Spectroscopic and photometric studies of low-metallicity star-forming dwarf galaxies - III. SBS 1415+437

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 μ v between 23 and 26 mag arcsec - 2 is relatively blue ∼0.56 ′ 0.03 mag, as compared to the (V - I) ∼ 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 ½8 of the solar value*, respectively. Hβ and Hα emission lines and Hδ and Hγ 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 - l) 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.

[1]  S. Yi.  Uncertainties of Synthetic Integrated Colors as Age Indicators , 2002, astro-ph/0210202.

[2]  Kyiv,et al.  The emission line sequence of H II galaxies , 2002, astro-ph/0301442.

[3]  P. Papaderos,et al.  The blue compact dwarf galaxy I Zw 18: A comparative study of its low-surface-brightness component , 2002, astro-ph/0207314.

[4]  T. Thuan,et al.  Hubble Space Telescope Observations of the Cometary Blue Compact Dwarf Galaxy UGC 4483: A Relatively Young Galaxy? , 2001, astro-ph/0111307.

[5]  U. Hopp,et al.  The Star Formation History of the Blue Compact Dwarf Galaxy UGCA 290 , 2001, astro-ph/0111248.

[6]  Kyiv,et al.  The evolutionary status of the low-metallicity blue compact dwarf galaxy SBS 0940+544. , 2001, astro-ph/0109256.

[7]  Kyiv,et al.  A Spectroscopic Study of Component C and the Extended Emission around I Zw 18 , 2001, astro-ph/0109257.

[8]  R. Green,et al.  The 4He Abundance in the Metal-deficient Blue Compact Dwarf Galaxies Tol 1214–277 and Tol 65 , 2001, astro-ph/0109255.

[9]  U. Hopp,et al.  The Stellar Content of NGC 6789, A Blue Compact Dwarf Galaxy in the Local Void , 2001, astro-ph/0102452.

[10]  L. Pilyugin.  On the oxygen abundance determination in HII regions. - High-metallicity regions , 2001, astro-ph/0101446.

[11]  P. Papaderos,et al.  An Imaging and Spectroscopic Study of the Very Metal-deficient Blue Compact Dwarf Galaxy Tol 1214−277 , 2000, astro-ph/0011227.

[12]  E. Bica,et al.  Spectral analysis of the nuclear stellar population and gas emission in six nearby galaxies , 2001 .

[13]  V. Chavushyan,et al.  Accurate optical positions for 2978 objects from the Second Byurakan Survey (SBS) with the Digitized Sky Survey , 2000 .

[14]  L. V. Zee,et al.  The Evolutionary Status of Isolated Dwarf Irregular Galaxies. I. UBV and Hα Imaging Observations , 2000 .

[15]  U. Hopp,et al.  Surface photometry of emission-line galaxies in low density regions , 2000 .

[16]  T. Thuan,et al.  A Spectroscopic Study of a Large Sample Of Wolf-Rayet Galaxies , 1999, astro-ph/9910432.

[17]  U. Hopp,et al.  A spectrophotometric catalogue of HII galaxies , 1999, astro-ph/9912490.

[18]  C. Foltz,et al.  The Young Age of the Extremely Metal-deficient Blue Compact Dwarf Galaxy SBS 1415+437 , 1999 .

[19]  L. Makarova.  Multi-colour photometry of nearby dwarf galaxies , 1999 .

[20]  V. Lipovetsky,et al.  HI observations of blue compact galaxies from the first and second Byurakan surveys , 1999 .

[21]  Tucson,et al.  Helium Abundance in the Most Metal-deficient Blue Compact Galaxies: I Zw 18 and SBS 0335–052 , 1999, astro-ph/9907228.

[22]  C. Leitherer,et al.  Synthetic Spectra of H Balmer and He I Absorption Lines. II. Evolutionary Synthesis Models for Starburst and Poststarburst Galaxies , 1999, astro-ph/9907116.

[23]  H. Hagen,et al.  The Hamburg/SAO survey for emission–line galaxies - II. The second list of 128 galaxies , 1999 .

[24]  T. Thuan,et al.  Heavy-Element Abundances in Blue Compact Galaxies , 1998, astro-ph/9811387.

[25]  C. Esteban,et al.  Faint Emission Lines and Temperature Fluctuations in M8 , 1998 .

[26]  H. Kobulnicky,et al.  On Measuring Nebular Chemical Abundances in Distant Galaxies Using Global Emission-Line Spectra , 1998, astro-ph/9811006.

[27]  G. Ferland,et al.  CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra , 1998 .

[28]  D. Schlegel,et al.  Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds , 1998 .

