257 research outputs found
All-sky Relative Opacity Mapping Using Night Time Panoramic Images
An all-sky cloud monitoring system that generates relative opacity maps over
many of the world's premier astronomical observatories is described.
Photometric measurements of numerous background stars are combined with
simultaneous sky brightness measurements to differentiate thin clouds from sky
glow sources such as air glow and zodiacal light. The system takes a continuous
pipeline of all-sky images, and compares them to canonical images taken on
other nights at the same sidereal time. Data interpolation then yields
transmission maps covering almost the entire sky. An implementation of this
system is currently operating through the Night Sky Live network of CONCAM3s
located at Cerro Pachon (Chile), Mauna Kea (Hawaii), Haleakala (Hawaii), SALT
(South Africa) and the Canary Islands (Northwestern Africa).Comment: Accepted for publication in PAS
Upregulation of peroxisome proliferator-activated receptor gamma coactivator gene ( PGC1A ) during weight loss is related to insulin sensitivity but not to energy expenditure
Aims/hypothesis: We investigated whether skeletal muscle peroxisome proliferator-activated receptor gamma coactivator-1 (PGC1A; also known as PPARGC1A) and its target mitofusin-2 (MFN2), as well as carnitine palmitoyltransferase-1 (CPT1; also known as carnitine palmitoyltransferase 1A [liver] [CPT1A]) and uncoupling protein (UCP)3, are involved in the improvement of insulin resistance and/or in the modification of energy expenditure during surgically induced massive weight loss. Materials and methods: Seventeen morbidly obese women (mean BMI: 45.9â±â4kg/m2) were investigated before, and 3 and 12months after, Roux-en-Y gastric bypass (RYGB). We evaluated insulin sensitivity by the euglycaemic-hyperinsulinaemic clamp, energy expenditure and substrate oxidation by indirect calorimetry, and muscle mRNA expression by PCR. Results: Post-operatively, PGC1A was enhanced at 3 (pâ=â0.02) and 12months (pâ=â0.03) as was MFN2 (pâ=â0.008 and pâ=â0.03 at 3 and 12months respectively), whereas UCP3 was reduced (pâ=â0.03) at 12months. CPT1 did not change. The expression of PGC1A and MFN2 were strongly (pâ<â0.0001) related. Insulin sensitivity, which increased after surgery (pâ=â0.002 at 3, pâ=â0.003 at 12months), was significantly related to PGC1A and MFN2, but only MFN2 showed an independent influence in a multiple regression analysis. Energy expenditure was reduced at 3months post-operatively (pâ=â0.001 vs before RYGB), remaining unchanged thereafter until 12months. CPT1 and UCP3 were not significantly related to the modifications of energy expenditure or of lipid oxidation rate. Conclusions/interpretation: Weight loss upregulates PGC1A, which in turn stimulates MFN2 expression. MFN2 expression significantly and independently contributes to the improvement of insulin sensitivity. UCP3 and CPT1 do not seem to influence energy expenditure after RYG
The Distance of the First Overtone RR Lyrae Variables in the MACHO LMC Database: A New Method to Correct for the Effects of Crowding
Previous studies have indicated that many of the RR Lyrae variables in the
LMC have properties similar to the ones in the Galactic globular cluster M3.
Assuming that the M3 RR Lyrae variables follow the same relationships among
period, temperature, amplitude and Fourier phase parameter phi31 as their LMC
counterparts, we have used the M3 phi31-logP relation to identify the M3-like
unevolved first overtone RR Lyrae variables in 16 fields near the LMC bar. The
temperatures of these variables were calculated from the M3 logP-logTe relation
so that the extinction could be derived for each star separately. Since blended
stars have lower amplitudes for a given period, the period amplitude relation
should be a useful tool for identifying which stars are affected by crowding.
