112 research outputs found
Cloning Dropouts: Implications for Galaxy Evolution at High Redshift
The evolution of high redshift galaxies in the two Hubble Deep Fields, HDF-N
and HDF-S, is investigated using a cloning technique that replicates z~ 2-3 U
dropouts to higher redshifts, allowing a comparison with the observed B and V
dropouts at higher redshifts (z ~ 4-5). We treat each galaxy selected for
replication as a set of pixels that are k-corrected to higher redshift,
accounting for resampling, shot-noise, surface-brightness dimming, and the
cosmological model. We find evidence for size evolution (a 1.7x increase) from
z ~ 5 to z ~ 2.7 for flat geometries (Omega_M+Omega_LAMBDA=1.0). Simple scaling
laws for this cosmology predict that size evolution goes as (1+z)^{-1},
consistent with our result. The UV luminosity density shows a similar increase
(1.85x) from z ~ 5 to z ~ 2.7, with minimal evolution in the distribution of
intrinsic colors for the dropout population. In general, these results indicate
less evolution than was previously reported, and therefore a higher luminosity
density at z ~ 4-5 (~ 50% higher) than other estimates. We argue the present
technique is the preferred way to understand evolution across samples with
differing selection functions, the most relevant differences here being the
color cuts and surface brightness thresholds (e.g., due to the (1+z)^4 cosmic
surface brightness dimming effect).Comment: 56 pages, 22 figures, accepted for publication in Ap
Mass and Gas Profiles in A1689: Joint X-ray and Lensing Analysis
We carry out a comprehensive joint analysis of high quality HST/ACS and
Chandra measurements of A1689, from which we derive mass, temperature, X-ray
emission and abundance profiles. The X-ray emission is smooth and symmetric,
and the lensing mass is centrally concentrated indicating a relaxed cluster.
Assuming hydrostatic equilibrium we deduce a 3D mass profile that agrees
simultaneously with both the lensing and X-ray measurements. However, the
projected temperature profile predicted with this 3D mass profile exceeds the
observed temperature by ~30% at all radii, a level of discrepancy comparable to
the level found for other relaxed clusters. This result may support recent
suggestions from hydrodynamical simulations that denser, more X-ray luminous
small-scale structure can bias observed temperature measurements downward at
about the same (~30%) level. We determine the gas entropy at 0.1r_{vir} (where
r_{vir} is the virial radius) to be ~800 keV cm^2, as expected for a high
temperature cluster, but its profile at >0.1r_{vir} has a power-law form with
index ~0.8, considerably shallower than the ~1.1 index advocated by theoretical
studies and simulations. Moreover, if a constant entropy ''floor'' exists at
all, then it is within a small region in the inner core, r<0.02r_{vir}, in
accord with previous theoretical studies of massive clusters.Comment: 18 pages, 20 figures, 7 tables, accepted for publication in MNRAS,
minor changes to match published versio
Using Weak Lensing Dilution to Improve Measurements of the Luminous and Dark Matter in A1689
The E/SO sequence of a cluster defines a boundary redward of which a reliable
weak lensing signal can be obtained from background galaxies, uncontaminated by
cluster members. For bluer colors, both background and cluster members are
present, reducing the distortion signal by the proportion of unlensed cluster
members. In deep Subaru and HST/ACS images of A1689 the tangential distortion
of galaxies with bluer colors falls rapidly toward the cluster center relative
to the lensing signal of the red background. We use this dilution effect to
derive the cluster light profile and luminosity function to large radius, with
the advantage that no subtraction of far-field background counts is required.
The light profile declines smoothly to the limit of the data, r<2Mpc/h, with a
constant slope, dlog(L)/dlog(r)=-1.12+-0.06, unlike the lensing mass profile
which steepens continuously with radius, so that M/L peaks at an intermediate
radius, ~100kpc/h. A flatter behavior is found for the more physically
meaningful ratio of dark-matter to stellar-matter, when accounting for the
color-mass relation of cluster members. The cluster luminosity function has a
flat slope, alpha=-1.05+-0.07, independent of radius and with no faint upturn
to M_i'<-12. We establish that the very bluest objects are negligibly
contaminated by the cluster V-i'<0.2, because their distortion profile rises
towards the center following the red background, but offset higher by ~20%.