[29]  T. Thuan,et al.  The Primordial Abundance of 4He Revisited , 1998 .

[30]  C. Esteban,et al.  Chemical composition of the Orion nebula derived from echelle spectrophotometry , 1998 .

[31]  William D. Vacca,et al.  New Models for Wolf-Rayet and O Star Populations in Young Starbursts , 1997, astro-ph/9711140.

[32]  France.,et al.  A standard stellar library for evolutionary synthesis - II. The M dwarf extension , 1997, astro-ph/9710350.

[33]  U. Hopp,et al.  “Baade's Red Sheet” Resolved into Stars with Hubble Space Telescope in the Blue Compact Dwarf Galaxy VII Zw 403 , 1997, astro-ph/9708240.

[34]  D. Schlegel,et al.  Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds , 1997, astro-ph/9710327.

[35]  R. Gruenwald,et al.  Spectroscopy of Seyfert 2 Galaxies, Liners, and H(II) Galaxies. , 1997 .

[36]  Frederic H. Chaffee,et al.  SBS 0335–052, A Probable Nearby Young Dwarf Galaxy: Evidence Pro and Con , 1997 .

[37]  R. Terlevich,et al.  The VRI colours of H ii galaxies , 1996, astro-ph/9610136.

[38]  V. Lipovetsky,et al.  The Primordial Helium Abundance: Systematic Effects and a New Determination , 1997 .

[39]  P. Papaderos,et al.  Optical structure and star formation in blue compact dwarf galaxies. I. Observations and profile decomposition , 1996 .

[40]  R. Patterson,et al.  Surface Photometry of Low Surface Brightness Dwarf Irregular Galaxies: Erratum , 1996 .

[41]  E. Skillman,et al.  Elemental Abundance Variations and Chemical Enrichment from Massive Stars in Starbursts. II. NGC 1569 , 1996, astro-ph/9706235.

[42]  U. Hopp,et al.  Surface photometry of galaxies in low density regions , 1996 .

[43]  V. Lipovetsky,et al.  Hubble Space Telescope Observations of the Unusual Blue Compact Dwarf Galaxy Markarian 996 , 1996 .

[44]  William D. Vacca,et al.  The Lyman-Continuum Fluxes and Stellar Parameters of O and Early B-Type Stars , 1996 .

[45]  V. Lipovetsky,et al.  Heavy element abundances in a new sample of low-metallicity blue compact galaxies , 1995 .

[46]  D. Alloin,et al.  Simulations of starburst spectral evolution superimposed on old populations: extension to dwarf ellipticals , 1995 .

[47]  V. Lipovetsky,et al.  The Primordial helium abundance from a new sample of metal-deficient blue compact galaxies , 1994 .

[48]  D. Geisler,et al.  A morphological and color study of Fornax low surface brightness galaxies in the Washington system , 1994 .

[49]  A. Kinney,et al.  Ultraviolet to near-infrared spectral distributions of star-forming galaxies: Metallicity and age effects , 1994 .

[50]  N. Caon,et al.  On the shape of the light profiles of Early Type galaxies , 1993, astro-ph/9309013.

[51]  Arlo U. Landolt,et al.  UBVRI Photometric Standard Stars in the Magnitude Range 11 , 1992 .

[52]  D. Garnett.  Electron temperature variations and the measurement of nebular abundances , 1992 .

[53]  A. Schmidt,et al.  On the meaning of a minimization procedure applied to a degenerate astrophysical problem , 1989 .

[54]  N. Grevesse,et al.  Abundances of the elements: Meteoritic and solar , 1989 .

[55]  R. Kirshner,et al.  A Spectroscopic Survey of Case Emission-Line Galaxies in the Direction of the Bootes Void , 1986 .

[56]  D. Hayes,et al.  VIDEO CAMERA /CCD STANDARD STARS (KPNO VIDEO CAMERA/CCD STANDARDS CONSORTIUM) , 1985 .

[57]  Lawrence H. Aller,et al.  Physics of thermal gaseous nebulae , 1984 .

[58]  Gary J. Ferland,et al.  Hazy, A Brief Introduction to Cloudy 96 , 1983 .

[59]  N. Sanduleak,et al.  Emission-line galaxies in the direction of the proposed void in Bootes , 1982 .

[60]  M. Seaton,et al.  Interstellar extinction in the UV , 1979 .

[61]  M. Brocklehurst,et al.  Calculations of Level Populations for the Low Levels of Hydrogenic Ions in Gaseous Nebulae , 1971 .

[62]  Jose Luis. Sersic,et al.  Atlas de Galaxias Australes , 1968 .