34 research outputs found
The ESO UVES Advanced Data Products Quasar Sample - II. Cosmological Evolution of the Neutral Gas Mass Density
Quasar foreground damped absorbers, associated with HI-rich galaxies allow to
estimate the neutral gas mass over cosmic time, which is a possible indicator
of gas consumption as star formation proceeds. The DLAs and sub-DLAs are
believed to contain a large fraction of neutral gas mass in the Universe. In
Paper I of the series, we present the results of a search for DLAs and sub-DLAs
in the ESO-UVES Advanced Data Products dataset of 250 quasars. Here we use an
unbiased sub-sample of sub-DLAs from this dataset. We build a subset of 122
quasars ranging from 1.5 <z_em < 5.0, suitable for statistical analysis. The
statistical sample is analyzed in conjunction with other sub-DLA samples from
the literature. This makes up a combined sample of 89 sub-DLAs over a redshift
path of . Redshift evolution of the number density and the line
density are derived for sub-DLAs and compared with the LLSs and DLAs
measurements from the literature. The results indicate that these three classes
of absorbers are evolving in the redshift interval 1 < z < 5. The column
density distribution, f(N,z), down to the sub-DLA limit is determined. The
flattening of f_(N,z) in the sub-DLA regime is present in the observations. The
redshift evolution of f_(N,z) down to sub-DLA regime is also presented,
indicating the presence of more sub-DLAs at high-redshift as compared to
low-redshift. f_(N,z) is further used to determine the neutral gas mass
density, Omega_g, at 1.5 < z < 5.0. The complete sample shows that sub-DLAs
contribute 8-20% to the total Omega_g from 1.5 < z < 5.0. In agreement with
previous studies, no evolution of Omega_g is seen from low-redshift to
high-redshift, suggesting that star formation solely cannot explain this
non-evolution and replenishment of gas and/or recombination of ionized gas is
needed. (Abridged)Comment: 20 pages, 10 figures, 7 table
Empirical Estimate of Lyman-alpha Escape Fraction in a Statistical Sample of Lyman-alpha Emitters
The Lyman-alpha (Lya) recombination line is a fundamental tool for galaxy
evolution studies and modern observational cosmology. However, subsequent
interpretations are still prone to a number of uncertainties. Besides numerical
efforts, empirical data are urgently needed for a better understanding of Lya
escape process. We empirically estimate the Lyman-alpha escape fraction
fesc(Lya) in a statistically significant sample of z ~ 0 - 0.3 galaxies in
order to calibrate high-redshift Lyman-alpha observations. An optical
spectroscopic follow-up of a sub-sample of 24 Lyman-alpha emitters (LAEs)
detected by GALEX at z ~ 0.2-0.3, combined with a UV-optical sample of local
starbursts, both with matched apertures, allow us to quantify the dust
extinction through Balmer lines, and to estimate the Lyman-alpha escape
fraction from the Halpha flux corrected for extinction in the framework of the
recombination theory. The global escape fraction of Lyman-alpha radiation spans
nearly the entire range of values, from 0.5 to 100 %, and fesc(Lya) clearly
decreases with increasing nebular dust extinction E(B-V). Several objects show
fesc(Lya) greater than fesc(continuum) which may be an observational evidence
for clumpy ISM geometry or for an aspherical ISM. Selection biases and aperture
size effects may still prevail between z ~ 0.2-0.3 LAEs and local starbursts,
which may explain the difference observed for fesc(Lya).Comment: 4 pages, 2 figures, accepted for publication in Astronomy and
Astrophysic
Color--Luminosity Relations for the Resolved Hot Stellar Populations in the Centers of M 31 and M 32
We present Faint Object Camera (FOC) ultraviolet images of the central
14x14'' of Messier 31 and Messier 32. The hot stellar population detected in
the composite UV spectra of these nearby galaxies is partially resolved into
individual stars, and their individual colors and apparent magnitudes are
measured. We detect 433 stars in M 31 and 138 stars in M 32, down to detection
limits of m_F275W = 25.5 mag and m_F175W = 24.5 mag. We investigate the
luminosity functions of the sources, their spatial distribution, their
color-magnitude diagrams, and their total integrated far-UV flux. Although M 32
has a weaker UV upturn than M 31, the luminosity functions and color-magnitude
diagrams of M 31 and M 32 are surprisingly similar, and are inconsistent with a
majority contribution from any of the following: PAGB stars more massive than
0.56 Msun, main sequence stars, or blue stragglers. Both the the luminosity
functions and color-magnitude diagrams are consistent with a dominant
population of stars that have evolved from the extreme horizontal branch (EHB)
along tracks with masses between 0.47 and 0.53 Msun. These stars are well below
the detection limits of our images while on the zero-age EHB, but become
detectable while in the more luminous (but shorter) AGB-Manque' and post-early
asymptotic giant branch (PEAGB) phases. The FOC observations require that only
a only a very small fraction of the main sequence population (2% in M 31 and
0.5% in M 32) in these two galaxies evolve though the EHB and post-EHB phases,
with the remainder evolving through bright PAGB evolution that is so rapid that
few if any stars are expected in the small field of view covered by the FOC.Comment: 35 pages, Latex. 19 figures. To appear in ApJ. Uses emulateapj.sty
and apjfonts.sty (included). Color plates distributed seperatedly: fig1.jpg
and fig2.jp