This larger amplitude is consistent with the greater estimated depth of the
faint blue galaxies, z~=2.0 compared to z~=0.85 for the red background, a
purely geometric effect related to cosmological parameters. Finally, we improve
upon our earlier mass profile by combining both the red and blue background
populations, clearly excluding low concentration CDM profiles.Comment: 17 pages, 21 figures, revised version in response to referee
comments,(added some discussion, references), conclusions unchanged. Accepted
for publication in Ap
Cloning Hubble Deep Fields I: A Model-Independent Measurement of Galaxy Evolution
We present a model-independent method of quantifying galaxy evolution in
high-resolution images, which we apply to the Hubble Deep Field (HDF). Our
procedure is to k-correct all pixels belonging to the images of a complete set
of bright galaxies and then to replicate each galaxy image to higher redshift
by the product of its space density, 1/V_{max}, and the cosmological volume.
The set of bright galaxies is itself selected from the HDF, because presently
the HDF provides the highest quality UV images of a redshift-complete sample of
galaxies (31 galaxies with I<21.9, \bar{z}=0.5, and for which V/V_{max} is
spread fairly). These galaxies are bright enough to permit accurate
pixel-by-pixel k-corrections into the restframe UV (\sim 2000 A). We match the
shot noise, spatial sampling and PSF smoothing of the HDF data, resulting in
entirely empirical and parameter-free ``no-evolution'' deep fields of galaxies
for direct comparison with the HDF. In addition, the overcounting rate and the
level of incompleteness can be accurately quantified by this procedure. We
obtain the following results. Faint HDF galaxies (I>24) are much smaller, more
numerous, and less regular than our ``no-evolution'' extrapolation, for any
interesting geometry. A higher proportion of HDF galaxies ``dropout'' in both U
and B, indicating that some galaxies were brighter at higher redshifts than our
``cloned'' z\sim0.5 population.Comment: 51 pages, 23 figures, replacement includes figures not previously
include
Young Red Spheroidal Galaxies in the Hubble Deep Fields: Evidence for a Truncated IMF at ~2M_solar and a Constant Space Density to z~2
The optical-IR images of the Northern and Southern Hubble Deep Fields are
used to measure the spectral and density evolution of early-type galaxies. The
mean optical SED is found to evolve passively towards a mid F-star dominated
spectrum by z ~ 2. We demonstrate with realistic simulations that hotter
ellipticals would be readily visible if evolution progressed blueward and
brightward at z > 2, following a standard IMF. The colour distributions are
best fitted by a `red' IMF, deficient above ~2 M_solar and with a spread of
formation in the range 1.5 < z_f < 2.5. Traditional age dating is spurious in
this context, a distant elliptical can be young but appear red, with an
apparent age >3 Gyrs independent of its formation redshift. Regarding density
evolution, we demonstrate that the sharp decline in numbers claimed at z > 1
results from a selection bias against distant red galaxies in the optical,
where the flux is too weak for morphological classification, but is remedied
with relatively modest IR exposures revealing a roughly constant space density
to z ~ 2. We point out that the lack of high mass star-formation inferred here
and the requirement of metals implicates cooling-flows of pre-enriched gas in
the creation of the stellar content of spheroidal galaxies. Deep-field X-ray
images will be very helpful to examine this possibility.Comment: 6 pages, 3 figures, submitted to Astrophysical Journal Letters,
typographical errors corrected, simulated images with different IMFs
illustrated at http://astro.berkeley.edu/~bouwens/ellip.htm
Large Einstein Radii: A Problem for LambdaCDM
The Einstein radius of a cluster provides a relatively model-independent
measure of the mass density of a cluster within a projected radius of ~ 150
kpc, large enough to be relatively unaffected by gas physics. We show that the
observed Einstein radii of four well-studied massive clusters, for which
reliable virial masses are measured, lie well beyond the predicted distribution
of Einstein radii in the standard LambdaCDM model. Based on large samples of
numerically simulated cluster-sized objects with virial masses ~ 1e15 solar,
the predicted Einstein radii are only 15-25'', a factor of two below the
observed Einstein radii of these four clusters. This is because the predicted
mass profile is too shallow to exceed the critical surface density for lensing
at a sizable projected radius. After carefully accounting for measurement
errors as well as the biases inherent in the selection of clusters and the
projection of mass measured by lensing, we find that the theoretical
predictions are excluded at a 4-sigma significance. Since most of the free
parameters of the LambdaCDM model now rest on firm empirical ground, this
