176 research outputs found
NIR Spectroscopy with the VLT of a sample of ISO selected Hubble Deep Field South Galaxies
A new population of faint galaxies characterized by an extremely high rate of
evolution with redshift up to z~1.5 has recently been discovered by ISO. These
sources are likely to contribute significantly to the cosmic far-IR
extragalactic background. We have carried out near-infrared VLT-ISAAC
spectroscopy of a sample of ISOCAM galaxies from the Hubble Deep Field South.
The rest-frame R-band spectral properties of the ISO population resembles that
of powerful dust-enshrouded active starburst galaxies.Comment: 8 pages, 3 figures, to appear in "ISO Surveys of a Dusty Universe",
eds. D. Lemke, M. Stickel, K. Wilke, typos correcte
Comparing the Host Galaxies of Type Ia, Type II and Type Ibc Supernovae
We compare the host galaxies of 902 supernovae, including SNe Ia, SNe II and
SNe Ibc, which are selected by cross-matching the Asiago Supernova Catalog with
the SDSS Data Release 7. We further selected 213 galaxies by requiring the
light fraction of spectral observations 15%, which could represent well the
global properties of the galaxies. Among them, 135 galaxies appear on the
Baldwin-Phillips-Terlevich diagram, which allows us to compare the hosts in
terms of star-forming, AGNs (including composites, LINERs and Seyfert 2s) and
"Absorp" (their related emission-lines are weak or non-existence) galaxies. The
diagrams related to parameters D(4000), H, stellar masses, SFRs
and specific SFRs for the SNe hosts show that almost all SNe II and most of SNe
Ibc occur in SF galaxies, which have a wide range of stellar mass and low
D(4000). The SNe Ia hosts as SF galaxies follow similar trends. A
significant fraction of SNe Ia occurs in AGNs and Absorp galaxies, which are
massive and have high D(4000). The stellar population analysis from
spectral synthesis fitting shows that the hosts of SNe II have a younger
stellar population than hosts of SNe Ia. These results are compared with those
of the 689 comparison galaxies where the SDSS fiber captures less than 15% of
the total light. These comparison galaxies appear biased towards higher
12+log(O/H) (0.1dex) at a given stellar mass. Therefore, we believe the
aperture effect should be kept in mind when the properties of the hosts for
different types of SNe are discussed.Comment: 15 pages, 9 figure
The nuclear spectrum of the radio galaxy NGC 5128 (Centaurus A)
We present near-infrared spectra of the nuclear disk in the nearby radio
galaxy NGC 5128 (Centaurus A). On the basis of the observed strengths of the [S
III] 0.9532um and [Fe II] 1.2567um lines, we classify NGC 5128 as a LINER.
Modeling of the strengths of these and additional lines suggests that the
nuclear region is powered by shocks rather than photoionization.Comment: 12 pages including 2 figures, accepted by ApJ Letter
The First VLT FORS1 spectra of Lyman-break candidates in the HDF-S and AXAF Deep Field
We report on low-resolution multi-object spectroscopy of 30 faint targets (R
\~ 24-25) in the HDF-S and AXAF deep field obtained with the VLT Focal
Reducer/low dispersion Spectrograph (FORS1). Eight high-redshift galaxies with
2.75< z < 4 have been identified. The spectroscopic redshifts are in good
agreement with the photometric ones with a dispersion at z<2
and at z>2. The inferred star formation rates of the
individual objects are moderate, ranging from a few to a few tens solar masses
per year. Five out of the eight high-z objects do not show prominent emission
lines. One object has a spectrum typical of an AGN. In the AXAF field two
relatively close pairs of galaxies have been identified, with separations of
8.7 and 3.1 proper Mpc and mean redshifts of 3.11 and 3.93, respectively.Comment: 5 pages Latex, with 2 PostScript figures. Astronomy and Astrophysics,
in pres
Sulfur, Chlorine, & Argon Abundances in Planetary Nebulae. I: Observations and Abundances in a Northern Sample
This paper is the first of a series specifically studying the abundances of
sulfur, chlorine, and argon in Type II planetary nebulae (PNe) in the Galactic
disk. Ratios of S/O, Cl/O, and Ar/O constitute important tests of differential
nucleosynthesis of these elements and serve as strict constraints on massive
star yield predictions. We present new ground-based optical spectra extending
from 3600-9600 Angstroms for a sample of 19 Type II northern PNe. This range
includes the strong near infrared lines of [S III] 9069,9532, which allows us
to test extensively their effectiveness as sulfur abundance indicators. We also
introduce a new, model-tested ionization correction factor for sulfur. For the
present sample, we find average values of S/O=1.2E-2(+/- 0.71E-2),
Cl/O=3.3E-4(+/- 1.6E-4), and Ar/O=5.0E-3(+/- 1.9E-3).Comment: 44 pages, 6 figures. Accepted for publication in the Astrophysical
Journa
WSO/UV: World Space Observatory/Ultraviolet
We summarize the capabilities of the World Space Observatory (UV) Project
(WSO/UV). An example of the importance of this project (with a planned launch
date of 2007/8) for the study of Classical Novae is given.Comment: 4 pages, To appear in the proceeedings of the "Classical Nova
Explosions" conference, eds. M. Hernanz and J. Jose, AI
Calibration of Nebular Emission-line Diagnostics: II. Abundances
(Abridged) We examine standard methods of measuring nebular chemical
abundances, including estimates based on direct T_e measurements, and also
bright-line diagnostics. We use observations of 4 LMC HII regions whose
ionizing stars have classifications ranging from O7 to WN3. We assume a 2-zone
T_e structure to compute ionic abundances. We compare with photoionization
models tailored to the properties of the individual objects, and emphasize the
importance of correctly relating T_e in the two zones, which can otherwise
cause errors of ~0.2 dex in abundance estimates. There are no spatial
variations to within 0.1 - 0.15 dex in any of the objects, even one hosting 3
WR stars.