We find that the low amplitude stars are brighter. We remove them from the
sample and derive an LMC distance modulus 18.49+/-0.11.Comment: 30 pages, 7 figures, accepted for publication in the Astronomical
Journa
HFF-DeepSpace photometric catalogs of the 12 Hubble frontier fields, clusters, and parallels : photometry, photometric redshifts, and stellar masses
We present Hubble multi-wavelength photometric catalogs, including (up to) 17 filters with the Advanced Camera for Surveys and Wide Field Camera 3 from the ultra-violet to near-infrared for the Hubble Frontier Fields and associated parallels. We have constructed homogeneous photometric catalogs for all six clusters and their parallels. To further expand these data catalogs, we have added ultra-deep KS-band imaging at 2.2. mu m from the Very Large Telescope HAWK-I and Keck-I MOSFIRE instruments. We also add post-cryogenic Spitzer imaging at 3.6 and 4.5. mu m with the Infrared Array Camera (IRAC), as well as archival IRAC 5.8 and 8.0. mu m imaging when available. We introduce the public release of the multi-wavelength (0.2-8 mu m) photometric catalogs, and we describe the unique steps applied for the construction of these catalogs. Particular emphasis is given to the source detection band, the contamination of light from the bright cluster galaxies (bCGs), and intra-cluster light (ICL). In addition to the photometric catalogs, we provide catalogs of photometric redshifts and stellar population properties. Furthermore, this includes all the images used in the construction of the catalogs, including the combined models of bCGs and ICL, the residual images, segmentation maps, and more. These catalogs are a robust data set of the Hubble Frontier Fields and will be an important aid in designing future surveys, as well as planning follow-up programs with current and future observatories to answer key questions remaining about first light, reionization, the assembly of galaxies, and many more topics, most notably by identifying high-redshift sources to target
Satellite content and quenching of star formation in galaxy groups at z ~ 1.8
We study the properties of satellites in the environment of massive star-forming galaxies at z ~ 1.8 in the COSMOS field, using a sample of 215 galaxies on the main sequence of star formation with an average mass of ~1011Mâ. At z> 1.5, these galaxies typically trace halos of mass âł1013Mâ. We use optical-near-infrared photometry to estimate stellar masses and star formation rates (SFR) of centrals and satellites down to ~ 6 Ă 109Mâ. We stack data around 215 central galaxies to statistically detect their satellite halos, finding an average of ~3 galaxies in excess of the background density. We fit the radial profiles of satellites with simple ÎČ-models, and compare their integrated properties to model predictions. We find that the total stellar mass of satellites amounts to ~68% of the central galaxy, while spectral energy distribution modeling and far-infrared photometry consistently show their total SFR to be 25-35% of the central's rate. We also see significant variation in the specific SFR of satellites within the halo with, in particular, a sharp decrease at <100 kpc. After considering different potential explanations, we conclude that this is likely an environmental signature of the hot inner halo. This effect can be explained in the first order by a simple free-fall scenario, suggesting that these low-mass environments can shut down star formation in satellites on relatively short timescales of ~0.3 Gyr
The importance of major mergers in the build up of stellar mass in brightest cluster galaxies at z=1
Recent independent results from numerical simulations and observations have
shown that brightest cluster galaxies (BCGs) have increased their stellar mass
by a factor of almost two between z~0.9 and z~0.2. The numerical simulations
further suggest that more than half this mass is accreted through major
mergers. Using a sample of 18 distant galaxy clusters with over 600
spectroscopically confirmed cluster members between them, we search for
observational evidence that major mergers do play a significant role. We find a
major merger rate of 0.38 +/- 0.14 mergers per Gyr at z~1. While the
