36 research outputs found
The Low-Redshift Quasar-Quasar Correlation Function from an Extragalactic Halpha Emission-Line Survey to z=0.4
We study the large-scale spatial distribution of low-redshift quasars and
Seyfert~1 galaxies using a sample of 106 luminous emission-line objects
() selected by their H emission lines in a
far-red objective prism survey (). Of the 106 objects, 25 were
previously known AGN (Veron-Cetty and Veron 2000), and follow-up spectroscopy
for an additional 53 objects (including all object pairs with separation r <
20 \hmpc) confirmed 48 AGN and 5 narrow emission-line galaxies (NELGs). The
calculated amplitude of the spatial two-point correlation function for the
emission-line sample is A = 0.4 \cdot \bar{\xi}(r < 20 \hmpc) \cdot 20^{1.8} =
142 \pm 53. Eliminating the confirmed NELGs from the sample we obtain the AGN
clustering amplitude . Using Monte Carlo simulations we reject
the hypothesis that the observed pair counts were drawn from a random
distribution at the 99.97% and 98.6% confidence levels for the entire sample
and the AGN subset respectively. We measure a decrease in the quasar clustering
amplitude by a factor of between and ,
and present the coordinates, redshifts, and follow-up spectroscopy for the 15
previously unknown AGN and 4 luminous NELGs that contribute to the clustering
signal.Comment: ApJ, in press, Vol 548, added follow-up spectroscop
The Las Campanas IR Survey: Early Type Galaxy Progenitors Beyond Redshift One
(Abridged) We have identified a population of faint red galaxies from a 0.62
square degree region of the Las Campanas Infrared Survey whose properties are
consistent with their being the progenitors of early-type galaxies. The optical
and IR colors, number-magnitude relation and angular clustering together
indicate modest evolution and increased star formation rates among the
early-type field population at redshifts between one and two. The counts of red
galaxies with magnitudes between 17 and 20 rise with a slope that is much
steeper than that of the total H sample. The surface density of red galaxies
drops from roughly 3000 per square degree at H = 20.5, I-H > 3 to ~ 20 per
square degree at H = 20, I-H > 5. The V-I colors are approximately 1.5
magnitudes bluer on average than a pure old population and span a range of more
than three magnitudes. The colors, and photometric redshifts derived from them,
indicate that the red galaxies have redshift distributions adequately described
by Gaussians with sigma_z ~ 0.2V-I3$ are primarily in the 1.5 < z < 2
range. We find co-moving correlation lengths of 9-10 Mpc at z ~ 1, comparable
to, or larger than, those found for early-type galaxies at lower redshifts. A
simple photometric evolution model reproduces the counts of the red galaxies,
with only a ~ 30% decline in the underlying space density of early-type
galaxies at z ~ 1.2. We suggest on the basis of the colors, counts, and
clustering that these red galaxies are the bulk of the progenitors of present
day early-type galaxies.Comment: 5 pages, 3 figures, accepted for publication in the ApJ Letter
The Las Campanas Infrared Survey. III. The H-band Imaging Survey and the Near-Infrared and Optical Photometric Catalogs
(Abridged) The Las Campanas Infrared Survey, based on broad-band optical and
near-infrared photometry, is designed to robustly identify a statistically
significant and representative sample of evolved galaxies at redshifts z>1. We
have completed an H-band imaging survey over 1.1 square degrees of sky in six
separate fields. The average 5 sigma detection limit in a four arcsecond
diameter aperture is H ~ 20. Here we describe the design of the survey, the
observation strategies, data reduction techniques, and object identification
procedures. We present sample near-infrared and optical photometric catalogs
for objects identified in two survey fields. We perform object detection in all
bandpasses and identify ~ 54,000 galaxies over 1,408 square arcminutes of sky
in the two fields. Of these galaxies, ~ 14,000 are detected in the H-band and ~
2,000 have the colors of evolved galaxies, I - H >3, at z > 1. We find that (1)
the differential number counts N(m) for the H-band detected objects has a slope
of 0.44 at H 19. In addition, we find that (2) the
differential number counts for the H detected red objects has a slope of 0.85
at H 20, with a mean surface density ~ 3,000 degree^{-2}
mag^{-1} at H=20. Finally, we find that (3) galaxies with red optical to
near-IR colors (I-H > 3) constitute ~ 20% of the H detected galaxies at H ~ 21,
but only 2% at H = 19. We show that red galaxies are strongly clustered, which
results in a strong field to field variation in their surface density.
Comparisons of observations and predictions based on various formation
scenarios indicate that these red galaxies are consistent with mildly evolving
early-type galaxies at z ~ 1, although with a significant amount of on-going
star formation as indicated by the large scatter in their V-I colors.Comment: 48 pages, 13 figures, accepted for publication in the Astrophysical
Journa
Cepheid limb darkening, angular diameter corrections, and projection factor from static spherical model stellar atmospheres
Context. One challenge for measuring the Hubble constant using Classical
Cepheids is the calibration of the Leavitt Law or period-luminosity
relationship. The Baade-Wesselink method for distance determination to Cepheids
relies on the ratio of the measured radial velocity and pulsation velocity, the
so-called projection factor and the ability to measure the stellar angular
diameters. Aims. We use spherically-symmetric model stellar atmospheres to
explore the dependence of the p-factor and angular diameter corrections as a
function of pulsation period. Methods. Intensity profiles are computed from a
grid of plane-parallel and spherically-symmetric model stellar atmospheres
using the SAtlas code. Projection factors and angular diameter corrections are
determined from these intensity profiles and compared to previous results.
