129 research outputs found
Unveiling the nature of the "Green Pea" galaxies
We review recent results on the oxygen and nitrogen chemical abundances in
extremely compact, low-mass starburst galaxies at redshifts between 0.1-0.3
recently named to as "Green Pea" galaxies. These galaxies are genuine
metal-poor galaxies ( one fifth solar) with N/O ratios unusually high for
galaxies of the same metallicity. In combination with their known general
properties, i.e., size, stellar mass and star-formation rate, these findings
suggest that these objects could be experiencing a short and extreme phase in
their evolution. The possible action of both recent and massive inflow of gas,
as well as stellar feedback mechanisms are discussed here as main drivers of
the starburst activity and their oxygen and nitrogen abundances.Comment: To appear in JENAM Symposium "Dwarf Galaxies: Keys to Galaxy
Formation and Evolution", P. Papaderos, G. Hensler, S. Recchi (eds.). Lisbon,
September 2010, Springer Verlag, in pres
An Atlas of z=5.7 and z=6.5 Ly alpha Emitters
We present an atlas of 88 z~5.7 and 30 z~6.5 Ly alpha emitters obtained from
a wide-field narrowband survey. We combined deep narrowband imaging in 120A
bandpass filters centered at 8150A and 9140A with deep BVRIz broadband imaging
to select high-redshift galaxy candidates over an area of 4180 square arcmin.
The goal was to obtain a uniform selection of comparable depth over the 7
targeted fields in the two filters. For the GOODS-N region of the HDF-N field,
we also selected candidates using a 120A filter centered at 9210A. We made
spectroscopic observations with Keck DEIMOS of nearly all the candidates to
obtain the final sample of Ly alpha emitters. At the 3.3A resolution of the
DEIMOS observations the asymmetric profile for Ly alpha emission with its steep
blue fall-off can be clearly seen in the spectra of nearly all the galaxies. We
show that the spectral profiles are surprisingly similar for many of the
galaxies and that the composite spectral profiles are nearly identical at z=5.7
and z=6.5. We analyze the distributions of line widths and Ly alpha equivalent
widths and find that the lines are marginally narrower at the higher redshift,
with median values of 0.77A at z=6.5 and 0.92A at z=5.7. The line widths have a
dependence on the Ly alpha luminosity of the form L(L alpha)^(0.3). We compare
the surface densities and the luminosity functions at the two redshifts and
find that there is a multiplicative factor of 2 decrease in the number density
of bright Ly alpha emitters from z=5.7 to z=6.5, while the characteristic
luminosity is unchanged.Comment: Accepted for publication in the Astrophysical Journa
Unveiling a population of galaxies harboring low-mass black holes with X-rays
We report the discovery of three low-mass black hole (BH) candidates residing in the centers of low-mass galaxies at z < 0.3 in the Chandra Deep Field-South Survey. These BHs are initially identified as candidate active galactic nuclei based on their X-ray emission in deep Chandra observations. Multi-wavelength observations are used to strengthen our claim that such emission is powered by an accreting supermassive BH. While the X-ray luminosities are low at L_X ~ 10^(40) erg s^(–1) (and variable in one case), we argue that they are unlikely to be attributed to star formation based on Hα or UV fluxes. Optical spectroscopy from Keck and the VLT allows us to (1) measure accurate redshifts, (2) confirm their low stellar host mass, (3) investigate the source(s) of photo-ionization, and (4) estimate extinction. With stellar masses of M_* < 3 × 10^9 M_☉ determined from Hubble Space Telescope/Advanced Camera for Surveys imaging, the host galaxies are among the lowest mass systems known to host actively accreting BHs. We estimate BH masses M_(BH) ~ 2 × 10^5 M_☉ based on scaling relations between BH mass and host properties for more luminous systems. In one case, a broad component of the Hα emission-line profile is detected, thus providing a virial mass estimate. BHs in such low-mass galaxies are of considerable interest as the low-redshift analogs to the seeds of the most massive BHs at high redshift which have remained largely elusive to date. Our study highlights the power of deep X-ray surveys to uncover such low-mass systems
Mineralogy, Three Dimensional Structure, and Oxygen Isotope Ratios of Four Crystalline Particles from Comet 81P/Wild 2
Preliminary examinations of small dust particles from comet 82P/Wild 2 revealed many expected and unexpected features. Among them the most striking feature is the presence of abundant crystalline material in the comet. Synchrotron radiation X-ray diffraction and microtomography are the most efficient methods to detect and describe bulk mineralogical features of crystalline cometary particles. In the present study, in addition to these two non-destructive techniques, electron microscopy and ion-probe mass spectrometry were carried out on the four crystalline particles
Ultracarbonaceous Antarctic micrometeorites recovered from snow at the Dome C - CONCORDIA station.
第6回極域科学シンポジウム[OA] 南極隕石11月17日(火) 国立国語研究所 2階 講
On the dependence between UV luminosity and Lyman-alpha equivalent width in high redshift galaxies
We show that with the simple assumption of no correlation between the
Ly-alpha equivalent width and the UV luminosity of a galaxy, the observed
distribution of high redshift galaxies in an equivalent width - absolute UV
magnitude plane can be reproduced. We further show that there is no dependence
between Ly-alpha equivalent width and Ly-alpha luminosity in a sample of
Ly-alpha emitters. The test was expanded to Lyman-break galaxies and again no
dependence was found. Simultaneously, we show that a recently proposed lack of
large equivalent width, UV bright galaxies (Ando et al. 2006) can be explained
by a simple observational effect, based on too small survey volumes.Comment: 7 pages, 3 figures, 2 tables, accepted in MNRA
An atlas of z = 5.7 and z = 6.5 Lyα emitters
We present an atlas of 88 z ~ 5.7 and 30 z ~ 6.5 Lyα emitters obtained from a wide-field narrowband survey. We
combined deep narrowband imaging in 120 Å bandpass filters centered at 8150 Å and 9140 Å with deep B V R I z
broadband imaging to select high-redshift galaxy candidates over an area of 4180 arcmin^2. The goal was to obtain
a uniform selection of comparable depth over the seven targeted fields in the two filters. For the GOODS-North
region of the Hubble Deep Field-North field, we also selected candidates using a 120 Å filter centered at 9210 Å.
