49 research outputs found
The CIDA-UCM-Yale Shallow Survey for Emission Line Galaxies
We present the CIDA-UCM-Yale (Centro de Investigaciones de Astronomia,
Universidad Complutense de Madrid and Yale University) survey for
Halpha+[NII]6549,6584 emission-line galaxies using objective-prism spectra. The
most important properties of a catalogue with 427 entries and significant
subsets are analysed. The complete sample contains 183 statistically confirmed
ELGs in a sky area of 151 sq.deg. and redshift up to 0.14. We determine the
parameters of the Halpha luminosity function using the Halpha+[NII] flux
directly measured on the ELGs spectra in this sample and the star formation
rate density derived is in agreement with the values reported in the
literature. Finally, we study the clustering properties of local star-forming
galaxies relative to quiescent ones from different perspectives. We find that
emission-line galaxies avoid dense regions of quiescent galaxies and we propose
a power-law expression to parametrise the relation between star formation rate
density and environment volume density of emission-line galaxies.Comment: 12 pages, 12 figures, accepted by MNRA
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
CIRSI: the Cambridge infrared survey instrument for wide-field astronomy
The search for galaxies at redshifts > becomes increasingly difficult in the visible since most of the light emitted by these objects is redshifted into the near IR. The recent development of high-performance near IR arrays has made it practical to built a wide field survey instrument for operation in the near IR part of the spectrum. CIRSI, the Cambridge IR Survey Instrument, uses four of the Hawaii-1 MCT arrays each of which has 1024 by 1024 pixels. This paper describes a number of the novel feature of CIRSI and summarizes the present performance achieved by CIRSI and the scientific programs it is principally engaged in
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&