Our data agree with the modeled R23 and S23 diagnostics of O and S. We
present the first theoretical tracks for S23, which are in excellent agreement
with a larger dataset. However, contrary to earlier suggestions, S23 is much
more sensitive to the ionization parameter than is R23, because S23 does not
sample S IV. We therefore introduce S234 = ([SII]+[SIII]+[SIV])/H-beta.
Predicted and observed spatial variations in S234 are dramatically reduced in
contrast to S23. The intensity of [SIV]10.5 microns is easily estimated from a
simple relation between [SIV]/[SIII] and [OIII]/[OII]. This method of
estimating S234 yields excellent agreement with our models, hence we give a
theoretical calibration for S234. The double-valued structure of S23 and S234
remains an important problem as for R23, and presently we consider the S
diagnostics reliable only at Z < 0.5 Z_sol. However, the slightly larger
dynamic range and excellent compatibility with theoretical predictions suggest
the S diagnostics to be more effective abundance indicators than R23.Comment: Accepted to ApJ. 24 pages, 11 figures, uses emulateapj.st
Energy Diagnoses of Nine Infrared Luminous Galaxies Based on 3--4 Micron Spectra
The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed
based on their ground-based 3--4 m spectra. Both the equivalent width of
the 3.3 m polycyclic aromatic hydrocarbon (PAH) emission feature and the
3.3 m PAH to far-infrared luminosity ratio () are
analyzed. Assuming nuclear compact starburst activity in these sources produces
the 3.3 m PAH emission as strongly as that in starburst galaxies with
lower far-infrared luminosities, the followings results are found: For six
IRLGs, both the observed equivalent widths and the ratios
are too small to explain the bulk of their far-infrared luminosities by compact
starburst activity, indicating that active galactic nucleus (AGN) activity is a
dominant energy source. For the other three IRLGs, while the 3.3 m PAH
equivalent widths are within the range of starburst galaxies, the
ratios after correction for screen dust extinction are a
factor of 3 smaller. The uncertainty in the dust extinction correction
factor and in the scatter of the intrinsic ratios for
starburst galaxies do not allow a determination of the ultimate energy sources
for these three IRLGs.Comment: 29 pages, 2 figures, Accepted for publication in Ap
A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. II. The Small Magellanic Cloud
We present 52-93 micron spectra, obtained with the Spitzer Space Telescope,
of luminous compact far-IR sources in the SMC. These comprise 9 Young Stellar
Objects (YSOs), the compact HII region N81 and a similar object within N84, and
two red supergiants (RSGs). The spectra of the sources in N81 (of which we also
show the ISO-LWS spectrum between 50-170 micron) and N84 both display strong
[OI] 63-micron and [OIII] 88-micron fine-structure line emission. We attribute
these lines to strong shocks and photo-ionized gas, respectively, in a
``champagne flow'' scenario. The nitrogen content of these two HII regions is
very low, definitely N/O<0.04 but possibly as low as N/O<0.01. Overall, the
oxygen lines and dust continuum are weaker in star-forming objects in the SMC
than in the LMC. We attribute this to the lower metallicity of the SMC compared
to that of the LMC. Whilst the dust mass differs in proportion to metallicity,
the oxygen mass differs less; both observations can be reconciled with higher
densities inside star-forming cloud cores in the SMC than in the LMC. The dust
in the YSOs in the SMC is warmer (37-51 K) than in comparable objects in the
LMC (32-44 K). We attribute this to the reduced shielding and reduced cooling
at the low metallicity of the SMC. On the other hand, the efficiency of the
photo-electric effect to heat the gas is found to be indistinguishable to that
measured in the same manner in the LMC, 0.1-0.3%. This may result from higher
cloud-core densities, or smaller grains, in the SMC. The dust associated with
the two RSGs in our SMC sample is cool, and we argue that it is swept-up
interstellar dust, or formed (or grew) within the bow-shock, rather than dust
produced in these metal-poor RSGs themselves. Strong emission from crystalline
water ice is detected in at least one YSO. (abridged)Comment: Accepted for publication in The Astronomical Journa
VLT-ISAAC near-IR Spectroscopy of ISO selected Hubble Deep Field South Galaxies
We report the results of near-infrared VLT-ISAAC spectroscopy of a sample of
12 galaxies at z = 0.4-1.4, drawn from the ISOCAM survey of the Hubble Deep
Field South. We find that the rest frame R-band spectra of the ISOCAM galaxies
resemble those of powerful dust-enshrouded starbursts. Halpha emission is
detected in 11 out of 12 objects down to a flux limit of 7x10^(-17) erg/cm^2/s,
corresponding to a luminosity limit of 10^41 erg/s at z = 0.6, (for an Ho = 50
and Omega = 0.3 cosmology). From the Halpha luminosities in these galaxies we
derive estimates of the star formation rate in the range 2--50 Mo/yr for
stellar masses 1--100 Mo. The raw Halpha-based star formation rates are an
order of magnitude or more lower than SFR(FIR) estimates based on ISOCAM LW3
fluxes. If the Halpha emission is corrected for extinction the median offset is
reduced to a factor of 3. The sample galaxies are part of a new population of
optically faint but infrared--luminous active starburst galaxies, which are
characterized by an extremely high rate of evolution with redshift up to z~1.5
and expected to contribute significantly to the cosmic far-IR extragalactic
background.Comment: Accepted for publication in the Astrophysical Journal Letters, 16
pages, 2 figure
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