uncertainties, which stem from the small size of our sample, are relatively
large, our rate is consistent with the results that are derived from numerical
simulations. If we assume that this rate continues to the present day and that
half of the mass of the companion is accreted onto the BCG during these
mergers, then we find that this rate can explain the growth in the stellar mass
of the BCGs that is observed and predicted by simulations. Major mergers
therefore appear to be playing an important role, perhaps even the dominant
one, in the build up of stellar mass in these extraordinary galaxies.Comment: 15 pages, 6 figures, accepted for publication in MNRAS. Reduced data
will be made available through the ESO archiv
Uv-to-fir analysis of spitzer/irac sources in the extended groth strip i: Multi-wavelength photometry and spectral energy distributions
We present an IRAC 3.6+4.5 microns selected catalog in the Extended Groth
Strip (EGS) containing photometry from the ultraviolet to the far-infrared and
stellar parameters derived from the analysis of the multi-wavelength data. In
this paper, we describe the method used to build coherent spectral energy
distributions (SEDs) for all the sources. In a companion paper, we analyze
those SEDs to obtain robust estimations of stellar parameters such as
photometric redshifts, stellar masses, and star formation rates. The catalog
comprises 76,936 sources with [3.6]<23.75 mag (85% completeness level of the
IRAC survey in the EGS) over 0.48 square degrees. For approximately 16% of this
sample, we are able to deconvolve the IRAC data to obtain robust fluxes for the
multiple counterparts found in ground-based optical images. Typically, the SEDs
of the IRAC sources in our catalog count with more than 15 photometric data
points, spanning from the UV to the FIR. Approximately 95% and 90% of all IRAC
sources are detected in the deepest optical and near-infrared bands. Only 10%
of the sources have optical spectroscopy and redshift estimations. Almost 20%
and 2% of the sources are detected by MIPS at 24 and 70 microns, respectively.
We also cross-correlate our catalog with public X-ray and radio catalogs.
Finally, we present the Rainbow Navigator public web-interface utility designed
to browse all the data products resulting from this work, including images,
spectra, photometry, and stellar parameters.Comment: 28 pages, 12 figures, Accepted for publication in ApJ. Access the
Rainbow Database at: http://rainbowx.fis.ucm.e
Infrared Luminosities and Dust Properties of z ~ 2 Dust-Obscured Galaxies
We present SHARC-II 350um imaging of twelve 24um-bright (F_24um > 0.8 mJy)
Dust-Obscured Galaxies (DOGs) and CARMA 1mm imaging of a subset of 2 DOGs, all
selected from the Bootes field of the NOAO Deep Wide-Field Survey. Detections
of 4 DOGs at 350um imply IR luminosities which are consistent within a factor
of 2 of expectations based on a warm dust spectral energy distribution (SED)
scaled to the observed 24um flux density. The 350um upper limits for the 8
non-detected DOGs are consistent with both Mrk231 and M82 (warm dust SEDs), but
exclude cold dust (Arp220) SEDs. The two DOGs targeted at 1mm were not detected
in our CARMA observations, placing strong constraints on the dust temperature:
T_dust > 35-60 K. Assuming these dust properties apply to the entire sample, we
find dust masses of ~3x10^8 M_sun. In comparison to other dusty z ~ 2 galaxy
populations such as sub-millimeter galaxies (SMGs) and other Spitzer-selected
high-redshift sources, this sample of DOGs has higher IR luminosities (2x10^13
L_sun vs. 6x10^12 L_sun for the other galaxy populations), warmer dust
temperatures (>35-60 K vs. ~30 K), and lower inferred dust masses (3x10^8 M_sun
vs. 3x10^9 M_sun). Herschel and SCUBA-2 surveys should be able to detect
hundreds of these power-law dominated DOGs. We use HST and Spitzer/IRAC data to
estimate stellar masses of these sources and find that the stellar to gas mass
ratio may be higher in our 24um-bright sample of DOGs than in SMGs and other
Spitzer-selected sources. Although larger sample sizes are needed to provide a
definitive conclusion, the data are consistent with an evolutionary trend in
