Alexei Yu. Kniazev

A Curious Milky Way Satellite in Ursa Major

In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. Its color-magnitude diagram (CMD) shows a well-defined subgiant branch, main sequence, and turnoff, from which we estimate a distance of ~30 kpc and a projected size of ~250 × 125 pc2. The CMD suggests a composite population with some range in metallicity and/or age. Based on its extent and stellar population, we argue that this is a previously unknown satellite galaxy of the Milky Way, hereby named Ursa Major II (UMa II) after its constellation. Using SDSS data, we find an absolute magnitude of MV ~ -3.8, which would make it the faintest known satellite galaxy. UMa IIs isophotes are irregular and distorted with evidence for multiple concentrations; this suggests that the satellite is in the process of disruption.

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.

SBS 0335–052, A Probable Nearby Young Dwarf Galaxy: Evidence Pro and Con*

The results of Multiple Mirror Telescope spectrophotometry of the extremely low-metallicity blue compact galaxy (BCG) SBS 0335-052 are presented. The oxygen abundance in central brightest part of the galaxy is found to be 12 + log(O/H) = 7.33+-0.01. The N/O, Ne/O, S/O and Ar/O abundance ratios are close to those derived in other BCGs, suggesting that heavy element enrichment in the HII region is due to massive star evolution. We detect auroral [OIII] 4363 emission in the inner part of HII region with a diameter of 3.6 kpc and find that the HII region inside this diameter is hot, T_e~20000K. The oxygen abundance in this region is nearly constant (12 + log(O/H) = 7.1 - 7.3), implying effective mixing of ionized gas on short time-scales. We also discuss the origin of blue underlying extended low-intensity emission detected in SBS 0335-052. The (V-I) and (R-I) color distributions suggest that a significant contribution to the extended envelope is due to ionized gas emission. However, the observed equivalent width of Hbeta emission in the extended envelope is 2-3 times lower than the value expected in the case of pure gaseous emission. These findings suggest that, along with the blue young (~10^7yr) stellar clusters, an older stellar population with age ~10^8yr may be present in the extended envelope of SBS 0335-052, having a total mass conclude that SBS 0335-052 is a young nearby dwarf galaxy with age ~10^8 yr.

Andromeda IX: A New Dwarf Spheroidal Satellite of M31

We report the discovery of a new dwarf spheroidal satellite of M31, Andromeda IX, based on resolved stellar photometry from the Sloan Digital Sky Survey (SDSS). Using both SDSS and public archival data, we have estimated its distance and other physical properties, and compared these to the properties of a previously known dwarf spheroidal companion, Andromeda V, also observed by SDSS. Andromeda IX is the lowest surface brightness galaxy found to date (μV, 0 ~ 26.8 mag arcsec-2), and at the distance we estimate from the position of the tip of Andromeda IXs red giant branch, (m - M)0 ~ 24.5 (805 kpc), Andromeda IX would also be the faintest galaxy known (MV ~ -8.3).

Andromeda X, a New Dwarf Spheroidal Satellite of M31: Photometry

We report the discovery of Andromeda X, a new dwarf spheroidal satellite of M31, based on stellar photometry from the Sloan Digital Sky Survey. Using follow-up imaging data we have estimated its distance and other physical properties. We find that Andromeda X has a dereddened central surface brightness of μV, 0 ~ 26.7 mag arcsec-2 and a total apparent magnitude of Vtot ~ 16.1, which at the derived distance modulus, (m - M)0 ~ 24.12-24.34, yields an absolute magnitude of MV ~ -8.1 ± 0.5; these values are quite comparable to those of Andromeda IX, a previously discovered low-luminosity M31 satellite. The discoveries of Andromeda X and of numerous other extremely faint satellites around M31 and the Milky Way in the past few years suggest that such objects may be plentiful in the Local Group.

DISCOVERY OF EIGHT NEW EXTREMELY METAL-POOR GALAXIES IN THE SLOAN DIGITAL SKY SURVEY

We report the discovery of eight new extremely metal-poor galaxies [XMPGs; ] and the 12 log (O/H) ! 7.65 recovery of four previously known or suspected XMPGs (I Zw 18, HS 08223542, HS 08374717, and A1116517) using Sloan Digital Sky Survey (SDSS) spectroscopy. These new objects were identified after an analysis of 250,000 galaxy spectra within an area of ∼3000 deg 2 on the sky. Our oxygen abundance determinations have an accuracy of ≤0.1 dex and are based on the temperature-sensitive [O iii] l4363 line and on the direct calculation of the electron temperature. We briefly discuss a new method of oxygen abundance determinations using the [O ii] ll7319, 7330 lines that is particularly useful for SDSS emission-line spectra with redshifts ≤0.024 since the [O ii] l3727 emission line falls outside of the SDSS wavelength range. We detect XMPGs with redshifts ranging from 0.0005 to 0.0443 and luminosities from 12.4 to 18.6 mag. Our eight new Mg XMPGs increase the number of known metal-deficient galaxies by approximately one-quarter. The estimated surface density of XMPGs is 0.004 deg for mag. 2 r ≤ 17.77 Subject headings: galaxies: abundances — galaxies: dwarf — galaxies: evolution

