164 research outputs found
The properties of the star-forming interstellar medium at z = 0.84-2.23 from HiZELS : mapping the internal dynamics and metallicity gradients in high-redshift disc galaxies.
We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine Hα-selected galaxies at z = 0.84-2.23 drawn from the HiZELS narrow-band survey. These galaxies have star formation rates of 1-27 M⊙ yr-1 and are therefore representative of the typical high-redshift star-forming population. Our ˜kpc-scale resolution observations show that approximately half of the sample have dynamics suggesting that the ionized gas is in large, rotating discs. We model their velocity fields to infer the inclination-corrected, asymptotic rotational velocities. We use the absolute B-band magnitudes and stellar masses to investigate the evolution of the B-band and stellar-mass Tully-Fisher relationships. By combining our sample with a number of similar measurements from the literature, we show that, at fixed circular velocity, the stellar mass of star-forming galaxies has increased by a factor of 2.5 between z = 2 and 0, whilst the rest-frame B-band luminosity has decreased by a factor of ˜ 6 over the same period. Together, these demonstrate a change in mass-to-light ratio in the B band of Δ(M/LB)/(M/LB)z=0 ˜ 3.5 between z = 1.5 and 0, with most of the evolution occurring below z = 1. We also use the spatial variation of [N II]/Hα to show that the metallicity of the ionized gas in these galaxies declines monotonically with galactocentric radius, with an average Δ log(O/H)/ΔR = -0.027 ± 0.005 dex kpc-1. This gradient is consistent with predictions for high-redshift disc galaxies from cosmologically based hydrodynamic simulations
Sample variance and Lyman α forest transmission statistics
We compare the observed probability distribution function (PDF) of the transmission in the H I Lyman α forest, measured from the Ultraviolet and Visual Echelle Spectrograph (UVES) ‘Large Programme’ sample at redshifts z = [2, 2.5, 3], to results from the GIMIC cosmological simulations. Our measured values for the mean transmission and its PDF are in good agreement with published results. Errors on statistics measured from high-resolution data are typically estimated using bootstrap or jackknife resampling techniques after splitting the spectra into chunks. We demonstrate that these methods tend to underestimate the sample variance unless the chunk size is much larger than is commonly the case. We therefore estimate the sample variance from the simulations. We conclude that observed and simulated transmission statistics are in good agreement; in particular, we do not require the temperature–density relation to be ‘inverted’
Possible Detection of Cosmological Reionization Sources
We compare the available catalogs of galaxies in the Hubble
Ultra-Deep Field (UDF) and in the Great Observatories Origins Deep Survey
(GOODS) with the expected properties of the sources of cosmological
reionization from our previous theoretical study. Our approach is based on the
mean surface brightness of the sources required for reionization and depends on
relatively few undetermined parameters. We find that the observed mean surface
brightness of galaxies at is sufficient for reionization,
provided that the sources are composed of hot metal-free or metal-poor stars,
regardless of whether reionization occurs over a short or long interval of
redshift. The broad agreement between the new observations and our predictions
suggests that we may have detected the sources responsible for some or even all
of the reionization of hydrogen.Comment: ApJL in press. Slightly revised version (mostly wording and some
extra references). Original version submitted on 21-March-2004. 10 pages, 1
figur
Deep CCD Surface Photometry of Galaxy Clusters I: Methods and Initial Studies of Intracluster Starlight
We report the initial results of a deep imaging survey of galaxy clusters.
The primary goals of this survey are to quantify the amount of intracluster
light as a function of cluster properties, and to quantify the frequency of
tidal debris. We outline the techniques needed to perform such a survey, and we
report findings for the first two galaxy clusters in the survey: Abell 1413,
and MKW 7 . These clusters vary greatly in richness and structure. We show that
our surface photometry reliably reaches to a surface brightness of \mu_v = 26.5
mags per arcsec. We find that both clusters show clear excesses over a
best-fitting r^{1/4} profile: this was expected for Abell 1413, but not for MKW
7. Both clusters also show evidence of tidal debris in the form of plumes and
arc-like structures, but no long tidal arcs were detected. We also find that
the central cD galaxy in Abell 1413 is flattened at large radii, with an
ellipticity of , the largest measured ellipticity of any cD galaxy
to date.Comment: 58 pages, 24 figures, accepted for publication in the Astrophysical
Journal. Version has extremely low resolution figures to comply with 650k
limit. High resolution version is available at
http://burro.astr.cwru.edu/johnf/icl1.ps.gz Obtaining high resolution version
is strongly reccomende
Extremely metal-poor Lyman limit system at z = 2.917 toward the quasar HE 0940-1050
We report on detailed Monte Carlo inversion analysis of the Lyman limit
system observed at z = 2.917 in the VLT/UVES spectrum of the quasar HE
0940-1050. Metal absorption lines of carbon and silicon in three ionization
stages and numerous atomic hydrogen lines have been analyzed simultaneously. It
is found that in order to match the observations, the shape of the ultraviolet
background ionizing spectrum of Haardt & Madau (1996) should be modified: a
spectrum with a higher intensity of the emission feature at 3 Ryd is required.