which the formation of massive galaxies at z~2 involves a sub-millimeter
bright, cold-dust and star-formation dominated phase followed by a 24um-bright,
warm-dust and AGN-dominated phase.Comment: 16 pages, 7 figures, 6 tables; accepted to the Ap
The Star-Formation Histories of z~2 DOGs and SMGs
The Spitzer Space Telescope has identified a population of ultra-luminous
infrared galaxies (ULIRGs) at z ~ 2 that may play an important role in the
evolution of massive galaxies. We measure the stellar masses of two populations
of Spitzer-selected ULIRGs, both of which have extremely red R-[24] colors
(dust-obscured galaxies, or DOGs) and compare our results with sub-millimeter
selected galaxies (SMGs). One set of 39 DOGs has a local maximum in their
mid-IR spectral energy distribution (SED) at rest-frame 1.6um associated with
stellar emission ("bump DOGs"), while the other set of 51 DOGs has a power-law
dominated mid-IR SED with spectral features typical of obscured AGN ("power-law
DOGs"). We use stellar population synthesis models applied self-consistently to
broad-band photometry in the rest-frame ultra-violet, optical, and
near-infrared of each of these populations and test a variety of stellar
population synthesis codes, star-formation histories (SFHs), and initial mass
functions (IMFs). Assuming a simple stellar population SFH and a Chabrier IMF,
we find that the median and inner quartile stellar masses of SMGs, bump DOGs
and power-law DOGs are given by log(M_*/M_sun) = 10.42_-0.36^+0.42,
10.62_-0.32^+0.36, and 10.71_-0.34^+0.40, respectively. Implementing more
complicated SFHs with multiple age components increases these mass estimates by
up to 0.5 dex. Our stellar mass estimates are consistent with physical
mechanisms for the origin of z~2 ULIRGs that result in high star-formation
rates for a given stellar mass. Such mechanisms are usually driven by a major
merger of two gas-rich systems, rather than smooth accretion of gas and small
satellites.Comment: 17 pages, 7 figures, 3 tables. Plus figures showing SEDs and best-fit
synthesized stellar population model. Accepted to the Ap
A panchromatic study of BLAST counterparts: total star-formation rate, morphology, AGN fraction and stellar mass
We carry out a multi-wavelength study of individual galaxies detected by the
Balloon-borne Large Aperture Submillimeter Telescope (BLAST) and identified at
other wavelengths, using data spanning the radio to the ultraviolet (UV). We
develop a Monte Carlo method to account for flux boosting, source blending, and
correlations among bands, which we use to derive deboosted far-infrared (FIR)
luminosities for our sample. We estimate total star-formation rates for BLAST
counterparts with z < 0.9 by combining their FIR and UV luminosities. Star
formation is heavily obscured at L_FIR > 10^11 L_sun, z > 0.5, but the
contribution from unobscured starlight cannot be neglected at L_FIR < 10^11
L_sun, z < 0.25. We assess that about 20% of the galaxies in our sample show
indication of a type-1 active galactic nucleus (AGN), but their submillimeter
emission is mainly due to star formation in the host galaxy. We compute stellar
masses for a subset of 92 BLAST counterparts; these are relatively massive
objects, with a median mass of ~10^11 M_sun, which seem to link the 24um and
SCUBA populations, in terms of both stellar mass and star-formation activity.
The bulk of the BLAST counterparts at z<1 appear to be run-of-the-mill
star-forming galaxies, typically spiral in shape, with intermediate stellar
masses and practically constant specific star-formation rates. On the other
hand, the high-z tail of the BLAST counterparts significantly overlaps with the
SCUBA population, in terms of both star-formation rates and stellar masses,
with observed trends of specific star-formation rate that support strong
evolution and downsizing.Comment: Accepted for publication in the Astrophysical Journal. 44 pages, 11
figures. The SED template for the derivation of L_FIR has changed (added new
figure) and the discussion on the stellar masses has been improved. The
complete set of full-color postage-stamps can be found at
http://blastexperiment.info/results_images/moncelsi
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