discrepancy may point to an additional mechanism that promotes the collapse of
clusters at an earlier time thereby enhancing their central mass density.Comment: 9 pages, 5 figures, accepted by MNRA
Spectral Evidence for Widespread Galaxy Outflows at z>4
We present discovery spectra of a sample of eight lensed galaxies at high
redshift, 3.7<z<5.2, selected by their red colors in the fields of four massive
clusters: A1689, A2219, A2390, and AC114. Metal absorption lines are detected
and observed to be blueshifted by 300-800 km/s with respect to the centroid of
Ly-alpha emission. A correlation is found between this blueshift and the
equivalent width of the metal lines, which we interpret as a broadening of
saturated absorption lines caused by a dispersion in the outflow velocity of
interstellar gas. Local starburst galaxies show similar behavior, associated
with obvious gas outflows. We also find a trend of increasing equivalent width
of Ly-alpha emission with redshift, which may be a genuine evolutionary effect
towards younger stellar populations at high redshift with less developed
stellar continua. No obvious emission is detected below the Lyman limit in any
of our spectra, nor in deep U or B-band images. The UV continua are reproduced
well by early B-stars, although some dust absorption would allow a fit to
hotter stars. After correcting for the lensing, we derive small physical sizes
for our objects, ~0.5-5 kpc/h for a flat cosmology with Omega_m=0.3,
Omega_Lambda=0.7. The lensed images are only marginally resolved in good seeing
despite their close proximity to the critical curve, where large arcs are
visible and hence high magnifications of up to ~20x are inferred. Two objects
show a clear spatial extension of the Ly-alpha emission relative to the
continuum starlight, indicating a ``breakout'' of the gas. The sizes of our
galaxies together with their large gas motion suggests that outflows of gas are
common at high redshift and associated with galaxy formation.Comment: 48 pages, 16 figures, ApJ, in press. Manuscript with full resolution
color images available at (http://astro.princeton.edu/~bfrye
Spectroscopic Confirmation of the Fifth Image of SDSS J1004+4112 and Implications for the M_BH-sigma_* Relation at z=0.68
We present the results of deep spectroscopy for the central region of the
cluster lens SDSS J1004+4112 with the Subaru telescope. A secure detection of
an emission line of the faint blue stellar object (component E) near the center
of the brightest cluster galaxy (G1) confirms that it is the central fifth
image of the lensed quasar system. In addition, we measure the stellar velocity
dispersion of G1 to be sigma_* = 352+-13 km/s. We combine these results to
obtain constraints on the mass M_BH of the putative black hole (BH) at the
center of the inactive galaxy G1, and hence on the M_BH-sigma_* relation at the
lens redshift z_l=0.68. From detailed mass modeling, we place an upper limit on
the black hole mass, M_BH < 2.1x10^{10}M_sun at 1-sigma level
(<3.1x10^{10}M_sun at 3-sigma), which is consistent with black hole masses
expected from the local and redshift-evolved M_BH-sigma_* relations,
M_BH~10^{9}-10^{10}M_sun.Comment: 4 pages, 4 figures, accepted to PASJ (PASJ Vol.60, No.5, in press
The Sextet Arcs: a Strongly Lensed Lyman Break Galaxy in the ACS Spectroscopic Galaxy Survey towards Abell 1689
We present results of the HST Advanced Camera for Surveys spectroscopic
ground-based redshift survey in the field of A1689. We measure 98 redshifts,
increasing the number of spectroscopically confirmed objects by sixfold. We
present two spectra from this catalog of the Sextet Arcs, images which arise
from a strongly-lensed Lyman Break Galaxy (LBG) at a redshift of z=3.038.
Gravitational lensing by the cluster magnifies its flux by a factor of ~16 and
produces six separate images with a total r-band magnitude of r_625=21.7. The
two spectra, each of which represents emission from different regions of the
LBG, show H I and interstellar metal absorption lines at the systemic redshift.
Significant variations are seen in Ly-alpha profile across a single galaxy,
ranging from strong absorption to a combination of emission plus absorption. A
spectrum of a third image close to the brightest arc shows Ly-alpha emission at
the same redshift as the LBG, arising from either another spatially distinct
region of the galaxy, or from a companion galaxy close to the LBG. Taken as a
group, the Ly-alpha equivalent width in these three spectra decreases with
increasing equivalent width of the strongest interstellar absorption lines. We
discuss how these variations can be used to understand the physical conditions
in the LBG. Intrinsically, this LBG is faint, ~0.1L*, and forming stars at a
modest rate, ~4 solar masses per year. We also detect absorption line systems
toward the Sextet Arcs at z=2.873 and z=2.534. The latter system is seen across
two of our spectra.Comment: Accepted for publication in Ap
- …