14 research outputs found
Detections of Lyman Continuum from Star-forming Galaxies at z~3 Through Subaru/Suprime-Cam Narrow-band Imaging
Knowing the amount of ionizing photons from young star-forming galaxies is of
particular importance to understanding the reionization process. Here we report
initial results of Subaru/Suprime-Cam deep imaging observation of the SSA22
proto-cluster region at z=3.09, using a special narrow-band filter to optimally
trace Lyman continuum (LyC) from galaxies at z~3. The unique wide field-of-view
of Suprime-Cam enabled us to search for ionizing photons from 198 galaxies (73
Lyman break galaxies (LBGs) and 125 Ly-alpha emitters (LAEs)) with
spectroscopically measured redshifts z~3.1. We detected LyC from 7 LBGs, as
well as from 10 LAE candidates. Some of the detected galaxies show significant
spatial offsets of LyC from non-ionizing UV emission. For some LBGs the
observed non-ionizing UV to LyC flux density ratios are smaller than values
expected from population synthesis models with a standard Salpeter initial mass
function (IMF) with moderate dust attenuation (which is suggested from the
observed UV slopes), even if we assume very transparent IGM along the
sightlines of these objects. This implies an intrinsically bluer spectral
energy distribution, e.g, that produced by a top-heavy IMF, for these LBGs. The
observed flux desity ratios of non-ionizing UV to LyC of 7 detected LBGs range
from 2.4 to 23.8 and the median is 6.6. The observed flux density ratios of the
detected LAEs are even smaller than LBGs, if they are truly at z~3.1. We find
that the median value of the flux density ratio for the deteced LBGs suggest
that their escape fractions is likely to be higher than 4%, if the LyC escape
is isotropic. The results imply that some of the LBGs in the proto-cluster at
z~3 have the escape fraction significantly higher than that of galaxies (in a
general field) at z~1 studied previously.Comment: 9 pages, 5 figures. Accepted for publication in Ap
Profiles of Lyman\alpha\ Emission Lines
We present the results of the observations of the Ly\alpha\ line profiles of
91 emission-line galaxies at z=3.1 with the spectral resolution of
\lambda/\delta\lambda (FWHM) = 1700, or 180 km/s. A significant fraction, ~50%
of the observed objects show the characteristic double peaks in their Ly\alpha
profile. The red peak is much stronger than the blue one for most of the cases.
The red peaks themselves also show weak but significant asymmetry and their
widths are correlated with the velocity separation of the red and the blue
peaks, which implies that the peaks are not isolated multiple components with
different velocities but the parts of the single line which is modified by the
absorption and/or scattering by the associated neutral hydrogen gas. The
characteristic profile can be naturally explained by the scattering in the
expanding shell of neutral hydrogen surrounding the Ly\alpha\ emitting region
while the attenuation by the inter-galactic medium should also be considered.
Our results suggest that the star-formation in these Ly\alpha\ emitters are
dominated by the young burst-like events which produce the intrinsic Ly\alpha\
emission as well as the gas outflow.Comment: 15 pages, Accepted for publication in Astrophysical Journa
The Subaru Ly-alpha blob survey: A sample of 100 kpc Ly-alpha blobs at z=3
We present results of a survey for giant Ly-alpha nebulae (LABs) at z=3 with
Subaru/Suprime-Cam. We obtained Ly-alpha imaging at z=3.09+-0.03 around the
SSA22 protocluster and in several blank fields. The total survey area is 2.1
square degrees, corresponding to a comoving volume of 1.6 x 10^6 Mpc^3. Using a
uniform detection threshold of 1.4 x 10^{-18} erg s^{-1} cm^{-2} arcsec^{-2}
for the Ly-alpha images, we construct a sample of 14 LAB candidates with
major-axis diameters larger than 100 kpc, including five previously known blobs
and two known quasars. This survey triples the number of known LABs over 100
kpc. The giant LAB sample shows a possible "morphology-density relation":
filamentary LABs reside in average density environments as derived from compact
Ly-alpha emitters, while circular LABs reside in both average density and
overdense environments. Although it is hard to examine the formation mechanisms
of LABs only from the Ly-alpha morphologies, more filamentary LABs may relate
to cold gas accretion from the surrounding inter-galactic medium (IGM) and more
circular LABs may relate to large-scale gas outflows, which are driven by
intense starbursts and/or by AGN activities. Our survey highlights the
potential usefulness of giant LABs to investigate the interactions between
galaxies and the surrounding IGM from the field to overdense environments at
high-redshift.Comment: MNRAS Letters accepted (6 pages, 4 figures, 2 tables
Discovery of a Damped Ly-alpha Absorber at z = 3.3 along a Galaxy Sight-line in the SSA22 Field
