301 research outputs found
Spectroscopy of Stellar-Like Objects Contained in the Second Byurakan Survey. I
The results of spectroscopic observations of 363 star-like objects from the
Second Byurakan Survey (SBS) are reported. This SBS's subsample has proven to
be a rich source of newly identified quasars, Seyfert type galaxies, degenerate
stars and hot subdwarfs. In the subsample here studied, we identified 35 new
QSOs, 142 White Dwarfs (WDs) the majority of which, 114 are of DA type, 55
subdwarfs (29 of which are sdB-type stars), 10 HBB, 16 NHB, 54 G-type and 25
F-type stars, two objects with composite spectra, four Cataclismic Variables
(CV), two peculiar emission line stars, 17 objects with continuous spectra, as
well as one planetary nebula. Among the 35 QSOs we have found two Broad
Absorption Line (BAL) QSOs, namely SBS 1423+500 and SBS 1435+500A. Magnitudes,
redshifts, and slit spectra for all QSOs, also some typical spectra of the
peculiar stars are presented. We estimate the minimum surface density of bright
QSOs in redshift range 0.3<z<2.2 to be 0.05 per sq. deg. for B<17.0 and 0.10
per sq. deg. for B<17.5.Comment: 22 pages, 3 tables, 4 figures, PASP in pres
Spectral Observations of Faint Markarian Galaxies of the Second Byurakan Survey. II
We continue the program of spectroscopic observations of objects from the
Second Byurakan Survey (SBS). This survey contains more than 1300 galaxies and
1700 star-like objects with m(pg)<19.5. Our work is aimed towards the
construction of a complete sample of faint Markarian galaxies. Here, we present
spectroscopic data for 43 galaxies. Amongst them six new Seyfert galaxies are
found, namely two Sy 1 type (SBS 1343+544 and SBS 1433+500), one Sy 2 type (SBS
1620+545) and three likely Sy 2 type galaxies (SBS 1205+556, SBS 1344+527, SBS
1436+597). SBS 1343+544 falls into the luminosity gap between low-redshift QSOs
and high luminosity Sefert galaxies. In the sample studied here, another 36
emission-line galaxies were spectroscopically confirmed. Thus far, 102 SBS
galaxies brighter than m(pg)=17.5 have been observed with the Cananea 2.1m GHO
telescope. The apparent magnitude and redshift distributions, the spectral
classification, the relative intensities of emission lines, and other
parameters, as well as slit spectra for all 43 observed galaxies are presented.Comment: 7 pages, 7 figures, 2 tables, Latex, aaspp4.sty and aj_pt.sty,
Submitted to Astronomical Journa
Compact Nuclei in Galaxies at Moderate Redshift: I. Imaging and Spectroscopy
This study explores the space density and properties of active galaxies to
z=0.8. We have investigated the frequency and nature of unresolved nuclei in
galaxies at moderate redshift as indicators of nuclear activity such as Active
Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged
galaxies with multi-component models using maximum likelihood estimate
techniques to determine the best model fit. We select those galaxies requiring
an unresolved, point source component in the galaxy nucleus, in addition to a
disk and/or bulge component, to adequately model the galaxy light. We have
searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies
containing compact nuclei. In our survey of 1033 galaxies, the fraction
containing an unresolved nuclear component greater than 3% of the total galaxy
light is 16+/-3% corrected for incompleteness and 9+/-1% for nuclei greater
than 5% of the galaxy light. Spectroscopic redshifts have been obtained for 35
of our AGN/starburst candidates and photometric redshifts are estimated to an
accuracy of sigma_z=0.1 for the remaining sample. In this paper, the first of
two in this series, we present the selected HST imaged galaxies having
unresolved nuclei and discuss the selection procedure. We also present the
ground-based spectroscopy for these galaxies as well as the photometric
redshifts estimated for those galaxies without spectra.Comment: 56 pages, 22 figures, to appear in ApJ Supplement Series, April 199
The Diverse Infrared Properties of a Complete Sample of Star-Forming Dwarf Galaxies
We present mid-infrared Spitzer Space Telescope observations of a complete
sample of star-forming dwarf galaxies selected from the KPNO International
Spectroscopic Survey. The galaxies span a wide range in mid-infrared
properties. Contrary to expectations, some of the galaxies emit strongly at 8
micron indicating the presence of hot dust and/or PAHs. The ratio of this
mid-infrared dust emission to the stellar emission is compared with the
galaxies' luminosity, star-formation rate, metallicity, and optical reddening.
