Fricke, Klaus J.

[["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","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","L27"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","L30"],["dc.bibliographiccitation.volume","415"],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T10:51:16Z"],["dc.date.available","2018-11-07T10:51:16Z"],["dc.date.issued","2004"],["dc.description.abstract","The discovery of the high-ionization [Ne V] lambda3426 Angstrom 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 L-x in the range 10(39)-10(40) erg s(-1), 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] lambda3426 Angstrom emission line."],["dc.identifier.doi","10.1051/0004-6361:20040006"],["dc.identifier.isi","000188936100005"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/48851"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","E D P Sciences"],["dc.relation.issn","0004-6361"],["dc.title","Discovery of the high-ionization emission line [Ne V] lambda 3426 in the 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","901"],["dc.bibliographiccitation.issue","2-4"],["dc.bibliographiccitation.journal","Astrophysics and Space Science"],["dc.bibliographiccitation.lastpage","908"],["dc.bibliographiccitation.volume","276"],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Cairos, L. M."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Vilchez, J. M."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T09:29:49Z"],["dc.date.available","2018-11-07T09:29:49Z"],["dc.date.issued","2001"],["dc.description.abstract","We are currently analysing image data for a large sample of blue compact dwarf galaxies (BCDs), obtained in multiple optical broad- and narrow-band filters. We present preliminary results of a multi-band analysis of two typical BCDs, Mrk 5 and I Zw 123, for which surface-brightness profiles, colour profiles, colour maps and H-alpha equivalent-width maps have been derived. We demonstrate how a combination of these different processing methods allows a separate analysis of the young and old stellar populations with respect to their colours and spatial distributions. By comparing the derived colours with the predictions of evolutionary synthesis models, we estimate ages of the distinct stellar populations. The surface-brightness profiles of Mrk 5 show an exponential decay at large photometric radii, with slopes typically found for BCDs. In the case of the very compact object I Zw 123, the surface-brightness profile of the underlying stellar component can be described either by an exponential or an R-1/4 law. We discuss briefly how noise effects can influence the intrinsic slope of surface brightness profiles at low surface-brightness levels. For compact objects with extended starbursts, the study of the underlying stellar population can thereby be rendered difficult."],["dc.identifier.doi","10.1023/A:1017529324764"],["dc.identifier.isi","000170945400070"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31141"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Kluwer Academic Publ"],["dc.publisher.place","Dordrecht"],["dc.relation.conference","Euroconference on the Evolution of Galaxies on Cosmological Timescales"],["dc.relation.eventlocation","PUERTO CRUZ, SPAIN"],["dc.relation.issn","0004-640X"],["dc.title","Optical multi-band analyses of blue compact dwarf galaxies"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","33"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","52"],["dc.bibliographiccitation.volume","361"],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Fricke, K. J."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Thuan, T. X."],["dc.date.accessioned","2018-11-07T10:26:08Z"],["dc.date.available","2018-11-07T10:26:08Z"],["dc.date.issued","2000"],["dc.description.abstract","\"Cometary\" Blue Compact Dwarf Galaxies (iI,C BCDs) are characterized by an off-center starburst close to the end of their elongated stellar bodies. This rare phenomenon may carry some clues on how collective star formation ignites and propagates in gas-rich low-mass stellar systems. This off-center burst may be a fortuitous enhancement of the otherwise moderate star-forming activity of a dwarf irregular (dI), or may be caused by a set of special properties of such systems or their environment. We attempt here a first investigation of this issue by analysing two prototypical examples of cometary dwarf galaxies, the nearby II,C BCDs Markarian 59 and Markarian 71, both containing an extraordinarily luminous HII region in the outskirts of a dI-like host. Using deep ground-based spectrophotometric data(1,2) and HST images(3), we study the physical state of the starburst regions and the structural properties of the underlying irregular galaxies. We find that the average metallicities show