Results. Our predicted geometric period-projection factor relation including
previously published state-of-the-art hydrodynamical predictions is not with
recent observational constraints. We suggest a number of potential resolutions
to this discrepancy. The model atmosphere geometry also affects predictions for
angular diameter corrections used to interpret interferometric observations,
suggesting corrections used in the past underestimated Cepheid angular
diameters by 3 - 5%. Conclusions. While spherically-symmetric hydrostatic model
atmospheres cannot resolve differences between projection factors from theory
and observations, they do help constrain underlying physics that must be
included, including chromospheres and mass loss. The models also predict more
physically-based limb-darkening corrections for interferometric observations.Comment: 8 pages, 6 figures, 2 tables, accepted for publication in A&
The Las Campanas Infrared Survey: Early-Type Galaxy Progenitors beyond z = 1
We have identified a population of faint red galaxies from a 0.62 deg^2 region of the Las Campanas Infrared Survey whose properties are consistent with their being the progenitors of early-type galaxies. The optical and IR colors, number-magnitude relation, and angular clustering together indicate modest evolution and increased star formation rates among the early-type field population at redshifts between 1 and 2. The counts of red galaxies with H magnitudes between 17 and 20 rise with a slope that is much steeper than that of the total H sample. The surface density of red galaxies drops from roughly 3000 deg^(-2) at H = 20.5, I-H > 3 to ~20 deg^(-2) at H = 20, I-H > 5. The V-I colors are approximately 1.5 mag bluer on average than a pure old population and span a range of more than 3 mag. The strength of the angular clustering of the red galaxies is an order of magnitude larger than that of the full galaxy sample. The colors, and photometric redshifts derived from them, indicate that the red galaxies have redshift distributions adequately described by Gaussians with Ï_z â 0.2 centered near z = 1, with the exception that galaxies having V-I 3 are primarily in the 1.5 ⟠z ⟠2 range. We invert the angular correlation functions using these n(z) and find comoving correlation lengths of r_0 â 9-10 h^(-1) Mpc at z â 1, comparable to, or larger than, those found for early-type galaxies at lower redshifts. A simple photometric evolution model reproduces the counts of the red galaxies, with only an ~30% decline in the underlying space density of early-type galaxies at z ~ 1.2. The colors indicate characteristic star formation rates of ~1 M_â yr^(-1) per 10^(10) M_â. We suggest on the basis of the colors, counts, and clustering that these red galaxies are the bulk of the progenitors of present-day early-type galaxies
The Las Campanas Infrared Survey â II. Photometric redshifts, comparison with models and clustering evolution
The Las Campanas Infrared (LCIR) Survey, using the Cambridge Infra-Red Survey Instrument (CIRSI), reaches HâŒ21 over nearly 1 deg^2. In this paper we present results from 744 arcmin^2 centred on the Hubble Deep Field South for which UBVRI optical data are publicly available. Making conservative magnitude cuts to ensure spatial uniformity, we detect 3177 galaxies to H=20.0 in 744 arcmin^2 and a further 842 to H=20.5 in a deeper subregion of 407 arcmin^2. We compare the observed opticalâinfrared (IR) colour distributions with the predictions of semi-analytic hierarchical models and find reasonable agreement. We also determine photometric redshifts, finding a median redshift of âŒ0.55. We compare the redshift distributions N(z) of E, Sbc, Scd and Im spectral types with models, showing that the observations are inconsistent with simple passive-evolution models while semi-analytic models provide a reasonable fit to the total N(z) but underestimate the number of zâŒ1 red spectral types relative to bluer spectral types. We also present N(z) for samples of extremely red objects (EROs) defined by opticalâIR colours. We find that EROs with R-H>4 and H4 comprise âŒ18 per cent of the observed galaxy population, while in semi-analytic models they contribute only âŒ4 per cent.
We also determine the angular correlation function w(Ξ) for magnitude, colour, spectral type and photometric redshift-selected subsamples of the data and use the photometric redshift distributions to derive the spatial clustering statistic Ο(r) as a function of spectral type and redshift out to zâŒ1.2. Parametrizing Ο(r) by Ο(rc,z)=[rc/râ(z)]^(-1.8), where r_c is in comoving coordinates, we find that râ(z) increases by a factor of 1.5â2 from z=0 to zâŒ1.2. We interpret this as a selection effect â the galaxies selected at zâŒ1.2 are intrinsically very luminous, about 1â1.5 mag brighter than Lâ. When galaxies are selected by absolute magnitude, we find no evidence for evolution in râ over this redshift range. Extrapolated to z=0, we find râ(z=0)âŒ6.5 h^(-1) Mpc for red galaxies and râ(z=0)âŒ2â4 h^(-1) Mpc for blue galaxies. We also find that, while the angular clustering amplitude of EROs with R-H>4 or I-H>3 is up to four times that of the whole galaxy population, the spatial clustering length râ(z=1) is âŒ7.5â10.5 h^(-1) Mpc, which is only a factor of âŒ1.7 times râ(z=1) for R-H<4 and I-H<3 galaxies lying in a similar redshift and luminosity range. This difference is similar to that observed between red and blue galaxies at low redshifts
Direct Determination of Hubble Parameter Using Type IIn Supernovae
We introduce a novel approach, a Dense Shell Method (DSM), for measuring
distances for cosmology. It is based on original Baade idea to relate absolute
difference of photospheric radii with photospheric velocity. We demonstrate
that this idea works: the new method does not rely on the Cosmic Distance
Ladder and gives satisfactory results for the most luminous Type IIn
Supernovae. This allows one to make them good primary distance indicators for
cosmology. Fixing correction factors for illustration, we obtain with this
method the median distance of 68^{+19}_{-15} (68%CL) Mpc to SN 2006gy and
median Hubble parameter 79^{+23}_{-17} (68%CL) km/s/Mpc.Comment: 6 pages, 1 figure, typos correcte