Three-dimensional spectroscopy with a fiber-fed NUV spectrograph
In the context of the NASA balloon borne experiment named Fireball (Faint Intergalactic Redshifted Emission BALLoon) dedicated to map the Intergalactic Medium, we designed a fiber-fed near ultraviolet spectrograph to work in the 200 nm atmospheric transmission window. We first describe the system level optimization leading to the atypical use in UV of a fiber Integral Field Unit at the focus of a one meter diameter parabolic mirror. For the qualification of the design we measured the absolute transmission of an UV polyimide 100 microns core fiber. The fiber bundle made of 400 fibers rearranged in a 50 mm slit feeds an F/2.5 spectrograph based on an Offner Littrow mount. We present the optical performances of this design with a high throughput and a well matched aperture ratio
Measurements of Far-UV Emission from Elliptical Galaxies at z=0.375
The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward
of rest-frame 2500 A. It is a ubiquitous phenomenon in nearby giant elliptical
galaxies, and is thought to arise primarily from low-mass evolved stars on the
extreme horizontal branch and beyond. Models suggest that the UV upturn is a
very strong function of age for these old stellar populations, increasing as
the galaxy gets older. In some models the change in UV/optical flux ratio is a
factor of 25 over timescales of less than 3 Gyr. To test the predictions for
rapid evolution of the UV upturn, we have observed a sample of normal
elliptical galaxies in the z=0.375 cluster Abell 370 with the Faint Object
Camera aboard the Hubble Space Telescope. A combination of two long-pass
filters was used to isolate wavelengths shortward of rest-frame 2700 A,
providing a measurement of the UV upturn at a lookback time of approximately 4
Gyr. Surprisingly, the four elliptical galaxies observed show a range of UV
upturn strength that is similar to that seen in nearby elliptical galaxies,
with an equivalent 1550-V color ranging from 2.9-3.4 mag. Our result is
inconsistent with some models for the UV upturn; other models are consistent
only for a high redshift of formation (z_f >= 4).Comment: 4 pages, Latex. 1 figure. To appear in ApJL. Uses emulateapj.sty and
apjfonts.sty. Revision includes minor ApJ edits & fixes typo
FIREBALL: the first ultraviolet fiber fed spectrograph
FIREBall (the Faint Intergalactic Redshifted Emission Balloon) is a balloon-borne 1m telescope coupled to an ultraviolet fiber-fed spectrograph. FIREBall is designed to study the faint and diffuse emission of the warm hot intergalactic medium, until now detected primarily in absorption. FIREBall is a pathfinding mission to test new technology and make new constraints on the temperature and density of this gas. FIREBall has flown twice, the most recent flight (June 2009) a fully functioning science flight. Here we describe the spectrograph design, current setup, and calibration measurements from the campaign
Three-dimensional spectroscopy with a fiber-fed NUV spectrograph
In the context of the NASA balloon borne experiment named Fireball (Faint Intergalactic Redshifted Emission BALLoon) dedicated to map the Intergalactic Medium, we designed a fiber-fed near ultraviolet spectrograph to work in the 200 nm atmospheric transmission window. We first describe the system level optimization leading to the atypical use in UV of a fiber Integral Field Unit at the focus of a one meter diameter parabolic mirror. For the qualification of the design we measured the absolute transmission of an UV polyimide 100 microns core fiber. The fiber bundle made of 400 fibers rearranged in a 50 mm slit feeds an F/2.5 spectrograph based on an Offner Littrow mount. We present the optical performances of this design with a high throughput and a well matched aperture ratio
FIREBALL: the Faint Intergalactic medium Redshifted Emission Balloon: overview and first science flight results
FIREBALL (the Faint Intergalactic Redshifted Emission Balloon) is a balloon-borne 1m telescope coupled to an ultraviolet fiber-fed spectrograph. FIREBALL is designed to study the faint and diffuse emission of the intergalactic medium, until now detected primarily in absorption. FIREBALL is a path finding mission to test new technology and make new constraints on the temperature and density of this gas. We report on the first successful science flight of FIREBALL, in June 2009, which proved every aspect of the complex instrument performance, and provided the strongest measurements and constraints on IGM emission available from any instrument
The FIREBall fiber-fed UV spectrograph
FIREBall (Faint Intergalactic Redshifted Emission Balloon) had a successful first engineering flight in July of 2007 from Palestine, Texas. Here we detail the design and construction of the spectrograph. FIREBall consists of a 1m telescope coupled to a fiber-fed ultraviolet spectrograph flown on a short duration balloon. The spectrograph is designed to map hydrogen and metal line emission from the intergalactic medium at several redshifts below z=1, exploiting a small window in atmospheric oxygen absorption at balloon altitudes. The instrument is a wide-field IFU fed by almost 400 fibers. The Offner mount spectrograph is designed to be sensitive in the 195-215nm window accessible at our altitudes of 35-40km. We are able to observe Lyα, as well as OVI and CIV doublets, from 0.3 < z < 0.9. Observations of UV bright B stars and background measurements allow characterization of throughput for the entire system and will inform future flights