823 research outputs found
Quasars Clustering at z approx 3 on Scales less sim 10 h^{-1} Mpc
We test the hypothesis whether high redshift QSOs would preferentially appear
in small groups or pairs, and if they are associated with massive, young
clusters. We carried out a photometric search for \Ly emitters on scales
Mpc, in the fields of a sample of 47 known
QSOs. Wide and narrow band filter color-magnitude diagrams were generated for
each of the fields. A total of 13 non resolved objects with a
significant color excess were detected as QSO candidates at a redshift similar
to that of the target. All the candidates are significantly fainter than the
reference QSOs, with only 2 of them within 2 magnitudes of the central object.
Follow-up spectroscopic observations have shown that 5, i.e., about 40% of the
candidates, are QSOs at the same redshift of the target; 4 are QSOs at
different z (two of them probably being a lensed pair at z = 1.47); 2
candidates are unresolved HII galaxies at z0.3; one unclassified and one
candidate turned out to be a CCD flaw. These data indicate that at least 10% of
the QSOs at z3 do have companions.
We have also detected a number of resolved, rather bright \Ly Emitter
Candidates. Most probably a large fraction of them might be bright galaxies
with [OII] emission, at z 0.3. The fainter population of our
candidates corresponds to the current expectations. Thus, there are no strong
indication for the existence of an overdensity of \Ly galaxies brighter than m
25 around QSOs at 3.Comment: 29 pages, 8 figures, tar gzip LaTex file, accepted to appear in Ap
New XMM-Newton observation of the Phoenix cluster: properties of the cool core
(Abridged) We present a spectral analysis of a deep (220 ks) XMM-Newton
observation of the Phoenix cluster (SPT-CL J2344-4243), which we also combine
with Chandra archival ACIS-I data. We extract CCD and RGS X-ray spectra from
the core region to search for the signature of cold gas, and constrain the mass
deposition rate in the cooling flow which is thought to be responsible of the
massive star formation episode observed in the BCG. We find an average mass
deposition rate of /yr in the temperature range 0.3-3.0 keV from MOS data. A
temperature-resolved analysis shows that a significant amount of gas is
deposited only above 1.8 keV, while upper limits of the order of hundreds of
/yr can be put in the 0.3-1.8 keV temperature range. From pn data we
obtain /yr, and the
upper limits from the temperature-resolved analysis are typically a factor of 3
lower than MOS data. In the RGS spectrum, no line emission from ionization
states below Fe XXIII is seen above , and the amount of gas cooling
below keV has a best-fit value
/yr. In addition, our analysis of the FIR SED of the BCG based on
Herschel data provides /yr, significantly lower
than previous estimates by a factor 1.5. Current data are able to firmly
identify substantial amount of cooling gas only above 1.8 keV in the core of
the Phoenix cluster. While MOS data analysis is consistent with values as high
as within , pn data provide
yr at c.l. at temperature below 1.8 keV. At present, this
discrepancy cannot be explained on the basis of known calibration uncertainties
or other sources of statistical noise.Comment: A&A in press, typos corrected, revised text according to published
versio
Far-ultraviolet imaging of the Hubble Deep Field-North: Star formation in normal galaxies at z < 1
We present far-ultraviolet (FUV) imaging of the Hubble Deep Field-North (HDF-N) taken with the Solar Blind Channel of the Advanced Camera for Surveys (ACS SBC) and the FUV MAMA detector of the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The full WFPC2 deep field has been observed at 1600 Å. We detect 134 galaxies and one star down to a limit of FUV_(AB) ~ 29. All sources have counterparts in the WFPC2 image. Redshifts (spectroscopic or photometric) for the detected sources are in the range 0 < z < 1. We find that the FUV galaxy number counts are higher than those reported by GALEX, which we attribute at least in part to cosmic variance in the small HDF-N field of view. Six of the 13 Chandra sources at z < 0.85 in the HDF-N are detected in the FUV, and those are consistent with starbursts rather than active galactic nuclei. Cross-correlating with Spitzer sources in the field, we find that the FUV detections show general agreement with the expected L_(IR)/L_(UV) versus β relationship. We infer star formation rates (SFRs), corrected for extinction using the UV slope, and find a median value of 0.3 M_☉ yr^(-1) for FUV-detected galaxies, with 75% of detected sources having SFR < 1 M_☉ yr^(-1). Examining the morphological distribution of sources, we find that about half of all FUV-detected sources are identified as spiral galaxies. Half of morphologically selected spheroid galaxies at z < 0.85 are detected in the FUV, suggesting that such sources have had significant ongoing star formation in the epoch since z ~ 1
A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images. II. Quantifying morphological k-correction in the COSMOS field at 1<z<2: Ks band vs. I band
We quantify the effects of \emph{morphological k-correction} at by
comparing morphologies measured in the K and I-bands in the COSMOS area.
