Alexander G. Pramskij

Strong Emission Line H II Galaxies in the Sloan Digital Sky Survey. I. Catalog of DR1 Objects with Oxygen Abundances from Te Measurements

We present the first edition of the SDSS H II galaxies with Oxygen abundances Catalog (SHOC), which is a listing of strong emission-line galaxies (ELGs) from the Sloan Digital Sky Survey (SDSS). Oxygen abundances have been obtained with the classic Te method. We describe the method exploiting the SDSS database to construct this sample. The selection procedures are described and discussed in detail, as well as some problems encountered in the process of deriving reliable emission line parameters. The method was applied to the SDSS Data Release 1 (DR1). We present 612 SDSS emission-line galaxies (624 separate SDSS targets in total), for which the oxygen abundances 12 + log(O/H) have rms uncertainties ≤0.20 dex. The subsample of 263 ELGs (272 separate SDSS targets) have an uncertainty ≤0.10 dex, while 459 ELGs (470 separate SDSS targets) have an uncertainty ≤0.15 dex. The catalog includes the main parameters of all selected ELGs, the intensities and equivalent widths of hydrogen and oxygen emission lines, as well as oxygen abundances with their uncertainties. The information on the presence of Wolf-Rayet blue and/or red bumps in 109 galaxies is also included. With the use of combined g, r, i SDSS images we performed visual morphological classification of all SHOC galaxies. Four hundred sixty-one galaxies (~75%) are classified as confident or probable blue compact galaxies (BCG/BCG?), 78 as irregular ones, 20 as low surface brightness galaxies (LSBG), 10 as obviously interacting, and 43 as spiral galaxies. In creating the catalog, 30 narrow-line active galactic nuclei and 69 LINERs were also identified; these are also presented apart of the main catalog. We outline briefly the content of the catalog, and the prospects of its use for statistical studies of the star formation and chemical evolution issues. Some of these studies will be presented in the forthcoming paper. Finally, we show that the method presented by Kniazev et al. for calculating O+/H+ using intensities of the [O II] λλ7320, 7330 lines for SDSS emission-line spectra in the absence of [O II] λ3727 line appears to yield reliable results over a wide range of studied oxygen abundances: 7.10 < 12 + log(O/H) < 8.5.

Low Surface Brightness Galaxies in the Sloan Digital Sky Survey. I. Search Method and Test Sample

In this paper we present results of a pilot study to use imaging data from the Sloan Digital Sky Survey (SDSS) to search for low surface brightness (LSB) galaxies. For our pilot study we use a test sample of 92 galaxies from the Impey et al. catalog distributed over 93 SDSS fields of the Early Data Release (EDR). Many galaxies from the test sample are either LSB or dwarf galaxies. To deal with the SDSS data most effectively, a new photometry software was created, which is described in this paper. We present the results of the selection algorithms applied to these 93 EDR fields. Two galaxies from the Impey et al. test sample are very likely artifacts, as confirmed by follow-up imaging. With our algorithms we were able to recover 87 of the 90 remaining test sample galaxies, implying a detection rate of ~96.5%. The three missed galaxies fall too close to very bright stars or galaxies. In addition, 42 new galaxies with parameters similar to the test sample objects were found in these EDR fields (i.e., ~47% additional galaxies). We present the main photometric parameters of all identified galaxies and carry out first statistical comparisons. We tested the quality of our photometry by comparing the magnitudes for our test sample galaxies and other bright galaxies with values from the literature. All these tests yielded consistent results. We briefly discuss a few unusual galaxies found in our pilot study, including an LSB galaxy with a two-component disk and 10 new giant LSB galaxies.

High-quality spectrophotometry of the planetary nebula in the Fornax dSph

We present results of NTT spectroscopy of the one known planetary nebula (PN) in the dwarf spheroidal galaxy Fornax, a gasdeficient Local Group galaxy that stopped its star formation activity a few hundred million years ago. We detected the [O iii] λ4363 line with a signal-to-noise ratio of ∼22. For the first time we detected the weak [S ii] λλ6717,6731 lines (I(6717+6731) ≈ 0.01 I(Hβ)), determined the electron number density (Ne(SII) = 750 cm −3 ), and calculated O, N, Ne, Ar, S, Cl, Fe, He and C abundances. The abundance analysis presented here is based on the direct calculation of the electron temperature Te and yields an oxygen abundance of 12+log(O/H) = 8.28 ± 0.02. The analysis of the O, Ne, Ar and S abundances shows that the original ISM oxygen abundance was 0.27 ± 0.10 dex lower and that third-dredge-up self-pollution in oxygen took place. The blue spectrum shows weak Wolf-Rayet features, and the progenitor star is classified as a weak emission-line star. Four of the five PNe in dwarf spheroidal galaxies are now known to show WR wind features. Overall, the metallicity of the progenitor of the PN fits in well with stellar spectroscopic abundances derived in previous studies as well as with the stellar age-metallicity relation of Fornax.