We find that the strength of the 8.0 micron dust emission to the stellar
emission ratio is more strongly correlated with the star-formation rate than it
is with the metallicity or the optical reddening in these systems. Nonetheless,
there is a correlation between the 8.0 micron luminosity and metallicity. The
slope of this luminosity-metallicity correlation is shallower than
corresponding ones in the B-band and 3.6 micron. The precise nature of the 8.0
micron emission seen in these galaxies (i.e., PAH versus hot dust or some
combination of the two) will require future study, including deep mid-IR
spectroscopy.Comment: 14 pages, accepted Ap
Exponential speed of mixing for skew-products with singularities
Let be the
endomorphism given by where is a positive real number. We prove that is
topologically mixing and if then is mixing with respect to Lebesgue
measure. Furthermore we prove that the speed of mixing is exponential.Comment: 23 pages, 3 figure
IC 225: a dwarf elliptical galaxy with a peculiar blue core
We present the discovery of a peculiar blue core in the elliptical galaxy IC
225 by using images and spectrum from the Sloan Digital Sky Survey (SDSS). The
outer parts of the surface brightness profiles of u-, g-, r-, i- and z-band
SDSS images for IC 225 are well fitted with an exponential function. The
fitting results show that IC 225 follows the same relations between the
magnitude, scale length and central surface brightness for dwarf elliptical
galaxies. Its absolute blue magnitude (M_B) is -17.14 mag, all of which suggest
that IC 225 is a typical dwarf elliptical galaxy. The g-r color profile
indicates a very blue core with a radius of 2 arcseconds, which is also clearly
seen in the RGB image made of g-, r- and i-band SDSS images. The SDSS optical
spectrum exhibits strong and very narrow nebular emission lines. The metal
abundances derived by the standard methods, which are 12+log(O/H) = 8.98,
log(N/O) = -0.77 and 12+log(S+/H+) = 6.76, turn out to be significantly higher
than that predicted by the well-known luminosity-metallicity relation. After
carefully inspecting the central region of IC 225, we find that there are two
distinct nuclei, separated by 1.4 arcseconds, the off-nucleated one is even
bluer than the nucleus of IC 225. The asymmetric line profiles of higher-order
Balmer lines indicate that the emission lines are bluer shifted relative to the
absorption lines, suggesting that the line emission arises from the off-center
core, whose nature is a metal-rich Hii region. To the best of our knowledge, it
is the first high-metallicity Hii region detected in a dwarf elliptical galaxy.Comment: 7 figures, accepted for publication in A
An Integrated Spectrophotometric Survey of Nearby Star-Forming Galaxies
We present integrated optical spectrophotometry for a sample of 417 nearby
galaxies. Our observations consist of spatially integrated, S/N=10-100
spectroscopy between 3600 and 6900 Angstroms at ~8 Angstroms FWHM resolution.
