1,160 research outputs found
Diffuse Lyman Alpha Haloes around Lyman Alpha Emitters at z=3: Do Dark Matter Distributions Determine the Lyman Alpha Spatial Extents?
Using stacks of Ly-a images of 2128 Ly-a emitters (LAEs) and 24 protocluster
UV-selected galaxies (LBGs) at z=3.1, we examine the surface brightness
profiles of Ly-a haloes around high-z galaxies as a function of environment and
UV luminosity. We find that the slopes of the Ly-a radial profiles become
flatter as the Mpc-scale LAE surface densities increase, but they are almost
independent of the central UV luminosities. The characteristic exponential
scale lengths of the Ly-a haloes appear to be proportional to the square of the
LAE surface densities (r(Lya) \propto Sigma(LAE)^2). Including the diffuse,
extended Ly-a haloes, the rest-frame Ly-a equivalent width of the LAEs in the
densest regions approaches EW_0(Lya) ~ 200 A, the maximum value expected for
young (< 10^7 yr) galaxies. This suggests that Ly-a photons formed via shock
compression by gas outflows or cooling radiation by gravitational gas inflows
may partly contribute to illuminate the Ly-a haloes; however, most of their
Ly-a luminosity can be explained by photo-ionisation by ionising photons or
scattering of Ly-a photons produced in HII regions in and around the central
galaxies. Regardless of the source of Ly-a photons, if the Ly-a haloes trace
the overall gaseous structure following the dark matter distributions, it is
not surprising that the Ly-a spatial extents depend more strongly on the
surrounding Mpc-scale environment than on the activities of the central
galaxies.Comment: 7 pages, 4 figures, accepted for publication in MNRA
UV Luminosity Function at z~4, 3, and 2
We use very deep (R_lim=27) UGRI imaging to study the evolution of the faint
end of the UV-selected galaxy luminosity function from z~4 to z~2. We find that
the number of sub-L* galaxies increases from z~4 to z~3 while the number of
bright ones appears to remain constant. We find no evidence for continued
evolution to lower redshift, z~2. If real, this differential evolution of the
luminosity function suggests that differentially comparing key diagnostics of
dust, stellar populations, etc. as a function of z and L may let us isolate the
key mechanisms that drive galaxy evolution at high redshift and we describe
several such studies currently underway.Comment: To appear in proceedings of the conference "Starbursts - from 30
Doradus to Lyman break galaxies" (IoA, Cambridge UK, Sep 2004), Astrophysics
& Space Science Library, eds. de Grijs R., Gonzalez Delgado R.M. (Kluwer:
Dordrecht
Galaxy Clustering at z~3
Galaxies at very high redshift (z~3 or greater) are now accessible to
wholesale observation, making possible for the first time a robust statistical
assessment of their spatial distribution at lookback times approaching ~90% of
the age of the Universe. This paper summarizes recent progress in understanding
the nature of these early galaxies, concentrating in particular on the
clustering properties of photometrically selected ``Lyman break'' galaxies.
Direct comparison of the data to predictions and physical insights provided by
galaxy and structure formation models is particularly straightforward at these
early epochs, and results in critical tests of the ``biased'', hierarchical
galaxy formation paradigm.Comment: Presented at Royal Society Discussion Meeting, March 1998, "Large
Scale Structure in the Universe", 14 pages LaTeX, 7 ps figures, uses
rspublic.sty (included
The z=0.8596 Damped Lyman Alpha Absorbing Galaxy Toward PKS 0454+039
We present {\it Hubble Space Telescope} and ground--based data on the
metal line absorption system along the line of sight to PKS
0454+0356. The system is a moderate redshift damped Lyman alpha system, with
~cm as measured from the {\it
Faint Object Spectrograph} spectrum. We also present ground--based images which
we use to identify the galaxy which most probably gives rise to the damped
system; the most likely candidate is relatively underluminous by QSO absorber
standards ( for and \kms Mpc), and
lies kpc in projection from the QSO sightline. Ground--based
measurements of Zn~II, Cr~II, and Fe~II absorption lines from this system allow
us to infer abundances of [Zn/H]=, [Cr/H]=, and [Fe/H]=,
indicating overall metallicity similar to damped systems at , and that
the depletion of Cr and Fe onto dust grains may be even {\it less} important
than in many of the high redshift systems of comparable metallicity. Limits
previously placed on the 21-cm optical depth in the system, together
with our new N(H~I) measurement, suggest a very high spin temperature for the
H~I, K.Comment: changed uuencode header to produce .Z file so that unix uncompress
command will work without modifying file nam
Medium-resolution spectroscopy of galaxies with redshifts 2.3 < z < 3.5
Using FORS2 at the ESO VLT we obtained medium resolution (R ~ 2000) spectra
of 12 galaxies with 2.37 < z < 3.40 in the FORS Deep Field. Two individual
spectra with good S/N and a composite of all 12 spectra were used to derive
properties of the stellar and interstellar absorption lines of galaxies in this
redshift range. Systematic differences between the individual spectra were
found for the strength and profiles of the intrinsic interstellar lines. For
eight spectra with sufficient S/N we measured the `1370' and `1425' metallicity
indices. From these indices we find for our sample that galaxies at z > 3 have
lower mean metallicity than galaxies at 2.5 < z < 3. However there remain
uncertainties concerning the absolute calibration of the metallicity tracers in
use for high-redshift galaxies. Additional modeling will be needed to resolve
these uncertainties.Comment: 10 pages, 4 figures. Accepted by A&
A Candidate Brightest Proto-Cluster Galaxy at z = 3.03
We report the discovery of a very bright (m_R = 22.2) Lyman break galaxy at z
= 3.03 that appears to be a massive system in a late stage of merging. Deep
imaging reveals multiple peaks in the brightness profile with angular
separations of ~0.''8 (~25 h^-1 kpc comoving). In addition, high
signal-to-noise ratio rest-frame UV spectroscopy shows evidence for ~5
components based on stellar photospheric and ISM absorption lines with a
velocity dispersion of sigma ~460 km s^-1 for the three strongest components.
Both the dynamics and high luminosity, as well as our analysis of a LCDM
numerical simulation, suggest a very massive system with halo mass M ~ 10^13
M_solar. The simulation finds that all halos at z = 3 of this mass contain
sub-halos in agreement with the properties of these observed components and
that such systems typically evolve into M ~ 10^14 M_solar halos in groups and
clusters by z = 0. This discovery provides a rare opportunity to study the
properties and individual components of z ~ 3 systems that are likely to be the
progenitors to brightest cluster galaxies.Comment: 14 pages, 3 figures, submitted to ApJ Letter
Star-forming Galaxies in the 'Redshift Desert'
We describe results of optical and near-IR observations of a large
spectroscopic sample of star-forming galaxies photometrically-selected to lie
in the redshift range 1.4 < z < 2.5, often called the ``redshift desert''
because of historical difficulty in obtaining spectroscopic redshifts in this
range. We show that the former ``redshift desert'' is now very much open to
observation.Comment: 10 pages, 6 figures, to appear in the Proceedings of the ESO/USM/MPE
Workshop on "Multiwavelength Mapping of Galaxy Formation and Evolution", eds.
R. Bender and A. Renzin
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