18,323 research outputs found
On the Origin of Near-Infrared Extragalactic Background Light Anisotropy
Extragalactic background light (EBL) anisotropy traces variations in the
total production of photons over cosmic history, and may contain faint,
extended components missed in galaxy point source surveys. Infrared EBL
fluctuations have been attributed to primordial galaxies and black holes at the
epoch of reionization (EOR), or alternately, intra-halo light (IHL) from stars
tidally stripped from their parent galaxies at low redshift. We report new EBL
anisotropy measurements from a specialized sounding rocket experiment at 1.1
and 1.6 micrometers. The observed fluctuations exceed the amplitude from known
galaxy populations, are inconsistent with EOR galaxies and black holes, and are
largely explained by IHL emission. The measured fluctuations are associated
with an EBL intensity that is comparable to the background from known galaxies
measured through number counts, and therefore a substantial contribution to the
energy contained in photons in the cosmos.Comment: 65 pages, 29 figures, Published in Science Nov 7 2014 (includes
supplementary material
CARMA Survey Toward Infrared-bright Nearby Galaxies (STING): Molecular Gas Star Formation Law in NGC4254
This study explores the effects of different assumptions and systematics on
the determination of the local, spatially resolved star formation law. Using
four star formation rate (SFR) tracers (H\alpha with azimuthally averaged
extinction correction, mid-infrared 24 micron, combined H\alpha and
mid-infrared 24 micron, and combined far-ultraviolet and mid-infrared 24
micron), several fitting procedures, and different sampling strategies we probe
the relation between SFR and molecular gas at various spatial resolutions and
surface densities within the central 6.5 kpc in the disk of NGC4254. We find
that in the high surface brightness regions of NGC4254 the form of the
molecular gas star formation law is robustly determined and approximately
linear and independent of the assumed fraction of diffuse emission and the SFR
tracer employed. When the low surface brightness regions are included, the
slope of the star formation law depends primarily on the assumed fraction of
diffuse emission. In such case, results range from linear when the fraction of
diffuse emission in the SFR tracer is ~30% or less (or when diffuse emission is
removed in both the star formation and the molecular gas tracer), to
super-linear when the diffuse fraction is ~50% and above. We find that the
tightness of the correlation between gas and star formation varies with the
choice of star formation tracer. The 24 micron SFR tracer by itself shows the
tightest correlation with the molecular gas surface density, whereas the
H\alpha corrected for extinction using an azimuthally-averaged correction shows
the highest dispersion. We find that for R<0.5R_25 the local star formation
efficiency is constant and similar to that observed in other large spirals,
with a molecular gas depletion time ~2 Gyr.Comment: accepted for publication in ApJ, vol 729, March 10 2011 issue; 30
pages; 14 figures; revised version includes referee's comments; results
unchange
The EDGE-CALIFA Survey: Interferometric Observations of 126 Galaxies with CARMA
We present interferometric CO observations, made with the Combined Array for Millimeter-wave Astronomy (CARMA) interferometer, of galaxies from the Extragalactic Database for Galaxy Evolution survey (EDGE). These galaxies are selected from the Calar Alto Legacy Integral Field Area (CALIFA) sample, mapped with optical integral field spectroscopy. EDGE provides good-quality CO data (3σ sensitivity before inclination correction, resolution ∼1.4 kpc) for 126 galaxies, constituting the largest interferometric CO survey of galaxies in the nearby universe. We describe the survey and data characteristics and products, then present initial science results. We find that the exponential scale lengths of the molecular, stellar, and star-forming disks are approximately equal, and galaxies that are more compact in molecular gas than in stars tend to show signs of interaction. We characterize the molecular-to-stellar ratio as a function of Hubble type and stellar mass and present preliminary results on the resolved relations between the molecular gas, stars, and star-formation rate. We then discuss the dependence of the resolved molecular depletion time on stellar surface density, nebular extinction, and gas metallicity. EDGE provides a key data set to address outstanding topics regarding gas and its role in star formation and galaxy evolution, which will be publicly available on completion of the quality assessment.Fil: Bolatto, Alberto. University of Maryland; Estados UnidosFil: Wong, Tony. University of Illinois at Urbana; Estados UnidosFil: Utomo, Dyas. University of California at Berkeley; Estados UnidosFil: Blitz, Leo. University of California at Berkeley; Estados UnidosFil: Vogel, Stuart N.. University of Maryland; Estados UnidosFil: Sánchez, Sebastián F.. Universidad Nacional Autónoma de México; MéxicoFil: Barrera-Ballesteros, Jorge. University Johns Hopkins; Estados UnidosFil: Cao, Yixian. University of Illinois; Estados UnidosFil: Colombo, Dario. Max Planck Institut Fur Radioastronomie; AlemaniaFil: Dannerbauer, Helmut. Universidad de La Laguna; EspañaFil: García-Benito, Rubén. Instituto de Astrofísica de Andalucía; EspañaFil: Herrera-Camus, Rodrigo. Max Planck Institute für Extraterrestrische Physik; AlemaniaFil: Husemann, Bernd. Max-Planck-Institut für Astronomie; AlemaniaFil: Kalinova, Veselina. Max Planck Institut für Radioastronomie; AlemaniaFil: Leroy, Adam K.. Ohio State University; Estados UnidosFil: Leung, Gigi. Max-Planck-Institut für Astronomie; AlemaniaFil: Levy, Rebecca C.. University of Maryland; Estados UnidosFil: Mast, Damian. Observatorio Astronomico de la Universidad Nacional de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Ostriker, Eve. University of Princeton; Estados UnidosFil: Rosolowsky, Erik. University of Alberta; CanadáFil: Sandstrom, Karin M.. University of California at San Diego; Estados UnidosFil: Teuben, Peter. University of Maryland; Estados UnidosFil: Van De Ven, Glenn. Max-Planck-Institut für Astronomie; AlemaniaFil: Walter, Fabian. Max-Planck-Institut für Astronomie; Alemani
Deep CCD Surface Photometry of Galaxy Clusters I: Methods and Initial Studies of Intracluster Starlight
We report the initial results of a deep imaging survey of galaxy clusters.