The Hamburg/SAO Survey for low metallicity blue compact H II galaxies (HSS–LM) - I. The first list of 46 strong-lined galaxies

We present the description and the first resultsof a new project devoted to the search for extremely metal- deficient blue compact/H -galaxies (BCGs) and to the creation of a well selected large BCG sample with strong emission lines. Such galaxies should be suitable for reliable determination of their oxygen abundance through the measurement of the faint (O ) λ4363 A line. The goals of the project are two-fold: a) to discover a significant number of new extremely metal- poor galaxies (Z 1/20 Z� ), and b) to study the metallicity distribution of local BCGs. Selection of candidates for follow-up slit spectroscopy is performed on the database of objective prism spectra of the Hamburg Quasar Survey. The sky region is limited by δ ≥ 0 ◦ and b II ≤− 30 ◦ . In this paper we present the results of the follow-up spectroscopy conducted with the Russian 6m telescope. The list of observed candidates contained 52 objects, of which 46 were confirmed as strong-lined BCGs (EW((O ) λ5007) ≥ 100 A). The remaining five lower excitation ELGs include three BCGs, and two galaxies classified as SBN (Starburst Nucleus) and DANS (Dwarf Amorphous Nucleus Starburst). One object is identified as a quasar with a strong Lyα emission line near λ5000 A (z ∼ 3). We provide a list with coordinates, measured radial velocities, B-magnitudes, equiv- alent widths EW((O ) λ5007) and EW(Hβ) and for the 46 strong-lined BCGs the derived oxygen abundances 12+log(O/H). The abundances range between 7.42 and 8.4 (corresponding to metallicities between 1/30 and 1/3 Z� ). The sample contains four galaxies with Z 1/20 Z� , of which three are new discoveries. This demonstrates the high efficiency of the new project to find extremely metal-deficient galaxies. The radial velocities of the strong-lined ELGs range between 500 and 19000 kms −1 with a median value of ∼6400 kms −1 . The typical B-magnitudes of the galaxies presented are 17. m 0−18. m 0.

The metallicities of UM 151, UM 408 and A 1228+12 revisited

We present the results of new spectrophotometry and heavy element abundance determinations for 3 dwarf galaxies UM 151, UM 408 and A 1228+12 (RMB 132). These galaxies have been claimed in the literature to have very low metallicities, corresponding to log(O=H) + 12 7.65, that are in the metallicity range of some candidate local young galaxies. We present higher S/N data for these three galaxies. UM 151 and UM 408 have sig- nicantly larger metallicities: log(O=H)+12 = 8.5 and 7.93, respectively. For A 1228+12 our new log(O= H) +1 2 = 7.73 is close to that recalculated from earlier data (7.68). Thus, the rederived metallicities allow us to remove these objects from the list of galaxies with Z 1=20 Z.

The Hamburg/SAO survey for emission-line galaxies - VI. The sixth list of 126 galaxies

We present the sixth list with results of the Hamburg/SAO Survey for Emission-Line Galaxies. The final list resulted from follow-up spectroscopy conducted with the 4.5 m MMT telescope in 1996, and with 2.2 m CAHA and 6 m SAO telescopes in 2000 to 2003. The data of this snap-shot spectroscopy survey confirmed 134 emission-line objects out of 182 observed candidates and allowed their quantitative spectral classification and redshift determination. We classify 73 emission-line objects as definite or probable blue compact or H galaxies (BCG), 8 as QSOs, 4 as Seyfert 1 and 2 galaxies. 30 low-excitation objects were classified as definite or probable starburst nuclei (SBN), 3 as dwarf amorphous nuclei starburst galaxies (DANS) and 2 as LINERs. Due to the low signal-to-noise ratio we could not classify 14 ELGs (NON). For another 9 galaxies we did not detect any significant emission lines. For 98 emission-line galaxies, the redshifts and/or line intensities are determined for the first time. For the remaining 28 previously-known ELGs we give either improved data the line intensities or some independent measurements. The detection rate of ELGs is ∼70%. This paper completes the classification of strong-lined ELGs found in the zone of the Hamburg/SAO survey. Together with previously known BCG/H  galaxies in this zone, this sample of ∼500 objects is the largest to date in a well bound region.

Spectroscopy of PNe in Sextans A, Sextans B, NGC 3109 and Fornax

Planetary nebulae (PNe) and HII regions provide a probe of the chemical enrichment and star formation history of a galaxy from intermediate ages to the present day. We present the first results of NTT spectroscopy of HII regions and/or PNe in four nearby dwarf galaxies: Sextans A, Sextans B, NGC 3109, and Fornax. For all PNe and some of the HII regions in these galaxies we have obtained elemental abundances via the classic Te-method based on the detection of the [OIII] 4363 line. The oxygen abundances in three HII regions of Sextans A are all consistent within the individual rms uncertainties. The oxygen abundance in the PN of Sextans A is however significantly higher. This PN is even more enriched in nitrogen and helium, implying its classification as a PN of Type I. The presumably unaffected PN abundances of S and Ar are well below those in the HII regions, indicating a lower metallicity at the epoch of the PN progenitor formation. For two HII regions in Sextans B, the oxygen abundances do not differ within the rms uncertainties. The third one is, however, twice as metal-rich, providing evidence for the inhomogeneity of the current metallicity distribution in Sextans B. For the PN in Sextans B we measured an O/H that is consistent with that of the low-metallicity HII regions. For NGC 3109 our preliminary results indicate that the oxygen abundances of PNe and HII regions are all within a small range of

Search for and study of extremely metal-deficient galaxies

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Spectrophotometry of Sextans A and B: Chemical Abundances of H II Regions and Planetary Nebulae*

0.15 dex. For the PN in Fornax, Ne, Ar and S abundances suggest that the ISM metallicity was

Study of DDO 68: nearest candidate for a young galaxy?

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