Ks-band data have indeed the advantage of probing old stellar populations for
, enabling a determination of galaxy morphological types unaffected by
recent star formation. In paper I we presented a new non-parametric method to
quantify morphologies of galaxies on seeing limited images based on support
vector machines. Here we use this method to classify
selected galaxies in the COSMOS area observed with WIRCam at CFHT. The obtained
classification is used to investigate the redshift distributions and number
counts per morphological type up to and to compare to the results
obtained with HST/ACS in the I-band on the same objects from other works. We
associate to every galaxy with and a probability between 0 and
1 of being late-type or early-type. The classification is found to be reliable
up to . The mean probability is . It decreases with redshift
and with size, especially for the early-type population but remains above
. The classification is globally in good agreement with the one
obtained using HST/ACS for . Above , the I-band classification
tends to find less early-type galaxies than the Ks-band one by a factor
1.5 which might be a consequence of morphological k-correction effects.
We argue therefore that studies based on I-band HST/ACS classifications at
could be underestimating the elliptical population. [abridged]Comment: accepted for publication in A&A, updated with referee comments, 12
pages, 10 figure
New Constraints on the Lyman Continuum Escape Fraction at z~1.3
We examine deep far-ultraviolet (1600 Angstrom) imaging of the Hubble Deep
Field-North (HDFN) and the Hubble Ultra Deep Field (HUDF) to search for leaking
Lyman continuum radiation from starburst galaxies at z~1.3. There are 21
(primarily sub-L*) galaxies with spectroscopic redshifts between 1.1<z<1.5 and
none are detected in the far-UV. We fit stellar population templates to the
galaxies' optical/near-infrared SEDs to determine the starburst age and level
of dust attenuation, giving an accurate estimate of the intrinsic Lyman
continuum ratio, f_1500/f_700, and allowing a conversion from f_700 limits to
relative escape fractions. We show that previous high-redshift studies may have
underestimated the amplitude of the Lyman Break, and thus the relative escape
fraction, by a factor of ~2. Once the starburst age and intergalactic HI
absorption are accounted for, 18 galaxies in our sample have limits to the
relative escape fraction, f_esc,rel < 1.0 with some limits as low as f_esc,rel
< 0.10 and a stacked limit of f_esc,rel < 0.08. This demonstrates, for the
first time, that most sub-L* galaxies at high redshift do not have large escape
fractions. When combined with a similar study of more luminous galaxies at the
same redshift we show that, if all star-forming galaxies at z~1 have similar
relative escape fractions, the value must be less than 0.14 (3 sigma). We also
show that less than 20% (3 sigma) of star-forming galaxies at z~1 have relative
escape fractions near unity. These limits contrast with the large escape
fractions found at z~3 and suggest that the average escape fraction has
decreased between z~3 and z~1. (Abridged)Comment: Accepted for publication in ApJ. aastex format. 39 pages, 11 figure
The Atacama Cosmology Telescope: Dynamical Masses and Scaling Relations for a Sample of Massive Sunyaev-Zel'dovich Effect Selected Galaxy Clusters
We present the first dynamical mass estimates and scaling relations for a
sample of Sunyaev-Zel'dovich effect (SZE) selected galaxy clusters. The sample
consists of 16 massive clusters detected with the Atacama Cosmology Telescope
(ACT) over a 455 sq. deg. area of the southern sky. Deep multi-object
spectroscopic observations were taken to secure intermediate-resolution
(R~700-800) spectra and redshifts for ~60 member galaxies on average per
cluster. The dynamical masses M_200c of the clusters have been calculated using
simulation-based scaling relations between velocity dispersion and mass. The
sample has a median redshift z=0.50 and a median mass M_200c~12e14 Msun/h70
with a lower limit M_200c~6e14 Msun/h70, consistent with the expectations for
the ACT southern sky survey. These masses are compared to the ACT SZE
properties of the sample, specifically, the match-filtered central SZE
amplitude y, the central Compton parameter y0, and the integrated Compton
signal Y_200c, which we use to derive SZE-Mass scaling relations. All SZE
estimators correlate with dynamical mass with low intrinsic scatter (<~20%), in
agreement with numerical simulations. We explore the effects of various
systematic effects on these scaling relations, including the correlation
between observables and the influence of dynamically disturbed clusters. Using
the 3-dimensional information available, we divide the sample into relaxed and
disturbed clusters and find that ~50% of the clusters are disturbed. There are
hints that disturbed systems might bias the scaling relations but given the
current sample sizes these differences are not significant; further studies
including more clusters are required to assess the impact of these clusters on