small scatter in the vicinity of the star-forming regions and along the major axis of Mkn 59 which suggests that mixing of heavy elements must have been efficient on scales of several kpc. The azimuthally averaged radial intensity distributions of the underlying host galaxies in either iI,C BCD can be approximated by an exponential law with a central surface brightness and scale length that is intermediate between typical iE/nE BCDs and dwarf irregulars. Spectral population synthesis models in combination with colour magnitude diagrams and colour profiles yield a most probable formation age of similar to 2 Gyr for the low surface brightness (LSB) host galaxies in both LI,C BCDs, with upper age limits of similar to 4 Gyr for Mkn 59 and similar to 3 Gyr for Mkn 71, i.e. significantly lower than the typical age of several Gyr derived for the LSB component of iE/nE BCDs. These findings raise the question whether iI,C systems form a distinct physical class within BCDs with respect to the age and structural properties of their hosts, or whether they represent an evolutionary stage connecting young i0 BCDs and \"classical\" iE/nE BCDs. In spite of the scarcity of available data, a review of the properties of analogous objects studied in the local universe and at medium redshifts provides some support for this evolutionary hypothesis."],["dc.identifier.isi","000089510600010"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/42976"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.title","The cometary blue compact dwarf galaxies Mkn 59 and Mkn 71 - A clue to dwarf galaxy evolution?"],["dc.type","review"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","619"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astrophysics and Space Science"],["dc.bibliographiccitation.lastpage","622"],["dc.bibliographiccitation.volume","284"],["dc.contributor.author","Papaderos, P."],["dc.contributor.author","Izotov, Y. I."],["dc.contributor.author","Noeske, K. G."],["dc.contributor.author","Cairos, L. M."],["dc.contributor.author","Guseva, N. G."],["dc.contributor.author","Thuan, T. X."],["dc.contributor.author","Fricke, K. J."],["dc.date.accessioned","2018-11-07T10:42:02Z"],["dc.date.available","2018-11-07T10:42:02Z"],["dc.date.issued","2003"],["dc.description.abstract","Using HST and ground-based optical and NIR imaging data, we investigate whether the blue compact dwarf (BCD) galaxy I Zw 18 possesses an extended low-surface brightness (LSB) old stellar population underlying its star-forming (SF) regions. We show that the exponential intensity decrease observed in the filamentary LSB envelope of the BCD out to 18\" (1.3 kpc at the adopted distance of 15 Mpc) is not due to an evolved stellar disc, but rather due to extended ionized gas emission. Broad-band images reveal, after subtraction of nebular line emission, a compact stellar LSB component extending slightly beyond the SF regions. This stellar host, being blue over a radius range of 5 exponential scale lengths and showing little colour contrast to the SF component, differs strikingly from the red LSB host of standard BCDs. This fact, in connection with the blue colours of component I Zw 18 C (see discussion in Papaderos et al. 2002), suggests that most of the stellar mass in I Zw 18 has formed within the last 0.5 Gyr. Furthermore, we show that the exponential intensity fall-off in the filamentary ionized envelope of I Zw 18 is not particular to this system but a common property of the ionized halo of many SF dwarf galaxies on galactocentric distances of several kpc. In the absence of an appreciable underlying stellar background, extended ionized gas emission dominates in the periphery of I Zw 18, superficially resembling an exponential stellar disc on optical surface brightness profiles. The case of I Zw 18 suggests caution in the search of more distant young galaxy candidates. Intense SF activity in the early phase of dwarf galaxy formation may result in an extended ionized gas halo which can be mistaken for an evolved stellar disc by studying only its exponential surface brightness profile."],["dc.identifier.doi","10.1023/A:1024022409637"],["dc.identifier.isi","000183320500064"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/46688"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Kluwer Academic Publ"],["dc.publisher.place","Dordrecht"],["dc.relation.conference","Conference on the Appropriate Modellings of Galaxy Evolution from their Cosmological Formation to their Presently Observable Structures"],["dc.relation.eventlocation","KIEL, GERMANY"],["dc.relation.issn","0004-640X"],["dc.title","Photometric studies of very metal-deficient blue compact dwarf galaxies: The exponential ionized gas halo of I Zw 18"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]