33 research outputs found
The Nature of Blue Cores in Spheroids: a Possible Connection with AGN and Star Formation
We investigate the physical nature of blue cores in early-type galaxies
through the first multi-wavelength analysis of a serendipitously discovered
field blue-nucleated spheroid in the background of the deep ACS/WFC griz
multicolor observations of the cluster Abell 1689. The resolved g-r, r-i and
i-z color maps reveal a prominent blue core identifying this galaxy as a
``typical'' case study, exhibiting variations of 0.5-1.0 mag in color between
the center and the outer regions, opposite to the expectations of reddened
metallicity induced gradients in passively evolved ellipticals. From a
Magellan-Clay spectrum we secure the galaxy redshift at . We find a
strong X-ray source coincident with the spheroid galaxy. Spectral features and
a high X-ray luminosity indicate the presence of an AGN in the galaxy. However,
a comparison of the X-ray luminosity to a sample derived from the Chandra Deep
Field South displays Lx to be comparable to Type I/QSO galaxies while the
optical flux is consistent with a normal star-forming galaxy. We conclude that
the galaxy's non-thermal component dominates at high-energy wavelengths while
we associate the spheroid blue light with the stellar spectrum of normal
star-forming galaxies. We argue about a probable association between the
presence of blue cores in spheroids and AGN activity.Comment: Accepted for publication in the Astrophysical Journal. 6 pages, 3
figures. Full resolution images available at
http://acs.pha.jhu.edu/~felipe/e-print
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
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
Deep Imaging of AXJ2019+112: The Luminosity of a ``Dark Cluster''
We detect a distant cluster of galaxies centered on the QSO lens and luminous
X-ray source AXJ2019+112, a.k.a. ``The Dark Cluster'' (Hattori et al 1997).
Using deep V,I Keck images and wide-field K_s imaging from the NTT, a tight red
sequence of galaxies is identified within a radius of 0.2 h^{-1} Mpc of the
known z=1.01 elliptical lensing galaxy. The sequence, which includes the
central elliptical galaxy, has a slope in good agreement with the model
predictions of Kodama et al (1998) for z~1. We estimate the integrated
rest-frame luminosity of the cluster to be L_V > 3.2 x 10^{11}h^{-2}L_{\sun}
(after accounting for significant extinction at the low latitude of this
field), more than an order of magnitude higher than previous estimates. The
central region of the cluster is deconvolved using the technique of Magain,
Courbin & Sohy (1998), revealing a thick central arc coincident with an
extended radio source. All the observed lensing features are readily explained
by differential magnification of a radio loud AGN by a shallow elliptical
potential. The QSO must lie just outside the diamond caustic, producing two
images, and the arc is a highly magnified image formed from a region close to
the center of the host galaxy, projecting inside the caustic. The
mass--to--light ratio within an aperture of 0.4 h ^{-1} Mpc is M_x/L_V=
224^{+112}_{-78}h(M/L_V)_{\sun}, using the X-ray temperature. The strong lens
model yields a compatible value, M/L_V= 372^{+94}_{-94}h(M/L_V)_{\sun}, whereas
an independent weak lensing analysis sets an upper limit of M/L_V <520
h(M/L_V)_{\sun}, typical of massive clusters.Comment: AAS Latex format, 24 pages, 9 figures. Fig 1a,b available at
http://astro.berkeley.edu/~benitezn/cluster.html . Submitted to ApJ on August
15t
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
CLASH: Weak-Lensing Shear-and-Magnification Analysis of 20 Galaxy Clusters
We present a joint shear-and-magnification weak-lensing analysis of a sample
of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19<z<0.69
selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our
analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam
on the Subaru Telescope. From a stacked shear-only analysis of the
X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a
total signal-to-noise ratio of ~25 in the radial range of 200 to 3500kpc/h. The
stacked tangential-shear signal is well described by a family of standard
density profiles predicted for dark-matter-dominated halos in gravitational
equilibrium, namely the Navarro-Frenk-White (NFW), truncated variants of NFW,
and Einasto models. For the NFW model, we measure a mean concentration of
at . We show this is in excellent agreement with Lambda
cold-dark-matter (LCDM) predictions when the CLASH X-ray selection function and
projection effects are taken into account. The best-fit Einasto shape parameter
is , which is consistent with the
NFW-equivalent Einasto parameter of . We reconstruct projected mass
density profiles of all CLASH clusters from a joint likelihood analysis of
shear-and-magnification data, and measure cluster masses at several
characteristic radii. We also derive an ensemble-averaged total projected mass
profile of the X-ray-selected subsample by stacking their individual mass
profiles. The stacked total mass profile, constrained by the
shear+magnification data, is shown to be consistent with our shear-based
halo-model predictions including the effects of surrounding large-scale
structure as a two-halo term, establishing further consistency in the context
of the LCDM model.Comment: Accepted by ApJ on 11 August 2014. Textual changes to improve clarity
(e.g., Sec.3.2.2 "Number-count Depletion", Sec.4.3 "Shape Measurement",
Sec.4.4 "Background Galaxy Selection"). Results and conclusions remain
unchanged. For the public release of Subaru data, see
http://archive.stsci.edu/prepds/clash
CLASH: Extreme Emission Line Galaxies and Their Implication on Selection of High-Redshift Galaxies
We utilize the CLASH (Cluster Lensing And Supernova survey with Hubble)
observations of 25 clusters to search for extreme emission-line galaxies
(EELGs). The selections are carried out in two central bands: F105W (Y105) and
F125W (J125), as the flux of the central bands could be enhanced by the
presence of [O III] 4959, 5007 at redshift of about 0.93-1.14 and 1.57-1.79,
respectively. The multi-band observations help to constrain the equivalent
widths of emission lines. Thanks to cluster lensing, we are able to identify 52
candidates down to an intrinsic limiting magnitude of 28.5 and to a rest-frame
[O III] 4959,5007 equivalent width of about 3737 angstrom. Our samples include
a number of EELGs at lower luminosities that are missed in other surveys, and
the extremely high equivalent width can be only found in such faint galaxies.
These EELGs can mimic the dropout feature similar to that of high redshift
galaxies and contaminate the color-color selection of high redshift galaxies
when the S/N ratio is limited or the band coverage is incomplete. We predict
that the fraction of EELGs in the future high redshift galaxy selections cannot
be neglected.Comment: 17 pages, 9 figures, 2 tables, Accepted for publication in AP