the scaling relations.Comment: 15 pages, 4 figures. Accepted for publication in The Astrophysical
Journal; matches published version. Full Table 8 with complete spectroscopic
member sample available in machine-readable form in the journal site and upon
request to C. Sif\'o
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
Evidence for Evolving Spheroidals in the Hubble Deep Fields North and South
We investigate the dispersion in the internal colours of faint spheroidals in
the HDFs North and South. We find that a remarkably large fraction ~30% of the
morphologically classified spheroidals with I<24 mag show strong variations in
internal colour, which we take as evidence for recent episodes of
star-formation. In most cases these colour variations manifest themselves via
the presence of blue cores, an effect of opposite sign to that expected from
metallicity gradients. Examining similarly-selected ellipticals in five rich
clusters with 0.37<z<0.83 we find a significant lower dispersion in their
internal colours. This suggests that the colour inhomogeneities have a strong
environmental dependence being weakest in dense environments where spheroidal
formation was presumably accelerated at early times. We use the trends defined
by the cluster sample to define an empirical model based on a high-redshift of
formation and estimate that at z~1 about half the field spheroidals must be
undergoing recent episodes of star-formation. Using spectral synthesis models,
we construct the time dependence of the density of star-formation. Although the
samples are currently small, we find evidence for an increase in
between z=0 to z=1. We discuss the implications of this rise in the context of
that observed in the similar rise in the abundance of galaxies with irregular
morphology. Regardless of whether there is a connection our results provide
strong evidence for the continued formation of field spheroidals over 0<z<1.Comment: 13 pages, 11 figures. To appear in MNRAS in response to referee's
Report. Figures and paper also available at
http://www.ast.cam.ac.uk/~fmenante/HDFs
ACS Observations of a Strongly Lensed Arc in a Field Elliptical
We report the discovery of a strongly lensed arc system around a field
elliptical galaxy in Hubble Space Telescope (HST) Advanced Camera for Surveys
(ACS) images of a parallel field observed during NICMOS observations of the HST
Ultra-Deep Field. The ACS parallel data comprise deep imaging in the F435W,
F606W, F775W, and F850LP bandpasses. The main arc is at a radius of 1.6 arcsec
from the galaxy center and subtends about 120 deg. Spectroscopic follow-up at
Magellan Observatory yields a redshift z=0.6174 for the lensing galaxy, and we
photometrically estimate z_phot = 2.4\pm0.3 for the arc. We also identify a
likely counter-arc at a radius of 0.6 arcsec, which shows structure similar to
that seen in the main arc. We model this system and find a good fit to an
elliptical isothermal potential of velocity dispersion
\kms, the value expected from the fundamental plane, and some external shear.
Several other galaxies in the field have colors similar to the lensing galaxy
and likely make up a small group.Comment: Accepted for publication in ApJ Letters. 10 pages, 3 figures. Figures
have been degraded to meet size limit; a higher resolution version and
addtional pictures available at http://acs.pha.jhu.edu/~jpb/UDFparc
Clusters at Half Hubble Time: Galaxy Structure and Colors in RXJ0152.7-1357 and MS1054-03
We study the photometric and structural properties of spectroscopically
confirmed members in the two massive X-ray--selected z=0.83 galaxy clusters
MS1054-03 and RXJ0152-1357 using three-band mosaic imaging with the Hubble
Space Telescope Advanced Camera for Surveys. The samples include 105 and 140
members of MS1054-03 and RXJ0152-1357, respectively, with ACS F775W magnitude <
24.0. We develop a promising new structural classification method, based on a
combination of the best-fit Sersic indices and the normalized root-mean-square
residuals from the fits; the resulting classes agree well with the visual ones,
but are less affected by galaxy orientation. We examine the color--magnitude
relations in detail and find that the color residuals correlate with the local
mass density measured from our weak lensing maps; we identify a threshold
density of , in units of the critical density, above which
the star formation appears to cease. For RXJ0152-1357, we also find a trend in
the color residuals with velocity, resulting from an offset of about 980 km/s
in the mean redshifts of the early- and late-type galaxies. Analysis of the
color--color diagrams indicates that a range of star formation time-scales are
needed to reproduce the loci of the galaxy colors. We also identify some
cluster galaxies whose colors can only be explained by large amounts, mag, of internal dust extinction. [Abstract shortened]Comment: 30 pages, emulateapj format; 23 figures, many in color. Accepted by
ApJ; scheduled for the 10 June 2006 issue. Some figures degraded; for a
higher resolution version, see: http://astro.wsu.edu/blakeslee/z1clusters
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