The metallicity extremes of the Sagittarius dSph: SALT spectroscopy of PNe

In this work we present the first spectroscopic results obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. We find that the Sagittarius dwarf spheroidal galaxy (Sgr) contains a youngest stellar population with [O/H] ≈ -0.2 and age t > 1 Gyr, and an oldest population with [O/H] = -2.0. The values are based on spectra of two planetary nebulae (PNe), using empirical abundance determinations. We calculated abundances for O, N, Ne, Ar, S, Cl, Fe, C and He. We confirm the high abundances of PN StWr2-21 with 12 + log(O/H) = 8.57 ± 0.02 dex. The other PN studied, BoBn 1, is an extraordinary object in that the neon abundance exceeds that of oxygen. The abundances of S, Ar and Cl in BoBn 1 yield the original stellar metallicity, corresponding to 12 + log(O/H) = 6.72 ± 0.16 dex which is 1/110 of the solar value. The actual [O/H] is much higher: third dredge-up enriched the material by a factor of ∼12 in oxygen, ∼240 in nitrogen and ∼70 in neon. Neon as well as nitrogen and oxygen content may have been produced in the intershell of low-mass asymptotic giant branch (AGB) stars. Well defined broad WR lines are present in the spectrum of StWr2-21 and absent in the spectrum of BoBn 1. This puts the fraction of [WR]-type central PNe stars to 67 per cent for dSph galaxies.

MULTI-WAVELENGTH OBSERVATIONS OF SUPERNOVA 2011ei: TIME-DEPENDENT CLASSIFICATION OF TYPE IIb AND Ib SUPERNOVAE AND IMPLICATIONS FOR THEIR PROGENITORS

We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least luminous SNe IIb or Ib observed to date. Our observations begin with a discovery within � 1 day of explosion and span several months afterward. Early optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that subside rapidly and are replaced by Type Ib-like He-rich features on the timescale of one week. High-cadence monitoring of this transition suggests that absorption attributable to a high velocity (& 12,000 km s −1 ) H-rich shell is not rare in Type Ib events. Radio observations imply a shock velocity of v � 0.13c and a progenitor star mass-loss rate of u M � 1.4 × 10 −5 M⊙ yr −1 (assuming wind velocity vw = 10 3 km s −1 ). This is consistent with independent constraints from deep X-ray observations with Swift-XRT and Chandra. Overall, the multi-wavelength properties of SN2011ei are consistent with the explosion of a lower-mass (3 4 M⊙), compact (R∗ . 1 × 10 11 cm), He core star. The star retained a thin hydrogen envelope at the time of explosion, and was embedded in an inhomogeneous circumstellar wind suggestive of modest episodic mass-loss. We conclude that SN2011ei’s rapid spectral metamorphosis is indicative of time-dependent classifications that bias estimates of explosion rates for Type IIb and Ib objects, and that important information about a progenitor star’s evolutionary state and mass-loss immediately prior to SN explosion can be inferred from timely multi-wavelength observations. Subject headings: supernovae: general — supernova: individual (SN2011ei)

The KPNO International Spectroscopic Survey. I. Description of the Survey

The KPNO International Spectroscopic Survey (KISS) is a new objective-prism survey for extragalactic emission-line objects. It combines many of the features of previous slitless spectroscopic surveys that were carried out with Schmidt telescopes using photographic plates with the advantages of modern CCD detectors. It is the first purely digital objective-prism survey, and extends previous photographic surveys to substantially fainter flux limits. In this, the first paper in the series, we give an overview of the survey technique, describe our data processing procedures, and present examples of the types of objects found by KISS. Our first H�-selected survey list detects objects at the rate of 18.1 per square degree, which is 181 times higher than the surface density of the Markarian survey. Since the sample is line-selected, there is an imposed redshift limit of z < � 0.095 due to the filter employed for the objective-prism observations. We evaluate the quality of the observed parameters derived from the survey data, which include accurate astrometry, photometry, redshifts, and line fluxes. Finally, we describe some of the many applications the KISS database will have for addressing specific questions in extragalactic astronomy. Subsequent papers in this series will present our survey lists of emission-line galaxy candidates. Subject headings: galaxies: emission-lines — galaxies: Seyfert — galaxies: starburst — surveys

Sloan digital sky survey imaging of low galactic latitude fields: technical summary and data release

The Sloan Digital Sky Survey (SDSS) mosaic camera and telescope have obtained five-band optical-wavelength imaging near the Galactic plane outside of the nominal survey boundaries. These additional data were obtained during commissioning and subsequent testing of the SDSS observing system, and they provide unique wide-area imaging data in regions of high obscuration and star formation, including numerous young stellar objects, Herbig-Haro objects, and young star clusters. Because these data are outside the survey regions in the Galactic caps, they are not part of the standard SDSS data releases. This paper presents imaging data for 832 square degrees of sky (including repeats), in the star-forming regions of Orion, Taurus, and Cygnus. About 470 deg2 are now released to the public, with the remainder to follow at the time of SDSS Data Release 4. The public data in Orion include the star-forming region NGC 2068/NGC 2071/HH 24 and a large part of Barnards loop.