It is also found that synthetic galactic spectra (or different mixtures of them
with power law spectra) cannot reproduce the observations, indicating that the
stellar contribution to the ionizing background is negligible at z ~= 3. For
the first time a very low carbon abundance of [C/H] = -2.93+/-0.13 and the
abundance ratio [Si/C] = 0.35+/-0.15 are directly measured in the Lyman limit
system with N(H I) = 3.2 10^{17} cm^{-2}. If the absorber at z = 2.917 provides
an example of a pristine gas enriched by the nucleosynthetic products of early
generations of stars, then the measured value of [Si/C] seems to indicate that
the initial mass functions for these stellar populations are constrained to
intermediate masses, M_up <= 25M_solar.Comment: 7 pages, 4 figures, A&A in pres
The properties of the star-forming interstellar medium at z=0.84-2.23 from HiZELS: mapping the internal dynamics and metallicity gradients in high-redshift disc galaxies
We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine H�-selected galaxies at z =0.84–2.23 drawn from the HiZELS narrow-band survey.
These galaxies have star-formation rates of 1–27M⊙ yr−1 and are therefore representative of the typical high-redshift star-forming population. Our �kpc-scale resolution
observations show that approximately half of the sample have dynamics suggesting that the ionised gas is in large, rotating disks. We model their velocity fields to infer
the inclination-corrected, asymptotic rotational velocities.We use the absolute B-band magnitudes and stellar masses to investigate the evolution of the B-band and stellar mass Tully-Fisher relationships. By combining our sample with a number of similar measurements from the literature, we show that, at fixed circular velocity, the stellar mass of star-forming galaxies has increased by a factor 2.5 between z =2 and z =0, whilst the rest-frame B-band luminosity has decreased by a factor �6 over the same
period. Together, these demonstrate a change in mass-to-light ratio in the B-band of �(M/ LB) / (M/ LB)z=0 �3.5 between z =1.5 and z =0, with most of the evolution occuring below z =1. We also use the spatial variation of [Nii] /H� to show that the metallicity of the ionised gas in these galaxies declines monotonically with galactocentric radius, with an average �log(O/H) /�R=−0.027±0.005 dex kpc−1. This gradient is consistent with predictions for high-redshift disk galaxies from cosmologically based hydrodynamic simulations.
Key words: galaxies: evolution – galaxies: formation – galaxies: high-redshif
Luminosity and mass function of galactic open clusters: I. NGC 4815
We present deep V and I photometry for the open cluster NGC 4815 and four
surrounding Galactic fields down to a limiting magnitude . These data
are used to study cluster spatial extension by means of star counts, and to
derive the luminosity (LF) and mass function (MF). The radius turns out to be
at V=19.0 level, whereas the mass amounts at down to V=20.8. From the color-magnitude diagram, we obtain the LFs
in the V and I bands, using both the standard histogram and an adaptive kernel.
After correction for incompleteness and field star contamination, the LFs have
been transformed into the present day mass functions (PDMF). The PDMFs from the
V and I photometry can be represented as a power-law with a slope and (the \cite{salp55} MF in this notation has
a slope ) respectively, in the mass range . Below this mass, the MF cannot be considered as
representative of the cluster IMF, as it is the result of the combined effect
of strong irregularities in the stellar background, probable internal dynamical
evolution of the cluster and/or interaction of the cluster with the dense
Galactic field. Unresolved binaries and mass segregation can only flatten the
apparent derived IMF, so we expect that the real IMF must be steeper than the
quoted slope by an unknown amount.Comment: 12 pages, 10 eps figures, in press in Astronomy and Astrophysic
The Low Surface Brightness Extent of the Fornax Cluster
We have used a large format CCD camera to survey the nearby Fornax cluster
and its immediate environment for low luminosity low surface brightness
galaxies. Recent observations indicate that these are the most dark matter
dominated galaxies known and so they are likely to be a good tracer of the dark
matter in clusters. We have identified large numbers of these galaxies
consistent with a steep faint end slope of the luminosity function (alpha~ -2)
down to MB ~ -12. These galaxies contribute almost the same amount to the total
cluster light as the brighter galaxies and they have a spatial extent that is
some four times larger. They satisfy two of the important predictions of N-body
hierarchical simulations of structure formation using dark halos. The
luminosity (mass ?) function is steep and the mass distribution is more
extended than that defined by the brighter galaxies. We also find a large
concentration of low surface brightness galaxies around the nearby galaxy
NGC1291.Comment: 16 pages, 6 figure
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