.issued","2008"],["dc.description.abstract","Context. Extremely metal-deficient [12 + log(O/H) less than or similar to 7.6] emission-line galaxies in the nearby universe are invaluable laboratories of extragalactic astronomy and observational cosmology since they allow us to study collective star formation and the evolution of galaxies under chemical conditions approaching those in distant protogalactic systems. However, despite intensive searches over the last three decades, nearby star-forming (SF) galaxies with strongly subsolar metallicity remain extremely scarce. Aims. We searched the Sloan Digital Sky Survey (SDSS) and the Six-Degree Field Galaxy Redshift Survey (6dFGRS) for promising low-metallicity candidates using a variety of spectroscopic criteria. Methods. We present long-slit spectroscopy with the 3.6 m ESO telescope of eight HII regions in seven emission-line dwarf galaxies, selected from the Data Release 4 of SDSS ( six galaxies) and from 6dFGRS ( one galaxy). In addition, we use SDSS imaging data to investigate the photometric structure of the sample galaxies. Results. From the 3.6 m telescope spectra, we determine the oxygen abundance of these systems to be 7.3 less than or similar to 12 + log(O/H) less than or similar to 7.6, placing them among the most metal-poor star-forming galaxies ever discovered. Our photometric analysis reveals a moderately blue, stellar host galaxy in all sample galaxies. Conclusions. 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 similar to 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."],["dc.identifier.doi","10.1051/0004-6361:200810028"],["dc.identifier.isi","000260559700010"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9950"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/52973"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Extremely metal-poor star-forming galaxies New detections and general morphological and photometric properties"],["dc.type","review"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]