Using galaxies as background light sources to map the Lya absorption lines is a novel approach to study Damped Lya Absorbers (DLAs). We report the discovery of an intervening z = 3.335 +- 0.007 DLA along a galaxy sight-line identified among 80 Lyman Break Galaxy (LBG) spectra obtained with our Very Large Telescope/Visible Multi-Object Spectrograph survey in the SSA22 field. The measured DLA neutral hydrogen (HI) column density is log (NHI/cm^{-2}) = 21.68 +- 0.17. The DLA covering fraction over the extended background LBG is > 70% (2 sigma), yielding a conservative constraint on the DLA area of > 1 kpc^2. Our search for a counterpart galaxy hosting this DLA concludes that there is no counterpart galaxy with star formation rate (SFR) larger than a few Msun yr^{-1}, ruling out an unobscured violent star formation in the DLA gas cloud. We also rule out the possibility that the host galaxy of the DLA is a passive galaxy with Mstar > 5 x 10^{10} Msun or a heavily dust-obscured galaxy with E(B-V) > 2. The DLA may coincide with a large-scale overdensity of the spectroscopic LBGs. The occurrence rate of the DLA is compatible with that of DLAs found in QSO sight-lines
Enhancement of H i absorption associated with the z = 3.1 large-scale proto-cluster and characteristic structures with AGNs sculptured over Gpc scale in the SSA22 field
In the SSA22 field which exhibits a large-scale proto-cluster at , we
carried out a spectroscopic survey for Lyman Break Galaxies (LBGs) with the
VLT/VIMOS and identified 78 confident LBGs at --4. We stacked their
spectra in the observer's frame by using a sophisticated method. Analyzing the
composite spectrum, we have revealed that the large-scale proto-cluster at
has a strong HI absorption dip of rest-frame equivalent width of
A. Another strong absorption dip found at is associated with a
modestly high-density LBG peak, similar to that at . We have also
detected an HI transparency peak at in the composite spectrum,
coincident with a void in the LBG distribution. In this paper, we also
investigated the relation between LBGs, HI gas and AGNs at --4 in the
SSA22 field. Two AGNs at and 3.801 are, respectively, associated with
the LBG concentration of an overdensity factor in the
present statistics. Another structure at is remarkable: 20 comoving
Mpc scale dense HI gas which is not associated with any apparent LBG
overdensity but involving a pair of AGNs. Such structure may be a new type of
the AGN-matter correlation. If the inhomogeneous structures over a comoving Gpc
scale found in this paper are confirmed with sufficient statistics in the
future, the SSA22 field will become a key region to test the standard cold dark
matter structure formation scenario.Comment: MNRAS accepted, 24 pages, 20 figures, 8 table
Ly blobs like company: the discovery of a candidate 100kpc Ly blob near to a radio galaxy with a giant Ly halo B3J2330+3927 at z = 3.1
We present the discovery of a candidate of giant radio-quiet Lyman-alpha
(Lya) blob (RQLAB) in a large-scale structure around a high-redshift radio
galaxy (HzRG) lying in a giant Lya halo, B3 J2330+3927 at redshift z=3.087. We
obtained Lya imaging around B3 J2330+3927 with Subaru/Suprime-Cam to search for
Lya emitters (LAEs) and absorbers (LAAs) at redshift z=3.09+-0.03. We detected
candidate 127 LAEs and 26 LAAs in the field of view of 31' x 24'. We found that
B3 J2330+3927 is surrounded by a 130 kpc Lya halo and a large-scale (60 x 20
comoving Mpc) filamentary structure. The large-scale structure contains one
prominent local density peak with an overdensity of greater than 5, which is 8'
(15 comoving Mpc) away from B3 J2330+3927. In this peak, we discovered a
candidate 100 kpc RQLAB. The existence of both types of Lya nebulae in the same
large-scale structure suggests that giant Lya nebulae need special large-scale
environments to form. On smaller scales, however, the location of B3 J2330+3927
is not a significant local density peak in this structure, in contrast to the
RQLAB. There are two possible interpretations of the difference of the local
environments of these two Lya nebulae. Firstly, RQLAB may need a prominent
(delta ~ 5) density peak of galaxies to form through intense star-bursts due to
frequent galaxy interactions/mergers and/or continuous gas accretion in an
overdense environment. On the other hand, Lya halo around HzRG may not always
need a prominent density peak to form if the surrounding Lya halo is mainly
powered by its radio and AGN activities. Alternatively, both RQLAB and Lya halo
around HzRG may need prominent density peaks to form but we could not
completely trace the density of galaxies because we missed evolved and dusty
galaxies in this survey.Comment: 6 pages, 4 figures. Accepted for publication in MNRAS Letters. Images
and source catalogs are available at
http://astro.dur.ac.uk/~rblk89/B3J2330/data/data.htm