The primary goals of this survey are to quantify the amount of intracluster
light as a function of cluster properties, and to quantify the frequency of
tidal debris. We outline the techniques needed to perform such a survey, and we
report findings for the first two galaxy clusters in the survey: Abell 1413,
and MKW 7 . These clusters vary greatly in richness and structure. We show that
our surface photometry reliably reaches to a surface brightness of \mu_v = 26.5
mags per arcsec. We find that both clusters show clear excesses over a
best-fitting r^{1/4} profile: this was expected for Abell 1413, but not for MKW
7. Both clusters also show evidence of tidal debris in the form of plumes and
arc-like structures, but no long tidal arcs were detected. We also find that
the central cD galaxy in Abell 1413 is flattened at large radii, with an
ellipticity of , the largest measured ellipticity of any cD galaxy
to date.Comment: 58 pages, 24 figures, accepted for publication in the Astrophysical
Journal. Version has extremely low resolution figures to comply with 650k
limit. High resolution version is available at
http://burro.astr.cwru.edu/johnf/icl1.ps.gz Obtaining high resolution version
is strongly reccomende
The First Release COSMOS Optical and Near-IR Data and Catalog
We present imaging data and photometry for the COSMOS survey in 15
photometric bands between 0.3um and 2.4um. These include data taken on the
Subaru 8.3m telescope, the KPNO and CTIO 4m telescopes, and the CFHT 3.6m
telescope. Special techniques are used to ensure that the relative photometric
calibration is better than 1% across the field of view. The absolute
photometric accuracy from standard star measurements is found to be 6%. The
absolute calibration is corrected using galaxy spectra, providing colors
accurate to 2% or better. Stellar and galaxy colors and counts agree well with
the expected values. Finally, as the first step in the scientific analysis of
these data we construct panchromatic number counts which confirm that both the
geometry of the universe and the galaxy population are evolving.Comment: 19 pages, 13 figures, 14 tables, Accepted to ApJS for COSMOS speciall
issu
The 2-10 keV XRB dipole and its cosmological implications
The hard X-ray (>2 keV) emission of the local and distant Universe as
observed with the HEAO1-A2 experiment is reconsidered in the context of large
scale cosmic structure. Using all-sky X-ray samples of AGN and galaxy clusters
we remove the dominant local X-ray flux from within a redshift of ~ 0.02. We
evaluate the dipolar and higher order harmonic structure in 4 X-ray colours.
The estimated dipole anisotropy of the unresolved flux appears to be consistent
with a combination of the Compton-Getting effect due to the Local Group motion
(dipole amplitude Delta = 0.0042) and remaining large scale structure (0.0023
<~ Delta <~ 0.0085), in good agreement with the expectations of Cold Dark
Matter models. The observed anisotropy does however also suggest a
non-negligible Galactic contribution which is more complex than current, simple
models of >2 keV Galactic X-ray emission. Comparison of the soft and hard
colour maps with a harmonic analysis of the 1.5 keV ROSAT all-sky data
qualitatively suggests that at least a third of the faint, unresolved ~ 18 deg
scale structure in the HEAO1-A2 data may be Galactic in origin. However, the
effect on measured flux dipoles is small (<~3%).
We derive an expression for dipole anisotropy and acceleration and
demonstrate how the dipole anisotropy of the distant X-ray frame can constrain
the amplitude of bulk motions of the universe. From observed bulk motions over
a local ~ 50 Mpc/h radius volume we determine 0.14 <~ Omega^0.6/b_x(0) <~ 0.59.Comment: 39 pages, Revised version accepted ApJ Main Journal, 3 new Figures +
additional tex
Spitzer IRAC Low Surface Brightness Observations of the Virgo Cluster
We present 3.6 and 4.5 micron Spitzer IRAC imaging over 0.77 square degrees
at the Virgo cluster core for the purpose of understanding the formation
mechanisms of the low surface brightness intracluster light features.
Instrumental and astrophysical backgrounds that are hundreds of times higher
than the signal were carefully characterized and removed. We examine both
intracluster light plumes as well as the outer halo of the giant elliptical
M87. For two intracluster light plumes, we use optical colors to constrain
their ages to be greater than 3 & 5 Gyr, respectively. Upper limits on the IRAC
fluxes constrain the upper limits to the masses, and optical detections
constrain the lower limits to the masses. In this first measurement of mass of
intracluster light plumes we find masses in the range of 5.5 x 10^8 - 4.5 x
10^9 and 2.1 x 10^8 - 1.5 x 10^9 solar masses for the two plumes for which we
have coverage. Given their expected short lifetimes, and a constant production
rate for these types of streams, integrated over Virgo's lifetime, they can
account for the total ICL content of the cluster implying that we do not need
to invoke ICL formation mechanisms other than gravitational mechanisms leading
to bright plumes. We also examined the outer halo of the giant elliptical M87.
The color profile from the inner to outer halo of M87 (160 Kpc) is consistent
with either a flat or optically blue gradient, where a blue gradient could be
due to younger or lower metallicity stars at larger radii. The similarity of
the age predicted by both the infrared and optical colors (> few Gyr) indicates
that the optical measurements are not strongly affected by dust extinction.Comment: 16 pages including appendix, 9 figures, ApJ accepte
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