60 research outputs found
Possible Young Stellar Objects without Detectable CO Emission
We found that at least 18 Young Stellar Object candidates invisible at
optical and near-infrared wavelengths, as well as ^12CO emission. They are IRAS
point sources with FIR colors similar to those of usual YSOs, and the infrared
spectral indices between 2.2 um and 25 um correspond to those of class I YSOs.
These peculiar far-infrared objects are highly concentrated around the galactic
plane and the distances are estimated to be around 1 kpc. Although their
distribution is away from molecular clouds, some of them seem to be associated
with large dark clouds or weak radio sources.Comment: 10 pages with 4 figures, LaTeX, accepted for publication in PASJ.
Images(fig2) are included in source file as JPEG files. PDF files are
avilable at ftp.kusastro.kyoto-u.ac.jp/pub/iwata/preprint
Lyman Break Galaxies at z~5: Rest-frame UV Spectra II
We present the results of spectroscopy of Lyman Break Galaxies (LBGs) at z~5
in the J0053+1234 field with the Faint Object Camera and Spectrograph on the
Subaru telescope. Among 5 bright candidates with z' < 25.0 mag, 2 objects are
confirmed to be at z~5 from their Ly alpha emission and the continuum
depression shortward of Ly alpha. The EWs of Ly alpha emission of the 2 LBGs
are not so strong to be detected as Ly alpha emitters, and one of them shows
strong low-ionized interstellar (LIS) metal absorption lines. Two faint objects
with z' \geq 25.0 mag are also confirmed to be at z~5, and their spectra show
strong Ly alpha emission in contrast to the bright ones. These results suggest
a deficiency of strong Ly alpha emission in bright LBGs at z~5, which has been
discussed in our previous paper. Combined with our previous spectra of LBGs at
z~5 obtained around the Hubble Deep Field-North (HDF-N), we made a composite
spectrum of UV luminous (M_1400 \leq -21.5 mag) LBGs at z~5. The resultant
spectrum shows a weak Ly alpha emission and strong LIS absorptions which
suggests that the bright LBGs at z~5 have chemically evolved at least to ~0.1
solar metallicity. For a part of our sample in the HDF-N region, we obtained
near-to-mid infrared data, which constraint stellar masses of these objects.
With the stellar mass and the metallicity estimated from LIS absorptions, the
metallicities of the LBGs at z~5 tend to be lower than those of the galaxies
with the same stellar mass at z \lesssim 2, although the uncertainty is very
large.Comment: 17 pages, 5 figures, accepted for publication in PAS
The Mean Ultraviolet Spectrum of a Representative Sample of Faint z~3 Lyman Alpha Emitters
We discuss the rest-frame ultraviolet emission line spectra of a large (~100)
sample of low luminosity redshift z~3.1 Lyman alpha emitters (LAEs) drawn from
a Subaru imaging survey in the SSA22 survey field. Our earlier work based on
smaller samples indicated that such sources have high [OIII]/[OII] line ratios
possibly arising from a hard ionising spectrum that may be typical of similar
sources in the reionisation era. With optical spectra secured from VLT/VIMOS,
we re-examine the nature of the ionising radiation in a larger sample using the
strength of the high ionisation diagnostic emission lines of CIII]1909,
CIV1549, HeII1640, and OIII]1661,1666 in various stacked subsets. Our analysis
confirms earlier suggestions of a correlation between the strength of Ly-alpha
and CIII] emission and we find similar trends with broad band UV luminosity and
rest-frame UV colour. Using various diagnostic line ratios and our stellar
photoionisation models, we determine both the gas phase metallicity and
hardness of the ionisation spectrum characterised by xi_ion - the number of
Lyman continuum photons per UV luminosity. We confirm our earlier suggestion
that xi_ion is significantly larger for LAEs than for continuum-selected Lyman
break galaxies, particularly for those LAEs with the faintest UV luminosities.
We briefly discuss the implications for cosmic reionisation if the metal-poor
intensely star-forming systems studied here are representative examples of
those at much higher redshift.Comment: 15 pages, 9 figures. Accepted for publication in MNRA
Lyman Break Galaxies at : Rest-Frame UV Spectra
We report initial results for spectroscopic observations of candidates of
Lyman Break Galaxies (LBGs) at in a region centered on the Hubble Deep
Field-North by using the Faint Object Camera and Spectrograph attached to the
Subaru Telescope. Eight objects with mag, including one AGN, are
confirmed to be at . The rest-frame UV spectra of seven LBGs
commonly show no or weak Lyalpha emission line (rest-frame equivalent width of
0-10\AA) and relatively strong low-ionization interstellar metal absorption
lines of SiII 1260, OI+SiII 1303, and CII 1334 (mean
rest-frame equivalent widths of them are \AA). These
properties are significantly different from those of the mean rest-frame UV
spectrum of LBGs at , but are quite similar to those of subgroups of
LBGs at with no or weak Lyalpha emission. The weakness of Lyalpha
emission and strong low-ionization interstellar metal absorption lines may
indicate that these LBGs at are chemically evolved to some degree and
have a dusty environment. Since the fraction of such LBGs at in our
sample is larger than that at , we may witness some sign of evolution
of LBGs from to , though the present sample size is very
small. It is also possible, however, that the brighter LBGs tend to show no or
weak Lyalpha emission, because our spectroscopic sample is bright (brighter
than ) among LBGs at . More observations are required to
establish spectroscopic nature of LBGs at .Comment: 16 pages, 3 figures, accepted by Ap
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