In addition, we present nuclear (2.5"x2.5") spectroscopy for 153 of these
objects. Our sample targets a diverse range of galaxy types, including
starbursts, peculiar galaxies, interacting/merging systems, dusty,
infrared-luminous galaxies, and a significant number of normal galaxies. We use
population synthesis to model and subtract the stellar continuum underlying the
nebular emission lines. This technique results in emission-line measurements
reliably corrected for stellar absorption. Here, we present the integrated and
nuclear spectra, the nebular emission-line fluxes and equivalent widths, and a
comprehensive compilation of ancillary data available in the literature for our
sample. In a series of subsequent papers we use these data to study optical
star-formation rate indicators, nebular abundance diagnostics, the
luminosity-metallicity relation, the dust properties of normal and starburst
galaxies, and the star-formation histories of infrared-luminous galaxies.Comment: Accepted for publication in ApJ
Delayed Photoionization Feedback in a Super Star Cluster in SBS0335-052E
SBS0335-052 is a well studied Blue Compact Dwarf galaxy with one of the
lowest metallicities of any known galaxy. It also contains 6 previously
identified Super Star Clusters. We combine archival HST NICMOS images in the Pa
alpha line and the 1.6 micron continuum of the eastern component, SBS0335-052E,
with other space and ground based data to perform a multi-wavelength analysis
of the super star clusters. We concentrate on the southern most clusters,
designated S1 and S2, which appear to be the youngest clusters and are the
strongest emitters of Pa alpha, radio, and x-ray flux. Our analysis leads to a
possible model for S1 and perhaps S2 as a cluster of very young, massive stars
with strong stellar winds. The wind density can be high enough to absorb the
majority of ionizing photons within less than 1000 AU of the stars, creating
very compact HII regions that emit optically thick radiation at radio
wavelengths. These winds would then effectively quench the photoionizing flux
very close to the stars. This can delay the onset of negative feedback by
photoionization and photodissociation on star formation in the clusters. This
is significant since SBS0335-052E resembles the conditions that were probably
common for high redshift star formation in galaxies near the epoch of
reionization.Comment: Accepted for publication in the Astrophysical Journa
The KPNO International Spectroscopic Survey. V. H-alpha-selected Survey List 3
The KPNO International Spectroscopic Survey (KISS) is an objective-prism
survey designed to detect extragalactic emission-line objects. It combines many
of the features of previous slitless spectroscopic surveys with the advantages
of modern CCD detectors, and is the first purely digital objective-prism survey
for emission-line galaxies (ELGs). Here we present the third list of ELG
candidates selected from our red spectral data, which cover the wavelength
range 6400 to 7200 A. In most cases, the detected emission line is H-alpha. The
current survey list covers the region of the NOAO Deep Wide-Field Survey
(NDWFS). This survey covers two fields; the first is 3 x 3 degrees square and
located at RA = 14h 30m, DEC = 34.5 deg (B1950), the second is 2.3 x 4.0
degrees and centered at RA = 2h 7.5m, DEC = -4.75 deg. A total area of 19.65
deg^2 is covered by the KISS data. A total of 261 candidate emission-line
objects have been selected for inclusion in the survey list (13.3 per deg^2).
We tabulate accurate coordinates and photometry for each source, as well as
estimates of the redshift, emission-line flux and line equivalent width based
on measurements of the digital objective-prism spectra. The properties of the
KISS ELGs are examined using the available observational data. When combined
with the wealth of multi-wavelength data already available for the NDWFS
fields, the current list of KISS ELGs should provide a valuable tool for
studying star-formation and nuclear activity in galaxies in the local universe.Comment: 18 pages, including 10 figures and 4 tables. Accepted for publication
in the December, 2005 A
HST observations of the blue compact dwarf SBS 0335-052: a probable young galaxy
We present HST WFPC2 V and I images and GHRS UV spectrophotometry of the
spectral regions around Ly and OI 1302 of the extremely metal-deficient
(Z~Zsun/41) blue compact dwarf (BCD) galaxy SBS 0335-052. All the star
formation in the BCD occurs in six super-star clusters (SSC) with ages =< 3-4
Myr. Dust is clearly present and mixed spatially with the SSCs. There is a
supershell of radius ~380 pc, delineating a large supernova cavity. The
instantaneous star formation rate is ~0.4 Msun yr^-1. Strong narrow Ly
emission is not observed. Rather there is low intensity broad (FWZI = 20 A)
Ly emission superposed on even broader Ly absorption by the HI
envelope. This broad low-intensity emission is probably caused by resonant
scattering of Ly photons. The BCD appears to be a young galaxy,
undergoing its very first burst of star formation. This conclusion is based on
the following evidence: 1) the underlying extended low-surface-brightness
component is very irregular and filamentary, suggesting that a significant part
of the emission comes from ionized gas; 2) it has very blue colors (-0.34 =<
(V-I) =< 0.16), consistent with gaseous emission colors; 3) the OI 1302
line is not detected in absorption in the GHRS spectrum, setting an upper limit
for N(O)/N(H) in the HI envelope of the BCD of more than 3000 times smaller
than the value in Orion.Comment: 20 pages and 6 Postscript figures. Submitted to Astrophysical Journa
- âŠ