16 research outputs found
UV Continuum Spectroscopy of a 6L* z=5.5 Starburst Galaxy
We have obtained a high S/N (22.3 hr integration) UV continuum VLT FORS2
spectrum of an extremely bright (z_850 = 24.3) z = 5.515 +/- 0.003 starforming
galaxy (BD38) in the field of the z = 1.24 cluster RDCS 1252.9-2927. This
object shows substantial continuum (0.41 +/- 0.02 \muJy at \lambda1300) and
low-ionization interstellar absorption features typical of LBGs at lower
redshift (z ~ 3); this is the highest redshift LBG confirmed via metal
absorption spectral features. The equivalent widths of the absorption features
are similar to z ~ 3 strong Ly\alpha absorbers. No noticeable Ly\alpha emission
was detected (F <= 1.4 * 10^-18 ergs cm^-2 s^-1, 3\sigma). The half-light
radius of this object is 1.6 kpc (0\farcs25) and the star formation rate
derived from the rest-frame UV luminosity is SFR_UV = 38 h^-2_0.7 M_sun yr^-1
(142 h^-2_0.7 M_sun yr^-1 corrected for dust extinction). In terms of recent
determinations of the z ~ 6 UV luminosity function, this object appears to be
6L*. The Spitzer IRAC fluxes for this object are 23.3 and 23.2 AB mag
(corrected for 0.3 mag of cluster lensing) in the 3.6\mu and 4.5\mu channels,
respectively, implying a mass of 1-6 * 10^10 M_sun from population synthesis
models. This galaxy is brighter than any confirmed z ~ 6 i-dropout to date in
the z_850 band, and both the 3.6\mu and 4.5\mu channels, and is the most
massive starbursting galaxy known at z > 5. -- Abstract AbridgedComment: Accepted to ApJ Letters. 4 pages in emulate ApJ format, 3 color
figures, 1 with lower resolution. Full resolution file available at
http://physics.ucsc.edu/~cdow/bd38/bd38.pd
Globular cluster system and Milky Way properties revisited
Updated data of the 153 Galactic globular clusters are used to readdress
fundamental parameters of the Milky Way. We build a reduced sample,
decontaminated of the clusters younger than 10Gyr, those with retrograde orbits
and/or evidence of relation to dwarf galaxies. The 33 metal-rich globular
clusters of the reduced sample extend basically to the Solar circle and
distribute over a region with projected axial-ratios typical of an oblate
spheroidal, . The 81
metal-poor globular clusters span a nearly spherical region of axial-ratios
extending from the central parts to the outer halo. A new
estimate of the Sun's distance to the Galactic center is provided, . The metal-rich and metal-poor radial-density distributions
flatten for and are well represented both by a power-law
with a core-like term and S\'ersic's law; at large distances they fall off as
. Both metallicity components appear to have a common origin,
which is different from that of the dark matter halo. Structural similarities
of the metal-rich and metal-poor radial distributions with the stellar halo are
consistent with a scenario where part of the reduced sample was formed in the
primordial collapse, and part was accreted in an early period of merging. This
applies to the bulge as well, suggesting an early merger affecting the central
parts of the Galaxy. We estimate that the present globular cluster population
corresponds to of the original one. The fact that the
volume-density radial distributions of the metal-rich and metal-poor globular
clusters of the reduced sample follow both a core-like power-law and S\'ersic's
law indicates that we are dealing with spheroidal subsystems in all scales.Comment: 14 pages and 6 figures. Astronomy & Astrophysics, accepted on NOv. 2
Bright Strongly Lensed Galaxies at Redshift z~ 6-7 behind the Clusters Abell 1703 and CL0024+161
We report on the discovery of three bright, strongly-lensed objects behind
Abell 1703 and CL0024+16 from a dropout search over 25 square arcminutes of
deep NICMOS data, with deep ACS optical coverage. They are undetected in the
deep ACS images below 8500 A and have clear detections in the J and H bands.
Fits to the ACS, NICMOS and IRAC data yield robust photometric redshifts in the
range z~6-7 and largely rule out the possibility that they are low-redshift
interlopers. All three objects are extended, and resolved into a pair of bright
knots. The bright i-band dropout in Abell 1703 has an H-band AB magnitude of
23.9, which makes it one of the brightest known galaxy candidates at z>5.5. Our
model fits suggest a young, massive galaxy only ~ 60 million years old with a
mass of ~ 1E10 solar mass. The dropout galaxy candidates behind CL0024+16 are
separated by 2.5" (~ 2 kpc in the source plane), and have H-band AB magnitudes
of 25.0 and 25.6. Lensing models of CL0024+16 suggest that the objects have
comparable intrinsic magnitudes of AB ~ 27.3, approximately one magnitude
fainter than L* at z~6.5. Their similar redshifts, spectral energy
distribution, and luminosities, coupled with their very close proximity on the
sky, suggest that they are spatially associated, and plausibly are physically
bound. Combining this sample with two previously reported, similarly magnified
galaxy candidates at z~6-8, we find that complex systems with dual nuclei may
be a common feature of high-redshift galaxies.Comment: 34 pages, 9 figure
An Empirical Study of the Relationship between Ly{\alpha} and UV selected Galaxies: Do Theorists and Observers `Select' the Same Objects?
Lyman Alpha Emitters (LAEs) are galaxies that have been selected on the basis
of a strong Ly{\alpha} emission line in their spectra. Observational campaigns
have dramatically increased the sample of known LAEs, which now extends out to
z=7. These discoveries have motivated numerous theoretical studies on the
subject, which usually define LAEs in their models based on sharp Ly{\alpha}
luminosity and equivalent width (EW) cuts. While broadly representative, this
procedure does not mimic the selection from observational programs in detail,
which instead use cuts in various colour-spaces. We investigate what
implications this disjoint may have for studies that aim to model LAEs. We
construct an empirical model for the number density of star forming galaxies as
a function of their UV and Ly{\alpha} luminosity, utilising measured
constraints on the luminosity functions (LFs) of drop-out galaxies, and their
luminosity dependent probability distribution function of Ly{\alpha} EW. In
particular, we investigate whether the LAE LFs can be reproduced by defining
LAEs using a (z-dependent) Ly{\alpha} luminosity and EW threshold. While we are
able to reproduce the observed distribution of Ly{\alpha} EW among LAEs out to
restframe EW 200 A, we find that our formalism over-predicts both the UV and
Ly{\alpha} LFs of LAEs by a factor of 2-3, and is inconsistent with
observations at the ~95% level. This tension is partially resolved if we assume
the Ly{\alpha} EW-distribution of drop-out galaxies to be truncated at
restframe EW>150 A. However the overprediction indicates that modeling LAEs
with simple REW and luminosity cuts does not accurately mimic observed
selection criteria, and can lead to uncertainties in the predicted number
density of LAEs. On the other hand, the predicted z-evolution is not affected.
We apply our formalism to drop-out galaxies at z>6, and predict the LFs of LAEs
at z=7-9.Comment: MNRAS in press. Minor changes: expanded comparison with previous
work, and fixed some typos in the equation