We made spectroscopic observations with Keck DEIMOS of nearly all the candidates to obtain the final sample of
Lyα emitters. At the 3.3 Å resolution of the DEIMOS observations the asymmetric profile for Lyα emission can be
clearly seen in the spectra of nearly all the galaxies. We show that the spectral profiles are surprisingly similar for
many of the galaxies and that the composite spectral profiles are nearly identical at z = 5.7 and z = 6.5.We analyze
the distributions of line widths and Lyα equivalent widths and find that the lines are marginally narrower at the
higher redshift, with median values of 0.77 Å at z = 6.5 and 0.92 Å at z = 5.7. The line widths have a dependence
on the Lyα luminosity of the form ~L^(0.3)_α . We compare the surface densities and the luminosity functions at the two
redshifts and find that there is a multiplicative factor of two decrease in the number density of bright Lyα emitters
from z = 5.7 to z = 6.5, while the characteristic luminosity is unchanged
Fluctuation - induced forces in critical fluids
The current knowledge about fluctuation - induced long - ranged forces is
summarized. Reference is made in particular to fluids near critical points, for
which some new insight has been obtained recently. Where appropiate, results of
analytic theory are compared with computer simulations and experiments.Comment: Topical review, 24 pages RevTeX, 6 figure
The star formation history and metal content of the "Green Peas". New detailed GTC-OSIRIS spectrophotometry of three galaxies
We present deep broad-band imaging and long-slit spectroscopy of three
compact, low-mass starburst galaxies at redshift z\sim0.2-0.3, also referred to
as Green Peas (GP). We measure physical properties of the ionized gas and
derive abundances for several species with high precision. We find that the
three GPs display relatively low extinction, low oxygen abundances, and
remarkably high N/O ratios We also report on the detection of clear signatures
of Wolf-Rayet (WR) stars in these galaxies. We carry out a pilot spectral
synthesis study using a combination of both population and evolutionary
synthesis models. Their outputs are in qualitative agreement, strongly
suggesting a formation history dominated by starbursts. In agreement with the
presence of WR stars, these models show that these GPs currently undergo a
major starburst producing between ~4% and ~20% of their stellar mass. However,
as models imply, they are old galaxies having had formed most of their stellar
mass several Gyr ago. The presence of old stars has been spectroscopically
verified in one of the galaxies by the detection of Mg I 5167, 5173 absorption
line. Additionally, we perform a surface photometry study based on HST data,
that indicates that the three galaxies posses an exponential low-surface
brightness envelope. If due to stellar emission, the latter is structurally
compatible to the evolved hosts of luminous BCD/HII galaxies, suggesting that
GPs are identifiable with major episodes in the assembly history of local BCDs.
These conclusions highlight the importance of these objects as laboratories for
studying galaxy evolution at late cosmic epochs.Comment: 30 pages, 9 figures and 7 tables. Accepted for publication in Ap
The WFC3 Infrared Spectroscopic Parallel (WISP) Survey
We present the WFC3 Infrared Spectroscopic Parallel (WISP) Survey. WISP is
obtaining slitless, near-infrared grism spectroscopy of ~ 90 independent,
high-latitude fields by observing in the pure parallel mode with Wide Field
Camera-3 on the Hubble Space Telescope for a total of ~ 250 orbits. Spectra are
obtained with the G102 (lambda=0.8-1.17 microns, R ~ 210) and G141 grisms
(lambda=1.11-1.67 microns, R ~ 130), together with direct imaging in the J- and
H-bands (F110W and F140W, respectively). In the present paper, we present the
first results from 19 WISP fields, covering approximately 63 square arc
minutes. For typical exposure times (~ 6400 sec in G102 and ~ 2700 sec in
G141), we reach 5-sigma detection limits for emission lines of 5 x 10^(-17)
ergs s^(-1) cm^(-2) for compact objects. Typical direct imaging 5sigma-limits
are 26.8 and 25.0 magnitudes (AB) in F110W and F140W, respectively. Restricting
ourselves to the lines measured with highest confidence, we present a list of
328 emission lines, in 229 objects, in a redshift range 0.3 < z < 3. The
single-line emitters are likely to be a mix of Halpha and [OIII]5007,4959 A,
with Halpha predominating. The overall surface density of high-confidence
emission-line objects in our sample is approximately 4 per arcmin^(2).These
first fields show high equivalent width sources, AGN, and post starburst
galaxies. The median observed star formation rate of our Halpha selected sample
is 4 Msol/year. At intermediate redshifts, we detect emission lines in galaxies
as faint as H_140 ~ 25, or M_R < -19, and are sensitive to star formation rates
down to less than 1 Msol/year. The slitless grisms on WFC3 provide a unique
opportunity to study the spectral properties of galaxies much fainter than L*
at the peak of the galaxy assembly epoch.Comment: 15 pages, 12 figures, submitted to Ap
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